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This site summarizes research articles about mammals for the general public.
Jim Ryan
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- April 26, 2012
- 10:00 AM
- 67 views
Face to Face With Primate Facial Diversity
by Jim Ryan in Wild Mammals
Why do some primates have boldly colored faces while other species exhibit only a monotone color with little pattern? Facial color patterns likely serve several functions in primates, including intraspecific communication, species recognition, and possibly ecological or physiological roles as well (Figure 1). One hypothesis is that facial color patterns are used primarily for species recognition, with more subtle color variations used to assess individual identity.
...Higher facial color complexity is indicated by reds and oranges and higher numbers. Primate species illustrated include: (1) Cacajao calvus, (2) Callicebus hoffmansi, (3) Ateles belzebuth, (4) Alouatta caraya, (5) Aotus trivirgatus, (6) Cebus nigritus, (7) Saimiri boliviensis, (8) Leontopithecus rosalia, (9) Callithrix kuhli, (10) Saguinus martinsi and (11) Saguinus imperator.
...According to the behavioral drive model, social behaviors drive the evolution of increasingly complex facial colors and fur patterns. An alternative hypothesis, the metachromism hypothesis, provides a non-adaptive explanation for primate color patterns. This hypothesis posits that primate lineages exhibit predictable sequences of color changes over time beginning with the ancestral agouti condition and progressively evolving a more uniform black or red color and ending with an unpigmented bleached color.
Sharlene Santana and her colleagues at the University of California, Los Angeles, set out to test these hypotheses using New World primates. They predicted that species living in smaller groups and in sympatry with more congener species would evolve more complex facial color patterns. In addition, they tested the metachromism hypothesis using a phylogenetic approach to trace color patterns through Neotropical primate lineages. They quantified facial color patterns using photos of adult males from a wide array of Neotropical primate species (Figure 2).
...Primate faces (here a white-faced capuchin monkey, Cebus capucinus) were subdivided into 14 areas (b) to record hair and skin color, and hair length. These 14 areas were grouped into 5 more general regions that varied across species.
...The results reveal that primate facial patterns do function in communication and species recognition. Primate species living in smaller groups and in regions with a higher number of congener species (species within the same genus) have evolved more complex patterns of facial color. ... In fact, ecological factors, and geographical patterns also shaped facial diversity in Neotropical primates (Figure 3). For example, primate species closer to the equator tended to have darker crowns and darker eye masks. Species living in the far western Neotropics tended to have darker noses and mouths, but lighter eye masks.
...Facial parts become darker (regions highlighted in black) or hair becomes longer (region highlighted in grey) in the directions indicated by the arrows.
...Perhaps darker facial regions in more tropical habitats serve to make individuals more cryptic or protect against the powerful UV radiation in these regions. ... Nevertheless, these results “demonstrate the interaction of behavioral and ecological factors in shaping one of the most outstanding facial diversities of any mammalian lineage.”
...Santana, S., Lynch Alfaro, J., & Alfaro, M. ... Adaptive evolution of facial colour patterns in Neotropical primates Proceedings of the Royal Society B: Biological Sciences, 279 (1736), 2204-2211 DOI: 10.1098/rspb.2011.2326
... Read more »
Santana, S., Lynch Alfaro, J., & Alfaro, M. (2012) Adaptive evolution of facial colour patterns in Neotropical primates. Proceedings of the Royal Society B: Biological Sciences, 279(1736), 2204-2211. DOI: 10.1098/rspb.2011.2326
- April 19, 2012
- 10:05 AM
- 58 views
Social Evolution in Mole-rats
by Jim Ryan in Wild Mammals
Naked mole-rats (Heterocephalus glaber) have received a lot of scientific attention because they are the only mammals with a eusocial mating system. Like honey bees, naked mole-rats have colonies with a single breeding “queen,” a few breeding males, and numerous non-breeding “workers” who forage and maintain the complex burrow system. It is not surprising then, that these unusual mammals have received the lion’s share of attention from scientists.
As fascinating as naked mole-rats are, they are but one of 22 species of mole-rats. Interestingly, mole-rats exhibit a very wide range of social behavior, from the eusocial naked mole-rat to species that are completely solitary. This variation in social structure makes them an ideal group for studying the factors that influence the evolution of social behavior in mammals.
Five scientists from the Czech Republic, Germany, and Malawi (Lovy et al., 2012) studied two mole-rat species that live in different ecological habitats in the same region of Malawi. The silvery mole-rat (Heliophobius argenteocinereus, Figure 1) is a solitary species that lives in high altitude grassland habitats, whereas Whyte’s mole-rat (Fukomys whytei) is social and lives in drier, lower-altitude woodlands. The authors sought to tease out what ecological factors drive the evolution of social behavior.
...A slivery mole-rat (Heliophobius sp). (from Chris Faulkes)
Because mole-rats are fossorial, soil quality and food availability are likely to play important roles in shaping their social systems (Figure 2). Whyte’s mole-rats in Malawi live in harsh habitats where soils are harder and food is relatively scarce. In contrast, silvery mole-rats inhabit cooler grasslands where soils are easier to burrow through and where food biomass was four times greater than in the woodlands.
...A principal component analysis showing the relationship between food availability and soil paramters for Heliophobius (NR, North Rumphi; NRa, North Rumphi alluvium; and FL, Fort Lister.) and for Fukomys (J, Jalawe). Open symbols represent burrow systems numbered from lowest to highest altitude.
...Although both solitary and social species of mole-rat coexist in the Nyika Plateau, Malawi, there is niche differentiation between silvery and Whyte’s mole-rats. What factors are responsible for separating the niches of these two species? The authors suggest that the solitary species could not survive in the poor, hard soils of the drier woodlands where patchy underground tubers are in short supply.
In addition, Heliophobius mole-rats, living in afromontane grasslands are subject to colder temperature and consequently have thicker fur and tolerate low temperatures better. Thus, it may be that Fukomys are ill-prepared to compete with Heliophobius at the cooler, higher-altitude grassland sites. In sum, neither food availability, nor soil density alone explain the observed niche differentiation and social structure in these mole-rats. Rather, it is likely to be a combination of thermoregulatory and competitive abilities, perhaps shaped by ecological factors, that explains the evolution of different social systems.
...Lövy, M., Šklíba, J., Burda, H., Chitaukali, W., & Šumbera, R. ... Ecological characteristics in habitats of two African mole-rat species with different social systems in an area of sympatry: implications for the mole-rat social evolution Journal of Zoology, 286 (2), 145-153 DOI: 10.1111/j.1469-7998.2011.00860.x
... Read more »
Lövy, M., Šklíba, J., Burda, H., Chitaukali, W., & Šumbera, R. (2012) Ecological characteristics in habitats of two African mole-rat species with different social systems in an area of sympatry: implications for the mole-rat social evolution. Journal of Zoology, 286(2), 145-153. DOI: 10.1111/j.1469-7998.2011.00860.x
- April 12, 2012
- 10:09 AM
- 95 views
Meet and Greet in the Dolphin World
by Jim Ryan in Wild Mammals
Many people believe that an important difference between humans and other animals is language--that what has brought us from fields and forests to our comfortable homes is our ability to communicate effectively with one another. And so the discovery that humans are not alone in their power of conversation is one that affects our definitions of our selves, and one opens many research opportunities for scientists.
Research into the calls made by bottlenose dolphins (Tursiops truncatus) at sea indicates that as dolphin groups encounter one another they exchange unique whistles; researchers claim that the whistles carried information about their identity and alliances with other individuals. In captivity, dolphins and parrots can learn to use signals to convey information about their surroundings, but there isn't much research about whether or not they use these techniques in the wild.
...Every bottlenose dolphin has a unique whistle that they develop at a young age and practice while alone. After a call has been established, males and females differ in their use of signature whistles: females' calls tend to stay stable for about a decade, while males' whistles change to reflect alliances with other individuals. They also have been known to copy the unique calls of their companions--similar to a human calling a friend's name to attract his attention.
By using passive acoustic localization while following pods in Saint Andrews Bay, Scotland the researchers found that unique whistle exchanges mainly occurred when groups first encountered each other (Figure 2). They ensured that the whistle exchanges were unique by running a sequence analysis, and also noted that none of the calls were repeated.
...(From Quick and Janik 2012)
Data was collected over the course of six months, and scientists used focal boats to follow pods of dolphins during good weather. Individuals were identified with photos of their dorsal fins, and groups were defined by the distance between dolphins (less than ten meters apart equaled a group). Then using both visual data indicating the position of each dolphin and auditory data, they determined which individual had used which call and when.
By analyzing this data, researchers affirmed that dolphins exchange signature whistles when meeting at sea, and believe that these calls are meant to convey information about their identity (Figure 3). They also found that only one dolphin from each group uses its signature whistle before joining with another group, which could have various explanations:
• that each group has a leader who decides whether or not the groups will join,
• that the unique whistles are used as a greeting ritual and that the dolphins use echolocation to identify each other individually,
• that they may have recently been separated and already know the composition of the group, or
• that they aren't picky about which individuals they interact closely with.
...A histogram of all whistle exchanges and joining events for dolphin groups. (From Quick and Janik 2012)
While this study shed new light on the way dolphins use sound to communicate, it also opened up many more questions about how these organisms use signature whistles to interact, and what that means in terms of how humans define themselves.
...Quick, N., & Janik, V. ... Bottlenose dolphins exchange signature whistles when meeting at sea Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.2537
... Read more »
Quick, N., & Janik, V. (2012) Bottlenose dolphins exchange signature whistles when meeting at sea. Proceedings of the Royal Society B: Biological Sciences. DOI: 10.1098/rspb.2011.2537
- March 29, 2012
- 12:29 PM
- 106 views
Opportunistic Torpor Down Under
by Jim Ryan in Wild Mammals
Placental mammals, including some rodents and many bat species, enter torpor to conserve energy when ambient temperatures fall and food becomes scarce. Prolonged torpor is characterized by highly reduced body temperature and metabolic rates. Torpor is less common in mammals from the southern hemisphere. In fact, only one marsupial is known to undergo a seasonal hibernation, the mountain pygmy-possum (Burramys parvus).
Now, James Turner and his colleagues from the University of New England in Australia report that seasonal torpor may be more common in marsupials than previously thought. They studied wild western pygmy-possums (Cercartetus concinnus), a small marsupial closely related to the mountain pygymy possum. These small possums (Figure 1) live in cooler temperate forests and semi-arid areas of southern Australia. By using implanted radio transmitters capable of measuring the animal’s body temperature, the research team was able to track the location and body temperature of seven possums over two winters.
...A photo of a closely related eastern pygmy-possum (Cercatetus nanus).
...These tiny marsupials used some form of torpor over 60% of the days in winter. Western pygmy-possums used both short duration torpor lasting less than 24 hours interspersed with longer torpor bouts lasting over 24 hours (Figure 2). Interestingly, on any given winter day some individuals exhibited short torpor bouts while others showed prolonged torpor (Figure 3). Such highly flexible torpor patterns are uncommon in mammals. These marsupials are nocturnal and entered short torpor bouts just before dawn. Individuals that entered longer duration bouts entered into torpor just after sunset and stayed in torpor for up to 186 hours.
...A plot of the body temperature (closed circles and black line) and ambient temperature (grey line) of two western pygmy-possums over a 6-week period. Short torpor bouts are illustrated by animal CcQ (top). Longer duration torpor was used by animal CcT (middle), with one section enlarged (bottom) to reveal a bout lasting over 7 days.
...The dashed line indicates the division between short (24 h) torpor bouts.
...The authors suggest that pygmy-possums may have “employed short torpor bouts as a response to a negative energy balance accrued while active during the previous night, whereas prolonged torpor was entered into on evenings where cold Ta indicated that activity might be too energetically expensive”.
Southern Australian winters are relatively mild and usually allow pygmy-possums to forage on warmer days. When temperatures drop for a day or more, the possums conserve energy by entering torpor and re-warm when ambient temperatures rise again.
...Turner, J., Warnecke, L., Körtner, G., & Geiser, F. ... Opportunistic hibernation by a free-ranging marsupial Journal of Zoology DOI: 10.1111/j.1469-7998.2011.00877.x
... Read more »
Turner, J., Warnecke, L., Körtner, G., & Geiser, F. (2011) Opportunistic hibernation by a free-ranging marsupial. Journal of Zoology. DOI: 10.1111/j.1469-7998.2011.00877.x
- March 8, 2012
- 09:29 AM
- 118 views
Right Whales Stressed by Shipping Traffic
by Jim Ryan in Wild Mammals
The destruction of the World Trade Towers by terrorists on September 11th 2001 was just such an event. It goes without saying that there were many consequences for humans, including two wars, increased airline screening, and shifts in the political landscape. But there were also consequences for other mammalian species as well.
Endangered North Atlantic right whales (Eubalaena glacialis) gather during the late summer on calving grounds in the Bay of Fundy, Canada (Figure 1). A substantial portion of the calving grounds lies in an important shipping lane. Low frequency noise produced by ship engines and propellers travels long distances in water and is believed to interfere with acoustic signaling by whales. Previous studies have shown that right whales alter their vocalizations in response to increased underwater noise.
...A map of the Bay of Fundy, Canada showing the Right Whale Conservation Area and the shipping lanes.
...Rosalind Rolland from the New England Aquarium in Boston, and seven colleagues from across the United States, were collecting data on social behavior in right whales in the Bay of Fundy in August and September 2001. When shipping traffic ceased following the events of September 11th, it presented the researchers with an unintended natural experiment. They realized that they had data that could test the hypothesis that shipping noise directly altered the behavior of North Atlantic right whales.
The researchers collected acoustic data, shipping traffic data, and fecal samples for right whales. The later were used to measure stress hormones (glucocorticoids) produced by the whales. Their results reveal a significant drop in low-frequency background noise in the days immediately following September 11th when shipping traffic stopped in the Bay of Fundy (Figure 2).
...Power spectrum of underwater background noise from 2 days before and 2 days after 11 September 2001. There is a significant decline in low-frequency (Rolland, R., Parks, S., Hunt, K., Castellote, M., Corkeron, P., Nowacek, D., Wasser, S., & Kraus, S. ... Evidence that ship noise increases stress in right whales Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.2429
... Read more »
Rolland, R., Parks, S., Hunt, K., Castellote, M., Corkeron, P., Nowacek, D., Wasser, S., & Kraus, S. (2012) Evidence that ship noise increases stress in right whales. Proceedings of the Royal Society B: Biological Sciences. DOI: 10.1098/rspb.2011.2429
- March 1, 2012
- 09:40 AM
- 156 views
Tarsiers -- Communication in the Ultrasound
by Jim Ryan in Wild Mammals
By contributing writer Sarah Buckleitner
It is difficult for humans to imagine that a world of color and sound exists outside of the one that we can perceive, but for some organisms that world is a reality. Usually these animals aren't ones that we can readily relate to; bats and dolphins are two examples that both possess the ability to hear and emit high-frequency sounds. And so the discovery that a fellow primate, the Philippine tarsier (Tarsius syrichta), may have the ability to emit sounds up to 91 kHz comes as a surprise to their human relatives who can hear sounds up to 20 kHz.
...A Philippine tarsier (Tarsius syrichta). (From Ramsier et al., 2012)
The possibility that tarsiers may be able to communicate in the pure ultrasound, is exciting--species that do this are rare, and the ability to communicate in such high frequencies could have a number of advantages.
Gathering scientific proof of these abilities was difficult; tarsiers are a threatened species and difficult to maintain in captivity. In order to have the least amount of impact, researchers captured the tarsiers in mist nets and brought them to a sound-attenuating chamber. They then used the auditory brainstem response method along with various software programs in order to test whether tarsiers could hear ultrasonic sounds.
When analyzing the sounds that tarsiers make to see if they occurred in the pure ultrasound, researchers recorded wild tarsiers on the islands of Bohol and Leyte with a special recording unit. Even while recording, it was clear that the tarsiers were utilizing pure ultrasound for communication (Figure 2); they frequently made sounds that the researchers could not hear, and were also recorded making calls in the pure ultrasound during human handling and in enclosures.
...A sound spectrogram of a tarsier vocalization showing the dominant frequency in the ultrasound range at roughly 70 kHz. (From Ramsier et al., 2012)
Sensitivity tests showed that Tarsius syrichta's high-frequency limit was approximately 91 kHz. Researchers were also successful in recording calls in the pure ultrasound (at around 70kHz) from eight different individuals. These calls are similar to other tarsier species, but those were all found to be below 34 kHz, and also included tones in less than 20 kHz.
It is thought that the ability to perceive and make ultrasonic sounds is beneficial to the tarsiers. They serve as sort of private channels on which individuals can communicate without attracting the attention of predators or giving away their location to prey. It is also thought that they make it easier for tarsiers to pick signals out of background noise, and that such sounds are energetically more efficient. Improved hearing may also be used to help tarsiers hunt at night; their eyes lack the tapetum lucidum (found in the retina) that allows most nocturnal predators to see effectively.
Through additional research, the researchers hope to more fully flesh out the advantage that ultrasonic communication provides for tarsiers.
...Ramsier, M., Cunningham, A., Moritz, G., Finneran, J., Williams, C., Ong, P., Gursky-Doyen, S., & Dominy, N. ... Primate communication in the pure ultrasound Biology Letters DOI: 10.1098/rsbl.2011.1149
... Read more »
Ramsier, M., Cunningham, A., Moritz, G., Finneran, J., Williams, C., Ong, P., Gursky-Doyen, S., & Dominy, N. (2012) Primate communication in the pure ultrasound. Biology Letters. DOI: 10.1098/rsbl.2011.1149
- February 23, 2012
- 10:44 AM
- 137 views
No Refueling Stopovers for Migrating Bats
by Jim Ryan in Wild Mammals
Migratory birds make refueling stops at one or more locations along their route. These stopover sites are critical; they provide food rich environments where birds can rapidly regain depleted fat stores before continuing their long treks. Likewise, several species of North American vespertilionid bats make long, north-south migrations each year. Silver-haired bats (Lasionycteris noctivagans) are a case in point. ... Previous research suggested that silver-haired bats make stopovers before attempting to cross Lake Erie. Are these stopovers used for refueling before the next stage of the journey?
To answer this question, a team of Canadian scientists lead by Liam McGuire captured 79 silver-haired bats at their stopover site at Long Point Ontario on the northern shore of Lake Erie. The researchers capture newly arrived bats, measured their body fat composition using quantitative magnetic resonance scanning, and fitted 30 of the bats with tiny radio transmitters (Figure 1).
...A roosting silver-haired bat (Lasionycteris noctivagans) with a tiny Lotek radio transmitter glued to its back.
...A series of radio towers (Figure 2) allowed the researchers to track the movements of the radio-tagged bats prior to their departure. The majority of bats were captured at dawn suggesting that they had just arrive at Long Point after flying all night from regions further to the north. The radio-tagged bats roosted in trees or on man-made structures during the day. While some tagged bats spent the following night foraging, most departed the night following their capture. Seven bats stayed two days, but rain the following night prevented departure for six of those bats (the bats prefer not to travel on rainy nights). The short stopover duration suggests that refueling was not the primary reason for stopping. Because these bats do not migrate during the day, it is likely that the stopover is more a temporary refuge allowing the bats to roost and enter torpor during the day.
...Additionally, when the bats departed Long Point, half headed straight across Lake Erie (a minimum distance of 38 km at Long Point).
...The body composition analysis was used to simulate migration characteristics for this species. Assuming a fight speed of 9 meters per second, the bats cover roughly 250 to 300 km per night. At this rate, the bats would arrive at their southern range in 5 to 6 nights. Interestingly, silver-haired bats arrive at Long Point with roughly 19% body fat, plenty of fuel to complete their migration without refueling. Thus, migrating bats appear to use daily torpor to conserve energy and therefore do not need to refuel during stopovers – a strategy very different from many migrating birds.
...McGuire, L., Guglielmo, C., Mackenzie, S., & Taylor, P. ... Migratory stopover in the long-distance migrant silver-haired bat, Lasionycteris noctivagans Journal of Animal Ecology, 81 (2), 377-385 DOI: 10.1111/j.1365-2656.2011.01912.x
... Read more »
McGuire, L., Guglielmo, C., Mackenzie, S., & Taylor, P. (2012) Migratory stopover in the long-distance migrant silver-haired bat, Lasionycteris noctivagans. Journal of Animal Ecology, 81(2), 377-385. DOI: 10.1111/j.1365-2656.2011.01912.x
- February 9, 2012
- 10:53 AM
- 215 views
When Did Cetaceans Evolve Echolocation?
by Jim Ryan in Wild Mammals
Modern whales include baleen whales (Mysticeti) and toothed whales (Odontoceti). Baleen whales are large, filter feeding whales that do not echolocate. Odontocete whales tend to be smaller in size, predatory, and are capable of producing high-frequency sounds used in echolocation. In addition, modern odonotcetes have an asymmetrical skull, where the bones of the skull roof extend posteriorly (telescoped) and are shifted to the left side of the skull (asymmetry) (Figure 1). This pronounced asymmetry is linked with the production of high frequency sounds and the reception of the returning echoes.
...Dorsal view of the skull of a bottlenosed dolphin (Tursiops truncatus) showing the posterior position of the nasals, frontals, maxilla, and premaxilla bones (telescoping) and the asymmetry of the bones surrounding the blow hole. (copyright Jim Ryan)
Modern mysticete and odontocete whales both arose from Eocene archaeocete whales. The skulls of archaeocete whales were presumed to by symmetrical. ... Julia Fahlke, working with Philip Gingerich, Robert Welsh, and Aaron Wood report in the Proceedings of the National Academy of Science that some archaeocete skulls show distinct asymmetry without telescoping (Figure 2).
...A graph of the mean deviation of the dorsal midline suture for 24 artiodactyl skulls (top row), which show a high degree of symmetry, compared with 6 archaeocete whale skulls (bottom, two protocetids and four basilosaurids). All six archaeocete species show asymmetry to the same side of the skull. (From Fahlke et al., 2012).
The researchers propose that Eocene archaeocetes evolved cranial asymmetry “as part of a complex of traits linked to directional hearing.” Some of the other traits associated with hearing high frequency sounds include the thinning of the pan-bone of the lower jaws (Figure 3), and isolation of the ear region from the rest of the skull.
...Dentary bones of a late Eocene archaeocete whale (Basilosaurus isis) showing the relative bone thickness. The thinnest region represents the location of the pan bone. (From Fahlke et al., 2012)
The authors propose the following sequence of events: 1) Eocene archaeocete whales evolved modest cranial asymmetry along with a change to more directional hearing of high frequency sounds. They also evolved thinner pan bones in the jaw to aid the reception of water borne sounds. 2) Later on, Oligocene odontocete whales evolved more refined high frequency echolocation, which further shifted the cranial roofing bones posteriorly (telescoping) and to the left side of the skull (asymmetry). 3) At the same time, Oligocene mysticete whales lost the skull asymmetry of their archaeocete ancestors as their skulls became modified for a bulk filter-feeding mode with low-frequency hearing. Thus, cranial asymmetry is probably an ancestral condition in whales.
...Fahlke, J., Gingerich, P., Welsh, R., & Wood, A. ... Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water Proceedings of the National Academy of Sciences, 108 (35), 14545-14548 DOI: 10.1073/pnas.1108927108
... Read more »
Fahlke, J., Gingerich, P., Welsh, R., & Wood, A. (2011) Cranial asymmetry in Eocene archaeocete whales and the evolution of directional hearing in water. Proceedings of the National Academy of Sciences, 108(35), 14545-14548. DOI: 10.1073/pnas.1108927108
- February 2, 2012
- 10:59 AM
- 214 views
Why Does a Blind, Fossorial Mammal Have Iridescent Fur?
by Jim Ryan in Wild Mammals
Golden moles (Chrysochloridae) are members of the mammalian Order Afrosoricida, an African group that also includes then tenrecs of Madagascar. Golden moles and true moles (Talpidae) evolved their fossorial habits independently. ... Scientists working with golden moles noticed that their silky fur often appears slightly iridescent (Figure 1).
...A Grant’s golden mole (Eremitalpa granti) showing it’s silky fur and leathery nose patch.
...Iridescence is common among insect and bird species, but has not been described before in mammals. Iridescence occurs when light is scattered by nanoscale ridges that are repeated over the surface of a structure such as a bird’s feather or a beetle’s carapace. In doing so, the structure appears to change in hue as the angle of view or angle of light changes.
Recently, a group of scientists reported in the journal Biology Letters (2012) that golden moles have iridescent fur (Figure 2).
...SEM images of iridescent and non-iridescent hairs from the golden mole species Chrysochloris asiatica, showing an iridescent (b) and non-iridescent hair (c) with an optical image (insert) of the cross section of a single hair. TEM images of a cross section of an iridescent (d) and non-iridescent hair (e), showing repeated dark and light bands in the cuticle.
...The fur of golden moles is sometimes described as having a greenish to purplish sheen. ... According to Snyder’s team (2012) golden moles have unusual hair structure that contributes to its weak iridescence. The hairs are flattened distally with extremely thin cuticular scales that make the hair surface appear almost smooth. Inside the hair cuticule, are repeated bands of light and dark, which resemble the wing cases of some iridescent beetles (Figure 3). Reflectance measurements suggest that the iridescent colors are produced when the multiple light-dark layers produce thin-film interference. This is enhanced by the fact that the hairs are flattened and have a relatively smooth reflective surface.
...Figure 3. (a) TEM image showing the alternating light and dark bands in the hair cuticule, and (b) optical modeling curves of reflectance for the golden mole Amblysomus hottentotus (solid line) and predicted (dashed line). (From Snyder et al., 2012)
Usually, animal coloration is the result of selection for camouflage or sexual ornamentation. Why would iridescent coloration evolve in a blind mammal that spends most of its life in darkness burrowing through the sand? Snyder and colleagues suggest that iridescent fur is an epiphenomenon; a by-product of evolution acting on some other aspect of the trait. They hypothesize that the smooth, flatten hairs with multiple layers evolved to reduce friction and damage as they burrow, and that the iridescence arises as a by-product of these mechanical functions.
...Snyder, H., Maia, R., D'Alba, L., Shultz, A., Rowe, K., Rowe, K., & Shawkey, M. ... Iridescent colour production in hairs of blind golden moles (Chrysochloridae) Biology Letters DOI: 10.1098/rsbl.2011.1168
... Read more »
Snyder, H., Maia, R., D'Alba, L., Shultz, A., Rowe, K., Rowe, K., & Shawkey, M. (2012) Iridescent colour production in hairs of blind golden moles (Chrysochloridae). Biology Letters. DOI: 10.1098/rsbl.2011.1168
- January 19, 2012
- 09:19 AM
- 195 views
Hibernation, Life in the Slow Lane
by Jim Ryan in Wild Mammals
Biologists are well aware of the trade offs between reproduction and survival for r versus K selected species. Theory predicts that r-selected species grow quickly, produce more offspring at a time, exhibit minimal parental care, and have relatively short lifespans. In contrast, K-selected organisms produce relatively few offspring at a time, have longer lifespans, and provide more parental care. Thus, these species tend to live in stable environments where they reproduce multiple times over their long lifespans and ensure relatively high offspring survival rates. Put simply, an organism can reproduce quickly, with large litters, and die early, or reproduce slowly over a longer lifespan.
This trade off between survival and reproduction is well understood for many mammals, but how do these life history strategies change in species that hibernate (Figure 1)? Three Austrian biologists, Christopher Turbill, Claudia Bieber, and Thomas Ruf (2011) conducted a meta-analysis of life history data for hibernating and non-hibernating mammals.
...Hibernation is typically understood to be an adaptation that saves energy in species that live year-round in highly seasonal climates. However, Turbill and colleagues suggest that there may be more to hibernation than just energetic savings. Hibernation also increases survival and is therefore likely to be associated with relatively slow life histories (Figure 2).
Figure 2. (a) Box plots of the monthly survival for adults estimated over the hibernation and active season for 19 hibernating mammal species. (b) Plot of the
annual survival probability of adult mammals as a function of body mass. Notice that survival probability is higher for hibernators (red symbols) compared to non-hibernators (blue symbols).
...Survival rates were higher during hibernation compared with the active season because hibernators were less available to predators. Interestingly, annual survival for hibernators was roughly 15 per cent longer than similar sized non-hibernating species. As predicted, when survival rates were higher, small hibernating mammals had longer maximum life spans, reproduced at a slower pace, matured later, and had longer generation times than non-hibernators of the same size.
However, when survival rate were similar for both hibernators and non-hibernators, life spans and reproductive rates were also similar (Figure 3). Put another way, “hibernators have a maximum life span matching the age expected from their relatively high rates of survival.”
Figure 3. (a) Plot of the annual survival probability and lifespan for hibernators (red) and non-hibernators (blue). (b) Plot of the annual reproductive output and maximum lifespan among hibernating and non-hibernating mammals. (From Turbill et al., 2011)
These results suggest that hibernation is associated with high rates of overwinter and annual survival, and this increase in survival is linked with the coevolution of slower life history. This is not to say that energetic savings are unimportant, but rather than increased survival rates may also be driving the evolution of more K-selected life history traits in hibernating mammals.
...Turbill, C., Bieber, C., & Ruf, T. ... Hibernation is associated with increased survival and the evolution of slow life histories among mammals Proceedings of the Royal Society B: Biological Sciences, 278 (1723), 3355-3363 DOI: 10.1098/rspb.2011.0190
... Read more »
Turbill, C., Bieber, C., & Ruf, T. (2011) Hibernation is associated with increased survival and the evolution of slow life histories among mammals. Proceedings of the Royal Society B: Biological Sciences, 278(1723), 3355-3363. DOI: 10.1098/rspb.2011.0190
- December 14, 2011
- 09:53 AM
- 1,175 views
Out of Asia: The Origin of Dogs
by Jim Ryan in Wild Mammals
Scientists agree that domestic dogs evolved from wolves (Canis lupus, Figure 1), but disagree on when and where that domestication event took place. Archaeological evidence suggests that humans domesticated wolves 10-15,000 years ago in Eastern Europe and/or the Middle East. This evidence is based on canid remains that look like domestic dogs found in association with human remains. In contrast, mitochondrial DNA and autosomal single nucleotide polymorphism (SNP) data from a large sample of dogs from around the world point to Asia south of the Yangtze River as the center of domestication.
...Peter Savolainen from the KTH-Royal Institute of Technology in Sweden may have a more definitive answer. Using dog Y-chromosome DNA samples from 151 dogs from around the world, 12 wolves and 2 coyotes, the team believes that wolves were domesticated in Asia south of the Yangtze River (Figure 2). The genetic data also reveal that there were additional, but relatively minor, genetic contributions from wolves at other locations subsequent to the original domestication event, which indicated that dogs may have subsequently hybridized with wolves.
...Circles represent dog haplotypes, squares are wolf haplotyles and hexagons are coyote haplotypes (black dots are hypothetical intermediates). Circle size is proportional to the frequency of the haplotype among dogs. ... (B) Distribution map of dog Y chromosome haplotypes.
...The researchers found 28 haplotypes distributed in five haplogroups. Haplotypes are combinations of alleles at adjacent or nearby locations on a chromosome that are transmitted together. The Y chromosome is of particular interest here because unlike other chromosomes, the Y chromosome does not come in pairs. This means that unlike autosomal haplotypes, a male shares essentially the same Y chromosome as his father, making these haplotypes especially useful for tracing lineages.
The haplotype data reveal that roughly 50% of all dog gene pools are shared. Only in Asia south of the Yangtze River is the full range of genetic diversity apparent. This implies that dog gene pools from all other regions of the world likely derive from this region of East Asia. For example, if wolves were also domesticated independently in Europe or the Middle East one would expect to see high genetic diversity in dogs from those locations as well. Instead the genetic diversity was very low in Europe. As the authors state, ”this offers strong evidence that domestication of wolf occurred primarily and possibly exclusively,” in Asia south of the Yangtze River.
The Y chromosome data from the present study along with mtDNA from previous studies also suggest that a relatively large number of wolves, probably several dozen to several hundred, were domesticated. Such repeated domestication suggests that taming wolves was a cultural trait shared by human populations from this region.
...Ding, Z., Oskarsson, M., Ardalan, A., Angleby, H., Dahlgren, L., Tepeli, C., Kirkness, E., Savolainen, P., & Zhang, Y. ... Origins of domestic dog in Southern East Asia is supported by analysis of Y-chromosome DNA Heredity DOI: 10.1038/hdy.2011.114
... Read more »
Ding, Z., Oskarsson, M., Ardalan, A., Angleby, H., Dahlgren, L., Tepeli, C., Kirkness, E., Savolainen, P., & Zhang, Y. (2011) Origins of domestic dog in Southern East Asia is supported by analysis of Y-chromosome DNA. Heredity. DOI: 10.1038/hdy.2011.114
- November 29, 2011
- 08:24 AM
- 275 views
Bat Radiations
by Jim Ryan in Wild Mammals
A new study involving bat skulls, bite force measurements and scat samples collected by an international team of evolutionary biologists is helping to solve a nagging question of evolution: Why some groups of animals develop scores of different species over time while others evolve only a few. Their findings appear in the current issue of Proceedings of the Royal Society B: Biological Sciences.
To answer this question, Elizabeth Dumont at the University of Massachusetts Amherst and Liliana Dávalos of Stony Brook University together with colleagues at UCLA and the Leibniz Institute for Zoo and Wildlife Research, Berlin, compiled large amounts of data on the diet, bite force and skull shape in a family of New World bats (Figure 1), and took advantage of new statistical techniques to date and document changes in the rate of evolution of these traits and the number of species over time.
...Photos of the heads and skulls of three of a nectar-eating bat (left) an insect-eating bat (middle) and a fruit-eating bat (right). The fruit-eating bats have shorter skulls, which allow more forceful bites.
...They investigated why there are so many more species of New World Leaf-Nosed bats, nearly 200, while their closest relatives produced only 10 species over the same period of time. Most bats are insect feeders, while the New World Leaf-Nosed bats eat nectar, fruit, frogs, lizards and even blood.
One hypothesis is that the evolution of a trait, such as head shape, that gives access to new resources can lead to the rapid evolution of many new species. As Dumont and Dávalos explain, connecting changes in body structure to an ecological opportunity requires showing that a significant increase in the number of species occurred in tandem with the appearance of new anatomical traits, and that those traits are associated with enhanced resource use.
"If the availability of fruit provided the ecological opportunity that, in the presence of anatomical innovations that allowed eating the fruit, led to a significant increase in the birth of new species, then skull morphology should predict both diet and bite force" they said. They found support for these predictions by analyzing thousands of evolutionary trees of more than 150 species, measuring over 600 individual bat skulls of 85 species, testing bite force in over 500 individual bats from 39 species in the field and examining thousands of scat samples to identify the bats’ diets.
They found that the emergence of a new skull shape in New World Leaf-Nosed bats about 15 million years ago led to an explosion of many new bat species (Figure 2). The new shape was a low, broad skull that allowed even small bats to produce the strong bite needed to eat hard fruits. The rate of birth of new species jumped as this new shape evolved, and this group of bats quickly increased the proportion of fruit in their diet. Change in shape slowed once this new skull had evolved.
...A phylogeny of 150 species of phyllostomid bats illustrating morphological diversity among subfamilies. ... The red arrow indicates the node where the most rapid diversification rate was found. (From Dumont et al., 2011)
It can be difficult for evolutionary biologists to demonstrate that traits related to anatomical changes, also called "morphological innovations" such as a new skull shape, give certain groups a survival advantage when new food sources, such as hard fruits, become available.
"This study conducted during the International Year of the Bat offers a clear example of how the evolution of new traits, in this case a skull with a new shape, allowed animals to use new resources and eventually, to rapidly evolve into many new species," Dumont says. "We found that when a new ecological niche opened up with an opportunity for bats that could eat hard fruits, they shifted their diet significantly, which in turn led to the evolution of new species."”
Story Source: The above story is reprinted with slight modification from materials provided by University of Massachusetts at Amherst and authored by Janet Lathrop.
...Dumont, E., Davalos, L., Goldberg, A., Santana, S., Rex, K., & Voigt, C. ... Morphological innovation, diversification and invasion of a new adaptive zone Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.2005
... Read more »
Dumont, E., Davalos, L., Goldberg, A., Santana, S., Rex, K., & Voigt, C. (2011) Morphological innovation, diversification and invasion of a new adaptive zone. Proceedings of the Royal Society B: Biological Sciences. DOI: 10.1098/rspb.2011.2005
- November 17, 2011
- 08:29 AM
- 310 views
Female Moaning: How Female Moose Control Mating
by Jim Ryan in Wild Mammals
One of the key questions in sexual selection theory is how do females choose the best mate? Research has generally focused on the role of male-male competition for access to receptive females, with less attention paid to female mate choice. Theory predicts that females should choose to mate with the most fit male available. In sexually dimorphic mammals, females may use body size as a surrogate for fitness, and choose to mate with the largest or most dominant males.
Alaskan moose (Alces alces) exhibit a polygynous mating system, where dominant (larger) males called harem masters defend small groups of females from other males (Figure 1). Terry Bowyer at Idaho State university and his colleagues studied moose populations in Danali National Park, Alaska for many years. In a recent paper, they report how females manipulate male behavior in order to ensure they mate with the larger, more dominant males.
...A male moose (Alces alces) during the fall mating season in Jackson Hole, Wyoming (From Flickr/Fisherga)
Over the course of three years, the researchers studied group of moose, focusing on the behavior of females. They reveal that female Alaskan moose moan only during courtship attempts. The researchers hypothesized that these protest moans are attempts by females to prevent courtship attempts by subordinate males. They predicted that females should give protest moans more often when courted or harassed by smaller males than when courted by larger males. Furthermore, they predicted that the rate of male-male conflict would increase after protest moans as the harem master arrived and attempted to drive off the other male.
Female protest moans increased during the primary rut, which takes place in October in Danali. A second spike in protest moans occurred in early November during the secondary rut (Figure 2). That protest moans coincided with other rutting behaviors is strong evidence that these moans are rut-related.
...A graph of the rate of protest moans given by female Alaskan moose from August to November.
...As predicted females gave fewer protest moans when courted by larger males.
...The percentage of male aggressive and non-aggressive behaviors during 15-minute periods with or without female protest moans.
...These results indicate that female moose use protest moans to reduce courtship by smaller males. Moaning alerts the harem master, who drives off the smaller male and mates with the female, thereby assuring that the females mates with a dominant male. Such indirect mate choice, where females manipulate males into conflict is rarely reported in mammals, but may be more common than previously believed.
...Bowyer, R., Rachlow, J., Stewart, K., & Ballenberghe, V. ... Vocalizations by Alaskan moose: female incitation of male aggression Behavioral Ecology and Sociobiology, 65 (12), 2251-2260 DOI: 10.1007/s00265-011-1234-y
... Read more »
Bowyer, R., Rachlow, J., Stewart, K., & Ballenberghe, V. (2011) Vocalizations by Alaskan moose: female incitation of male aggression. Behavioral Ecology and Sociobiology, 65(12), 2251-2260. DOI: 10.1007/s00265-011-1234-y
- November 10, 2011
- 11:52 AM
- 273 views
Out of Africa: Caviomorph Origins
by Jim Ryan in Wild Mammals
South America was isolated from Africa and the North American continent during most of the Cenozoic. As a result, early mammalian immigrants evolved in isolation resulting in a unique assemblage of terrestrial mammals. Approximately 34 million years ago (Eocene-Oligocene) global cooling and drying periods are believed to have spurred major faunal changes in South America terrestrial fauna,
including the arrival of caviomorph rodents.
One question that has long puzzled mammalogists is how did caviomorphs get to South America? Did they arrive via dispersal from Africa? Did they enter across the Central American isthmus during the Miocene? The exact mode and timing of the caviomorph invasion remained hotly debated because early (pre-Oligocene) rodent fossils from South America were non-existent.
All that changed with the recent description of several new Middle Eocene (approximately 41 million year old) rodent fossils from Amazonian Peru (Figure 1). A group of European and South American researchers describe five small stem caviomorph rodents that may help clarify the debate.
Figure 1. Scanning electron microscope images of fossil caviomorph teeth belonging to a new genus and species, Cachiyacuy contamanensis. (From Antoine et al.
...The newly described caviomorphs are remarkably small compared to later caviomorphs. However, their small size and dental morphology are similar to African phiomorph rodents. In addition, the new fossils are 41 million years old, which demonstrates that proto-caviomorphs entered South America much earlier than previously thought at a time when the climate was more tropical (Figure 2). The new fossil evidence strongly supports the Middle Eocene caviomorph/phiomorph split, which is also consistent with molecular data.
Figure 2. A phylogeny and dispersal scenario of Palaeogene caviomorph rodents including the newly discovered fossils and related taxa. (From Antoine et al.
...Thus, it appears that Africa is the “homeland for the last common ancestor of caviomorphs.” Furthermore, the evidence from reconstructions of South Atlantic “palaeowinds and palaeocurrents during the Middle Eocene” suggest that Eocene African hystricognaths entered South America via sweepstakes dispersal across the Atlantic from Africa to South America.
...Antoine, P., Marivaux, L., Croft, D., Billet, G., Ganerod, M., Jaramillo, C., Martin, T., Orliac, M., Tejada, J., Altamirano, A., Duranthon, F., Fanjat, G., Rousse, S., & Gismondi, R. ... Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.1732
... Read more »
Antoine, P., Marivaux, L., Croft, D., Billet, G., Ganerod, M., Jaramillo, C., Martin, T., Orliac, M., Tejada, J., Altamirano, A.... (2011) Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society B: Biological Sciences. DOI: 10.1098/rspb.2011.1732
- November 3, 2011
- 09:04 AM
- 299 views
Who’s Your Daddy – Extra Pair Paternity in “Monogamous” Arctic Foxes
by Jim Ryan in Wild Mammals
Less than 3% of mammals are thought to be socially monogamous. However, with the advent of molecular techniques for establishing paternity, some presumably “monogamous” mammals may exhibit relatively high levels of extra pair paternity (EPP), or “cheating.”
Arctic fox (Vulpes lagopus, Figure 1) are a case in point. The arctic fox forage alone, but the social group usually consists of a breeding pair and their young (and occasionally a non-breeding female). Until just a few years ago Arctic foxes were considered strictly monogamous. ... It is still not clear how common EPPs are in Arctic fox populations.
...Paternal care (care provided by the father) may help females raise successful litters in harsh Arctic environments. Scientists predict that paternal care may be critical to pup survival when food abundance is low, or when the distribution of food is very patchy. When food is abundant in one area, the density of breeding fox pairs will also be high in that area, leading to increased probability of females seeking extrapair copulations.
Three Canadian scientists (Cameron et al., 2011) recently tested these predictions on Bylot Island in the Arctic (Figure 2). On this island, the presence of a goose colony provided a localized, high-density food source (spatial variation) and cyclic eruptions of lemming populations provided a temporally variable food resource.
...Arctic fox study area (gray polygon) and goose colony (dark polygon) on Bylot Island, Nunavut, Canada. Active fox dens are indicated with open triangles and inactive dens by black triangles. Dens are identified by a three digit code followed by the last two digits of the year and an E if EPPs were detected or I if only intrapair paternity was detected.
...The mating systems of Arctic foxes on Bylot Island were monitored over five years using a combination of behavioral observation of family groups and molecular analyses. The results indicate that social monogamy is the rule, but extrapair paternity is relatively common. At least 31% of pups were fathered by a male who was not part of the “family group.” Furthermore, the probability of EPP was correlated with food availability. Incidences of EPP was greatest with in the goose colony (86%) and declined steeply with increasing distance from the goose colony (Figure 3).
...Mating system of female arctic foxes as a function of the distance between their den(s) and the center of the goose colony on Bylot Island, Canada. Litters (open circles) were the result of either intrapair (0.0) or extrapair copulations (1.0).
...The researchers conclude that, “In arctic foxes, behavioral strategies, such as extraterritorial movements and EPP, that increase gene flow are probably important for the genetic structure of populations.”
...Cameron, C., Berteaux, D., & Dufresne, F. ... Spatial variation in food availability predicts extrapair paternity in the arctic fox Behavioral Ecology, 22 (6), 1364-1373 DOI: 10.1093/beheco/arr158
... Read more »
Cameron, C., Berteaux, D., & Dufresne, F. (2011) Spatial variation in food availability predicts extrapair paternity in the arctic fox. Behavioral Ecology, 22(6), 1364-1373. DOI: 10.1093/beheco/arr158
- October 22, 2011
- 11:16 AM
- 291 views
Tropical Bats Take it Slow
by Jim Ryan in Wild Mammals
Finding enough food to sustain the energy costs of foraging is a problem faced by all mammals. However, it is made more difficult for mammals that feed on unpredictable and limited prey. ... Molossus molossus (Figure 1), for example, is an aerial insectivore that forages in groups over large areas. Not only must they expend large amounts of energy to fuel these foraging flights, but they only forage for approximately one hour each night. How can they maintain a positive energy balance with such high energetic costs and apparently low energy gains?
...Previous research shows that flying bats expend roughly 15 times the energy they do at rest. Furthermore, small bats have higher resting metabolic rates and lose more heat because of their relatively high surface area to volume ratio. Thus, small aerial feeding bats in temperate zones often enter torpor each day as a way to conserve precious energy.
...German researchers (Dechmann et al. 2011) may have found the answer. They attached tiny transmitters to molossid bats that were designed to measure heart rates. These transmitters sent back data for 48 hours before falling off the bats. The data was used to estimate energy budgets over a two-day period. The researchers hypothesized that the daily energy expenditure (DEE) would be high in these neotropical bats because they have very brief foraging periods and do not undergo daily torpor.
The researchers were surprised to find that these bats exhibited low mean heart rates. This corresponded to a DEE of only half what a similarly sized bat would experience. In addition, field metabolic rates (FMRs), predicted from doubly labeled water were 10 times higher than the DEE predicted from heart rate telemetry for a 10g bat. How were the molossid bats in this study able to conserve so much energy?
One possibility is that molossid bats lower their energy consumption during roosting in a manner similar to daily torpor (Figure 2). The heart rate data reveal that molossid bats do reduce their heart rates while roosting, but not so much that it would be called “torpor.” The authors suggest that “lowered metabolism” in tropical bats may be much more common that previously believed.
...Heart rate measurements from seven bats tracked for 48 hours. The two days were averaged and plotted over a 24 hour period.
...Dechmann, D., Ehret, S., Gaub, A., Kranstauber, B., & Wikelski, M. ... Low metabolism in a tropical bat from lowland Panama measured using heart rate telemetry: an unexpected life in the slow lane Journal of Experimental Biology, 214 (21), 3605-3612 DOI: 10.1242/jeb.056010
... Read more »
Dechmann, D., Ehret, S., Gaub, A., Kranstauber, B., & Wikelski, M. (2011) Low metabolism in a tropical bat from lowland Panama measured using heart rate telemetry: an unexpected life in the slow lane. Journal of Experimental Biology, 214(21), 3605-3612. DOI: 10.1242/jeb.056010
- October 16, 2011
- 11:37 AM
- 295 views
Continuous Tooth Replacement in a Mole-rat
by Jim Ryan in Wild Mammals
Mammals are characterized by diphyodonty, only two generations of teeth, among other traits. However, a few mammals have evolved a form of continuous tooth replacement. For example, Manatees (Trichechus) add extra teeth at the back of the jaw as teeth near the front are worn away or lost. Such a conveyor-belt type of tooth replacement is exceedingly rare in mammals. The only other mammal know to exhibit continuous tooth replacement of this type is a metatherian, the pygmy-rock wallaby (Petrogale concinna). Elephants have a superficially similar type of tooth replacement, but they replace their teeth sequentially and do not form any extra teeth in the process.
As a new report in the Proceedings of the National Academy of Sciences, researchers have now added the silvery mole-rat (Heliophobius argenteocinereus, Figure 1) to the short list of mammals with continuous tooth replacement (Gomes Rodrigues et al. ... These chisel tooth rodents not only possess a conveyor-like tooth replacement, but they are also hypsodont; have high crowned teeth (Figure 2).
...A silvery mole-rat (Heliophobius argenteocinereus).
...Photos (A-C) and drawings of the teeth in Heliophoius argenteocinereus. (A-C) A lateral view of the upper and lower tooth rows with the mandible removed. (D) The pattern of dental replacement in the silvery mole-rat with the arrow indicating the direction of the movement of teeth. (From Gomes Rodrigues et al.
...The researchers propose that the conveyor-like tooth replacement evolved in the silvery mole-rat because of their “hyper-chisel tooth digging behavior; they dig tunnels with their procumbent incisors thereby exposing their cheek teeth to extremely abrasive dirt, which causes their hypsodont cheek teeth to wear rapidly.
Manatees, the pygmy-rock wallaby, and silvery mole-rats undoubtedly evolved continuous tooth replacement convergently; they have different habitats, diets, and are distantly related phylogenetically. Nevertheless, all three groups share three dental traits: extra teeth (supernumerary teeth), delayed eruption, and dental mesial drift (Figure 3). The later character occurs when cheek teeth drift forward as a result of pressure from teeth erupting at the back of the toothrow.
...Phylogenetic tree of dental characteristics related to continuous tooth replacement in several mammals. Column one is the jugal dental formula. The remaining columns represent presence mesial drift (MD), supernumerary teeth (ST), delayed dental eruption (DE), hypsodonty (H), and in column six, replacement of a premolar (P), molar (M), or continuous dental replacement (CDR). (From Gomes Rodrigues et al.
...The authors suggest that epithelial tissues involved in tooth formation may persist as a permanent dental lamina, thereby permitting continual replacement of teeth in Heliophobius.
...Gomes Rodrigues, H., Marangoni, P., Sumbera, R., Tafforeau, P., Wendelen, W., & Viriot, L. ... Continuous dental replacement in a hyper-chisel tooth digging rodent Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1109615108
... Read more »
Gomes Rodrigues, H., Marangoni, P., Sumbera, R., Tafforeau, P., Wendelen, W., & Viriot, L. (2011) Continuous dental replacement in a hyper-chisel tooth digging rodent. Proceedings of the National Academy of Sciences. DOI: 10.1073/pnas.1109615108
- September 15, 2011
- 09:29 AM
- 603 views
Pre-natal Hormones Shape Female Social Interactions
by Jim Ryan in Wild Mammals
In many mammals the female uterus is divided into two horns, a right and a left. ... For example, a pregnant dog might have four fetuses developing in the right uterine horn and three more developing in the left horn. ... A female fetus surrounded by two male siblings will be exposed to increased testosterone levels (androgens) produced by her brothers to be.
...In rodents, one of the traits associated with female masculinization is a greater anogenital distance (the distance between the anal opening and the vaginal opening). Masculinized female offspring also exhibit more play-fighting, which is associated with aggressiveness. Non-masculinized females typically engage in more “sociopositive” behaviors. Are there any lasting effects of female masculinization in adults, and do those effects alter fitness?
Daniel Blumstein and his colleagues from the University of California (LA) set out to answer these questions in a population of yellow-bellied marmots (Marmota flaviventris) in Colorado (Figure 1). This population has been studied extensively since 2002 and all the marmots in 10 social groups are individually marked. Juveniles were live trapped as soon as the emerged from the natal den, marked, and their anogenital distance recorded. The social behaviors of 202 female colony members were monitored from April to September for seven years.
...A yellow-bellied marmot (Marmota flaviventris) on a talus slope in the Sierra Nevada Mountains (From Flickr/Miguel Vieira)
Females with larger anogenital distances were assumed to have been masculinized in utero. Interestingly, masculinized females initiated more play and played with more unique partners (Figure 2). ... Males typically engage in more allogrooming and playfighting and both behaviors are controlled by androgens (In previous studies, females who were given excess testosterone also engaged in more male-like behaviors).
...The relationship between anogenital distance and play (left) and sociopositive behaviors (right).
...Playfighting in young marmots is similar to the agonistic behaviors of adults. Thus, it is possible that young masculinized females that engage in these behaviors may gain a competitive advantage over other females later in life. However, masculinized yearling females did not exhibit higher levels of male-like behaviors.
Finally, masculinized females interacted with more individuals and showed more willingness to explore their environment; exploration is a typically male behavior in marmots. This may explain why previous studies showed that masculinized females dispersed at higher rates that non-masculinized females. Thus, the in utero environment can have lasting effects on female behavior.
...Monclus, R., Cook, T., & Blumstein, D. ... Masculinized female yellow-bellied marmots initiate more social interactions Biology Letters DOI: 10.1098/rsbl.2011.0754
... Read more »
Monclus, R., Cook, T., & Blumstein, D. (2011) Masculinized female yellow-bellied marmots initiate more social interactions. Biology Letters. DOI: 10.1098/rsbl.2011.0754
- September 8, 2011
- 09:52 AM
- 503 views
Can Hyenas Count?
by Jim Ryan in Wild Mammals
During a pivotal scene in West Side Story, the Jets and the Sharks meet to prepare to rumble. As the gangs assembled each side likely tried to assess their opponent’s strength. This ability to assess numerical advantage is highly advantageous in any species where conflict between groups is common.
Spotted hyenas (Crocuta crocuta) live in large fission-fussion clans where smaller groups often forage separately (Figure 1). The composition and size of these subgroups varies over time as clan members move in and out of these smaller units. Hyenas are also highly aggressive and do not tolerate strangers in their home areas. As a consequence, occasionally lethal attacks occur when small groups from different clans meet.
...A group of spotted hyeans (Crocuta crocuta) detect the kill made by a lion.
...Do individual hyenas assess numbers of opponents before engaging in aggressive conflicts? Game theory predicts that they should, especially when large numerical imbalances occur. A group from Kay Holekamp’s lab at Michigan State University set out to test whether wild hyenas can assess the numbers of potential opponents. They used playback experiments on wild hyenas living in the Masai Mara plains of East Africa.
First, the researchers made digital recordings of the whoop calls of unfamiliar hyenas (i.e. hyenas from Tanzania, Malawi, and Senegal). They organized the calls into three groupings of three calls each: one group consisted of three whoop calls from the same individual (A,A,A); a second included a whoop call from one unfamiliar hyena followed by a call from a second unfamiliar hyena and a third call from the first hyena (A,B,A); and a third recording that contained calls from three different hyenas (A,B,C). The research playback these calls to members of two hyena clans in the Mara and observed their behavior.
Lone hyenas became highly vigilant to playbacks of multiple unfamiliar intruders (Figure 2). Equally important was that hyenas could distinguish the number of unique intruders; they became increasingly vigilant to calls of two and three unfamiliar hyenas (Figure 3).
...Average time 12 lone hyenas spent oriented towards the speaker in 34 playback trials.
...Mean time spent oriented towards the speaker when hearing calls from one, two, or three intruders. (From Benson-Amram et al., 2011)
Finally, small groups of hyenas were more likely to approach the playback speakers (a potentially risky behavior) when their numbers exceeded the number of “intruders” calling (i.e. three intruders). Thus, it appears that spotted hyenas can recognize individuals by their contact calls and use that information to assess the number of potential intruders before engaging them in battle.
...Benson-Amram, S., Heinen, V., Dryer, S., & Holekamp, K. ... Numerical assessment and individual call discrimination by wild spotted hyaenas, Crocuta crocuta Animal Behaviour DOI: 10.1016/j.anbehav.2011.07.004
... Read more »
Benson-Amram, S., Heinen, V., Dryer, S., & Holekamp, K. (2011) Numerical assessment and individual call discrimination by wild spotted hyaenas, Crocuta crocuta. Animal Behaviour. DOI: 10.1016/j.anbehav.2011.07.004
- September 1, 2011
- 09:37 AM
- 514 views
Sex at Sea – How to Avoid the Beach Master
by Jim Ryan in Wild Mammals
The southern elephant seal, Mirounga leonina, is a textbook example of an extremely polygynous mammal. As the breeding season begins dominant males fight for control of dozens to hundreds of females on his section of beach real estate (Figure 1). Females within the harem, are monopolized by the dominant male (called a beach master). The beach master is believed to father the vast majority of offspring from his harem females. This system evolved because terrestrial birthing sites (beaches) are rare and females are forced to congregate on the few available beaches. In addition, females show high site fidelity, returning to the same breeding/birthing beaches each season.
...Two adult male elephant seals battle for the rights to a harem of females.
...Because so few males get to breed, theory predicts that subordinate males should seek alternative mating strategies. After all, there is pressure on these males to seek any copulations they can get. Indeed, subordinate bachelor males often patrol the surf zone waiting for an opportunity to steal copulations when the beach master is preoccupied. In contrast, females are not thought to seek alternative mating strategies because they benefit genetically by mating with the dominant male. However, new research indicates that female elephant seals may have a few tricks up their sleeves.
Female elephant seals were thought to breed annually, but de Bruyn and colleagues (2011) used 25 years of mark-recapture data to show that females may skip a breeding season and haul out to give birth every other year instead (Figure 2). Since mating was believed to occur only on the breeding beaches (after pupping), the scientists wanted to know where were these females mating?
...Females that bred annually, from first breeding to disappearance, are represented by solid black bars. Females that breed annually at least twice before skipping a breeding season are the hatch bars and females that showed a more random interrupted breeding pattern are the white bars.
...By using satellite-tracking, the scientists were able to show that two females skipped the annual haul out but returned to give birth the following season (Figure 3). Fortuitously, one of the two tracked females was a 2-year-old virgin female. ... Tracking data showed that it was unlikely that either female mated while hauled out on a remote beach or on ice flows.
...The tracking data shows that both females were at sea at the time they would have become pregnant prior to returning to Marion Island to pup.
...The alternative “at sea” mating strategy has important implications for our understanding of polygyny in elephant seals. As the authors state, “ If polygyny does not preclude females from adopting alternative mating strategies, the term ‘polygyny’ may be misleading.”
...de Bruyn, P., Tosh, C., Bester, M., Cameron, E., McIntyre, T., & Wilkinson, I. ... Sex at sea: alternative mating system in an extremely polygynous mammal Animal Behaviour, 82 (3), 445-451 DOI: 10.1016/j.anbehav.2011.06.006
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de Bruyn, P., Tosh, C., Bester, M., Cameron, E., McIntyre, T., & Wilkinson, I. (2011) Sex at sea: alternative mating system in an extremely polygynous mammal. Animal Behaviour, 82(3), 445-451. DOI: 10.1016/j.anbehav.2011.06.006
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