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Ecographica
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- March 29, 2009
- 04:20 PM
- 1,619 views
The Hunting Modes of a Wolf Spider
by Johnny in Ecographica
Taking a break from stalking prey amid the jungle of leaf litter in my front yard, this spider sprinted across my patio last Monday night. I managed to drop my compass next to him (the edge of which has a two inch ruler) and approximate his Cephalothorax-to-spinneret length at about 7/8 of an inch.
... Read more »
Casas, J., Steinmann, T., & Dangles, O. (2008) The Aerodynamic Signature of Running Spiders. PLoS ONE, 3(5). DOI: 10.1371/journal.pone.0002116
- March 2, 2009
- 12:00 AM
- 1,530 views
Vertebrate Proxies of Climate Change
by Johnny in Ecographica
Vertebrate Proxies of Climate Change ... Read more »
Elizabeth A. Hadly. (1997) Evolutionary and ecological response of pocket gophers (Thomomys talpoides) to late-Holocene climatic change. Biological Journal of the Linnean Society, 60(2), 277-296. DOI: 10.1111/j.1095-8312.1997.tb01496.x
- May 10, 2009
- 10:13 AM
- 1,504 views
Frog Ears and Ultrasonic Playback
by Johnny in Ecographica
The “hole-in-the- head” frog (Huia cavitympanum) - so called because of its recessed ear drums- resides in hillside forest ecosystems of Borneo and Southeast Asia at elevations between 250 and 1000 meters. It is unique among the Ranidae for its ability to vocalize and hear ultrasound calls – well outside of the human range of hearing. ... Read more »
Arch, V., Grafe, T., Gridi-Papp, M., & Narins, P. (2009) Pure Ultrasonic Communication in an Endemic Bornean Frog. PLoS ONE, 4(4). DOI: 10.1371/journal.pone.0005413
- April 11, 2009
- 08:33 AM
- 1,478 views
Phylogenomics and Metazoan Evolution
by Johnny in Ecographica
During the course of constructing a “Tree of Life” based on more than 120 gene sequences and fifty-five different species, a group of scientists led by Gert Wörheide of Munich have reached two conclusions; one, all Porifera (sponges) share a common sponge-like ancestor, and two, that ancestor did not give rise to the Bilateria.... Read more »
Shubin, N., Tabin, C., & Carroll, S. (2009) Deep homology and the origins of evolutionary novelty. Nature, 457(7231), 818-823. DOI: 10.1038/nature07891
- April 11, 2009
- 10:35 PM
- 1,443 views
Cretaceous Multituberculata from Australia
by Johnny in Ecographica
Several mammalian families have been identified from the Aptian formation (where the current fossil was found), most of which are believed to represent species endemic to Australia; however one family – the Ornithorhynchidae – have also been found in Argentina.... Read more »
Beck, R., Godthelp, H., Weisbecker, V., Archer, M., & Hand, S. (2008) Australia's Oldest Marsupial Fossils and their Biogeographical Implications. PLoS ONE, 3(3). DOI: 10.1371/journal.pone.0001858
- January 31, 2009
- 12:00 AM
- 1,332 views
Sex with Flexible Partners: Socio-Ecological Reproductive Strategy #1
by Johnny in Ecographica
Reproductive strategy, simultaneous hermaphroditism... Read more »
Verena S. Brauer, Lukas Schärer, & Nico K. Michiels. (2007) PHENOTYPICALLY FLEXIBLE SEX ALLOCATION IN A SIMULTANEOUS HERMAPHRODITE. Evolution, 61(1), 216-222. DOI: 10.1111/j.1558-5646.2007.00018.x
Eric A. Fischer. (1987) Mating behavior in the black hamlet — gamete trading or egg trading?. Environmental Biology of Fishes, 18(2), 143-148. DOI: 10.1007/BF00002602
- February 15, 2009
- 12:00 AM
- 1,330 views
Sexual Selection, Good Genes and Condition-Dependent Handicaps
by Johnny in Ecographica
In regards to mate choice, ‘Choose, but choose wisely’ is the mantra of the discriminating female when seeking-out male suitors. By selecting the most fit, well-matched mates, females are able to reap the benefits of their own inclusive fecundity and be better positioned to obtain the dividends of more numerous, healthy offspring. Moreover, in looking to the future - beyond the perception and sight of Natural Selection - increased female-to-male genetic compatibility may contribute to the transmission of variability or adaptations that may ultimately factor into the fate of the population or the species as a whole. Mate choice matters; both in the here-and-now and in the long term.On the average, the female gender is better positioned to choose mates because they are most commonly (but not always) the limiting gender in a population. Females take on the greater burdens of producing ova and caring for young; they also tend to be fewer in number within a given population. The power of mate choice belongs to the female; but on what grounds is her selection made, and what criteria are weighed and measured prior to committing to a costly reproductive venture? Certainly, any mate is better than no mate at all, but when the opportunity presents itself wouldn’t it be beneficial to capitalize on the availability of the most virile, successful or healthy male – how to choose?Generally, selection of mates can be thought of as functioning along one of four lines; (1) through identifying Good Genes, (2) receiving Direct Benefit, (3) via Sensory Bias and (4) by Fisherian Runaway. These methods of mate selection may operate independently, collectively or in conjunction with other aspects of local ecology and Natural Selection – they’re not exclusive. The ability to identify “good genes” will be the focus here, with Direct Benefit, Sensory Bias and Fisherian Runaway reserved for later posts.Identifying good genes…Although human fertility clinics utilize modern molecular techniques to perform genetic assessments, “Good Genes” typically aren’t identified by non-human kinfolk in laboratory settings; rather evaluations are undertaken on the fly using an organism’s innate sensory capabilities.In its simplest form, avoidance of certain physiological cues such as developmental deformities can aid a female in filtering-out unworthy genetic sets; unusual appearances, irregular gaits or abnormal vocalizations of male callers tend to stand-out to females and are almost always avoided. In other cases elaborate courtship rituals, fighting or induced ovulation tactics may be summoned into play as a means of determining the superlative mate through tests of endurance and strength. To maintain a lockstep with these challenges and to achieve female demands, males adapt to take on behaviors, morphologies and displays that maximize their chances of being selected – they sing, dance, bribe and mesmerize. The males strive to impress, because if they succeed, they’ll be selected as a mate and be provided the opportunity to pass on their genetic compliment. Of course, all of these additional behaviors and adaptations come at a price, even beyond that associated with the routine cost of maintenance, additional nutritional requirements and energy expenditures, since predators can also be attracted to flamboyant colors and patterns. As a result of this dynamic set of circumstances, male sexually selected characteristics may sometimes seem less like a benefit and more like a “handicap.”Handicaps are those conditions that improve an animal’s chance at being selected as a reproductive mate while at the same time being detrimental to its survival. Essentially, handicaps exist as one of three types; Zahavian Handicaps, Condition-Dependent Handicaps and Revealing Handicaps.Zahavian Handicaps (named for biologist Amotz Zahavi) describe the idea that only the strongest, most fit males could afford to take on the risk and cost associated with elaborate morphologies, colors or behaviors, and for this reason those males exhibiting such characteristics are preferred to females as reproductive partners. In short, if a peacock can lug around a massive, brilliantly colored tail and still somehow manage to survive in spite of its increased visibility to predators and cost of feather development, it must be extremely healthy! Indeed, a proponent of Zahavian Handicaps would make the argument that peahens find the boldness of the peacock to be quite sexy.Revealing Handicaps are those sexually dimorphic characterizes which tend to be indicative of the presence of parasites or disease. The hypothesis was put forward by biologists W.D. Hamilton and Marlene Zuk in 1982 and details a scenario in which animals exhibit colorations based on the presence, or immunity against, specific parasites and diseases. These colorations can then be interpreted by mates prior to copulation as a means of determining the health of a potential partner.[House Finch at my Feeder]Conditional-Dependent Handicaps are those in which dimorphic characters are depicted as an overall indicator of an animal’s current health. For example, the coloration of a song bird may indicate its diet or foraging ability. Linking to current science news, research conducted by Assistant Professor Kevin McGraw of Arizona State University, indicates that dietary uptake of carotenoids by house finches (Carpodacus mexicanus) function in just such a way. McGraw explains (From ScienceDaily, here):"We are proposing a positive fitness feedback loop for these 'self-loving molecules,' given how high carotenoid accumulation can improve one's state and one's interest in selecting carotenoid richness in mates and food. This provides a window into how major sexual selection models, such as sensory biases and assortative mating, may be explained by a common, nutritional and narcissistic currency."In addition, the role of carotenoids in other areas of physiology is becoming apparent, including color vision, according to McGraw,"Carotenoids play fascinating and multifaceted roles in the lives of animals. For years, we have known that, as antioxidants, they boost human health and, as colorants, make birds colorful and sexually attractive. Now, we are blending as well as expanding these paradigms and studying how consumption of carotenoids can improve or 'tune' their color vision, promote the health of offspring as they develop in the egg, and possibly improve male sperm quality."More detail on identifying Good Genes in potential mates will be provided at a later time, and Direct Benefit, Sensory Bias and Fisherian Runaway will also be examined.Arizona State University (2009, February 13). Carotenoids Are Cornerstone Of Bird's Vitality. ScienceDaily. Retrieved February 15, 2009, from http://www.sciencedaily.com/releases/2009/02/090213114154.htmW. Hamilton, M Zuk (1982). Heritable true fitness and bright birds: a role for parasites? Science, 218 (4570), 384-387 DOI: 10.1126/science.7123238Mark Kirkpatrick, Michael J. Ryan (1991). The evolution of mating preferences and the paradox of the lek Nature, 350 (6313), 33-38 DOI: 10.1038/350033a0A. Pomiankowski (1987). Sexual Selection: The Handicap Principle Does Work -- Sometimes Proceedings of the Royal Society of London. Series B, Biological Sciences (1934-1990), 231 (1262), 123-145 DOI: 10.1098/rspb.1987.0038... Read more »
W. Hamilton, & M Zuk. (1982) Heritable true fitness and bright birds: a role for parasites?. Science, 218(4570), 384-387. DOI: 10.1126/science.7123238
- September 13, 2009
- 03:18 PM
- 1,303 views
The Selfish Bee’s Genes and the Selfish Gene’s Bees
by Johnny in Ecographica
Because of the deputation of workers as caregivers, the assigned reproductive responsibilities of the Hymenopteran queen, and other observed caste-like divisions of labor, eusocial invertebrates such as bees and ants are often presented as the exemplars of group selection theory. However, recent research published in Molecular Ecology suggests that the loyalties and actions displayed by some members of these social groups hint at far more self-centered motivations. ... Read more »
ALVES, D., IMPERATRIZ-FONSECA, V., FRANCOY, T., SANTOS-FILHO, P., NOGUEIRA-NETO, P., BILLEN, J., & WENSELEERS, T. (2009) The queen is dead-long live the workers: intraspecific parasitism by workers in the stingless bee . Molecular Ecology. DOI: 10.1111/j.1365-294X.2009.04323.x
- June 5, 2009
- 12:37 PM
- 1,300 views
Ecological Divergence in the Swallowtail
by Johnny in Ecographica
The influence of climate change on the Earth’s ecology can be as conspicuous as a hurricane, or it can be as subtle as a butterfly’s preference in oviposition sites… The interaction between environmental condition and evolutionary trajectory represents a complex and dynamic system in which the slightest deviation can be compounded to produce remarkably substantial outcomes. The idea that slight perturbances in a system’s initial state can result in large effects, is a tenet of Chaos Theory; more appropriately for this post however, this mathematical idea can be referred to as “the butterfly effect.”
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Mercader, R., Aardema, M., & Scriber, J. (2008) Hybridization leads to host-use divergence in a polyphagous butterfly sibling species pair. Oecologia, 158(4), 651-662. DOI: 10.1007/s00442-008-1177-9
- March 14, 2009
- 01:40 PM
- 1,286 views
Trilobites, Paleoecology and Anomalocaris
by Johnny in Ecographica
Trilobites, Paleoecology and Anomalocaris... Read more »
Dunne, J., Williams, R., Martinez, N., Wood, R., & Erwin, D. (2008) Compilation and Network Analyses of Cambrian Food Webs. PLoS Biology, 6(4). DOI: 10.1371/journal.pbio.0060102
- March 6, 2009
- 12:00 AM
- 1,246 views
Isotopes Used in Tracking Migration and Dispersal of Birds
by Johnny in Ecographica
Today, Megan J. Sellick, et al, published an article in PLoS One discussing the value of using hydrogen and strontium isotopes, taken from the feathers of tree swallows, to track migratory dispersion.
... Read more »
Megan J. Sellick, T. Kurt Kyser, Michael B. Wunder, Don Chipley, & D. Ryan Norris. (2009) Geographic Variation of Strontium and Hydrogen Isotopes in Avian Tissue: Implications for Tracking Migration and Dispersal. PLoS ONE, 4(3). DOI: 10.1371/journal.pone.0004735
- January 24, 2009
- 12:00 AM
- 1,240 views
Fire Ants Attack: Lizards Adapt
by Johnny in Ecographica
Genetic mutation leads to social polymorphism in invasive Solenopsis, reptile fauna struggles to adapt... Read more »
Tracy Langkilde. (2009) Fence Lizard. Bulletin of the Ecological Society of America, 90(1), 36-37. DOI: 10.1890/0012-9623-90.1.36
M. J. B. Krieger. (2005) Molecular Evolutionary Analyses of the Odorant-Binding Protein Gene Gp-9 in Fire Ants and Other Solenopsis Species. Molecular Biology and Evolution, 22(10), 2090-2103. DOI: 10.1093/molbev/msi203
- March 16, 2009
- 08:04 AM
- 1,236 views
Symbiosis and Evolution in Aphids
by Johnny in Ecographica
Below is a hodgepodge of info discussing the symbiotic relationship between pea aphids (Acyrthosiphon pisum) and the bacteria Buchnera aphidicola as it relates to adaptation and evolution. By and large, the discussion centers on recent research by Naruo Nikoh and Atsushi Nakabachi; however several other sources are listed at the bottom of this post – including the Douglas Lab’s website which is a great place to follow-up on the latest aphid-symbiosis research.Most aphids host mutualistic bacteria, Buchnera aphidicola, which live inside specialized cells called bacteriocytes. Buchnera are vital to the aphids well being as they provide essential amino acids that are scarce in its diet. Now research published in the open access journal BMC Biology suggests that the aphids' ability to host Buchnera depends on genes they acquired from yet another species of bacteria via lateral gene transfer (LGT). symbiotic bacteria Buchnera are located in specialized cells called bacteriocytes (shown green in figure) in the aphid body cavity. [Drawing by Tomás Lazo]Atsushi Nakabachi from Japan's RIKEN institute with his colleagues had previously uncovered two clusters of mRNA sequences from the bacteriocyte of the pea aphid Acyrthosiphon pisum that were encoded in the aphid genome, but similar to bacterial genes. Naruo Nikoh from The Open University of Japan and Nakabachi determined these sequences in full for more detailed analysis, and used real-time quantitative RT-PCR experiments to investigate the genes' expression levels in the aphid bacteriocytes.Phylogenetic Analysis (Figure 3 - From Article) The evidence points to LGT from bacteria to aphids. Genetic family trees show that one of the genes came from a bacterium closely related to Wolbachia, a common inherited symbiotic microbe, which infects a high proportion of insects. The aphid strain used for the study is free from Wolbachia and other closely related bacteria, but the transferred gene could be a remnant of an infection in the distant past. The evidence suggests that the aphids use these acquired genes to host Buchnera, which has lost many genes that appear to be essential for bacterial life. The association between aphids and Buchnera is over 100 million years old, and has evolved so that today neither the bacteria nor the host can reproduce without the other.According to Nakabachi, "the cases presented here are of special interest in that these transferred bacterial genes not only retain their functionality, but are highly expressed in the bacteriocyte that is differentiated so as to harbour Buchnera, which lack such genes."LGT (also referred to as horizontal gene transfer) occurs when genetic material from one organism finds its way into another organism other than its offspring. Genetic engineering uses LGT deliberately, but there is increasing evidence that LGT has taken place in many organisms (usually between unicellular organisms) naturally. This has caused a major shift in how biologists view genetic family trees.Symbiotic relationships have a great deal to teach us regarding evolution.Such interdependent relationships are not unusual in the natural world. What is unusual, report Helen Dunbar, Nancy Moran, and colleagues in a new study published [last year] in the open access journal PLoS Biology, is that a single point mutation in Buchnera's genome can have consequences for its aphid partner that are sometimes detrimental, and sometimes beneficial.The authors probe Buchnera's and A. pisum's ability to tolerate heat. When exposed to high temperatures, Buchnera is supposed to activate special "heat-shock" genes whose products help to protect proteins from heat-related degradation. By using microarrays to assess activity of A. pisum and Buchnera genes, the researchers discovered that after a four-hour exposure to 35 °C temperature, some of their laboratory strains of Buchnera upregulated the heat-shock genes, but others did not. Further analysis showed the genetic basis for the difference: a single missing nucleotide in an adenine-filled stretch of DNA, called a promoter, that's involved in activating the heat-shock gene. Testing at a range of temperatures from 15 °C to 35 °C showed that activation of the heat-shock gene was consistently lower in the lines with the missing nucleotide than in the normal bacteria.What does this mean for A. pisum's ability to tolerate tough conditions? To answer that, the researchers asked whether exposing juvenile aphid hosts of Buchnera with either long or short promoters to four hours of high temperatures (35 or 38 °C) affected their ability to reproduce. They found that few of the aphids with bacteria bearing short promoters reproduced after the heat treatment, while those with bacteria bearing the longer promoters had no trouble. In addition, aphids that had been exposed to the high temperatures and had the short-promoter-bearing bacteria weighed less as adults and had far fewer Buchnera inside them than did their counterparts with long-promoter-bearing bacteria.Given these seemingly huge disadvantages to dropping a single adenine, it's hard to believe the mutation could last long in a Buchnera population. Yet, by sequencing and comparing the Buchnera associated with various A. pisum lines, the researchers discovered that the short-promoter option had arisen and been fixed twice in laboratory stock and was also found at frequencies of 21% and 13%, respectively, in bacteria in field-collected aphids from Wisconsin and New York.Population genetic theory predicts that when a mutation is maintained in a population at high frequencies, it likely confers some benefit to its bearer. What could be the advantage of carrying a gene that causes one to lose the ability to reproduce at high temperatures?A clue to the answer comes from the wild populations in which the mutation was not found: those living in Arizona and Utah. Could the bacterial mutation confer a competitive advantage that's only relevant in cooler climates? To find that out, the researchers performed a second test using a range of four-hour exposure temperatures. They discovered that short-promoter bacteria-bearing aphids produced progeny faster than did the normal ones when raised at 15 °C or 20 °C. Thus, though aphids containing bacterial symbionts with the heat-shock-promoter mutation fare worse than normal aphids after exposure to high temperatures, they do better under cool conditions, giving the mutation a selective advantage that causes it to be maintained in the population.In addition to their explorations of A. pisum and its Buchnera, Moran's team also looked for and found multiple-adenine stretches related to heat-shock genes in Buchnera symbiotic with other aphid species. This offers fertile ground for further study of the intriguing interplay among aphids, bacteria, and temperature.Sources: Eureka Alert, PhysOrg and Douglas LabNikoh, N., & Nakabachi, A. (2009). Aphids acquired symbiotic genes via lateral gene transfer BMC Biology, 7 (1) DOI: 10.1186/1741-7007-7-12Dunbar, H., Wilson, A., Ferguson, N., & Moran, N. (2007). Aphid Thermal Tolerance Is Governed by a Point Mutation in Bacterial Symbionts PLoS Biology, 5 (5) DOI: 10.1371/journal.pbio.0050096... Read more »
Dunbar, H., Wilson, A., Ferguson, N., & Moran, N. (2007) Aphid Thermal Tolerance Is Governed by a Point Mutation in Bacterial Symbionts. PLoS Biology, 5(5). DOI: 10.1371/journal.pbio.0050096
- September 21, 2009
- 09:49 AM
- 1,234 views
Organic Chemistry and a Walkingstick Insect
by Johnny in Ecographica
The “two-striped” walkingstick (Anisomorpha buprestoides) is a familiar species in the southeastern United States. Here in Florida, there are a few varieties, each of which can be distinguished in field by the color of the parallel stripes that run down the length of their back. For example, the male and female pictured below (snapshots taken last week) are commonly referred to as the “brown two-striped” walkingstick. Other colormorphs include the “white two-striped” and the “orange two-striped”.... Read more »
Dossey, A., Walse, S., & Edison, A. (2008) Developmental and Geographical Variation in the Chemical Defense of the Walkingstick Insect Anisomorpha buprestoides. Journal of Chemical Ecology, 34(5), 584-590. DOI: 10.1007/s10886-008-9457-8
- February 13, 2010
- 02:37 PM
- 1,219 views
How to Study Invasive Species, a Conservation and Ecological Imperative
by Johnny in Ecographica
...the invasive could theoretically replace the native with little ill effect to the ecosystem; the invasive could fill the niche left void by the out-competed native plant without disrupting the energetics of the plant community as a whole. BUT, at the same time, a newly arrived invasive species may have a distinct advantage over a native transient because it is completely foreign to the ecosystem. For example, being unrecognized by its new environment the invasive may, for a period of time, be buffered against attack by herbivores, parasites and other stressors that may be actively reducing the fitness of the locals. ... Read more »
Simberloff, D. (2010) Invasions of Plant Communities – More of the Same, Something Very Different, or Both?. The American Midland Naturalist, 163(1), 220-233. DOI: 10.1674/0003-0031-163.1.220
- January 31, 2009
- 01:18 AM
- 1,201 views
Sex with Flexible Partners #2
by Johnny in Ecographica
During the first installment in this series on reproductive strategy (available here) the topic of hermaphroditism was introduced and a quick summary of simultaneous hermaphroditism was provided. Moving forward from that discussion, this short essay will provide a synopsis of a category of hermaphroditism referred to as “sequential hermaphroditism.”Recall from the first essay that simultaneous hermaphroditism refers to organisms that can function as both a female and a male during a single mating session. These individuals have the ability to produce both ova and sperm and, with social dynamics temporarily laid aside, can essentially mate with any adult member of its population. Using this abbreviated definition of simultaneous hermaphroditism, notice that the word “function” has a specific meaning in this context; not only does it imply the presence of reproductive organs, but it also requires the action of using those organs during mating - this is a minor, but important point.For example, a “functional female” is an organism that undertakes the female role within the context of its social hierarchy and produces only ova during a single mating session; it exhibits the outward coloration and morphology of a female member of its species. If that functional female organism should then be taken into a laboratory, dissected by a biologist and found to have male gonad tissue as an addition to its female anatomy, it would still be considered a functional female, even though male tissues were found to be present. The same applies for a “functional male;” it would still be considered a functional male even if female reproductive tissues were later discovered. This is a significant delineation when discussing hermaphroditic organisms because frequently sexual characteristics are very difficult to distinguish. For example, on close examination of fishes belonging to the genus Lythrypnus they are often found to possess reproductive tissues of both females and males; this may erroneously lead some to conclude that the fish are simultaneously hermaphroditic, but in fact individuals function entirely as one of the two sexes when in the wild; it’s either a male or a female, not both. If at some point Lythrypnus changes its function from one sex to the other, it still wouldn’t be classified as a simultaneous hermaphrodite – because it still wouldn’t function as two sexes simultaneously – rather, it would be said to be “Sequentially Hermaphroditic.”[Lythrypnus] Sequential hermaphroditism can occur in one of two ways; either a functional male can change to a functional female, or vice versa, a female can change to a male. Organisms which are born male and later become female are said to exhibit “protandry.” Here, the prefix “proto-” is derived from Latin and translates as “first;” the root word “andro” refers to androgen, a steroid hormone responsible for masculine characteristics. Protandry therefore means “first a male.” Correspondingly, “protogyny,” means “first a female” and is used when describing the trait of a female undergoing sex change to a male. Both protandry and protogyny are used as reproductive strategies in a variety of hermaphroditic organisms. Sometimes sex changes occurs at a predetermined age in conjunction with the normal growth and maturation process, in other cases this change can occur as a response to environmental or social triggers. With the polychaete worm Ophryotrocha puerilis, sex change occurs as a strategy for dealing with the expense of creating ova, the same expense that lead to the compromise of egg trading in the Hamlet fish (Hypoplectius) mentioned in the first essay.Recall from the Hamlet fish discussion that because of anisogamy - a size difference between male and female gametes - the cost of producing ova is greater than that associated with making sperm; eggs are expensive, sperm are cheap. Bearing this in mind, it follows that the females of a species with greatest access to resources will tend to grow larger and, in turn, be able to produce more eggs than females with more-limited access to resources. The larger the female, the greater fecundity she exhibits. Monogamous polychaete worms take this lesson to heart, within the male-female pair bond the female is the larger of the two annelids. The male polychaete typically develops more slowly and is normally smaller in size; therefore the assigning of burdensome egg development duties to the larger member of the duet is a better reproductive strategy. At least until the male hits a growth spurt![Ophryotrocha puerilis]Although the male polychaete is a slow starter in regards to growth, at a certain point in adulthood he really hits his stride and rapidly outsizes the female. This creates a reproductive opportunity for the pair-bond. With increased size, the male is now better positioned to handle egg development. There’s only one problem – he’s a male! Not wasting any time, the male changes to a female and takes up the task of producing female gametes. In concert with this change, the old female, now the smaller of the two, changes to a male and begins to produce sperm. This double sex change improves the sexual efficacy of the pair and results in more offspring produced. However, there is one additional complication with this highly plastic stratagem…Now that the original female has changed to male and is no longer responsible for egg production, her primed-up metabolism, which up to this point had to supply energy to both her and her eggs, causes the fish to really “pack on the pounds.” In time, the original female, which is now male, is once again larger than the egg-producing female of the pair-bond...No worries though, the pair just change back to their original sexes – that’s what being a flexible partner is all about.In talking about sequential hermaphroditism strategy in relation to body size, the polychaete worm exhibited a relationship known as the “size-advantage hypothesis.” The size-advantage hypothesis explains that when an organism reproduces best as one sex whilst either “young and small” or while “old and big,” sex changes can occur when transitioning between these two categories. The male worm benefited from being young and small, but as it got older and larger this benefit was reduced; in order to benefit from being older and bigger it had to change sexes – to a female.It should be mentioned that like the sequential variety, some simultaneous hermaphrodites utilize this size-advantage relationship as well. The freshwater snail Helisoma trivolvis makes use of it every time it encounters a potential mate. Unlike the Hamlet fish, Helisoma doesn’t share in the costs of egg production, when two snails meet whichever one happens to be the larger takes on the role of the female for that particular mating period.[Helisoma trivolvis] During the next Sex with Flexible Partners installment, the size-advantage hypothesis will be tested in situations for which the “eggs are expensive, sperm are cheap” rule doesn’t necessarily apply and the topic of hermaphroditism as a reproductive strategy will be drawn to a close. P MUNDAY, P BUSTON, R WARNER (2006). Diversity and flexibility of sex-change strategies in animals Trends in Ecology & Evolution, 21 (2), 89-95 DOI: 10.1016/j.tree.2005.10.020Kohei Ohta, Mayumi Hirano, Takayuki Mine, Hiroshi Mizutani, Akihiko Yamaguchi, Michiya Matsuyama (2007). Body color change and serum steroid hormone levels throughout the process of sex change in the adult wrasse, Pseudolabrus sieboldi Marine Biology, 153 (5), 843-852 DOI: 10.1007/s00227-007-0856-0C. G. Norton, A. F. Johnson, R. L. Mueller (2008). Relative size influences gender role in the freshwater hermaphroditic snail, Helisoma trivolvis Behavioral Ecology, 19 (6), 1122-1127 DOI: 10.1093/beheco/arn099... Read more »
P MUNDAY, P BUSTON, & R WARNER. (2006) Diversity and flexibility of sex-change strategies in animals. Trends in Ecology , 21(2), 89-95. DOI: 10.1016/j.tree.2005.10.020
Kohei Ohta, Mayumi Hirano, Takayuki Mine, Hiroshi Mizutani, Akihiko Yamaguchi, & Michiya Matsuyama. (2007) Body color change and serum steroid hormone levels throughout the process of sex change in the adult wrasse, Pseudolabrus sieboldi. Marine Biology, 153(5), 843-852. DOI: 10.1007/s00227-007-0856-0
C. G. Norton, A. F. Johnson, & R. L. Mueller. (2008) Relative size influences gender role in the freshwater hermaphroditic snail, Helisoma trivolvis. Behavioral Ecology, 19(6), 1122-1127. DOI: 10.1093/beheco/arn099
- March 8, 2009
- 12:00 AM
- 1,184 views
Sexual Competition and Lemurs
by Johnny in Ecographica
Ivan Norscia, Daniela Antonacci and Elisabetta Palagi recently published an article in which inter- and intrasexual competition between wild prosimians is examined from the perspective of economic power distributions and as a metaphor for financial markets. [Lemur, Propithecus verreauxi] Essentially, their findings indicate that competition for females by males typically manifests as an “olfactory tournament” in which males try to “out bid” rivals by more proactively scent marking. This strategy accurately reflects dominance between males and is less costly than engaging in combative or otherwise aggressive behaviors.Intersexual competition (male-female selection) in the lemur is accomplished via a strategy of “commodity exchange” in which males offering the best resources (food) or services (grooming) are preferred and ultimately gain advantage through more frequent copulations.The article (available here) is clearly written and is jargon free; it could have just as easily appeared in a Pop-Sci magazine as a journal. For this reason, as well as to compliment my prior posts discussing sexual selection, I’ve pasted the Introduction and Videos below.NOTE- I removed references for ease of reading; please refer to the original article linked above for corroboration."In biology, as well as in economics and politics, power is a key concept for understanding asymmetrical dyadic relationships. Distributive power can originate from both dominance (when force is used) and leverage (when the use of force is not possible). An individual has leverage over another when that individual possesses something that the other needs but cannot acquire through coercion. In this case, trading becomes essential for mutually beneficial interactions within social groups, both in economical and biological markets. An important feature of market models is that the expected future gains are actively influenced by playing off potential partners against each other. The typical game theory approach includes only two players and, although this is changing within economics as well as biology, the classical models do not take into account partner choice. In contrast, the biological market theory includes multi-player models, that is theoretical games with at least three or more “players” (traders, in the market systems). Two or more classes of traders (sex classes, rank classes, etc.) exchange commodities in biological markets to their mutual benefit. Different group members can offer different kinds of commodities in exchange for alternative ones that they do not currently possess. Usually, competition acts as the driving force within the same trader class (including all members offering the same kind of commodity) while cooperation can occur between different trader classes.
Male countermarking behaviour on a female scent deposition In the mating market, the balance of power tilts in favour of females whenever males cannot force females into mating (as it happens in sexually monomorphic species or when females form coalitions). Consequently, males depend on females for breeding opportunities and must compete to prove their superiority to females, thus increasing their possibility to be selected. Males can engage in both contest competition via physical/ritualized fighting and outbidding competition, in which a male plays off rivals by making a better offer. In the latter case, males can secure the favours of a female by advertising their quality (e.g. the dominance status) through visual or olfactory displays and/or by being more generous than others in providing a commodity in exchange for female access (competitive altruism). One of the most valuable commodity that can be offered in social mammal groups is grooming, which is used for parasite removal, stress reduction, and as social cement to start, consolidate, or repair relationships. Grooming is a commodity that can be exchanged for itself or for breeding opportunities.
Copulation followed by a grooming session Sociality is widespread among mammals and particularly among anthropoid primates (monkeys and apes). In prosimians (the most ancestral group of primates) sociality is the exception more than the rule. Among Malagasy prosimians (lemurs), few species combine a powerful olfactory system (retained from basal mammals) and puzzling features like group living, female priority over resources, and absence of sexual dimorphism. Such combination of features makes gregarious lemurs the ideal model to understand the biological bases of mate selection by females, who cannot be accessed by force or using food as exchange commodity. In particular, we selected the diurnal species Propithecus verreauxi of south/southwest Madagascar to find out which male strategies are successful to maximize breeding opportunities."
Copulation in which intromission and thrusting were unambiguously observed Ivan Norscia, Daniela Antonacci, Elisabetta Palagi (2009). Mating First, Mating More: Biological Market Fluctuation in a Wild Prosimian PLoS ONE, 4 (3) DOI: 10.1371/journal.pone.0004679... Read more »
Ivan Norscia, Daniela Antonacci, & Elisabetta Palagi. (2009) Mating First, Mating More: Biological Market Fluctuation in a Wild Prosimian. PLoS ONE, 4(3). DOI: 10.1371/journal.pone.0004679
- January 25, 2009
- 11:31 PM
- 1,161 views
Brassica oleracea: Artificial Selection is Delicious!
by Johnny in Ecographica
Brassica oleracea: Artificial Selection is Delicious!While reading through a few abstracts at the Journal of Insect Science - looking for information regarding introduced predators as biological controls for invasive insect species - I came across an article discussing Delphastus catalinae (ladybird beetles, image at below right) as a control agent for Bemisia tabaci (whiteflies). Whiteflies are major pests, and have recently gained infamy for attacks in Florida.A good description from a recent Florida news article: “The whitefly is not a fly, but a flying insect that is very similar to some scale insects. It has sucking mouthparts and some species are known to cause sooty mold, but this species does not. Heavy feeding by the adult and the immature stages — which are immobile, flattened and translucent with red eyes — cause yellowing of the foliage and significant defoliation. The undersides of leaves are coated with a pebbly like, whitish residue, which is the empty casings or “skins” left behind by the immature stages as they molt and develop into the adult stage.”Luckily, D. catalinae is a voracious predator and both its larval and adult stages feed on B. tabaci’s eggs, larvae and adults. A couple of courting B. tabaci are pictured below.At any rate, moving on to the intended point of this post - although the mentioned research centered on the affects of temperature variation on Delphastus’ predatory capabilities, the article happened to mention that one of the plant species that may most benefit from Delphastus’ protection is Brassica oleracea.Rummaging through my mental file cabinet in an attempt to reference B. oleracea, I soon came to the realization that the species has undergone a tremendous amount of artificial selection and is a mainstay of modern dies.In its wild state B. oleracea is known as “wild cabbage” and looks rather like a common weed you might find in your backyard, here's a photo:However, through artificial selection the plant has proven to be highly flexible and has been bred for its delicious leaves, inflorescence, stalks, leaf buds and roots. Some of the common names for varieties of B. oleracea include; broccoli, cauliflower, brussel sprouts, kale, kohlrabi and cabbage.... Read more »
Legaspi J, Legaspi BC, Simmons AM, Soumare M. (2008) Life table analysis for immatures and female adults of the predatory beetle, Delphastus catalinae, feeding on whiteflies under three constant temperatures. Journal of Insect Science.
- May 30, 2009
- 02:43 PM
- 1,158 views
Mangroves, Eutrophication and Dead Zones
by Johnny in Ecographica
Recent research demonstrates that contrary to previous studies nutrient influx of Nitrogen and Phosphorous into coastal forests may contribute to mortality in the highly adapted mangrove trees. In a time of advancing Dead Zones, these findings hasten warnings about the dire consequences of poor-conservation efforts in regards to the world’s starkly limited water resources. ... Read more »
Lovelock, C., Ball, M., Martin, K., & C. Feller, I. (2009) Nutrient Enrichment Increases Mortality of Mangroves. PLoS ONE, 4(5). DOI: 10.1371/journal.pone.0005600
- May 24, 2009
- 08:54 AM
- 1,124 views
A Pliocene Hominin as Prey Item
by Johnny in Ecographica
With all of the fanfare over human origins and primate evolution the last few days, I thought that it would be appropriate to take a quick look at an article recently published in The American Journal of Physical Anthropology. The article, “Plio-Pleistocene eagle predation on fossil cercopithecids from the Humpata Plateau, southern Angola,” discusses the taphonomic evidence for the taking of primates by predatory bird around the Pliocene/Pleistocene boundary at the renowned Taung site in South Africa – including the taking of a hominin.... Read more »
Gilbert, C., McGraw, W., & Delson, E. (2009) Brief communication: Plio-Pleistocene eagle predation on fossil cercopithecids from the Humpata Plateau, southern Angola. American Journal of Physical Anthropology. DOI: 10.1002/ajpa.21004
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