Christopher X J. Jensen
Associate Professor, Pratt Institute

Evolution 2010 Day 4 (June 28th)

Posted 28 Jun 2010 / 0

View from the screen, as I try to capture some of the best science I have listened to and seen

Early in the morning there were no whole sessions that consistently peaked my interest, so I spent my morning bouncing between a variety of talks. Tomas Brodin gave an interesting talk entitled “Can environmental filtering of animal personalities promote speciation?”. Working with frogs that disperse from the mainland to nearby islands outside Umea, Sweden, Brodin provided convincing evidence that the frogs who colonize islands show bolder behavior in the lab during their early adult stage of development. His work suggests that there can be “environmental filtering” of different genotypes for behavior, and he is going to pursue the genetic basis for these “personality differences” in his future work.

There are a lot of people interested in speciation who look at hybrid zones created when the home ranges of previous-isolated species come back in contact with each other, often due to changes in climate. In his talk “Maintenance of phenotypic variation despite hybridization in a secondary contact zone in tree squirrels (Tamiasciurus)”, Andreas Chavez presented work suggesting that viable F2 hybrids of two species of squirrels (Douglas and Red) are being generated in an area of northern Washington state where their ranges overlap. Now that the existence of these hybrids has been established, there is a lot of interesting work to be done establishing their viability, particularly in relation to predator vulnerability.

Adrian Paterson discussed the relationship between penguin phylogenies derived from genetic data and the distribution of behavioral traits in his talk “Black or White? The evolution of behavioral traits in penguins”. Although the genetic phylogeny resolves well, most behavioral traits are not distributed in concordance with the inferred phylogeny, suggesting that many penguin behaviors are the product of convergent evolution.

Mollie Manier gave an interesting talk about sperm competition in Drosophila species (“Mechanisms of competitive fertilization success in conspecific and heterospecific matings of Drosophila”). Female Drosophila store sperm in two kinds of structures, a pair of spermathecae and a single seminal receptacle (SR). The SR is where fertilization occurs, so the spermathecae serve only a storage function. Using transgenic sperm that glow different colors, it is possible to look at the dynamics of sperm competition. Manier’s experiment was complex and I did not follow the entire pathway of her data, but she seemed to show that it is possible for females to displace the sperm of earlier matings in favor of a new mating. The intensity of this effect seems to vary from species to species.

Elizabeth Leger’s talk “Natural selection in the wild as a part of large-scale restoration” demonstrated the importance of using an evolutionary perspective to help make decisions about restoration efforts. In Nevada, where fires knock out native plants and facilitate the invasion of exotics, there is an ongoing (and expensive!) effort to actively seed native plants wherever fire creates the conditions that might allow for invasive establishment. Unfortunately this effort has been largely unsuccessful due to poor survival of the transplanted natives. What Leger showed in common garden experiments was that there is a mismatch between the local environment and the genotype of the native species used to generate seed. She demonstrated that being a “native species” certainly does not guarantee the possession of a “locally native genotype”. The cause of this mismatch? Apparently it is selective breeding of plants for traits desired by large seed-producing companies outside of Nevada; these cultivars of native species have poor drought tolerance. Leger reported that her results have caused the seed industry to hate her, but have allowed managers to make better decisions. It is nice to see such a clean diagnosis of the evolutionary basis of an applied problem.

Douglas Yu presented an interesting paper related to cooperation called “Let the right one in: a microeconomic approach to partner choice in mutualisms”. He pointed out that most models and synthetic reviews of mutualisms focus on post-association mechanisms for choosing beneficial partners. The work he presented concerns pre-association mechanisms that allow hosts to screen potential mutualistic partners for their beneficial traits. An example of this kind of screening behavior is displayed by the bobtail squid, which harbors symbiotic light-generating bacteria. As these symbiotic bacteria are horizontally rather than vertically transferred, there is an incentive for the squid to screen out potentially-parasitic strains and only allow the mutualistic strain to establish. This is accomplished by producing levels of oxygen that can only be detoxified by the desirable light-producing metabolism of the mutualistic bacterial strain. Yu pointed out that this kind of screening can be understood by a class of microeconomic models that tackle the “hidden action” problem of hiring a job candidate of uncertain quality.

I spent the rest of the morning in a sexual selection session. Kevin Judge presented a multimedia-rich talk about sexual conflict in Cyphoderris buckelli entitled “Material benefits of sexual cannibalism in a primitive acoustic insect”. Like many other insect species, this katydid exhibits a mating system where males provision females. In this case, the male has a set of fleshy wings which he can expose to attract a female. The female then mounts the male and attempts to chew on these wings, sucking out some of his blood in the process. The male then attaches himself to the female through the use of a gin trap at the end of his body, compelling her to mate with him. This sets up a conflict, as the male has an incentive to withdraw his wings as soon as he can grab hold of the female, whereas the female has an incentive to avoid being grabbed for as long as possible while she cannibalizes the male. If this wasn’t all gruesome enough in verbal description, Judge also had videos of this conflict in action. In his experiment he tested the prediction that females will be more likely to allow mating when they are in poor nutritional condition; he did find that hungry females feed more, inflict more damage on males, and mate more often.

Roberto Munguia-Steyer discussed male-male conflicts in a species of spider in his talk entitled “Male dimorphism across ten populations in the wild: harem size, sneaker mating opportunities and gonadic investment in the arachnid Serracutisoma proximum”. Like many populations where males protect female “harems” (really just areas where females aggregate) in order to maximize their chances of being the only male to inseminate the females, these populations have developed two male behavioral strategies: territoriality and sneakiness. Through observational studies, Munguia-Steyer showed that these behavioral types correlate with differences in morphology: territorial males possess longer front legs for the purpose of wrestling away introgressing males, whereas the sneaker males have smaller front legs (more similar to the females). Smaller males were also shown to move more, consistent with the opportunistic roaming behavior hypothesized for the sneaker strategy. Interestingly, there was no asymmetry between males in terms of their gonadic allocation. Based on the reality that every sneaker male is likely to have his sperm competed against at least the territorial male, one might think that the sneaker males might have evolved increased sperm abundance or viability, but Munguia-Steyer showed that dissected gonads are of comparable mass in territorial and sneaker males. Based on his field observations, this seemed to arise from the fact that the territorial males defending the largest harems were also the most inundated with sneakers. Both morphs may have equal need to allocate as much as possible to sperm competitiveness, removing any asymmetry.

In the same session dedicated to sexual selection, Matthieu Delcourt delivered a talk entitled “Genetics and nature of condition dependence in a multi-component sexual display”. Using Drosophila serrata as a model system, Delcourt sought to understand how “condition dependence” might be affected by sexual selection. The condition dependence (really plasticity) described was a difference in the amount of a contact pheromone produced in two different nutritional environments. He showed that female preference is for males who display this conditional dependence, although there seemed to be a conflict between what females wanted and what male genetic variability would allow, calling into question whether sexual selection could really select for male plasticity. I wasn’t totally clear on why females might want males that show this plasticity; presumable the females must be directly or indirectly selecting for some male trait that will benefit their offspring, but this study did not identify this benefit.

Tim Billo presented a very well-executed study entitled “Effects of sexual selection on the structure and evolution of calls in two recently diverged bird species”. Using two species of Manakins, he tested the prediction that lekking males will display greater stereotypy in vocalizations directed at females than males due to the stabilizing effects of female choice. Using playback to generate male responses directed at both males and females, Billo showed that there is greater variation in male-directed vocalizations than those directed at females. In addition, the stereotyped female-directed calls of each species are distinctly different, suggesting a means by which these adjacent species might maintain reproductive isolation. The study presented used two separated (allopatric) populations, but these species also interact over a hybrid zone, and Billo’s next work will be to look at characteristics across this gradient.

One of the most elegant and thorough experiments presented thus far came from Caroline Nieberding under the title “Sexual selection on olfactive communication in males of the butterfly Bicyclus anynana: a comparison with selection pressures in female moths”. Nieberding was investigating the role of bombykol, a sex pheromone used for communication in organisms ranging from elephants to butterflies. Although this pheromone is conserved across many species, its specific meaning is species-specific and relates to its blend with other pheromones. Her investigation focused on the butterfly androconia, a specialized wing scale found on male butterflies that produces pheromones. First Nieberding quantified female response to various pheromones which had be accurately identified by gas chromatography. Then  she removed the androconia of some males and found that this lowered their mating success. Finally, she perfumed males whose androconia had been removed with different synthetic blends of pheromones; these males regained the mating success of their peers with intact androconia, providing strong evidence that the androconia produces a particular blend of pheromones. In an additional step, Nieberding was able to show that the blend of pheromones that is most attractive to females is that of a middle-aged male, suggesting that females are using pheromone blends to assess mate quality.

One interesting commonality between many of the sexual selection talks I attended was the near-complete rejection of Bateman’s principle. Female promiscuity is now assumed, and the picture of sexual conflict has been clarified now that the idea of the coy female has been cast aside. There’s still a lot of work to be done to dispatch this idea outside the walls of gatherings like Evolution 2010: popular conceptions and even textbooks still have a Bateman-esque tone despite advances in our understanding of male and female reproductive strategies.

Each talk at the Evolution meeting is supposed to be only twelve minutes long, with three minutes for questions that also allow for people to move from talk to talk. Some people are miraculously concise and finish with plenty of time to spare, but it is much more common for talks to take the entire fifteen minutes or even to be cut short (or on rate occasions be allowed to obnoxiously go over time). The brevity of time alloted to each talk limits what can be communicated; the worst talks try to shoe-horn complex concepts or data appropriate to an hour-long talk into the fifteen minute slot, most talks just limit what they try to communicate, and an occasional talk manages to elegantly communicate complex ideas within the severe time constraints. Leithen M’Gonigle presented a talk entitled “Ploidy and the evolution of parasitism” with that rare combination of complexity and necessary brevity. His task was to prevent conceptually-complex variants of a model of host-parasite interactions without losing his audience; his solution was to use cartoons. This may sound funny, but the effective use of visuals allowed him to keep his audience on track with the variants of the model, allowing the significance of the results to shine through. What his simulations show is that whether or not the evolution of polyploidy aids in the evolution of parasitism will depend on what mechanism the host uses to identify and fight off the parasite. Under the matching alleles model (MAM), parasites use an allele that matches one of the hosts to evade the host defenses. This sets up an incentive for polyploidy, as having a diverse set of alleles expands the diversity of hosts you can infect. In contrast, if the appropriate representation of the host defense system is the inverse multiple alleles model (IMAM), parasites can only infect hosts without the allele they possess, and having fewer copies of an allele is advantageous.

Theodore Stankowich presented an interesting talk entitled “Black, White, and Stinky: The Evolution of Aposematic Defenses in Terrestrial Carnivores”. He wanted to determine what the connection is between potentially-aposematic coat coloration patterns and the use of anal gland secretions. While we all know the skunk as an advanced form of anal gland defense, there are also other species that use this defense in a variety of less sophisticated forms. Using a set of characteristic scores, Stankowich used model selection to determine how different factors affect the defensive strategy and coat color combination. He ended up identifying four strategies amongst the carnivores he considered: those with uniform coat color and no anal secretion defense (relying on crypsis), those with spotted coats and no anal secretion defense (relying on crypsis in arboreal habitats), those with spotted coats and anal secretion defense (cryptic from afar, but aposematic up close), and those with bold black and white stripes and anal secretion defense (living in habitats where hiding is not an option, strongly aposematic).

Samantha Price presented a thought-provoking talk entitled “You are what you eat: diet and body size evolution in mammals”. She was interested in the evolution of different trophic strategies, specifically the transition between carnivorous, omnivorous, and herbivorous diets. Using a phylogeny of 3500 terrestrial mammals (no bats, no marine mammals) she analyzed the rate of translation between these different states. Not surprisingly, the shift from herbivore directly to carnivore was not present in her extensive data set. This seems pretty obvious just based on the categorization system she used, as herbivores and carnivores are end states whereas ominvores exist along a continuum between strict herbivory and strict carnivory. What was more interesting was the finding that the transition from carnivore to omnivore to herbivore was much more common than the reverse. This suggests that becoming a carnivore is a larger evolutionary challenge, and Price explained this finding as a logical consequence of the trophic pyramid, wherein opportunities for carnivory are fewer than those for more basal herbivores and omnivores. She also found that herbivores tend to be larger and more abundant whereas carnivores are lower in abundance and smaller. While these findings were not earth-shattering, they do provide a new angle on an age-old comparison.

The final talk of the night was the Society for the Study of Evolution Presidential address given by H. Allen Orr entitled “Change in Evolutionary Biology”. Like Jonathan Losos, who gave the American Society of Naturalists Presidential talk two nights before, Orr expressed some trepidation in giving a talk that was supposed to represent the organization but also inevitably would be based on his perspectives. Like Losos he delivered this humble admission and then followed it up with an unflinching powerhouse of a talk.

Orr began by discussing comparisons with physics engendered by discussions with his wife, who is physicist. As compared with evolutionary biology, Orr contends that physics is far more daring, unafraid and even encouraging of “crazy ideas”. He characterized some ideas in evolution as being radical (neutral evolution, gene-centered evolution, punctuated equilibrium, and some parts of evo-devo) but came to the overall conclusion that for the most part evolutionary biology is a very conservative science. In trying to figure out why evolutionary biology has been so conservative, Orr suggested both bad and good reasons. The bad reasons include the fact that we are a scientific field “under siege” by creationist attacks, and this defensive posture makes the field afraid to make mistakes. The grant culture similarly rewards slow incremental progress over radical or revolutionary ideas. The good reason that evolutionary biology has been conservative is that bad ideas bog down a field for a long time, and this conservatism towards new ideas has prevented us from going down costly dead ends. Orr then diagnosed the difference between evolutionary biology and physics as one driven by the costs of debunking bad ideas. The revolutionary spirit of physics produces a lot of bad ideas, but because physicists have access to conclusive experiments and lots of data, these bad ideas are not costly (supercollider budgets notwithstanding) because they are quickly rejected. In contrast, evolutionary biology has historically not been good at quickly rejecting bad ideas, which has led to a number of historical eras in which little theoretical progress was made.

Turning towards his own main interest, the science of speciation, Orr illustrated the nature of this tension between new ideas and available data. He characterized the period following the modern synthesis (within which Dobzhansky and Mayr established the basic theories of speciation) as “forty years of silence”. During this time there were plenty of crazy ideas, but because these ideas could not be adequately tested, none were rejected and the field stagnated. Enter in a new source of data in the 1980’s (the birth of molecular genetics) and suddenly evolutionary biology experienced a great leap forward. Bad ideas were exposed to testing and rejected, leaving behind only those ideas which could survive comparison to data.

Orr contends that an injection of data has four profound effects on a scientific field. First, it shows where and when scientists were wrong in their own ideas. This natural selection of ideas in the environment of data is critical to progress in all sciences, and Orr did a great job of humbly pointing out where he was wrong and reinforcing “being wrong” as a necessary component of successful science. Second, data allows us to know where others were wrong, clearing the field of idle speculation and leaving a few surviving ideas further scrutiny. Third, data often provides big surprises, yielding new insights that were not part of prevailing wisdom. Finally and perhaps most important, an abundance of data lower the cost of speculation, allowing a field the freedom to blossom into a new era of creative thought.

Orr believes that the abundance of cheap genomic data is going to usher in a new era a rapid progress in evolutionary biology. In some sense, this genomic data gives us the chance to adopt the more radical approach of physics because the cost of testing potentially bad ideas has gone way down. I love the idea that science only works when it can provide the environment in which to select out bad ideas, and I am apt to buy into most of what Orr had to say. On two points I have some misgivings. First, I really fear that the abundance of data may also lead to reinforcement of evolutionary orthodoxy. Why? Well, the problem with lots of data is that you need to start somewhere in sifting through it all, and I think that most evolutionary biologists will still look to test dominant paradigms rather than testing radical new ideas. I also think that genes are not the complete data set we sometimes treat them to be. This is bad for science but good for humanity, as the real emergence of most living things occurs when the environment and genes interact. Although knowing a lot about genes certainly helps us to understand their interaction with the environment, data looking at this interaction is still hard-earned. My fear is that evolutionary biologists may take the path that is easy, relying too heavily on genes as an isolated source of data, rather than the more productive but laborious path of understanding the interactions between genes and environments that drive developmental processes. This would usher in a new era of unbalanced science rather than a new era of rapid discovery.

Poster sessions serve as a great way to spur in-depth discussion and bring potential collaborators together

I was able to attend this meeting thanks in part to funding from the Pratt Institute Faculty Development Fund.

Conferences, Evolution, Society for the Study of Evolution

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