Evolution 2014: Day 1

My first session of the day was spent entirely in a Symbiosis session. I am fascinated by symbiosis, particularly mutualistic symbiosis, so I am always looking for cool new stories to help illustrate the concept for my students. This session featured a lot of talks on microbial symbionts, which are also of interest to me. The host taxa featured varied widely — I heard about lemurs, crayfish, aphids, beetles, kudzu bugs, and sponges — but many of the stories were the same. While all the talks illuminated the pattern of symbiosis found in their focal species, discovering this pattern of association is a lot easier than explaining it.

Andrew Smith showed that pea aphids — which harbor a bacteria which harbors a phage that confers resistance to a parasitoid — maintain different symbionts in different regions, suggesting coevolution with local enemies. Jannelle Couret provided strong evidence that Kudzu bugs do much better when they possess a microbial symbiont, and that the symbiont’s value depends on what plant (kudzu or soybeans) serves as the host. It is not yet know why or how the symbiont conveys this benefit, but early evidence suggests that lack of the symbiont leads to morphological changes in the digestive tract of these bugs. Bronwyn Williams showed how the phylogenies of crayfish and their annelid parasites are not all that concordant, which brings up some very interesting questions about how these host-parasite pairs have coevolved and to what degree the parasites have been capable of dispersing across geographically boundaries that separate their host species. Erin McKenney used microbial DNA to show that the gastro-intestinal flora of three different lemur species (one fruit eater, one generalist, and one leaf eater) develop differently from birth through weaning. Bob Thacker also used microbial DNA — in his research on sponge microbiomes — to show that different species of sponges tend to harbor different strains of bacteria.

My second session, Coevolution of Mutualists/Hosts/Parasites kept the symbiotic theme going (Why is it that there are there separate “coevolution of symbionts” and “symbiosis” categories? Do symbiotic organisms ever fail to coevolve with each other?). Cécile Gracianne showed that the genetic diversification of sea beets does not match the diversification of their nematode parasites, although the boundaries created by different clusters of sea beet diversity do create boundaries that subsume clusters of nematode diversity. Mary McKenna presented some really interesting work on the thyme plant and the volatile organic compound it produces, thymol. She showed convincingly that thyme plants can positively influence the formation of nitrogen-fixing root nodules in leguminous plants. How is not clear, but it could be due to thymol’s antimicrobial properties, which have the potential to knock out the microbial competitors of the rhizobium bacteria that form root nodules. It would be pretty cool if thyme plants were helping their legume neighbors — who we would usually assume are competitors for at least water and light — and in turn reaping the benefits of more fertile soil. Equally impressive to her results was the way that McKenna used a series of small student research projects — many of which seemed to be at the undergraduate or masters level — to create this larger picture of thymol’s potential importance to the plant-rhizobium mutualism. David Hembry works with leafflower plants and their associated mutualistic moths, and has discovered a fascinating difference between continental and island populations: while the continental communities of pollinators and their hosts maintain a modular structure, island communities are more nested. Given what we know about the general instability of island species relative to those on continents, this is a fascinating result, suggesting that community destabilization may drive community structure on islands.

My afternoon was more symbiosis with a little sexual selection thrown in for good measure. To keep the symbiotic theme going, I attended the Microbiomes and Microbial Symbionts session. Julie Horvath used genetic assays to identify differences in the microbiomes of different primate armpits, including humans. She showed that analysis of the microbial OTU’s of different primate species revealed a phylogenetic pattern of skin microbiome composition: as we have evolved in separate lineages, we have also evolved in the way we interact with our microbial symbionts (at least — that is — in our armpits).

My second session of the afternoon was one of many dedicated to Sexual Selection. Kelly LaRue discussed the interesting duets of Drosophila virilis. Whereas in Drosophila melanogaster only males sing (suggesting sexual selection via female choice), in D. virilis both males and females sing in a kind of back-and-forth “duet”. By deafening both males and females, LaRue was able to show that females must hear the male’s song in order to mate whereas males can rely on either the female song (in the dark but when not deafened) or female visual cues (in the light but when deafened). Her findings are interesting because they suggest both a female choice (for males who sing) and a female test (by duetting with males and only mating with males who successfully respond to female song). How or why this choice-test pairing exists is not clear.

For me, today was the day of the Operational Taxonomic Unit (OTU) and the phylogeny standing side by side. I saw a lot of talks that showed the phylogenies of hosts as they relate to the OTU’s of these hosts’ microbiomes: not all that surprising really given how many symbiosis/coevolution talks I attended. I was however, quite struck by a couple of things that seem to be “contemporary” that were not just a few years ago:

• The accessibility of both sequencing and analysis tools for identifying microbial DNA have obviously both gone up dramatically, because many people are assessing the composition of microbial communities using this technology; and
• For the most part people do not know what to do with this data. I saw plenty of pattern, but very little explanation of those patterns. It is unclear whether this is because microbiomes are incredibly complex or whether we don’t have the tools and models to yet explain them (or both).

L. Lacey Knowles, Past President of the Society for Systematic Biology, gave the evening’s keynote address, “Phylogenomics and Next-Generation Inferences: the Future of Phylogenetics in an Era of Big Data“. I would say that my knowledge of systematic biology and its methods is pretty cursory, but I tried to hang. Her talk was mostly about the question of how much data we need in order to reliably resolve phylogenies, and what we might do with all the data modern sequencing technologies are providing. She showed some compelling evidence that more sequences produce diminishing returns if your goal is simply to produce a phylogeny. She suggested that next generation sequencing needs to be used to produce “next generation inferences”; in other words, we should be looking for new questions that can be answered by using all this data.

The Coveted Evolution Film Festival “Charles Bobble Head” Award

Can I gush for a moment about how amazing the Evolution Film Festival was? Not only did we get the chance to watch a short film featuring Jonathan Losos and then ask him questions about it, but we were also treated to twelve amazing short films inspired by evolutionary concepts.

The feature film of the affair was called the Origin of Species. Produced by the Howard Hughes Medical Institute, this film somehow got Sean B. Carroll to serve as the host and narrator while Losos led us through the basics questions that underly his research on Anolis lizards. We actually saw two films: a fifteen minute version that covered evolutionary tradeoffs, niche partitioning, convergent evolution, and the construction of phylogenies and also a four-minute version that focused exclusively on predation experiments. These are really neat videos because they provide such a valuable “first person” perspective on the work of this important scientist. Their aim is to be used in high school and introductory undergraduate classrooms, and I think that they strike the right balance between accuracy and accessibility for this target audience. The only shortcoming I saw related to the issue of curricular modularity: while the shorter film would slot in nicely into a unit on the role of environment in shifting selective regimes, the longer film covered large swaths of my introductory evolution curriculum and therefore would not necessary find a home in any particular portion of my course.

The short films were inspiring. Most are films made by scientists who are creative on the side, a fact that makes the quality of these films all the more remarkable. We were asked to pick a top two from this series of sub-three-minute gems, which was really a very difficult task.

“Please tap again” by Ana Endara was a great vignette on how scientists approach a problem and use measurements to answer questions about the natural world (in this case the fungal-parasite-hollowed trunks of tropical trees).

In what has to be the most compelling presentation of simulation results I have seen, Randy Olson and Bjørn Østman‘s “Using Fitness Landscapes to Visualize Evolution in Action” effectively captured the diverse dynamics of multiple fitness optima:

“The Genetics of Mouse Burrowing” by Ariana Kam used super-high-quality stop animation (featuring joint-articulated mice!) to show how researchers had unravelled the genetic basis of mouse burrowing behaviors:

“Dinosaur” by Lori & Joel Henriques paired a very sweet and scientific-fact-filled song with great pen-progression animation:

“Bird Clines” by Stilianos Louca, Matthew Osmond, Philippe Fernandez, Alison Porter, Megan Vaughan, Catherine Hoffman, Michael Scott, Adrienne Contasti, Michael Scott, Andrew MacDonald, Ross Whippo, and Evan Hersh of the University of British Columbia was one elaborate inside joke for those of us who understand the importance of species diversity clines:

“Sex-Y Science: Sex Ratios in Patchy Populations” by Allison Neal of the University of Vermont was my runner-up; I will definitely use this clear and fun-to-watch stop-animation short to get my students thinking about sex ratios:

Maybe it is because I cannot resist a punk rock soundtrack, but the winner for me was “Drift” by Will Ryan, Lauren Anderson, Monique Boileau, Sarah Jezierny, Julia Kunberger, and Zach Boudreau at Florida State University:

This animated short totally captured the manic serendipity of genetic drift as a series of fit rabbits continually found themselves falling victim to stochastic forces. “Drift” captured the darkness of randomness that is central to the neutral evolutionary processes.

Thanks so much to Jory Weintraub and Robin Smith for organizing this amazing component of the Evolution 2014 meeting!