A subset of the Molecular Ecologist team is attending this year’s Evolution meeting in Portland, Oregon. As part of our coverage of the meeting, we’ve been recapping the highlights of each day here on the blog, and occasionally previewing upcoming presentations. You can find all of the TME contributors on Twitter using the sidebar on the right or compiled in a handy Twitter list here, check in on meeting news using the hashtag #Evol2017>. You can also view a still-expanding list of video recordings of presentations at the meeting on the Evolution 2017 YouTube channel.
There were still a lot of talks I wanted to see on Tuesday, which is a first, I think — I can’t remember an Evolution meeting where there was no point in the schedule that I didn’t see something I was excited about. But at this point in the week I had no energy left for session-hopping, and I spent the whole morning in the Mutualism section at the expense of missing a bunch of friends’ talks (er, hi, Stacy and Robb). But in my feeble defense, there were a lot of great talks in this session:
Justin Van Goor — The enemy of my enemy is my friend: nematode infection of non-pollinating fig wasp antagonists and the consequences for the fig-fig wasp pollination mutualism
Van Goor is digging into the impact of a parasitic nematode that infects the wasps that visit rock-strangling figs. The nematodes infect pollinating fig wasps and non-pollinating wasps, but have a much bigger impact on the population density of the non-pollinators — possibly helping to reduce their negative impact of fig fecundity.
Katherine Muller — Host-derived resources may support long-term saprophytic survival of dormant rhizobia
Rhizobia bacteria fix nitrogen in symbiosis with legume roots, but they also have a free-living phase, and it’s not clear how the time rhizobia spend out of symbiosis shapes selection on their ability to perform well in symbiosis. Muller is studying how rhizobia accumulate energy-dense polyhydroxybutyrate over the course of symbiosis and then spend it while living in the soil — and trying to determine whether PHB goes toward making cooperative rhizobia strains more fit in that free-living context, or whether it fuels a low-energy dormancy until the next legume growing season.
Liana Burghardt — Select and re-sequence reveals fitness tradeoffs and loci underlying symbiotic and free-living fitness in a legume-rhizobium mutualism
Burghardt is tackling a similar question to Muller, by experimentally evolving a diverse population of rhizobia strains in soil, in liquid culture, and in symbiosis with two different host genotypes. Although different strains are selected out of the population in each of the two hosts, fitness on the different hosts is correlated — and rhizobial strains’ fitness is correlated with their hosts’ performance, though there’s a lot of unexplained variation around that trend. (NB: Burghardt is working with Peter Tiffin, one of my postdoctoral mentors)
Yee Mey Seah — Molecular dynamics of a nascent microbial mutualism
In another evolve-and-resequence mutualism study, Seah is working with two microbial species that metabolize each other’s waste products in a syntrophic mutualism. Deep sequencing of coevolving populations may let her differentiate genome regions experiencing different kinds of natural selection in the course of the mutualism, which got me very excited.
While it might be biased to have enjoyed all the talks in the Spotlight session I presented in, I could easily highlight every talk both the SSE Spotlight Sessions Genetic transmission at the population level or Sex in the Wild. So, I instead drew two talks from each session at random!
Cathy Rushworth – SSE Spotlight Session: Genetic transmission at the population level – How to make an apomict: asymmetrical crossing success in Boechera species.
Cathy presented a lightning talk on hybridization between B. stricta and B. retrofracta. They hydridize, but there’s variation across the asexual hybrids. It turns out there’s unidirectional crossing success … one cross is more successful than another when you go out in the field and figure out who the mom of an asexual hybrid is!
(Brief shoutout to Georgy Sandler who is an undergrad and gave an amazing lightning talk!! He showed Y chromosomes were enriched for pollen expressed genes!)
Christopher Wilson – SSE Spotlight Session: Sex in the wild – Keeping up with pathogens for fifty million years without sex: ecological and evolutionary insights from bdelloid rotifers.
Sex is still one of the hardest problems in evolutionary biology … enter bdelloid rotifers who throw our hypotheses as to why sex is advantages out the window. They’ve not had sex in a long time (if ever). Yet, there are more than 60 described parasites of bdelloids that are pretty darn virulent (bdelloid corpses were shown with fungi growing out of them!). One clade of parasites, the Rotiferophthora, has been obligate with bdelloids for 42.6 million years and hasn’t jumped around across species. While some recent studies have suggested that bdelloids may exchange genes through horizontal transfer and replace meiotic sex, Wilson presented a recent biorxiv paper suggesting some of these studies may have had cross contamination (see the paper here). So, bdelloid rotifers remain an evolutionary scandal … how can they persist in the face of the onslaught of pathogens without sex? Maybe we need some more exotic hypotheses to extend the Red Queen??