Evolution 2014: Day 3

After a couple of pretty busy days at the Evolution 2014 meeting, I figured that I would go selective on the talks, take a little field trip away from the meeting, and make sure that I was ready for my own talk the following day.

For the morning I only attended one talk: John Wiens‘ “A twisted view of ecology and speciation” in the ASN Solicited Symposium “Beyond reproductive isolation: microevolutionary controls on macroevolutionary speciation dynamics”. Wiens sought to consider the role that niche conservatism — rather than niche divergence — plays in speciation. Niche conservatism can act as a force of speciation when a species is divided into two populations separated by an area of unsuitable habitat. This may seem like the classic case of allopatric speciation, which in some ways it is. But the important point is that it is failure to adapt to the habitat separating the two populations (i.e. niche conservatism) that allows for speciation to occur; this contrasts with niche divergence, which has been shown in many cases to lead to speciation. Wiens made the point that if the species did not show niche conservatism, its separation would not be effective and speciation would not occur. He acknowledged that eventually reproductive isolating mechanisms would have to arise before the separated populations came back in contact with each other; the role of these mechanisms is well-appreciated, but the importance of niche conservatism often is not.

In presenting his idea to a colleague Wiens was told that this perspective was valid but a bit “twisted”. He decided to wear this label as a badge of honor, and has undertaken both theoretical and empirical projects designed to demonstrate the importance of niche conservatism to the allopatric speciation process. He showed the results of a model constructed and analyzed by Xia Hua that showed that speciation due to niche conservatism is most likely to occur when species with a low degree of niche lability are separated into two “islands” of suitable habitat by an abrupt change in environment. He also showed empirical results showing that Desmognathus species divergence can be explained best by noting that the space between species — where both species are absent — contains habitat that is radically different from the habitats occupied by either species in their new native ranges.

In today’s afternoon talks I picked out three that were of interest to me. I have been interested in the work of jeff smith (and also his postdoctoral supervisors Joan Strassman and David Queller) for awhile, so I went to see his talk “Looking for signatures of social conflict in secondary metabolites of cooperative amoebae”. If you know Dictyostelium well, you know that it displays rather remarkable cooperation. If there is cooperation there is likely to be conflict, and smith was looking for a particular kind of conflict in Dicty: chemical warfare. Specifically, he was interested in determining whether a class of secondary metabolites — polyketides — are being used to “cheat” when Dicty individuals find themselves in chimeric (mixed) aggregations. If such compounds were being used in this way, smith suggested that they should evolved rapidly by positive selection to create novel polyketide variants in fruiting bodies. So far he only has evidence of rapid evolution of these compounds and that they are expressed in fruiting bodies, so this work is ongoing.

Erol Akçay presented some interesting if not entirely clear theoretical insights in his talk “Fitness feedbacks and alignment of interests in mutualisms”. The basic idea that he wanted to tackle was that for mutualisms to evolve, the fitness of each interacting organisms myst be aligned; when fitness interests conflict, mutualisms can be destabilized. Through a population genetics model he showed that there are some situations in which mutualism can evolve despite a lack of fitness alignment. There are also scenarios under which mutualism does not evolve despite fitness alignment. He also used data pulled from a big plant-rhyzobium study to estimate parameters in his model, but I could not pick up on whether this showed that real organisms occupy these counter-intuitive parameter spaces that he uncovered through modeling.

Trevor Price gave the evening’s American Society of Naturalists Presidential Address, “Social selection and the evolution of color patterns“. His talk was focused on sexual and social selection in birds. He showed the great diversity in color and pattern found in new world warblers and contrasted them with the birds he studies, old world warblers, whose variations are more modest but no less significant. He was interested in the question of how and why birds of different species choose their mate, in particular in reference to visual displays, going so far as to suggest that we might understand what the avian equivalent of “falling in love” might be. Key to understanding this sort of attraction is understanding where it falls on what I would call the sexual to social selection spectrum. As Price pointed out, pure sexual selection can produce preferences that are initially independent of ecology, functionally arbitrary up until the point that a trait becomes so extreme that its harm outweighs its benefit (think peacocks with feathers so long that they cannot escape tiger predation). In contrast, social selection for a mate involves non-arbitrary assessments of ability to provide parental care, provisioning, and/or defense. Price pointed out that even when mate selection falls more towards the purely-sexually-selected end of the spectrum, the influence of ecology is still important. In the case of warblers, a lot of their variation in coloration can be understood by where they live. Whereas Price’s less dramatic old world warblers live out in the open in a high light environment, many new world warblers live under the canopy where light is filtered. Initial work that Price has completed with his graduate student suggests that the eyes of female birds from each continent differ in their light sensitivity, which might account for the different selective pressures females exert on male coloration.