A week after the closing day of the 2017 Evolution Meetings, the Molecular Ecologists have all dispersed from Portland. Still, the conference was so big that there’s a lot we missed the first time around — many great talks were scheduled against each other. Fortunately, hundreds of talks were recorded on video and posted online, so it’s possible to go back and catch up with them all. Over the next few days, we’ll highlight some recommendations from the conference’s well-organized YouTube channel.
Micah Freedman’s “Contemporary evolution of monarch butterflies in their introduced range” is a good example of a talk I’d have been excited to see if I weren’t double-booked elsewhere — monarchs have some fascinating natural history, including cool tripartite interactions with their hosts plants and damaging microbial parasites, and recent rapid evolution is a topic that’s been on my radar for a while. Here’s the abstract, with the video following:
Monarch butterflies are best known from their North American range, where they migrate extremely long distances–up to 4,000 km over the lifetime of an individual–to track seasonally available milkweed host plants. Over the past 200 years, monarch butterflies have achieved a nearly global distribution, and can now be found on every major Pacific island group. These introduced island populations are almost all residents (i.e. they breed year-round and do not migrate seasonally). Because each Pacific island population is derived from the ancestrally migratory North American population, these isolated island populations can be treated as replicate exeriments for investigating phenotypic evolution associated with the loss of migration.
Here, I present evidence suggesting that Pacific island monarch butterflies are undergoing contemporary evolution associated with the loss of migration. Using a combination of contemporary wild-caught individuals and museum specimens dating back to 1871, I show that monarch forewing morphology is changing predictably across multiple island groups. Specifically, time series data indicate that Pacific island monarch forewings have become both signifcantly smaller and signficantly more round through time. These findings are consistent with (1) relaxation of selection previously imposed by the demands of long-distance migration and/or (2) directional selection for smaller, rounder wings to promote maneuverability. Results are discussed in the context of functional tradeoffs associated with divergent wing morphologies and recently published genomic data that compares migratory and resident populations of monarch butterflies.