Humans, selection, evolution and ecological timescales … a potent cocktail

It’s been awhile since I last was able to write for TME. But, finally, I’ve stolen away some time to write about a recent study in Ecology Letters that I couldn’t put down once I started reading it. Yes, it’s about mating systems which should be no surprise to regular readers of TME, but if the semester wasn’t over, I’d require my Science Communication students to read it as an incredible example of science and storytelling. I digress momentarily to a blog post I read awhile back at about the same time I accepted a role as a regular contributor at TME. I’ve tried to take the  “think like a fiction author” to heart in writing for TME and peer-reviewed papers alike. As a result, I’m always on the look out for papers that are compellingly written.

Kuester et al. (2016) elegantly describe the impacts of human-mediated agents of selection on mating systems. Using the common morning glory as an example, they found that herbicide-resistant populations self-fertilize more than herbicide-susceptible populations. Specifically, resistant plants exhibited lower outcrossing rates and higher maternal inbreeding coefficients.
But, are these self-fertilizing populations dead ends, succumbing to the costs of inbreeding depression?

Not necessarily … the authors put forth three hypotheses that all come back around to the establishment of a population in a new habitat. Agricultural plants that experience selection following herbicide applications are analogs of species colonizing new habitats (à la Baker’s Law, see this post). The capacity to undergo uniparental reproduction enables establishment, but is by no means the habitual mating system.
(1) Mechanisms that promote self-pollination of herbicide-resistant individuals reduces gene flow from non-resistant individuals. This ensures offspring are adapted to the marginal environment – the one with lots of herbicides.
(2) Higher selfing and the ‘segregation effect’ could also explain these patterns, whereby an allele that causes higher selfing forms associations with homozygotes for beneficial alleles – accelerating response to selection.
(3) Finally, good old Baker’s Law, would fit the outcomes found in this paper as resistant individuals that have a great propensity to self-pollinate would be at a relative advantage to those that can’t (Kuester et al. 2016).

Human impacts on plant mating patterns […] go beyond the indirect consequences of environmental manipulations[,] such as forest fragmentation and metal contamination.

As a result, there can be pretty profound impacts on the evolutionary propensity of a species. And, I’d argue this goes beyond just the resistance to pesticides. The issue is that we simply don’t know enough about mating systems. We’ve probably just scratched the very surface of these patterns. These types of studies warrant further attention as humans can substantially alter the evolutionary response of natural populations of organisms within ecological timescales.
Adam Kuester, Eva Fall, Shu-Mei Chang, and Regina S. Baucom. (2016 online early) Shifts in outcrossing rates and changes to floral traits are associated with the evolution of herbicide resistance in the common morning glory. Ecology Letters

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