Evolution in spatially structured populations

The goal of my research is to develop population genetic models to provide an understanding of mechanisms by which abiotic and biotic interactions generate selection on dispersal.

research_dispersal_smallIn populations at an adaptive equilibrium with their local environment, selection should favor philopatry over dispersal to different environments. But, theory shows that spatial environmental variation alone selects against dispersal. Yet, the vast majority of species exhibit some level of dispersal, mediated by behavior or morphology. Parasites are a particularly puzzling example. Many parasites are highly mobile, use different hosts within a life cycle, and have broad host ranges.

Sample simulation of the evolution of migration rate assuming strong interactions. The simulation starts in the lower left. Plotted is the cumulative change in frequency of the migration mutant after each generation for 5,000 generations. Species local maladaptation is indicated by color (red: host; blue: parasite). Published in Drown, Dybdahl and Gomulkiewicz (2013).
Sample simulation of the evolution of migration rate assuming strong interactions. The simulation starts in the lower left. Plotted is the cumulative change in frequency of the migration mutant after each generation for 5,000 generations. Species local maladaptation is indicated by color (red: host; blue: parasite). Published in Drown, Dybdahl and Gomulkiewicz (2013).

In natural populations in many cases, instead of favoring philopatry, environmental variability appears to do the opposite: it favors higher dispersal rates as a “bet hedging” strategy. Increased dispersal rates can be favored when particular forms of spatial variability are combined with temporal variability in fitness. I have found that coevolution of antagonistic interactions generates copious spatial variability in fitness in much the same way that host-parasite arms races generate temporal variability in fitness in models of the evolution of sex and recombination. In Drown, Dybdahl and Gomulkiewicz (2013), I show that antagonistic host-pathogen interactions generate both spatial and temporal fluctuations in fitness and thus favor increased dispersal rates. Under certain conditions, where interactions are strong, I find that there is a continuous evolutionary escalation in dispersal rates, which contributes to explaining the ubiquity of dispersal in nature . The long term evolution of dispersal described by my model provides an understanding of the empirical evidence of local adaptation necessary for host-parasite interactions to drive the evolution of host and pathogen dispersal.

Drown DM, Dybdahl MF, and Gomulkiewicz R. 2013. Consumer-resource interactions and the evolution of migration. Evolution 67: 3290-3304.