Sunday, April 11, 2010

Spatiotemporal variation in natural selection

Forthcoming in Evolution

Weese, D.J., S.P. Gordon, A.P. Hendry, and M.T. Kinnison. Spatiotemporal variation in linear natural selection on body color in wild guppies (Poecilia reticulata)

Despite a number of good examples of the ecological consequences of ongoing evolutionary change (i.e., contemporary evolution), establishing the generality of these eco-evolutionary interactions remains an important challenge. The relevance of such effects in any given situation will depend, at least partly, on the temporal dynamism of the evolutionary mechanisms (selection, gene flow, mutation) that are functionally linked to ecological processes. Testing for contemporary evolution has been facilitated by the recent development of analytical methods that estimate the strength and pattern of natural selection in wild populations using multiple regressions to predict individual fitness from trait values (the slopes of these regressions are called selection coefficients). By replicating these measurements in time, we can reveal the temporal scale at which eco-evolutionary effects are likely to be important.

Along with my co-authors, I used a series of mark-recapture experiments to investigate variation in natural selection on body color in Trinidadian guppies. Among-population variability in male colour is predicted to reflect a balance between the benefits of colour (attracting females) and the costs of colour (attracting predators). consistent with this idea, our natural selection coefficients were negative, colourful guppies generally had lower survival than did drab guppies. However, we also found that selection in this system is highly variable both spatially (among populations) and temporally (within the same population). Surprisingly, this variation was not consistently associated with the presence of dangerous guppy predators. These findings suggest complicated and dynamic interactions among sexual selection, natural selection, predation, and phenotypic evolution in this system. These types of interactions operating on very fine spatiotemporal scales suggest that eco-evolutionary dynamics may be commonplace, and relevant to ecological processes occurring in contemporary time.

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