Evol Ecol Res 10: 721-733 (2008)     Full PDF if your library subscribes.

Contingency and determinism during convergent contemporary evolution in the polymorphic land snail, Cepaea nemoralis

Małgorzata Ożgo1 and Michael T. Kinnison2

1Institute of Biology, Pomeranian University, Słupsk, Poland and 2Department of Biological Sciences, University of Maine, Orono, Maine, USA

Correspondence: M. Ożgo, Institute of Biology, Pomeranian University, Arciszewskiego 22B, 76-200 Słupsk, Poland.
e-mail: mozgo.biol@interia.pl


Questions: How replicable is short-term evolution? Do populations recently exposed to analogous habitat gradients show analogous adaptations? Conversely, how important are chance historic events and genetic constraints in shaping the unique aspects of contemporary evolution?

Organisms: Three Cepaea nemoralis population pairs, each pair inhabiting adjacent open and shaded habitats in sub-optimal climatic conditions of south-eastern Poland. Population pairs likely arose through separate, single introductions and were isolated from other populations.

Methods: We compared the frequencies of genetically determined shell variants 18–28 years after the establishment of the populations.

Conclusions: The manner by which adaptive divergence proceeded varied by geographic location, but the effect in terms of darkness of the shells was convergent, resulting in higher frequencies of dark-shelled snails in shaded habitats and light-shelled snails in open habitats. Estimated selection coefficients were large (0.236, 0.370, and 0.420) with respect to other studies for this species. The relatively simple inheritance system of shell colour in this species ensures that observed differences are heritable and allows insights into the likely historical roles of genetic architecture and restricted genetic variation in driving shared and unique elements of adaptive divergence.

Keywords: climatic selection, genetic architecture, introduced species, microclimate, natural selection, parallel evolution.

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