Abstract
Despite accumulating evidence for selection within natural systems, the importance of random genetic drift opposing Wright's and Fisher's views of evolution continue to be a subject of controversy. The geographical diversification of aposematic signals appears to be a suitable system to assess the factors involved in the process of adaptation since both theories were independently proposed to explain this phenomenon. In the present study, the effects of drift and selection were assessed from population genetics and predation experiments on poison-dart frogs, Ranitomaya imitator, of Northern Peru. We specifically focus on the transient zone between two distinct aposematic signals. In contrast to regions where high predation maintains a monomorphic aposematic signal, the transient zones are characterized by lowered selection and a high phenotypic diversity. As a result, the diversification of phenotypes may occur via genetic drift without a significant loss of fitness. These new phenotypes may then colonize alternative habitats if successfully recognized and avoided by predators. This study highlights the interplay between drift and selection as determinant processes in the adaptive diversification of aposematic signals. Results are consistent with the expectations of the Wright's shifting balance theory and represent, to our knowledge, the first empirical demonstration of this highly contested theory in a natural system.
Highlights
Understanding how populations adapt to different selective environments is a central theme in evolutionary biology
Fisher’s large population size theory (LST) [1] and Wright’s shifting balance theory (SBT) [2,3] of evolution were developed to explain the process of adaptation
In Fisher’s LST, only mutations generate the diversity on which selection acts, while in Wright’s SBT, the random variation of alleles frequencies by genetic drift is a decisive factor in finding adaptive opportunities [5]
Summary
Understanding how populations adapt to different selective environments is a central theme in evolutionary biology. Fisher’s large population size theory (LST) [1] and Wright’s shifting balance theory (SBT) [2,3] of evolution were developed to explain the process of adaptation. In both theories, natural selection is the only evolutionary force capable of producing adaptation. Natural selection is the only evolutionary force capable of producing adaptation They differ in the role accorded to neutral evolutionary processes [4,5]. Due to the difficulty in demonstrating the entire SBT process within a single system, especially in natural populations, this theory is still highly criticized [4,6,8]
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