Abstract
BackgroundSince Darwin's pioneering work, evolutionary changes in isolated island populations of vertebrates have continued to provide the strongest evidence for the theory of natural selection. Besides macro-evolutionary changes, micro-evolutionary changes and the relative importance of natural selection vs. genetic drift are under intense investigation. Our study focuses on the genetic differentiation in morphological and life-history traits in insular populations of a small mammal the bank vole Myodes glareolus.ResultsOur results do not support the earlier findings for larger adult size or lower reproductive effort in insular populations of small mammals. However, the individuals living on islands produced larger offspring than individuals living on the mainland. Genetic differentiation in offspring size was further confirmed by the analyses of quantitative genetics in lab. In insular populations, genetic differentiation in offspring size simultaneously decreases the additive genetic variation (VA) for that trait. Furthermore, our analyses of differentiation in neutral marker loci (Fst) indicate that VA is less than expected on the basis of genetic drift alone, and thus, a lower VA in insular populations could be caused by natural selection.ConclusionWe believe that different selection pressures (e.g. higher intraspecific competition) in an insular environment might favour larger offspring size in small mammals. Island selection for larger offspring could be the preliminary mechanism in a process which could eventually lead to a smaller litter size and lower reproductive effort frequently found in insular vertebrates.
Highlights
Since Darwin's pioneering work, evolutionary changes in isolated island populations of vertebrates have continued to provide the strongest evidence for the theory of natural selection
According to their phylogenetic analyses, the increase in body size might only hold true in some mammalian groups. They argued that earlier reviews were biased by a few extreme examples in some mammalian groups, and these reviews might have ignored many examples where body size has not changed. It has been suggested [15,16] that future studies should be focused more clearly on the possible differences in natural selection caused by island characters [17], ecological mechanisms [18] and species specific mechanisms
We have shown that the rapid selection caused by intraspecific competition can significantly regulate the proportion of genetic reproductive tactics in mainland populations [20]
Summary
Since Darwin's pioneering work, evolutionary changes in isolated island populations of vertebrates have continued to provide the strongest evidence for the theory of natural selection. The generality of the island rule has been criticized by Meiri and colleagues [14,15] According to their phylogenetic analyses, the increase in body size might only hold true in some mammalian groups (e.g. murid rodents). They argued that earlier reviews were biased by a few extreme examples in some mammalian groups (e.g. elephants), and these reviews might have ignored many examples where body size has not changed It has been suggested [15,16] that future studies should be focused more clearly on the possible differences in natural selection caused by island characters (size and isolation) [17], ecological mechanisms (e.g. predation rate and inter/intraspecific competition) [18] and species specific mechanisms (e.g. evolutionary constraints caused by additive genetic variation)
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