Decrease in litter size in the shrew Crocidura suaveolens (Mammalia, Insectivora) from Corsica (France): Evolutionary response to insularity?

Abstract

Populations of the lesser white-toothed shrew, Crocidura suaveolens (Pallas, 1811), from Corsica show an increase in adult body size associated with a decrease in litter size. The average number of embryos in wild Corsican females is smaller (mean 2.6, n = 62) than in mainland females (mean 4.6, n = 173). A breeding experiment was run for 4 years, yielding three generations. Under standard breeding conditions, the differences between island and mainland populations were maintained and were significant (median litter size was 2 for Corsica and 5 for the mainland). These differences in life-history traits were therefore proved experimentally to be genetically determined. Hypotheses concerning the mechanisms responsible for these differences are discussed.