Diet composition of carbon and nitrogen (C:N) could affect diet-tissue isotopic discrimination and elemental turnover rate in consumers but studies that test the nature of these changes are scarce. We compared carbon and nitrogen isotopic discrimination and turnover rates in individuals of Pallas' long-tongued bats Glossophaga soricina fed diets with protein soya isolate or amaranth grains as their main source of protein. Diets were of similar protein biological value but the soya diet had higher nitrogen content (2.2%N) and lower C:N ratio (39.6) than the amaranth diet (1.3%N, C:N=40.5). Most bats on the soya diet gained body mass whereas most bats on the amaranth diet lost body mass. Half-lives of carbon (24.3±3.8 days) and nitrogen (25.6±4.4 days) in bats switched to the soya diet were very similar. In contrast, in the bats switched to the amaranth diet, carbon half-life (39.7±3.4 days) was longer than that of nitrogen (25.0±6.0 days). The enrichment in ¹⁵N between diet and blood was higher when bats were fed the amaranth diet (4.4±0.2‰) than when they were fed the soya diet (3.3±0.2‰). Similarly, bats on the amaranth diet had higher ¹³C enrichment (2.0±0.2‰) than bats on the soya diet (0.1±0.1‰). Our results support recent hypotheses of the effect of nutrition on diet-tissue isotopic discrimination and turnover rate, and further shows that blood stable isotope analysis is an adequate approach to track seasonal dietary shifts in wild bats.

The MHC class II loci encoding cell surface antigens exhibit extremely high allelic polymorphism. There is considerable uncertainty in the literature over the relative roles of recombination and de novo mutation in generating this diversity. We studied class II sequence diversity and allelic polymorphism in two populations of Peromyscus maniculatus, which are among the most widespread and abundant mammals of North America. We find that intragenic recombination (or gene conversion) has been the predominant mode for the generation of allelic polymorphism in this species, with the amount of population recombination per base pair exceeding mutation by at least an order of magnitude during the history of the sample. Despite this, patchwork motifs of sites with high linkage disequilibrium are observed. This does not appear to be consistent with the much larger amount of recombination versus mutation in the history of the sample, unless the recombination rate is highly non-uniform over the sequence or selection maintains certain sites in linkage disequilibrium. We conclude that selection is most likely to be responsible for preserving sequence motifs in the presence of abundant recombination.