Stable isotope signatures and the trophic diversification of akodontine rodents

Stable isotope analyses are frequently used to study trophic interactions, diet, and community processes, but they have seldom been applied to investigate the trophic niche structure of entire clades. In this paper, we assess stable isotopes information in a phylogenetic context to evaluate trophic evolution across the phylogeny of a diversified group of Neotropical cricetid rodents. A total of 139 hair samples of 47 species of Akodontini rodents were collected from five museum mammal collections and submitted to stable isotope analyses for delta C-13 and delta N-15 values. The resulting isotopic values were compared among the four main clades within the tribe. The phylogenetic signal of isotope values was estimated using a phylogenetic tree of Akodontini. Our results corroborate previous impressions that, in general, akodontines include more animal matter in their diet than other Neotropical rodents, but the lack of information for some species precludes more specific inferences. Some species appear to have relatively restricted niches, but the large variance observed in other species may be related to dietary and habitat differences related to ecological factors throughout the distribution of wide-ranging species. We found low phylogenetic signal for delta C-13 and delta N-15 values, suggesting that different regions within the isotopic niche space were occupied independently many times throughout akodontine evolutionary history. The delta C-13/delta N-15 bi-plot indicates that the four main lineages occupy the trophic niche space in similar ways, although differing in trophic diversity. Our results represent new ecological information and an approach that can be useful in studying the evolution of trophic niches, and highlight the importance of museum specimen-based research for evolutionary ecology studies.