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STABLE ISOTOPIC SIGNATURE AND TROPHIC DIVERSIFICATION OF AKODONTINE RODENTS
Stable isotopes record natural processes, measuring assimilated components that leave intrinsic signatures on organic tissues. They are frequently used to study trophic interactions, resource consumption and community processes, but applied less often in a macroevolutionary context. The Akodontini, the second most diverse among sigmodontine rodents, appear to be rich in insectivorous species, but direct evidence of diet for most species of the tribe is lacking. We collected 139 hair samples of 47 species of Akodontini rodents from five mammal collections, representing the first attempt to gather isotopic data and analyze it in an explicitly phylogenetic context over a macroevolutionary scale. The samples were submitted to stable isotope analyses for δ13C and δ15N values on a continuous flow – mass spectrometry system at the Stable Isotope Facility of University of Wyoming. The resulting δ13C and δ15N values were averaged by species and interpreted as isotopic niche space. We compared the results of stable isotopes with the inferred diet for the analyzed species from the literature, usually obtained through stomach content analysis. The δ13C and δ15N values were plotted on the δ13C/δ15N bi-plots using the software PAST v.3. The trophic niche of each of the four main lineages, defined according to the more recent Akodontini phylogenetic hypothesis, was delimited through Stable Isotope Bayesian Ellipses (SIBER). Six polygon dispersion metrics, followed by hypothesis-testing procedures for differences in centroid location and dispersion metrics, were applied to the dataset, allowing comparisons between the isotopic niche space occupied by each lineage. The stable isotope values were mapped onto the phylogeny of Sigmodontinae pruned to include only our sampled species. The δ13C and δ15N values were tested for phylogenetic signal using Blomberg’s K and Pagel’s ƛ. The analyses were performed using the packages ‘siar’, ‘SIBER’ and ‘phytools’ packages on the R environment. Our results corroborate previous impressions that, in general, akodontine rodents consume more animal matter than many other Neotropical rodents, but the lack of ecological information for some species precludes more specific inferences. Some species apparently have relatively restricted niches, while the large variance observed in other species may reflect dietary and habitat differences related to ecological factors throughout their wide distribution. We found low phylogenetic signal for δ13C and δ15N values. The δ13C/δ15N 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 that can be useful in studying the evolution of trophic niches, highlighting the importance of museum specimen-based research for evolutionary ecology studies.
trophic niche, diet, SIBER, δ13C, δ15N
Rafaela Velloso Missagia, Bruce Patterson, Fernando Araújo Perini