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Olsen B.J.,University of Maine, United States | Greenberg R.,Smithsonian Institution | Walters J.R.,Virginia Polytechnic Institute and State University | Fleischer R.C.,Center for Conservation and Evolutionary Genetics
Behavioral Ecology | Year: 2013

The evolutionary origins of sexual dimorphism are credited to both natural and sexual selection. Sexual dimorphism in feeding structures, however, provides some of the clearest examples of ecologically driven dimorphism. Studies of bird bills have significantly aided these claims, but bird bills are also commonly used in pair formation behaviors, and thus their morphology could be subject to sexual selection. We tested 4 hypotheses of the evolution of sexual dimorphism using the feeding structure of a sexually dimorphic and a nondimorphic subspecies of the swamp sparrow, Melospiza georgiana. The increased bill volume of males was not explained by simple allometric relationships, ecological niche divergence between the sexes, or correlations with territory defense. Male bill volume was positively selected by female mate choice, as relative male bill volume predicted both the presence of and degree of cuckoldry. Further, male bill volume increased with age, and females may thus receive benefits by choosing larger billed males for social (direct benefits) or extrapair (indirect benefits) mates. It is clear from this example that sexual selection can play a role in the evolution of sexually dimorphic feeding structures, even in bird bills, which are a classic system for ecologically driven sexual dimorphism. © The Author 2013.

Latch E.K.,University of Wisconsin - Milwaukee | Latch E.K.,Center for Conservation and Evolutionary Genetics | Boarman W.I.,Conservation Science Research and Consulting | Walde A.,Walde Research and Environmental Consulting | Fleischer R.C.,Center for Conservation and Evolutionary Genetics
PLoS ONE | Year: 2011

Characterizing the effects of landscape features on genetic variation is essential for understanding how landscapes shape patterns of gene flow and spatial genetic structure of populations. Most landscape genetics studies have focused on patterns of gene flow at a regional scale. However, the genetic structure of populations at a local scale may be influenced by a unique suite of landscape variables that have little bearing on connectivity patterns observed at broader spatial scales. We investigated fine-scale spatial patterns of genetic variation and gene flow in relation to features of the landscape in desert tortoise (Gopherus agassizii), using 859 tortoises genotyped at 16 microsatellite loci with associated data on geographic location, sex, elevation, slope, and soil type, and spatial relationship to putative barriers (power lines, roads). We used spatially explicit and non-explicit Bayesian clustering algorithms to partition the sample into discrete clusters, and characterize the relationships between genetic distance and ecological variables to identify factors with the greatest influence on gene flow at a local scale. Desert tortoises exhibit weak genetic structure at a local scale, and we identified two subpopulations across the study area. Although genetic differentiation between the subpopulations was low, our landscape genetic analysis identified both natural (slope) and anthropogenic (roads) landscape variables that have significantly influenced gene flow within this local population. We show that desert tortoise movements at a local scale are influenced by features of the landscape, and that these features are different than those that influence gene flow at larger scales. Our findings are important for desert tortoise conservation and management, particularly in light of recent translocation efforts in the region. More generally, our results indicate that recent landscape changes can affect gene flow at a local scale and that their effects can be detected almost immediately.

Gutierrez E.E.,City University of New York | Gutierrez E.E.,National Museum of Natural History Smithsonian Institute | Gutierrez E.E.,Center for Conservation and Evolutionary Genetics | Boria R.A.,City University of New York | And 2 more authors.
Ecography | Year: 2014

Based on our own empirical data and a literature review, we explore the possibility that biotic interactions, specifically competition, might be responsible for creating, and/or maintaining, geographic isolation. Ecological niche modeling was first used to test whether the distributions of 2 species of Neotropical marsupials (Marmosa robinsoni and M. xerophila) fit the predicted geographic pattern of competitive exclusion: one species predominates in areas environmentally suitable for both species along real contact zones. Secondly, we examined the connectivity among populations of each species, interpreted in the light of the niche models. The results show predominance of M. xerophila along its contact zone with M. robinsoni in the Península de Paraguaná in northwestern Venezuela. There, M. robinsoni has an extremely restricted distribution despite climatic conditions suitable for both species across the peninsula and its isthmus. The latter two results suggest that M. xerophila may be responsible for the geographic isolation of the peninsular populations of M. robinsoni with respect to other populations of the latter species in northwestern Venezuela. These results may represent an example of allopatry caused, or at least maintained, by competition. Our results and a review of numerous studies in which biotic interactions restrict species distributions (including at the continental scale) support a previously overlooked phenomenon: biotic interactions can isolate populations of a species. We propose 2 general mechanisms, intrusion and contraction, to classify allopatric conditions caused by various classes of biotic interactions. We present a necessary modification of the concept of ecological vicariance to include biotic interactions as possible vicariant agents regardless of whether genetic differentiation occurs or not. © 2014 The Authors.

PubMed | Center for Conservation and Evolutionary Genetics, Smithsonian Conservation Biology Institute and Center for Species Survival and
Type: Journal Article | Journal: Conservation physiology | Year: 2016

The relationship between amphibian immune function and disease susceptibility is of primary concern given current worldwide declines linked to the pathogenic fungus Batrachochytrium dendrobatidis (Bd). We experimentally infected lowland leopard frogs (Lithobates yavapaiensis) with Bd to test the hypothesis that infection causes physiological stress and stimulates humoral and cell-mediated immune function in the blood. We measured body mass, the ratio of circulating neutrophils to lymphocytes (a known indicator of physiological stress) and plasma bacterial killing ability (BKA; a measure of innate immune function). In early exposure (1-15 days post-infection), stress was elevated in Bd-positive vs. Bd-negative frogs, whereas other metrics were similar between the groups. At later stages (29-55 days post-infection), stress was increased in Bd-positive frogs with signs of chytridiomycosis compared with both Bd-positive frogs without disease signs and uninfected control frogs, which were similar to each other. Infection decreased growth during the same period, demonstrating that sustained resistance to Bd is energetically costly. Importantly, BKA was lower in Bd-positive frogs with disease than in those without signs of chytridiomycosis. However, neither group differed from Bd-negative control frogs. The low BKA values in dying frogs compared with infected individuals without disease signs suggests that complement activity might signify different immunogenetic backgrounds or gene-by-environment interactions between the host, Bd and abiotic factors. We conclude that protein complement activity might be a useful predictor of Bd susceptibility and might help to explain differential disease outcomes in natural amphibian populations.

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