Metabolite compositions on skins of eastern hellbenders Cryptobranchus alleganiensis alleganiensis differ with location and captivity.

Eastern hellbenders Cryptobranchus alleganiensis alleganiensis, large aquatic salamanders, are declining over most of their range. The amphibian-killing fungus Batrachochytrium dendrobatidis (Bd) has contributed to global amphibian declines and has been detected on eastern hellbenders, but infection intensities were lower than those of species that are more susceptible to Bd. The factors limiting Bd on hellbenders may include antifungal metabolites produced by their skin microbiota. We used a metabolite fingerprinting technique to noninvasively identify the presence, but not identity, of metabolites associated with eastern hellbenders. We surveyed the skin of wild eastern hellbenders to test whether the composition and richness (i.e. number of metabolites) of their metabolites are explained by Bd status or location. Furthermore, we surveyed for metabolites on captive eastern hellbenders to test whether metabolite compositions were different between captive and wild eastern hellbenders. Bd detection was not associated with either metabolite richness or composition. Both metabolite composition and richness differed significantly on hellbenders from different locations (i.e. states). For metabolite composition, there was a statistical interaction between location and Bd status. Metabolite richness was greater on captive eastern hellbenders compared to wild hellbenders, and metabolite compositions differed between wild and captive eastern hellbenders. The methods we employed to detect metabolite profiles effectively grouped individuals by location even though metabolite composition and richness have high levels of intraspecific variation. Understanding the drivers and functional consequences of assemblages of skin metabolites on amphibian health will be an important step toward understanding the mechanisms that result in disease vulnerability.

Inferring population connectivity in eastern massasauga rattlesnakes (Sistrurus catenatus) using landscape genetics.

Assessing the environmental factors that influence the ability of a threatened species to move through a landscape can be used to identify conservation actions that connect isolated populations. However, direct observations of species' movement are often limited, making the development of alternate approaches necessary. Here we use landscape genetic analyses to assess the impact of landscape features on the movement of individuals between local populations of a threatened snake, the eastern massasauga rattlesnake (Sistrurus catenatus). We linked connectivity data with habitat information from two landscapes of similar size: a large region of unfragmented habitat and a previously studied fragmented landscape consisting of isolated patches of habitat. We used this analysis to identify features of the landscape where modification or acquisition would enhance population connectivity in the fragmented region. We found evidence that current connectivity was impacted by both contemporary land-cover features, especially roads, and inherent landscape features such as elevation. Next, we derived estimates of expected movement ability using a recently developed pedigree-based approach and least-cost paths through the unfragmented landscape. We then used our pedigree and resistance map to estimate resistance polygons of the potential extent for S. catenatus movement in the fragmented landscape. These polygons identify possible sites for future corridors connecting currently isolated populations in this landscape by linking the impact of future habitat modification or land acquisition to dispersal ability in this species. Overall, our study shows how modeling landscape resistance across differently fragmented landscapes can identify habitat features that affect contemporary movement in threatened species in fragmented landscapes and how this information can be used to guide mitigation actions whose goal is to connect isolated populations.

Pedigree-based assessment of recent population connectivity in a threatened rattlesnake.

Managing endangered species in fragmented landscapes requires estimating dispersal rates between populations over contemporary timescales. Here, we developed a new method for quantifying recent dispersal using genetic pedigree data for close and distant kin. Specifically, we describe an approach that infers missing shared ancestors between pairs of kin in habitat patches across a fragmented landscape. We then applied a stepping-stone model to assign unsampled individuals in the pedigree to probable locations based on minimizing the number of movements required to produce the observed locations in sampled kin pairs. Finally, we used all pairs of reconstructed parent-offspring sets to estimate dispersal rates between habitat patches under a Bayesian model. Our approach measures connectivity over the timescale represented by the small number of generations contained within the pedigree and so is appropriate for estimating the impacts of recent habitat changes due to human activity. We used our method to estimate recent movement between newly discovered populations of threatened Eastern Massasauga rattlesnakes (Sistrurus catenatus) using data from 2996 RAD-based genetic loci. Our pedigree analyses found no evidence for contemporary connectivity between five genetic groups, but, as validation of our approach, showed high dispersal rates between sample sites within a single genetic cluster. We conclude that these five genetic clusters of Eastern Massasauga rattlesnakes have small numbers of resident snakes and are demographically isolated conservation units. More broadly, our methodology can be widely applied to determine contemporary connectivity rates, independent of bias from shared genetic similarity due to ancestry that impacts other approaches.