Landscape Genetics of Salamander Populations at Mammoth Cave National Park

Habitat connectivity affects the distribution of genetic diversity among populations by influencing the movements of individuals and the resulting pattern of gene flow across landscapes. It has become evident that amphibians are experiencing a period of worldwide population declines brought about by environmental change. An understanding of the effects of habitat structure on landscape connectivity is important for developing effective amphibian conservation strategies. The purpose of this study is to investigate the effect of landscape characteristics on gene flow and population structure of the marbled salamander (Ambystoma opacum) in Mammoth Cave National Park, Kentucky, USA. Salamander larvae were sampled from 50 ponds and screened at eight microsatellite loci to estimate genetic population structure. We used the R package ResistanceGA to build and evaluate models of landscape resistance using five different habitat categories: coniferous forest, dry deciduous forest, wet deciduous forest, human influence, and surface water. Our data reveal strong support for an ‘isolation by distance’ model in which interpond distances are a reliable predictor of the pattern of gene flow observed

Competition and mimicry: the curious case of chaetae in brachiopods from the middle Cambrian Burgess Shale

Background: One of the first phyla to acquire biomineralized skeletal elements in the Cambrian, brachiopods represent a vital component in unraveling the early evolution and relationships of the Lophotrochozoa. Critical to improving our understanding of lophotrochozoans is the origin, evolution and function of unbiomineralized morphological features, in particular features such as chaetae that are shared between brachiopods and other lophotrochozoans but are poorly understood and rarely preserved. Micromitra burgessensis and Paterina zenobia from the middle Cambrian Burgess Shale are among the most remarkable examples of fossilized chaetae-bearing brachiopods. The form, functional morphology, evolutionary and ecological significance of their chaetae are studied herein. Results: Like in Recent forms, the moveable but semi-rigid chaetae fringe both the dorsal and ventral mantle margins, but in terms of length, the chaetae of Burgess Shale taxa can exceed twice the maximum length of the shell from which it projects. This is unique amongst Recent and fossil brachiopod taxa and given their size, prominence and energy investment to the organism certainly had an important functional significance. Micromitra burgessensis individuals are preserved on hard skeletal elements, including conspecific shells, Tubulella and frequently on the spicules of the sponge Pirania muricata, providing direct evidence of an ecological association between two species. Morphological analysis and comparisons with fossil and extant brachiopod chaetae point to a number of potential functions, including sensory, defence, feeding, defouling, mimicry and spatial competition. Conclusions: Our study indicates that it is feasible to link chaetae length to the lack of suitable substrate in the Burgess Shale environment and the increased intraspecific competition associated with this. Our results however, also lend support to the elongated chaetae as an example of Batesian mimicry, of the unpalatable sponge Pirania muricata. We also cannot discount brachiopod chaetae acting as a sensory grille, extending the tactile sensitivity of the mantle into the environment, as an early warning system to approaching predators