Search

Landscape heterogeneity plays an important role in population structure and divergence, particularly for species with limited vagility. Here, we used a landscape genetic approach to identify how landscape and environmental variables affect genetic structure and color morph frequency in a polymorphic salamander. The eastern red‐backed salamander, Plethodon cinereus, is widely distributed in northeastern North America and contains two common color morphs, striped and unstriped, that are divergent in ecology, behavior, and physiology. To quantify population structure, rates of gene flow, and genetic drift, we amplified 10 microsatellite loci from 648 individuals across 28 sampling localities. This study was conducted in northern Ohio, where populations of P. cinereus exhibit an unusually wide range of morph frequency variation. To test whether genetic distance was more correlated with morph frequency, elevation, canopy cover, waterways, ecological niche or geographic distance, we used resistance distance and least cost path analyses. We then examined whether landscape and environmental variables, genetic distance or geographic distance were correlated with variation in morph frequency. Tests for population structure revealed three genetic clusters across our sampling range, with one cluster monomorphic for the striped morph. Rates of gene flow and genetic drift were low to moderate across sites. Genetic distance was most correlated with ecological niche, elevation and a combination of landscape and environmental variables. In contrast, morph frequency variation was correlated with waterways and geographic distance. Thus, our results suggest that selection is also an important evolutionary force across our sites, and a balance between gene flow, genetic drift and selection interact to maintain the two color morphs. [ABSTRACT FROM AUTHOR]

Asian pheretimoid earthworms (e.g. Amynthas and Metaphire spp.) are invading North American forests and consuming the vital detrital layer that forest floor biota [including the keystone species Plethodon cinereus (Eastern Red-backed Salamander)], rely on for protection, food, and habitat. Plethodon cinereus population declines have been associated with leaf litter loss following the invasion of several exotic earthworm species, but there have been few studies on the specific interactions between pheretimoid earthworms and P. cinereus. Since some species of large and active pheretimoids spatially overlap with salamanders beneath natural cover objects and in detritus, they may distinctively compound the negative consequences of earthworm-mediated resource degradation by physically disturbing important salamander activities (foraging, mating, and egg brooding). We predicted that earthworms would exclude salamanders from high quality microhabitat, reduce foraging efficiency, and negatively affect salamander fitness. In laboratory trials, salamanders used lower quality microhabitat and consumed fewer flies in the presence of earthworms. In a natural field experiment, conducted on salamander populations from “non-invaded” and “pheretimoid invaded” sites in Ohio, salamanders and earthworms shared cover objects ~60% less than expected. Earthworm abundance was negatively associated with juvenile and male salamander abundance, but had no relationship with female salamander abundance. There was no effect of pheretimoid invasion on salamander body condition. Juvenile and non-resident male salamanders do not hold stable territories centered beneath cover objects such as rocks or logs, which results in reduced access to prey, greater risk of desiccation, and dispersal pressure. Habitat degradation and physical exclusion of salamanders from cover objects may hinder juvenile and male salamander performance, ultimately reducing recruitment and salamander abundance following Asian earthworm invasion. [ABSTRACT FROM AUTHOR]

Polymorphic species provide an opportunity to examine the process of sympatric divergence as it occurs. The Eastern Red-backed Salamander, Plethodon cinereus, is a polymorphic species that has served as a model organism in behavioral and ecological studies. Recent work suggests that the two most common color phenotypes (striped and unstriped) exhibit weak assortative mating and are diverging along a number of niche dimensions including temperature optima, diet, and response to predators. Males and females of P. cinereus are territorial and this behavior is thought to function in the context of prey and mate acquisition. Striped males have been shown to gain access to larger, and presumably more fecund, females. We posited that this pattern emerges through differential territorial behavior between the two phenotypes. We predicted that striped and unstriped salamanders would differ in their use of cover objects in the field, and in their aggressive responses to intruders in the laboratory. We examined salamander cover use and movement by placing artificial cover objects (ACOs) on the forest floor and monitoring them for 3.5 years. We compared residency time, number of recaptures, and number of ACOs occupied between the two phenotypes. The proportion of striped salamanders that were territorial residents was significantly greater than the proportion of unstriped salamanders that were territorial residents. Striped salamanders also exhibited significantly longer territorial residency, were recaptured more often, and were more often found under multiple, adjacent cover objects than unstriped salamanders. In the laboratory, we examined territorial behavior of the two morphs. As residents, striped salamanders were more aggressive and less submissive than were unstriped residents. When compared to intruders, resident salamanders of both morphs behaved more aggressively, but significant differences between resident and intruder behavior were only detected for the striped phenotype. These differences in aggression and cover object use may help to explain how striped males gain access to larger females and may be important in the interpretation of sympatric niche divergence and assortative mating by color in this species. [ABSTRACT FROM AUTHOR]

1. When studying speciation, researchers commonly examine reproductive isolation in recently diverged populations. Polymorphic species provide an opportunity to examine the role of reproductive isolation in populations that may be in the process of divergence. 2. We examined a polymorphic population of Plethodon cinereus (red-backed salamanders) for evidence of sympatric ecological separation by colour morphology. Recent studies have correlated temperature and climate with colour morphology in this species, but no studies have looked at differences in diet or mate choice between colour morphs. We used artificial cover objects to assess salamander diet, mating preference and surface activity over a 2-year period at a field site in north-eastern Ohio. 3. We detected differences in diet between two colour morphs, striped and unstriped. The diets of striped individuals were significantly more diverse and were made up of more profitable prey than the diets of unstriped salamanders. 4. Opposite sex pairs were made up of individuals of the same colour morph and striped males were found more often with larger females than were unstriped males. 5. We corroborate findings of earlier studies suggesting that the unstriped form is adapted to warmer conditions. Unstriped individuals were the first to withdraw from the forest floor as temperatures fell in the late fall. We found no evidence that the colour morphs responded differently to abiotic factors such as soil moisture and relative humidity, and responses to surface temperatures were also equivocal. 6. We conclude that the two colour morphs exhibit some degree of ecological separation and tend to mate assortatively, but are unlikely to be undergoing divergence given the observed frequency of intermorph pairings. [ABSTRACT FROM AUTHOR]