Polymorphic species provide an excellent system to study population divergence because different phenotypes often face diverse selection pressures within their shared environment. Previous studies have demonstrated that different color morphs of Plethodon cinereus (striped and unstriped), which vary in their degree of melanin-based coloration, vary temporally in their seasonal activity and differ in metrics associated with stress physiology. Despite the known association between melanin-based coloration and disease resistance among vertebrates, few studies have examined this relationship in amphibians. In a laboratory experiment, we exposed juvenile and adult P. cinereus to the pathogenic chytrid fungus [Batrachochytrium dendrobatidis (Bd)] and tested the hypothesis that the different color morphs would differ in their response to Bd. If the degree of melanization is positively associated with immune traits in this species, we predicted that unstriped salamanders would be more resistant to Bd and would exhibit higher survival rates compared to striped salamanders. Our results suggest that unstriped salamanders have a higher prevalence of infection when they do not behaviorally avoid Bd. Unstriped salamanders also exhibited higher rates of Bd-induced mortality compared to striped salamanders. These results conflict with our initial predictions and with general findings suggesting that individuals with higher levels of melanin production are more resistant to disease. Behavioral traits of the unstriped morph, including responses to predators and interactions with territorial opponents, may contribute to increased levels of stress and reduced resistance to infection. Future studies that directly manipulate glucocorticoid levels and/or temperature are needed to better understand the differences in Bd resistance in this species.

When introduced species invade ecosystems, alterations in community structure can emerge from the competitive and predatory interactions that occur between introduced and native guild members. Because a number of recent studies have shown that large predatory invertebrates can both compete with and prey on small vertebrates and because introductions of non-native species may play a role in amphibian declines, the effects of introduced centipedes Lithobius forficatus and native centipedes Scolopocryptops sexspinosus on juveniles of the red-backed salamander Plethodon cinereus were examined. In laboratory arenas, juvenile salamanders exhibited submissive behaviour in response to the odours of both species of centipede. There were no significant differences in salamander response to the two centipede odour treatments, but compared to controls, juveniles of P. cinereus spent significantly more time in escape and in a flattened submissive posture when presented with native centipede odours. Despite significant size differences between centipedes and juvenile salamanders, no predation of salamanders by either species of centipede occurred in any pairings. Juveniles exhibited more chemosensory behaviour towards native centipedes and towards their odours and exhibited marked reductions in aggressive posturing when centipedes were present. Field and laboratory data suggest that juveniles of P. cinereus and centipedes were negatively associated. In laboratory trials, the native centipede excluded juvenile salamanders from cover objects and we found fewer instances of co-occurrence in the field than expected. These studies are the first to examine the behavioural interactions between juveniles of P. cinereus and invertebrate predators, one introduced and one native, of eastern deciduous forest-floor food webs.

Many aspects of ectotherm physiology are temperature‐dependent. The immune system of temperate‐dwelling ectothermic host species is no exception and their immune function is often downregulated in cold temperatures. Likewise, species of ectothermic pathogens experience temperature‐mediated effects on rates of transmission and/or virulence. Although seemingly straightforward, predicting the outcomes of ectothermic host−pathogen interactions is quite challenging. A recent hypothesis termed the thermal mismatch hypothesis posits that cool‐adapted host species should be most susceptible to pathogen infection during warm temperature periods whereas warm‐adapted host species should be most susceptible to pathogens during periods of cool temperatures. We explore this hypothesis using two ecologically and physiologically differentiated color morphs of the Eastern Red‐backed Salamander (Plethodon cinereus) and a pathogenic chytrid fungus (Batrachochytrium dendrobatidis; hereafter “Bd”) using a fully factorial laboratory experiment. At cool temperatures, unstriped salamanders (i.e., those that are tolerant of warm temperatures) had a significantly higher probability of Bd infection compared with cool‐tolerant striped salamanders, consistent with the thermal mismatch hypothesis. However, we found no support for this hypothesis when salamanders were exposed to Bd at warm temperatures: the probability of Bd infection in the cool‐tolerant striped salamanders was nearly identical in both cool and warm temperatures, opposite the predictions of the thermal mismatch hypothesis. Our results are most consistent with the fact that Bd grows poorly at warm temperatures. Alternatively, our data could indicate that the two color morphs do not differ in their tolerance to warm temperatures but that striped salamanders are more tolerant to cool temperatures than unstriped salamanders.