A Guide to Sexing Salamanders in Central Appalachia, United States

Documenting the sex of individuals encountered during wildlife research and monitoring activities is important for understanding and tracking changes in populations. However, sexing salamanders can be particularly difficult because secondary sex characters are often subtle or only visible during the breeding season, and guidance on species-specific sex determination is lacking from most field guides. The purpose of this guide is to provide a reference to assist biologists in the Central Appalachian region with identifying sex of live adult salamanders. In the main text we provide summary tables and figures to serve as concise references in the field. We provide individual species accounts that contain concise yet comprehensive information for each species based on the published literature, as well as many images depicting sexually dimorphic characters. Our focal region encompasses partial or entire distributions for 56 species of salamanders in 5 families (Ambystomidae, Cryptobranchidae, Plethodontidae, Proteidae, and Salamandridae). We identified seven morphological characters that are strongly sexually dimorphic and useful for sexing live, nonanesthetized, adult salamanders in the field, with males of individual species exhibiting one to five of the characters. We identified more than 20 additional characters that are weakly sexually dimorphic, difficult to distinguish in the field, or species-specific. Our guide serves as a synthesis of sexually dimorphic characters for salamanders in Central Appalachia, and we anticipate it will have broad value for researchers, monitoring programs, and salamander enthusiasts in eastern and central North America.

Male mate preference as an agent of fecundity selection in a polymorphic salamander

Color polymorphisms are associated with variation in other traits which may affect individual fitness, and these color-trait associations are expected to contribute to nonrandom mating in polymorphic species. The red-backed salamander (Plethodon cinereus) exhibits a polymorphism in dorsal pattern: striped and unstriped, and previous studies have suggested that they may mate nonrandomly. However, the mechanism(s) contributing to this behavior remain unclear. Here we consider the role that male preference may have in driving mating behavior in P. cinereus. We limit our focus to striped individuals because this morph is most likely to be choosy given their dominant, aggressive behavioral profiles relative to unstriped males. Specifically, we evaluated (a) whether striped males preferentially associate with females with respect to her dorsum color, size, and body condition and (b) if so, whether female traits are evaluated via visual or chemical cues. We also considered whether the frequency of another male social behavior, nose taps, was associated with mate preferences. We found that striped male P. cinereus nose tapped more often to preferred females. However, males only assessed potential mates via chemical cues, preferring larger females overall. Reproductive phenology data on a sample of gravid females drawn from the same population indicated that the color morphs do not differ in reproductive traits, but larger females have greater fecundity. Given our findings, we conclude that female P. cinereus are under fecundity selection, mediated by male preference. In this manner, male mating behavior contributes to observations of nonrandom mate associations in this population of P. cinereus.

Experimental evaluation of agonistic behaviour, chemical communication, spacing, and intersexual associations of the Eastern Red-backed Salamander (Plethodon cinereus) near its northern range limit

Territorial behaviour is the use of aggression and advertisement in the defense of a fixed area. In the Eastern Red-backed Salamander (Plethodon cinereus (Green, 1818)), territoriality is prevalent in Virginia, USA, near the southern extent of its range, but few studies have examined whether northern populations exhibit territorial behaviour. We tested for some prerequisites of territorial behaviour in P. cinereus at the northern extent its range, near North Bay, Ontario, Canada. In laboratory trials, we found that adult male P. cinereus exhibited a modest degree of aggression, and intruding salamanders attempted to escape the experimental chamber more often than residents. We also found that P. cinereus were able to differentiate between familiar and unfamiliar substrates, suggesting pheromonal communication and a potential for territorial advertisement. However, while male–female pairs were common at six sampling sites during the mating season, adult salamanders consistently exhibited a random spatial distribution during the nonmating season. Our study suggests that local P. cinereus exhibit low-level aggression but may not defend fixed areas. One possibility is that P. cinereus may generally not benefit from territorial behaviour in cooler climates, as evapotranspiration rates will be lower and foraging activity less restricted compared with more southern climates.

Ecological separation in a polymorphic terrestrial salamander

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.

Multiple paternity in a salamander with socially monogamous behaviour

In the majority of birds and mammals, social monogamy is not congruent with genetic monogamy. No research to date has compared social and genetic monogamy in amphibians. We analysed paternity in clutches of red-backed salamanders (Plethodon cinereus), a species in which social monogamy has been demonstrated in the laboratory, and 28% of individuals in the forest are found in male-female pairs in the noncourtship season. We collected 16 clutches of eggs of P. cinereus in the southern Appalachian Mountains of Virginia and collected tail clippings from attending mothers. We genotyped embryos and adults at five microsatellite loci in order to analyse paternity of clutches. Most clutches (84.6%) had multiple sires, with two to three sires per clutch. In this study, 25% of clutches had males in addition to females attending eggs. None of the mothers of these clutches were genetically monogamous. All attending males sired some of the offspring in the clutch that they attended (between 9% and 50%) but never sired a majority in that clutch. We conclude that, at least in this population, social monogamy in P. cinereus is not concomitant with genetic monogamy.

Social monogamy in a territorial salamander

Social monogamy, which does not necessarily imply mating or genetic monogamy, is important in the formation of male-female pair associations. We operationally define social monogamy as occurring when two heterosexual adults, exclusive of kin-directed behaviour, direct significantly less aggression and significantly more submission towards each other, and/or spend significantly more time associating with each other relative to other adult heterosexual conspecifics. Long-term pair associations (i.e. those lasting through a lengthy breeding season) that are characteristic of social monogamy are common in some taxa but are virtually unknown in amphibians. Recent studies, however, have suggested that red-backed salamanders, Plethodon cinereus, have complex (for amphibians) social systems. Our laboratory experiments tested the hypothesis that red-backed salamanders found in pairs in the forest display behaviours consistent with social monogamy. During the summer noncourtship season, newly collected male-females pairs showed no preference to associate with their partners more than with a novel conspecific of the opposite sex. However, during the autumn courtship season, paired males and females significantly directed preferential behaviours towards their partners rather than towards a surrogate or a novel paired salamander. Focal animals showed no significant preferences when presented with their partner and a novel single salamander, but they never directed preferential behaviours towards a novel salamander (whether paired or single) or a surrogate. These results are the first to suggest that a salamander species engages in social monogamy. Furthermore, our results suggest that social monogamy may not inhibit paired males and females from displaying alternative strategies: preferring partners when extrapair associations may be disadvantageous (i.e. the extrapair animal is already paired) but not preferring partners when extrapair associations may be advantageous (i.e. the extrapair animal is single). Copyright 2000 The Association for the Study of Animal Behaviour.