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.

Diet diversity and clutch size of aquatic and terrestrial salamanders.

Terrestrial species of salamanders generally have a higher diversity of prey in their stomachs and produce smaller and less frequent clutches than do species living in wetter habitats. This may be a consequence of differences in prey availability in the two types of habitats. Prey frequently fluctuate in availability in terrestrial areas as a result of fluctuations in rainfall and the inability of salamanders to forage efficiently during dry periods; the salamanders respond with a generalist diet and relatively K-selected reproductive tactics. In wetter habitats, prey fluctuations are probably dampened due to more constant conditions of moisture; salamanders respond with a more specialized diet and relatively r-selected reproductive tactics.

Fluctuations in prey availability and food limitation for a terrestrial salamander.

A Virginia population of the forest-dwelling salamander Plethodon cinereus was repeatedly sampled over four years to determine volume and number of prey ingested under varying conditions of moisture and temperature. The proportion of the population on a daily negative energy budget was estimated by comparing actual foraging success with laboratory determined values of energetic requirements at various temperatures.Prey became "limited" in availability during rainless periods, apparently because salamanders were not able to forage in dry leaf litter. Foraging success increased with increasing rainfall. Food was a "limiting" resource for a majority of the population on most sampling days, as determined by energy budget analysis. While ambient moisture regulated food availability, ambient temperature set the metabolic requirements and assimilation efficiencies for the population. Consequently, food was more limiting on dry, warm days and less so on wet, cool days. These data support the hypothesis that intraspecific competition frequently occurs for a food resource that is periodically limited in availability.

Competitive Exclusion as a Factor Influencing the Distributions of Two Species of Terrestrial Salamanders.

The salamander Plethodon richmondi shenandoah is restricted to areas of talus on Hawksbill Mountain, Shenandoah National Park, Virginia, while P. cinereus inhabits the soil outside the talus. To test the hypothesis that the former species is excluded from the soil by the latter species, three enclosures were constructed in each of four habitats: (i) in talus consisting only of bare rocks, (ii) in talus where soil has infiltrated between but not under rocks, (iii) in isolated pockets of shallow soil within the rocky confines of the talus, and (iv) in deep soil outside the talus. In each habitat one enclosure contained an isolated sample of shenandoah, another an isolated sample of cinereus, and the third a mixture of the two species. The above testes indicated that: (i) neither species survived the extremely dry conditions of the bard rocks for more than a week, (ii) shenandoah expressed a higher survivorship than did cinereus in this relatively dry habitat, (iii) in the shallow soil shenandoah had lower survivorship in the presence of cinereus than it did in isolation, and (iv) in the deep soil shenandoah had poorer survivorship than cinereus in the mixed species enclosure and poorer survivorship than its isolated control. P. cinereus apparently inhibits the presence of shenandoah in areas of soil, while shenandoah survives better under rocky conditions. However, the talus is a suboptimal habitat for shenandoah, since its survivorship in isolated enclosures is significantly better in the presence of soil. It seems unlikely that salamanders other than cinereus could exclude shenandoah from the soil or that other animals exert a strong influence. Predation, diseases, and parasites also do not appear to exclude shenandoah from areas of deep soil. Competitive exclusion by cinereus has probably restricted the distribution of shenandoah to the suboptimal talus refugium.