Homing and Egg Discrimination in the Western Slimy Salamander,Plethodon albagula(Caudata: Plethodontidae)

In some species of vertebrates egg brooding is a costly form of parental care. Therefore, misdirection of parental care can significantly lower a female’s fitness. Because of the maternal investment and increased survivorship to offspring from egg guarding, a brooding female should home to her nest site after being displaced a short distance and discriminate between her own eggs and eggs from other females. In this study, we experimentally tested, in the field, alternative hypotheses concerning homing ability and egg discrimination in a population of nesting western slimy salamanders (Plethodon albagula). Fourteen brooding females were displaced 1 m to the left or right of their nest sites (determined randomly) for the homing experiment. Furthermore, brooding females (n = 13) were presented with their own clutches, which were displaced 50 cm to the left or right (determined randomly), and unfamiliar egg clutches at their original nest sites. The females were released at an equal distance from both egg clutches. After 24 hours, 12 displaced females (86%) had returned to their own nest sites and were brooding their egg clutches. Also, after 24 hours, nine test females had returned to their own nest sites and were brooding the unfamiliar egg clutches. No control or test females were present at the other new nest site locations. Therefore, we suggest that brooding femaleP. albagulado home to their nest sites and exhibit indirect egg discrimination.

Social Interactions in Two Sympatric Salamanders: Effectiveness of a Highly Aggressive Strategy

In terrestrial plethodontid salamanders, aggressive behaviour is thought to function in the spacing of territorial residents among contested cover objects on the forest floor. Such behaviour, when exhibited toward heterospecifics, plays an important role in the competitive interactions between species. We compared levels of aggressive behaviour in intra- and interspecific contexts in two species of sympatric salamanders (Plethodon ouachitae and P. albagula) that have similar ecological requirements but differ in adult size. We also tested the effectiveness of such behaviour in holding cover objects (territorial foci) in the laboratory and on the forest floor. We predicted that if one species were more aggressive than the other, then that species would have greater success in obtaining and holding cover objects. In laboratory trials, residents of P. ouachitae (the smaller species) were extremely aggressive in both intra- and interspecific contexts. Individuals of P ouachitae delivered bites at a rate 14 times that of previously studied species of Plethodon and were significantly more likely to escalate to biting when tested as territorial residents (in intra- and interspecific trials) and as intruders (in interspecific trials). Plethodon albagula exhibited a lower level of aggression, similar to other species of Plethodon. In laboratory trials, in which salamanders competed for cover objects of differing quality, residents of P. ouachitae were effective in expelling conspecific intruders, and they were marginally effective at expelling intruding P. albagula. Residents of P. albagula were less effective in expelling conspecific intruders and did not expel intruding P. ouachitae. We conclude that the extreme aggression exhibited by P. ouachitae enabled it to expel intruders from artificial cover objects and to invade cover objects held by larger heterospecific residents. Field data supported intraspecific defence of cover objects by P. ouachitae, but results for P. albagula were inconclusive. These results are consistent with the geographic distributions of these species (P. ouachitae typically outnumbers P. albagula in the Ouachita Mountains) and provide an example of a behavioural mechanism overcoming a size-related disadvantage.

The coccidia (Apicomplexa: Eimeriidae) of Caudata (Amphibia), with descriptions of two new species from North America

Over 300 caudate Amphibia were surveyed for coccidia in North America. Two new species of coccidia (Apicomplexa: Eimeriidae) are described. Oocysts of Eimeria opacum sp.nov. from Ambystoma opacum are spherical to subspherical, rarely ellipsoidal, 29.5 × 28.1 (27–32 × 22–31) μm, and have a shape index (length/width) of 1.05 (1.0–1.4). A micropyle, oocyst residuum, and polar granule are absent. Sporocysts are ellipsoidal to kidney-bean shaped, 17.4 × 9.1 (16–21 × 8–11) μm, with a shape index of 1.92 (1.6–2.3). Sporocysts are unusual in that they are encased in a second, more fragile wall that thins to form membranes at the poles; Stieda and substieda bodies are absent. Oocysts of Isospora hightoni sp.nov. from Plethodon albagula are spherical, rarely subspherical, 22.9 × 22.8 (21–24 × 21–24) μm, with a shape index of 1.0 (1.0–1.04). A micropyle and polar granule are absent, but a delicate oocyst residuum was noted in 13/40 (33%) of the oocysts. Sporocysts are ellipsoidal, 16.6 × 11.1 (14.5–17.5 × 10.5–12) μm, with a shape index of 1.5 (1.4–1.6); Stieda and substieda bodies are present. In addition to the species described herein, a taxonomic summary is provided of the known coccidia from Caudata, with the species E. nipponensis sp.nov., E. pyrrhogaster sp.nov., and E. saitamaensis sp.nov. assigned to previously reported coccidia erroneously assigned to named species.