Influences of facultative paedomorphosis on kin selection in a larval salamander, Ambystoma talpoideum

Kin selection in larval amphibians is hypothesized to increase survival to metamorphosis. While kin selection may benefit amphibians with obligate metamorphosis, increased survival within sibships may exert fitness costs on facultatively paedomorphic species, such as increased competition among kin. Consequently, it is unclear whether such species should engage in kin selection. We investigated kin selection in a facultatively paedomorphic salamander, Ambystoma talpoideum, using laboratory behavioural trials and microcosm experiments. Individuals were most aggressive towards familiar siblings, and full-sibship groups incurred more injuries than mixed-sibship groups; however, familiar siblings ultimately exhibited higher survival. Thus, while short-term responses appeared to reflect the hypothesized costs of kin recognition, long-term patterns of survival did not support this hypothesis. The inconsistencies between results suggest that short-term studies may not capture ontogenetic variation in kin selection, and that long-term studies are needed to better test the hypothesized effects of kin selection on survival and metamorphosis.

Effects of Exogenous Corticosterone on Circulating Leukocytes of a Salamander (Ambystoma talpoideum) with Unusually Abundant Eosinophils

When animals become stressed, their levels of glucocorticoid hormones increase, causing white blood cells to move from tissues to circulation or vice versa. The primary alteration is an increase in the abundance of circulating neutrophils and a decrease in lymphocytes in circulation. A lesser-known effect is a decrease in the number of circulating eosinophils. Salamanders in the genusAmbystomahave unusually high numbers of circulating eosinophils, and as such, any effect of stress hormones on circulating leukocytes (especially eosinophils) of these species should be especially pronounced. We conducted an experiment to determine the effect of corticosterone administration on leukocyte counts (from blood smears) ofA. talpoideumsalamanders. Salamanders were captured and sampled as reference animals(n=11), given a sham injection(n=8), or injected with 0.1cc of a 100 μg/mL corticosterone solution(n=28). After 24 hours, relative neutrophil counts were higher and relative lymphocyte counts lower, in the corticosterone group than the sham and control groups. Absolute counts showed that this effect was driven by a reduction in lymphocytes, since neutrophil counts were statistically similar across treatments. Importantly, relative and absolute numbers of eosinophils decreased in the sham and corticosterone groups, confirming the sensitivity of this cell to stress in amphibians.