AN EXPERIMENTAL-ANALYSIS OF JOINT NESTING IN THE SALAMANDER HEMIDACTYLIUM-SCUTATUM (CAUDATA, PLETHODONTIDAE) - THE EFFECTS OF POPULATION-DENSITY

Three nesting behaviour patterns are documented in the plethodontid sa lamander Hemidactylium scutatum. A female may lay eggs (1) in a solita ry nest and brood them, (2) in a joint nest and brood them as well as eggs of other females, or (3) in a joint nest that is brooded by anoth er female. The hypothesis that population density was positively assoc iated with joint nesting was tested by following two populations for 5 years and by experimentally manipulating the population density of ne sting females in artificial habitats for the latter 2 years. The propo rtion of joint nests did not vary with density, although joint nests t ended to contain eggs of more females at the high population density. Joint nests were usually brooded by one female; thus, most females tha t laid eggs in joint nests did not brood them at high density. The rep roductive success, as measured by survival of embryos, of solitary and joint nesters was equivalent. Joint nests were deserted less often, h owever, which decreased the probability of catastrophic mortality. The number of days of brooding was significantly positively correlated wi th loss of body mass of females, suggesting a cost to brooding behavio ur. Joint nesting with solitary brooding is not explained by aggressiv e usurpation of nests or by brood parasitism. (C) 1995 The Association for the Study of Animal Behaviour