INTRASPECIFIC AND INTERSPECIFIC INTERFERENCE BEHAVIOR AMONG SEXUAL AND ASEXUAL GECKOS

The level of inter- and intraspecific aggression between three species of gekkonid lizards was investigated with laboratory contests between pairs of individuals. Two of these species, Lepidodactylus lugubris and Hemidactylus garnotii, are asexual parthenogens. The third species, Hemidactylus frenatus, is sexual and has been implicated in an apparent competitive exclusion of the asexual species in the urban 'house gecko niche' on tropical Pacific islands. Hemidactylus frenatus males were more likely to approach and bite an asexual female and less likely to be spatially displaced by the approach of an asexual female than vice versa, suggesting that competitive exclusion is at least partially caused by behavioural interactions. Sexual males are more aggressive than sexual females in interspecific encounters with asexual females, so the presence of males in the sexual population increases the competitive advantage of the sexual population over that of the asexual population. Recent studies of aggression in Cnemidophorus lizards have shown reduced aggression in asexual species compared with that of closely related sexual species, and reduced aggression intra-clonally versus inter-clonally in the asexual species. As in Cnemidophorus, sexual H. frenatus females were more aggressive towards each other than were asexual H. garnotii females belonging to a single clone. However, no difference was found between intra- and inter-clonal aggression in two genetic clones of L. lugubris. The potential for interspecific predation of juveniles as an interference mechanism was also evaluated experimentally. Hemidactylus frenatus was capable of preying on L. lugubris hatchlings but the reverse was not true. This is also consistent with the observed competitive superiority of H. frenatus in the field. © 1992 The Association for the Study of Animal Behaviour.