Benefits of parental care: Do juvenile lizards obtain better-quality habitat by remaining with their parents?

Evolutionary theory suggests that parental care is favoured by natural selection when the benefits to offspring fitness outweigh the costs of parental expenditure. The nature of such benefits may differ among species, however, especially in species reflecting independent evolutionary origins of parental care. Black rock skinks (Egernia saxatilis, Scincidae) of south-eastern Australia are viviparous rock-dwelling lizards with prolonged parent-offspring association; adult pairs vigorously defend their home range - and, when present, their offspring - against conspecifics. We addressed the hypothesis that, by remaining within their parents' (vigorously defended) home range, juveniles thereby obtain access to better-quality habitats. Measurements of biologically significant variables (crevice size, sun exposure, vegetation cover) revealed little difference between shelter-rocks used by solitary ('orphan') juveniles and those within family groups containing adults. Indeed, the only consistent differences involved larger (and therefore, less predator-proof) crevices for juveniles within family groups than for solitary conspecifics. Our data thus falsify the hypothesis that parental care evolves because of benefits associated with habitat quality; instead, it appears that parental protection of juveniles against infanticidal conspecifics may be the most plausible benefit to parent-offspring association in this system.