Does maternal care evolve through egg recognition or directed territoriality?

The mechanism which facilitates the evolution of maternal care is ambiguous in egg-laying terrestrial vertebrates: does the ability of mothers to recognize their own eggs lead them under some circumstances to begin providing care, or can maternal care evolve from simply being in close proximity to eggs (e.g., through territorial behavior)? This question is difficult to answer because in most species parental care is either absent altogether or present; in few species do we have the opportunity to observe intraspecific variation in the expression of parental care. We studied a population of long-tailed skinks (Eutropis longicaudata) in which females have recently evolved maternal care from a non-caring state. Females on Orchid Island, Taiwan remain with their eggs during incubation, and when doing so actively deter egg predation by egg-eating snakes (Oligodon formosanus); in all other populations females lack post-ovipositional maternal care. Nest-guarding females on Orchid Island: (1) s...