Abstract
Parents are expected to evolve tactics to care for eggs or offspring when providing such care increases fitness above the costs incurred by this behavior. Costs to the parent include the energetic demands of protecting offspring, delaying future fecundity, and increased risk of predation. We used cost-benefit models to test the ecological conditions favoring the evolution of parental care, using lizard populations that differ in whether or not they express maternal care. We found that predators play an important role in the evolution of maternal care because: (1) evolving maternal care is unlikely when care increases predation pressure on the parents; (2) maternal care cannot evolve under low levels of predation pressure on both parents and offspring; and (3) maternal care evolves only when parents are able to successfully defend offspring from predators without increasing predation risk to themselves. Our studies of one of the only known vertebrate species to exhibit interpopulation differences in the expression of maternal care provide clear support for some of the hypothesized circumstances under which maternal care should evolve (e.g., when nests are in exposed locations, parents are able to defend the eggs from predators, and egg incubation periods are brief), but do not support others (e.g., when nest-sites are scarce, life history strategies are “risky”, reproductive frequency is low, and environmental conditions are harsh). We conclude that multiple pathways can lead to the evolution of parental care from a non-caring state, even in a single population of a widespread species.
Highlights
Parental care should evolve when the benefits of providing care increase offspring survival above the costs of reduced survival and future reproduction of adults [1,2,3]
We focus on the fitness consequences of maternal care, where mothers benefit by increasing egg hatching rates but incur a cost in terms of the survival of the nest-guarding female and reduced opportunity for future reproduction
Because parental care by male reptiles is virtually nonexistent [1], here we focus on the conditions under which maternal care is likely to evolve (ESS1 and ESS3)
Summary
Parental care should evolve when the benefits of providing care increase offspring survival above the costs of reduced survival and future reproduction of adults [1,2,3]. Offspring benefit from parental care through an increased chance of survival, which is relatively easy to measure, but the costs for parents are complex, and much more difficult to detect [4]. One of the principle constraints with predicting the circumstances under which parental care evolves is that the ecological form of the cost and benefit functions is unknown, making models difficult to test empirically [2]. Models are normally tested using focal species which vary in the type or intensity of care provided (but in which all populations express care to some degree), or to examine interspecific variation in care strategies. Because parental care is either absent altogether or present in the vast majority of species, our capacity to understand the direct ecological influences of parental care evolution at the population level is limited
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