Patterns of parental care in Neotropical glassfrogs: fieldwork alters hypotheses of sex-role evolution.

Many animals provide parental care to offspring. Parental sex-roles vary extensively across taxa, and such patterns are considered well documented. However, information on amphibians is lacking relative to other vertebrate groups. We combine natural history observations with functional and historical analyses to examine the evolution of egg care in glassfrogs (Centrolenidae). Parental care was considered rare and predominately provided by males. Our field observations of 40 species revealed that care occurs throughout the family, and the caregiving sex changes across lineages. We discovered that a brief period of maternal care is widespread and occurs in species previously thought to lack care. Using a combination of female-removal experiments, prey-choice tests with egg-eating katydids, and parental disturbance-tolerance assays, we confirm the adaptive benefits of short-term maternal care in wild Cochranella granulosa and Teratohyla pulverata. To examine historical transitions between caregiving sexes, we assembled a molecular phylogeny and estimated ancestral care states using our data and the literature. We assessed patterns indicative of sex-specific constraints by testing whether transitions between the sexes are associated with changes in care levels. Our analyses support that male-only care evolved 2-3 times from female-only care, and this change is associated with substantial increases in care levels - a pattern supporting the hypothesis that male-only care evolved via constraints on maternal expenditure. Many groups of amphibians remain poorly studied, with emerging evidence indicating that care patterns are more diverse than currently appreciated. Natural history remains fundamental to uncovering this diversity and generating testable hypotheses of sex-role evolution.