Ecology and evolution of parent–embryo interactions in neotropical glassfrogs
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Parental care is important to offspring survival in many species. Because care benefits young and is often costly to parents, it can generate fitness trade-offs that influence the evolution of family life. In particular, interactions within families are predicted to generate variation in care, which in turn causes selection on traits used to give, receive, and influence care. My dissertation examines whether such socially dynamic processes have influenced the evolution of parental and embryo behavior in glassfrogs (Centrolenidae). These Neotropical frogs have terrestrial eggs, aquatic larvae, and multiple origins of male-only care. Embryos can plastically alter hatching age, which might allow them to adaptively respond to variation in egg care. I test for parent–embryo coevolution by combining field observations (40 species), experiments (8 species), and phylogenetic comparative analyses. First, I test historical and functional hypotheses of parental care evolution. I found that uniparental egg-care is ubiquitous in centrolenids, can be provided by either sex, and benefits young. Elaborate male-only care evolved repeatedly from simpler female-only care, a pattern consistent with constraints on female-care levels. Second, I examine the diversification of male-only care, testing whether maternal changes to egg-clutch traits influence embryo dependency and if such changes are associated with male-only care. Evidence indicates that reduced female expenditure on egg-jelly evolved with, and increases the importance of, elaborate male care. Next, I evaluate whether embryos respond to behavioral and evolutionary changes in parenting. Embryos behaviorally delay hatching when parents continue caring, and evidence indicates that evolutionary increases in hatching plasticity evolved with increases in care duration. I tested if male mating success causes variation in male care, and thereby influences embryo behavior. I found that increased mating success extends male care, making nests safer, and embryos delay hatching accordingly. Finally, I examine selective tradeoffs influencing hatching plasticity by measuring hatchling phenotypes and fitness correlates. Across species, delayed hatching provides performance benefits during the larval stage. Overall, my work reveals coevolutionary interactions among mothers, fathers, and embryos. It supports that embryos respond to parentally mediated changes in egg environments and elucidates how family life alters selection on parental and embryo traits.