Parental care is beneficial for offspring, costly for mothers, and limited by family size in an egg-feeding frog

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Abstract

Care that parents provide to offspring often comes at the cost of other reproductive opportunities, generating parent–offspring conflict and sibling rivalry whenever there are resource shortfalls. Although these family dynamics are most often studied in birds, convergent family structures can be found in diverse lineages, including in frogs that feed their developing young with unfertilized trophic eggs. We used observations in a captive colony of the strawberry poison frog (Oophaga pumilio) to test the hypothesis that parental care is a limiting resource within families of this egg-feeding frog, and thus could generate conflicts of interest. We found that maternal provisioning was valuable to offspring: Trophic egg provisioning was positively associated with larval survival, size at metamorphosis, and postmetamorphic survival. Maternal care came at the cost of other reproductive opportunities: Females produced fewer reproductive clutches when caring for tadpoles than when dependent young were absent. Even under presumably benign captive conditions, resources were limited within reproductive cycles. Tadpoles in larger broods received smaller meals, and although survival increased across brood sizes of 1–3 tadpoles, the largest broods (4 tadpoles) suffered reduced survival. Finally, older tadpoles received larger meals, a pattern consistent with the prediction that females would favor their most valuable offspring. These results suggest that relationships within O. pumilio families are constrained by resource limitation. Because of a convergent family structure coupled with substantial metabolic and natural history differences, egg-feeding frogs will provide an excellent complement to birds when addressing the causes and consequences of conflicts of interest within families.

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