Climate and mating systems as drivers of global diversity of parental care in frogs

Aim: Amphibians exhibit unusually diverse reproductive modes, including a wide array of parental care strategies. The evolutionary drivers of this diversity, however, remain unclear. Here, we investigate three major factors that might predict interspecific variation in parental care strategies: climate, intrasexual selection and social environment. We hypothesize that some forms of care evolved to cope with harsh conditions, such as dry or unpredictable habitats. We contrast this prediction with the hypothesis that parental roles have co-evolved with the social environment and mating systems. Location: Global. Major taxa studied: Frogs and toads (Amphibia: Anura). Time period: Extant taxa that represent c. 220 Myr of evolutionary history. Methods: Using geographical and behavioural data for 971 species of frogs and toads that represent 45 anuran families, we quantified the global distribution of four forms of parenting separately for males and females: nest building, nest and/or tadpole attendance, carrying and nourishment. We used phylogenetic comparative analyses to investigate whether climate, social environment and mating systems predicted interspecific variation in parental care. Results: Our results showed that climatic effects contribute to parental care diversity: in cool and humid climates the males provide offspring attendance, whereas in predictable temperatures endotrophy occurs, whereby the female provides all nutrients for the offspring until metamorphosis. In addition, we found other associations between mating systems and forms of parental care: uniparental clutch attendance by males is present in species with territorial defence, whereas cooperative nest building co-occurs with sperm competition. The type of parental care is not associated with adult sex ratios. Main conclusions: No specific form of care is associated with hostile environments; in fact, some forms of care occur in beneficial conditions, whereas others are used independently from the climate. Instead, parenting diversity has co-evolved closely with mating systems in frogs.