Parental Response to Breeding Pool Water Level Change in Ranitomeya imitator

Abstract

For parental care behavior to be effective in providing benefit to offspring requires the accurate fulfillment of offspring needs. Environmental changes alter the stressors placed on offspring, and parental care must change to meet these altered needs. Behavioral plasticity in parental care has been observed previously in amphibians, notably in males of the glass frog Hyalinobatrachium fleischmanni, which alter the lengths of time spent brooding eggs depending on ambient humidity and egg hydration levels. Dendrobatids, or poison dart frogs, often lay their eggs terrestrially and transport tadpoles to adequate aquatic habitats. Previous research has shown that parental investment in offspring care tends to increase in conjunction with smaller breeding pools. Among dendrobatids, the mimic poison dart frog Ranitomeya imitator is well known for raising its young in small phytotelmata, and for its unique reproductive system of monogamous biparental care of eggs and tadpoles. The small pools R. imitator raise their offspring in are ephemeral and small in volume, making them vulnerable to desiccation. Although R. imitator guard breeding pools from competitors and provide trophic eggs as food for tadpoles, there is no evidence that they provide water to tadpoles. To examine the behavioral responses of adults and the physiological responses of tadpoles of Ranitomeya imitator to water level changes in the breeding pool, we exposed 10 breeding pairs of frogs to three different treatment levels of water level change. Over the course of biweekly water changes, the fast treatment experienced a 2.5 ml water level decrease, the slow treatment decrease experienced a 1.25 ml water level decrease, and the control experienced no water level decrease. Adults were recorded attending to their tadpoles in artificial breeding pools, and the proportion of time each pair spent on different parental care behaviors was compared between groups. Soon after metamorphosis, metamorphs were weighed and measured. Parental care behaviors did not significantly differ in proportion between fast, slow, and control water level treatment groups. Significant differences were found between treatment groups in tadpole snout-vent length and weight in grams. Duration of the larval stage positively correlated with water level treatment, and the most significant differences between treatment groups were found between the fast and control treatment groups. These results suggest that when exposed to rapidly decreasing water levels R. imitator tadpoles are selected to optimize the tradeoff between body mass and larval stage duration. Plasticity in growth exhibited in tadpoles may be an adaptation to the ephemerality of the phytotelm environment, enabling tadpoles to escape from the aquatic environment more quickly. Future research into this system should examine the impacts of the tradeoff between body mass and larval stage duration on post-metamorphosis life history. Such research could have implications for the persistence of this species and other dendrobatid frogs under climate change.