Mystery solved: unravelling the life history of the enigmatic and ancient Philippine frog Barbourula busuangensis (Anura: Bombinatoridae)

The biology of the poorly known Philippine frog Barbourula busuangensis has been a challenging mystery since the discovery of the species one hundred years ago. Based on extensive fieldwork and examination of scientific col­lections, we present novel information on its reproductive biology, including the discovery and morphological descrip­tion of the tadpole. This species exhibits characteristics of a K-strategist, with large, unpigmented eggs in small number relative to body size (low Ovarian Size Factor, mean = 6.56). Field observations suggest a prolonged reproductive period, with gravid females present across seasons, and possible egg retention for at least up to two months. We describe for the first time to science their unique tadpoles, which are rheophilous, endotrophic, and nidicolous. These tadpoles lack keratinized mouthparts (rostrodonts and tooth rows) and have a large sucker-like oral disc used for adhesion within rock crevices in river cave systems, where they develop. Camera recordings at nest site revealed the presence of an adult with the larvae, suggesting parental care. Overall, our findings offer significant insights into the life history of this secre­tive species, and point to a new, undescribed reproductive mode for anurans, thus contributing to our knowledge on the evolution of reproductive strategies of tropical species in different ecological contexts.