Restricting living space: Development and larval morphology in sticky frogs (Microhylidae: Kalophrynus) with different reproductive modes

We compare reproductive features, development, and larval morphology in three closely related species of sticky frogs (Kalophrynus Tschudi, 1838) inhabiting the lowland and mountain forests of Vietnam and displaying a variety of reproductive modes. While K. interlineatus breeds in open temporary ponds, K. honbaensis and K. cryptophonus are phytotelm-breeders using tree hollows and bamboo stems for reproduction. Their tadpoles also differ in trophic specialization: larval K. interlineatus are typical suspension-feeders, whereas K. honbaensis and K. cryptophonus are obligatorily oophagous. All three species differ in egg and clutch sizes, duration of embryonal period and hatching stage, and the structure of the larval digestive tract and skeleton. Based on external and internal morphology, we conclude that tadpoles of K. interlineatus and K. cryptophonus represent two “extremes” of the adaptive spectrum of microhylid larvae, while K. honbaensis displays a set of transitory traits. Relying on these new findings in anuran biology, we discuss reproductive, ontogenetic, and morphological rearrangements during the transition from pond breeding to phytotelm breeding and from microphagy to macrophagy as well as the significance of the revealed adaptations to different habitats and larval life modes.