Androgen levels in a Bornean voiceless frog, Rana blythi

Abstract

Male Rana blythi and males of three other species of voiceless frogs from Bornean rain forests lack the suite of secondary sex characteristics typical of most anurans: nuptial pads, vocal sacs, enlarged forearm flexors, and male advertisement calls. At the same time, basal species in the voiceless frog lineage exhibit an extreme type of male parental care: the males carry the tadpoles on their backs. This unusual form of male parental care evolves at the same point in the phylogenetic history of the group as the loss of the secondary sex characteristics. This suggests that these voiceless frogs may have lowered androgen levels. Hormone assays from blood samples of R. blythi show that plasma levels of testosterone, androstenedione, and 5α-dihydrotestosterone are considerably lower in wild-caught R. blythi than those reported for other frog species when similar sample collection methods were employed.