Serous cutaneous glands in the paludiculine frog Physalaemus biligonigerus (Anura, Leptodactylidae): patterns of cytodifferentiation and secretory activity in prematomorphic specimens

The development of serous cutaneous glands is described in tadpoles of the leptodactylid frog Physalaemus biligonigerus, with attention to the cytodifferentiation processes of the secretory unit (adenomere). Secretory differentiation causes the adenomere to assume the structure of a syncytium and triggers biosynthesis of the serous product (poison),consisting of granules with peculiar repeating substructure. The secretory granules resemble glomerular-like aggregates of randomly orientated tubular subunits. This complex substructure derives from the rearrangement of the dense, compact material released by the Golgi apparatus in the form of small, membrane-bounded particles. Both early and advanced features of P. biligonigerus poison closely resemble those found during serous gland development in the Italian treefrog Hyla intermedia. The similar aspects described during serous biosynthesis in these leptodactylid and hylid frogs suggest they are phylogenetically informative. On the other hand, the peculiar features of their poisons may reflect the differential patternings of their secretory repertories along the divergent phylogenetic paths, which led these frogs to be currently included in different families.