Ultrastructure of cutaneous poison glands in South-American frogs: a comparison between Physalaemus albonotatus and Leptodactylus chaquensis (Anura: Leptodactylidae)

Serous (poison) cutaneous glands of the leptodactylid species Physalaemus albonotatus and Leptodactylus chaquensis have been compared under light and transmission electron microscopes. Glands in the two species share structural traits common in anurans, including the peripheral contractile sheath (myoepithelium) and the syncytial secretory unit which produces, stores and modifies the poison. At the ultrastructural level, early steps of poison production are also similar and fit the usual path of the proteosynthesis, involving rer and Golgi stacks (dictyosomes) in the peripheral syncytial cytoplasm. On the contrary, several differences are obvious during the maturational processes that lead post-Golgian products to their ultimate ultrastructural traits. In P. albonotatus, the dense product released from the dictyosomes acquires a thick repeating substructure, which however becomes loser in the inner portion of the syncytium. In L. chaquensis, serous maturation involves gradual condensation, and opaque, somewhat “vacuolized” granules are formed . These different maturational paths expressed during poison manufacturing in the species under comparison agree with the polyphyletic origin of the family Leptodactylidae. On the other hand, data collected from P. albonotatus fit previous findings from P. biligonigerus and stress the view that poisons produced by congeneric species share similar (or identical) ultrastructural features.