Fine structures on the surface of nuptial pads of male hylid and rhacophorid frogs.

Nuptial pads, secondary sexual characteristics of male frogs, develop on the first digit of the hand of Hyla japonica in the family Hylidae and of Rhacophorus schlegelii in the family Rhacophoridae, and on both the first and second digits of the rhacophorids Buergeria buergeri and B. japonica. By scanning electron microscopy (SEM), it was seen that numerous mounds covered the surface of the pads. Mounds were similarly hemispherical in R. schlegelii and B. buergeri and flat in B. japonica. The mounds of H. japonica were irregular in shape and size and some of them stood in rows. Fine columnar protuberances were present all over the surfaces of the mounds in this species. Numerous peg-like protuberances projected radially upward from the top of the mounds in B. buergeri and B. japonica. Irregular-shaped, leaf-like protuberances bearing knobby or rod-shaped apical protrusions were present on the top of the mounds in R. schlegelii. In pads observed by transmission electron microscopy, the outermost epithelial monolayer of the mounds was generally thick, especially at the top, compared to that of the rest of the skin. Epidermal cells in this layer were well keratinized, devoid of organelles, and contained closely packed, fine filaments within a dense matrix. Apical accessory protuberances projecting from the outermost cells were also packed with dense filamentous materials, showing rigid comb-like structures. © 1994 Wiley-Liss, Inc.