Generation glands of cordylid lizards: mechanism of secretion transfer to the environment

Cordylid lizards possess two types of holocrine epidermal glands involved in chemical communication, femoral glands and generation glands. We investigated how the glandular products of generation glands are dispersed to the environment, as it is assumed in earlier studies that glandular material of cordylid generation glands is transferred to the substrate via abrasion, similar to the situation in femoral glands. By means of scanning electron microscopy, we established that the outer gland surfaces of adult Cordylus cordylus, Hemicordylus capensis and Pseudocordylus microlepidotus show only localized signs of wear and tear, indicative of a very low abrasion rate. Using standard histological techniques and light microscopy, we studied the appearance of multi-layer generation glands in a series of individuals of different ages in Cordylus macropholis. In this species, generation glands are already conspicuous in neonates. The significant relationship between SVL and the number of generation layers that we recorded for C. macropholis suggests that abrasion is not the routine method of dispersal of glandular material. We did record significant differences in cross-sectional area and height between the outer and inner layers of multi-layer generation glands of Cordylus macropholis, but this is more likely attributable to 'desiccation' of the outer layer, rather than abrasion. Although we found signs of abrasion in cordylid generation glands, these appear minor. Evidence seems to suggest that a substantial part of the mature glandular generations remains intact and that probably only a liquid/semi-liquid component is dispersed to the environment. More research is, however, needed to confirm this.