Lizard communication

Abstract: Chemical signals are essential for intersexual communication in many animals, including lizards. While faeces have been suggested to contain socially relevant chemical stimuli, epidermal gland secretions are generally believed to be the leading source of chemosignals involved in lizard communication. Early research has shown that sex hormones affect epidermal gland activity, with androgens stimulating gland/pore size and/or gland productivity. However, the functional significance of hormone-induced glandular activity in lizard chemical communication remains unclear. In this study, we manipulated testosterone (T) concentrations in male Podarcis muralis lizards. While T-supplementation did not change pore size, it did increase secretion production substantially. Chemosensory tests showed that female conspecifics tongue-flick at a higher rate and more quickly towards the secretion of males with experimentally increased T levels than towards the secretion of control males, suggesting that females can discriminate between males with dissimilar T levels based on chemical cues of secretion alone. Based on the scent of faeces, however, females were unable to discriminate between males with differential T levels. Also, females reacted more quickly when offered larger amounts of secretion – irrespective of whether secretions were obtained from control or T-increased males. This result indicates that secretion quantity affects chemosignal detectability in Podarcis muralis.

Abstract: The epidermal glands of lizards are considered an important source of semiochemicals involved in lizard communication. Many features of the lizard epidermal gland system vary among and within species (e.g. gland number, size, and shape), and some are believed to reflect the degree of intra- and interspecific variation in glandular secretion production, and by extension, the chemical signalling investment of lizards. Traditionally, herpetologists estimate secretion production based on the number of glands or the size of the glands, rather than quantifying the amount of secretion produced. Still, the reliability of these proxies for secretion production has never been validated. Here, I explored the relationship among secretion production (in mass), pore size (surface area, diameter), and gland number in three species of lacertid lizards ( Acanthodactylus boskianus , Timon lepidus , Holaspis guentheri ), and tested which proxies predicted secretion production variation best, and examined whether the same trend is true for all species. The findings of this study show that the total secretion production of lacertids is highly variable among and within species. Variation in secretion production among-species (but not within-species) could partly be explained by variation in body size. While both measures of pore size were positively related with secretion production, my tests revealed the model with only pore diameter as contributing variable explaining absolute secretion production variation (both within and across species) as the best one. Although gland number appeared a suboptimal estimate for secretion production in the three lacertids under study, only family-wide, multi-species comparative tests counting large within-species sample sizes can provide further insight on the matter.