Reliable proxies for glandular secretion production in lacertid lizards
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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.