Abstract
Identifying the factors that underlie signal divergences remains challenging in studies of animal communication. Regarding the chemical signalling, different compounds can be found in some species but be absent in others. We hypothesized that if the costs that are associated with the expression of some compounds are too high, their presence in the signal may be restricted. However, these compounds may be expressed and be functional when those costs are relaxed. Vitamin E (α-tocopherol), a dietary compound with metabolic relevancy, acts as an honest chemical sexual signal in many lizards but no in others such as the Carpetan Rock lizard (Iberolacerta cyreni). We investigated whether dietary supplementation favours the expression of this vitamin in scents of I. cyreni. We show that dietary constraints can preclude the expression of vitamin E in chemical secretions of wild males because was expressed when it was experimentally provided in the diet. Vitamin E supplementation also heightened the immune response of males and increased the interest of their scent for females, highlighting the vitamin E as a chemical sexual signal in this species. We suggest that diet could decisively act as a driver of intra- and interspecific divergences in the chemical signalling of lizards.
Highlights
The ‘handicap paradigm’ proposes that individuals that are able to afford the costs associated with the elaboration and maintenance of secondary sexual characters are favoured by selection because these individuals display honest signals that truly convey useful information on the quality of bearers to the receivers[1, 2]
In vitamin E dietary supplemented males (E-males), we found steroids as the main compounds (69% of total ion current (TIC))
The present study showed that the expression of an honest chemical sexual signal could be significantly affected by its dietary availability to the point of precluding its entire expression in all of the individuals of a population or species, which probably explained the absence of VE in femoral secretions of wild I. cyreni[10, 16]
Summary
The ‘handicap paradigm’ proposes that individuals that are able to afford the costs associated with the elaboration and maintenance of secondary sexual characters are favoured by selection because these individuals display honest signals that truly convey useful information on the quality of bearers to the receivers (competitors and potential mates)[1, 2]. VE participates in many metabolic and physiological pathways, lizards of some species allocate large amounts of this vitamin in chemical secretions that are deposited outside of the body. The magnitude of such allocation has been correlated with the quality of males in some species, which may explain the preference of females for the scent of those males[24,25,26]. In addition to a signalling function of male quality, a pre-existing sensory bias in females for a chemosensory search of VE in their food might explain why females preferred chemical secretions of males with higher proportions of VE27, 28
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