Visual communication from a functional and evolutionary perspective: what does the Anolis dewlap say?
1 December 2016
UAntwerpen, Campus Drie Eiken, gebouw O, O.05 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken
Raoul Van Damme & Bieke Vanhooydonck
PhD defence Tess Driessens - Faculty of Science, Department of Biology
Animals communicate using a variety of signals that can differ dramatically among and even within species. The Anolis dewlap, i.e. an extendable flap of skin below a lizard’s throat, represents a classic example of a visual signal that shows considerable variation in size, colour, pattern and use. The aims of my PhD dissertation are to study the signalling functions of the Anolis dewlap and the evolutionary processes underlying interpopulational dewlap diversity, by using the brown anole lizard (Anolis sagrei). Complementary to previous studies, I investigated these topics in males and females.
Behavioural experiments showed that the dewlap in A. sagrei functions primarily in social contexts and, in particular, during courtship. Although having a less conspicuous design and lower display rates than in males, the female dewlap clearly has a signalling function too. Dewlap components convey information on sexual identity and in males, also on health state. Nevertheless, the information conveyed by dewlap components can vary substantially among populations, e.g. relative male dewlap size is an honest signal of biting capacity only in some A. sagrei populations.
Identifying the evolutionary processes that underlie the observed intraspecific dewlap diversity is challenging, mainly due to the methodological difficulties to accurately quantify the strength of selective processes in the field. Nevertheless, I could show indirect support for species recognition in shaping complex dewlap colour patterns in A. sagrei males. Furthermore, I could demonstrate that climate-related environmental conditions help in explaining intraspecific diversity in male and female dewlap colouration and patterning. More precisely, I found that males and females occurring in ‘xeric’ environments had a higher proportion of solid dewlaps with higher UV-reflectance.
Lizards inhabiting ‘mesic’ environments had primarily marginal dewlaps showing high reflectance in red. Furthermore, I found that A. sagrei males increase dewlap displays in environments characterized by lower visibility and complex habitat structures, likely to enhance signal transmission. Hopefully, my PhD dissertation can provide groundwork for future research on the function and evolution of the Anolis dewlap, and may additionally stimulate an increased interest in the so far ‘scarcely studied’ female ornaments.