Evolution of color signals in lizards

Animal communication is arguably one of the most complex aspects of animal behaviour and a cornerstone for the evolution of sociality. From the most complex of animal societies to the simplest form of sexual reproduction, social interactions hinge on the transmission of information via animal signals. Not surprisingly, even after decades of study, we are still far from a comprehensive understanding of the evolution of animal signals. The general aim of my PhD will be to address open evolutionary questions in the study of animal communication by studying the evolution of colour signals in lizards, using the genus Podarcis as a model.

Podarcis filfolensis, Malta

Podarcis filfolensis, Malta

European Podarcis lizards are an emerging model in the study of animal colour signals, and an excellent system to study the adaptive radiation of colour signals. Adaptive radiations generally provide unique ‘laboratories’ to study general evolutionary principles, and hence to understand the processes underlying the emergence and maintenance of the planet’s biodiversity.The genus Podarcis currently comprises at least 23 species with continental, insular, or continental-insular distributions occupying a rich variety of habitats. Podarcis lizards show cryptic dorsal colorations designed to avoid predators and enhance thermoregulation, and conspicuous ventral or lateral colourations that function as chromatic signals. Ventral colourations are pigment-based and appear to play a role in mate choice, while laterally most Podarcis display UV-reflecting colour patches, which seem to act as indicators of quality.

Among my general aims, I will address both general principles and some poorly understood questions in the evolution of animal colour signals:

  • Understanding why signals are reliable enough to be evolutionarily stable in the face of deception has been, and to a great degree still is, a major challenge in evolutionary biology, but we have scarcely any knowledge about the evolutionary processes affecting interspecific variability in signal reliability (i.e. strength of design/information correlation).
  • Many pigments are derived from the diet and hence pigment-based signals seem adequate indicators of relatively labile physiological-dependent traits, while structural colour signals seem better suited as indicators of more stable traits dependent on long-term developmental changes, but the hypothesis that these two types of signals may have evolved to reflect generally distinct condition-dependent traits has yet to be addressed.
  • Study the effect of the visual niche, predation pressure and degree of intra-specific competition on the evolution of lizard dorsal (i.e. cryptic) vs. lateral (i.e. likely to be involved in intraspecific communication) colourations and overall conspicuousness.
  • Studying the co-evolution of pigment and structural colorations in relation to different socio-sexual factors is also bound to provide clues about the factors (e.g. predation and sexual selection intensity) constraining/favouring the appearance and maintenance of ventral colour polymorphisms, which are relatively common in Podarcis.
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