Animal colouration is a remarkable illustration of nature’s capacity for “endless forms most beautiful”. Yet, the drivers of this diversity remain largely unexplained. In particular, we have a limited understanding of the origin of novel colour variants and if and how genetic architecture biases adaptive change. These problems evoke an unresolved debate between Charles Darwin and Alfred Russel Wallace. Darwin considered sex differences in colouration – sexual dichromatism – to evolve gradually as a result of sexual selection for bright colours in males. Colours often signal dominance, fighting ability or other aspects of male quality. Wallace on the other hand pointed out that females often are colourful, too, and that bright colouration therefore is likely to appear in both sexes at first, only to occasionally disappear in females under natural selection for crypsis to reduce predation.
We have used the remarkable phenotypic diversification of the Balearic wall lizards (Podarcis pityusensis and P. lilfordi) to shed light on the Darwin-Wallace debate, as well as to provide unprecedented information on the origin and diversification of colour ornaments in general.
The overall aim of EvoColour is to advance our understanding of the origin and evolution of colour diversity –how it is shaped by genetic constraints and sexual and natural selection. We aimed to:
a) Establish the evolutionary history of Balearic wall lizards
b) Reconstruct evolutionary transitions in male and female colouration
c) Establish associations between evolutionary change and indicators of sexual and natural selection
d) Raise awareness about the diversity and biological importance of Balearic wall lizards
To conclude
Balearic wall lizards exhibit a higher degree of sexual dichromatism than previously anticipated, particularly in P. pityusensis. In this project, we have visited approximately 60 populations belonging to the two species under study. We have sampled all existing populations of P. pityusensis and a representative sample of P. lilfordi. We have collected unprecedented morphometric, colour, and genetic data for both species, expanding the scope of sampled populations beyond the original design. Additionally, we have reconstructed the evolutionary history of the Balearic wall lizards and mapped the evolutionary transitions in male and female coloration for all body regions. We are now in the final stages of analysis, where we have tested key indicators of natural and sexual selection. Furthermore, we have undertaken initiatives aimed at enhancing stakeholders and the public understanding of the ecological and evolutionary significance of the Balearic lizard.
