Genetic differentiation predicts body size divergence between island and mainland populations of common wall lizards (Podarcis muralis)

Tobias Uller (1, 2) , Hanna Laakkonen (1) , Sozos Michaelides (2, 3) , Geoffrey M While (2, 4) , Aurélie Coulon (5, 6) , Fabien Aubret (7)

1 Skane University Hospital [Lund]
2 Department of Zoology [Oxford]
3 URI - University of Rhode Island
4 UTAS - University of Tasmania [Hobart, Australia]
5 CESCO - Centre d'Ecologie et des Sciences de la COnservation
6 CEFE - Centre d’Ecologie Fonctionnelle et Evolutive
7 SETE - Station d'écologie théorique et expérimentale

Small-bodied vertebrates sometimes evolve gigantism on islands, but there is a lack of consistent association with ecological factors or island characteristics. One possible reason is that, even if the ecological conditions are right, body size might fail to diverge on islands that were isolated recently or if there is gene flow between islands and the mainland. We studied body size, ventral colour polymorphism and genetic structure across nine islands and adjacent mainland populations of common wall lizards (Podarcis muralis) off the western coast of France. Population genetic data suggested that island populations might have maintained gene flow after their geographical isolation from the mainland. Island lizards were larger and heavier than mainland lizards on average, but the extent of gigantism varied substantially between islands. Island size and distance from the mainland were poor predictors of body size, but lizards from populations that were highly genetically differentiated from the mainland were larger than lizards from less differentiated populations. Colour morphs that were rare on the mainland tended to be more common on islands. We propose that genetic isolation or bottlenecks promote body size evolution in island lizards, which makes it challenging to identify ecological causes of island gigantism without complementary genetic information. ADDITIONAL KEYWORDS: body size-colour polymorphism-common wall lizard-genetic bottleneck-genetic differentiation-genetic isolation-island gigantism-Podarcis muralis.

Mots clés: genetic isolation; genetic differentiation; genetic bottleneck; common wall lizard; colour polymorphism; body size; island gigantism; Podarcis muralis

Domaines: Evolution [q-bio.PE]; Génétique animale; Génétique des populations [q-bio.PE]

Tobias Uller, Hanna Laakkonen, Sozos Michaelides, Geoffrey M While, Aurélie Coulon, et al.. Genetic differentiation predicts body size divergence between island and mainland populations of common wall lizards (Podarcis muralis). Biological Journal of the Linnean Society, 2019, 127 (4), pp.771-786. ⟨10.1093/biolinnean/blz052⟩. ⟨mnhn-02934357⟩