Reproduction and growth in island and mainland populations of a lacertid lizard

Abstract Changes in life-history traits constitute a crucial component of the ‘island syndrome’, whereby island-dwelling organisms often differ considerably in many aspects of their biology from mainland relatives. A recurrent pattern is the production of fewer, larger offspring on islands, suggesting that insular conditions (relaxed predation and interspecific competition, but increased intraspecific competition) select for a shift towards the ‘slower’ end of the life-history strategies. However, this idea is based primarily on observations of mammals, particularly rodents, and its generality has been questioned by large-scale comparative analyses in birds and lizards. Here, we document intraspecific variation in reproductive strategies and intrinsic growth rates of Podarcis siculus, comparing mainland and island populations in common-garden conditions. Island lizards produced fewer but larger offspring, whereas mainland lizards exhibited higher reproductive output with smaller offspring. Furthermore, growth trajectories differed significantly, with island juveniles growing at a slower rate than their mainland counterparts despite larger hatchling sizes. These findings align with expectations of life-history changes in island conditions, where lower predation pressure and resource availability might favour larger, more competitive hatchlings that grow at a slower pace. This highlights the role of ecological and evolutionary pressures in shaping life-history traits.