Sex-specific shifts in morphology and colour pattern polymorphism during range expansion of an invasive lizard

Aim: Human-assisted range expansion of animals to new environments can lead to phenotypic shifts over ecological time-scales. We investigated whether phenotypic changes are sex-specific using an invasive lizard (Lampropholis delicata). 

Location: Pacific region (Hawaiian Islands, Lord Howe Island, New Zealand, eastern Australia). 

Methods: Using our knowledge of the introduction history of L. delicata, we examined museum specimens of individuals collected across the native and introduced range to determine whether shifts in morphology or colour pattern polymorphism had occurred during its range expansion, and if so, whether they differed between the sexes. 

Results: Sexual dimorphism in both size and shape was documented within the native range of the delicate skink. However, during range expansion, phenotypic shifts were observed in shape, but not size. In two of the three invasive populations, these phenotypic shifts were sex-specific. In the Hawaiian Islands, changes in shape were driven by males, whereas in New Zealand it was due to shifts in females. Similarly, changes in the frequency of a colour pattern polymorphism, a mid-lateral stripe shown to have sex-specific impacts on fitness (positive in females, negative in males), occurred following colonization of the Hawaiian Islands and Lord Howe Island. In Hawaii, the incidence of the polymorphism increased over time in females, and decreased in males. 

Main conclusions: Phenotypic shifts during the range expansion of invasive species may be sex-specific, and are potentially related to the degree of realized niche shift that has occurred between the source and introduced range.