Climatic and geographic variation as a driver of phenotypic divergence in reproductive characters and body sizes of invasive Gambusia holbrooki

Understanding the invasion success of alien species includes developing knowledge on how the biological traits of their populations respond to spatial differences in environmental conditions. For invasive fishes, while the influence of latitudinal and climatic gradients on their biological traits over large spatial scales is well established, there is less certainty in how these vary over smaller scales. Here, we tested the influence of a climatic and geographic gradient on the reproductive traits and body sizes of the invasive mosquitofish Gambusia holbrooki across five climatic regions in Turkey. The results revealed that the environmental conditions across eight sites provided two gradients: a latitudinal gradient (where northern sites were cooler with less rainfall) and a coastal–inland gradient (where changes were apparent from coastal areas and into inland areas). These gradients had marked effects on the traits of both sexes. In sites in coastal and southern areas, males had significantly larger gonopodia and females had greater fecundity than in inland and warmer areas, and with both sexes having body sizes that were smaller. The spatial differences in the male traits were suggested as being driven by differences in selection pressures at the sites that related to differences in their population abundances. The results revealed that environmental conditions across a relatively small spatial scale had some strong influences on the expression of specific biological traits of these mosquitofish populations, but with further work needed to test how these influences affect their invasion success.