Predator Driven Trait Changes in Anolis smaragdinus

Abstract

Background: Research on the evolution of traits in regard to predator-prey relationships can illuminate the effects of migrating species and invasive species on native populations, which is increasingly relevant with heightened anthropogenic environmental disturbances shifting territories of native species.

Methods: We used a replicated field experiment to test the effects that predators have on the phenotype of Anolis smaragdinus in the Bahamas. It was predicted that A. smaragdinus would rapidly evolve over six generations to have shorter fore and hind limb lengths due to the presence of the predator, Leiocephalus carinatus, driving A. sagrei and A. smaragdinus into higher habitats, which selects for shorter limb lengths.

Results: ANCOVAs were performed for male and female A. smaragdinus, where only two of the thirteen measured traits, ulna length and third toe length in females, were found to have a significant year by treatment interaction between 2011 and 2017. We observed a general reduction in mean trait size when predators are present. Therefore, predators may be driving A. smaragdinus to higher perching sites which selects for smaller limb length. Also, it was found that populations of A. smaragdinus may be able to evolve in as little as six generations when predators and competitors are present.

Limitations: A longer study is needed to see if other trait changes would become significant over time, since the residual means are trending in one direction. Another suggestion is to do a study with fewer experimental islands and larger founder populations. This would violate the meaning of a true founder population; however, it may allow A. smaragdinus to become fully integrated within the new environment and lead to a smaller chance of extinction.

Conclusion: The study showed that the introduction of predators may cause significant phenotypic changes in female A. smaragdinus’ ulna and third toe length, while also showing a general reduction in mean trait size when predators are present. Therefore, predators may be driving A. smaragdinus to higher perching sites which selects for smaller limb length. However, the study did not show a significant change in either the fore limb length or the hind limb length between 2011 and 2017 which was predicted originally.