Rapid ecomorphological divergence between island and mainland populations of the Peruvian Lava Lizard (Microlophus peruvianus) in Northern Peru

Abstract

Island-mainland systems provide ideal scenarios in which to study the influence that contrasting ecological
pressures have on closely related taxa. In exceptional cases, recent colonization events or anthropogenic introduction of
continental individuals to islands can facilitate the study of rapid phenotypic divergence 
experienced by newly formed insular populations. The Peruvian Lava Lizard (Microlophus peruvianus) 
is an abundant and conspicuous species found along the Peruvian coastal desert. This species was 
introduced to several offshore Peruvian islands in the 1940s as a potential biological control of 
guano-bird ectoparasites. Less than a century later, some populations of M. peruvianus still thrive 
in some of these islands. Relative to continental environments, the islands have barren, sparsely 
vegetated andscapes, and terrestrial vertebrates are generally scarce. Thus, potential differences 
in the availability of microhabitats and prey and the presence of predators might have imposed 
distinct selective pressures on island and mainland popu- ations, consequently resulting in the 
evolution of diverging phenotypes. In this study we compared the morphology of an insular and a 
continental population of M. peruvianus and found significant differences possibly driven by the 
contrasting ecological pressures they experience. For example, the larger heads of mainland lizards 
might allow them to take advantage of the higher diversity of prey found in the continent, which 
apparently includes items of relatively greater hardness that require stronger bite forces to 
subdue and consume. Similarly, the relatively longer hindlimb traits found in mainland individuals 
might allow them to navigate their habitat with higher speed, a beneficial trait in open terrains. 
In contrast, high speeds might not be as necessary for island individuals due to high population 
density and lack of predators that often characterize insular habitats. Despite strong 
morphological divergence, further studies on the ecological and population dynamics at both 
localities are necessary to clarify these potential ecomorphological relationships. Besides 
highlighting the importance of insular environments in driving phenotypic diversity, this study 
represents the first morphological comparison between populations found in the Peruvian desert and 
its offshore islands, a virtually unexplored island-mainland system.