Competing Natural and Sexual Selection: Variation in the Visual Signals of Wall Lizards

Date published: July 28, 2014

Source: Behavioral Ecology

Summary: A study suggests that coloration and conspicuousness of wall lizards evolved under conflicting demands of natural and sexual selection.

            A study suggests that coloration and conspicuousness of wall lizards evolved under conflicting demands of natural and sexual selection, according to a study published in 2014 by Kate Marshall and Martin Stevens from the University of Cambridge in the journal Behavioral Ecology.

            Three populations of Aegean wall lizards were studied from the islands of Skopelos, Syros, and Foelgandros. The authors investigated four main points: whether the lizards were more conspicuous to conspecifics (members of the same species) than to predators, if males were more conspicuous than females as a result of sexual competition, if there was variation in visual signals between different parts of the body, and whether the conspicuousness of the lizards differed among the three populations. Lizards must be noticeable enough to attract potential mates but they must also remain somewhat camouflaged to avoid detection by predators, resulting in conflicting natural and sexual selection.

            The results showed that lizards were more noticeable to conspecifics than to avian predators across all body regions in all three populations. Avian predators can only perceive relatively high wavelengths of UV light while lizards can perceive a much higher range. The increased conspicuousness to conspecifics was caused in part by the use of short UV wavelengths to remain noticeable to potential mates yet avoid detection by predators.

            In the Skopelos population, males exhibited increased conspicuousness over females, but in the Syros population, both males and females displayed higher conspicuousness of certain body regions. The Syros population has a higher population density, which can lead to increased sexual competition, even for females, resulting in the need for both males and females to attract mates. This is indicative of evolution because the conspicuousness varied among populations to best suit the needs of the lizards.

            It was also shown that there was variation in conspicuousness between body parts of the lizards. In the Skopelos and Syros populations, the flanks of the lizards were more conspicuous than the backs. Avian predators view the lizards from above, so their backs were more camouflaged, and because potential mates view the lizards from the side on the ground, the sides of the lizards were more noticeable.

             The Foelgandros population of lizards did not exhibit the significant differences in conspicuousness between body parts that was found in the other two populations. This is likely because the Foelgandros island lacks a number of the avian predators that are on the other islands, so the lizards have a lower risk of detection and therefore less of a need for camouflaged backs.

            The findings of the study indicate that the coloration of the lizards has evolved to make the lizards better suited to their environment. The competing demands of natural selection, which would make the lizards less noticeable to their predators, and sexual selection, which would result in lizards being more conspicuous to potential mates, led to different conspicuousness between certain body regions and differences between males and females. These differences are indicative of evolution.

Journal Reference:

Marshall, K.L.A, and Stevens, M. 2014. Wall lizards display conspicuous signals to conspecifics and reduce detection by avian predators. Behavioral Ecology 25: 1325-1337.