Evolution of Color Change

The phylogeny of a behavior in a specific species refers to the evolution of that behavior. The phylogeny describes the origins of a behavior, as well as the selective pressure or circumstances that lead to its current form.

Chameleon color change is very important in social-signaling contexts (discussed in detail in Adaptive Value). It is thought that the highly developed vision of chameleons influenced the evolution of color change as a form of social communication. Chameleons face the problem of needing to be conspicuous at times, but cryptic in others. Their color change solves this problem by allowing chameleons to have vibrant display colors when needed, like when a male is trying to attract a female to mate, but concealed at other times, such as when a predator is in their vicinity (Cooper and Greenberg, 1992).

Why Does Color-Changing Ability Vary So Much by Species?

This question is one that cannot be easily answered. Color-change serves many purposes for chameleons, from thermoregulation to communication to protection, that it cannot be inferred by looking at any single aspect. Each aspect generates different testable predications, (outlined in Stuart-Fox and Moussalli, 2009, 2011), but all contribute to the evolution of color change.

Sexual Selection

It is commonly accepted that chameleon color change undergoes sexual selection. Factors of sexual selection include seasonality and synchronicity of reproduction, spatial organization and density of chameleon populations, as well as predation pressure.

However, these factors have not been studied to any significant degree to explain the strength of sexual selection for color change with and between species of chameleons. Stuart-Fox and Moussalli believe that indicators of strong sexual selection would be highly skewed reproductive success and greater sexual dimorphism, but this has not been researched across species of chameleons.

In Adaptation, it is mentioned that Furcifer labordi females show highly contrasting colors when rejecting a mate, yet Furcifer verrucosus females do not change color, despite the species being closely related. Predation pressure differences between the species is thought to be a possible explanation for this, or possibly because F. labordi experience more competition over mates due to more synchronous reproduction (Karsten et al., 2009c).

When trying to explain the evolution and morphological diversity of color change in chameleons, the intensity of intrasexual selection, and its relationship to ecology and life history, is crucial. As the charts on Adaptive Value show, the color changing abilities between species vary immensely, yet the coloration and associated behaviors have been studied in only a handful of chameleon species. In order to truly get an idea of the phylogenetic basis of chameleon color change, these areas need to be researched in more depth and in many more species.