Print PageIn general, taxa are said to exhibit color polymorphism when two or more morphs occur within a single population. However, there are instances where selection or limited gene flow can cause entire populations to become fixed for a single morph, resulting in separate populations of the same species exhibiting separate and distinct color morphs. These morphs can be maintained through numerous mechanisms such as natural selection via selective predation. The mottled rock rattlesnake (Crotalus lepidus lepidus) is a montane species that exhibits striking levels of color polymorphism correlated with two distinct substrate types, which are geographically isolated. Habitat substrate in the eastern part of their range is composed primarily of light colored limestone, whereas in the western region the substrate is primarily dark volcanic rocks. We hypothesized that predation on high contrast color and blotched patterns maintain these distinct color morphs. To test this we performed a predation experiment in the wild by deploying model snakes at 12 sites evenly distributed within the two regions where the different morphs are found. Two color and two blotched treatments were used to mimic the eastern and western morphs resulting in a 2 x 2 factorial design.
Results/Conclusions
We found that models contrasting with substrate coloration suffered significantly more avian attacks relative to models mimicking substrates. In regards to the two regions, neither of the blotched treatments was damaged by avian predators or non-predator disturbers more or less often. These results are consistent with the hypothesis that color pattern has, at least in part, been maintained by selective predation, and indicate that selective predation may also maintain blotching patterns but only when combined with differential behaviors.
