Parasites are an ever-present threat to the organisms they interact with. Reptiles, like anoles, are often heavily infested with mites, an ectoparasite that drinks the lizard’s blood and are often visible on the surface of the skin. Despite the ubiquity of mite infestations on reptiles, the fitness costs of these infestations and the factors that cause mite load to vary among individuals within populations are surprisingly understudied.
Adam Rosso, a masters student in Christian Cox’s lab at Georgia Southern University, studied the factors that drive variation in mite infestation among individuals in a population of slender anoles (Anolis apletophallus) in Panama. Slender anoles are sexually dimorphic; males have much larger dewlaps than females. Adam counted mite loads on hundreds of lizards and asked a series of questions, including: How does mite load differ between the sexes? Do the sexes differ in where they are being parasitized on their bodies? Can ecological factors such as habitat use and body temperature affect mite load?
First, Adam found that males have more mites than females, but this was due entirely to their larger dewlaps. In fact, females actually had more mites on other parts of their bodies (such as on their hind and forelimbs). But it gets even more interesting: Adam found that mite infestation increases with dewlap area in males but not in females, suggesting that mites prefer male dewlaps over female dewlaps. Neither field-active body temperature nor perch characteristics predicted mite loads in either sex, suggesting that dewlaps are the main factor influencing ectoparasitism in this population. Adam’s results suggest that there may be an important cost to producing a large dewlap in males. More generally, if parasite loads and dewlap sizes are seen as honest signals in anoles, the results of Adam’s work could have implications for understanding sexual selection and morphological evolution in this group of lizards.
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