Panamanian slender anole (Anolis apletophallus) (Photo Credit: Dr. Christian Cox)
Male sexual signals, and their often-associated distinct phenotypic and behavioral displays, have been hypothesized to have evolved from multiple sources. Two of which include the Good Genes hypothesis, which suggests sexual signals serve as an honest signal to potential mates, and the Immunocompetence Handicap hypothesis, which indicates trade-offs to elaborate signals. However, Dr. Christian Cox, an assistant professor in the Biology Department at Florida International University, thinks of these as a continuum rather than opposing hypotheses. The vibrant dewlaps of Anolis species serve as an excellent model system to address questions related to this continuum. Dr. Cox’s lab has documented sex-biased parasitism, which he discussed on Monday at SICB 2020.
The Panamanian slender anole (Anolis apletophallus) is known to host ectoparasitic trombiculid mites (also known as chigger mites). In this species, males and females are roughly the same size and, as with most anole species, males carry a large, colorful dewlap beneath their chins. Dr. Cox asked whether males and females of this species differ in the attachment site and intensity of mite infestations and whether any other factors (e.g., energetics) might influence infection. Using a combination of field and laboratory studies, Dr. Cox and his colleagues quantified the number of mites, prevalence, and intensity of infestation on individuals. He also measured mass, snout-vent length, and dewlap size. Following this, he collected fat bodies, livers, and gonads to investigate differences in energetics.
Dr. Cox found that males were more likely to have mites on their dewlap whereas females had more mites in the inguinal and axillary regions. Additionally, large males had more mites than smaller ones and there was a significant correlation between the size of the dewlap and the number of mites. Dr. Cox also found that there was a negative relationship between fat body mass and the total number of mites. In other words, males with a heavier fat body had less mites. In females, there was a positive relationship between gonad size and the number of mites. These findings suggest sex-dependent factors influence ectoparasite load and are indicative of trade-offs to male sexual signals.