SICB 2019: Mite Loads Impact Energy Allocation in Male Lizards

Different environments promote different life history strategies. The way an organism allocates resources in an environment can have large consequences on growth, reproduction, and immune function. Furthermore, energy allocation tradeoffs may differ between sexes. The energetic costs of immunity can differ between sexes due to differences in energetic demands and ecology. However, the reason some organisms exhibit sex-based energy allocation, and the causes of this phenomenon, remain enigmatic.

Zachariah Degon, an undergraduate student at Georgia Southern University, and colleagues examined the relationships between ectoparasite load, organ mass, fat body mass, and total body size in the Panamanian anole, Anolis apletophallus. Mainland populations of adult male (n=72) and female (n=34) A. apletophallus were sampled in Gamboa, Panama during the reproductive season. Each lizard was visually inspected for mites. The density of mites, and the location of each mite on the lizard body, were recorded. Lizards were dissected and all fat-storing organs were removed. Fat-storing organs included the fat bodies, livers, and gonads. Organs were dried and weighed before measuring organ mass. They found that overall males had more mites than females, and that this difference was driven by the high density of mites located on male dewlaps. Larger lizards, regardless of sex, had higher mite loads. Higher fat body mass was linked to decreased mite loads, although this was only true for male lizards. Liver mass had no effect on mite load in either species. However, mite load increased with ovary mass in females, but there was no relationship between testes mass and mite load in males.

Overall, sex-based differences in energy allocation may have important implications for maintaining immune function in variable environments. Male A. apletophallus had higher mite loads due to their heavily parasitized dewlaps. And interestingly, males with increased fat body masses had lower mite loads. This suggests that males may be allocating energy away from storage and towards increasing immune function.