Sexual size dimorphism can vary dramatically among populations, a pattern that may be due to sex-specific trade-offs between growth and maintenance. John David Curlis, a Masters student in Christian Cox’s lab at Georgia Southern and a former undergrad in Bob Cox’s lab at the University of Virginia, tested this hypothesis in two populations of brown anoles (Anolis sagrei) in the Bahamas. These two populations – one from Exuma, one from Eleuthera – differ in male but not female body size, and so they also differ in SSD. John David and the Drs. Cox thus predicted that the population of brown anoles from Exuma with faster male growth would have lower male resting metabolic rates than the population from Eleuthera with slower male growth. Since females on the two islands have similar growth rates, they predicted that females would have similar resting metabolic rates.
The team first found that the average metabolic rate was higher for males on Eleuthera than Exuma in both day and night, but this difference was not significant. As predicted, they did not find a difference between females of the two populations. They next tested whether metabolic rate differed between the populations at different temperatures, and found that Eleuthera males had higher metabolic rates at 25°C and 30°C, but not at 35°C. Again, females didn’t differ in metabolic rate at any temperature.
Altogether, the results of this study suggest that population differences in body size may be related to population differences in the allocation of energy between growth and metabolism, and interestingly, that these differences can be sex-specific.