Image courtesy of Flickr.
For years, evolutionary biologists thought they understood how morphology—body shape and structure—affects the performance of an animal: for example, how size and limb length influence the sprint speed of a lizard. Performance regulates fitness, or how likely the lizard is to survive and reproduce, making these morphology-performance relationships important for understanding lizard evolution. There’s just one problem: most of these studies used exclusively male lizards.
Male lizards are often easier to find and capture, making them more practical research subjects than females. But if morphology-performance relationships differ between sexes, then research focusing on just males provides an incomplete picture.
New research by Martha Muñoz, assistant professor of ecology and evolutionary biology at Yale, and researchers from Ohio Wesleyan University examined how morphology-performance relationships differ between sexes in the common wall lizard, Podarcis muralis. Previous studies found that as the bodies and limbs of male lizards got larger, their sprint speed increased, which Muñoz and her colleagues also observed in the males they studied. However, in female lizards, they found the opposite relationship—females with smaller body dimensions ran faster than larger females. This is because female lizards curve their bodies while running to increase their stride length, while males do not.
Research that exclusively focuses on males may not be fully able to predict how populations will survive and change over generations. “The female is often—not always, but often—the sex that invests more resources in reproduction,” Muñoz said. More generally, Muñoz’s findings show the importance of acknowledging that patterns seen in data from a subset of individuals may not hold true across the entire population. “There’s much to be learned by looking at either males or females, of course, but we must keep in mind there is information one might lose by examining patterns in only one sex,” Muñoz said.