Male eastern fence lizards, Sceloporus undulatus, are spiny lizards who sport pretty drab colors except for the vibrant blues on the sides of their bellies and on their throats, which help attract the ladies. Sometimes, however, the females will show some blue on their chin as well. In the wild, females with traits that resemble male secondary sexual traits, such as ornamentation, may suffer reproduction costs. Yet it’s still pretty common to see females donning these sorts of “masculinized” features because ornaments might be under the same genetic control in both sexes.
Sure enough, males discriminate against “bearded” female lizards. But according to new findings presented at the annual Society for Integrative and Comparative Biology meeting in Florida this week, these ladies carry some secret advantages.
Last year, Lindsey Swierk and Tracy Langkilde of Pennsylvania State University revealed in Biology Letters that male fence lizards, when given a choice, preferred to court females with typical light-colored bellies over bearded ladies with pale blue patches. And the bearded ladies who did get to mate laid eggs that weighed less and hatched later. To the right are male (left) and bearded female (right) fence lizards for comparison. Click here for the bellies of males, bearded ladies, and typical females.
So, why do some females continue to display beards? In fact, in some lizard populations, 70 percent of the females show some blue, suggesting that there must be some unknown tradeoff. In new work, the Penn State team investigated the link between testosterone levels and female coloration. Females with experimentally elevated levels of the hormone, they found, have lower hatching success of eggs, and they produced smaller offspring that didn’t survive as well as untreated females.
However, the team also found that the bearded ladies possess secret advantages. Females showing some blue reached fast sprint speeds of 1.5 meters per second, Science reports, compared with the 1.2 meters per second achieved by non-blue females. The team also captured young lizards of known maternity from the wild, and after two months in the lab, more blue-borne babies survived than offspring of non-blue moms. “These results suggest previously unreported, possible fitness advantages for bearded ladies,” Langkilde tells Science. Plus, maybe overly eager suitors mistaken bearded ladies for other males and don’t harass them as much.
Images: cliff collings/shutterstock.com (top), Langkilde Lab’s Lizard Log (middle)