Male Lizards Prefer Feminine Mates to 'Bearded Ladies'

Lizards prefer mates with less testosterone, avoiding the "bearded ladies" of their species, a new study found.

In male fence lizards of the species Sceloporus undulatus, testosterone production triggers the production of a bright blue "badge" on their throats and abdomens. Many females also sport this ornamentation, though theirs is less vibrant and covers a smaller area on the body.

"Just as some human females have male-pattern facial hair, albeit less pronounced than in males, some female fence lizards display the typically-male blue markings," Tracy Langkilde, an associate professor of biology at Penn State University, said in a statement.

"However, whereas in human females the masculine characteristics are less common within the population, in fence lizards, we see the opposite pattern: About three quarters of the females are so-called 'bearded ladies,' making masculinized females much more common than their counterparts with little or no blue ornamentation."

Through a series of studies, the researchers found that while males are willing to mate with the blue female lizards, they prefer those without.

"The question is 'why'?" asked graduate student Lindsey Swierk. "Is it possible the males mistake the bearded ladies for fellow males? Or are bearded ladies somehow less fit and, therefore, less attractive to males?"

By studying the differences between the reproductive output of the blue-tinged females and those without, the researchers found the "bearded ladies" laid clutches that weighed less and about 13 days later in the mating season.

"The lower mass may indicate that the eggs have smaller yolks and so the embryos don't have as many available nutrients," Langkilde said. "As for the timing, the 13-day difference is significant. It means that the bearded ladies' offspring hatch later, so they have less time to gather food and to prepare for overwinter hibernation, which is a tough period that few babies survive."

The researchers believe that this preference may be causing a shift in the population.

"It is possible that, over the course of several generations, we will see the more-feminine lizards winning out over their bearded-lady sisters," Langkilde said. "In time, the percentage of bearded ladies could dwindle and the balance could shift. However, another possibility is that bearded ladies have some other evolutionary advantage that keeps their numbers high within populations."