Male Lizards Steer Clear Of Females With Similar Throat Bands
November 7, 2013

Male Lizards Steer Clear Of Females With Similar Throat Bands

April Flowers for - Your Universe Online

A team of researchers from Penn State University recently examined the relationship between body-color patterning and mating behavior in fence lizards, Sceloporus undulatus, which are found ranging across the Eastern US.

Tracy Langkilde, an associate professor of biology at Penn State University, and Lindsey Swierk, a graduate student in Langkilde’s lab, found that the sex lives of these lizards are more complicated than you might think.

Males have ornamental blue "badges" on their throats and abdomens, linked to testosterone, that are used in courtship displays and in aggressive encounters with rival males. Surprisingly, the majority of the females, so-called "bearded ladies," have similar blue-colored ventral badges on their necks.

The LA Times reports that the team captured 24 pregnant females and raised their young in the lab. They paired the lizards off randomly in order to keep track of the amount of time the males spent with each female.

According to the research team, male lizards are significantly less amorous when a female is sporting a brilliant blue neck beard than when she has less coloring, and less testosterone. The findings of this study were published in the journal Biology Letters.

The team notes that the males aren't as picky as they sound, however. The males aren't turning away the bearded ladies entirely as mates, but when given a choice they preferred the more feminine look.

“We found that, although males do not say ‘no’ to bearded ladies, they clearly discriminate against blue-ornamented females, opting more often to court females without coloring,” said Swierk.

National Geographic reports that there might be a good evolutionary reason for this preference. The study found that more blandly colored lizards laid more viable eggs -- clutches that were heavier and had more nutrients. These females also lay earlier in the season, giving their brood more time to develop and therefore offering an important survival advantage. The males selecting more reproductively fit females are an example of classic sexual selection.

“We don’t know whether the females laid later because they mated later -- so, maybe the males don’t like these blue females, and so these females are just left on the shelf and are the last ones to get mated with -- or there’s something else going on whereby they yolk up their eggs later even if they got fertilized early,” said Langkilde.

This begs the question: if the bearded ladies aren't as reproductively viable, why are they so predominant?

On average, the researchers found that 76 percent of female fence lizards were bearded ladies. In some populations, that number reaches as high as 95 percent. According to the team, there are several factors at play.

It is possible that the love lives of the fence lizards are in a period of evolutionary flux.

“It is possible that we’re catching a snapshot of the evolutionary process—[that] bearded ladies are very slowly being ‘selected out’ of the population,” said Swierk. She added that changes in social or environmental conditions may be making the bearded-lady phenotype less effective.

Another scenario is that it might be a question of attitude. The brassy bearded ladies are simply more likely to get their man.

“Bearded ladies also may be more sexually aggressive so, although the males don’t prefer them, they may initiate more of the courtship and mating and produce as many or more offspring for this reason,” said Langkilde.

Previous research by the same team found that female lizards find the blue coloring highly attractive, unlike the males. This leads to another potential explanation for how bearded ladies keep their genes in the population: They pass on their great “beards” to their male offspring, who reap the mating benefits.

“Bearded ladies may benefit by having especially sexy sons," said Langkilde.