Male lizards tend to steer clear of bearded lady lizards

Trust science on this: Guys are generally not eager to mate with a high-testosterone bearded lady.

But what goes on with other animals that share “male” ornamentation? Do the females pay a heavy price for aping the decoration of their sexual counterparts? If so, why would that trait survive?

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The eastern fence lizard may offer some answers, according to a study published online Tuesday in the journal Biology Letters.

Mature males of the Sceloporus undulatus species found throughout the Eastern U.S. display a distinctive blue “beard,” or ventral badge, a testosterone-linked pigmentation that also shows up in varying intensity among some females in any population.

“Males really don’t like females that have these ornaments,” said Tracy Langkilde, a Penn State University evolutionary ecologist and coauthor of the study. Such sexual selection tends to doom disliked traits, which often signal of some sort of weakness that could affect reproductive success.

Langkilde and doctoral student Lindsey Swierk, her colleague, set out to find out if this was so among lizards. They captured 24 pregnant females and raised their young in the lab. Then they paired them off randomly, keeping track of the amount of time the males spent with various females.

Sure enough, the males spent less time with the blue-bearded females. More significantly, the blue-bearded females produced eggs later than others, a time lapse that researchers suggest could make it harder for the hatched offspring to get adequate food for winter. And although the blue-bearded female lizards laid just as many eggs as their less-pigmented cohorts, the total mass of their eggs was lower.

“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.

The results raise questions about the development of sexual dimorphism -- the divergence of characteristics between sexes in the same species. It could be that blue badges are slowly passing out of fashion among the lizards as dimorphism accelerates, researchers suggested.

Maybe there is a hidden advantage to being the bearded lady, though. High testosterone exacts a price, including a weaker immune system. But for males, the advantages of testosterone, including aggression and stamina, often outweigh the costs.

Perhaps the blue-bearded females have caught on to their counterparts’ evolutionary gambit, balancing sexual disfavor with a better ability to gather food or defend territory conferred by higher testosterone.

For now, the questions just leave Langkilde and Swierk scratching their beardless chins.