When it comes to human 'bearded ladies' - named for a condition known as hirsutism, which causes them to grow an excessive amount of bodily hair - you're going to have a tough time coming up with enough pros to match the cons. But if you’re a bearded lady lizard, you just might have some aces up your sleeve.
A new study has been published in Biology Letters today that reveals how female eastern fence lizards with male characteristics fare when it comes to dating and babies. Native to North America, eastern fence lizards (Sceloporus undulatus) can grow up to 19 cm long, and the males are generally the same size as the females. The males are easily recognisable though, thanks to the bright blue, black-rimmed ‘badges’ that decorate both sides of their throats and abdomens. These features are particularly visible during the species’ courtship displays, and the brighter the blue, the sexier the male is to the opposite sex. And as things often go in sexually dimorphic species - where the sexes are distinguished by some kind of physical difference in colour, shape or size - the more plain and unadorned the female, the more attractive she is.
Sometimes, though, female eastern fence lizards can also sport these coloured badges. They're less bright, and less blue than the male version, but they're still quite distinct. And depending on the particular population, the prevalence of females with male badges can range from 44 to 95%. That’s a pretty huge percentage, even on the lowest end of the scale, so Tracy Langkilde, an associate professor of biology at Penn State University, and graduate student, Lindsey Swierk, decided to investigate exactly how male badges affect the bearded lady lizards in their pursuit of a mate and healthy offspring.
First, Langkilde and Swierk found that the males clearly considered the unadorned females to be the more attractive option. So yes, 'sexier'. This could be because they're considered more feminine, because the badges are likely driven by high levels of testosterone. It’s even possible that the males find these bearded ladies unattractive because they’ve actually mistaken them for other males.
Next they compared the reproductive success of the unadorned females to the bearded ladies, and found that the bearded ladies also had a harder time when it came to producing offspring. Which begs the question: why do the bearded ladies persist, and in such great numbers?
Langkilde and Swierk collected over 100 female eastern fence lizards from wild populations in Arkansas, Alabama and Mississippi to observe, 76% of which bore badges. They found that although the bearded ladies and the unadorned females produced the same amount of eggs, the bearded ladies’ egg clutches weighed less. This could mean that they contained smaller yolks, so less nutrients for the developing embryos. These smaller egg clutches were also laid an average of 13 days later than the unadorned females’ egg clutches, and they hatched around eight days later too. So the bearded lady hatchlings were disadvantaged from day one, with less food to gather, and less time in which to gather it before the colder months force them into hibernation. And hibernation can be deadly if you haven’t fattened yourself up sufficiently first.
So being a bearded lady lizard with an interest in procreating can be a pretty tough gig.
But it’s not all bad news. There might also be some real pros to being a bearded lady lizard, which explains why these 'less fit' females haven’t been bred out of the species. While Langkilde and Swierk are continuing to breed their lizards to see how likely bearded ladies are to produce bearded daughters, they suggest that the bearded ladies could be producing unattractive daughters, but extremely attractive sons. “If the bearded lady’s daughters are also bearded, this could further reduce the fitness of the mother, as our results suggest that her daughters would have lower survival and reproductive success,” says Langkilde. “However, if her sons are extraordinarily blue, this could increase her fitness, as blue males are preferred by females.” Which could mean lots and lots of grandchildren for the bearded ladies.
“If bearded ladies have ‘sexier sons’, this could maintain the bearded lady phenotype in the population,” Swierk adds.
Another possibility is that all that extra testosterone could be making the bearded ladies tougher, and so better at fighting off predators and rival females.
The testosterone could also be making them more aggressive, especially in the lizard equivalent of the bedroom. “Bearded ladies 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,” says Langkilde.
Landkilde and Swierk plan to investigate these possibilities, and also hope to explain why the female contingent of some populations of eastern fence lizards can be almost entirely (95%) made up of these apparently hideous, disadvantaged bearded lizard ladies.
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