Bearded ladies

In sexual dimorphic species, it happens that females sometimes have rudimentary male structures, such as ornate markings. These structures are often code for by the same genes in male and females, however in females they incur both social and reproductive costs.  A study looking at Eastern Fence Lizards (Sceloporus undulates), examined the reproductive success of females with and without these structure.

a) males b) ornate female- 'brearded lady' c) standard female

The male Eastern Fence Lizards have bright blue throat marking, which they use when courting females and warding off other males. The females tend to have white throats and bellies, and a general brow colouration, though some females have a blue tinge – ‘bearded ladies’.

In experiments, done by Pennsylvania State University, the effect of being a ‘bearded lady’ was assessed. The team captured and raised lizards in the lab, and then observed mating behaviour. Researches presented males with two females, one with ornate marking, and one without. They found that males preferred female without makings, spending more time on court ship. Ornate females also had a lower reproductive output, and eggs that were laid hatched later then non-ornate females. This showed that ‘Bearded lady’ lizards suffer a cost from their features.

Where there is a cost there must be some benefit, and the exact benefits are not resolved. There a a few postulated benefits, include more aggressive females-due to higher testosterone- which serves which may serve in female-female completion or in predator defence. The trait could be a “snapshot” of a phenotype that is about to be lost from the gene pool.  The reasoning for this trait still waits to be revealed.

Reference: 

Swierk, L, Langkilde, T 2013, ‘Bearded ladies: females suffer fitness consequences when bearing male traits’, The Royal Society, vol.9 no.6.