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Laura Klappenbach

Anoles Sidestep Battle of the Sexes

By March 16, 2010

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Male and female brown anoles are embroiled in an ongoing genetic tug-of-war. On average, male anoles are 30% longer and 150% heftier than their female counterparts. This difference in stature among the sexes is a form of sexual dimorphism and it means that when it comes to producing offspring, brown anoles may be vulnerable to a phenomenon known as 'sexual conflict'.

Sexual conflict arises when males and females of a species experience different selection pressures. For example, if you're a male brown anole, it's better to be bigger. If you're a female, it's better to be smaller. So what happens when it comes time to produce offspring? If large fathers are more fit and they produce large daughters, the daughters don't reap any benefits by having a fit (large) father. In fact, they may be less fit than if they had been sired by a small father (and had been smaller themselves, as a result). In general, high-fitness parents often produce low-fitness offspring of the opposite sex.

But the story doesn't end there for the brown anole. This species seems to have developed a way to moderate the battle of the sexes over size. It turns out that female brown anoles produce more daughters when they mate with sires that are smaller (thus ensuring smaller daughters). Conversely, when females mate with sires that are larger, they produce more sons (ensuring larger sons). This bias for producing sons when the father is large and daughters when the father is small means that the offspring on average more fit. A clever solution to what could have been a battle of the sexes for the brown anoles.

Refs:

Cox, R., & Calsbeek, R. (2010). Cryptic Sex-Ratio Bias Provides Indirect Genetic Benefits Despite Sexual Conflict Science DOI: 10.1126/science.1185550

Photo Science / AAAS.

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