It pays to be sexually promiscuous if you are a female guppy, according to research published in a recent issue of the Journal of Evolutionary Biology.
The study on the Trinidad guppy (Poecilia reticulata) by Miguel Barbosa, Maria Dornelas and Anne Magurran examined the effects of sexual promiscuity on the male offspring of female guppies.
The authors wanted to address the question as to whether polyandry (having young with more than one male) would produce sons tending to possess a particular feature (directional selection) or a variety of features (diversifying selection).
In another study to be published in a forthcoming issue of the journal Environmental Biology of Fishes, Barbosa and Magurran had demonstrated that female guppies were willing participants in having sex with multiple males (and not as a result of being sexually harassed by the males).
Taking this one step further, the authors wanted to know what benefits would accrue from having offspring with more than one male.
The authors compared the phenotypic diversity (using colour and frequency of sexual behaviour as parameters) of male offspring from multiply and singly sired broods from 40 female wild-caught guppies (from the lower Tacarigua River in Trinidad) for each treatment.
Using statistical methods, they show that polyandry produced young with a higher proportion of bright coloration: sons from the polyandrous mating treatment had on average greater areas of orange/red, green/bronze and blue colour pigments, but a smaller area of black spots, indicating directional selection.
At the same time, the sons from the polyandrous treatment were also more phenotypically diverse than those from the monandrous treatment, indicating diversifying selection.
According to the authors, polyandry produces offspring that would be more reproductively successful due to: (1) their enhanced coloration, which would attract more females and (2) their varied phenotypes, which reduces the probability of reproductive failure (by allowing bet-hedging adaptations to a changing environment) and competition among offspring.
For more information, see the paper: Barbosa, M, M. Dornelas and AE Magurran (2010) Effects of polyandry on male phenotypic diversity. Journal of Evolutionary Biology 23, pp. 2442–2452.
Also see: Barbosa, M and AE Magurran (2011) Evidence of female-promoted polyandry in Trinidadian guppies. Environmental Biology of Fishes 90: 95–102.