Zebra finch courtship.
Credit: Wolfgang Forstmeier
LONDON: Female zebra finches who cheat on their long-term partners inherit this trait from their promiscuous fathers, suggest results from a German study.
This research could help explain why female birds actively seek out such relationships, despite there being no significant evolutionary benefit attached, say scientists.
"The reasons for males to have extra-pair copulations are very clear: they benefit in terms of producing more young and by inheriting the genes for that promiscuous behaviour, the behaviour spreads in the population," explained lead study author Wolfgang Forstmeier from The Max Planck Institute for Ornithology in Seewiesen.
"However, the genes for promiscuous behaviour are also inherited by the daughters... these females then also behave promiscuously, as their fathers did."
Why birds cheat
Exactly why a significant proportion of females from socially monogamous species mate with multiple partners has long been debated by evolutionary biologists.
While the cheating females are thought to gain 'good genes' for their offspring by mating with a male that is fitter than their long-term partner, the benefits of their infidelity may be small. The cuckolded partner may lower the amount of parental care he provides, and the female is at risk of catching a sexually transmitted disease.
As reported in a recent paper in the journal PNAS, Forstmeier and colleagues demonstrated that zebra finches who were placed with foster parents still displayed the same mating behaviour as their genetic parents, showing a genetic basis for cheating.
"To be accurate, the genetic inheritance happens equally from mothers and fathers to their offspring," said Forstmeier. "We highlight that daughters inherited their behaviour from their fathers, because the daughters' behaviour is what puzzles us (since it looks maladaptive), and the fathers' promiscuous behaviour is what gets favoured by sexual selection."
It's all in the genes
The team first investigated how actively 800 male and 754 female zebra finches courted each other when introduced for brief periods.
Video surveillance was used to see how females in a supposedly monogamous pair responded to advances from their partner, compared with those from strange males. They found that some females were very keen to cheat, whereas others were more monogamous in their behaviour.
Genetic paternity analysis using a microsatellite method was used to test how many offspring the male birds sired in foreign nests and how many offspring female birds produced with foreign males.
The team found that female birds who were open to multiple sexual relationships were significantly more likely to have fathers who were promiscuous than female birds who were faithful to their partners.
Kate Durrant, an expert in bird behaviour from the University of Nottingham in the UK, commented: "I think these results are important for the field of evolutionary biology, as behavioural ecologists have long been puzzled by the willingness of females to engage in extra-pair partnerships even when they are a risk to life and limb."
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Female Songbirds that Sex Cheat Just Like Promiscuous Dad
Males who are highly physically and functionally aesthetically attractive to females generally are likely to have more mating and sexual receptivity prospects from females in general and to be able to negotiate from among females their getting the most attractive female mates over less physically and functionally attractive males, on a voluntary and non-mercenary basis. Much like a generally highly aesthetically attractive female can get all the sex she wants from within the pool of young adult physically fit and healthy heterosexual, sexually available males, normally and naturally in a constant mood for sex with attractive females, the most attractive males to females, if socially-sexually tactful and competent, may be able to get the best aesthetic picks from among the females. High-sex-drive alpha and temperament-type-A males from among the highly attractive males that mate and reproduce with above-normal sex-drive attractive females will, together with this type of female, likely produce both attractive and high-sex-drive male and female offspring, of which the females, when in a state of sexual hunger, will likely mate with their choice of sexually available attractive males, for whom they has a hankering, most of which, given their testosterone and adrenaline driven male sexuality, will impulsively and compulsive be sexually receptive to these attractive females. Good sex with a lustful pretty female is an intoxicating experience for lucky recipient males and it can be expected that the reciprocal is true for high-sex-drive females when it comes to males who are sexually desirable to them. Because sex can feel so good and is a visually aesthetic experience to them, too, in this scenario, they are likely to seek it out again and again on their own terms, as when they are ready and in the mood and whom (to them, gorgeous guys and sugar daddies), since the sex supply and demand dynamic is a suppliers market of and favoring females overwhelmed by the demand market of males (with the supply market constricted by female pregnancies, the discharge period of their menstrual cycles and, in humans, laws and training to avoid sex outside of marriage to prevent untimely, unwanted and disgraceful pregnancy, despite prophylactic and medicinal birth-control means and apart from STD prevention). Height range (tallness that is not extreme, circa 7 feet and above), a toned and normal, fit body shape, good or stylish grooming, pleasant or handsome facial features, verbal normalcy, and good interpersonal or social skills attract females -- aesthetics, fitness and healthy appearance and functioning.