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August 03, 2010
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Birds may boost chick survival through infidelity
July 28, 2010
Courtesy of the University of East Anglia
and World Science staff
Why is mate infidelity so
common among animals? A new study indicates female birds may increase their
chicks' survival through their unfaithful ways, suggesting one
reason why nature may have kept this unsavory practice in her
toolkit.
Although in many animals females may pair up with a specific “social” mate who helps raise the pairs' offspring, DNA fingerprinting studies across a wide range of animals reveals that offspring are often sired by males other than the pair male.
Scientists have wondered why females engage in such infidelity – what is the benefit of being fertilised by these other males that don’t help raise the offspring.
Seychelles warbler birds are one species whose females pair with the same male for life, yet often prefer to be fertilised by other males. This seems to increase the genetic quality of their offspring, according to authors of the study.
These fertilisations, they found, can result in a higher diversity of certain immune-system genes that detect disease in
offspring. The result is longer-lived offspring. The study, led by David Richardson of the University of East Anglia, U.K, is published in the current issue of the research journal
Molecular Ecology.
The investigation is one of a number of new studies that have revealed
possible roles for infidelity in the animal kingdom. Research
published earlier this year found that some species of fruit flies
might not even be able to survive without female promiscuity.
In the new study, more than 97 per cent of warblers on the tiny island of Cousin in the Seychelles were
tracked over a decade, their blood sampled, and their breeding attempts followed. The researchers monitored the fates of 160 birds
born on the island between 1997 and 1999.
They found that females paired to males with a low diversity of disease-detecting genes, called major histocompatibility complex or MHC, increase the gene diversity of their offspring by gaining extra-pair fertilisations from males with higher diversity. This extra pair fertility was found to be common – accounting for 40 per cent of offspring.
Offspring born of the infidelity have higher genetic diversity in these disease-detecting genes than they would have had if sired by the cuckolded pair male, the research found. The scientists also this higher diversity to be associated with longer juvenile survival, increasing lifespan up to more than twofold.
"On average extra-and within-pair offspring survived equally well,” Richardson explained. But “by not being faithful to a pair male with low MHC diversity, females are ensuring that their offspring do not end up with below average levels of MHC diversity.”
However, "the association between survival and MHC diversity levelled off with increasing diversity, so choosing males with above average MHC diversity would not have resulted in any additional fitness benefits for the offspring.”
"One thing that remains unknown,” he added, “is what mechanism drives the patterns of MHC-dependent extra-pair mate choice. Experiments are needed to determine whether females actively choose more diverse MHC males or whether other factors like male-male competition or sperm competition play a role."
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Why does mate infidelity occur so frequently throughout the animal kingdom? A newly released 10-year study indicates female birds may increase their offspring's survival through their unfaithful ways. Although in many animals females may pair up with a specific “social” mate who helps raise the pairs' offspring, DNA fingerprinting studies across a wide range of animals reveals that offspring are often sired by males other than the pair male. Scientists have wondered why females engage in such infidelity – what is the benefit of being fertilised by these other males that don’t help raise the offspring. Seychelles warbler birds are one species whose females pair with the same male for life, yet often prefer to be fertilised by other males. This seems to increase the genetic quality of their offspring, according to authors of the study. These fertilisations, they found, can result in a higher diversity of certain immune-system genes that detect disease in offspring. The result is longer-lived offspring. The study, led by David Richardson of the University of East Anglia, U.K, is published in the current issue of the research journal Molecular Ecology. Since 1997 more than 97 per cent of warblers on the tiny island of Cousin in the Seychelles were tracked, their blood sampled, and their breeding attempts followed. The researchers monitored the fate of 160 birds hatched on the island between 1997 and 1999, over 10 years. They found that females paired to males with a low diversity of disease-detecting genes, called major histocompatibility complex or MHC, increase the gene diversity of their offspring by gaining extra-pair fertilisations from males with higher diversity. This extra pair fertility was found to be common – accounting for 40 per cent of offspring. Offspring born of the infidelity have higher genetic diversity in these disease-detecting genes than they would have had if sired by the cuckolded pair male, the research found. The scientists also this higher diversity to be associated with longer juvenile survival, increasing lifespan up to more than twofold. "On average extra-and within-pair offspring survived equally well,” Richardson explained. But “by not being faithful to a pair male with low MHC diversity, females are ensuring that their offspring do not end up with below average levels of MHC diversity.” However, "the association between survival and MHC diversity levelled off with increasing diversity, so choosing males with above average MHC diversity would not have resulted in any additional fitness benefits for the offspring.” "One thing that remains unknown,” he added, “is what mechanism drives the patterns of MHC-dependent extra-pair mate choice. Experiments are needed to determine whether females actively choose more diverse MHC males or whether other factors like male-male competition or sperm competition play a role."