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    Wassup Baby Bird? The 'Casanova' Gene In Zebra Finches
    By News Staff | June 15th 2011 12:06 PM | 12 comments | Print | E-mail | Track Comments
    You may have heard that doves mate for life but they are a rarity in bird species.   In most, infidelity is a widespread phenomenon even though for females the costs are high because the cuckolded partners often reduce their parental care and extra lovers also may transmit diseases.

    Yet female birds are just as promiscuous as males and researchers from the Max Planck Institute for Ornithology in Seewiesen set out to investigate why.   In a genetic long-term study of zebra finches they found that females inherit the disposition for their infidelity from their fathers.

    So men get the blame even when females sleep around?

    The common thinking that most bird species lead a monogamous way of life was dispelled when scientists used molecular genetic methods over the past 20 years and found that many juveniles do not originate from their social fathers. Initially, the explanation for these extra-pair paternities seemed plausible; the males could enhance their reproductive success through a higher number of offspring and females received high quality genes when they were keeping an eye out for attractive mates.

    Recently, scientists have cast doubt on this explanation as the actual benefits for the females were not as high as expected by theory. To the contrary, the negative aspects even prevailed. The cuckolded males often reduce their parental effort and also support from extra-pair mates cannot be expected because they rather help their own mate. Therefore the question remained as to why some females actively seek other males for extra-pair matings.


    Behavioral ecologist(!) Wolfgang Forstmeier and colleagues at the Max Planck Institute for Ornithology in Seewiesen say they have now found a possible explanation for this phenomenon.

     For eight years they investigated the sexual behavior of over 1500 zebra finches, first by subkecting unmated male and female birds to a test of their sexual motivation or libido. Afterwards a subset of the finches was transferred into aviaries in order to test how socially monogamously mated individuals behaved to each other within a large group. Using a video surveillance system the researchers could observe how mated females were reacting to advances of their own partner and of stranger males. In addition, the researchers conducted genetic paternity analysis by using a micro-satellite marker method in order to determine the number of offspring that a male had sired in a foreign nest. They also identified the number of offspring that a female produced together with an extra-pair male.


    How you doin'?

    Apparently the readiness of females to engage in extra-pair contacts was inherited from their fathers that had been cheating on their partners as well. They claim the predisposition for infidelity shows a moderate, but evolutionarily crucial, genetic basis. Since the readiness for infidelity is passed on from the fathers to the daughters the researchers arrived at a new interpretation of female infidelity.

    "It is not essential that there is an evolutionary benefit for the females", says Wolfgang Forstmeier, author of the study. "It is rather sufficient that the male ancestors had benefits that resulted from their promiscuity. A "Casanova-gene" will increase its frequency within a population as long as the benefits to the male gene carriers outweigh the costs for the female gene carriers".

    Whether the hypothesis of a correlated evolution of male and female infidelity can be transferred to humans is for the future, though look for an evolutionary psychologist to survey some college students and have a paper out by next week.  

    "The question to what extent it is the same genes that influence female and male behaviour in a similar way has to be answered in follow-up studies," says Forstmeier.

    Comments

    Steve Davis

    "They claim the predisposition for infidelity shows a moderate, but evolutionarily crucial, genetic basis...
    "It is not essential that there is an evolutionary benefit for the females", says Wolfgang Forstmeier, author of the study.
    "It is rather sufficient that the male ancestors had benefits that resulted from their promiscuity. A "Casanova-gene" will increase its frequency within a population as long as the benefits to the male gene carriers..."
     Except that there is no such thing as a gene for a behaviour, let alone a "Casanova gene." Behaviours can have a genetic influence, but not a genetic basis.
    Hank
    Well, what do you want us to believe, science or behavioral ecology??
    Steve Davis
    I prefer evolutionary psychological behavioral ecology!
    Hank
    That can be after I finish these studies in Quantum Paleontology and Theoretical Phys Ed.
    Steve Davis
    You win. I can't top that!
    rholley
    though look for an evolutionary psychologist to survey some college students and have a paper out by next week. 
    Something like this?  (from Springwatch)



    Robert H. Olley / Quondam Physics Department / University of Reading / England
    Gerhard Adam
    I think we have to be careful in comparing the rampant anthropomorphism of the press reports with the actual paper.

    It is meaningless to talk of "cheating", or "infidelity", etc. since these are human value terms and simply aren't applicable to these birds unless one is willing to engage in studies regarding their social reactions to such events.  It doesn't appear that this is an issue for the Zebra Finches.

    The paper doesn't mention a "Casanova" gene, because the issue was to determine whether or not promiscuity was selected across sexes or within sexes.  The point being that if the social bonding of the Zebra Finches originated from an ancestral group that did not have such bonds, then presumably there was some selection pressure that strengthened the pair-bonding between the sexes. 
    If social pair bonding evolved from a nonpair-bonding ancestral condition, then it likely did so by a genetic mechanism that was shared between the sexes (thus evolving in both sexes at the same time). Mutations affecting that mechanism might weaken or strengthen the pair bond and thereby increase or decrease promiscuity in both sexes in a correlated manner.
    http://www.pnas.org/content/early/2011/06/03/1103195108.full.pdf+html
    As a result, it was suggested that this might be due to a single genetic influence rather than being co-evolved. So despite the implications about female "costs", the paper states:
    There is an ongoing debate about whether females obtain a net benefit from extrapair mating or not (2, 36–38).
    http://www.pnas.org/content/early/2011/06/03/1103195108.full.pdf+html
    Bearing in mind that "no benefit" does not equate to "cost".

    An additional consideration is what the effects of captivity played on this scenario versus behavior in wild circumstances.
    In the wild, zebra finches show much lower levels of extrapair paternity (2%of the offspring) (43, 44) than in captivity (28%)(45), although the extrapair behavior seemed remarkably similar between those two situations (7, 45, 46). Wild-caught birds studied in captivity showed intermediate levels of extrapair paternity (12–15%) (47), suggesting that both captivity and domestication may contribute to differences in extrapair paternity levels.
    http://www.pnas.org/content/early/2011/06/03/1103195108.full.pdf+html
    As indicated this indicates some major differences in behavior, although that was not the point of focus in the paper.  Instead the point was merely to demonstrate whether or not there could be a singular genetic influence across the sexes, implying that perhaps such a situation could exist, even if it proved to be non-beneficial to the female.

    However, it is important to note that males produced approximately 33% of their eggs in extra-pairs bonds, which included matings with non-paired females.  Therefore it is easy to see that this would produce a benefit for the males in providing more offspring than a single-pair bond could provide.  For the females, it is less clear, because, while 29% of their eggs were produced from extra-pair bonds, they didn't lay more eggs because of the matings.

    This does indicate that it certainly isn't a dominant behavior (especially when examining them in the wild), but it does suggest that perhaps these extra-pair matings might be more opportunistic in ensuring that more fertilizations occur that might otherwise (since the number of eggs is essentially constant).  I'm not sure that it means anything specific, but whatever results one wants to interpret from this report, it has nothing to do with humans and most definitely it has nothing to do with evolutionary psychology.
    Mundus vult decipi
    Hank
    I think we have to be careful in comparing the rampant anthropomorphism of the press reports with the actual paper...The paper doesn't mention a "Casanova" gene, because the issue was to determine whether or not promiscuity was selected across sexes or within sexes. 
    Well, the author of the paper, Wolfgang Forstmeier, does say just that - "A "Casanova-gene" will increase its frequency within a population as long as the benefits to the male gene carriers outweigh the costs for the female gene carriers."

    It's not like this piece is made up from whole cloth or unfairly contrived from a paper without flaw when the author is the one who invoked the term 'Casanova' gene.
    Gerhard Adam
    It's not like this piece is made up from whole cloth or unfairly contrived from a paper without flaw when the author is the one who invoked the term 'Casanova' gene.
    You're right.  I was focusing on the paper and not the quote.  Sometimes these guys just need to learn to keep quiet and let their paper do the talking.  I can't think of a more anthropomorphic term to use, as well as completely misrepresenting what is actually occurring.

    I'm afraid that if they would have let him keep talking, he might have proposed a follow-up study which tried to determine whether the males in extra-pair bonds tried to phone their partners after a long week-end, and how many of them left their "wives".
    Mundus vult decipi
    Hank
    It is a flaw in some that they feel the need to put things in context we will all understand - but it leads to a worse understanding for the people who need that sort of analogy.   And it gets their work ridiculed in Science 2.0 titles.
    Gerhard Adam
    Well, one can hope that such titles might exert a "selection pressure" on researchers, so that they might learn to curtail such comments.  Of course, I'm assuming that such knowledge is heritable and has a genetic component .... probably, no such luck, eh?
    Mundus vult decipi
    rholley
    LubnaA beautiful one-liner from Egypt, on similar behaviour in Homo sapiens:

    This whole subject is unworthy of any attention, least of all in this column.

    Robert H. Olley / Quondam Physics Department / University of Reading / England