May 21, 2009

Female mice prefer outbred males

BMC Evol Biol. 2009 May 16;9(1):104. [Epub ahead of print]

Females prefer the scent of outbred males: good-genes-as-heterozygosity?

Ilmonen P, Stundner G, Thosz M, Penn DJ.

ABSTRACT: BACKGROUND: There is increasing interest to determine the relative importance of non-additive genetic benefits as opposed to additive ones for the evolution of mating preferences and maintenance of genetic variation in sexual ornaments. The 'good-genes-as-heterozygosity' hypothesis predicts that females should prefer to mate with more heterozygous males to gain more heterozygous (and less inbred) offspring. Heterozygosity increases males' sexual ornamentation, mating success and reproduction success, yet few experiments have tested whether females are preferentially attracted to heterozygous males, and none have tested whether females' own heterozygosity influences their preferences. Outbred females might have the luxury of being more choosey, but on the other hand, inbred females might have more to gain by mating with heterozygous males. We manipulated heterozygosity in wild-derived house mice (Mus musculus musculus) through inbreeding and tested whether the females are more attracted to the scent of outbred versus inbred males, and whether females' own inbreeding status affects their preferences. We also tested whether infecting both inbred and outbred males with Salmonella would magnify females' preferences for outbred males. RESULTS: Females showed a significant preference for outbred males, and this preference was slightly more pronounced among inbred females. We found no evidence that Salmonella infection increased the relative attractiveness of outbred versus inbred males; however, we found no evidence that inbreeding affected males' disease resistance in this study. CONCLUSIONS: Our findings support the idea that females are more attracted to outbred males, and they suggest that such preferences may be stronger among inbred than outbred females, which is consistent with the 'good-genes-as-heterozygosity' hypothesis. It is unclear whether this odour preference reflects females' actual mating preferences, though it suggests that future studies should consider females' as well as males' heterozygosity. Our study has implications for efforts to understand how mate choice can provide genetic benefits without eroding genetic diversity (lek paradox), and also conservation efforts to determine the fitness consequences of inbreeding and the maintenance of genetic diversity in small, inbred populations.



  1. we could test this:

    Fine monoracial woman and see how attractive various types of Hispanics and Central Asians are compared to Monoracial men. Test for the level of admixture before hand...

  2. Has anyone bothered to test how aggressive inbred male mice are toward outbred male mice?

    Female preference may be driven as much by a "let's you and him fight" dynamic where the female's genetic program's default is that if an outbred male is within pheromone distance, he must have won a bunch of fights.

  3. "Less inbred males won more encounters and tended to have higher scores of aggression level than more inbred males.


  4. Definition of terms:

    "We trapped wild house mice from a single population (Safaripark, Gänserndorf) near Vienna,
    Austria and bred the F2 generation to produce full-sib inbred (sister-brother-mating; Wright’s
    inbreeding coefficient; f=0.25) and outbred mice (matings between unrelated individuals;

    The "outbred" mice are "unrelated" members of a single population, while the inbred mice are products of brother/sister mating.

  5. Fine monoracial woman and see how attractive various types of Hispanics and Central Asians are compared to Monoracial men. Test for the level of admixture before hand...I don't see what race has to do with this particular study. That type of experiment would just introduce an unnecessary confounding variable. In your example, we would have to control for women's like/dislike of Hispanic or Central Asian men to isolate the effect of heterozygosity itself.

    For humans, a good study would sample from several populations, and look -in each one- whether more heterozygous/homozygous individuals differed in their attractiveness. Heterozygosity could be estimated directly from the genome, as in this study.

  6. Although the term 'hybrid vigour', or 'heterosis', is usually used in relation to hybrids between two inbred lines it's presumably more widely applicable than just then. Heterozygosity implies heterosis, and so some level of hybrid vigour. This study is most likely to show the results of heterosis, nothing more complicated than that.

  7. Also from the Eklund paper: Paired encounters were staged between males of the three offspring groups, when the males reached maturity.The staging seems rather important to my question. It should be as close as possible to the likely natural gene-flow scenario: A group of relatively inbred mice in an established territory dominated by the urine markings of their males, invaded by an outbred male.

    Also, I emphasize relatively because it seems there is a range of outbreeding up to and including the point at which hybrid sterility sets in. In other words: What is he likely gene flow rate in nature?

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