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Evolution. 2014 Jul;68(7):2119-27. doi: 10.1111/evo.12387. Epub 2014 Mar 28.

XY females do better than the XX in the African pygmy mouse, Mus minutoides.

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  • 1Institut des Sciences de l'Evolution de Montpellier, UMR 5554, Universit√© Montpellier II, Montpellier, France.


All therian mammals have a similar XY/XX sex-determination system except for a dozen species. The African pygmy mouse, Mus minutoides, harbors an unconventional system in which all males are XY, and there are three types of females: the usual XX but also XX* and X*Y ones (the asterisk designates a sex-reversal mutation on the X chromosome). The long-term evolution of such a system is a paradox, because X*Y females are expected to face high reproductive costs (e.g., meiotic disruption and loss of unviable YY embryos), which should prevent invasion and maintenance of a sex-reversal mutation. Hence, mechanisms for compensating for the costs could have evolved in M. minutoides. Data gathered from our laboratory colony revealed that X*Y females do compensate and even show enhanced reproductive performance in comparison to the XX and XX*; they produce significantly more offspring due to (i) a higher probability of breeding, (ii) an earlier first litter, and (iii) a larger litter size, linked to (iv) a greater ovulation rate. These findings confirm that rare conditions are needed for an atypical sex-determination mechanism to evolve in mammals, and provide valuable insight into understanding modifications of systems with highly heteromorphic sex chromosomes.

© 2014 The Author(s). Evolution © 2014 The Society for the Study of Evolution.


Breeding performance; X* chromosome; life-history traits; sex chromosome evolution; sex-determination system; sex-reversed females

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