title: XY females do better than the XX in the African pygmy mouse, Mus minutoides.
abstract: 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.
authors.affiliation: Institut des Sciences de l'Evolution de Montpellier, UMR 5554, Université Montpellier II, Montpellier, France. paul.saunders@univ-montp2.fr.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Saunders
authors.forename: Julie
authors.initials: J
authors.lastname: Perez
authors.forename: Massilva
authors.initials: M
authors.lastname: Rahmoun
authors.forename: Ophélie
authors.initials: O
authors.lastname: Ronce
authors.forename: Pierre-André
authors.initials: PA
authors.lastname: Crochet
authors.forename: Frédéric
authors.initials: F
authors.lastname: Veyrunes
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D005260:Female; D008297:Male; D051379:Mice / Q000235:genetics*; D019849:Sex Determination Processes / Q000235:genetics*; D014960:X Chromosome / Q000235:genetics*; D014998:Y Chromosome / Q000235:genetics*
keywords: Breeding performance; X* chromosome; life-history traits; sex chromosome evolution; sex-determination system; sex-reversed females