XY FEMALES DO BETTER THAN THE XX IN THE AFRICAN PYGMY MOUSE, MUS MINUTOIDES

• Published in: Evolution Vol. 68; no. 7; pp. 2119 - 2127
• Main Authors: Saunders, Paul A., Perez, Julie, Rahmoun, Massilva, Ronce, Ophélie, Crochet, Pierre-André, Veyrunes, Frédéric
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 01.07.2014; Wiley Subscription Services, Inc; Oxford University Press
• Subjects: Animals; Breeding; Breeding performance; BRIEF COMMUNICATION; Chromosomes; Evolution; Evolution, Molecular; Evolutionary biology; Female; Female animals; Genes; Genotypes; life-history traits; Litter size; Male; Mammals; Mice - genetics; Mus minutoides; Mutation; P values; Reproduction; Rodents; sex chromosome evolution; Sex chromosomes; Sex Determination Processes - genetics; sex-determination system; sex-reversed females; Sexes; X chromosome; X Chromosome - genetics; Y Chromosome - genetics; sex-reversed females; life-history traits; sex chromosome evolution; Breeding performance; sex-determination system; X chromosome
• ISSN: 0014-3820; 1558-5646
• DOI: 10.1111/evo.12387

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.