Genotypic sex shapes maternal care in the African Pygmy mouse, Mus minutoides

Sexually dimorphic behaviours, such as parental care, have long been
thought to be mainly driven by gonadal hormones. In the past two decades,
a few studies have challenged this view, highlighting the direct influence
of the sex chromosome complement (XX vs XY or ZZ vs ZW). The African pygmy
mouse, Mus minutoides, is a wild mouse species with naturally occurring XY
sex reversal induced by a third, feminizing X* chromosome, leading to
three female genotypes: XX, XX* and X*Y. Here, we show that sex reversal
in X*Y females shapes a divergent maternal care strategy (maternal
aggression, pup retrieval and nesting behaviours) from both XX and XX*
females. Although neuroanatomical investigations were inconclusive, we
show that the dopaminergic system in the anteroventral periventricular
nucleus of the hypothalamus is worth investigating further as it may
support differences in pup retrieval behaviour between females. Combining
behaviours and neurobiology in a rodent subject to natural selection, we
evaluate potential candidates for the neural basis of maternal behaviours
and strengthen the underestimated role of the sex chromosomes in shaping
sex differences in brain and behaviours. All things considered, we further
highlight the emergence of a third sexual phenotype, challenging the
binary view of phenotypic sexes.