Cell types with specialized functions fundamentally regulate animal behaviour, and yet the genetic mechanisms that underlie the emergence of novel cell types and their consequences for behaviour are not well understood¹. Here we show that the monogamous oldfield mouse (Peromyscus polionotus) has recently evolved a novel cell type in the adrenal gland that expresses the enzyme AKR1C18, which converts progesterone into 20α-hydroxyprogesterone. We then demonstrate that 20α-hydroxyprogesterone is more abundant in oldfield mice, where it induces monogamous-typical parental behaviours, than in the closely related promiscuous deer mice (Peromyscus maniculatus). Using quantitative trait locus mapping in a cross between these species, we ultimately find interspecific genetic variation that drives expression of the nuclear protein GADD45A and the glycoprotein tenascin N, which contribute to the emergence and function of this cell type in oldfield mice. Our results provide an example by which the recent evolution of a new cell type in a gland outside the brain contributes to the evolution of social behaviour.

具有特殊功能的细胞类型从根本上调节动物行为，但新细胞类型出现的遗传机制及其对行为的影响尚不清楚¹。在这里，我们展示了一夫一妻制的老田小鼠（Peromyscus poliionotus）最近在肾上腺中进化出了一种新的细胞类型，它表达酶 AKR1C18，该酶将孕酮转化为 20α-羟基孕酮。然后，我们证明 20α-羟基孕酮在 oldfield 小鼠中比在密切相关的杂乱鹿小鼠（Peromyscus maniculatus）中更丰富，它诱导一夫一妻制典型的父母行为。利用这些物种之间杂交的数量性状基因座作图，我们最终发现了驱动核蛋白 GADD45A 和糖蛋白生腱蛋白 N 表达的种间遗传变异，这有助于 Oldfield 小鼠中这种细胞类型的出现和功能。我们的结果提供了一个例子，说明大脑外腺体中新细胞类型的最新进化有助于社会行为的进化。