Female MHC type affects male testosterone levels and sperm number in the horse (Equus caballus)

Odours of vertebrates often contain information about the major histocompatibility complex (MHC), and are used in kin recognition, mate choice or female investment in pregnancy. It is, however, still unclear whether MHC-linked signals can also affect male reproductive strategies. We used horses (Equus caballus) to study this question under experimental conditions. Twelve stallions were individually exposed either to an unfamiliar MHC-similar mare and then to an unfamiliar MHC-dissimilar mare, or vice versa. Each exposure lasted over a period of four weeks. Peripheral blood testosterone levels were determined weekly. Three ejaculates each were collected in the week after exposure to both mares (i.e. in the ninth week) to determine mean sperm number and sperm velocity. We found high testosterone levels when stallions were kept close to MHC-dissimilar mares and significantly lower ones when kept close to MHC-similar mares. Mean sperm number per ejaculate (but not sperm velocity) was positi...

脊椎动物的气味通常携带有关于主要组织相容性复合体（major histocompatibility complex, MHC）的信息，并可应用于亲缘识别、配偶选择或雌性孕期的资源投入。然而目前仍不明确MHC相关信号是否亦可影响雄性的生殖策略。本研究以家马（Equus caballus）为实验对象，在可控实验条件下开展相关探究。将12匹种马分别采用两种暴露顺序：先暴露于一只不熟悉的MHC相似母马，随后再暴露于一只不熟悉的MHC相异母马，或反之。单次暴露时长为四周。每周采集外周血样本以测定睾酮水平。在完成两种母马暴露后的第9周，分别采集三次射精样本，用于测定平均精子数量与精子运动速度。研究结果显示，当种马与MHC相异母马近距离饲养时，其外周血睾酮水平显著升高；而当与MHC相似母马共处时，睾酮水平则显著降低。单次射精的平均精子数量（而非精子运动速度）呈正向……