Data from: Stallion semen quality depends on MHC matching to teaser mare

The major histocompatibility complex (MHC) has repeatedly been found to influence mate choice of vertebrates, with MHC-dissimilar mates typically being preferred over MHC-similar mates. We used horses (Equus caballus) to test whether MHC matching also affects male investment into ejaculates after short exposure to a female. Semen characteristics varied much among stallions. Controlling for this variance with a full-factorial within-subject experimental design, we found that a short exposure to an MHC-dissimilar mare enhanced male plasma testosterone and led to ejaculates with elevated sperm numbers as compared to exposure to an MHC-similar mare. Sperm velocity seemed not affected by the treatment. Overall genetic similarity between stallions and mares (determined from polymorphic microsatellites on 20 different chromosomes) played no significant role here. The MHC type of the teaser mare also affected characteristics of cold-stored sperm after 24 and 48h. As expected from ejaculate economics, sperm viability was elevated after exposure to an MHC-dissimilar mare. However, oxidative stress and the percentage of sperm with a high DNA fragmentation was mostly increased after exposure to an MHC-dissimilar mare, depending also on whether the teaser mare was in estrous or not. We conclude that males can quickly adjust ejaculate quality relative to a female’s MHC, and that this male reaction to the social environment can also affect important characteristics of cold-stored semen.主组织相容性复合体（major histocompatibility complex, MHC）已被反复证实可调控脊椎动物的配偶选择行为，实验证据普遍显示，脊椎动物更偏好与自身MHC相异的交配对象，而非MHC匹配度较高的个体。本研究以家马（Equus caballus）为实验模型，旨在检验：在短时间接触雌性个体后，雄性是否会依据与雌性的MHC匹配度调整其射精投入。不同种公马的精液性状存在显著个体差异，本研究采用被试内全因子实验设计控制该组间变异，结果表明：相较于接触MHC相似的母马，短暂接触MHC相异的母马可显著提升雄性的血浆睾酮水平，并使其射出的精液中精子总数增加。精子运动速度似乎不受该实验处理的影响。种公马与母马间的整体遗传相似性（通过分布于20条不同染色体上的多态性微卫星（polymorphic microsatellites）位点测定）在此过程中未发挥显著作用。刺激母马的MHC类型同样会影响冷藏精子（cold-stored sperm）在储存24小时与48小时后的性状。基于射精经济学的理论预期，接触MHC相异的母马后，精子活力有所提升。然而，根据刺激母马是否处于发情期（estrous）的不同，接触MHC相异的母马后，精液的氧化应激水平以及DNA碎片化程度较高的精子占比大多会升高。综上，雄性个体可根据雌性的MHC类型快速调整射精质量；且雄性对社会环境的这种适应性反应，还会对冷藏精液的关键性状产生显著影响。