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.主要组织相容性复合体（major histocompatibility complex, MHC）已被多次证实可影响脊椎动物的配偶选择，通常相较于MHC相似的配偶，个体更偏好MHC相异的配偶。本研究以家马（Equus caballus）为实验对象，旨在验证在短暂接触雌性个体后，MHC匹配度是否同样会影响雄性对射精的资源投入。种公马的精液性状个体间差异显著。本研究采用被试内全因子实验设计控制该个体差异，结果发现：相较于接触MHC相似的母马，短暂接触MHC相异的母马可提升雄性的血浆睾酮水平，并使其射精的精子数量增加。精子运动速度似乎不受该实验处理的影响。种公马与母马的整体遗传相似度（通过20条不同染色体上的多态性微卫星标记测定）在此过程中未发挥显著作用。试情母马的MHC类型同样会影响冷藏精子在储存24小时和48小时后的性状。正如精液资源分配理论所预期的那样，接触MHC相异的母马后，精子活力有所提升。然而，接触MHC相异的母马后，氧化应激水平以及高DNA碎片率精子的占比大多会升高，且该效应同样取决于试情母马是否处于发情期。本研究结论为：雄性可根据雌性的MHC类型快速调整精液质量，且雄性对社会环境的这种响应同样会对冷藏精液的关键性状产生影响。