Department for Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Savoyenstrasse 1, 1160 Vienna, Austria.
BMC Evol Biol. 2012 Feb 15;12:20. doi: 10.1186/1471-2148-12-20.
In mammals, males typically have shorter lives than females. This difference is thought to be due to behavioural traits which enhance competitive abilities, and hence male reproductive success, but impair survival. Furthermore, in many species males usually show higher parasite burden than females. Consequently, the intensity of selection for genetic factors which reduce susceptibility to pathogens may differ between sexes. High variability at the major histocompatibility complex (MHC) genes is believed to be advantageous for detecting and combating the range of infectious agents present in the environment. Increased heterozygosity at these immune genes is expected to be important for individual longevity. However, whether males in natural populations benefit more from MHC heterozygosity than females has rarely been investigated. We investigated this question in a long-term study of free-living Alpine chamois (Rupicapra rupicapra), a polygynous mountain ungulate.
Here we show that male chamois survive significantly (P = 0.022) longer if heterozygous at the MHC class II DRB locus, whereas females do not. Improved survival of males was not a result of heterozygote advantage per se, as background heterozygosity (estimated across twelve microsatellite loci) did not change significantly with age. Furthermore, reproductively active males depleted their body fat reserves earlier than females leading to significantly impaired survival rates in this sex (P < 0.008). This sex-difference was even more pronounced in areas affected by scabies, a severe parasitosis, as reproductively active males were less likely to survive than females. However, we did not find evidence for a survival advantage associated with specific MHC alleles in areas affected by scabies.
Increased MHC class II DRB heterozygosity with age in males, suggests that MHC heterozygous males survive longer than homozygotes. Reproductively active males appear to be less likely to survive than females most likely because of the energetic challenge of the winter rut, accompanied by earlier depletion of their body fat stores, and a generally higher parasite burden. This scenario renders the MHC-mediated immune response more important for males than for females, which implies a relatively stronger selection pressure on MHC genes in males than in females.
在哺乳动物中，雄性的寿命通常比雌性短。这种差异被认为是由于行为特征所致，这些特征增强了竞争能力，从而提高了雄性的生殖成功率，但却降低了生存能力。此外，在许多物种中，雄性通常比雌性携带更高的寄生虫负担。因此，对于降低对病原体易感性的遗传因素的选择强度可能因性别而异。主要组织相容性复合体（MHC）基因的高度变异性被认为有利于检测和抵御环境中存在的多种传染性病原体。这些免疫基因的杂合性增加预计对个体的长寿很重要。然而，在自然种群中，雄性从 MHC 杂合性中获益是否多于雌性，这一问题很少被研究。我们在对自由生活的阿尔卑斯山羊（Rupicapra rupicapra）的长期研究中调查了这个问题，这是一种多配偶制的山地有蹄类动物。
在这里，我们表明，如果 MHC 类 II DRB 基因座呈杂合状态，雄性山羊的存活时间明显更长（P = 0.022），而雌性山羊则不然。雄性的存活改善不是杂合优势本身的结果，因为背景杂合度（在 12 个微卫星基因座上估计）随年龄变化没有显著变化。此外，生殖活跃的雄性比雌性更早地耗尽体脂储备，导致该性别死亡率显著降低（P < 0.008）。在受疥癣影响的地区，这种性别差异更为明显，因为生殖活跃的雄性比雌性更不可能存活。然而，我们没有发现与受疥癣影响的地区相关联的特定 MHC 等位基因的存活优势的证据。
随着年龄的增长，雄性 MHC 类 II DRB 杂合度的增加表明，MHC 杂合雄性比纯合雄性存活时间更长。生殖活跃的雄性似乎比雌性更不可能存活，这很可能是由于冬季求偶期的能量挑战，伴随着更早地耗尽体脂储备，以及普遍更高的寄生虫负担。这种情况使得 MHC 介导的免疫反应对雄性比雌性更为重要，这意味着 MHC 基因在雄性中受到的选择压力比在雌性中更强。
