Although littermates in altricial mammals usually experience highly similar environmental conditions during early life, considerable differences in growth and health can emerge among them. In a study on subadults of a European rabbit (Oryctolagus cuniculus) population with low MHC polymorphism, we tested whether litter-sibling differences in endoparasitic coccidia load and body mass at the end of the vegetation period were associated with within-litter differences in starting body mass (measured around 2 weeks prior to weaning) and in immune-genetic (MHC class II DRB) constitution. We hypothesized that siblings with a lighter starting mass might be more susceptible to endoparasite infections and thus, negative effects of a more unfavourable MHC constitution might be particularly pronounced in such individuals. Within-litter comparisons revealed that animals with a lighter starting mass reached a relatively lower body mass in autumn. Furthermore, there were indications for an allele-specific heterozygote advantage, as animals with heterozygous combinations of the allele Orcu-DRB*4 had relatively lower hepatic coccidia loads than their littermates with certain homozygous allele combinations. Consistent with our hypothesis, significantly higher hepatic coccidia loads and tendentially lower autumn body masses in homozygous compared to heterozygous individuals for the allele Orcu-DRB*4 were evident in initially lighter but not in heavier siblings, suggesting synergistic effects between an unfavourable MHC constitution and a light starting mass. Taken together, these effects might lead to notable differences in fitness among litter siblings, as a low body mass and a high endoparasite burden are key factors limiting young rabbits’ survival during winter.

尽管幼年哺乳动物的同窝仔通常在生命早期经历高度相似的环境条件，但它们之间在生长和健康方面可能会出现相当大的差异。在对欧洲兔（成孔兔）亚成体的研究中）具有低MHC多态性的人群，我们测试了植被期结束时内寄生球菌负荷和体重的同窝兄弟姐妹差异是否与初始体重（断奶前2周左右测量）的凋落物内部差异相关。免疫遗传（MHC II类DRB）组成。我们假设起始体重较轻的兄弟姐妹可能更容易受到体内寄生虫感染的影响，因此，在此类个体中，MHC组成更不利的负面影响尤其明显。凋落物内部的比较显示，开始体重较轻的动物在秋季达到了相对较低的体重。此外，有迹象表明等位基因特异性杂合子优势，因为具有等位基因Orcu-DRB * 4杂合子组合的动物的肝球菌负荷要比具有某些纯合子等位基因组合的同窝仔猪低。与我们的假设相符，等位基因Orcu-DRB * 4与纯合子相比，纯合子的肝球菌负荷明显高于纯合子，秋季体重较轻，但在较重的同胞中却没有，这表明不利的MHC构成与MHC组成和轻的起始质量。综上所述，这些影响可能导致同窝兄弟姐妹之间的健康差异显着，因为低体重和高体内寄生虫负担是限制幼兔冬季存活的关键因素。与我们的假设相符，等位基因Orcu-DRB * 4与纯合子相比，纯合子的肝球菌负荷明显高于纯合子，秋季体重较轻，但在较重的同胞中却没有，这表明不利的MHC构成与MHC组成和轻的起始质量。综上所述，这些影响可能导致同窝兄弟姐妹之间的健康差异显着，因为低体重和高体内寄生虫负担是限制幼兔冬季存活的关键因素。与我们的假设相符，等位基因Orcu-DRB * 4与纯合子相比，纯合子的肝球菌负荷明显高于纯合子，秋季体重较轻，但在较重的同胞中却没有，这表明不利的MHC构成与MHC组成和轻的起始质量。综上所述，这些影响可能导致同窝兄弟姐妹之间的健康差异显着，因为低体重和高体内寄生虫负担是限制幼兔冬季存活的关键因素。提示不利的MHC组成与轻质起始物质之间的协同作用。综上所述，这些影响可能导致同窝兄弟姐妹之间的健康差异显着，因为低体重和高体内寄生虫负担是限制幼兔冬季存活的关键因素。提示不利的MHC组成与轻质起始物质之间的协同作用。综上所述，这些影响可能导致同窝兄弟姐妹之间的健康差异显着，因为低体重和高体内寄生虫负担是限制幼兔冬季存活的关键因素。