Selection-pressures differ with population density, but few studies investigate how this can affect reproductive physiology. European badger (Meles meles) density varies from solitary to group-living across their range, with reported mating periods throughout the entire year to specific seasonal periods. Badger reproduction is evolutionarily distinct, interrupting the direct progression from conception to gestation with delayed implantation (DI), allowing for superfecundation (SF). To establish the tactical mating flexibility afforded by DI*SF, we used cross-sectional population-level seasonal variation of circulating sex-steroids for 97 females from a high-density population. Oestradiol was highest in spring among non-parous females, then lower in summer, and remained low during following seasons, suggesting that the mating period was restricted to just spring. Oestrone was consistently higher than oestradiol; it was elevated in spring, lowest during summer, peaked in autumn, and remained elevated for pregnant females in winter. This suggests that oestrone sustains pre-implanted blastocysts throughout DI. Progesterone was low throughout, except during winter pregnancy, associated with implantation and luteal development. In contrast to multiple mating periods reported by lower-density studies, our oestradiol data suggest that, at high-density, females exhibit only one mating period (congruent with testosterone patterns in males studied previously in this same population). While additional mating periods during DI enhance fertility assurance at low-density, at high-density, we propose that when coitus is frequent, fertilisation is assured, precluding the need for further cycles and associated mating risks. This endocrinologically flexible DI*SF mating strategy likely represents a form of balancing selection, allowing badgers to succeed at a range of regional densities.

选择压力因人口密度而异，但很少有研究调查这如何影响生殖生理学。欧洲獾 ( Meles meles) 密度在其范围内从独居到群居不等，报告的交配期贯穿全年到特定的季节性时期。獾的繁殖在进化上是不同的，通过延迟植入 (DI) 中断从受孕到妊娠的直接进展，从而允许超级受精 (SF)。为了确定 DI*SF 提供的战术交配灵活性，我们对来自高密度人群的 97 名女性使用了循环性类固醇的横截面人群水平季节性变化。雌二醇在非经产雌性中春季最高，夏季较低，随后的季节保持较低水平，表明交配期仅限于春季。雌酮始终高于雌二醇；它在春季升高，夏季最低，秋季达到顶峰，并在冬季对怀孕的女性保持升高。这表明雌酮在整个 DI 中维持植入前的囊胚。孕酮在整个过程中都很低，除了在冬季怀孕期间，与着床和黄体发育有关。与低密度研究报告的多个交配期相比，我们的雌二醇数据表明，在高密度下，雌性仅表现出一个交配期（与先前在同一人群中研究的雄性的睾酮模式一致）。虽然 DI 期间的额外交配期增强了低密度和高密度的生育保证，但我们建议，当频繁交配时，可以确保受精，排除进一步周期和相关交配风险的需要。这种内分泌灵活的 DI*SF 交配策略可能代表了一种平衡选择的形式，