Data from: Evidence of inbreeding depression but not inbreeding avoidance in a natural house sparrow population

Inbreeding is common in small and threatened populations, and often has a negative effect on individual fitness and genetic diversity. Thus, inbreeding can be an important factor affecting the persistence of small populations. In this study we investigated the effects of inbreeding on fitness in a small, wild population of house sparrows (Passer domesticus) on the island of Aldra, Norway. The population was founded in 1998 by four individuals (one female and three males). After the founding event the adult population rapidly increased to about 30 individuals in 2001. At the same time the mean inbreeding coefficient among adults increased from 0 to 0.04 in 2001, and thereafter fluctuated between 0.06 and 0.10, indicating a highly inbred population. We found a negative effect of inbreeding on lifetime reproductive success which seemed to be mainly due to an effect of inbreeding on annual reproductive success. This resulted in selection against inbred females. However, the negative effect of inbreeding was less strong in males, suggesting that selection against inbred individuals is at least partly sex-specific. To examine whether individuals avoided breeding with close relatives we compared observed inbreeding and kinship coefficients in the population with those obtained from simulations of random mating. We found no significant differences between the two, indicating weak or absent inbreeding avoidance. We conclude that there was inbreeding depression in our population. Despite this, birds did not seem to actively avoid mating with close relatives, perhaps as a consequence of constraints on mating possibilities in such a small population.

近交（inbreeding）在小型受威胁种群中较为常见，且通常会对个体适合度与遗传多样性产生负面影响。因此，近交可能是影响小型种群存续的关键因素之一。
本研究以挪威阿尔德拉岛（Aldra）上的小型野生家雀（Passer domesticus）种群为研究对象，探讨了近交对其适合度的影响。该种群于1998年由4只个体奠基建立，其中雌性1只、雄性3只。奠基后，成体种群数量迅速增长，并于2001年达到约30只。与此同时，成体个体的平均近交系数（inbreeding coefficient）从0提升至2001年的0.04，此后在0.06至0.10的区间内波动，表明该种群已处于高度近交状态。
本研究发现，近交对个体终生繁殖成功率存在负面影响，且该效应主要源于近交对年度繁殖成功率的作用。这一效应进而引发了对近交雌性的选择淘汰。然而，近交对雄性的负面影响相对较弱，这表明对近交个体的选择淘汰至少在一定程度上具有性别特异性。
为探究种群个体是否会规避与近亲交配，本研究将观测获得的种群近交系数与亲缘系数（kinship coefficient），与随机交配模拟得到的对应数值进行了对比。结果显示两组数值无显著差异，表明该种群的近交规避行为较弱，或完全不存在。
综上，本研究种群存在近交衰退（inbreeding depression）现象。尽管存在该现象，但该种群的家雀似乎并未主动规避与近亲交配，这或许是由于此类小型种群的交配机会存在约束。