Losdat Sylvain, Germain Ryan R, Nietlisbach Pirmin, Arcese Peter, Reid Jane M
Institute of Biological and Environmental Sciences School of Biological Sciences University of Aberdeen Aberdeen Scotland.
Institute of Biology University of Neuchâtel Neuchâtel Switzerland.
Ecol Evol. 2018 Jan 12;8(3):1842-1852. doi: 10.1002/ece3.3721. eCollection 2018 Feb.
Inbreeding is widely hypothesized to shape mating systems and population persistence, but such effects will depend on which traits show inbreeding depression. Population and evolutionary consequences could be substantial if inbreeding decreases sperm performance and hence decreases male fertilization success and female fertility. However, the magnitude of inbreeding depression in sperm performance traits has rarely been estimated in wild populations experiencing natural variation in inbreeding. Further, the hypothesis that inbreeding could increase within-ejaculate variation in sperm traits and thereby further affect male fertilization success has not been explicitly tested. We used a wild pedigreed song sparrow () population, where frequent extrapair copulations likely create strong postcopulatory competition for fertilization success, to quantify effects of male coefficient of inbreeding () on key sperm performance traits. We found no evidence of inbreeding depression in sperm motility, longevity, or velocity, and the within-ejaculate variance in sperm velocity did not increase with male . Contrary to inferences from highly inbred captive and experimental populations, our results imply that moderate inbreeding will not necessarily constrain sperm performance in wild populations. Consequently, the widely observed individual-level and population-level inbreeding depression in male and female fitness may not stem from reduced sperm performance in inbred males.
近亲繁殖被广泛认为会影响交配系统和种群存续，但这种影响将取决于哪些性状表现出近亲繁殖衰退。如果近亲繁殖降低精子性能，进而降低雄性的受精成功率和雌性的生育能力，那么种群和进化方面的后果可能会很严重。然而，在经历自然近亲繁殖变异的野生种群中，很少有人估计精子性能性状的近亲繁殖衰退程度。此外，近亲繁殖可能会增加射精内精子性状的变异，从而进一步影响雄性受精成功率这一假设尚未得到明确验证。我们利用一个有谱系记录的野生歌带鹀种群，其中频繁的婚外交配可能会在交配后对受精成功产生激烈竞争，以此来量化雄性近亲繁殖系数对关键精子性能性状的影响。我们没有发现精子活力、寿命或速度存在近亲繁殖衰退的证据，并且射精内精子速度的方差也没有随着雄性近亲繁殖系数的增加而增大。与高度近亲繁殖的圈养种群和实验种群得出的推断相反，我们的结果表明适度的近亲繁殖不一定会限制野生种群的精子性能。因此，在雄性和雌性适合度方面广泛观察到的个体水平和种群水平的近亲繁殖衰退，可能并非源于近亲繁殖雄性的精子性能下降。
