School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
Proc Biol Sci. 2010 Nov 22;277(1699):3483-91. doi: 10.1098/rspb.2010.0514. Epub 2010 Jun 16.
As populations decline to levels where reproduction among close genetic relatives becomes more probable, subsequent increases in homozygous recessive deleterious expression and/or loss of heterozygote advantage can lead to inbreeding depression. Here, we measure how inbreeding across replicate lines of the flour beetle Tribolium castaneum impacts on male reproductive fitness in the absence or presence of male-male competition. Effects on male evolution from mating pattern were removed by enforcing monogamous mating throughout. After inbreeding across eight generations, we found that male fertility in the absence of competition was unaffected. However, we found significant inbreeding depression of sperm competitiveness: non-inbred males won 57 per cent of fertilizations in competition, while inbred equivalents only sired 42 per cent. We also found that the P(2) 'offence' role in sperm competition was significantly more depressed under inbreeding than sperm 'defence' (P(1)). Mating behaviour did not explain these differences, and there was no difference in the viability of offspring sired by inbred or non-inbred males. Sperm length variation was significantly greater in the ejaculates of inbred males. Our results show that male ability to achieve normal fertilization success was not depressed under strong inbreeding, but that inbreeding depression in these traits occurred when conditions of sperm competition were generated.
随着人口减少到近亲繁殖变得更有可能的水平，随后纯合隐性有害表达的增加和/或杂合子优势的丧失可能导致近交衰退。在这里，我们测量了在缺乏或存在雄性间竞争的情况下，粉斑螟（Tribolium castaneum）重复系之间的近交如何影响雄性生殖适应性。通过强制实行一夫一妻制交配，消除了交配模式对雄性进化的影响。经过 8 代的近交，我们发现没有竞争时雄性的生育力不受影响。然而，我们发现精子竞争力显著的近交衰退：非近亲繁殖的雄性在竞争中赢得了 57%的受精，而近亲繁殖的对应物仅产生了 42%的受精。我们还发现，在近交条件下，精子竞争中的 P(2)“进攻”作用比精子“防御”（P(1)）显著更受压抑。交配行为不能解释这些差异，并且近亲繁殖或非近亲繁殖的雄性所产生的后代的存活率没有差异。近亲繁殖雄性的精子长度变异显著更大。我们的研究结果表明，在强近交条件下，雄性实现正常受精成功的能力没有受到抑制，但在产生精子竞争的条件下，这些特征出现了近交衰退。
