Ebel Emily R, Phillips Patrick C
Institute of Ecology and Evolution and Department of Biology, 5289 University of Oregon, 97403, Eugene, Oregon, USA.
Present address: Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA, 94305, USA.
BMC Evol Biol. 2016 Feb 9;16:36. doi: 10.1186/s12862-016-0604-5.
Inbreeding increases homozygosity and exposes deleterious recessive alleles, generally decreasing the fitness of inbred individuals. Interestingly, males and females are usually affected differently by inbreeding, though the more vulnerable sex depends on the species and trait measured.
We used the soil-dwelling nematode Caenorhabditis remanei to examine sex-specific inbreeding depression across nine lineages, five levels of inbreeding, and hundreds of thousands of progeny. Female nematodes consistently suffered greater fitness losses than their male counterparts, especially at high levels of inbreeding.
These results suggest that females experience stronger selection on genes contributing to reproductive traits. Inbreeding depression in males may be further reduced by sex chromosome hemizygosity, which affects the dominance of some mutations, as well as by the absence of sexual selection. Determining the relative contributions of sex-specific expression, genes on the sex chromosomes, and the environment they are filtered through-including opportunities for sexual selection-may explain the frequent though inconsistent records of sex differences in inbreeding depression, along with their implications for conservation and the evolution of mating systems.
近亲繁殖会增加纯合性并暴露有害的隐性等位基因，通常会降低近亲繁殖个体的适应性。有趣的是，近亲繁殖对雄性和雌性的影响通常不同，不过更易受影响的性别取决于所研究的物种和性状。
我们利用土壤线虫雷氏小杆线虫，在九个谱系、五种近亲繁殖水平以及数十万后代中检测了性别特异性的近亲繁殖衰退情况。雌性线虫的适应性损失始终比雄性线虫更大，尤其是在高度近亲繁殖的情况下。
这些结果表明，雌性在影响生殖性状的基因上受到更强的选择。雄性的近亲繁殖衰退可能会因性染色体半合子状态（这会影响某些突变的显性）以及缺乏性选择而进一步降低。确定性别特异性表达、性染色体上的基因以及它们所经历的环境（包括性选择机会）的相对贡献，可能有助于解释近亲繁殖衰退中性别差异的频繁但不一致的记录，以及它们对保护和交配系统进化的影响。
