Data from: Intrinsic differences between males and females determine sex-specific consequences of inbreeding

Background
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.

Results
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.

Conclusions
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.

背景
近交（inbreeding）可提升个体的纯合性（homozygosity），暴露有害隐性等位基因（deleterious recessive alleles），总体上降低近交个体的适合度（fitness）。值得注意的是，近交对雌雄个体的影响通常存在差异，而更易受影响的性别则取决于物种与所测定的性状。

结果
本研究以栖息于土壤的雷氏隐杆线虫（Caenorhabditis remanei）为实验材料，在9个谱系、5个近交水平下，针对数十万子代开展性别特异性近交衰退（inbreeding depression）分析。结果显示，雌性线虫的适合度下降幅度始终高于雄性个体，在高近交水平下这一差异尤为显著。

结论
上述结果表明，雌性个体中参与生殖性状调控的基因所承受的选择压力更强。雄性的近交衰退程度可进一步被两种机制缓解：一是性染色体半合子状态（sex chromosome hemizygosity），该状态会影响部分突变的显隐性；二是性选择（sexual selection）的缺失。明确性别特异性表达、性染色体上的基因以及其所处的筛选环境（包括性选择机会）的相对贡献，或可解释近交衰退性别差异中频繁出现却又不一致的观测结果，同时也能阐明该现象对物种保护（conservation）与交配系统（mating systems）演化的潜在意义。