Sex differences in life span: Females homozygous for the X chromosome do not suffer the shorter life span predicted by the unguarded X hypothesis
Sex differences in life span: Females homozygous for the X chromosome do not suffer the shorter life span predicted by the unguarded X hypothesis
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DOI：
10.1111/evo.13434
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发表时间：
2018-03-01
期刊：
影响因子：
3.3
通讯作者：
Friberg, Urban
中科院分区：
文献类型：
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作者：
Brengdahl, Martin;Kimber, Christopher M.;Friberg, Urban
在许多物种中，两性的寿命不同。人们提出了三种假说来解释这种有趣的模式，涉及不同的驱动因素：性选择、细胞质基因组的不对称遗传和X（Z）染色体的半合子性（无保护X假说）。其中，无保护的X受到的实验关注最少。这一假说表明，异配子性别遭受寿命缩短，因为其单一的X（Z）染色体上的隐性有害等位基因无条件地表达。在黑腹果蝇中，X染色体异常大（约占基因组的20%），为评估涉及X染色体的理论提供了一个强有力的模型。在这里，我们通过强迫D来测试无保护的X假设。从实验室种群中分离黑腹果蝇雌性，使其表达与雄性相同程度的隐性X-连锁等位基因，使用仅对X染色体纯合的雌性。我们没有发现X纯合性导致寿命缩短或卵至成虫存活率降低的证据。相比之下，男性和女性的常染色体纯合子都遭受类似的，显着减少这些特征。无保护的X假说的逻辑是无可争议的，但我们的研究结果表明，在何种程度上隐性有害的X-连锁等位基因抑制性能在异配子性别似乎太小，解释一般的性别差异寿命。
Life span differs between the sexes in many species. Three hypotheses to explain this interesting pattern have been proposed, involving different drivers: sexual selection, asymmetrical inheritance of cytoplasmic genomes, and hemizygosity of the X(Z) chromosome (the unguarded X hypothesis). Of these, the unguarded X has received the least experimental attention. This hypothesis suggests that the heterogametic sex suffers a shortened life span because recessive deleterious alleles on its single X(Z) chromosome are expressed unconditionally. In Drosophila melanogaster, the X chromosome is unusually large (approximate to 20% of the genome), providing a powerful model for evaluating theories involving the X. Here, we test the unguarded X hypothesis by forcing D. melanogaster females from a laboratory population to express recessive X-linked alleles to the same degree as males, using females exclusively made homozygous for the X chromosome. We find no evidence for reduced life span or egg-to-adult viability due to X homozygozity. In contrast, males and females homozygous for an autosome both suffer similar, significant reductions in those traits. The logic of the unguarded X hypothesis is indisputable, but our results suggest that the degree to which recessive deleterious X-linked alleles depress performance in the heterogametic sex appears too small to explain general sex differences in life span.