Wilson Alex C C, Delgado Ryan N, Vorburger Christoph
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona, United States of America.
Institute of Integrative Biology, ETH Zürich, Zürich, Switzerland; Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, Switzerland.
PLoS One. 2014 Dec 30;9(12):e116348. doi: 10.1371/journal.pone.0116348. eCollection 2014.
Commonly, a single aphid species exhibits a wide range of reproductive strategies including cyclical parthenogenesis and obligate parthenogenesis. Sex determination in aphids is chromosomal; females have two X chromosomes, while males have one. X chromosome elimination at male production is generally random, resulting in equal representation of both X chromosomes in sons. However, two studies have demonstrated deviations from randomness in some lineages. One hypothesis to account for such deviations is that recessive deleterious mutations accumulate during bouts of asexual reproduction and affect male viability, resulting in overrepresentation of males with the least deleterious of the two maternal X chromosomes. This hypothesis results in a testable prediction: X chromosome transmission bias will increase with time spent in the asexual phase and should therefore be most extreme in the least sexual aphid life cycle class. Here we test this prediction in Myzus persicae. We used multiple heterozygous X-linked microsatellite markers to screen 1085 males from 95 lines of known life cycle. We found significant deviations from equal representation of X chromosomes in 15 lines; however, these lines included representatives of all life cycles. Our results are inconsistent with the hypothesis that deviations from randomness are attributable to mutation accumulation.
通常，单一蚜虫物种表现出广泛的生殖策略，包括周期性孤雌生殖和专性孤雌生殖。蚜虫的性别决定是由染色体决定的；雌性有两条X染色体，而雄性有一条。在产生雄性时X染色体的消除通常是随机的，导致儿子中两条X染色体的比例相等。然而，两项研究表明，在某些谱系中存在偏离随机性的情况。解释这种偏离的一个假说是，隐性有害突变在无性繁殖过程中积累并影响雄性的生存能力，导致具有两条母本X染色体中危害最小的那条X染色体的雄性比例过高。这一假说产生了一个可检验的预测：X染色体传递偏差将随着在无性阶段所花费的时间增加而增加，因此在最少有性生殖的蚜虫生命周期类别中应该最为极端。在这里，我们在桃蚜中检验了这一预测。我们使用多个杂合的X连锁微卫星标记对来自95个已知生命周期品系的1085只雄性进行了筛选。我们发现15个品系中X染色体的比例存在显著偏离相等比例的情况；然而，这些品系包括了所有生命周期的代表。我们的结果与偏离随机性可归因于突变积累这一假说不一致。
