Frequency and inheritance of non-male producing clones in Daphnia magna: evolution towards sex specialization in a cyclical parthenogen?
Frequency and inheritance of non-male producing clones in Daphnia magna: evolution towards sex specialization in a cyclical parthenogen?
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DOI：
10.1111/j.1420-9101.2011.02288.x
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发表时间：
2011-07-01
影响因子：
2.1
通讯作者：
Haag, C. R.
中科院分区：
文献类型：
--
作者：
Galimov, Y.;Walser, B.;Haag, C. R.
在水蚤（枝角类，甲壳纲），孤雌生殖与有性生殖交替。属于同一孤雌生殖系的两性个体在遗传上是相同的，它们的性别由环境决定。以前，非雄性生产（NMP）基因型已被描述在蚤状水蚤组的物种。如果这些基因型与产生雄性和雌性的正常（MP）基因型共存，则这些基因型只能持续通过有性生殖的阶段，因此育种系统多态性类似于植物中众所周知的雌雄同体（雌性与两性体共存）。在这里，我们表明，同样的繁殖系统多态性也发生在大型蚤，一个物种，已经从D。100多年前的pulex。根据种群的不同，D.当实验性地暴露于通常导致仅雄性窝的推定的性激素法呢酸甲酯的浓度时，大雌性不产生雄性。这些NMP女性的自然育雏从来没有包含男性，与高比例的男性后代MP女性从相同的人口。一系列杂交试验的结果表明，NMP是由一个显性等位基因在一个单一的核位点（或几个紧密连锁的位点）：NMP × MP杂交总是产生50%的NMP和50%的MP后代，而MP × MP杂交总是产生100%的MP后代。基于细胞色素c氧化酶亚基I序列，我们发现不同群体的NMP基因型分属于三个高度分化的线粒体谱系，可能代表了D. magna.因此，NMP基因型在周期性孤雌生殖的演变可能比以前认为的更常见。此外，MP基因型与NMP基因型共存，可能已经响应了后者的存在，部分专业化的男性生产。因此，D. magna可能是一个从纯粹的环境性别决定系统进化到部分遗传性别决定系统的模型。
In Daphnia (Cladocera, Crustacea), parthenogenetic reproduction alternates with sexual reproduction. Individuals of both sexes that belong to the same parthenogenetic line are genetically identical, and their sex is determined by the environment. Previously, non-male producing (NMP) genotypes have been described in species of the Daphnia pulex group. Such genotypes can only persist through phases of sexual reproduction if they co-occur with normal (MP) genotypes that produce both males and females, and thus the breeding system polymorphism is similar to gynodioecy (coexistence of females with hermaphrodites), which is well known in plants. Here we show that the same breeding system polymorphism also occurs in Daphnia magna, a species that has diverged from D. pulex more than 100 MY ago. Depending on the population, between 0% and 40% of D. magna females do not produce males when experimentally exposed to a concentration of the putative sex hormone methyl farnesoate that normally leads to male-only clutches. Natural broods of these NMP females never contained males, contrasting with high proportions of male offspring in MP females from the same populations. The results from a series of crossing experiments suggest that NMP is determined by a dominant allele at a single nuclear locus (or a several closely linked loci): NMP x MP crosses always yielded 50% NMP and 50% MP offspring, whereas MP x MP crosses always yielded 100% MP offspring. Based on cytochrome c oxidase subunit I-sequences, we found that NMP genotypes from different populations belong to three highly divergent mitochondrial lineages, potentially representing three independent evolutionary origins of NMP in D. magna. Thus, the evolution of NMP genotypes in cyclical parthenogens may be more common than previously thought. Moreover, MP genotypes that coexist with NMP genotypes may have responded to the presence of the latter by partially specializing on male production. Hence, these populations of D. magna may be a model for an evolutionary transition from a purely environmental to a partially genetic sex determination system.