Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Zürich, Switzerland.
Curr Biol. 2011 Mar 8;21(5):433-7. doi: 10.1016/j.cub.2011.01.070. Epub 2011 Feb 25.
The evolutionary maintenance of sex is one of the big unresolved puzzles in biology. All else being equal, all-female asexual populations should enjoy a two-fold reproductive advantage over sexual relatives consisting of male and female individuals. However, the "all else being equal" assumption rarely holds in real organisms because asexuality tends to be confounded with altered genomic constitutions such as hybridization and polyploidization or to be associated with parthenogenesis-inducing microbes. This limits the ability to draw general conclusions from any particular system. Here we describe a new system that permits unbiased comparisons of sexual and asexual reproduction: the parasitic wasp Lysiphlebus fabarum. Crossing experiments demonstrated that asexual reproduction has a simple genetic basis in this species and is consistently inherited as a single-locus recessive trait. We further show that the asexuality-inducing allele exhibits complete linkage to a specific allele at a microsatellite marker: all asexual lines in the field were homozygous for this allele, and the allele cosegregated perfectly with asexual reproduction in our experimental crossings. This novel system of contagious asexuality allows the production of closely related individuals with different reproductive modes, as well as the monitoring of the asexuality-inducing allele in natural and experimental populations.
性的进化维持是生物学中一个尚未解决的大难题。在其他条件相同的情况下，全雌性的无性种群应该比由雄性和雌性个体组成的有性亲属享有两倍的繁殖优势。然而，“其他条件相同”的假设在实际生物体中很少成立，因为无性繁殖往往与改变的基因组组成有关，如杂交和多倍体化，或者与诱导孤雌生殖的微生物有关。这限制了从任何特定系统中得出普遍结论的能力。在这里，我们描述了一个新的系统，该系统允许对有性和无性繁殖进行无偏比较：寄生蜂 Lysiphlebus fabarum。杂交实验表明，在这个物种中，无性繁殖具有简单的遗传基础，并且作为单基因隐性特征一致遗传。我们进一步表明，诱导无性繁殖的等位基因与微卫星标记上的特定等位基因完全连锁：田间所有的无性系都是这个等位基因的纯合子，并且在我们的实验杂交中，这个等位基因与无性繁殖完美共分离。这种新型的传染性无性繁殖系统允许产生具有不同繁殖方式的密切相关的个体，并且可以在自然和实验种群中监测诱导无性繁殖的等位基因。
