Tabata Jun, Ichiki Ryoko T, Tanaka Hirotaka, Kageyama Daisuke
National Institute for Agro-Environmental Sciences, 3-1-3 Kannondai, Tsukuba, Ibaraki 305-8604, Japan.
Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki 305-8686, Japan.
PLoS One. 2016 Jun 20;11(6):e0156587. doi: 10.1371/journal.pone.0156587. eCollection 2016.
Asexual reproduction, including parthenogenesis in which embryos develop within a female without fertilization, is assumed to confer advantages over sexual reproduction, which includes a "cost of males." Sexual reproduction largely predominates in animals, however, indicating that this cost is outweighed by the genetic and/or ecological benefits of sexuality, including the acquisition of advantageous mutations occurring in different individuals and the elimination of deleterious mutations. But the evolution of sexual reproduction remains unclear, because we have limited examples that demonstrate the relative success of sexual lineages in the face of competition from asexual lineages in the same environment. Here we investigated a sympatric occurrence of sexual and asexual reproduction in the pineapple mealybug, Dysmicoccus brevipes. This pest invaded southwestern Japan, including Okinawa and Ishigaki Islands, in the 1930s in association with imported pineapple plants. Our recent censuses demonstrated that on Okinawa sexually reproducing individuals can coexist with and even dominate asexual individuals in the presence of habitat and resource competition, which is considered to be severe for this nearly immobile insect. Molecular phylogeny based on partial DNA sequences in the mitochondrial and nuclear genomes, as well as the endosymbiotic bacterial genome, revealed that the asexual lineage diverged from a common sexual ancestor in the relatively recent past. In contrast, only the asexual lineage exhibiting obligate apomictic thelytoky was discovered on Ishigaki. Co-existence of the two lineages cannot be explained by the results of laboratory experiments, which showed that the intrinsic rate of increase in the sexual lineage was not obviously superior to that of the asexual lineage. Differences in biotic and/or abiotic selective forces operating on the two islands might be the cause of this discrepancy. This biological system offers a unique opportunity to assess the relative success of sexual versus asexual lineages with an unusual morphology and life cycle.
无性繁殖，包括孤雌生殖（即胚胎在雌性体内无需受精即可发育），被认为比有性繁殖具有优势，因为有性繁殖存在“雄性成本”。然而，有性繁殖在动物界占据主导地位，这表明这种成本被有性繁殖在基因和/或生态方面的益处所抵消，这些益处包括获得不同个体中出现的有利突变以及消除有害突变。但是有性繁殖的进化过程仍不明确，因为我们仅有有限的例子能够证明在相同环境中，面对无性繁殖谱系的竞争时，有性繁殖谱系的相对成功。在此，我们研究了菠萝粉蚧（Dysmicoccus brevipes）有性繁殖和无性繁殖的同域现象。这种害虫在20世纪30年代随着进口菠萝植株入侵了日本西南部，包括冲绳和石垣岛。我们最近的普查表明，在冲绳，有性繁殖个体能够与无性繁殖个体共存，甚至在存在栖息地和资源竞争的情况下占据主导地位，而对于这种几乎不活动的昆虫来说，这种竞争被认为是激烈的。基于线粒体、核基因组以及内共生细菌基因组中的部分DNA序列构建的分子系统发育显示，无性繁殖谱系在相对较近的过去从一个共同的有性祖先分化而来。相比之下，在石垣岛仅发现了表现为专性无融合生殖产雌孤雌生殖的无性繁殖谱系。实验室实验结果无法解释这两个谱系的共存现象，实验表明有性繁殖谱系的内在增长率并不明显高于无性繁殖谱系。作用于两个岛屿的生物和/或非生物选择压力的差异可能是造成这种差异的原因。这个生物系统为评估具有独特形态和生命周期的有性繁殖与无性繁殖谱系的相对成功提供了一个独特的机会。
