Matsubayashi K W, Kohyama T I, Kobayashi N, Yamasaki S, Kuwajima M, Katakura H
The Faculty of Arts and Science, Kyushu University, Fukuoka, Fukuoka, Japan.
Faculty of Earth and Environmental Sciences, Hokkaido University, Sapporo, Hokkaido, Japan.
J Evol Biol. 2017 Jun;30(6):1110-1123. doi: 10.1111/jeb.13071. Epub 2017 Apr 26.
Adaptation to different environments can promote population divergence via natural selection even in the presence of gene flow - a phenomenon that typically occurs during ecological speciation. To elucidate how natural selection promotes and maintains population divergence during speciation, we investigated the population genetic structure, degree of gene flow and heterogeneous genomic divergence in three closely related Japanese phytophagous ladybird beetles: Henosepilachna pustulosa, H. niponica and H. yasutomii. These species act as a generalist, a wild thistle (Cirsium spp.) specialist and a blue cohosh (Caulophyllum robustum) specialist, respectively, and their ranges differ accordingly. The two specialist species widely co-occur but are reproductively isolated solely due to their high specialization to a particular host plant. Genomewide amplified fragment-length polymorphism (AFLP) markers and mitochondrial cytochrome c oxidase subunit I (COI) gene sequences demonstrated obvious genomewide divergence associated with both geographic distance and ecological divergence. However, a hybridization assessment for both AFLP loci and the mitochondrial sequences revealed a certain degree of unidirectional gene flow between the two sympatric specialist species. Principal coordinates analysis (PCoA) based on all of the variable AFLP loci demonstrated that there are genetic similarities between populations from adjacent localities irrespective of the species (i.e. host range). However, a further comparative genome scan identified a few fractions of loci representing approximately 1% of all loci as different host-associated outliers. These results suggest that these three species had a complex origin, which could be obscured by current gene flow, and that ecological divergence can be maintained with only a small fraction of the genome is related to different host use even when there is a certain degree of gene flow between sympatric species pairs.
即使存在基因流，适应不同环境也可通过自然选择促进种群分化，这一现象通常发生在生态物种形成过程中。为阐明自然选择在物种形成过程中如何促进和维持种群分化，我们研究了三种近缘的日本植食性瓢虫的种群遗传结构、基因流程度和异质基因组分化：黄斑食植瓢虫、日本食植瓢虫和保户食植瓢虫。这些物种分别作为广食性、野生蓟（蓟属）专食性和类叶升麻（粗壮类叶升麻）专食性昆虫，其分布范围也相应不同。这两种专食性物种广泛共存，但仅因其对特定寄主植物的高度专一性而生殖隔离。全基因组扩增片段长度多态性（AFLP）标记和线粒体细胞色素c氧化酶亚基I（COI）基因序列表明，全基因组存在与地理距离和生态分化相关的明显差异。然而，对AFLP位点和线粒体序列的杂交评估显示，这两种同域分布的专食性物种之间存在一定程度的单向基因流。基于所有可变AFLP位点的主坐标分析（PCoA）表明，相邻地区的种群之间存在遗传相似性，而与物种（即寄主范围）无关。然而，进一步的比较基因组扫描发现，少数约占所有位点1%的位点作为与不同寄主相关的异常值。这些结果表明，这三个物种有一个复杂的起源，可能被当前的基因流所掩盖，并且即使同域物种对之间存在一定程度的基因流，只有一小部分基因组与不同寄主利用相关，生态分化仍可维持。
