Departamento de Bioquímica, Xenética e Inmunoloxía, Facultade de Bioloxía, Universidade de Vigo, Campus de Vigo, Vigo, Spain.
J Evol Biol. 2013 Jul;26(7):1472-87. doi: 10.1111/jeb.12152. Epub 2013 May 11.
Hybrid zones of ecologically divergent populations are ideal systems to study the interaction between natural selection and gene flow during the initial stages of speciation. Here, we perform an amplified fragment length polymorphism (AFLP) genome scan in parallel hybrid zones between divergent ecotypes of the marine snail Littorina saxatilis, which is considered a model case for the study of ecological speciation. Ridged-Banded (RB) and Smooth-Unbanded (SU) ecotypes are adapted to different shore levels and microhabitats, although they present a sympatric distribution at the mid-shore where they meet and mate (partially assortatively). We used shell morphology, outlier and nonoutlier AFLP loci from RB, SU and hybrid specimens captured in sympatry to determine the level of phenotypic and genetic introgression. We found different levels of introgression at parallel hybrid zones and nonoutlier loci showed more gene flow with greater phenotypic introgression. These results were independent from the phylogeography of the studied populations, but not from the local ecological conditions. Genetic variation at outlier loci was highly correlated with phenotypic variation. In addition, we used the relationship between genetic and phenotypic variation to estimate the heritability of morphological traits and to identify potential Quantitative Trait Loci to be confirmed in future crosses. These results suggest that ecology (exogenous selection) plays an important role in this hybrid zone. Thus, ecologically based divergent natural selection is responsible, simultaneously, for both ecotype divergence and hybridization. On the other hand, genetic introgression occurs only at neutral loci (nonoutliers). In the future, genome-wide studies and controlled crosses would give more valuable information about this process of speciation in the face of gene flow.
生态分歧种群的杂交区是研究物种形成初期自然选择和基因流相互作用的理想系统。在这里，我们在海洋蜗牛石鳖的生态分歧生态型之间的并行杂交区中进行了扩增片段长度多态性（AFLP）基因组扫描，该物种被认为是研究生态物种形成的模型案例。有脊带（RB）和光滑无带（SU）生态型适应不同的岸线和微生境，尽管它们在中岸相遇和交配的地方呈同域分布（部分选择性交配）。我们使用贝壳形态、来自 RB、SU 和杂交标本的异常和非异常 AFLP 基因座，这些标本在同域捕获，以确定表型和遗传渗入的程度。我们在并行杂交区发现了不同程度的基因渗入，非异常基因座显示出更多的基因流，伴随着更大的表型渗入。这些结果与所研究种群的系统地理学无关，但与当地的生态条件有关。异常基因座的遗传变异与表型变异高度相关。此外，我们利用遗传和表型变异之间的关系来估计形态特征的遗传力，并确定潜在的数量性状基因座，以便在未来的杂交中进行验证。这些结果表明，生态学（外生选择）在这个杂交区中起着重要作用。因此，基于生态的分歧自然选择同时负责生态型分歧和杂交。另一方面，遗传渗入仅发生在中性基因座（非异常）上。在未来，全基因组研究和受控杂交将提供更多关于面对基因流的物种形成过程的有价值信息。
