Institut des Sciences de l'Evolution de Montpellier, Université Montpellier, Montpellier, France.
CNRS Institut des Sciences de l'Evolution, UMR5554 UM-CNRS-IRD-EPHE, Sète, France.
Evolution. 2019 Apr;73(4):817-835. doi: 10.1111/evo.13696. Epub 2019 Mar 11.
Diverging semi-isolated lineages either meet in narrow clinal hybrid zones, or have a mosaic distribution associated with environmental variation. Intrinsic reproductive isolation is often emphasized in the former and local adaptation in the latter, although both reduce gene flow between groups. Rarely are these two patterns of spatial distribution reported in the same study system. Here, we report that the long-snouted seahorse Hippocampus guttulatus is subdivided into discrete panmictic entities by both types of hybrid zones. Along the European Atlantic coasts, a northern and a southern lineage meet in the southwest of France where they coexist in sympatry-i.e., in the same geographical zone-with little hybridization. In the Mediterranean Sea, two lineages have a mosaic distribution, associated with lagoon-like and marine habitats. A fifth lineage was identified in the Black Sea. Genetic homogeneity over large spatial scales contrasts with isolation maintained in sympatry or close parapatry at a fine scale. A high variation in locus-specific introgression rates provides additional evidence that partial reproductive isolation must be maintaining the divergence. We find that fixed differences between lagoon and marine populations in the Mediterranean Sea belong to the most differentiated SNPs between the two Atlantic lineages, against the genome-wide pattern of structure that mostly follow geography. These parallel outlier SNPs cluster on a single chromosome-wide island of differentiation. Since Atlantic lineages do not map to lagoon-sea habitat variation, genetic parallelism at the genomic island suggests a shared genetic barrier contributes to reproductive isolation in contrasting contexts-i.e., spatial versus ecological. We discuss how a genomic hotspot of parallel differentiation could have evolved and become associated both with space and with a patchy environment in a single study system.
分歧的半隔离谱系要么在狭窄的连续杂交带相遇，要么与环境变化相关的马赛克分布。内在生殖隔离在前者中经常被强调，而局部适应在后者中被强调，尽管两者都减少了群体之间的基因流动。这两种空间分布模式很少在同一个研究系统中同时报告。在这里，我们报告说，长吻海马 Hippocampus guttulatus 被两种类型的杂交带分为离散的混合实体。在欧洲大西洋沿岸，北部和南部的谱系在法国西南部相遇，它们在那里共存于同域，即处于同一地理区域，几乎没有杂交。在地中海，两个谱系呈马赛克分布，与泻湖和海洋生境相关。在黑海发现了第五个谱系。大空间尺度上的遗传同质性与在同域或近同域的精细尺度上保持的隔离形成对比。局部特异性渐渗率的高度变异性提供了额外的证据，表明部分生殖隔离必须维持分化。我们发现，地中海的泻湖和海洋种群之间的固定差异属于两个大西洋谱系之间分化程度最高的 SNP，而不是遵循地理分布的全基因组结构模式。这些平行的局域 SNP 聚类在一个染色体宽度的分化岛上。由于大西洋谱系与泻湖-海洋生境变化不相关，基因组岛上的遗传平行性表明，一个共同的遗传障碍有助于在不同的背景下，即空间和生态，产生生殖隔离。我们讨论了一个基因组热点的平行分化是如何进化的，并在单个研究系统中与空间和斑块状环境相关联的。
