Data from: Microsatellite length variation in candidate genes correlates with habitat in the gilthead sea bream Sparus aurata

The genetic basis and evolutionary implications of local adaptation in high gene flow marine organisms are still poorly understood. In several Mediterranean fish species, alternative migration patterns exist between individuals entering coastal lagoons that offer favorable conditions for growth and those staying in the sea where environmental conditions are less subject to rapid and stressful change. Whether these coexisting strategies are phenotypically plastic or include a role for local adaptation through differential survival needs to be determined. Here, we explore the genetic basis of alternate habitat use in western Mediterranean populations of the gilthead sea bream (Sparus aurata). Samples from lagoonal and open sea habitats were typed for 3 candidate gene microsatellite loci, 7 anonymous microsatellites and 44 AFLP markers to test for genotype-environment associations. While anonymous markers globally indicated high levels of gene flow across geographic locations and habitats, non-neutral differentiation patterns correlated with habitat type were found at two candidate microsatellite loci located in the promoter region of the Growth hormone and Prolactin genes. Further analysis of these two genes revealed that a mechanism based on habitat choice alone could not explain the distribution of genotype frequencies at a regional scale, thus implying a role for differential survival between habitats. We also found an association between allele size and habitat type, which, in the light of previous studies, suggests that polymorphisms in the proximal promoter region could influence gene expression by modulating transcription factor binding, thus providing a potential explanatory link between genotype and growth phenotype in nature.

高基因流海洋生物的局部适应的遗传基础及其进化意义，目前仍未得到充分阐释。在数种地中海鱼类中，存在两种不同的迁徙策略：一类个体进入具备适宜生长条件的沿海潟湖，另一类则留在海洋环境中——后者的环境条件较少经历剧烈且具有胁迫性的变化。目前仍需明确，这些共存的生存策略究竟属于表型可塑性，还是通过差异化存活实现局部适应的结果。本研究以西地中海海域的金头鲷（gilthead sea bream, Sparus aurata）种群为研究对象，探讨其不同栖息地利用模式的遗传基础。研究对采自潟湖与外海栖息地的样本，通过3个候选基因微卫星（microsatellite）位点、7个匿名微卫星位点以及44个扩增片段长度多态性（AFLP）标记进行基因分型，以检验基因型与环境之间的关联。尽管匿名标记整体显示，不同地理区域与栖息地间存在高水平的基因流，但在位于生长激素（Growth hormone）与催乳素（Prolactin）基因启动子区域的两个候选微卫星位点上，发现了与栖息地类型相关的非中性分化模式。对这两个基因的进一步分析表明，仅基于栖息地选择的机制无法解释区域尺度下的基因型频率分布，这暗示不同栖息地间存在差异化的存活选择压力。本研究还发现了等位基因长度与栖息地类型之间的关联；结合既往研究来看，这表明近端启动子区域的多态性可通过调控转录因子（transcription factor）结合来影响基因表达，从而为自然界中基因型与生长表型间的关联提供了潜在的解释机制。