Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, USA.
Center for Coastal Marine Sciences, California Polytechnic State University, San Luis Obispo, CA, USA.
J Evol Biol. 2021 Aug;34(8):1212-1224. doi: 10.1111/jeb.13789. Epub 2021 Jul 6.
The large geographic distribution of the eastern oyster, Crassostrea virginica, makes it an ideal species to test how populations have adapted to latitudinal gradients in temperature. Despite inhabiting distinct thermal regimes, populations of C. virginica near the species' southern and northern geographic range show no population differences in their physiological response to temperature. In this study, we used comparative transcriptomics to understand how oysters from either end of the species' range maintain enantiostasis across three acclimation temperatures (10, 20, and 30°C). With this approach, we identified genes that were differentially expressed in response to temperature between individuals of C. virginica collected from New Brunswick, Canada and Louisiana, USA. We observed a core set of genes whose expression responded to temperature in both populations, but also an even larger set of genes with expression patterns that were unique to each population. Intriguingly, the genes with population-specific responses to temperature had elevated F and Ka/Ks ratios compared to the genome-wide average. In contrast, genes showing only a response to temperature were found to only have elevated F values suggesting that divergent F may be due to selection on linked regulatory regions rather than positive selection on protein coding regions. Taken together, our results suggest that, despite coarse-scale physiological similarities, natural selection has shaped divergent gene expression responses to temperature in geographically separated populations of this broadly eurythermal marine invertebrate.
东方牡蛎（Crassostrea virginica）的地理分布范围广泛，使其成为测试种群如何适应温度纬度梯度的理想物种。尽管生活在不同的热区，但在该物种的南部和北部地理范围内的 C. virginica 种群，其对温度的生理反应没有表现出种群差异。在这项研究中，我们使用比较转录组学来了解来自该物种分布范围两端的牡蛎如何在三个适应温度（10、20 和 30°C）下保持对温度的稳定性。通过这种方法，我们确定了在加拿大新不伦瑞克省和美国路易斯安那州采集的 C. virginica 个体之间，对温度有差异表达的基因。我们观察到一组核心基因，它们在两个种群中的表达都对温度有反应，但也有一组更大的基因，其表达模式是每个种群所特有的。有趣的是，与全基因组平均值相比，对温度具有种群特异性反应的基因具有更高的 F 和 Ka/Ks 比值。相比之下，只对温度有反应的基因被发现只有更高的 F 值，这表明分歧的 F 值可能是由于对连接的调控区域的选择，而不是对蛋白质编码区域的正选择。总之，我们的研究结果表明，尽管在粗尺度上具有相似的生理特征，但自然选择已经塑造了地理上分离的该广泛广温海洋无脊椎动物种群对温度的不同基因表达反应。
