Insights into the strategy of micro-environmental adaptation: Transcriptomic analysis of two alvinocaridid shrimps at a hydrothermal vent

Diffusing fluid at a deep-sea hydrothermal vent creates rapid, acute physico-chemical gradients that correlate strongly with the distribution of the vent fauna. Two alvinocaridid shrimps, Alvinocaris longirostris and Shinkaicaris leurokolos occupy distinct microhabitats around these vents and exhibit different thermal preferences. S. leurokolos inhabits the central area closer to the active chimney, while A. longirostris inhabits the peripheral area. In this study, we screened candidate genes that might be involved in niche separation and microhabitat adaptation through comparative transcriptomics. The results showed that among the top 20% of overexpressed genes, gene families related to protein synthesis and structural components were much more abundant in S. leurokolos compared to A. longirostris. Moreover, 15 out of 25 genes involved in cellular carbohydrate metabolism were related to trehalose biosynthesis, versus 1 out of 5 in A. longirostris. Trehalose, a non-reducing disaccharide, is a multifunctional molecule and has been proven to act as a protectant responsible for thermotolerance in Saccharomyces cerevisiae. Putative positively selected genes involved in chitin metabolism and the immune system (lectin, serine protease and antimicrobial peptide) were enriched in S. leurokolos. In particular, one collagen and two serine proteases were found to have experienced strong positive selection. In addition, sulfotransferase-related genes were both overexpressed and positively selected in S. leurokolos. Finally, genes related to structural proteins, immune proteins and protectants were overexpressed or positively selected. These characteristics could represent adaptations of S. leurokolos to its microhabitat, which need to be confirmed by more evidence, such as data from large samples and different development stages of these alvinocaridid shrimps.深海热液喷口的扩散流体可形成剧烈变化的理化梯度，该梯度与喷口动物群落的分布显著相关。阿尔文虾科虾类（Alvinocaridid shrimps）中的两个物种——长额阿尔文虾（Alvinocaris longirostris）与细肢新卡虾（Shinkaicaris leurokolos）——在喷口周边占据迥异的微生境，并表现出不同的温度偏好。细肢新卡虾（S. leurokolos）栖息于靠近活跃喷口烟囱的中心区域，而长额阿尔文虾（A. longirostris）则分布于外围区域。本研究通过比较转录组学（comparative transcriptomics）技术，筛选出可能参与生态位分化与微生境适应的候选基因。分析结果表明，在表达上调的前20%基因中，细肢新卡虾内与蛋白质合成及结构组分相关的基因家族丰度远高于长额阿尔文虾。此外，参与细胞碳水化合物代谢的25个基因中，有15个与海藻糖（trehalose）生物合成相关；而长额阿尔文虾的对应比例仅为5个基因中的1个。海藻糖是一种非还原性二糖，属于多功能分子，已被证实可作为酿酒酵母（Saccharomyces cerevisiae）耐热性的保护因子。细肢新卡虾中富集了参与几丁质代谢与免疫系统的候选正选择基因，相关基因涵盖凝集素（lectin）、丝氨酸蛋白酶（serine protease）及抗菌肽（antimicrobial peptide）。尤为关键的是，1个胶原基因与2个丝氨酸蛋白酶基因受到了强烈的正选择作用。此外，细肢新卡虾中与磺基转移酶（sulfotransferase）相关的基因既呈现表达上调，又受到了正选择作用。综上，与结构蛋白、免疫蛋白及保护因子相关的基因均呈现表达上调或正选择特征。上述特征或可反映细肢新卡虾对其微生境的适应机制，相关结论仍需更多证据予以验证，例如扩大样本量及覆盖不同发育阶段的实验数据。