魁蚶种群杂交适应性及引种对土著种群遗传结构的影响研究

Anthropogenic assaults on the environment are causing both wild and captive populations to become increasingly fragmented and vulnerable to inbreeding depression and loss of evolutionary potential. Translocations are being increasingly proposed as a way of conserving intraspecific biodiversity in fragmented landscapes. However, hybridization often occurs during mixing geographically isolated and genetically divergent sources. Enthusiasm for the benefits of intentional hybridization is tempered by the possibility mixing may induce outbreeding depression, introgressive hybridization and genetic assimilation. That is, interpopulation hybridization could suffer a loss in fitness due either to the disruption of intrinsic interactions between genes, or disruption of extrinsic interactions between genes and environment. The resource recovery and aquaculture of Scapharca broughtonii, which is an important economic marine shellfish in China, is getting more and more importance due to its habitat destruction and over exploitation. However, the knowledge of interpopulation hybridization of S. broughtonii is scarce. In this project, deep and systematic researches on mechanism of fitness variance (fertilization rate, hatching rate, metamorphosis rate, growth rate and survival rate) and genetic architecture (allele frequency, private allele, heterozygosity, genetic differentiation coefficient, gene flow, genetic distance and genetic structure) of different population in S. broughtonii will be conducted by combining intentional hybridization experiments and molecular genetic techniques. This project seeks to: identify the fitness variance of in different hybrids and illustrate the relationship between fitness and genetic variability; ascertain whether the translocations have positive or negative impacts on genetic architecture of native populations. The proposed project will provide guidelines for conservation managements and captive breeding in S. broughtonii, and also provide basic data and information for studies on the population evolution, species evolution, and so on, in marine bivalves.

引种可以使地理上隔离和遗传上分化的类群产生杂交，由杂交导致的远交衰退、基因渐渗和遗传同化可能会对物种的遗传组成产生负面影响。魁蚶(Scapharca broughtonii)是我国重要的海洋经济贝类，受生境破坏和过度开发的影响，自然种群数量逐年下降。近年来魁蚶的资源恢复和增养殖广泛开展，但频繁的引种和苗种交换对土著种群的基因库构成了威胁。本项目拟结合室内人工杂交和微卫星标记遗传分析技术，通过比较不同杂交组合在同一生境下的生长、存活等适应性的差异，评估引入种群和杂交种群的定植潜力，揭示引入种群对土著种群影响的生态学机制；通过分析种群间的等位基因频率、特有等位基因、杂合度、基因分化系数、基因流等遗传结构参数，查清以异地引种为主的人为干扰对土著种群遗传结构的影响。研究结果可以为魁蚶的种质资源保护及遗传育种提供科学依据和理论指导，也可为海洋贝类的种群演化及物种进化等研究提供基础资料。

魁蚶是我国重要的海洋经济贝类，受生境破坏和过度开发的影响，自然种群数量逐年下降，近年来魁蚶的资源恢复和增养殖开始广泛开展，但频繁的引种和苗种交换对土著种群的基因库构成了威胁。本研究利用人工繁育的中国种群魁蚶幼体和稚贝，查明了环境因子对魁蚶幼虫、稚贝生长、发育和存活的影响。发现叉鞭金藻是魁蚶幼虫的最适宜饵料，且与小球藻混合投喂效果较好，眼点幼虫比例与存活率显著高于其它试验组；发现饥饿1～2d较短时间对幼虫的特定生长率、眼点幼虫比例、壳长的影响不显著；查明了叉鞭金藻是魁蚶稚贝的适宜饵料，且与小球藻混合投喂对稚贝增长促进效果较好；发现不同温度、盐度环境下，魁蚶稚贝在水温26ºC和盐度30时生长最快，壳长与壳宽平均生长速率分别为4.64±0.04%•d-1和4.76±0.11%• d-1。基于简化基因组的种群遗传学研究，查明了我国和韩国、朝鲜不同种群魁蚶的种群遗传特征。以中国、韩国和朝鲜共7种群、70个魁蚶样本为素材，基于2b-RAD技术构建了标签测序文库，基于10108个有效 SNPs，分析了种群间的等位基因频率、特有等位基因、杂合度、基因分化系数、进化树等遗传参数；发现中国魁蚶4个种群的遗传分化不明显，聚类与进化树分析为一个类群，遗传分化指数FST仅为0.0009-0.0040，因此我国群体间的亲本与苗种交流对种群的遗传结构影响可能不大；但中国4个种群与韩国、朝鲜种群的遗传分化明显，聚类与进化树分析明显分为不同的类群，中国与韩国种群的FST指数达0.1276-0.1864，中国与朝鲜种群的FST指数为0.0401-0.0424。因此，不同国家间的魁蚶种群交流可能通过杂交渐渗对土著种群的遗传特征造成影响，建议慎重开展人为的引种交流应。以上研究结果可以为魁蚶的苗种繁育技术优化、生境选择、种质资源保护及遗传育种提供科学依据和理论指导 。