Phylogeography of the Sponge Suberites diversicolor in Indonesia: Insights into the Evolution of Marine Lake Populations

The existence of multiple independently derived populations in landlocked marine lakes provides an opportunity for fundamental research into the role of isolation in population divergence and speciation in marine taxa. Marine lakes are landlocked water bodies that maintain a marine character through narrow submarine connections to the sea and could be regarded as the marine equivalents of terrestrial islands. The sponge Suberites diversicolor (Porifera: Demospongiae: Suberitidae) is typical of marine lake habitats in the Indo-Australian Archipelago. Four molecular markers (two mitochondrial and two nuclear) were employed to study genetic structure of populations within and between marine lakes in Indonesia and three coastal locations in Indonesia, Singapore and Australia. Within populations of S. diversicolor two strongly divergent lineages (A & B) (COI: p = 0.4% and ITS: p = 7.3%) were found, that may constitute cryptic species. Lineage A only occurred in Kakaban lake (East Kalimantan), while lineage B was present in all sampled populations. Within lineage B, we found low levels of genetic diversity in lakes, though there was spatial genetic population structuring. The Australian population is genetically differentiated from the Indonesian populations. Within Indonesia we did not record an East-West barrier, which has frequently been reported for other marine invertebrates. Kakaban lake is the largest and most isolated marine lake in Indonesia and contains the highest genetic diversity with genetic variants not observed elsewhere. Kakaban lake may be an area where multiple putative refugia populations have come into secondary contact, resulting in high levels of genetic diversity and a high number of endemic species.封闭型海湖存在多个独立起源的种群，为研究隔离在海洋分类群（marine taxa）的种群分化与物种形成过程中所发挥的作用提供了理想的基础研究契机。海湖是一类通过狭窄海底通道与海洋相连、从而维持海洋水体特性的封闭水域，可被视作海洋版的陆地岛屿。多色韧海绵（Suberites diversicolor，隶属于多孔动物门（Porifera）、寻常海绵纲（Demospongiae）、韧海绵科（Suberitidae））是印度-澳大利亚群岛海湖生境的典型代表物种。本研究采用4种分子标记（2种线粒体标记与2种核标记），对印度尼西亚境内海湖内部、海湖之间，以及印度尼西亚、新加坡和澳大利亚的3个沿海采样点的种群遗传结构进行了分析。在多色韧海绵的种群内部，研究人员发现了两个高度分化的支系（A与B），其COI（Cytochrome Oxidase Subunit I）基因序列分歧率为0.4%，ITS（Internal Transcribed Spacer）序列分歧率为7.3%，二者或为隐存物种。支系A仅分布于东加里曼丹的卡卡班海湖（Kakaban Lake），而支系B则存在于所有采样种群中。在支系B内部，尽管存在空间遗传种群结构，但海湖种群的遗传多样性水平较低。澳大利亚种群与印度尼西亚种群存在显著的遗传分化。在印度尼西亚境内未检测到东西向地理阻隔，而这一阻隔在其他海洋无脊椎动物类群中已有大量报道。卡卡班海湖是印度尼西亚境内面积最大、隔离程度最高的海湖，其拥有最高的遗传多样性，且存在其他采样区域未发现的遗传变异。卡卡班海湖或为多个推测的避难所种群发生二次接触的区域，由此造就了极高的遗传多样性与大量特有物种。