Scripps Institution of Oceanography, University of California San Diego, La Jolla, 92093 , USA.
Centre for Biodiversity Genomics, University of Copenhagen, 2100, Copenhagen, Denmark.
BMC Biol. 2023 May 29;21(1):129. doi: 10.1186/s12915-023-01628-9.
Common seadragons (Phyllopteryx taeniolatus, Syngnathidae) are an emblem of the diverse endemic fauna of Australia's southern rocky reefs, the newly recognized "Great Southern Reef." A lack of assessments spanning this global biodiversity hotspot in its entirety is currently hampering an understanding of the factors that have contributed to its diversity. The common seadragon has a wide range across Australia's entire temperate south and includes a geogenetic break over a former land bridge, which has called its status as a single species into question. As a popular aquarium display that sells for high prices, common seadragons are also vulnerable to illegal capture.
Here, we provide range-wide nuclear sequences (986 variable Ultraconserved Elements) for 198 individuals and mitochondrial genomes for 140 individuals to assess species status, identify genetic units and their diversity, and trace the source of two poached individuals. Using published data of the other two seadragon species, we found that lineages of common seadragons have diverged relatively recently (< 0.63 Ma). Within common seadragons, we found pronounced genetic structure, falling into three major groups in the western, central, and eastern parts of the range. While populations across the Bassian Isthmus were divergent, there is also evidence for secondary contact since the passage opened. We found a strong cline of genetic diversity from the range center tapering symmetrically towards the range peripheries. Based on their genetic similarities, the poached individuals were inferred to have originated from around Albany in southwestern Australia.
We conclude that common seadragons constitute a single species with strong geographic structure but coherence through gene flow. The low genetic diversity on the east and west coasts is concerning given that these areas are projected to face fast climate change. Our results suggest that in addition to their life history, geological events and demographic expansions have all played a role in shaping populations in the temperate south. These insights are an important step towards understanding the historical determinants of the diversity of species endemic to the Great Southern Reef.
普通海龙（Phyllopteryx taeniolatus，海龙科）是澳大利亚南部多岩石暗礁中多样特有动物群的象征，这些暗礁被新认定为“大南方暗礁”。目前，由于缺乏对这一全球生物多样性热点地区的全面评估，人们对促成其多样性的因素还不太了解。普通海龙广泛分布于澳大利亚整个温带南部，包括一个跨越前陆桥的地理遗传断裂，这使其是否为单一物种受到质疑。作为一种在水族馆高价出售的受欢迎的展示动物，普通海龙也容易受到非法捕捞的影响。
在这里，我们提供了 198 个个体的全范围核序列（986 个可变的超保守元件）和 140 个个体的线粒体基因组，以评估物种状况，确定遗传单元及其多样性，并追溯两只被盗海龙的来源。利用其他两种海龙物种的已发表数据，我们发现普通海龙的谱系最近才分化（<0.63Ma）。在普通海龙中，我们发现了明显的遗传结构，分为西部、中部和东部三个主要群体。虽然巴斯海峡两岸的种群存在分歧，但自海峡开通以来，也有证据表明存在二次接触。我们发现，从范围中心向范围边缘呈对称递减的遗传多样性强梯度。根据它们的遗传相似性，被盗个体被推断起源于澳大利亚西南部的奥尔巴尼附近。
我们得出结论，普通海龙是一个具有强烈地理结构但通过基因流保持一致性的单一物种。东海岸和西海岸的遗传多样性较低，这令人担忧，因为这些地区预计将面临快速的气候变化。我们的研究结果表明，除了它们的生活史外，地质事件和人口扩张都在塑造南部温带地区的种群方面发挥了作用。这些见解是理解大南方暗礁特有物种多样性的历史决定因素的重要一步。
