Data from: Stretched to the limit; can a short pelagic larval duration connect adult populations of an Indo-Pacific diadromous fish (Kuhlia rupestris)?

Freshwater species on tropical islands face localized extinction and the loss of genetic diversity. Their habitats can be ephemeral due to variability in freshwater run-off and erosion. Even worse, anthropogenic effects on these ecosystems are intense. Most of these species are amphidromous or catadromous (i.e. their life cycle includes a marine larval phase), which buffers them against many of these effects. A long pelagic larval duration (PLD) was thought to be critical to ensure the colonization and persistence in tropical islands, but recent findings indicated that several species with short PLDs are successful in those ecosystems. To test the potential of a short PLD in maintaining genetic connectivity and forestalling extirpation, we studied Kuhlia rupestris, a catadromous fish species with an extensive distribution in the western Pacific and Indian Oceans. Using a combination of molecular genetic markers (13 microsatellite loci and two gene regions from mtDNA) and modelling of larval dispersal, we show that a short PLD constrains genetic connectivity over a wide geographical range. Molecular markers showed that the short PLD did not prevent genetic divergence through evolutionary time and speciation has occurred or is occurring. Modelling of larvae dispersal suggested limited recent connectivity between genetically homogeneous populations across the Coral Sea. However, a short PLD can maintain connectivity on a subocean basin scale. Conservation and management of tropical diadromous species needs to take into account that population connectivity may be more limited than previously suspected in those species.

热带岛屿的淡水物种正面临局地灭绝与遗传多样性丧失的威胁。其栖息地可能因淡水径流波动与侵蚀作用而短暂无常。更为严峻的是，人类活动对这些生态系统的干扰强度极高。此类物种大多为两洄游（amphidromous）或降海洄游（catadromous）类群，即其生命周期包含海洋幼体阶段，这一特性可使其免受诸多此类胁迫。长期以来，学界认为较长的浮游幼体期（pelagic larval duration, PLD）是保障热带岛屿物种定植与种群存续的关键因素，但最新研究显示，部分浮游幼体期较短的物种同样能在这类生态系统中成功繁衍。为验证短浮游幼体期在维持遗传连通性、阻止种群局地灭绝方面的潜力，我们以岩生银鲈（Kuhlia rupestris）为研究对象——这是一种广泛分布于西太平洋与印度洋的降海洄游鱼类。本研究结合分子遗传标记（13个微卫星位点与两段线粒体DNA（mitochondrial DNA, mtDNA）基因区域）与幼体扩散模拟实验，结果表明较短的浮游幼体期会限制大范围地理尺度下的遗传连通性。分子标记分析显示，短浮游幼体期并未阻碍演化进程中的遗传分化，物种形成过程业已发生或正在进行。幼体扩散模拟结果显示，珊瑚海两岸的遗传均质种群间近期连通性有限。不过，短浮游幼体期仍可在次大洋盆尺度上维持种群连通性。热带降海洄游淡水物种的保护与管理工作，需考虑到这类物种的种群连通性可能较此前预想的更为有限。