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风险。其栖息地会因淡水径流波动与侵蚀作用而呈现临时性特征。更为严峻的是，人类活动对这些淡水生态系统的影响强度极高。其中多数物种为两溯洄游（amphidromous）或降海洄游（catadromous）类群——即其生命周期包含海洋幼体阶段，这一特性可帮助它们抵御诸多上述威胁。
此前学界曾认为，较长的海洋浮游幼体期（pelagic larval duration, PLD）是热带岛屿淡水物种成功定殖并持续存续的关键条件，但最新研究发现，部分拥有较短PLD的物种同样可在这类生态系统中繁盛生存。
为验证较短PLD在维持遗传连通性与防止局地灭绝方面的潜力，我们以岩原银汉鱼（Kuhlia rupestris）为研究对象——这是一种广泛分布于西太平洋与印度洋海域的降海洄游鱼类。我们结合分子遗传标记（13个微卫星位点与线粒体DNA（mtDNA）的两个基因区域）与幼体扩散模拟分析，证实较短的PLD会限制大范围地理区间内的遗传连通性。
分子标记结果显示，较短的PLD并未阻碍物种在演化历程中产生遗传分化，物种形成过程已然发生或正在进行中。幼体扩散模拟结果表明，珊瑚海区域内遗传同质化种群间的近期连通性十分有限。但值得注意的是，较短的PLD仍可在次洋盆尺度上维持种群连通性。
热带洄游性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比此前学界预期的更为有限。