Understanding age-specific dispersal in fishes through hydrodynamic modelling, genetic simulations and microsatellite DNA analysis

Many marine species have vastly different capacities for dispersal during larval, juvenile and adult life stages, and this has the potential to complicate the identification of population boundaries and the implementation of effective management strategies such as marine protected areas. Genetic studies of population structure and dispersal rarely disentangle these differences and usually provide only lifetime-averaged information that can be considered by managers. We address this limitation by combining age-specific autocorrelation analysis of microsatellite genotypes, hydrodynamic modelling and genetic simulations to reveal changes in the extent of dispersal during the lifetime of a marine fish. We focus on an exploited coral reef species, Lethrinus nebulosus, which has a circum-tropical distribution and is a key component of a multispecies fishery in northwestern Australia. Conventional population genetic analyses revealed extensive gene flow in this species over vast distances (up to 1500 km). Yet, when realistic adult dispersal behaviours were modelled, they could not account for these observations, implying adult dispersal does not dominate gene flow. Instead, hydrodynamic modelling showed that larval L. nebulosus are likely to be transported hundreds of kilometres, easily accounting for the observed gene flow. Despite the vast scale of larval transport, juvenile L. nebulosus exhibited fine-scale genetic autocorrelation, which declined with age. This implies both larval cohesion and extremely limited juvenile dispersal prior to maturity. The multidisciplinary approach adopted in this study provides a uniquely comprehensive insight into spatial processes in this marine fish.

许多海洋物种在幼体、稚体与成体不同生命阶段的扩散能力差异悬殊，这一特性可能会为种群边界界定以及海洋保护区（marine protected areas）等高效管理策略的实施平添复杂挑战。现有针对种群结构与扩散模式的遗传学研究，极少能够厘清这类阶段特异性的扩散差异，通常仅能提供终身平均的扩散数据，供管理者参考。为解决这一研究局限，本研究结合微卫星基因型（microsatellite genotypes）的年龄特异性自相关分析、水动力模拟（hydrodynamic modelling）与遗传模拟，以揭示某海洋鱼类整个生命周期内扩散范围的动态变化。本研究聚焦于一种受开发利用的珊瑚礁物种——星斑裸颊鲷（Lethrinus nebulosus），该物种呈环热带分布，是澳大利亚西北部多物种渔业的关键组成部分。常规种群遗传学分析显示，该物种存在大范围的基因交流，最远可达1500千米。然而，当基于真实成体扩散行为开展模拟时，却无法解释上述观测结果，这表明成体扩散并非该物种基因交流的主导因素。与之相反，水动力模拟结果显示，星斑裸颊鲷的幼体可被洋流输送数百千米，这足以解释观测到的基因交流现象。尽管幼体扩散范围极广，但稚体星斑裸颊鲷却表现出精细尺度的遗传自相关现象，且该相关性随年龄增长而减弱。这一结果意味着，幼体存在聚集行为，且稚体在性成熟前的扩散能力极为有限。本研究采用的多学科研究范式，为该海洋鱼类的空间生态过程提供了前所未有的全面认知。