Data from: Local adaptation despite high gene flow in the waterfall-climbing Hawaiian goby, Sicyopterus stimpsoni.

Environmental heterogeneity can promote the emergence of locally adapted phenotypes among subpopulations of a species, whereas gene flow can result in phenotypic and genotypic homogenization. For organisms like amphidromous fishes that change habitats during their life history, the balance between selection and migration can shift through ontogeny, making the likelihood of local adaptation difficult to predict. In Hawaiian waterfall-climbing gobies, it has been hypothesized that larval mixing during oceanic dispersal counters local adaptation to contrasting topographic features of streams, like slope gradient, that can select for predator avoidance or climbing ability in juvenile recruits. To test this hypothesis, we used morphological traits and neutral genetic markers to compare phenotypic and genotypic distributions in recruiting juveniles and adult subpopulations of the waterfall-climbing amphidromous goby, Sicyopterus stimpsoni, from the islands of Hawai'i and Kaua'i. We found that body shape is significantly different between adult subpopulations from streams with contrasting slopes and that trait divergence in recruiting juveniles tracked stream topography more so than morphological measures of adult subpopulation differentiation. Although no evidence of population genetic differentiation was observed among adult subpopulations, we observed low but significant levels of spatially and temporally variable genetic differentiation among juvenile cohorts, which correlated with morphological divergence. Such a pattern of genetic differentiation is consistent with chaotic genetic patchiness arising from variable sources of recruits to different streams. Thus, at least in S. stimpsoni, the combination of variation in settlement cohorts in space and time coupled with strong postsettlement selection on juveniles as they migrate upstream to adult habitats provides the opportunity for morphological adaptation to local stream environments despite high gene flow.

环境异质性可推动物种种群亚种群产生局部适应性表型，而基因流则会导致表型与基因型的均质化。对于如两域洄游鱼类（amphidromous fishes）这类在生活史中会改变栖息环境的生物而言，选择压力与个体迁移之间的平衡会随个体发育发生偏移，进而使得局部适应性的发生概率难以预测。
针对夏威夷的攀瀑鰕虎鱼（waterfall-climbing gobies）类群，有假说提出：海洋扩散阶段的幼体混合过程，会抵消种群对溪流不同地形特征（如坡度）的局部适应性——这类地形特征会对幼体补充个体的避敌能力或攀附能力产生定向选择。为验证该假说，本研究以夏威夷岛与考艾岛的斯氏攀瀑鰕虎鱼（Sicyopterus stimpsoni）为研究对象，利用形态性状与中性遗传标记，对比分析其幼体补充个体与成年亚种群的表型及基因型分布格局。
研究发现：来自坡度差异显著的溪流的成年亚种群，其体型存在显著差异；且幼体补充个体的性状分歧与溪流地形的关联程度，显著高于成年亚种群形态分化所反映的地形关联度。尽管未在成年亚种群间检测到种群遗传分化，但我们在幼体同龄群中发现了程度较低但显著的、随空间与时间变化的遗传分化，且该分化与性状分歧存在相关性。这种遗传分化模式，与不同溪流的幼体补充来源异质性所导致的混沌遗传斑块性（chaotic genetic patchiness）相一致。因此，至少在斯氏攀瀑鰕虎鱼（S. stimpsoni）中，幼体定居群落在空间与时间上的异质性，加上幼体洄游至成年栖息环境过程中经历的强烈定居后选择压力，即便存在高强度基因流，仍为种群适应溪流局部环境的形态性状演化提供了可能。