Data from: Juvenile divergence in adaptive traits among seven sympatric fish eco-morphs arises before moving to different lacustrine habitats

Identifying the mechanisms initiating sympatric diversification in vertebrates has remained a conceptual challenge. Here we analyze an assemblage of sympatric charr (Salvelinus malma) morphs from landlocked Lake Kronotskoe basin as a model to uncover the divergence pathways in freshwater fishes during the early life history stages. All morphs have distinct developmental biology, but a similar developmental rate retardation compared to the ancestor. Our study reveals that adult morphological differences, which acquire functionality at maturation, originate in the early juvenile stages due to heterochrony in skeletogenesis and allometric changes triggered by variation in metabolic activity. The craniofacial differences among the morphs result from asynchronous development of several skeletal modules. The accelerated ossification of teeth-armed bones occurs in predatory feeding morphs, while cranial cover ossification is promoted in benthivorous morphs. These contrasting growth patterns have led to seven phenotypes that span a range far beyond the ancestral variability. The most distinct morphs are a riverine-spawning, epilimnetic predator and a lacustrine-spawning, profundal benthic feeder. Taken together, we argue that the adaptive morphological differentiation in these sympatric freshwater fishes is driven by diverging patterns in ossification rate and metabolic activity against a background of uneven somatic growth. This divergence is primarily associated with basic environmental differences on the nursery grounds that might be unrelated to resource use. This non-heritable phenotype divergence is then exposed to natural selection that could result in further adaptive genetic changes.

阐明驱动脊椎动物发生同域分化（sympatric diversification）的核心机制，长期以来都是学界面临的一项概念性难题。本研究以封闭型克罗诺茨基湖（Lake Kronotskoe）流域内的一群同域分布花羔红点鲑（Salvelinus malma）形态群为研究模型，旨在揭示淡水鱼类早期生活史阶段的分化路径。所有形态群均具备独特的发育生物学特征，且相较于其祖先类群，均表现出相似的发育速率迟滞现象。本研究发现：成体形态差异——这类差异在个体成熟后才会获得完整功能——起源于幼体早期阶段，其成因是骨骼发生过程中的异时发育（heterochrony），以及代谢活性差异所引发的异速生长变化。各形态群间的颅面差异，源自多个骨骼模块的异步发育。具齿骨骼的骨化加速现象出现在掠食性摄食形态群中，而颅盖骨化则在底食性（benthivorous）形态群中更为显著。这种差异化的生长模式最终造就了7种表型，其性状分布范围远超祖先类群的变异区间。其中差异最为显著的两个形态群分别为：溯河产卵的湖上层（epilimnetic）掠食者，以及湖内产卵的深底栖（profundal）食者。综合来看，本研究认为：这类同域分布淡水鱼类的适应性形态分化，是在不均衡躯体生长的背景下，由骨化速率与代谢活性的分化模式共同驱动的。这种分化最初主要与育幼场的基础环境差异相关，而这类差异可能与资源利用并无关联。这种非遗传性的表型分化随后会受到自然选择的作用，进而可能引发进一步的适应性遗传变异。