Sympatric speciation occurs without geographical barriers and is thought to often be driven by ecological specialization of individuals that eventually diverge genetically and phenotypically. Distinct morphologies between sympatric populations occupying different niches have been interpreted as such differentiating adaptive phenotypes, yet differences in performance and thus likely adaptiveness between them were rarely tested. Here, we investigated if divergent body shapes of two sympatric crater lake cichlid species from Nicaragua, one being a shore-associated (benthic) species while the other prefers the open water zones (limnetic), affect cruising (Ucrit ) and sprinting (Usprint ) swimming abilities - performances particularly relevant to their respective lifestyles. Furthermore, we investigated species differences in oxygen consumption (MO2 ) across different swimming speeds and compare gene expression in gills and white muscle at rest and during exercise. We found a superior cruising ability in the limnetic Amphilophus zaliosus compared to the benthic Amphilophus astorquii, while sprinting was not different, suggesting that their distinct morphologies affect swimming performance. Increased cruising swimming ability in A. zaliosus was linked to a higher oxygen demand during activity (but not rest), indicating different metabolic rates during exercise - a hypothesis supported by coinciding gene expression patterns of gill transcriptomes. We identified differentially expressed genes linked to swimming physiology, regulation of swimming behaviour and oxygen intake. A combination of physiological and morphological differences may thus underlie adaptations to these species' distinct niches. This complex ecological specialization probably resulted in morphological and physiological trade-offs that contributed to the rapid establishment and maintenance of divergence with gene flow.

中文翻译：

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分为分歧：局部适应的同伴慈鲷丽鱼在游泳表现，生理和基因表达上的差异。

同胞形态的形成没有地理障碍，并且通常被认为是个体的生态专业化驱动的，这些个体最终在基因和表型上有所不同。占据着不同生态位的同胞人口之间的独特形态已被解释为这种差异化的适应性表型，但性能差异以及因此可能的适应性很少受到检验。在这里，我们研究了来自尼加拉瓜的两种同伴火山口湖丽鱼科动物物种的不同体形，其中一种是与海岸相关的（底栖性）物种，而另一种偏爱开放水域（边缘），会影响巡航（Ucrit）和冲刺（Usprint）游泳能力-与他们各自的生活方式特别相关的表演。此外，我们调查了不同游泳速度下氧气消耗（MO2）的物种差异，并比较了休息和运动过程中腮和白肌的基因表达。我们发现，与底栖的Amphilophus astorquii相比，在边缘的Amphilophus zaliosus中具有更好的巡航能力，而短跑也没有不同，表明它们的独特形态会影响游泳性能。zaliosus游动游泳能力的提高与活动（而非休息）期间较高的需氧量有关，表明运动期间的新陈代谢速率不同-转录组的基因表达模式重合支持的假说。我们鉴定了与游泳生理，游泳行为和摄氧量调节相关的差异表达基因。因此，生理和形态差异的结合可能是适应这些物种不同生态位的基础。这种复杂的生态专业化可能导致形态和生理上的折衷，这有助于快速建立和维持与基因流的差异。