Data from: Diving into divergence: differentiation in swimming performances, physiology and gene expression between locally-adapted sympatric cichlid fishes

Sympatric speciation occurs without strict vicariance and is thought to
often be driven by ecological specialization of subpopulations 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 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 and sprinting swimming abilities - performances
particularly relevant to their respective lifestyles. Furthermore, we
investigated species differences in oxygen consumption 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 A. astorquii, while
sprinting was not different, suggesting that their distinct morphologies
affect swimming performance. Increased cruising ability in A. zaliosus was
however 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 likely resulted in morphological and
physiological trade-offs that contributed to the rapid establishment and
maintenance of divergence with gene flow.