Convergent latitudinal erosion of circadian systems in a rapidly diversifying order of fishes
- 1Department of Biology and Biochemistry, University of Houston, Houston, Texas, United States of America
- 2Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts, United States of America
Abstract
Biological clocks allow organisms to anticipate cyclical environmental changes, yet in high-latitude or deep-sea habitats, the diel cues that entrain these rhythms are often seasonally diminished or absent. Fishes of the order Perciformes have rapidly diversified across these arrhythmic ecosystems, raising the question of whether changes to circadian rhythms and biological clock genetic architecture are a component of their evolutionary success. Here, we used a comparative genomic approach to investigate patterns of core biological clock gene loss across 96 perciform and five outgroup species. We found widespread and lineage-specific loss in core clock genes, particularly in the convergently evolving polar and deep-sea suborders Notothenioidei and Cottoidei. This trend of clock gene loss was significantly amplified with higher-latitude species. To determine if these genomic signatures reflect a functional loss of rhythmicity, we performed metabolic phenotyping on three notothenioid species. We found a consistent lack of circadian metabolic oscillations during the late austral fall across all notothenioids, including the sub-Antarctic sister lineage to the cryonotothenioid adaptive radiation, Eleginops maclovinus. Experimental data across Perciformes, combined with suborder-wide patterns of gene loss, suggest that a release from circadian constraints occurred early in their diversification, potentially facilitating the repeated expansion of these fishes into polar and deep-sea habitats. Author summary: Most animals rely on internal biological clocks to align their behavior and metabolism with predictable environmental cycles. Disruption of these clocks is linked to disease across many species. However, in extreme environments such as the deep sea or polar oceans, the common environmental cues that biological clocks entrain on can be irregular or absent for extended periods. Perciform fishes have repeatedly colonized and diversified in these challenging habitats. What has happened to their biological clocks? By analyzing genome assemblies from 96 perciform species, we identified a widespread and repeated loss of core circadian “clock” genes within this clade. This genetic decay was most pronounced in high-latitude polar species. To assess whether these genomic changes correspond to altered circadian biology, we measured metabolic rates in Antarctic and sub-Antarctic fishes. Both groups lacked detectable metabolic rhythms, including species with no apparent loss of clock genes. Together with data from other perciform species, these findings suggest that some lineages can flexibly abandon circadian rhythms, and that this may have occurred early within specific perciform clades. This flexibility could help to facilitate their success in environments with highly irregular seasonal cycles, where relaxed selection pressures may further drive the degradation of circadian clock components.
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BibTeX
@article{wright2026convergent,
title = {{Convergent latitudinal erosion of circadian systems in a rapidly diversifying order of fishes}},
author = {Daniel B. Wright and Yangfan Zhang and Jacob M. Daane},
journal = {PLOS Genetics},
year = {2026},
month = aug,
doi = {10.1371/journal.pgen.1012287},
url = {https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1012287},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Convergent latitudinal erosion of circadian systems in a rapidly diversifying order of fishes
AU - Daniel B. Wright
AU - Yangfan Zhang
AU - Jacob M. Daane
PY - 2026
DA - 2026/08/31
JO - PLOS Genetics
DO - 10.1371/journal.pgen.1012287
UR - https://journals.plos.org/plosgenetics/article?id=10.1371/journal.pgen.1012287
AB - Biological clocks allow organisms to anticipate cyclical environmental changes, yet in high-latitude or deep-sea habitats, the diel cues that entrain these rhythms are often seasonally diminished or absent. Fishes of the order Perciformes have rapidly diversified across these arrhythmic ecosystems, raising the question of whether changes to circadian rhythms and biological clock genetic architecture are a component of their evolutionary success. Here, we used a comparative genomic approach to investigate patterns of core biological clock gene loss across 96 perciform and five outgroup species. We found widespread and lineage-specific loss in core clock genes, particularly in the convergently evolving polar and deep-sea suborders Notothenioidei and Cottoidei. This trend of clock gene loss was significantly amplified with higher-latitude species. To determine if these genomic signatures reflect a functional loss of rhythmicity, we performed metabolic phenotyping on three notothenioid species. We found a consistent lack of circadian metabolic oscillations during the late austral fall across all notothenioids, including the sub-Antarctic sister lineage to the cryonotothenioid adaptive radiation, Eleginops maclovinus. Experimental data across Perciformes, combined with suborder-wide patterns of gene loss, suggest that a release from circadian constraints occurred early in their diversification, potentially facilitating the repeated expansion of these fishes into polar and deep-sea habitats. Author summary: Most animals rely on internal biological clocks to align their behavior and metabolism with predictable environmental cycles. Disruption of these clocks is linked to disease across many species. However, in extreme environments such as the deep sea or polar oceans, the common environmental cues that biological clocks entrain on can be irregular or absent for extended periods. Perciform fishes have repeatedly colonized and diversified in these challenging habitats. What has happened to their biological clocks? By analyzing genome assemblies from 96 perciform species, we identified a widespread and repeated loss of core circadian “clock” genes within this clade. This genetic decay was most pronounced in high-latitude polar species. To assess whether these genomic changes correspond to altered circadian biology, we measured metabolic rates in Antarctic and sub-Antarctic fishes. Both groups lacked detectable metabolic rhythms, including species with no apparent loss of clock genes. Together with data from other perciform species, these findings suggest that some lineages can flexibly abandon circadian rhythms, and that this may have occurred early within specific perciform clades. This flexibility could help to facilitate their success in environments with highly irregular seasonal cycles, where relaxed selection pressures may further drive the degradation of circadian clock components.
SN - 1553-7404
ER -