Atlantic cod (Gadus morhua) ecotypes, not inversion frequencies, underlie divergence in egg buoyancy
Abstract
Life-history divergence between Atlantic cod (Gadus morhua) ecotypes in Skagerrak is maintained despite gene flow. Fjord and North Sea ecotypes differ in growth, body size, and reproductive ecology. One environmental heterogeneity in Skagerrak is salinity, as coastal habitats experience substantially lower and more variable salinities than offshore waters. Egg buoyancy is highly sensitive to salinity and represents a critical life-history trait shaping survival and recruitment. Inversions on chromosomes 2, 7, and 12 in cod are linked to salinity adaptation and might be important for egg buoyancy and survival. Here, we conducted a buoyancy test on Atlantic cod eggs, spawned from North Sea and Fjord ecotypes, using Coombs apparatus. Ecotypes and genotypes for the inversions on chromosomes 2, 7, and 12 were determined in all individuals (N = 242). We predicted that inversion genotypes and ecotypes would be associated with egg buoyancy. We found that buoyancy was variable and followed a bimodal distribution sorted by ecotype, with Fjord and North Sea individuals having mean buoyancies at neutral salinity (at 7 °C) of 27 and 31 ppt, respectively. Therefore, individuals with intermediate buoyancies might be selected against. This finding is consistent with our expectations, as Fjord ecotypes experience lower salinities compared with North Sea ecotypes. Interestingly, there was little evidence that the inversions on chromosomes 2, 7, and 12 impacted buoyancy. Overall, we provide experimental evidence of the relative contributions of ecotypic background and inversions on a key life-history trait, which helps to explain the maintained divergence among ecotypes.
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BibTeX
@article{krohman2026atlantic,
title = {{Atlantic cod (Gadus morhua) ecotypes, not inversion frequencies, underlie divergence in egg buoyancy}},
author = {Rebecca Krohman and Simon Henriksson and Esben Moland Olsen and Halvor Knutsen and Rebekah A Oomen},
journal = {Journal of Heredity},
year = {2026},
month = may,
doi = {10.1093/jhered/esag042},
url = {https://doi.org/10.1093/jhered/esag042},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Atlantic cod (Gadus morhua) ecotypes, not inversion frequencies, underlie divergence in egg buoyancy
AU - Rebecca Krohman
AU - Simon Henriksson
AU - Esben Moland Olsen
AU - Halvor Knutsen
AU - Rebekah A Oomen
PY - 2026
DA - 2026/05/22
JO - Journal of Heredity
DO - 10.1093/jhered/esag042
UR - https://doi.org/10.1093/jhered/esag042
AB - Life-history divergence between Atlantic cod (Gadus morhua) ecotypes in Skagerrak is maintained despite gene flow. Fjord and North Sea ecotypes differ in growth, body size, and reproductive ecology. One environmental heterogeneity in Skagerrak is salinity, as coastal habitats experience substantially lower and more variable salinities than offshore waters. Egg buoyancy is highly sensitive to salinity and represents a critical life-history trait shaping survival and recruitment. Inversions on chromosomes 2, 7, and 12 in cod are linked to salinity adaptation and might be important for egg buoyancy and survival. Here, we conducted a buoyancy test on Atlantic cod eggs, spawned from North Sea and Fjord ecotypes, using Coombs apparatus. Ecotypes and genotypes for the inversions on chromosomes 2, 7, and 12 were determined in all individuals (N = 242). We predicted that inversion genotypes and ecotypes would be associated with egg buoyancy. We found that buoyancy was variable and followed a bimodal distribution sorted by ecotype, with Fjord and North Sea individuals having mean buoyancies at neutral salinity (at 7 °C) of 27 and 31 ppt, respectively. Therefore, individuals with intermediate buoyancies might be selected against. This finding is consistent with our expectations, as Fjord ecotypes experience lower salinities compared with North Sea ecotypes. Interestingly, there was little evidence that the inversions on chromosomes 2, 7, and 12 impacted buoyancy. Overall, we provide experimental evidence of the relative contributions of ecotypic background and inversions on a key life-history trait, which helps to explain the maintained divergence among ecotypes.
SN - 0022-1503
SN - 1465-7333
ER -