Biology subjects

Krohman, R.

Publications and source records attributed to Krohman, R..

2 recordsLinked to original sources

bioRxiv2025

Atlantic cod (Gadus morhua) ecotypes, not inversion frequencies, underlie divergence in egg buoyancy distribution

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. Genotypes for the inversions on chromosomes 2, 7, and 12 and ecotype were determined in all individuals (N=242). We hypothesized that individuals with different inversion genotypes and ecotypes would have divergent buoyancies. 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{degrees}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 to 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.

evolutionary biology↗

bioRxiv2025

Chromosomal inversions assist acute salinity and temperature adaptation in Atlantic cod (Gadus Morhua) eggs

Chromosomal inversions, on chromosomes 2, 7, and 12 in Atlantic cod (Gadus morhua), have been consistently associated with environmental gradients, particularly salinity and temperature, across the species natural range. While these correlations suggest a role for local adaptation, the underlying selective mechanisms remain unresolved. Critically, few experiments have yet tested the fitness consequences of these inversions under controlled environmental conditions. Such work is essential to establish causality. Here, we conducted an acute stressor experiment with ten treatments of combined temperature and low salinity stress. Cod eggs (N = 1265) were placed into each treatment for 24 hours, and the number of individuals that floated initially and finally was counted. The ability of an egg to float is directly related to its survival, as sunk individuals cannot survive, and individuals lose buoyancy after they die. Inversion genotypes for the inversions on chromosomes 2, 7, and 12 were determined for individuals from the T03-S25, T07-S25, T16-S25, and T16-S35 treatments. We found that sinking increased with temperature and that more individuals sank in 25 ppt than in 35 ppt after 24 hours. Interestingly, some individuals in the 25 ppt treatments recovered (sank initially but floated finally) after 24 hours. We found evidence that the inversions on chromosomes 2 and 12 might assist with temperature and salinity adaptation, respectively, in cod eggs, while the inversion on chromosome 7 did not affect floating. Our results can inform the management and conservation of this endangered species. Summary statementWe show that chromosomal inversions found in Atlantic cod help with adaptation to short-term temperature and salinity stress at the egg stage.

evolutionary biology↗