Cecilia Helmerson

• Han, Kwi Young; Brennan, Reid S.; Monk, Christopher T.; Jentoft, Sissel; Helmerson, Cecilia & Dierking, Jan [Vis alle 13 forfattere av denne artikkelen] (2025). Genomic evidence for fisheries-induced evolution in Eastern Baltic cod. Science Advances. 11(26). doi: 10.1126/sciadv.adr9889. Fulltekst i vitenarkiv Vis sammendrag

  Overfishing is one human-driven perturbation driving major evolutionary pressure on marine populations. Fishing is often highly selective for particular traits and elicits marked phenotypic changes, while the evolutionary basis of such trait change remains unresolved. Here, we used a unique time series of the overexploited Eastern Baltic cod ( Gadus morhua ) to investigate growth trends during 25 years of heavy fishing along with hypothesized genetic changes at the full genome level. A growth analysis demonstrated a 48% decrease in asymptotic body length from 1996 to 2019 while a genome-wide association analysis revealed outlier loci and gene candidates linked to growth performance. The contributing loci showed signals of directional selection with high autocovariance of allele frequency change and significant overlap with regions of high genetic differentiation. Our findings suggest a genomic basis of fisheries-driven growth impairment and underscore implications for conservation policy regarding the adaptive potential of marine populations.

• Helmerson, Cecilia; Durant, Joël; Hoff, Siv Nam Khang; Brieuc, Marine Servane Ono; Berg, Paul Ragnar & Jorde, Per Erik [Vis alle 14 forfattere av denne artikkelen] (2025). A century of anthropogenic perturbations impact genomic signatures of the iconic migratory Atlantic cod. Science Advances. 11(31). doi: 10.1126/sciadv.adp3342. Fulltekst i vitenarkiv Vis sammendrag

  Anthropogenic stressors have led to marked ecosystem perturbations, including population declines and shifts in habitat range for key marine fish species. Understanding how these changes affect genome-wide characteristics, causing long-term evolutionary responses, is still in its infancy. Genome-wide retrospective assessment of the iconic migratory Atlantic cod ( Gadus morhua ) from the Barents Sea, unraveled varying degree of admixture with the nonmigratory coastal ecotype throughout the 20th century, and intriguingly more intensified during recent decades. These genomic changes were supported by an increased number of individuals displaying the heterozygous state of the chromosomal inversion coupled to migratory behavior in Atlantic cod. Ecological models and genome-wide scans identified that some of the observed frequency shifts, coupled to neural development, metabolic, and growth regulation, covaried with intensified fisheries, reduced generation time, and ocean warming. Our results demonstrate how anthropogenic perturbations impact the dynamics between two well-known ecotypes of Atlantic cod and thus, their genomic signatures, with potential implications for future management programs.

• Helmerson, Cecilia; Weist, Peggy; Brieuc, Marine Servane Ono; Maurstad, Marius Filomeno; Schade, Franziska Maria & Dierking, Jan [Vis alle 14 forfattere av denne artikkelen] (2023). Evidence of hybridization between genetically distinct Baltic cod stocks during peak population abundance(s). Evolutionary Applications. 16(7), s. 1359–1376. doi: 10.1111/eva.13575. Fulltekst i vitenarkiv Vis sammendrag

  Range expansions can lead to increased contact of divergent populations, thus increasing the potential of hybridization events. Whether viable hybrids are produced will most likely depend on the level of genomic divergence and associated genomic incompatibilities between the different entities as well as environmental conditions. By taking advantage of historical Baltic cod (Gadus morhua) otolith samples combined with genotyping and whole genome sequencing, we here investigate the genetic impact of the increased spawning stock biomass of the eastern Baltic cod stock in the mid 1980s. The eastern Baltic cod is genetically highly differentiated from the adjacent western Baltic cod and locally adapted to the brackish environmental conditions in the deeper Eastern basins of the Baltic Sea unsuitable for its marine counterparts. Our genotyping results show an increased proportion of eastern Baltic cod in western Baltic areas (Mecklenburg Bay and Arkona Basin)—indicative of a range expansion westwards—during the peak population abundance in the 1980s. Additionally, we detect high frequencies of potential hybrids (including F1, F2 and backcrosses), verified by whole genome sequencing data for a subset of individuals. Analysis of mitochondrial genomes further indicates directional gene flow from eastern Baltic cod males to western Baltic cod females. Our findings unravel that increased overlap in distribution can promote hybridization between highly divergent populations and that the hybrids can be viable and survive under specific and favourable environmental conditions. However, the observed hybridization had seemingly no long-lasting impact on the continuous separation and genetic differentiation between the unique Baltic cod stocks.

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• Kersten, Oliver Sven; Garcia, Lourdes Martinez; Pulido, Angélica; Ferrari, Giada; Baalsrud, Helle Tessand & Helmerson, Cecilia [Vis alle 18 forfattere av denne artikkelen] (2024). Long-term population dynamics of Atlantic cod revealed by Ancient DNA and Genomics. Fulltekst i vitenarkiv
• Helmerson, Cecilia Jenny Margareta Thomas (2017). Through time and climate change - SNP variation in Northeast arctic cod throughout and beyond the 20th Century. Fulltekst i vitenarkiv
• Helmerson, Cecilia Jenny Margareta Thomas (2016). Genomic analysis of 20th Century Northeast Arctic cod Gadus morhua (L.). Fulltekst i vitenarkiv

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