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Data from: Evolutionary relationships between landlocked and anadromous Atlantic salmon populations in the North Shore region of the Gulf of St. Lawrence

Carbonneau, Alexandre12; Tremblay, Jean-Pierre13; Normandeau, Eric14; Ferchaud, Anne-Laure5; Bernatchez, Louis16; April, Julien7

Published May 19, 2026 on Dryad. https://doi.org/10.5061/dryad.v6wwpzh7v

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May 19, 2026 version files 1.53 MB

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Abstract

Although Atlantic salmon (Salmo salar) are typically anadromous, some complete their life cycle in freshwater. A widely documented scenario suggests that this resident tactic arose independently in each river via isolation from anadromous Atlantic salmon populations after the last ice age. Yet, the origin of residency remains poorly studied in the North Shore region of the Gulf of St. Lawrence (Canada). To address this, we genotyped 189 resident and 196 anadromous individuals from five watersheds at 43 microsatellite markers. We found marked genetic differences between tactics within rivers, likely resulting from different levels of gene flow associated with geographic isolation, suggesting that residents may not have always been isolated as expected from this tactic. Moreover, we observed greater genetic differentiation between tactics within rivers than between residents from different rivers, supporting a shared ancestral source, likely shaped by two colonization events or ancestral intracontinental gene flow. These findings bring nuances and complexity to the views on the origin of residency in Atlantic salmon, and are valuable for guiding conservation practices.