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Contrasting patterns of population structure and breeding dispersal exhibited between sister taxa in a small river system: new insights from population genetics and sibling analysis on Atlantic salmon (Salmo salar) and brown trout (Salmo trutta)
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DOI：10.1186/s40462-026-00678-2.png)
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Abstract
En 中文
The movement of individuals from one breeding site to another (i.e. breeding dispersal) can have important consequences for fitness and population genetics. Whilst closely related species are expected to be phenotypically similar in many respects, they can nevertheless exhibit important differences in behaviour and ecology that can have repercussions for population structure. Here we use genetic information (microsatellite data) collected on two sister species – Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) – that overlap in their spawning and freshwater rearing habitats within a small (ca. 100 km2) catchment in western Ireland. We first explore differences in the spatial extent of within-season breeding dispersal. To do so, we combine sibship reconstruction analysis with distances between siblings’ sampling locations and introduce the ratio of half-sibling to full-sibling pair distances as a novel proxy measure for breeding dispersal (IBD). We then use a range of population genetic analyses to assess the genetic structure of both species. The IBD value was 1.8 times higher in Atlantic salmon than in brown trout, and distances between breeding sites were much greater in salmon (typically within 4 kilometres) than in trout (typically within 600 metres). No genetic structure was detected in Atlantic salmon. In contrast, fine-scale genetic structuring was observed in the brown trout data with at least two genetic clusters being detected, confirming similar patterns reported in previous studies. Our results support the hypothesis that Atlantic salmon engage in more spatially extensive breeding dispersal behaviour than brown trout, which in turn may explain why trout but not salmon exhibit population genetic structure in this system. Collectively, our findings showcase how the same genetic data can be used to gain complementary insights into the movement behaviours of individuals and the genetic structuring of populations, with implications for conservation management. They furthermore emphasise a hitherto overlooked role for intra-seasonal breeding dispersal in shaping spatial genetic connectivity in polygamous species.
Keywords:
Breeding dispersal
Genetic structure
Atlantic salmon
Brown trout
Gene flow
Sibship reconstruction
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