Micro-scale distribution of brown trout: an opportunity for kin selection?

Fourteen microsatellite loci were used to analyse the degree of relatedness between and within cohorts of stream-living brown trout (Salmo trutta L.). Differences in degree of relatedness were found between cohorts with mature and older having the highest intracohort relatedness. The higher genetic relatedness among the mature and older trout is interpreted as indications of clustering of related mature and older trout prior to spawning in the vicinity of spawning grounds. Young-of-the-year trout showed a lower degree of association with related trout of the same cohort than did mature and older trout. It is argued that the clustering of mature and older trout may facilitate kin selection and that the low degree of association among related young-of-the-year trout could be explained by juvenile fish avoiding competition for territories with related individuals.