The “dilution effect” concept in disease ecology offers the intriguing possibility that clever manipulation of less competent hosts could reduce disease prevalence in populations of more competent hosts. The basic concept is straightforward: host species vary in suitability (competence) for parasites, and disease transmission decreases when there are more incompetent hosts interacting with vectors or removing free‐living stage...

Four tributaries of Lake St‐Jean (Québec, Canada) are used for spawning and juvenile habitat by land‐locked Atlantic salmon. Spawning runs have drastically declined since the mid‐1980s, and consequently, a supportive‐breeding programme was undertaken in 1990. In this study, we analysed seven microsatellite loci and mtDNA, and empirically estimated effective population sizes to test the hypotheses that (i) fish spawning in diff...