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Iteroparity is a bet-hedging strategy where individuals spread the risk of reproductive failure over time. The occurrence of iteroparity (i.e. proportion of repeat spawners in annual returns) varies among Atlantic salmon (Salmo salar) populations, yet information on its ecological importance is limited. We compiled multi-decadal time series on the spawning history composition of Atlantic salmon annual returns across ten populations of the northwest Atlantic and West Greenland mixed-stock fishery landings to: (i) describe spatio-temporal patterns of iteroparity at the continental scale; (ii) quantify the reproductive contributions of repeat spawners; and (iii) test the hypothesis that iteroparity acts as a population safeguard during periods of low recruitment through repeat spawners' contributions. Despite high variability in the representation of repeat spawners among populations and years (range: 0–24.7%; average: 5.0%), we identified broad-scale spatio-temporal shifts in iteroparity, with increases in mid-latitudinal and northern populations (from 3.1% to 7.6%) and declines in southern areas (from 4.1% to 2.7%), between the 1971–1992 and 1993–2017 periods. Our findings highlight the potential for increased prevalence of iteroparity when threats are mitigated (e.g. fishing pressure), with measurable benefits to population processes manifested by the high reproductive contributions of repeat spawners, especially in years of low maiden spawner abundance. [ABSTRACT FROM AUTHOR]

Outbreeding between segregating populations can be important from an evolutionary, conservation and economical-agricultural perspective. Whether and how outbreeding influences maternal effects in wild populations has rarely been studied, despite both the prominent maternal influence on early offspring survival and the known presence of fitness effects resulting from outbreeding in many taxa. We studied several traits during the yolk-feeding stage in multigenerational crosses between a wild and a domesticated Atlantic salmon (Salmo salar) population up to their third-generation hybrid in a common laboratory environment. Using cross-means analysis, we inferred that maternal additive outbreeding effects underlie most offspring traits but that yolk mass also underlies maternal dominant effects. As a consequence of the interplay between additive and dominant maternally controlled traits, offspring from first-generation hybrid mothers expressed an excessive proportion of residual yolk mass, relative to total mass, at the time of first feeding. Their residual yolk mass was 23-97% greater than those of other crosses and 31% more than that predicted by a purely additive model. Offspring additive, epistatic and epistatic offspring-by-maternal outbreeding effects appeared to further modify this largely maternally controlled cross-means pattern, resulting in an increase in offspring size with the percentage of domesticated alleles. Fitness implications remain elusive because of unknown phenotype-by-environment interactions. However, these results suggest how mechanistically co-adapted genetic maternal control on early offspring development can be disrupted by the effects of combining alleles from divergent populations. Complex outbreeding effects at both the maternal and offspring levels make the prediction of hybrid phenotypes difficult. [ABSTRACT FROM AUTHOR]

The incidence and magnitude of multiple paternity were estimated for a natural, unmanipulated spawning population of Atlantic salmon Salmo salar. Egg nests were surveyed in the autumn and sub-samples were excavated the following spring. Parentage data derived from microsatellite DNA revealed an unexpectedly high level of multiple paternity. Within a single redd, females may mate with as many as 16 different males, including small mature male parr and large anadromous males. Multiple paternity was most pronounced in areas of highest redd density, corresponding with increased abundances of mature male parr. In addition, there was considerable variation in success among males, although this variability did not depend upon the number of males participating in spawning. This work underscores the value of undertaking genetic studies on the mating systems of fishes in unmanipulated, natural environments. [ABSTRACT FROM AUTHOR]