Time spent in distinct life history stages has sex-specific effects on reproductive fitness in wild Atlantic salmon.

Kenyon B Mobley,Mikko Ellmén,Hanna Granroth‐Wilding,Jaakko Erkinaro,Panu Orell,Craig R Primmer

doi:10.1111/mec.15390

Abstract

In species with complex life cycles, life history theory predicts that fitness is affected by conditions encountered in previous life history stages. Here, we use a 4-year pedigree to investigate if time spent in two distinct life history stages has sex-specific reproductive fitness consequences in anadromous Atlantic salmon (Salmo salar). We determined the amount of years spent in fresh water as juveniles (freshwater age, FW, measured in years), and years spent in the marine environment as adults (sea age, SW, measured in sea winters) on 264 sexually mature adults collected on a river spawning ground. We then estimated reproductive fitness as the number of offspring (reproductive success) and the number of mates (mating success) using genetic parentage analysis (>5,000 offspring). Sea age is significantly and positively correlated with reproductive and mating success of both sexes whereby older and larger individuals gained the highest reproductive fitness benefits (females: 62.2% increase in offspring/SW and 34.8% increase in mate number/SW; males: 201.9% offspring/SW and 60.3% mates/SW). Younger freshwater age was significantly related to older sea age and thus increased reproductive fitness, but only among females (females: -33.9% offspring/FW and -32.4% mates/FW). This result implies that females can obtain higher reproductive fitness by transitioning to the marine environment earlier. In contrast, male mating and reproductive success was unaffected by freshwater age and more males returned at a younger age than females despite the reproductive fitness advantage of later sea age maturation. Our results show that the timing of transitions between juvenile and adult phases has a sex-specific consequence on female reproductive fitness, demonstrating a life history trade-off between maturation and reproduction in wild Atlantic salmon.

Highlights

Many organisms have complex life cycles and undergo discrete life history stages in two or more distinct habitats (Moran, 1994)
Trade-offs between the duration of time spent at specific life history stages, such as the timing to switch to a new feeding habitat or when to achieve sexual maturity, are hypothesized (Roff, 1993; Stearns, 1992)
We investigated sex-specific trade-offs in reproductive fitness and the time spent during two life history stages of anadromous Atlantic salmon

Summary

Introduction

Many organisms have complex life cycles and undergo discrete life history stages in two or more distinct habitats (Moran, 1994) Transitions between these life history stages are typically accompanied by major shifts in physiology, behaviour and ecology, making them inherently risky and energetically expensive. Trade-offs between the duration of time spent at specific life history stages, such as the timing to switch to a new feeding habitat or when to achieve sexual maturity, are hypothesized (Roff, 1993; Stearns, 1992). Investigating how trade-offs in the duration of time spent in specific life history stages shape reproductive fitness between the sexes may help to understand the evolutionary causes and consequences of sexual conflict

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