Maturation in Atlantic salmon (Salmo salar, Salmonidae): a synthesis of ecological, genetic, and molecular processes

Kenyon B Mobley,Andrew House,Jacqueline Moustakas-Verho,Tutku Aykanat,Andrés Salgado,Jukka-Pekka Verta,Marion Sinclair-Waters,Johanna Kurko,Antti Miettinen,Yann Czorlich,Craig R Primmer

doi:10.1007/s11160-021-09656-w

Abstract

Over the past decades, Atlantic salmon (Salmo salar, Salmonidae) has emerged as a model system for sexual maturation research, owing to the high diversity of life history strategies, knowledge of trait genetic architecture, and their high economic value. The aim of this synthesis is to summarize the current state of knowledge concerning maturation in Atlantic salmon, outline knowledge gaps, and provide a roadmap for future work. We summarize the current state of knowledge: 1) maturation in Atlantic salmon takes place over the entire life cycle, starting as early as embryo development, 2) variation in the timing of maturation promotes diversity in life history strategies, 3) ecological and genetic factors influence maturation, 4) maturation processes are sex-specific and may have fitness consequences for each sex, 5) genomic studies have identified large-effect loci that influence maturation, 6) the brain-pituitary–gonadal axis regulates molecular and physiological processes of maturation, 7) maturation is a key component of fisheries, aquaculture, conservation, and management, and 8) climate change, fishing pressure, and other anthropogenic stressors likely have major effects on salmon maturation. In the future, maturation research should focus on a broader diversity of life history stages, including early embryonic development, the marine phase and return migration. We recommend studies combining ecological and genetic approaches will help disentangle the relative contributions of effects in different life history stages to maturation. Functional validation of large-effect loci should reveal how these genes influence maturation. Finally, continued research in maturation will improve our predictions concerning how salmon may adapt to fisheries, climate change, and other future challenges.

Highlights

Sexual maturation is a key process necessary for reproduction
The ever-increasing research on Atlantic salmon maturation consolidates the species as a tractable vertebrate model system for studying various aspects of maturation (Chakradhar 2018)
Our goal for this synthesis is to provide a current overview of research on maturation in Atlantic salmon with the express purpose to identify major themes where information is lacking and highlight potential areas for future research

Summary

Introduction

Sexual maturation (hereto forward maturation) is a key process necessary for reproduction. Atlantic salmon exhibit high diversity in life history strategies due, in part, to considerable variation in the timing of maturation and the number of reproductive episodes (iteroparity vs semelparity) and the potential for males to participate in reproduction at the parr stage (Einum et al 2002; Erkinaro et al 2019; Hutchings et al 2019; Jonsson and Jonsson 1993, 2011; Thorpe 2007). Earlier smolting individuals tend to spend more time at sea before returning to rivers to spawn (Erkinaro et al 2019; Jonsson and Jonsson 2011; Salminen 1997) and have higher reproductive fitness due to generally achieving larger size (Mobley et al 2020). The timing of maturation in Atlantic salmon represents a classic evolutionary trade-off: individuals that spend more time at sea before returning to fresh water to spawn have higher reproductive success due to their larger size and have a higher risk of mortality prior to first reproduction (Fleming and Einum 2011; Mobley et al 2020). Due to the vast geographical distances that salmon cover at this stage (O’Connell et al 2006), it is

Method

QTL reaches chromosome-wide significance for late maturation: ssa18

Conclusions and recommendations

Findings

Methods