Reproductive timing phenotypes in female salmon: true alternatives or extreme variants?

Journal of Fish Biology

2015

This study examines whether the anal fin undergoes secondary sexual development similar to other reproductive traits in salmonids. This hypothesis was tested by comparing the anal-fin size of female kokanee salmon Oncorhynchus nerka that were in the early and late stages of sexual development. Females in an advanced stage of maturation had significantly larger anal fins relative to females in an early state of maturation (+4-7%), indicating that the anal fin undergoes secondary sexual development. The magnitude of this secondary growth was comparable with snout length (+9-10%), which is known to undergo secondary sexual development in female salmonids. When morphological trait dimensions were compared between the sexes, the anal fin was the only morphological trait found to have a female-biased sexual size dimorphism. This is the first study to show that the anal fin of female salmonids undergoes secondary sexual development.

“…The arrival of O . nerka to the spawning channel begins in late August and ends in late September, making for a 3–4 week arrival period (Warren & Morbey, ).…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Evidence for the secondary sexual development of the anal fin in female kokanee salmonOncorhynchus nerka

Thorn

Journal of Fish Biology

2015

“…The silver‐arriving phenotype is considered to be a female reproductive tactic to minimize dig‐up ( i.e. redd superimposition) by later‐nesting females (Morbey & Guglielmo, 2006; Warren & Morbey, 2011). Although progress has been made in understanding silver and red‐arriving females by studying aspects of their reproductive timing and physiology (Morbey & Ydenberg, 2003; Morbey & Guglielmo, 2006; Warren & Morbey, 2011), no study has yet compared their behaviour during migration.…”

Section: Introductionmentioning

confidence: 99%

“…redd superimposition) by later‐nesting females (Morbey & Guglielmo, 2006; Warren & Morbey, 2011). Although progress has been made in understanding silver and red‐arriving females by studying aspects of their reproductive timing and physiology (Morbey & Ydenberg, 2003; Morbey & Guglielmo, 2006; Warren & Morbey, 2011), no study has yet compared their behaviour during migration. Similar to the proximate mechanisms that may underlie protandry (Coppack & Pulido, 2009), silver‐arriving females may arrive earlier than red‐arriving females because they depart pre‐migratory feeding areas earlier, have pre‐migratory feeding areas nearer to breeding areas or migrate upstream faster.…”

Section: Introductionmentioning

confidence: 99%

“…The relationship between maturation state and migration speed was tested in female O. nerka , using colour as a proxy for maturation state (Warren & Morbey, 2011). Faster migration by less mature (more silver) females would help explain their earlier arrival than more mature (more red) females and would be consistent with the hypothesis that advanced reproductive development compromises swimming performance or the hypothesis that migration speed is sensitive to colour‐dependent predation risk.…”

Section: Introductionmentioning

confidence: 99%

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Migration timing of female kokanee salmon Oncorhynchus nerka: diel patterns and effects of maturation state

Warren

Journal of Fish Biology

2012

Diel patterns of migration and migration speed were compared between reproductive timing phenotypes in female kokanee salmon Oncorhynchus nerka. Females of varying degrees of reproductive maturation were captured on their migration route to the Meadow Creek Spawning Channel (British Columbia, Canada), were tagged with passive-integrated transponders (PIT tags) and were subsequently monitored with stationary receivers. Females showed crepuscular migration timing, with approximately equal detections at dawn and dusk. In particular, peaks of movement were associated with the appearance of the sun over the mountains in the east and the disappearance of the sun over the mountains in the west. Over 25 m, migration speed was 1·0 body lengths (measured as fork length; L(F)) s(-1) and did not depend on maturation state. Over 3 km, migration speed was much slower (0·2-0·3 L(F) s(-1)) than over the short distance, with less mature females migrating more slowly than more mature females. Less mature females appeared to be in less of a hurry to reach breeding areas compared with more mature females.

Time scale matters: genetic analysis does not support adaptation‐by‐time as the mechanism for adaptive seasonal declines in kokanee reproductive life span

Jensen

Russello

2014

Ecology and Evolution

Self Cite

Seasonal declines of fitness-related traits are often attributed to environmental effects or individual-level decisions about reproductive timing and effort, but genetic variation may also play a role. In populations of Pacific salmon (Oncorhynchus spp.), seasonal declines in reproductive life span have been attributed to adaptation-by-time, in which divergent selection for different traits occurs among reproductively isolated temporal components of a population. We evaluated this hypothesis in kokanee (freshwater obligate Oncorhynchus nerka) by testing for temporal genetic structure in neutral and circadian-linked loci. We detected no genetic differences in presumably neutral loci among kokanee with different arrival and maturation dates within a spawning season. Similarly, we detected no temporal genetic structure in OtsClock1b, Omy1009uw, or OmyFbxw11, candidate loci associated with circadian function. The genetic evidence from this study and others indicates a lack of support for adaptation-by-time as an important evolutionary mechanism underlying seasonal declines in reproductive life span and a need for greater consideration of other mechanisms such as time-dependent, adaptive adjustment of reproductive effort.