title: Time scale matters: genetic analysis does not support adaptation-by-time as the mechanism for adaptive seasonal declines in kokanee reproductive life span.
abstract: 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.
authors.affiliation: Department of Biology, Western University London, Ontario, N6A 5B7, Canada.
authors.forename: Yolanda E
authors.initials: YE
authors.lastname: Morbey
authors.affiliation: Department of Biology, University of British Columbia, Okanagan Campus Kelowna, British Columbia, V1V 1V7, Canada.
authors.forename: Evelyn L
authors.initials: EL
authors.lastname: Jensen
authors.affiliation: Department of Biology, University of British Columbia, Okanagan Campus Kelowna, British Columbia, V1V 1V7, Canada.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Russello
keywords: Adaptation-by-time; evolutionary mechanisms; isolation-by-time; reproductive timing; seasonal declines in fitness-related traits