A combination of genetic and phenotypic characterization of spring- and autumn-spawning herring suggests gene flow between populations

Abstract

Atlantic herring (Clupea harengus) has complex population structure and dynamics including diverse life histories and spawning times with spring and autumn spawning as the most common modes. Originally, spawning herring were phenotypically identified based on their maturity development or otolith microstructure by determining seasonal specific larval growth patterns. Recently, genetic markers have revealed clear genetic differentiation between spring- and autumn-spawning populations. All three methods were applied to herring caught at the same locations during spring and autumn to determine the coherence of methods. In a selected subset, most herring (∼77%) had an otolith microstructure and genetic assignment coinciding with the phenotypically assigned spawning season. Non-spawning herring (<5%) that were classified as belonging to the current spawning season using genotyping and otolith-typing were assigned as skipped spawners. For ∼8% of spawning herring, the genetic and otolith assignment contradicted the phenotypically assigned spawning season, characteristic of straying individuals. Otolith-typing contradicted the genetic and phenotypical assignment in ∼7% of the cases, potentially representing individuals reuniting back to the spawning season favoured by their genotype. Although the viability of offspring from these individuals remains undocumented, it is suggested that the observed switching of spawning season may contribute to gene flow between herring populations.

Comparison of Otolith Microstructure of Herring Larvae and Sibling Adults Reared Under Identical Early Life Conditions

“…Selection studies comparing otolith growth of larvae and survivors (adults) on for example strong and weak year classes might reveal new insights on the recruitment dynamics of herring. Further, this validation strengthens other studies where conclusions are drawn from microstructure analysis of adult otoliths which have management (Clausen et al, 2007) or ecological (Berg et al, 2020b) implications.…”

Ecological adaptation in Atlantic herring is associated with large shifts in allele frequencies at hundreds of loci

“…Interestingly, examinations of the otoliths from fish in this sample, using the method by Clausen et al (Clausen et al, 2007), showed that they hatched in spring. Thus, this must represent a group of herring that has switched spawning season from spring to autumn, maybe because their nutritional status was insufficient to support spawning (McQuinn, 1997), demonstrating that spawning time in herring is controlled by a combination of genetic and environmental factors (Bekkevold et al, 2007;Berg et al, 2020).…”

The genetic architecture underlying ecological adaptation in Atlantic herring is not consistent with the infinitesimal model

“…10 , showed that they hatched in spring. Thus, this must represent a group of herring that has switched spawning season from spring to autumn, maybe because their nutritional status was insufficient to support spawning 11 , demonstrating that spawning time in herring is controlled by a combination of genetic and environmental factors 12,13 .…”