Divergent origins of sympatric herring population components determined using genetic mixture analysis

The origin and reproductive interactions of sympatric, spatially separated spawning components of Atlantic herringClupea harengushave received long-standing interest. In the western Baltic most herring spawn in spring, with smaller components spawning in winter. We used microsatellite DNA analysis and a novel Bayesian genetic mixture analysis approach to compare the genetic relationships of 2 western Baltic winter-spawning aggregations with those of their sympatric spring-spawning components, and combined information for genetic markers and morphological traits (otolith-determined hatching time and growth relationships) to test alternative hypotheses for the origin of winter spawners.

We show that genetic relationships between sympatric components differ greatly between the 2 locations; the results indicate that winter spawning has arisen via 2 fundamentally different processes: (1) as a result of ‘spawning-time switching’ in a local spring-spawning component and (2) via 1 or more founder events from an extant winter-spawning population into an area otherwise dominated by spring spawners.