Evolution and disappearance of sympatric Coregonus albula in a changing environment - a case study of the only remaining population pair in Sweden

During the past 50 years Fennoscandian populations of spring-spawning Baltic cisco (Coregonus albula), sympatric to common autumn-spawners, have declined or disappeared; e.g., three out of four known spring-spawning populations in Sweden are regarded as extinct. Over the same period, climate has changed and populations have been subject to other anthropogenic stressors. We compared historic (1960s) and recent (1990-2000s) morphological data from the still existent sympatric cisco populations in Lake Fegen, Sweden. Phenotypic changes were found for spring-spawners making them more similar to the sympatric autumn-spawners (that had remained virtually unchanged). Based on results for other salmoniform fishes, a phenotypically plastic response to increased temperature during early development appears unlikely. The recent material was also analysed with microsatellite markers; long-term effective population size in spring-spawners was estimated to be about 20 times lower than autumn-spawners...