Institute of Freshwater Research, Drottningholm. Report No 57 : Spéciation of Scandinavian Coregonus

1. This paper is a revision, in the light of newevidence, of an earlier one (Svärdson 1957) on the same subject. 2. The biological species concept is adopted. Lake Locknesjön, headwater of the Gimånriver, is inhabited by three indigenous species. The large sparsely-rakered whitefish has 19 gill rakers, the lesser sparsely-rakered whitefish 22 and the southern densely-rakered whitefish 42 rakers. Their ecology is different. Experiments show that the morphological as well as the ecological traits are mostly genetically based. 3. The river whitefish with about 30 gillrakers is a fourth Scandinavian species. Normally it runs the lower parts of the rivers. It was introduced in Lake Lockne sjön in the 1940s and from Lake Vänern to upperlakes of the Indalsälven river system in 1870. If it lived allopatrically it was not changed, but if it lived sympatrically with native species introgression have occurred. In Lake Vänern it lives, spontaneously, sympatrically with both large and lesser sparsely rakered whitefish. The alleged evolution of a new species in postglacial times (Svärdson 1970) was based on introduced fish whose origin was mistaken. 4. The northern densely-rakered whitefish is a fifth species. In Lake Storvindeln it has more than 60 gill rakers and is close to the “riverpeled” of north-western U.S.S.R. It grades by introgression to some 45 rakers in other lakes but proves its specific rank by living sympatrically with all the other forms. 5. The blue whitefish, with 30—35 gill rakers, is the sixth and most competitive species. It has a tendency to oust the southern densely-rakered species as well as the lesser sparsely-rakered one. Its specific status is proved by sympatric coexistence with all the other forms in several lakes. 6. There are five sympatric whitefish species in Lake Vänern as well as in the Arjeplog lakes of the Skellefte river. Two species live in the Baltic Sea. 7. The order of postglacial arrival from the Ancylus Lake could be studied in lakes of the upper Ljusnan river and a complex introgression pattern in the Gimån river system is discussed. 8. The spring-spawning cisco Coregonus trybomi, sp. nov., is described and its place of origin and postglacial dispersal across the Baltic Ice Lake in Younger Dryas is discussed. 9. Isolating mechanisms in Coregonus are poor. Species groups behave towards one another (like ciscoes versus whitefish) as semispecies only, which could be interbred by man and produce viable, self-reproducing populations. 10. The Siberian C. peled is thought to have split by multiple invasions into a western Soviet species (“river peled”), C. pallasi (northern densely-rakered whitefish), C. nilssoni (southern densely-rakered whitefish) and C. wartmanni (blue whitefish). The last mentioned species has a northern subspecies,C. w. megalops, in northern Fenno-Scandinaviaand along the Arctic coast area. 11. The Siberian C. pidschian has in the same way produced three species, C. fera, C.acronius and C. lavaretus in western Europe. Each of them has a preglacial and a postglacial subspecies. Vernacular specific names are large sparsely-rakered, lesser sparsely rakered and river whitefish. 12. The Siberian cisco, C. sardine lia, is split intomany species. A western Soviet Union speciesis C. kiletz, Scandinavian are C. albula and C. trybomi while the British and western European C. vandesius is found to be possibly a biological species of its own. 13. The stability of Coregonus nasus and some other species (C. muksun, C. tugun andC. autumnalis) is found to correlate to riverine life, while the multiplying species (C. peled, C. pidschian and C. sardinella) more easily develop lake-spawning populations. They are consequently more widelyspread, from western Europe to the Atlantic drainage of North America. 14. Geographical isolation is a paramount prerequisite for spéciation in Coregonus. Tolerance against genetic imbalance exists because of polyploid ancestry. Introgressionis thus an important spéciation factor