Chromosome numbers and chromosomal polymorphism in Finnish species of Galerucella Crotch (Chrysomelidae, Coleoptera)

N okkala , S. and N okkala , C. 1987. Chromosome numbers and chromosomal polymorphism in Finnish species of Galeruceh Crotch (Chrysomelidae, Coleoptera). ‐ Hereditas 106: 51–58. Lund, Sweden. ISSN 0018–0661. Received February 27, 1986 Chromosome numbers and chromosomal polymorphism in Finnish species of Galerucella were studied. The chromosome number of G. nymphaeae (L.), G. lineoh (F.), and G. calmariensis (L.) was found to be Zn = 34 (16+Xy p ); of G. tenella (L.) 2n = 26 (12+Xy p ); and of G. pusilla (Duft.) 2 n = 16 (7+neoXY). The primitive chromosome number of the genus appears to be 2n = 34. Pericentric inversions, translocations and centric fusions were found to be the principal chromosomal mutations modifying the karyotype in the genus. In G. nymphaeae , sex chromosome polymorphism caused by an unusually large Y chromosome was found. The occurrence of the large Y chromosome was confined to a form of G. nymphaeae living on aquatic plants, allowing the conclusion that the forms of G. nymphaeae living on aquatic and terrestrial plants are reproductively isolated. Hence, they represent individual species, G. nymphaeae (L.) feeding on aquatic plants and G. sagittariae (Gyll.) feeding on terrestrial plants. All species studied were found to carry B‐chromosomes of their own type, excluding G. nymphaeae and G. sagittariae , where B‐chromosomes appeared to be similar. The size of B‐chromosomes was found to vary from dot‐like in G. nymphaeae group to a large metacentric in G. tenella , the latter comprising about 15 % of the total length of the karyotype. All B‐chromosomes, except those in G. calmariensis , are isopycnotic during meiotic prophase and able to form a chiasmatic bivalent, when two B's are present.