Some aspects of the cytology of European newts (genus Triturus).

Of the 9 species of European newts, 7 are examined in this study. All have 24 (2n) bi-armed chromosomes. Giemsa C-banding and base-pair specific fluorochrome banding are employed to characterise the karyotypes. Triturus cristatus and T. marmoratus have an unusual chromosomal situation. All individuals are heteromorphic for the largest chromosome (chromosome 1). Chromosomes 1 are heteromorphic for a region comprising most of the long arm which shows different banding patterns between the two homologues (chromosomes 1A and 1B). The heteromorphic regions are largely heterochromatic and are asynaptic and achiasmate at meiosis in both sexes. Banding patterns of the heteromorphic regions varies between the subspecies of cristatus and T. marmoratus. Individuals which are homomorphic for either chromosomes 1A or 1B show arrested development and eventual death at tail bud stage of embryogenesis, resulting in a 50% mortality of all offspring. A model for, the evolution of the heteromorphism is suggested. The sex chromosomes of Triturus are in an early stage of differentiation. The male is the heterogametic sex. Most species show a C-band heteromorphism between the tips of the long arms of the X and Y chromosomes. Evidence is presented which suggests that the Y-sex factors are contained within the small, often heterochromatic, region at the tip of the long arm of the Y chromosome. Subspecies of T. cristatus and T. marmoratus are considered as a separate species group from the other Triturus species. The T. cristatus subspecies and T. marmoratus have karyotypes which share many homologies in the distribution of C-bands. There is little evidence for much structural rearrangements differentiating the species/subspecies, but quantitative C-heterochromatic change can be extensive. The remaining Triturus species show evidence for both structural and heterochromatic change. Chromosome studies can not usefully assess taxonomic affinities within Triturus, but have shown some interesting lines of karyotypic evolution.