Variations and Taxonomic Significance of the Chromosome Numbers in The Nearctic Species of the GenusLeptothorax(S.S.) (Formicidae: Hymenoptera)

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Abstract
The taxonomic situation of the genus Leptothorax (sensu stricto = subgenus Leptothorax sensu Smith 1950) appears particularly puzzling in North America when using morphological characters alone. This paper analyses the taxonomic impact of the complex variations observed in the chromosome numbers of the presently recognized species. The method of Imai modified for some details was applied to specimens obtained from colonies reared in laboratory. These were collected between 1978 and 1984, in different regions of Québec and in Alberta for Canada, in New Hampshire and Utah for USA. Over 250 slides of testes (male pupae) or brain (female prepupae) were prepared. Results for the nearctic species are compared to European data. For the traditional muscorum taxon as applied in North America the haploid numbers varied from 15 to 23 including supernumerary chromosomes. At least four distinct species can be extracted from these results. Male diploidy is documented. Different tendencies are stressed between the actual subgenera Leptothorax and Myrafant.