Etude de l'espèce polytypique Idotea chelipes et d'Idotea bathica basteri (Isopodes valvifères)

Abstract

Karyological studies of a polytypic species Idotea chelipes within three subspecies chelipe, bocqueti and mediterranea and idotea balthica basteri have been investigated. The specimens were collected at six localities in the Arcachon basin, on the west coast and the north lagoons of Tunisia. Stable karyotype (n= 29 and 2n = 58)characterizes all the taxons studied. The present investigations confirms the chromosomic number (n= 29) of I. chelipes and I. b. basteri and determines that of I. ch. bocqueti and I. ch. mediterranea (n= 29 and 2n = 58). The mitotic karyotype consists of one pair of satellite chromosomes, one pair of small acrocentric chromosomes and fifty four pairs of meta, submeta and telocentric chromosomes. Karyological investigations did not reveal the existence of the sex trivalent. So, at mitotic anaphase, two chromosomes migrate more slowly to opposite poles than the daugther complex. These late chromosomes can be considered as sex-chromosomes. Karyological features of the organisms can be used as a tool in taxonomy. So the relative stability of chromosomes number in the two species I. chelipes and I. balthica indicated the limit of this criterion's application. Our results shows that I. chelipes speciation was accompanied by morphobiologically and allozomic divergences and not by a variation of the chromosomic number.