| Research Abstract |
The Gagrellula ferruginea-group, consisting of three species (G.ferruginea, G.grandis, G.sp.), shows great karyotypic variability both between and within species. Geographical patterns of the karyotype differentiation and the role of the chromosomal hybrid zones in the speciation process of the group were investigated. The principal results obtained are as follows : (1) The number of chromosomes ranged from 2n=10 to 24 in G.ferruginea, 2n=18-20 in G.sp. and 2n=20 in G.grandis. Of these, G.ferruginea, occupying the widest ranges in the group, was most variable in both karyotypes and external morphology. Basically, no close association was found between differentiations in karyotypes and external morphology. (2) G.ferruginea showed greatest diversity in chromosome number in the area surrounding Tango Mountains in northern Kink district, Honshu ; where the number ranges from 2n=14 to 20. At the every points where two populations with different chromosome numbers abut, a hybrid zone was always found. (3) Two geographic races (Kyushu-Hiroshima race and Daises race) of "Gagrellula ferruginea" meet in the western of Hiroshima Prefecture, with a slight overlap of their ranges. In the overlap zone, relative length of legs to body significantly differed between the two races ; indicating occurrence of character displacement. (4) It was found that two geographical populations with different chromosome numbers show prezygotic reproductive isolation more or less, though it is usually far from complete and hence hybrid zones are formed.
|
