KARYOTYPE ANALYSIS OF THE FRESHWATER DUGESIA PLANARIANS FROM YUNNAN PROVINCE,CHINA

Abstract

In order to provide evidence for taxonomy,evolutionary biology,biogeography and phylogenetics of the ge-nus Dugesia,the chromosomes and karyotypes of the freshwater planarians,Dugesia sp.,collected from Shuhe town in Lijiang City,Longwangtang pond in Baoshan City,and Xiaozhaongdian town in Xianggelila City,Yunnan Province,were studied.The adult planarians,15—20 mm in length and 1.5—2.0 mm in width,were used.After starving for a week,each planarian was transversally cut into five pieces,the planarian pieces were cultured in distilled water for three or four days to regenerate.For the karyological analysis,the metaphase chromosomes were prepared from regenerating blastemas by an air-drying method.Chromosome numbers of over 100 well-spreaded cells were counted and the chro-mosomes were photographed using Leica DMLB light microscope.The karyotype parameters of five well-spreaded metaphase plates from five individuals were measured.Relative length(r.l.) was calculated as chromosome length ×100/ total length of haploid genome.Centromeric index(c.i.) was calculated as length of the short arm×100/ total length of the chromosome.Arm ratio(a.r.) was calculated as length of the long arm/that of the short arm.Mean values and standard deviations(S.D.) were calculated from five metaphase plates obtained from a minimum of five fissiparous specimens from each experimental population.The karyotype were arranged firstly according to the gradually decreasing lengths of chromosomes and then the centromeric indices.The chromosomes were classified based on the criteria pro-posed by Levan,et al(1964).The results showed that planarians collected from Shuhe town had a diploid chromosome number of 16 with a karyotype formula of 2n=2x=16=16m.Planarians collected from Longwangtang pond had both the triploid 24(2n=3x=24=24m) and partial diploid 16(2n=2x=16=16m),i.e,which were mixoploids.It was noteworthy that the planarians collected from Xiaozhaongdian town had a triploid aneuploid chromosome number of 26 with a karyotype formula of 2n=3x+2=24+2=21m+3st+2m,but a few were 25(2n=3x+1=24+1=21m+3st+1m) or 24(2n=3x=24=21m+3st).The karyological results of the planarians collected from Xiaozhaongdian town were obviously different from those of Dugesia japonica and other species in Dugesia,The main factor that affected the karyological results might be the change of environment(altitude,water temperature,atmospheric pressure and UV radiation).Per-haps it was the change of chromosomes and karyotypes that led to speciation and the evolution of species.Based on the results of karyotype analysis of freshwater planarians,Dugesia sp.,from the three places,classification of freshwater planarians and chromosome aneuploidy had been discussed in this paper.In order to obtain more precise karyological data of Dugesia planarian,other sensitive techniques such as chromosome banding,fluorescent staining or in situ hy-bridization should be useful to get more evidence for taxonomy,genetics,evolutionary biology,biogeography and phy-logenetics of Dugesia.