Genetic diversity of six populations of Atractomorpha sinensis and Atractomorpha peregrina in Shanxi Province, China

Abstract

Ten enzymes (AAT, CK, G3PDH, HEX, IDH, LDH, MDH, ME, PGI, PGM) were examined using horizontal starch gel electrophoresis to estimate the levels of genetic variation within and among six natural populations of two grasshopper species Atractomorpha sinensis and A. peregrina from Shanxi, China. The collecting sites were geographically distant from each other from south to north: Quwo district, Linfen city; Xiangyuan county, Changzhi; Jinyuan district, Taiyuan city; Yuanping county, Xinzhou city and Fanshi county of Xinzhou. A.sinensis showed 43 alleles at 16 loci but A. peregrine showed 39 alleles at 15 loci (Idh-1 was deficient). The zymograms showed that some common alleles were shared at several loci in these two species (Aat-1-b, Aat-2-b, G3pdh-a, Ck-1-b and Ldh-b). However, Hex-1-a, Hex-2-a, Hex-3-a, Idh-2-b, Mdh-2-b, Mdh-1-f, Pgi-b, Pgm-b had common alleles in A. sinensis and Hex-1-b, Hex-2-b, Hex-3-b, Idh-2-a, Mdh-2-a, Mdh-1-d, Pgi-a, Pgm-c were of high frequency in A. peregrine instead. Most of the observed genotype frequencies were found to significantly deviate from the Hardy-Weinberg expectations in both species. A tendency of clinal distribution of allele frequency was observed at three loci. The frequency of the moderately migrating allele Me-c (0.318-0.740) in A. peregrina, Hex-1-a (0.800-1.000) and Ldh-b (0.487-0.750) in A. sinensis demonstrated increased frequency from north to south. Such tendency suggests that the allele frequency in these three loci may be correlated with the species  geographic distributions. A. sinensis showed higher genetic diversity than A. peregrina as indicated by higher mean number of alleles per locus (A = 1.9-2.3 in A. sinensis and 1.7-2.2 in A. peregrina), percentage of polymorphic loci (56.3%-68.8% in A. sinensis and 43.8%-56.3% in A. peregrina), and the observed heterozygosities (H_o = 0.072-0.096 in A. sinensis and 0.070-0.107 in A. peregrina). The observed heterozygosities of the six populations were all noticeably lower than the Hardy-Weinberg expectations, mostly due to heterozygote deficiency in the populations of both species. The overall mean F_ST were small (F_ST = 0.045, P>0.05 in A. sinensis populations and 0.087, P>0.05 in A. peregrina populations). Nei s genetic identity (I) estimates indicate low intraspecific (>0.95) but higher interspecific (0.377-0.447) genetic diversity. The cluster analysis based on modified Roger s genetic distance (D) showed that the two species were divided into two branches. Both species are of limited dispersal capacity and a moderate geographical barrier might significantly restrict the gene exchange among populations, resulting in accumulation of local genetic differentiations. The A. sinensis populations used in this study were separated from each other by 155.2 to 271.4 km and the A. peregrina populations were separated from each other by 78.8 to 174.9 km with observable physical barriers. The allozyme data showed only minimal genetic differentiation at population level, most likely as a result of gene exchange. It is reasoned that natural factors and human agricultural activities might have facilitated migration and dispersal for the two species.