Low heterogeneity in populations of the terrestrial earthworm,Metaphire peguana (Rosa, 1890), in Thailand,as revealed by analysis of mitochondrial DNA COI sequences and nuclear allozymes

The genetic variation of a widely distributed terrestrial earthworm species, Metaphire peguana (Rosa, 1890), was examined in Thailand using allozyme and mitochondrial (mt)DNA cytochrome oxidase subunit 1 (COI) sequence analyses. A total of 274 individuals were collected from 13 localities in Thailand and scored for 12 enzyme systems (18 presumptive allozyme loci) using horizontal starch gel electrophoresis. Fourteen of these presumed loci were found to be polymorphic. In addition, a 660 bp fragment of the COI mtDNA gene was amplified and sequenced from one representative individual for each of the 13 geographical regions. The expected heterozygosity (H_exp) was relatively low, ranging from 0.059–0.147 with an overall mean of 0.092 ± 0.02 and there was no significant isolation by distance pattern for the 13 populations (localities) across the entire study area (P-value > 0.05). Genetic divergences among the samples were low, with a low genetic distance (mean = 0.048) and uncorrected p-distance (mean = 0.02) indicating frequent gene flow among these populations in Thailand. The monophyly of M. peguana across these regions was supported by Neighbor joining, Maximum likelihood and Bayesian inference based phylogenetic analysis of the mtDNA COI sequences with no geographic location dependent pattern. This may be due to anthropogenic movement of M. peguana in soil or with plant scions throughout this region.