Species diversity of Terrestrial Earthworms in Nan province

Abstract

The terrestrial earthworms in Nan province were identified using external and internal morphological characters. A total of twenty species and one subspecies from 4 genera of terrestrial earthworms were recorded. There are eighteen species and 1 subspecies of Megascolecidae: Amynthas alexandri, A. borealis, A. exiguus exiguus, A. longicauliculatus, A. phatubensis, A. srinan, A. tontong, Amynthas sp. 1, Amynthas sp. 2, Amynthas sp. 3, Amynthas sp. 4, Metaphire anomala, M. birmanica, M. grandipenes, M. houlleti, M. peguana, M. posthuma, Metaphire sp. 1 and Metaphire sp. 2, a species of Glossoscolecidae (Pontoscolex corethrurus), and one species of Octochaetidae (Dichogaster bolaui). There are six species; A. borealis, A. phatubensis, A. srinan, A. tontong, M. birmanica, and M. grandipenes recorded in Thailand for the first time. The genetic variation of the Metaphire peguana, which is a common species in Thailand was examined. A total of 274 individuals were collected from 13 localities in Thailand. Using horizontal starch gel electrophoresis, 17 presumptive allozyme loci were screened across all the samples and 14 of these presumed loci, from 11 enzyme systems, were found to be polymorphic. The expected heterozygosity (Hexp) was moderate to high ranging from 0.059 - 0.147 with an overall mean of 0.092 ± 0.02 which relative lower than other earthworms. Genetic heterogeneity among samples showing relatively high (Fst = 0.318), may have been involved in an extensive local fragmentation under various selection forces. Genetic differentiation among the samples was low, with a low genetic distance (D = 0.002 - 0.171, mean = 0.048 ± 0.040 indicating the frequent gene flows among populations in Thailand. This is probably cocoons of M. peguana contaminated with soil or scions during propagation processes.