Molecular Phylogeny of Pheretimoid Earthworms (Haplotaxina: Megascolecidae) Based on Mitochondrial DNA in Hainan Island, China

Abstract

In the Chinese Hainan Island, Amynthas and Metaphire are two dominated pheretimoid earthworm species belonging to the family Megascolecidae. They differ from earthworms in the adjacent regions in their morphology and at the molecular level, which could have occurred due to the unique geography of Hainan Island. Hainan Island is made of two tectonic parts linked to South China and Indochina blocks, respectively. In addition, there is an apparent complicated link between Hainan Island and mainland China because of the different plate movements and sea level changes. In order to understand the evolution of pheretimoid earthworms in Hainan Island, we first investigated the earthworm biodiversity here. Bayesian phylogenetic tree was then constructed from 3511 base pairs from five mitochondrial genes: COI, COII, 16S, 12S, and ND1. Their divergent time was finally traced based on the molecular clock of 2.0-2.4% substitutions/Ma. The results showed three species differentiations between Hainan and Guangdong earthworm species. According to the paleogeography of Asiatic regions (including Hainan Island itself), we hypothesized that the Hainan pheretimoid earthworms might originate from Southeast Asia, and then they dispersed to the south and finally arrived at South China and Hainan Island. Meanwhile, due to the geology movement of the adjacent plates, there was also the migration of earthworms among adjacent regions. Furthermore, we also considered that the relationship between genera Metaphire and Amynthas might be reconsidered as one genus.

A molecular phylogenetic study of pheretimoid species (Megascolecidae) in Mindanao and associated islands, Philippines

“…It is suggested in James [10] and Chang et al [11] that Amynthas may either be paraphyletic or polyphyletic implying that the development or loss of either the nephridia on spermathecal ducts and/or the secondary male pores happened more than once in the pheretimoid taxa. In another study on molecular phylogeny of pheretimoids in Hainan Island, China, it is proposed that Amynthas and Metaphire be reconsidered as one genus [13]. Our results reinforce these older concerns about the monophyly of pheretimoid genera.…”

“…Previous and recent molecular phylogenetic studies on pheretimoids are on Amynthas and Metaphire in China and Taiwan (eg. [11,12,13]) and James' [10] work was the first molecular phylogenetic study on Philippine earthworms that includes species in Pheretima s. str. The specimens he worked on were collected from Luzon group of islands using the data of mitochondrial 16S rDNA and nuclear 28S rDNA.…”

Temporal Changes in the Function of Bacterial Assemblages Associated With Decomposing Earthworms

“…Electroshocking has been shown to have minimal effects on soil biota ( Staddon et al, 2003 ). Species identification of the earthworm individuals was based on morphological characteristics such as body color, first dorsal pore, clitellum position, and the number of body segments ( Zhao et al, 2015 ). For those individuals that were identified as A. corticis , only intact and mature adult earthworms with similar body size (about 3-g fresh weight) were retained for use in the experimental setup in order to circumvent the effects of minor factors (e.g., integrity and age) on results.…”

Disentangling earthworm taxonomic stumbling blocks using molecular markers

“…Thus it sustains the decisions of nomenclature experts and thus primarily contributes to biodiversity assessments from local to global scales. Therefore, adopting DNA barcoding has enhanced the accuracy of earthworm studies and in particular, greatly benefited the community of soil biologists in the description of many novel species over the past few years (Blakemore 2013;Zhao et al 2015;Aspe et al 2016;Csuzdi et al 2017;Seesamut et al 2018;Lone et al 2020); see Table 1 for more details. Furthermore, DNA barcoding has also shown its congruent results with other nuclear and mitochondrial genes (Pop et al 2007;King et al 2008) and many such papers are published in peer-reviewed journals.…”