Taxonomy, Phylogeny And Paleogeography Of Pheretimoid Earthworm Species In Hainan Island(China)

Earthworm is ideal for investigating or verifying paleogeographic processes and specifically vicariance processes from present distributions because of their stable characteristics and poor ability of movement. It is the second largest island in southernmost China. Tectonically, Hainan Island lies at the southern margin of the South China Block, adjacent to the northern Indochina Block. In Cenozoic, Hainan Island connected to and separated from the Chinese mainland several times which enabled the flora and fauna to migrate back and forth from the mainland to Hainan Island. Hainan Island is one of the hotspots for biodiversity. However, there is little information on earthworms.The objectives of my thesis are:(1) to investigate the earthworm biodiversity in Hainan Island;(2) to analyze the corresponding relationship between morpho-anatomical characteristics and earthworm species, including those in its adjacent regions(Laos, Guangdong province, Taiwan Island and Korea);(3) to analyze the molecular phylogeny of earthworms in Hainan Island and try to reconstruct their ancestral states;(4) estimate the evolutionary history of pheretimoind earthworms in Hainan Island, mainly in Asia.In present study, 68 new pheretimoid earthworm species with 2 new sub-species, 1 new record genus and 1 new record species in Hainan Island were identified. Up to now, there are 107 species and subspecies, belonging to 12 genera and 7 families in Hainan Island. And it includes 80 endemic species.Characteristics under sexual selection always play an important role in the evolutionary process of earthworms, followed by these under environmental selection. The ancestral states of pheretimoid earthworm species in Hainan Island were as followings: small individuals, no pigment, two pairs of spermathecal pores, last pair of spermathecal pore in the intersegment 8/9, superficial male pore, present genital papillae, developed prostate, small spermatheca duct, diverticulum and seminal chamber. Furthermore, the taxonomic position of Amynthas and Metaphire should be re-considered.Results also showed that there were mainly three species differientions between Guangdong and Hainan Island earthworms in mid-Cenozoic. And it matched with the geographical history of Hainan Island. As a result, we hypothesized that the pheretimoid earthworms of Hainan Island orgined from Southeast Asia. During Carboniferous and Permien, the earthworms dispersed from Southeast Asia to South Hainan Island and South China separately. Then in Triassic, the amalgamation between North and South China Blocks pushed the species to disperse to North China. During Quaternary, the coldest weather may lead to the death or the migration of earthworm species of North China. Meanwhile, the fluctuation of sea level in this period could also affect the distribution of earthworms among Hainan Island, Taiwan Island and China mainland.In the future, the analysis of molecular genetics in other regions could be considered to verify the relationship of the genera Amynthas and Metaphire in Megascolecidae, such as nuclear genes: globin chain C or ITS. Research in population level should be considered to study the evolutionary process of earthworms in small scale such as Hainan Island. Finally, what should be also paid attention is that there is nearly no pheretimoid earthworms in North China, while they are the dominated species in South Korea and Japan.