Diversity And Evolutionary Significance Of Tardigrades In Plateau Lakes Of Yunnan Province

At present,more than 1380 species of tardigrade have been reported worldwide.However,most of them are terrestrial Tardigrades,and there are relatively few reports and studies of freshwater Tardigrades.So far,only a few freshwater Tardigrades in China have been reported.There is a certain gap in the research on freshwater Tardigrades.Both morphological and molecular evidences suggest that the Tardigrada is closely related to the Arthropod and the Onychophora,which together form the Panarthropods.Their origin and early evolution are closely related to Cambrian Lobopodian.The Cambrian Chengjiang biota in Yunnan Province produces a large number of well-preserved fossils of Cambrian Lobopodian and other Panarthropods.Therefore,an in-depth understanding of the morphological characteristics,functions,behaviors,and other informations of living Tardigrades,as well as their morphological comparisons with Cambrian Panarthropods,will help to understand the morphological functions of fossils and answer the phylogenetic relationships and evolutionary history between Tardigrades and other Panarthropods.In this paper,we investigated a number of plateau lakes in Yunnan Province,including Lugu Lake,Erhai Lake,Fuxian Lake and Dianchi Lake,and found a total of 3families,6 genus,13 species of Tardigrades.We found 2 new Chinese record species(Pseudobiotus spinifer,Pseudobiotus vladimiri)and 3 new record species in Yunnan Province(Pseudobiotus megalonyx 、 Dactylobiotus ovimutans 、 Dactylobiotus parthenogeneticus).They are completely freshwater Tardigrades.In addition,a large number of egg-bearing individuals of the genus Pseudobidocus which had never been reported in China,were found in the Erhai Lake,and the parental caring and feeding behaviors were preliminarily observed.The following phenomenas were found: 1.It’ s breeding period was affected by temperature and food.The amount of eggs laid varies,ranging from 5 to 8.2.The state of the Tadigrades(active or dead)and the scattering of eggs caused by molt damage don’t seem to affect the hatching of eggs,which indicates that the parent doesn’t fully take care of the eggs in molting.3.When the eggs in the molt have not fully hatched,the worm body has broken free and discarded the molt.4.Carrying or not carrying eggs shows different reproductive strategies of Tadigrades 5.The mouth is pushed out for feeding through the contraction of the pharyngeal bulb,and the time outside the mouth is uncertain.This feeding behavior hasn’t been described in detail before.Through the establishment of morphological phylogenetic tree,the relationship among Tardigrade fossils,extant species,and related taxa is analyzed and discussed.The result shows that the phylogenetic relationships between the various groups in this paper support the Tactopoda hypothesis,which holds that arthropods and Tardigrades are sister groups.In summary,this paper systematically studies the biodiversity,geographical distribution,ecological behavior and phylogenetic development of Tardigrades in the plateau lakes of Yunnan Province for the first time,and makes some discoveries.This provides basic information for the distribution of Tardigrades in plateau lakes in Yunnan Province,accumulates raw data on the ecological behavior of Tardigrades,and explores the relationship between Tardigrada and other taxa of Panarthropoda.