Preliminary report on freshwater oligochaetes from some districts of Tamil Nadu (India), along with DNA barcode sequence of a commercially important oligochaete in Chennai

A survey of aquatic Oligochaeta was conducted at Thiruvallur, Chennai, Kanchipuram, Villupuram and Nilgiris districts of Tamil Nadu from October 2015 to June 2016. Eleven taxa were recorded from a total of 922 specimens examined, eight of them were identified to species level. Five naidids identified during the present study: Branchiodrilus semperi, Dero dorsalis, Dero digitata, Dero indica and Dero zeylanica, and six tubificid taxa Branchiura sowerbyi, Tubificidae sp. 1, Tubificidae sp. 2, Tubificidae sp. 3, Limnodrilus hoffmeisteri and L. udekemianus. Dero dorsalis constitute the first report for Kanchipuram district. A DNA barcode sequence (GenBank accession no. MF125273) of the commercially important Limnodrilus hoffmeisteri, commonly known as ‘Tubifex worms’ in Chennai, was obtained and compared with other published COI sequences from that morphospecies from around the world.

Impact of secondary salinisation on the structure and diversity of oligochaete communities

Secondary salinisation has become one of the most important factors responsible for changes in the aquatic biota. Earlier research has focused on macroinvertebrates including oligochaetes in anthropogenically saline rivers and streams, but studies on oligochaetes in anthropogenically saline stagnant waters remain scarce. Therefore, this study was conducted to assess changes in the species composition as well as the abundance and biomass of oligochaete communities along a large salinity gradient in the anthropogenic inland water bodies located in the Upper Silesian Coal Basin (Southern Poland), which is one of the largest coal basins in Europe. Herein, a total of 27 oligochaete species including five alien species were assessed, namely, Potamothrix bavaricus, Potamothrix hammoniensis, Potamothrix moldaviensis, Psammoryctides albicola, and Psammoryctides barbatus. The results confirmed that the freshwater oligochaetes could tolerate elevated water salinity and showed highest densities and taxa richness in intermediate salinity. Moreover, the waters with the highest salinity had an extremely low number of oligochaete species. A salinity level above 2800 mg L−1 led to significant loss of diversity of the oligochaetes, and consequently, these habitats were colonized by halotolerant species, especially Paranais litoralis, whose abundance increased with increasing salinity gradient.

Simultaneous preservation of the DNA quality, the community composition and the density of freshwater oligochaetes for the development of genetically based biological indices

IntroductionOligochaetes are recognized as valuable bioindicators of sediment quality in streams and lakes. The development of an oligochaete index based on the identification of specimens using DNA barcodes requires a method for simultaneously preserving the DNA quality and information on the specimen density and oligochaete community composition. Absolute ethanol optimally preserves DNA but fixation of freshwater oligochaetes with this medium can cause disintegration and fragmentation of specimens. Here, we investigated the possibility to preserve oligochaete specimens in low-pH formalin and in neutral buffered formalin for up to four weeks before genetic analyses and tested if the addition of absolute ethanol to formalin-fixed oligochaetes resulted in a loss of specimens and/or species.MethodsWe performed guanidine extraction and polymerase chain reaction (PCR) amplification/sequencing of a fragment of the cytochrome c oxidase I (COI) gene on tissue fragments preserved in low-pH formalin for up to 3 weeks and in neutral buffered formalin for up to 4 weeks. In addition, we compared the density and taxonomic composition of formalin-fixed oligochaetes of several sieved sediment samples before and after the addition of absolute ethanol.ResultsThe COI fragment of all oligochaete specimens preserved in neutral buffered formalin for up to 28 days was successfully amplified by PCR and obtained sequences were complete and of high quality. The amplification success rate for low-pH formalin fixed specimens declined after 7 days of storage. The addition of absolute ethanol to formalin-fixed oligochaete communities did not alter density or diversity estimates.DiscussionOur results indicate that sediment samples can be stored in neutral buffered formalin for up to 4 weeks and the sieved material can then be transferred to absolute ethanol, without affecting DNA quality, density and community composition of oligochaetes. Based on these results, a protocol for preserving freshwater oligochaetes, describing all the steps from collection of sediments to preservation of the biological material in absolute ethanol, is proposed. This method of fixation/preservation is of relevance for establishing DNA barcode reference databases, inventories of genetic diversity and developing genetically based biological indices.

Global panorama of studies about freshwater oligochaetes: main trends and gaps

Freshwater oligochaetes have been studied over the years in a wide range of habitats around the world. To analyse the data published about freshwater oligochaetes in the 31 year period between 1985 and 2015, we searched for documents in the ISI Web of Science, Scopus and SciELO databases. A total of 979 works were evaluated from 184 periodicals. The United States is the country with the most publications about aquatic oligochaetes, followed by France, Germany and Italy. Works related to the ecology and ecotoxicology of these organisms are most abundant. Studies carried out in the laboratory are most frequent, consisting of investigations involving bioassays, morphology, genetics and molecular biology. The results also show that spring, cave water bodies and swamps have been studied less than any other aquatic habitat and that countries of the Southern Hemisphere are under-represented in the studies of aquatic oligochaetes. Hence, there is a need for increased efforts to fill in gaps in the knowledge about these oligochaetes.

Three new species of Tubificinae, Oligochaeta, from two plateau lakes in Southwest China

Three new species of Tubificinae (Naididae, Oligochaeta), Varichaetadrilus vestibulatus n. sp., Aulodrilus apeniatus n. sp., and Ilyodrilus mesoprostatus n. sp., are reported from Fuxian Lake and Xingyun Lake of Yunnan Province, Southwest China. V. vestibulatus differs from its allies by possessing modified spermathecal chaetae and thinner cylindrical penial sheaths. A. apeniatus is unique in the genus by having no penis. I. mesoprostatus is distinguishable from congeners by its prostate glands joining middle portion of atria and having concave, cone-shaped cuticular penial sheaths. Twenty-eight species of freshwater oligochaetes have hitherto been recorded from Yunnan Province, including five endemic species from three plateau lakes.

Freshwater oligochaetes of India: A review

The present review deals with freshwater oligochaetes of India which records the presence of 102 species of freshwater oligochaetes belonging to 17 genera and 4 families. Besides this, a brief description of their global and Indian distribution has also been made along with their ecology, morphology of typical oligochaetes methods of their collection and preparation for taxonomic study has also been given. A thorough survey of various states is needed for the distribution of oligochaetes systematically.