Studies on molecular characterisation and phylogenetic analysis of dragonflies and damselflies (Odonata: Insecta) of selected habitats of Kerala

Abstract

Odonata is a primitive order of class Insecta. The order is divided into three suborders- Anisoptera, Zygoptera and Anisozygoptera. Anisoptera is the suborder of dragonflies and damselflies belonging to the suborder Zygoptera. Anisozygoptera is a living fossil and has only 3 species representatives globally. Odonates are hemimetabolous insects and both larval and adult forms are predators. They are amphibiotic; egg and larval development take place in water and adults are aerial. Odonates are naturally considered as biocontrol agents and bioindicators. Various habitats of high land, midland and low land regions of 5 districts of Kerala were selected for the study. A total of 73 locations were observed in the Thrissur, Ernakulam, Palakkad, Wayanad and Idukki districts of Kerala. The observed habitats include streams, rivers, ponds, lakes, paddy fields, ditches and estuaries. A total of 71 species (33 species of damselflies and 38 species of dragonflies) were observed during the study. They belong to 10 families and 43 genera. The Western Ghats endemic species recorded during the work were Aciagrion approximans krishna, Agriocnemis keralensis, Pseudagrion indicum and Protosticta gravelyi. The rarely found species Paracercion malayanum is the first record from central and northern Kerala. Taxonomic keys for the observed 71 species of odonates were prepared. Traditionally organisms were classified based on morphological features. Many research workers pointed out the limitations of traditional taxonomy. These challenges can be overcome by molecular taxonomic approaches. The results of phylogenetic analysis become more convincing when multiple marker genes are included in the study. So, the present work focused on mitochondrial COI gene and nuclear 18S rRNA gene for the molecular characterisation and phylogenetic assessment of selected odonates of Kerala. Molecular characterisation of 34 species belonging to 28 genera was done. Partial COI gene, 18S rRNA gene sequences and translated protein sequences were generated. Of these, twelve COI gene sequences and twenty three 18S rRNA gene sequences are the first worldwide GenBank records. Mitochondrial COI sequences can be used for precise and faster identification of odonate species and phylogenetic studies. Nuclear 18S rRNA gene sequences are beneficial in higher level phylogenetic analysis. Phylogenetic analyses of two suborders and selected families, based on partial COI and 18S rRNA gene sequences were carried out and genetic divergence values among odonates were estimated. The efficiency of partial COI and 18S rRNA marker genes in resolving relationships was studied. A detailed comparison of trees based on both marker genes revealed the efficiency of COI over the 18S rRNA gene in resolving family and suborder trees. Phylogenetic analyses of the 27 genera were done based on COI gene sequences. The results of the analyses and the calculated genetic divergence values provided insights into intraspecific and interspecific genetic variation of odonates across large geographic distances. The majority of odonates selected for the study showed low genetic variability over long distances (different countries and continents) except for eight species. When comparing the results, genetic variability was lesser in damselflies and considerably high in dragonflies. The estimated interspecific divergence values within each genus showed that maximum and minimum interspecific divergence values were possessed by genus Tholymis and genus Dysphaea respectively. Another finding of the study was the close genetic similarity observed between morphologically dissimilar and geographically distant species.