Mitochondrial DNA diversity and PCR-based sex determination of Irrawaddy dolphin (Orcaella brevirostris) from Chilika Lagoon, India

Abstract

Of the only known two Lagoon populations of Irrawaddy dolphins (Orcaella) in the world, one is residing in the Chilika Lagoon in Orissa state, India. In addition to accidental deaths in gill net fishery and mechanized boat operations, there has been exploitation of the species for their oil. Extreme patchy distribution and vulnerability to becoming entangled in fishing gear has made it a focus of conservation concern. Information on genetic diversity of populations has considerable potential for informing conservation plans. The present paper reports the first genetic study of O. brevirostris from Chilika Lagoon based on mtDNA sequencing and PCR-based sex identification from 11 individuals. Control region sequence comparison showed two haplotypes and cytochrome b a single haplotype in the Chilika population of the species. Phylogenetic analysis indicated distinct clades within the Asian samples, with the Indian population showing closest genetic proximity to the haplotypes from Thailand. Sex of the animal was determined by PCR-based method. It is important to continue to examine the population discreteness and genetic variation of Irrawaddy dolphin in Chilika Lagoon vis-à-vis its global geographic distribution for formulating the conservation plans of the species.

Mitochondrial DNA diversity and population structure in the Irrawaddy dolphin (Orcaella brevirostris) from the Gulf of Thailand and the Mekong River

“…For additional phylogeographic comparisons and to define haplotypes shared among subpopulations in Southeast Asia, we used all available sequences from the Chilika Lagoon in India (Jayasankar et al . ), Indonesia, coastal Cambodia, Philippines, and Thailand (Beasley et al . ) (GenBank Accession numbers GQ507771‐80, GQ851929, GQ922337‐47, and EU121128).…”

“…Globally, there are likely to be less than 7,000 individuals of the genus Orcaella distributed among six countries of Asia and Australia (Jayasankar et al 2011). Asian and Australian stocks were designated as separate species in 2005: Orcaella brevirostris for the Asian species and Orcaella heinsoni for the Australian species (Beasley et al 2005).…”

“…To date, no systematic genetic sampling and analyses have been undertaken for O. brevirostris along its range. There is only one published descriptive study presenting mitochondrial diversity of the population found in the Chilika Lagoon in India (Jayasankar et al 2011) and, recently, a study on genetic diversity and demographic trends of the Mekong River population was published, suggesting reduced genetic diversity and steep population declines, with the current population representing only 5.2% of the ancestral population size (Kr€ utzen et al 2018).…”

“…A total of 17 sequences out of 23 Gulf of Thailand samples and 28 sequences from 32 Mekong River samples were obtained in this study (486 bp length). We included in our analyses 11 sequences (from 11 samples) obtained from Chilika Lagoon, India, by Jayasankar et al (2011) and two sequences from Vietnam available from GenBank (accession numbers JQ814472/73). When a consensus region of 400 bp was analyzed and compared with 16 previously published control region sequences (available on GenBank), 19 haplotypes where identified (Fig.…”

First mitochondrial DNA analysis of the spectacled porpoise (Phocoena dioptrica) from Tierra del Fuego, Argentina

“…The analysis of the processes involved in the population structure of cetaceans is difficult to attain due to their high mobility and the few physical barriers of the environment in which they live. Studies of intraspecific variation using molecular markers such as mitochondrial DNA (mtDNA) have been useful in the analysis of the population structure of these species (Pichler et al 1998;Rosel and Rojas-Bracho 1999;Avise 2004;Pimper et al 2010;Taguchi et al 2010;Jayasankar et al 2011).…”