One Species or Two? Vicariance, Lineage Divergence and Low mtDNA Diversity in Geographically Isolated Populations of South Asian River Dolphin

Abstract

Despite their endangered status, the taxonomic relationship between the two geographically isolated South Asian river dolphin populations has never been comprehensively assessed and remains contentious. Here we present the first dedicated evaluation of the molecular phylogenetic relationship between the Indus (Platanista gangetica minor) and Ganges (Platanista gangetica gangetica) River dolphins using mitochondrial DNA from the control region and cytochrome b, extracted from museum specimens. The 458 bp partial control region sequences from 26 Indus River dolphin samples exhibited no variation. Only six haplotypes were identified in the 31 (18 Indus; 13 Ganges) complete (856 bp) control region sequences obtained, none were shared between subspecies, and there were five fixed differences between them. Similarly low genetic diversity was found in a 541 bp section of the cytochrome b gene (n = 29). The lack of shared haplotypes and fixed differences resulted in ΦST for the partial control region sequences of 0.932 (p < 0.0001) and FST of 0.843 (p < 0.0001), indicating the long-term absence of gene flow and clear genetic differentiation between the two geographically isolated populations. An externally calibrated molecular clock estimated that Indus and Ganges dolphins diverged around 550,000 years ago (95 % posterior probability 0.13-1.05 million years ago), possibly when dolphins from the Ganges dispersed into the Indus during drainage capture. © 2014 Springer Science+Business Media New York

Why we should develop guidelines and quantitative standards for using genetic data to delimit subspecies for data‐poor organisms like cetaceans

“…There have been only very limited taxonomic studies to date but both genetic (Braulik et al . ) and skull morphology data (Braulik ) raise the possibility that these subspecies are full species. This change could have considerable consequences in terms of elevating their conservation priority and making funding available for more conservation action and research.…”

“…The Indus has been separate from the other river systems for several million years, and the estuaries are separated by several thousand kilometers of marine waters and peninsular India, meaning that movement between the "subspecies" almost certainly has not occurred for a considerable time. There have been only very limited taxonomic studies to date but both genetic (Braulik et al 2014) and skull morphology data (Braulik 2012) raise the possibility that these subspecies are full species. This change could have considerable consequences in terms of elevating their conservation priority and making funding available for more conservation action and research.…”

Foraging and feeding ecology of Platanista: an integrative review

“…Indus and Ganges dolphins have been geographically isolated from one another for 0.5 million years (Braulik et al. ), and may differ in some aspects of their foraging ecology. Despite technical difficulties in studying Platanista in captivity today or in observing them underwater, we believe that our review generates useful hypotheses for future experimental confirmation.…”

“…With a possible species split pending (see Braulik et al. ), we considered the Ganges and Indus subspecies ( Platanista gangetica gangetica and Platanista gangetica minor ) as putatively similar in terms of biology and ecology. We found literature spanning anatomical‐ecomorphological‐physiological studies, researche in captivity and in the wild, population surveys, behaviour, stomach contents, acoustics, convergent morphological traits, phylogenetic, and evolutionary studies.…”

Factors affecting the persistence of endangered Ganges River dolphins (Platanista gangetica gangetica)

“…Such evolutionary traps could be more effectively studied in certain locations (e.g., seasonal migration patterns to the Mohana tributary of the Karnali River of Nepal, and habitat occupancy below the Sapta Koshi Barrage). Further, Braulik et al () found low mtDNA variability in the Ganges dolphins, indicating habitat‐specific behavior or more localized occupancy behaviors might further contribute to the loss of genetic diversity. However, they argued that this could be the result of interactive effects of low population sizes and localized sensitive behaviors.…”