Mitochondrial DNA analysis reveals extremely low genetic diversity in a managed population of the Critically Endangered Gharial (Gavialis gangeticus, Gmelin, 1789)

Abstract

T genetic diversity of small populations is low due to various factors such as severe population declines, the founder effect and genetic bottlenecks (Banks et al., 2013). Such populations tend to lose variability rapidly as a consequence of various biotic and abiotic factors through genetic drift (Ellegren & Galtier, 2016). Drifts, regardless of any balancing force, can bring sudden and drastic changes in the allele frequency (Liao & Reed, 2009). The magnitude of such events are greater in a small population with little or no gene flow. Increased homozygosity and an increase in the frequency of recessive deleterious alleles, known as inbreeding, are immediate effects of reduced variability (Frankham et al., 1999). Long periods of isolation and inbreeding eventually lead to the decreased evolutionary adaptive potential of individuals and populations (Allendorf, 2010; Frankham et al., 1999; Galov et al., 2011; Lande et al., 1987; Liao & Reed, 2009). A decline in adaptive potential may drastically increase the extinction risk of a species locally or globally. Hence, monitoring the level of genetic variation is important for planning conservation strategies for wild and managed populations. Species living in freshwater ecosystems are the most threatened due to natural (increasing surface temperature, non-uniform rainfall pattern) and anthropogenic (pollution, incidental capture, disturbance) factors. The gharial Gavialis gangeticus Gmelin (1789) is a Critically Endangered (Lang et al., 2019) freshwater crocodilian species endemic to the northern part of the Indian subcontinent (Hussain, 1999; Lang et al., 2019). The unique long-slender snout of the gharial, an adaptation for catching fish, makes it more vulnerable to accidental mortality in fishing nets (Berkovitz & Shellis, 2016; Hasan & Alam, 2016). Habitat destruction, poaching and accidental mortality in fishing gear brought the species to near-extinction. Between the 19th century and the mid-20th century, the population declined by an estimated 85 % (Hussain, 2009; Whitaker et al., 1974). Many gharial populations were extirpated in the early 1970s. By 1979, the largest known population was the one in the Chambal River, in which there were 107 individuals (all size classes) (Whitaker & Daniel, 1980). Mitochondrial DNA analysis reveals extremely low genetic diversity in a managed population of the Critically Endangered Gharial (Gavialis gangeticus, Gmelin, 1789)