POPULATION GENETIC STRUCTURE OF FINLESS PORPOISES, NEOPHOCAENA PHOCAENOIDES, IN CHINESE WATERS, INFERRED FROM MITOCHONDRIAL CONTROL REGION SEQUENCES

Abstract

Seven hundred and twenty base pairs (bp) of the mitochondrial control region from 73 finless porpoises, Neophocaena phocaenoides, in Chinese waters were sequenced. Thirteen variable sites were determined and 17 haplotypes were defined. Of these, 5 and 7 were found only in the Yellow Sea population and the South China Sea population, respectively, whereas no specific haplo‐type was found in the Yangtze River population. Phylogenetic analyses using NJ and ML algorithm did not divide the haplotypes into monophyletic clades representing recognized geographic populations of finless porpoises in Chinese waters, suggesting the existence of migration and gene flow among populations. Analysis of molecular variance showed the obvious population genetic structure (φst= 0.41, P < 0.05); however, the structure was mainly between either the Yangtze River population or the Yellow Sea population and the South China Sea population. The genetic diversity (nucleotide diversity and haplotypic diversity) of the Yellow Sea population was significantly higher than those of the Yangtze River population and the South China Sea population, suggesting the relatively later divergence of the latter two populations and supporting the Yellow Sea population as the original center of Neophocaena.

Accelerating population decline of Yangtze finless porpoise (Neophocaena asiaeorientalis asiaeorientalis)

“…Following the probable extinction of the Yangtze River dolphin or baiji (Lipotes vexillifer) in the first decade of the twenty-first century (Turvey et al, 2007), the Yangtze finless porpoise has become the only cetacean species to be found in the Yangtze River. However, progressive declines in the number of porpoises observed during boat surveys (Zhang et al, 1993;Wei et al, 2002;Zhao et al, 2008), drastic loss of suitable habitats resulting in apparent distribution gaps in the formerly contiguous population (Wang et al, 2000;Zhao et al, 2008;Wang, 2009), and low levels of genetic diversity (Yang et al, 2002(Yang et al, , 2008bXia et al, 2005;Zheng et al, 2005) all suggest that the Yangtze finless porpoise may follow the baiji and also become extinct in the wild in the near future. The apparent decline of the porpoise population in the Yangtze mainstem, from more than 2550 animals in 1991 (Zhang et al, 1993) to fewer than 1225 animals in 2006 (Zhao et al, 2008), raises an important question: how many years do we have left to reverse the decline of this cetacean?…”

“…This decline is being driven by high levels of mortality resulting from anthropogenic impacts such as incidental by-catch in legal and illegal fishing gear, ship collisions, widespread sand dredging, pollution, and water development projects along the middle and lower reaches of the Yangtze River (Wang et al, 2000Yang et al, 2002Yang et al, , 2008aXia et al, 2005;Zheng et al, 2005;Zhao et al, 2008;Wang, 2009). The Yangtze is known as the ''golden channel'' of central China, and supports the livelihoods of hundreds of millions of people through agriculture, aquaculture and industrial activities.…”

High MHC DQB Variation and Asymmetric Allelic Distribution in the Endangered Yangtze Finless Porpoise, Neophocaena phocaenoides asiaeorientalis

“…Different patterns of DQB diversity might be explained by differences in population size, as larger populations have more genetic diversity. The Yangtze population, however, is smaller than the marine populations, is limited to fresh water, and has experienced a recent bottleneck based on low mtDNA diversity (Yang et al 2002;Zheng et al 2005). Thus, population size does not explain the high DQB diversity in Yangtze finless porpoises.…”

“…Mitochondrial DNA variation was primarily maintained by gene flow and genetic drift. Thus, the mtDNA diversity in the Yangtze finless porpoise might reflect the colonization of the finless porpoise from the ocean, with higher diversity found in the first areas colonized (Yang et al 2002;Zheng et al 2005). In contrast, the MHC locus did not evolve neutrally.…”

“…Several ongoing studies are focused on genetic diversity and population genetic structure. Previous studies suggest that finless porpoises have low genetic diversity at various loci, including random amplified polymorphic DNA, inter-simple sequence repeat, and mtDNA molecular markers, and moderate genetic diversity at microsatellite loci Xia et al 2005;Yang et al 2002;Zheng et al 2005). Despite low levels of mtDNA genetic diversity, significant population genetic structure was detected among the Yangtze River populations .…”