The loss of genetic diversity in the Chinese paddlefish (Psephurus gladius Martens) as revealed by DNA fingerprinting.

TLDR: Compared genetic diversity of historical collections of Chinese paddlefishes with recent collections is compared, to see whether there has been a loss of genetic diversity in this species as its range and population size have changed.

Abstract: Examining patterns of genetic diversity has become an integral component of many management plans concerning endangered species. Chinese paddlefish (Psephurus gladius Martens), a large-sized freshwater fish, is the only member of the family Polyodontidae present in Asia and in the main stream of the Yangtze river. Since the Gezhouba Dam, which was built in 1981, blocked the channel and prevented sturgeon from swimming into the lower-middle section of the Yangtze river, currently the Chinese paddlefish is found only in the upper main stem of the Yangtze river. Furthermore, in the last two decades, the over-catching, habitat destruction and pollution have caused a rapid reduction of the wild population of Chinese paddlefishes, such that the species is now listed as endangered (Category I of the State Key Protected Wildlife List, in the CR Category of the IUCN and on Appendix II of the CITES; Yue et al. 1998). Multiple factors are implicated in species extinction, including habitat loss, and fragmentation, demographic instability, inbreeding and other genetic factors (Lande 1988). If one of these factors, namely recent changes in genetic diversity, can be tested and perhaps rejected, then research and management can focus on the other extinction mechanisms. Moreover, species endangerment often derives from the erosion of genetic diversity (Chen 1993). The loss of genetic diversity predicts lower individual fitness and lower population adaptability (Lande 1998). Consequently, information on genetic diversity may contribute to a better understanding of the causes of species endangerment and thereby help in the development of management strategies for species conservation. Genetic diversity surveys in endangered populations typically determine the variation currently maintained in the population rather than the magnitude or rate of loss of genetic diversity over time (Matocq et al. 2001). Finding evidence of temporal changes in genetic diversity is challenging. Difficulties include finding appropriate molecular markers, methods of analysis (Luikart et al. 1998) and establishing a baseline or reference point from previous specimens against which to measure change (Taylor et al. 1994). DNA fingerprinting is a good marker system for small populations (Wan et al. 2004) and has revealed the loss of genetic diversity (Wan and Fang 2002, 2003; Wan et al. 2003a), genetic variation between subpopulations (Fang et al. 2002a, 2003), and genetic differentiation of populations (Wan et al. 2003b) of endangered animals. Besides a reliable genetic marker, detecting the loss of genetic diversity also requires archival specimens from which DNA can be obtained. A considerable number of historic samples were preserved by formalin-fixation. The formalin-induced cross-linking between DNA and proteins resulted in the extraction of only fragmented DNA from fixed samples, limiting the use of these archival specimens in conservation genetics (Wan et al. 2004). However, a recent study reported the isolation of high molecular weight DNA from formalin-fixed samples and the successful use of such DNA for fingerprinting studies (Fang et al. 2002b). In this study, we compared genetic diversity of historical collections of Chinese paddlefishes with recent collections, to see whether there has been a loss of genetic diversity in this species as its range and population size