Molecular and cytological investigations

Abstract

Molecular and eytogenetie studies of eyprinid fishes eontinue to eontribute to our understanding of this diverse and fascinating group. Advanees in teehnology have facilitated the resolution of eharaeters that were formerly beyond measurement. Although some eharaeters derived from these studies have been employed in investigations of gene evolution. genomie organiz-ation. and meehanistie aspects of organismie evolution. most applieations with eyprinid fishes have addressed questions regarding historieal evolution. Le. phylogenetie relationships and. to a lesser extent. zoogeography. These teehniques have also been applied at the population level, but to a lesser degree. Studies of gene products or the genes themselves have revealed variation at several levels of organization. Highly variable eharaeters are valuable in assessing geographie patterns of gene flow among populations. including the limits of gene pools whose uniqueness requires taxonomie reeognition. Less variable eharaeters are useful in the study of subfamilial. and inter-and intragenerie relationships. These high er taxonomie levels are attracting great interest in research on eyprinids. as weIl as on other fishes. Here we present information on eyprinid allozymie. isozymie. and eytogene-tie eharaeteristies and their research applieations. Some additional modern moleeular methods hold eonsiderable potential but have yet to be used widely with eyprinids. For North Ameriean species. we employ taxonomie assign-ments of Mayden (1989) (see also Chapter 8). 4.2 ALLOZYMES AND ISOZYMES Allozyme electrophoresis is a precise and cost-effective method for comparing populations. species. and closely related genera (Bush and Kitto. 1978). Buth I. J. Winfield et al. (eds.), Cyprinid Fishes © Ian J. Winfield and Joseph S. Nelson 1991 84 Molecular and cytologicaI investigations (l984a) reviewed applications of allozyme variation in studies of cyprinid fishes, and as he predicted, allozyme data are increasingly used, especially for investigations of hybridization and introgression, population structure, bio-chemie al identification of taxa, and phylogenetic systematics. The numerous studies published since 1984 do not result from any technological break-through in the generation of allozyme data, but rather reflect an increased interest in cyprinid fishes throughout the world and the spread of the basie technology making these studies possible. Allozymes provide a particulate data base that can be generated cheaply, using supplies and materials common to basic biochemistry. Allozymes are among the least expensive biochemie al tools. Isozyme characters (sensu Whitt, 1983, 1987; Buth, 1984b), including