Applications of electrophoretic data in avian systematics

-This paper is a survey of applications of electrophoretic techniques in ornithology, with an emphasis on post-1970 publications. The majority of electrophoretic studies of birds have been limited in a variety of ways. Many have dealt with "domesticated" species or have been limited to the examination of blood and/or egg-white proteins. Problems in comparing results from different studies have arisen because of: (1) dissimilar electrophoretic techniques; (2) varying numbers of taxa; (3) nonstandardized enzyme and locus nomenclature; and, especially, (4) different methods of data analysis. These methodological problems must be addressed in order to broaden the utility of electrophoretic data in avian systematics. I suggest that the enzyme names recognized by the International Union of Biochemistry be used exclusively and that a standardized locus nomenclature, comparable with that used in other vertebrate classes, be developed. The predominating use of allozyme characters can be supplemented by "isozyme characters" (e.g. different numbers of genes, heteropolymer assembly, and regulation of expression sensu Buth in press), which possibly could be applied to a determination of systematic relationships of higher-level taxonomic ranks. Allozyme and/or isozyme data should be retained in particulate form (i.e. not summarized as genetic distances). The use of outgroups to assign evolutionary direction is encouraged. Received 2 May 1983, accepted 19 April 1984. THE evolutionary relationships among birds have long been a matter of interest. Among vertebrates, birds seem to constitute a rather homogeneous assemblage, a situation that has contributed to the difficulty of establishing detailed systematic relationships. In attempting to determine these relationships, avian systematists have relied upon a number of taxonomic characteristics. Most have used morphological features (e.g. intestinal convolutions, musculature, nasal bones, and palate type), although some have used ecological, ethological, geographical, or physiological attributes (Van Tyne and Berger 1976). With the application of biochemical techniques to systematic analyses, a new suite of characters became available. Techniques that have used biochemical characters and that have been applied in ornithological studies include DNA-DNA hybridization (Sibley and Ahlquist 1980), immunoelectrophoresis (Ryttman et al. 1980), micro-complement fixation (Ho et al. 1976), and electrophoresis (studies reviewed herein). Historically, electrophoresis has been the most important in terms of numbers of studies using biochemical techniques to solve problems in avian biology. Electrophoresis continues to be a cost-effective method of collecting large amounts of data and providing alternative data sets for comparison with results obtained through other biochemical techniques. Electrophoresis is a useful tool in examining a variety of genetic and developmental phenomena. In avian biology, it has been used to obtain quantitative estimates of genetic variation in natural populations, to study the patterns of gene activation, and to examine the genetic control of various proteins. Another important application of these data has been as a systematic tool. It was noted quite early that biochemical data would be useful in systematic studies (e.g. McCabe and Deutsch 1952, Sibley 1960, Gysels 1963), but ". . . even by 1970, a major review of electrophoretic literature included almost no discussion of uses of electrophoretic data in systematics, other than for description and identification of species" (Avise 1974: 465). Even now, there are relatively few comprehensive studies using this data base to elucidate systematic relationships among birds, particularly at higher taxonomic ranks (but see Sibley 1970 and Sibley and Ahlquist 1972 for exceptions). Electrophoretic data provide alternative suites of characters that can be used to discern systematic relationships among birds. Initially, it was thought that biochemical (molecular) characters were more conservative than other types 717 The Auk 101: 717-729. October 1984 This content downloaded from 157.55.39.243 on Thu, 06 Oct 2016 05:02:24 UTC All use subject to http://about.jstor.org/terms 718 RONALD H. MATSON [Auk, Vol. 101 of characters and therefore had greater utility. That is, it was thought that these characters would reflect the evolutionary history of the group under investigation, despite possible adaptive changes or convergences (Sibley 1965). Avise (1974) stated that electrophoretic characters were more precise and objective than other types of characters. Although it has been shown that these are not necessarily valid attributes of biochemical characters (Selander 1971, Wiley 1981), these characters are still useful in systematic studies. Some advantages to the use of electrophoretic data include high inheritance of characters, the expression of which is usually not subjected to environmental effects, and codominant phenotypic expression (Whitt 1983), which permits an accurate estimation of the allelic and genotypic composition of the sample. Although it was initially believed that electrophoretic techniques would resolve many systematic problems, a perusal of the avian literature indicates that this has not been the case. If past studies are examined, however, problems can be evaluated and mistakes rectified so that the full potential of this technique can be realized. In this paper, I will discuss problematic areas identified in past electrophoretic studies and make suggestions to insure that future investigators will be better able to apply this technique to problems of avian systematics. Barrowclough (1983) and Corbin (1983) have recently reviewed ornithological papers employing electrophoresis (and other biochemical techniques) in microevolutionary and certain systematic studies. This review will be limited to papers in which electrophoretic data have been applied to avian systematics or in which such data have contributed to systematic applications. I will further restrict my comments to papers published between 1970 and 1984; for a review of earlier papers see Sibley et al. (1974).