Chemosystematics-Analyses of Populational Differentiation and Variability of Ancestral and Recent Populations of Juniperus ashei

Three types of data were used to analyze 28 natural populations of Juniperus ashei: 16 morphological characters, 152 terpenoids, and 23 peroxidases. In this paper the peroxidase electromorphs were treated as ordinary qualitative chemical characters to examine the feasibility of using isozymes for taxonomic purposes and as indicators of populational variability. The data sets were subjected to various numerical analyses to examine regional trends, ancestral affinities, and variability within populations. Principal coordinate analysis was used to resolve the major coordinates of variation from the similarity matrix of each data set. Coordinate loadings were then contoured for the first three coordinates of each similarity matrix to aid the visualization of the regional trends. The terpenoids and morphology showed a series of uniform populations from central Texas into the Ozarks with divergent populations on the south and west portions of the range, extending into northern Mexico. No regional trends were apparent in the peroxidases and no corresponding modes of variation were seen between the peroxidases and the other two data sets. Pleistocene vegetation is reviewed and migration paths are speculated upon. Advanced and primitive character states are discussed. The uniform body of J. ashei populations from central Texas to the Ozarks appear to be advanced (recent), whereas the divergent populations seem to be more primitive (ancestral). A method called differential similarities is introduced to analyze the clinal gradation of J. ashei toward J. saltillensis in Mexico. Intrapopulational variability was analyzed by use of the average similarity within populations and the coefficient of phenetic variation (CPV). In general, the recent populations had high similarities and low variability, and the ancestral populations had lower average similarities and higher CPVs with both the morphological and terpenoid data. The pattern of variation in the peroxidases could not be generalized upon, but appeared to be mosaic. Peroxidases did not appear useful in this analysis when subjected to standard numerical analysis procedures. The evolution of J. ashei into its present distribution appears to have had at least two phases composed of very uniform, recent migrations and persistent, variable, relict populations perhaps extending close to the geographic origin of this taxon in northern Mexico. The use of chemical characters has gained widespread acceptance during the past decade to the point that a graduate student thesis in systematics is now unusual if no chemical data are utilized. Because of the relative ease of use, flavonoids are widely utilized in systematic and evolutionary plant studies. The early works on Asplenium (Smith & Levin, 1963), Lemnaceae (McClure & Alston, 1966) and Baptisia (Alston & Turner, 1963) are classics, required reading for chemosystematic students. Likewise, classic is the work on betalains by Mabry and coworkers (summarized in this symposium). Whereas flavonoids and betalains have been extensively used above the species level (probably due to the qualitative nature of the methods), terpenoids, due to the quantitative nature of gas/liquid chromatography, have been more widely used at or below 1 I thank Walter Kelley for field assistance and the use of the peroxidase data which he diligently gathered. This research was supported by NSF Grants GB24320 and GB37315X. Computer time was furnished by Colorado State University. 2 Science Research Center, Hardin-Simmons University, Box 1095, Gruver, Texas 79040. ANN. MISSOURi BOT. GARD. 64: 184-209. 1977. This content downloaded from 157.55. 39.102 on Mon, 03 Oct 2016 04:39:31 UTC All use subject to http://about.jstor. org/terms 1977] ADAMS-JUNIPERUS ASHEI 185 the species level. The gymnosperms have been the focus of many studies of populational differentiation which have uncovered dines (Flake et al., 1969, 1973), chemical races (Smith et al., 1969), hybridization (see von Rudloff, 1975 for an excellent review), and ancestral migrations (Adams, 1975a; Zavarin & Snajberk, 1973). In the angiosperms, work on the monterpenes of Bursera (Mooney & Emboden, 1968) demonstrated the use of these compounds in the detection of clinal variation. Of course, the work on the Australian Eucalyptus species has been of tremendous use in the classification of populations of these taxa and is well known. Although studies using terpenoid characters to analyze populational differentiation are well known, the analysis of population variability in relation to important population biology questions such as the founder's effect, genetic drift, the effects of small versus large populations and central versus peripheral sites on variability have not been addressed. The relatively recent rise in the use of isoenzyme data has rekindled an interest in the examination of these questions. Gottlieb (at this symposium) has reviewed the literature on isozymes and their use in systematics. Nevertheless, it seems in order to mention that the "isozyme bandwagon" has become the current fad before we have developed a very thorough knowledge about the molecular basis of the electromorphs distinguished on gels. Before the widespread use of isozymes, the study of variability within populations seems to have stagnated with the exception of the numerical taxonomic school (including morphometrics). Gilmartin (1969a, 1969b, 1974, 1976) has introduced a new idea called the coefficient of phentic variation (CPV) to examine the combined effects of many characters on variability. The CPV is merely the standard deviation of the mean similarity among a group of operational taxonomic units (OTUs) divided by that mean similarity. Whereas the mean similarity of a group tells about the average affinities, the CPV shows how homogeneous are the similarities of one group versus another group. Since the CPV is normalized by the mean similarity, different character sets can be compared as well as different levels of organization (i.e., population vs. species vs. genus). To my knowledge, the CPVs have not been used to study population variability with the exception of the studies by Gilmartin. The purpose of this paper is to examine population differentiation and variability in Juniperus ashei Buch. using three contrasting sets of characters: morphological characters, volatile terpenoids from leaves, and leaf peroxidases. The literature on J. ashei has been reviewed by Adams & Turner (1970). Juniperus ashei is a taxon of a rather restricted range, occurring on limestone outcrops from northern Mexico to southern Missouri (Fig. 1). The Edwards Plateau region of central Texas supports dense populations covering thousands of acres, whereas the disjunct populations (Lubbock-Post, Texarkana, Arbuckle Mountains, Ozark Mountains, and northern Mexico) often have nearly pure stands of J. ashei, but seldom cover such large areas. Being a fairly conspicuous conifer tree, one can be relatively confident in the taxonomic distribution records which imply that there are few, if any, trees between the disjunct populations and the Edwards Plateau populations. Thus, this would appear to This content downloaded from 157.55. 39.102 on Mon, 03 Oct 2016 04:39:31 UTC All use subject to http://about.jstor. org/terms 186 ANNALS OF THE MISSOURI BOTANICAL GARDEN [VOL. 64