A Relationship of Genetic Variation Within and among Populations: An Extension of the Kluge-kerfoot Phenomenon

Pierce, B. A. and J. B. Mitton (Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder, Colorado 80309) 1979. A Relationship of Genetic Variation Within and Among Populations: An Extension of the Kluge-Kerfoot Phenomenon. Syst. Zool. 28:63-70.-A positive correlation between intrapopulation variation and among population diversity has been demonstrated for morphometric characters (the Kluge-Kerfoot phenomemon). This study extends the relationship to allozyme variation. Four sets of statistics are utilized to partition genetic variation into within and among population components of diversity and the strength of association between these components is assessed by means of rank order correlation. All but one of the seven species tested demonstrate significant, positive correlation coefficients for all four of the diversity measures. Although both selective and stochastic mechanisms may generate such a relationship, it appears that stochastic forces do not totally account for the correlations seen in the data sets analyzed here. [Kluge-Kerfoot phenomenon; intrapopulation variation; among population diversity; allozyme variation.] Fundamental to evolutionary biology is an understanding of the nature of morphological variation and its underlying genetic diversity. Those factors responsible for the maintenance of variation within a population are not well understood and are currently the subject of much debate. A complementary and equally important topic of evolutionary theory concerns the basis of interpopulation diversity. The relationship between variation within populations and variation among populations was the focus of a seminal paper by Kluge and Kerfoot in 1973. In an analysis of seven vertebrate morphometric data sets, Kluge and Kerfoot (1973) were able to demonstrate a strong, significant correlation between within population variation and a measure of differentiation among populations. Sokal (1976) reexamined their methods and suggested some modifications in their technique. Sokal's calculations, however, also yielded a similar pattern of within and among population variation both in the original data sets of Kluge and Kerfoot and in additional data sets on invertebrates. An example of the relationship between variation within and among populations may be found in an analysis of seven meristic variables of the killifish, Fundulus heteroclitus, from four populations (Fig. 1). The Kluge-Kerfoot phenomenon of a positive relationship between within and among population variation is of potential importance to biologists studying the nature of character divergence. It may also prove to be a valuable predictive tool to those interested in the ecological divergence of populations. By examining levels of intrapopulation variation, one may be capable of statistically predicting the types of niches and environments a species is capable of occupying. For example, if one observes low intrapopulation variability in temperature tolerance, one could predict from the Kluge-Kerfoot relationship that interpopulation variation in temperature tolerance will also be low, and the organism will be limited in its range of thermal environments. In spite of its potential importance to evolutionary biology, the mechanisms responsible for the Kluge-Kerfoot phenomenon remain obscure. Kluge and Kerfoot (1973) explained the relationship by proposing that normalizing selection limits intrapopulation variability, and they suggested that divergence of characters among populations is a function of selection acting upon the levels of within pop-