SELECTIVE MORTALITY AND REPRODUCTION IN A NATURAL POPULATION OF BUFO BOREAS.

Abstract

Controversy surrounding the evolutionary relevance of enzyme variation has added new impetus to theoretical investigations into the forces responsible for genetic polymorphism (e.g., Christiansen and Feldman, 1975; King and Ohta, 1975; Ohta and Kimura, 1975; Hedrick et al., 1976; Gillespie, 1977; Lewontin et al., 1978). These considerations have traditionally centered upon various forms of natural selection or, in its absence, random processes. It is, then, particularly important to seek and study selection in natural populations if we hope to understand more fully its role in the maintenance of genetic variation. Survivorship, as a component of fitness, must not be regarded as the sole determinant of reproductive success, yet it is clearly important. Consequently, there is reason to seek genotype-related differences in rates of mortality in natural populations. A simple first step is the search for changes in the genetic composition of a population over time. Literature addressing the question of genetic change in natural populations is restricted mainly to chromosomal analysis (Dobzhansky, 1970; Dobzhansky et al., 1976) and the monitoring of simple morphological differences (Ford, 1975). Surprisingly few studies have addressed the problem utilizing the electrophoretic technique although it has been successfully employed to monitor genetic changes in laboratory populations (Kojima and Yarbrough, 1967; Yarbrough and Kojima, 1967; Kojima, 1971; Powell, 1971; MacDonald and Ayala,