SPECIATION IN NORTH AMERICAN FIELD CRICKETS: EVIDENCE FROM ELECTROPHORETIC COMPARISONS.

Abstract

Understanding the dynamics of the speciation process is of central importance to the study of evolution. It is of particular interest to know what changes (physiological, developmental, behavioral, ecological, chromosomal) are directly associated with the evolution of reproductive isolation, how rapidly and under what circumstances (allopatry, sympatry, etc.) such changes occur, and the relative importance of selection and stochastic factors in producing these changes. A widely accepted model of geographic speciation (Mayr, 1963a; Dobzhansky, 1970) suggests that new species arise in isolated populations through the gradual accumulation of genetic differences. It has become increasingly clear that speciation events do not always conform to this pattern (Bush, 1975b; White, 1978). Alternative models of speciation have been developed to explain observed relationships among closely related species. These include models of sympatric speciation with temporal isolation, habitat isolation, host race formation, or some combination of these (or other) factors acting to restrict gene flow (Alexander and Bigelow, 1960; Bush, 1974, 1975a; Tauber and Tauber, 1977a, b; Tauber et al., 1977). Studies of field crickets (Orthoptera: Gryllidae) have emphasized the importance of life cycle evolution in the speciation process (Bigelow, 1962; Masaki, 1965; Alexander, 1968; Harrison, 1978). From observations of closely related species of Gryllus in eastern North America, Alexander and Bigelow (1960) argued that seasonal isolation of breeding adults can provide an effective barrier to gene flow and eventually lead to speciation without geographic isolation. Here I report the results of an electrophoretic survey of genetic variation in seven species of Gryllus from North America. Relationships based on biochemical characters are significantly different from those previously established on the basis of morphology, song, distribution, and habitat. These observations provide a new framework for constructing models of speciation in the genus Gryllus.