| dc.description.abstract | An important question in evolutionary biology today is exactly how and when do the genetic changes which accompany evolutionary divergence occur? This study examines two competing hypotheses, with the major difference between the two being the tempo in which organismal and or genetic changes occur. The traditional view that most evolutionary change is gradual and cummulative within lineages - phyletic gradualism - is challenged by the more recent theory that the majority of evolutionary change is concentrated within speciation episodes - rectangular evolution. These two models lead to distinct predictions of mean amounts of genetic distance between species in species-rich versus species-poor phylads of equal evolutionary age. Genetic distance may be measured with any of a number of quantifiable parameters, i.e. gross karyotype, structural genes, morphologies, or DNA. In this study, the DNA of North American cyprinid fishes (minnows) was examined quantitatively. Results were consistent with earlier work done with these fishes using different parameters of measurement. Despite the extensive speciation of Cyprinidae, changes in nuclear genome size, as well as karyotypic, structural gene, and morphological changes do not support a rectangular mode of evolution. | en |
