Showing papers by "A. Townsend Peterson published in 1991"

Geographic Variation in the Ontogeny of Beak Coloration of Gray-Breasted Jays (Aphelocoma ultramarina)

Abstract: This is the publisher's version, also available electronically from http://www.jstor.org/stable/1368965#references_tab_contents.

Gene flow in scrub jays : frequency and direction of movement

Abstract: Based on strong differences in plumage coloration between coastal California (californica subspecies group) and Great Basin (woodhouseii subspecies group) populations of Scrub Jays (Aphelocoma coerulescens), museum specimens representing gene flow between the two forms are identified. A total of 27 examples of apparent genetic exchange between two forms (individuals of one subspecies group taken within the range of the other) is documented. Immigration rates are on the order of one per hundred or one per thousand individuals, a rate sufficient to prevent differentiation by genetic drift alone if effective population sizes are in the range of 100-550 individuals. Gene flow east-to-west across the Mojave Desert is two to seven times stronger than west-to-east movement. This directional bias has theoretical implications because an important assumption (symmetry of gene flow patterns) of most theoretical treatments of the effects of gene flow is violated. If effective population sizes are comparable in the two forms, then the bias in gene flow should lead to an overall greater rate of differentiation in the genetically more isolated woodhouseii populations.

Sociality and Ontogeny of Coloration in the Blue-and-Black Jays

Abstract: ABSTRAcr. -To test the hypothesis that heterochronic changes in color maturation act to integrate avian social groups, the relationship between social-group size and maturation rates of four morphological characters was analyzed in the blue-and-black jays (Cyanocorax spp., formerly Cissilopha). Contrary to patterns found in the New World jay assemblage as a whole and to theoretical predictions, sociality and maturation rates are uncorrelated within the blue-and-black jays. Such a relationship is also lacking in at least one of the other two New World jay lineages that exhibit delayed soft-part color maturation. These results suggest that maturation rates do not track sociality closely and that the occurrence of delayed maturation of soft-part coloration in some New World jay taxa may best be accounted for by phylogenetic inertia. Received 9 May 1990, accepted 10 Sept. 1990.