Contrasting genetic structures in sister species of North American scrub-jays

Threatened Florida scrub-jays (Aphelocoma coerulescens) breed communally, a re restricted to xeric sandy scrub habitat, generally disperse fewer than t hree territory diameters. Closely related Western scrub-jays (A. californic a) do not breed communally, have a broader habitat range, disperse greater distances, and are not threatened. We compared the genetic structure of 445 individuals in 11 populations in Florida with 157 individuals in eight pop ulations of Western scrub-jays. At ten microsatellite loci, Florida had 24 out of 47 total alleles, while Western scrub-jays had 44. The Florida popul ations were more differentiated (G(ST) = 0.048) than were a set of five Cal ifornia populations (G(ST) = 0.015). A randomization extension of a Mantel test showed a stronger correlation between geographic and Cavalli-Sforza ge netic distances among Western than Florida populations. Neighbour-joining t rees clustered Florida populations from the same sandy ridge systems, sugge sting that habitat continuity is more important than geographic proximity i n allowing gene flow and preventing differentiation. For Western population s, isolation by distance appears to be the major determinant of genetic str ucture. Our results suggest that contrasting genetic structures may arise b etween closely related species, as a result of differences in ecology and s ocial system. Conserving extant genetic variation in Florida jays will requ ire maintaining viable populations in each of the major sandy ridge systems .