Congruent population structure inferred from dispersal behaviour and intensive genetic surveys of the threatened Florida scrub-jay (Aphelocoma coerulescens).

The delimitation of populations, defined as groups of individuals linked by gene flow, is possible by the analysis of genetic markers and also by spatial models based on dispersal probabilities across a landscape. We combined these two complimentary methods to define the spatial pattern of genetic structure among remaining populations of the threatened Florida scrub-jay, a species for which dispersal ability is unusually well-characterized. The range-wide population was intensively censused in the 1990s, and a metapopulation model defined population boundaries based on predicted dispersal-mediated demographic connectivity. We subjected genotypes from more than 1000 individual jays screened at 20 microsatellite loci to two Bayesian clustering methods. We describe a consensus method for identifying common features across many replicated clustering runs. Ten genetically differentiated groups exist across the present-day range of the Florida scrub-jay. These groups are largely consistent with the dispersal-defined metapopulations, which assume very limited dispersal ability. Some genetic groups comprise more than one metapopulation, likely because these genetically similar metapopulations were sundered only recently by habitat alteration. The combined reconstructions of population structure based on genetics and dispersal-mediated demographic connectivity provide a robust depiction of the current genetic and demographic organization of this species, reflecting past and present levels of dispersal among occupied habitat patches. The differentiation of populations into 10 genetic groups adds urgency to management efforts aimed at preserving what remains of genetic variation in this dwindling species, by maintaining viable populations of all genetically differentiated and geographically isolated populations.

Isolation and characterization of microsatellite markers from three species of swallows in the genus Tachycineta: T. albilinea, T. bicolor and T. leucorrhoa.

We describe 30 microsatellite loci developed from three species of swallows in the genus Tachycineta: T. bicolor (tree swallow), T. albilinea (mangrove swallow), and T. leucorrhoa (white-rumped swallow). These commonly studied birds nest in secondary cavities and are distributed from Alaska to Argentina. Primer pairs were designed for each species individually and tested for cross-amplification in 40-48 individuals of all three species. Polymorphism ranged from 5 to 65 alleles per locus (mean = 19.1). These markers will allow comparative studies of extra-pair paternity rates among members of the genus as well as the assessment of population structure.

Eleven microsatellite loci isolated from the banded wren (Thryothorus pleurostictus).

We describe 11 microsatellite loci isolated from the Banded Wren (Thryothorus pleurostictus), a Neotropical species for which understanding the genetic mating system is important for testing questions about the species' unusual vocal behavior. Screening of these loci revealed extremely low allelic variation in a Costa Rican population. Allelic variation at these and other previously developed loci is substantially higher in two other wren species, the southern house wren (Troglodytes aedon bonariae) and rufous-and-white wren (Thryothorus rufalbus), suggesting that the low allelic diversity in the banded wren results from demographic bottlenecks rather than locus-sampling artifacts.

Aluminum-resistant Arabidopsis mutants that exhibit altered patterns of aluminum accumulation and organic acid release from roots.

Al-resistant (alr) mutants of Arabidopsis thaliana were isolated and characterized to gain a better understanding of the genetic and physiological mechanisms of Al resistance. alr mutants were identified on the basis of enhanced root growth in the presence of levels of Al that strongly inhibited root growth in wild-type seedlings. Genetic analysis of the alr mutants showed that Al resistance was semidominant, and chromosome mapping of the mutants with microsatellite and random amplified polymorphic DNA markers indicated that the mutants mapped to two sites in the Arabidopsis genome: one locus on chromosome 1 (alr-108, alr-128, alr-131, and alr-139) and another on chromosome 4 (alr-104). Al accumulation in roots of mutant seedlings was studied by staining with the fluorescent Al-indicator dye morin and quantified via inductively coupled argon plasma mass spectrometry. It was found that the alr mutants accumulated lower levels of Al in the root tips compared with wild type. The possibility that the mutants released Al-chelating organic acids was examined. The mutants that mapped together on chromosome 1 released greater amounts of citrate or malate (as well as pyruvate) compared with wild type, suggesting that Al exclusion from roots of these alr mutants results from enhanced organic acid exudation. Roots of alr-104, on the other hand, did not exhibit increased release of malate or citrate, but did alkalinize the rhizosphere to a greater extent than wild-type roots. A detailed examination of Al resistance in this mutant is described in an accompanying paper (J. Degenhardt, P.B. Larsen, S.H. Howell, L. V. Kochian [1998] Plant Physiol 117: 19-27).