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.

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 Alchelating 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. Al toxicity is a global problem that limits crop productivity on acidic soils. Al is the most abundant metal in the earth's crust, and in acidic soils (pH Ͻ 5.5) the phytotoxic species Al 3ϩ is solubilized to levels that inhibit root growth and crop yield (Kochian, 1995). Large areas of the world contain acidic soils (Ͼ30% of the arable land), so Al toxicity is a very important worldwide agricultural problem (Von Uexkull and Mutert, 1995). Despite the agronomic importance of this problem, little is known about fundamental mechanisms of Al toxicity and resistance. It has been well documented that many plant species exhibit significant genetic variability in their ability to resist Al toxicity (Delhaize and Ryan, 1995; Kochian, 1995, and refs. therein). Although it is clear that certain plant genotypes have evolved mechanisms that confer Al resistance, the cellular and molecular basis for Al resistance is still poorly understood.DegenhardtThere are two strategies that plants can use to deal with Al toxicity: exclusion from the root apex or development of the ability to tolerate Al once it enters the plant symplasm (Delhaize and Ryan, 1995;Kochian, 1995). Because of the complex interactions between Al and the plant, it is very likely that there are a number of different mechanisms that plants use to confer Al resistance. This is supported by genetic studies of Al resistance, which have shown it to be a dominant, multigenic trait controlled by one or a few major...

Many animals repeat standardized displays multiple times while attracting a mate or deterring a rival. In such contexts it is possible that the ability to perform each display or signal type in a consistent fashion is under direct selection. Studies on sexual selection on song learning in birds have focused on differences in repertoire size with less attention to the potential importance of being able to perform each song/syllable type with high consistency. We present evidence that tropical mockingbirds decrease the variation between renditions of each syllable type as they grow older (i.e., become more consistent) and that more consistent males in this species tend to have higher dominance status and reproductive success. These findings stress the importance of consistency in the performance of sexual displays and suggest that this parameter may be very relevant even in species that are selected for high vocal diversity (i.e., large repertoires). In addition to signalling dominance status and age, we hypothesize that syllable type consistency may also be an indicator of the integrity of brain function in birds analogous to the tests used for neuropsychological assessment in humans.

ABSTRACT. Feathers are increasingly collected as a nondestructive source of DNA for avian genetic research. Although feather samples are not optimal in some important ways than more robust blood or tissue samples, feather sampling requires less training for field workers, results in shorter handling times for the organism, generates no hazardous wastes, and requires simpler storage procedures. Along with these largely positive attributes comes a set of challenges, particularly the relatively low copy number of DNA present in feather samples. We compared the utility and reliability of feathers to the more traditional blood samples as sources of DNA for polymerase chain reaction (PCR)-based molecular sexing of Black-capped Chickadees (Poecile atricapilla). DNA from 102 individuals was extracted separately from both single rectrices and from blood samples, and the sex of each bird was then determined using standard PCR-based methods. We found complete agreement between sex determinations based on feather versus blood DNA extractions. Slight variations in lab protocols were necessary to obtain consistent results from these two DNA sources; and we briefly discuss other sources of error that could occur in feather-based molecular sexing studies. This controlled comparison of feather versus blood samples demonstrates that plucked rectrices provide a highly reliable source of DNA for molecular sexing of wild birds. SINOPSIS. Una comparación entre el uso de plumas versus muestras de sangre como fuentes de ADN para estudios moleculares de determinación de sexoSe está incrementando la modalidad de usar plumas como una fuente no destructiva de ADN para llevar a cabo investigación genética en aves. Aunque las muestras tomadas de plumas, en algunas instancias no sonóptimas que muestras más robustas como sangre y tejido, el uso de estas no requiere adiestramiento especial, toman menos tiempo en la manipulación del ave, no generan desperdicios peligrosos y requieren un almacenaje sencillo. Aunque hay atributos positivos en el uso de plumas, también existe el problema de obtener una muestra baja de ADN. Examinamos la utilidad y confiabilidad de muestras de plumas en comparación con técnicas más tradicionales como obtención de muestras de sangre como una fuente de ADN para el sexado de Poecile atricapilla utilizando PCR. A tales efectos se extrajo ADN, de rectrices, de 102 individuos y un número similar de muestras de sangre para determinar el sexo usando PCR. Encontramos resultados similares con ambos métodos. Sin embargo, fueron necesarios pequeñas variaciones en el protocolo de laboratorio para obtener resultados consistentes, de ambas fuentes de ADN. Discutimos algunas fuentes de error que pueden ocurrir cuando se utilizan plumas para la determinación del sexo utilizando técnicas moleculares. Este estudio demuestra que las rectrices son una fuente confiable para obtener buenas muestras de ADN y poder determinar el sexo en aves silvestres.

Both cytokinin (N6-benzyladenine [BA]) and auxin (2,4-dichlorophenoxyacetic acid [2,4-D]) stimulate the accumulation of an mRNA, represented by the cDNA pLS216, in Nicotiana plumbaginifolia suspension culture cells. The kinetics of RNA accumulation were different for the two hormones; however, the response to both was transient, and the magnitude of the response was dose dependent. Runoff transcription experiments demonstrated that the transient appearance of the RNA could be accounted for by feedback regulation of transcription and not by the induction of an RNA degradation system. The feedback mechanism appeared to desensitize the cells to further exposure of the hormone. In particular, cells became refractory to the subsequent addition of 2,4-D after the initial RNA accumulation response subsided. A very different response was observed when the second hormone was added to cells that had been desensitized to the first hormone. Under such conditions, BA produced a heightened response in cells desensitized to 2,4-D and vice versa. These findings support a model in which cytokinin further enhances the auxin response or prevents its feedback inhibition. The hormone-induced RNA accumulation was blocked by the protein kinase inhibitor staurosporin. On the other hand, the protein phosphatase inhibitor okadaic acid stimulated expression, and, in particular, okadaic acid was able to stimulate RNA accumulation in cells desensitized to auxin. This suggests that hormone activation involves phosphorylation of critical proteins on the hormone signaling pathway, whereas feedback inhibition may involve dephosphorylation of these proteins. The sequence of pLS216 is similar to genes in other plants that are stimulated by multiple agonists such as auxins, elicitors, and heavy metals, and to the gene encoding the stringent starvation protein in Escherichia coli. It is proposed that this gene family in various plants be called multiple stimulus response (msr) genes.