Biomedical subjects

David L Erickson

Publications and source records attributed to David L Erickson.

8 recordsLinked to original sources

PubMed2006

Proceedings of the SMBE Tri-National Young Investigators' Workshop 2005. Reconstructing the origins and dispersal of the Polynesian bottle gourd (Lagenaria siceraria).

The origin of the Polynesian bottle gourd (Lagenaria siceraria), an important crop species in prehistoric Polynesia, has remained elusive. Most recently, a South American origin has been favored as the bottle gourd could have been introduced from this continent with the sweet potato by Polynesian voyagers around A.D. 1,000. To test the hypothesis of an American origin for the Polynesian bottle gourd, we developed seven markers specific to bottle gourd (two chloroplast and five nuclear). The nuclear markers were developed using a new technique where polymorphic inter simple sequence repeat (ISSR) markers are converted into single-locus polymerase chain reaction and sequencing markers--an approach that will be useful for developing markers in other taxa. All seven markers were sequenced in 36 cultivars of bottle gourd from Asia, the Americas, and Polynesia. The results support a dual origin for the Polynesian bottle gourd: the chloroplast markers are exclusively of Asian origin, but the nuclear markers show alleles originating in both the Americas and Asia. Because hybridization of Polynesian bottle gourds with post-European introductions cannot be excluded, ancient DNA from archaeological material will be useful for further elucidating the prehistoric movements of this species in Polynesia. This work has implications not only for the dispersal of the Polynesian bottle gourd but also for the domestication and dispersal of the species as a whole.

Cell Nucleus↗

PubMed2006

Serotype differences and lack of biofilm formation characterize Yersinia pseudotuberculosis infection of the Xenopsylla cheopis flea vector of Yersinia pestis.

Yersinia pestis, the agent of plague, is usually transmitted by fleas. To produce a transmissible infection, Y. pestis colonizes the flea midgut and forms a biofilm in the proventricular valve, which blocks normal blood feeding. The enteropathogen Yersinia pseudotuberculosis, from which Y. pestis recently evolved, is not transmitted by fleas. However, both Y. pestis and Y. pseudotuberculosis form biofilms that adhere to the external mouthparts and block feeding of Caenorhabditis elegans nematodes, which has been proposed as a model of Y. pestis-flea interactions. We compared the ability of Y. pestis and Y. pseudotuberculosis to infect the rat flea Xenopsylla cheopis and to produce biofilms in the flea and in vitro. Five of 18 Y. pseudotuberculosis strains, encompassing seven serotypes, including all three serotype O3 strains tested, were unable to stably colonize the flea midgut. The other strains persisted in the flea midgut for 4 weeks but did not increase in numbers, and none of the 18 strains colonized the proventriculus or produced a biofilm in the flea. Y. pseudotuberculosis strains also varied greatly in their ability to produce biofilms in vitro, but there was no correlation between biofilm phenotype in vitro or on the surface of C. elegans and the ability to colonize or block fleas. Our results support a model in which a genetic change in the Y. pseudotuberculosis progenitor of Y. pestis extended its pre-existing ex vivo biofilm-forming ability to the flea gut environment, thus enabling proventricular blockage and efficient flea-borne transmission.

Animals↗

PubMed2006

Intraspecific hybridization and the recovery of fitness in the native legume Chamaecrista fasciculata.

Genetic incompatibilities and low offspring fitness are characteristic outcomes of hybridization between species. Yet, the creative potential of recombination following hybridization continues to be debated. Here we quantify the outcome of hybridization and recombination between adaptively divergent populations of the North American legume Chamaecrista fasciculata in a large-scale field experiment. Previously, hybrids between these populations demonstrated hybrid breakdown, suggesting the expression of adaptive epistatic interactions underlying population genetic differentiation. However, the outcome of hybridization ultimately rests on the performance of even later generation recombinants. In experiments that compared the performance of recombinant F6 and F2 generations with nonrecombinant F1 and parental genotypes, we observed that increasing recombination had contrasting effects on different life-history components. Lifetime fitness, defined as the product of survivorship and reproduction, showed a strong recovery of fitness in the F6. The overall gain in fitness with increased recombination suggests that hybridization and recombination may provide the necessary genetic variation for adaptive evolution within species. We discuss the mechanisms that may account for the gain in fitness with recombination, and explore the implications for hybrid speciation and phenotypic evolution.

Biological Evolution↗

PubMed2005

An Asian origin for a 10,000-year-old domesticated plant in the Americas.

New genetic and archaeological approaches have substantially improved our understanding of the transition to agriculture, a major turning point in human history that began 10,000-5,000 years ago with the independent domestication of plants and animals in eight world regions. In the Americas, however, understanding the initial domestication of New World species has long been complicated by the early presence of an African enigma, the bottle gourd (Lagenaria siceraria). Indigenous to Africa, it reached East Asia by 9,000-8,000 before present (B.P.) and had a broad New World distribution by 8,000 B.P. Here we integrate genetic and archaeological approaches to address a set of long-standing core questions regarding the introduction of the bottle gourd into the Americas. Did it reach the New World directly from Africa or through Asia? Was it transported by humans or ocean currents? Was it wild or domesticated upon arrival? Fruit rind thickness values and accelerator mass spectrometer radiocarbon dating of archaeological specimens indicate that the bottle gourd was present in the Americas as a domesticated plant by 10,000 B.P., placing it among the earliest domesticates in the New World. Ancient DNA sequence analysis of archaeological bottle gourd specimens and comparison with modern Asian and African landraces identify Asia as the source of its introduction. We suggest that the bottle gourd and the dog, two "utility" species, were domesticated long before any food crops or livestock species, and that both were brought to the Americas by Paleoindian populations as they colonized the New World.

Africa↗

PubMed2004

Ecological determinants of genetic diversity in an expanding population of the shrub Myrica cerifera.

The ecological mechanisms that contribute to the acquisition of genetic diversity in an expanding population of the shrub, Myrica cerifera, on an island habitat were investigated. Genealogical reconstruction was used to assess the contribution of early reproductive colonists to subsequent recruitment. In addition, through determination of parentage, the source of recruiting seedlings was identified and the contribution of seed and pollen dispersal into the colonizing sites was inferred. The relative contribution of different sources of gene flow was determined directly and an investigation was made into how variability in breeding patterns may have contributed to observed levels of genetic variability. It was expected that early colonists that could flower would contribute to subsequent recruiting cohorts, and that the limited number of such early reproductive colonists would lead to variance in mating success, inbreeding, or bottlenecks which could reduce genetic diversity and increase genetic differentiation among subsequent recruiting cohorts. Analyses of parentage (with paternity exclusion probability > 95%) for all recruiting plants demonstrated that in fact, there was little contribution by the early reproductive colonists to subsequent cohorts, and that immigration from outside the study sites in the form of seed dispersal accounted for over 94% of the recruitment in the study plots, with pollen dispersal accounting for less than 3% gene flow. No genetic bottleneck or evidence of reproductive skew in the recruiting cohorts were found, suggesting that propagule dispersal was from many source individuals in other established populations.

Gene Frequency↗

PubMed2004

Quantitative trait locus analyses and the study of evolutionary process.

The past decade has seen a proliferation of studies that employ quantitative trait locus (QTL) approaches to diagnose the genetic basis of trait evolution. Advances in molecular techniques and analytical methods have suggested that an exact genetic description of the number and distribution of genes affecting a trait can be obtained. Although this possibility has met with some success in model systems such as Drosophila and Arabidopsis, the pursuit of an exact description of QTL effects, i.e. individual gene effect, in most cases has proven problematic. We discuss why QTL methods will have difficulty in identifying individual genes contributing to trait variation, and distinguish between the identification of QTL (or marker intervals) and the identification of individual genes or nucleotide differences within genes (QTN). This review focuses on what ecologists and evolutionary biologists working with natural populations can realistically expect to learn from QTL studies. We highlight representative issues in ecology and evolutionary biology and discuss the range of questions that can be addressed satisfactorily using QTL approaches. We specifically address developing approaches to QTL analysis in outbred populations, and discuss practical considerations of experimental (cross) design and application of different marker types. Throughout this review we attempt to provide a balanced description of the benefits of QTL methodology to studies in ecology and evolution as well as the inherent assumptions and limitations that may constrain its application.

Adaptation, Biological↗

PubMed2004

Pseudomonas aeruginosa relA contributes to virulence in Drosophila melanogaster.

The stringent response is a mechanism by which bacteria adapt to nutritional deficiencies through the production of the guanine nucleotides ppGpp and pppGpp, produced by the RelA enzyme. We investigated the role of the relA gene in the ability of an extracellular pathogen, Pseudomonas aeruginosa, to cause infection. Strains lacking the relA gene were created from the prototypical laboratory strain PAO1 as well as the mucoid cystic fibrosis isolate 6106, which lacks functional quorum-sensing systems. The absence of relA abolished the production of ppGpp and pppGpp under conditions of amino acid starvation. We found that strains lacking relA exhibited reduced virulence in a D. melanogaster feeding assay. In conditions of low magnesium, the relA gene enhanced production of the cell-cell signal N-[3-oxododecanoyl]-l-homoserine lactone, whereas relA reduced the production of the 2-heptyl-3-hydroxy-4-quinolone signal during serine hydroxamate induction of the stringent response. In the relA mutant, alterations in the Pseudomonas quinolone system pathways seemed to increase the production of pyocyanin and decrease the production of elastase. Deletion of relA also resulted in reduced levels of the RpoS sigma factor. These results suggest that adjustment of cellular ppGpp and pppGpp levels could be an important regulatory mechanism in P. aeruginosa adaptation in pathogenic relationships.

Amino Acids↗

PubMed2002

Pseudomonas aeruginosa quorum-sensing systems may control virulence factor expression in the lungs of patients with cystic fibrosis.

Individuals with cystic fibrosis (CF) are commonly colonized with Pseudomonas aeruginosa. The chronic infections caused by P. aeruginosa are punctuated by acute exacerbations of the lung disease, which lead to significant morbidity and mortality. As regulators of virulence determinants, P. aeruginosa quorum-sensing systems may be active in the chronic lung infections associated with CF. We have examined the levels of autoinducer molecules and transcript accumulation from the bacterial populations found in the lungs of patients with CF. We detected biologically active levels of N-(3-oxododecanoyl)-L-homoserine (3-oxo-C12-HSL) and N-butyryl-L-homoserine lactone (C4-HSL) in sputum from CF patients. Interestingly, it appears that C4-HSL is less frequently detected than 3-oxo-C12-HSL in the lungs of patients with CF. We also examined the transcription of the autoinducer synthase gene lasI and showed that it is frequently expressed in the lungs of patients with CF. We observed a significant correlation between the expression of lasI and four target genes of the Las quorum-sensing system. Taken together, our results indicate that quorum-sensing systems are active and may control virulence factor expression in the lungs of patients with CF.

Bacterial Proteins↗