Spatial and Temporal Aspects of Populations Revealed by Mitochondrial DNA

The evolutionary analysis of DNA sequences bridges phylogenetics and population genetics. Ancient DNA (aDNA) alJows the study of extinct genotypes, populations, and species, as well as dichronic comparisons of extant populations and species. Thus a DNA forges an empirical link between history and two inherently historical fields of research. Fortunately, the conceptual frameworks of phylogenetics and population genetics can easily be extended to encompass advances being made in the study of aDNA

Invasion genetics of New World medflies: testing alternative colonization scenarios

The Mediterranean fruit fly (Ceratitis capitata) is an invasive agricultural pest with a wide host range and a nearly global distribution. Efforts to forgo the medfly\u27\u27s spread into the United States are dependent on an understanding of population dynamics in newly established populations elsewhere. To explore the potential influence of demographic and historical parameters in six medfly populations distributed from Mexico to Peru, we created population genetic null models using Monte Carlo simulations. Null expectations for genetic differentiation (F ST) were compared with actual sequence variation from four highly polymorphic nuclear loci. Four colonization scenarios that were modeled led to unique genetic signatures that could be used to interpret empirical data. Unless current gene flow across Latin America was assumed to be very high, we could reject colonizations consisting of multiple introductions, each of low genetic diversity. Further, if simulated populations were small (N e = 5 × 102 individuals per population), small invasions from a single source consistently produced F ST values comparable to those currently observed in Latin America. In contrast, only large invasions from diverse sources were compatible with the observed data for large populations (N e 5 × 103). This study demonstrates that alternative population genetic hypotheses can be tested empirically even when departures from equilibrium are extreme, and that population genetic theory can be used to explore the processes that underlie biological invasions

Climactic Niche Model for Overwintering Monarch Butterflies in a Topographically Complex Region of California

We use climatic conditions that are associated with known monarch butterfly overwintering groves in California to build a Maxent model, and focus on the fine scale probability of overwintering grove occurrence in a topographically complex region of the state (Santa Barbara County). Grove locations are known from recent and historical surveys and a long-term citizen science database. The climatic niche model performs well, predicting that overwintering habitat is most likely to occur along the coast and at low elevations, as shown by empirical data. We then use climatic variables in conjunction with climate change scenarios to model the future location of overwintering habitat, and find a substantial shift in the predicted distribution. Under a plausible scenario, the probability of occurrence of overwintering habitat directly reflects elevation, with coastal regions having a reduced probability relative to today, and higher elevation sites increasing in probability. Under a more extreme scenario, high probability sites are only located along ridgelines and in mountaintop regions of the county. This predicted shift in distribution is likely to have management implications, as sites that currently lack monarchs may become critical to conservation in the future. Our results suggest that estimating the size of the western overwintering population in the future will be problematic, unless annual counts compensate for a shift in the distribution and a potential change in the number and location of occupied sites

Retinoic acid reduces human neuroblastoma cell migration and invasiveness: effects on DCX, LIS1, neurofilaments-68 and vimentin expression

<p>Abstract</p> <p>Background</p> <p>Neuroblastoma is a severe pediatric tumor, histologically characterised by a variety of cellular phenotypes. One of the pharmacological approaches to neuroblastoma is the treatment with retinoic acid. The mechanism of action of retinoic acid is still unclear, and the development of resistance to this differentiating agent is a great therapy problem.</p> <p>Doublecortin, a microtubule-associated protein involved in neuronal migration, has recently been proposed as a molecular marker for the detection of minimal residual disease in human neuroblastoma. Nevertheless, no information is available on the expression of doublecortin in the different cell-types composing human neuroblastoma, its correlation with neuroblastoma cell motility and invasiveness, and the possible modulations exerted by retinoic acid treatment.</p> <p>Methods</p> <p>We analysed by immunofluorescence and by Western blot analysis the presence of doublecortin, lissencephaly-1 (another protein involved in neuronal migration) and of two intermediate filaments proteins, vimentin and neurofilament-68, in SK-N-SH human neuroblastoma cell line both in control conditions and under retinoic acid treatment. Migration and cell invasiveness studies were performed by wound scratch test and a modified microchemotaxis assay, respectively.</p> <p>Results</p> <p>Doublecortin is expressed in two cell subtypes considered to be the more aggressive and that show high migration capability and invasiveness.</p> <p>Vimentin expression is excluded by these cells, while lissencephaly-1 and neurofilaments-68 are immunodetected in all the cell subtypes of the SK-N-SH cell line. Treatment with retinoic acid reduces cell migration and invasiveness, down regulates doublecortin and lissencephaly-1 expression and up regulates neurofilament-68 expression. However, some cells that escape from retinoic acid action maintain migration capability and invasiveness and express doublecortin.</p> <p>Conclusion</p> <p>a) Doublecortin is expressed in human neuroblastoma cells that show high motility and invasiveness;</p> <p>b) Retinoic acid treatment reduces migration and invasiveness of the more aggressive cell components of SK-N-SH cells;</p> <p>c) The cells that after retinoic acid exposure show migration and invasive capability may be identified on the basis of doublecortin expression.</p

A Seed Infecting Fungus (Tilletia ehrhartae) Could Provide a Partial Biological Control Mechanism for Invasive Veldt Grass (Ehrharta calycina)

Invasive species can disrupt or alter the natural ecosystem function, composition, and diversity of an area. Veldt grass, (Ehrharta calycina), is an exotic species causing plant diversity in areas to decline. The hypothesis tested was that the Veldt grass individuals would show a response to a host-specific pathogen, Tilletia ehrhartae. This study was conducted at two locations Los Osos and Guadalupe-Nipomo Dunes National Wildlife Refuge (GNDNWR) in California. We established four quadrats in Los Osos and six within GNDNWR using the nearest- neighbor method to collect infected/uninfected individuals of Veldt grass. All results were analyzed with t-tests and chi-squared statistics. Our results indicated no significance for an increase in vigor associated with escape from infection. However, our results were significant for stem height relative to infection status. Future work includes the effect of local seed predators and efficiency of co-germination

Consequences of a Genetic Bottleneck in California Condors: A Mitochondrial DNA Perspective

The California Condor (Gymnogyps californianus) has recently survived a severe population bottleneck. The entire population was reduced to 27 individuals in 1982. The number of genetic founders was even smaller. We obtained 482 base pairs of DNA sequence from the mitochondrial control region (CR) of all founder individuals that potentially represented unique maternal haplotypes. Four unique haplotypes were present in the genetic founders. One of these haplotypes is unique to Topatopa, a male brought into captivity in 1967, whose haplotype will not persist in the future population. Haplotype diversity (h) was reduced by 25% between the founder population and our census of the 2002 population. Nucleotide diversity (θ) did not vary significantly between the founders and the current population. Our results provide insights into condor genetics. First, where recessive deleterious alleles have been expressed in progeny (e.g., chondrodystrophy) the breeding pair shares the same mitochondrial haplotype. Second, we identifi ed the presence of a nuclear copy of the mitochondrial control region and provide condor specific primer sequences to preferentially amplify DNA of mitochondrial origin. Third, we confirm low levels of genetic diversity in the captive population as suggested by previous research. Forth, we question whether the low level of diversity is a consequence of the 20th century bottleneck, or if diversity has been historically low over a much longer time scale

Low genetic diversity in an endangered species: recent or historic pattern?

Examining patterns of genetic diversity has become an integral component of many management plans concerning endangered species, yet interpreting the processes underlying such patterns remains challenging. We demonstrate low genetic diversity in a critically endangered small mammal population. A common interpretation of this pattern would be that it is the result of a known, recent decline in this population. We test this interpretation and find it to be incorrect. Instead, by using museum voucher specimens, we show that the pattern of low genetic diversity is historical. This study demonstrates the importance of choosing appropriate reference groups by which to interpret modern levels of genetic diversity in endangered species. We conclude that analysis of archival specimens may be essential in cases where genetic diversity is driving conservation management decisions because it may allow us to distinguish the effects of low genetic diversity from the process of losing diversity. We recognize that this approach can be limited due to several sampling issues: archival material may not be available, statistical power needs to be evaluated, sample sizes and sequence lengths may be suboptimal due to intrinsic difficulties associated with amplification of degraded DNA. These issues are discussed and possible solutions identified

Determining the source of individuals: multilocus genotyping in nonequilibrium population genetics

Recently founded populations represent an enormous challenge for genetic analysis: new populations are often genetically impoverished, making it hard to find sufficiently variable markers, and what little variation is present tends to be ancestral, rendering phylogenetic methods inappropriate. Recently, novel genetic markers and new statistical analyses have made multilocus genotyping an invaluable tool in the fledgling field of nonequilibrium population genetics. Such advances are not of mere academic interest but address questions of great economic, medical and conservation significance

Population Genetics of the Commercially Important Cabezon

The Marine Life Management Act, closure of several near-shore demersal fisheries and the establishment of no-take marine reserves are recent embodiments of long standing disagreements between California’s fishing industries and California regulatory agencies (CDFG 2002). Fundamental arguments are over data on population trends and local versus regional population recruitment patterns. Species of concern in the latest closure included the “rockfish-cabezon-greenling” complex (Musick et al. 2000). This project deals with one of the target species of the closures. We propose to estimate population genetic structure in a species central to the commercial and recreational over-fishing debate: the cabezon (Scorpaenichthys marmoratus)