Founder Placement and Gene Dispersal Affect Population Growth and Genetic Diversity in Restoration Plantings of American Chestnut

AbstractSetosphaeria turcica is a major fungal pathogen of maize and causes the foliar disease Northern corn leaf blight (NCLB). It originates from tropical regions and expanded into Central Europe since the 1980s, simultaneously with a rapid increase of maize cultivation area in this region. To investigate evolutionary processes influencing the rapid expansion of S. turcica we sequenced 121 isolates from Central Europe, Western Europe and Kenya. Population genetic inference revealed five genetically distinct clusters that differ by their geographic distribution and emergence dates. One genetically diverse cluster is restricted to Kenya, and the four European clusters consist of three distinct clonal lineages with low genetic diversity and one genetically diverse cluster with several clonal sublineages. A comparison of two different coalescent models for genetic diversity in the most frequent and geographically widespread clonal lineage in Europe supported a model of neutral, strongly exponential population growth over models accounting for different types of selection. In contrast to Kenyan isolates, European isolates did not show sexual recombination despite the presence of both mating types MAT1-1 and MAT1-2 in Europe. Within clonal lineages phenotypic variation in virulence to different monogenic resistances likely originated from repeated de novo mutations in virulence genes of S. turcica. k-mer based association mapping between genetic clusters did not identify genomic regions associated with pathogen races but few genomic regions that are significantly differentiated between two clonal lineages and contain putative effector genes. Our results suggest that the rapid colonization of Europe by different clonal lineages of S. turcica was not driven by selection of virulent races but reflects a neutral demographic process of fast pathogen population growth fostered by a rapid expansion of the maize cultivation area in this region.

Download Full-text

EVALUATION OF THE GENETIC DIVERSITY OF THE AMERICAN CHESTNUT

HortScience ◽

10.21273/hortsci.31.5.750d ◽

1996 ◽

Vol 31 (5) ◽

pp. 750d-750

Author(s):

Hongwen Huang ◽

Fenny Dane ◽

J.D. Norton

Keyword(s):

Genetic Diversity ◽

New York ◽

North Carolina ◽

Plant Material ◽

Rapd Markers ◽

American Chestnut ◽

Shoot Buds ◽

Chestnut Tree ◽

Geographic Populations ◽

Isozyme Loci

The genetic diversity within and between geographic populations of the American chestnut tree was evaluated with allozyme and RAPD markers. Winter dormant or mature shoot buds from American chestnut trees collected in Alabama, Georgia, North Carolina, Virginia, Pennsylvania, Ohio, Michigan, and Connecticut were used for isozyme assays. Genetic diversity statistics calculated for 20 isozyme loci indicated that the highest level of heterozygosity was detected in the Alabama and Connecticut populations, the lowest level in the Great Smoky Mountain populations. RAPD analyses were conducted on American chestnut plant material. The best results were obtained with seed tissue. Seed from New York, Virginia, and Pennsylvania populations and buds from Alabama and Georgia populations were evaluated for RAPD markers scattered throughout the chestnut genome.

Download Full-text

065 Genetic Diversity of the Allegheny Chinkapin (Castanea pumila var. pumila)

HortScience ◽

10.21273/hortsci.34.3.452c ◽

1999 ◽

Vol 34 (3) ◽

pp. 452C-452

Author(s):

Fenny Dane

Keyword(s):

Genetic Diversity ◽

Rapd Marker ◽

Cryphonectria Parasitica ◽

American Chestnut ◽

Disease Spread ◽

Conservation Strategies ◽

Chestnut Blight ◽

Geographic Populations ◽

Natural Range ◽

Conservation Plan

American species in the genus Castanea are susceptible to chestnut blight, caused by the Asian fungus Cryphonectria parasitica. This disease spread throughout the natural range of the American chestnut and reduced the species from a timber and nut producing tree to an understory shrub. The lesser known member of the genus, the chinkapin, has also been affected by this disease and a conservation plan is needed. Genetic diversity within and between geographic populations of the Allegheny chinkapin was evaluated to provide baseline genetic information pertinent to conservation of the species. Nuts of Allegheny chinkapin trees from populations in Mississippi, Florida, Alabama, Virginia, and Ohio were collected and evaluated for isozyme and RAPD marker polymorphism. The genetic diversity of these populations will be compared with that of Ozark chinkapin and American chestnut populations. Conservation strategies will be discussed.

Download Full-text

Increasing temperature weakens the positive effect of genetic diversity on population growth

10.1101/2021.05.13.444034 ◽

2021 ◽

Author(s):

Alexandra L Singleton ◽

Samantha Votzke ◽

Andrea Yammine ◽

Jean P Gibert

Keyword(s):

Genetic Diversity ◽

Population Growth ◽

Global Climate ◽

Extinction Risk ◽

Genetic Stocks ◽

Gxe Interactions ◽

Plastic Changes ◽

Warming World ◽

Increasing Temperature ◽

Positive Effect

Genetic diversity and temperature increases associated with global climate change, are known to independently influence population growth and extinction risk. Whether increasing temperature may influence the effect of genetic diversity on population growth, however, is not known. We address this issue in the model protist system Tetrahymena thermophila. We test the hypothesis that at temperatures closer to the species thermal optimum (i.e., the temperature at which population growth is maximal), genetic diversity should have a weaker effect on population growth compared to temperatures away from the thermal optimum. To do so, we grew populations of T. thermophila with varying levels of genetic diversity at increasingly warmer temperatures and quantified their intrinsic population growth rate, r. We found that genetic diversity increases population growth at cooler temperatures, but that as temperature increases, this effect almost completely disappears. We also show that a combination of changes in the amount of expressed genetic diversity (G), plastic changes in population growth across temperatures (E), and strong GxE interactions, underlie this temperature effect. Our results uncover important but largely overlooked temperature effects that have implications for the management of small populations with depauperate genetic stocks in an increasingly warming world.

Download Full-text

Giraffe translocation population viability analysis

Endangered Species Research ◽

10.3354/esr01022 ◽

2020 ◽

Vol 41 ◽

pp. 245-252

Author(s):

DE Lee ◽

E Fienieg ◽

C Van Oosterhout ◽

Z Muller ◽

M Strauss ◽

...

Keyword(s):

Genetic Diversity ◽

Population Growth ◽

Genetic Load ◽

Population Viability Analysis ◽

Population Viability ◽

Sensitivity Analyses ◽

Source Population ◽

Viability Analysis ◽

Probability Of Extinction ◽

Founding Populations

Most populations of giraffes have declined in recent decades, leading to the recent IUCN decision to upgrade the species to Vulnerable status, and some subspecies to Endangered. Translocations have been used as a conservation tool to re-introduce giraffes to previously occupied areas or establish new populations, but guidelines for founding populations are lacking. To provide general guidelines for translocation projects regarding feasibility, we simulated various scenarios of translocated giraffe populations to identify viable age and sex distributions of founding populations using population viability analysis (PVA) implemented in Vortex software. We explored the parameter space for demography and the genetic load, examining how variation in founding numbers and sex ratios affected 100 yr probability of population extinction and genetic diversity. We found that even very small numbers of founders (N ≤ 10 females) can appear to be successful in the first decades due to transient positive population growth, but with moderate population growth rate and moderate genetic load, long-term population viability (probability of extinction <0.01) was only achieved with ≥30 females and ≥3 males released. To maintain >95% genetic diversity of the source population in an isolated population, 50 females and 5 males are recommended to compose the founding population. Sensitivity analyses revealed first-year survival and reproductive rate were the simulation parameters with the greatest proportional influence on probability of extinction and genetic diversity. These simulations highlight important considerations for translocation success and data gaps including true genetic load in wild giraffe populations.

Download Full-text

Genetic Diversity of Castanea pulia var. ozarkensis

HortScience ◽

10.21273/hortsci.33.3.526e ◽

1998 ◽

Vol 33 (3) ◽

pp. 526e-527

Author(s):

Fenny Dane ◽

Shona Harrison ◽

Hongwen Huang

Keyword(s):

Genetic Diversity ◽

Cryphonectria Parasitica ◽

American Chestnut ◽

Chestnut Blight ◽

Ozark Highlands ◽

The Past ◽

Geographic Populations ◽

Natural Range ◽

Rapd Polymorphism ◽

Taxonomic Studies

The genus Castanea includes several species, some of which, like the American chestnut (C. dentata) and chinkapin (C. pumila), are susceptible to chestnut blight, caused by the Asian fungus Cryphonectria parasitica. Blight spread throughout the natural range of the American chestnut, destroying several billion trees within the past 50 years. Although the plight of the American chestnut is well-known, the chinkapin has been neglected. Taxonomic studies indicated two varieties, the Ozark chinkapin, var. ozarkensis, limited to the Ozark Highlands of Arkansas, Missouri, and Oklahoma, and the Allegheny chinkapin, var. pumila, found from New Jersey to Florida and Texas. The genetic diversity within and between 11 geographic populations of the Ozark chinkapin was evaluated to provide baseline genetic information pertinent to the conservation and restoration of this species. Nuts or dormant buds of chinkapin trees were evaluated for isozyme and RAPD polymorphism. The genetic variability of the Ozark chinkapin populations was relatively high when compared to the American chestnut, and most of the diversity resides within the populations. Conservation considerations for restoration of the Ozark chinkapin will be discussed.

Download Full-text