Population Sizes, Rhinocyllus conicus Use, and Patterns of Genetic Variation of Cirsium ownbeyi, a Rare Native Thistle, in Wyoming

2019 ◽  
Vol 79 (1) ◽  
pp. 12
Author(s):  
F. Leland Russell ◽  
Robby L. McMinn ◽  
Lauren A. Konrade ◽  
James B. Beck
Keyword(s):  
Genetic Variation ◽  
Rhinocyllus Conicus ◽  
Population Sizes

Consequences of climatic change for distributions

2019 ◽  
pp. 165-184
Author(s):  
Brian Huntley
Keyword(s):  
Genetic Variation ◽  
Gene Flow ◽  
Species Distributions ◽  
Climatic Changes ◽  
Adaptive Genetic Variation ◽  
Spatial Structuring ◽  
Modelling Studies ◽  
Population Sizes ◽  
Fossil Records

Species’ distributions, population sizes, and community composition are affected, directly and indirectly, by climatic changes, leading to changes in location, extent, and/or quality of distributions, range fragmentation or coalescence, and temporal discontinuities in suitable conditions. Quaternary fossil records document these responses, emphasizing individualism of species’ responses and impermanence of communities. Recent observations document similar changes attributable to recent climatic changes, including rapid decreases and increases in ranges and/or populations. Both also document extinctions associated with rapid climatic changes. Modelling studies predict substantial changes in species’ distributions, population sizes, and communities in response to future climatic changes. Implicit assumptions that genetic variation enabling adaptation is ubiquitous throughout species’ ranges, or that gene flow may be sufficiently rapid to allow adaptation, may be invalid. Work is needed to investigate spatial structuring of adaptive genetic variation and rates of gene flow, and to develop new models. Without this, species extinction risks may be severely underestimated.

scholarly journals Feedback Between Coevolution and Epidemiology Can Help or Hinder the Maintenance of Genetic Variation in Host-Parasite Models

2020 ◽  
Author(s):  
Ailene MacPherson ◽  
Matthew J. Keeling ◽  
Sarah P. Otto
Keyword(s):  
Genetic Variation ◽  
Population Fluctuations ◽  
Red Queen ◽  
Neutral Drift ◽  
Disease Epidemiology ◽  
Two Factors ◽  
Population Sizes ◽  
Host Genetic ◽  
Host Parasite ◽  
The Impact

AbstractUnderstanding if and when coevolution helps maintains genetic variation in hosts of a directly-transmissible pathogen is fundamental to quantifying the prevalence and impact of coevolution on disease epidemiology. Here, we extend our previous work on the maintenance of genetic variation in a classic matching-alleles coevolutionary model by exploring the effects of ecological and epidemiological feedbacks, where both allele frequencies and population sizes are allowed to vary over time. In general, we find that coevolution rarely maintains more host genetic variation than expected under neutral genetic drift alone. When and if coevolution maintains or depletes genetic variation relative to neutral drift is determined, predominantly, by two factors: the deterministic stability of the Red Queen allele frequency cycles and the frequency at which pathogen fixation occurs, as this results in directional selection and the depletion of genetic variation in the host. Compared to purely coevolutionary models with constant host and pathogen population sizes, ecological and epidemiological feedbacks stabilize Red Queen cycles deterministically, but population fluctuations in the pathogen increase the rate of pathogen fixation, especially in epidemiological models. Taken together our results illustrate the importance of considering the ecological and epidemiological context in which coevolution occurs when examining the impact of Red Queen cycles on genetic variation.

scholarly journals Slower environmental change hinders adaptation from standing genetic variation

2017 ◽  
Author(s):  
Thiago S. Guzella ◽  
Snigdhadip Dey ◽  
Ivo M. Chelo ◽  
Ania Pino-Querido ◽  
Veronica F. Pereira ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Environmental Change ◽  
Environmental Changes ◽  
Extreme Environment ◽  
Small Population ◽  
Population Bottlenecks ◽  
Genotype By Environment ◽  
Standing Variation ◽  
Large Populations ◽  
Population Sizes

AbstractEvolutionary responses to environmental change depend on the time available for adaptation before environmental degradation leads to extinction. Explicit tests of this relationship are limited to microbes where adaptation depends on the order of mutation accumulation, excluding standing genetic variation which is key for most natural species. When adaptation is determined by the amount of heritable genotype-by-environment fitness variance then genetic drift and/or maintenance of similarly fit genotypes may deter adaptation to slower the environmental changes. To address this hypothesis, we perform experimental evolution with self-fertilizing populations of the nematode Caenorhabditis elegans and develop a new inference model that follows pre-existing genotypes to describe natural selection in changing environments. Under an abrupt change, we find that selection rapidly increases the frequency of genotypes with high fitness in the most extreme environment. In contrast, under slower environmental change selection favors those genotypes that are worse at the most extreme environment. We further demonstrate with a second set of evolution experiments that, as a consequence of slower environmental change, population bottlenecks and small population sizes lead to the loss of beneficial genotypes, while maintenance of polymorphism impedes their fixation in large populations. Taken together, these results indicate that standing variation for genotype-by-environment fitness interactions alters the pace and outcome of adaptation under environmental change.

Genetic variation in the greenback flounder Rhombosolea tapirina GÜnther (Teleostei, Pleuronectidae) and the implications for aquaculture

2000 ◽  
Vol 51 (1) ◽  
pp. 23 ◽  
Author(s):  
Tony van den Enden ◽  
Robert W. G. White ◽  
Nicholas G. Elliott
Keyword(s):  
Genetic Variation ◽  
New Zealand ◽  
Genetic Distance ◽  
West Coast ◽  
Gel Electrophoresis ◽  
Effective Population ◽  
Average Heterozygosity ◽  
The West ◽  
Order Of Magnitude ◽  
Population Sizes

Samples of the greenback flounder, Rhombosolea tapirina, were collected from five Tasmanian sites and from one site each off Victoria and New Zealand. Thirty enzyme-coding loci were analysed by gel electrophoresis. Seventeen loci were variable, nine of which were polymorphic in at least four samples. Average heterozygosity across all 30 loci was relatively high at 0.086 ± 0.032. There were significant genetic differences between the Australian and New Zealand samples, with a genetic distance of 0.041, which was an order of magnitude larger than that observed between any Australian samples. Samples from the west coast of Tasmania and from Victoria were genetically isolated from each other and from the remaining four Tasmanian samples; the latter showed little variation among themselves. Reductions in genetic variation (heterozygosity and alleles) were observed in two cultured cohorts when compared with the wild-caught samples, with corresponding low estimates of effective population sizes compared with putative breeding numbers. No genetic variation was detected between normal and malpigmented individuals from the same culture cohort.

scholarly journals Three types of rescue can avert extinction in a changing environment

2015 ◽  
Vol 112 (33) ◽  
pp. 10557-10562 ◽  
Author(s):  
Ruth A. Hufbauer ◽  
Marianna Szűcs ◽  
Emily Kasyon ◽  
Courtney Youngberg ◽  
Michael J. Koontz ◽  
...  
Keyword(s):  
Genetic Variation ◽  
Genetic Variability ◽  
Inbreeding Depression ◽  
Small Populations ◽  
Genetic Rescue ◽  
Microcosm Experiment ◽  
High Quality ◽  
Evolutionary Rescue ◽  
Population Sizes ◽  
Number Of Individuals

Setting aside high-quality large areas of habitat to protect threatened populations is becoming increasingly difficult as humans fragment and degrade the environment. Biologists and managers therefore must determine the best way to shepherd small populations through the dual challenges of reductions in both the number of individuals and genetic variability. By bringing in additional individuals, threatened populations can be increased in size (demographic rescue) or provided with variation to facilitate adaptation and reduce inbreeding (genetic rescue). The relative strengths of demographic and genetic rescue for reducing extinction and increasing growth of threatened populations are untested, and which type of rescue is effective may vary with population size. Using the flour beetle (Tribolium castaneum) in a microcosm experiment, we disentangled the genetic and demographic components of rescue, and compared them with adaptation from standing genetic variation (evolutionary rescue in the strictest sense) using 244 experimental populations founded at either a smaller (50 individuals) or larger (150 individuals) size. Both types of rescue reduced extinction, and those effects were additive. Over the course of six generations, genetic rescue increased population sizes and intrinsic fitness substantially. Both large and small populations showed evidence of being able to adapt from standing genetic variation. Our results support the practice of genetic rescue in facilitating adaptation and reducing inbreeding depression, and suggest that demographic rescue alone may suffice in larger populations even if only moderately inbred individuals are available for addition.

scholarly journals Low genetic variation in a Pacific cycad: conservation concerns for Cycas seemannii (Cycadaceae)

Oryx ◽  
2002 ◽  
Vol 36 (1) ◽  
pp. 41-49 ◽  
Author(s):  
Gunnar Keppel
Keyword(s):  
Genetic Variation ◽  
Genetic Differentiation ◽  
New Caledonia ◽  
Conservation Status ◽  
Iucn Red List ◽  
Factors Affecting ◽  
Abundance Estimates ◽  
In The Wild ◽  
Population Sizes ◽  
Fragmented Population

The conservation status of Cycas seemannii, native to Vanuatu, New Caledonia, Fiji and Tonga, is assessed based on isozyme analysis, abundance estimates and factors affecting the survival of the species. Genetic variation in the species is low and genetic differentiation between populations is high, as compared to plants in general and to other cycads. Lower genetic variation was detected in a fragmented population as compared to less disturbed populations. Low gene flow was also detected, implying little contact between the various populations. A conservative estimate of 17,000 individuals remaining in the wild was obtained, with more than half of these located on the islands of Vanuatu. Accounts of past abundance suggest declining population sizes, most likely the result of repeated burning. Other factors that may be contributing to the decline are decreasing importance to and protection by humans, habitat alteration for agricultural and developmental purposes, and poor dispersal and recolonisation potential. An assessment based on the present estimated abundance and what is known of recent declines in numbers, indicates that the species should be categorised as Vulnerable on the IUCN Red List. On some of the densely populated islands, such as Viti Levu in Fiji and Nukualofa in Tonga, the species is locally Endangered or Critically Endangered. Possible conservation measures are suggested, and it is emphasised that populations on different islands must be considered separately because of their genetic differentiation.

scholarly journals Comparative losses of quantitative and molecular genetic variation in finite populations of Drosophila melanogaster

2005 ◽  
Vol 85 (1) ◽  
pp. 47-55 ◽  
Author(s):  
DEAN M. GILLIGAN ◽  
DAVID A. BRISCOE ◽  
RICHARD FRANKHAM
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Variation ◽  
Molecular Genetic ◽  
Neutral Theory ◽  
Similar Rate ◽  
Sampling Errors ◽  
Effective Population ◽  
Quantitative Genetic ◽  
Population Sizes ◽  
Molecular Genetic Variation

Quantitative genetic variation, the main determinant of the ability to evolve, is expected to be lost in small populations, but there are limited data on the effect, and controversy as to whether it is similar to that for near neutral molecular variation. Genetic variation for abdominal and sternopleural bristle numbers and allozyme heterozygosity were estimated in 23 populations of Drosophila melanogaster maintained at effective population sizes of 25, 50, 100, 250 or 500 for 50 generations, as well as in 19 highly inbred populations and the wild outbred base population. Highly significant negative regressions of proportion of initial genetic variation retained on inbreeding due to finite population size were observed for both quantitative characters (b=−0·67±0·14 and −0·58±0·11) and allozyme heterozygosity (b=−0·79±0·10), and the regression coefficients did not differ significantly. Thus, quantitative genetic variation is being lost at a similar rate to molecular genetic variation. However, genetic variation for all traits was lost at rates significantly slower than predicted by neutral theory, most likely due to associative overdominance. Positive, but relatively low correlations were found among the different measures of genetic variation, but their low magnitudes were attributed to large sampling errors, rather than differences in the underlying processes of loss.

scholarly journals Comparison of genetic variation between rare and common congeners of Dipodomys with estimates of contemporary and historical effective population size

2021 ◽  
Author(s):  
Michaela Halsey ◽  
John Stuhler ◽  
Natalia J Bayona-Vasquez ◽  
Roy N Platt ◽  
Jim R Goetze ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Genetic Variation ◽  
Population Size ◽  
Effective Population Size ◽  
Population Fluctuations ◽  
Nucleotide Polymorphisms ◽  
Effective Population ◽  
Single Nucleotide ◽  
Demographic Dynamics ◽  
Population Sizes

Organisms with low effective population sizes are at greater risk of extinction because of reduced genetic diversity.   Dipodomys elator  is a kangaroo rat that is classified as threatened in Texas and field surveys from the past 50 years indicate that the distribution of this species has decreased. This suggests geographic range reductions that could have caused population fluctuations, potentially impacting effective population size. Conversely, the more common and widespread  D. ordii  is thought to exhibit relative geographic and demographic stability. Genetic variation between  D. elator  and  D. ordii  samples was assessed using 3RAD, a modified restriction site associated sequencing approach. It was hypothesized that  D. elator  would show lower levels of nucleotide diversity, observed heterozygosity, and effective population size when compared to  D. ordii . Also of interest was identifying population structure within contemporary samples of  D. elator  and detecting genetic variation between temporal samples that could indicate demographic dynamics. Up to 61,000 single nucleotide polymorphisms were analyzed. It was determined that genetic variability and effective population size in contemporary  D. elator  populations were lower than that of  D. ordii, that there is only slight, if any, structure within contemporary  D. elator  populations, and there is little genetic differentiation between spatial or temporal historical samples suggesting little change in nuclear genetic diversity over 30 years. Results suggest that genetic diversity of  D. elator  has remained stable despite claims of reduced population size and/or abundance, which may indicate a metapopulation-like system, whose fluctuations might counteract any immediate decrease in fitness.

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