Browsing by Subject "Gene flow"

Now showing 1 - 4 of 4
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    Experiments and models to understand gene flow from transgenic fish in different environments.
    (2010-01) Pennington, Kelly Marie
    Transgenic fishes are nearing commercialization for aquaculture around the world. Farmed transgenic fish would likely escape from typical production facilities and interbreed with wild relatives. We tested methodologies for predicting the risk of gene flow from transgenic fish. We conducted the first study of gene flow in confined populations of transgenic animals. In two experiments several generations long, we released growth-enhanced transgenic (T) Japanese medaka (Oryzias latipes) into populations of wild-type (W) medaka in semi-natural environments. Transgene frequencies varied in the first experiment, but transgene frequencies all decreased in the second experiment. We measured six fitness traits in both genotypes, and found that T males were more fertile than W, but W males obtained more matings than T males. Next, we compared fitness traits of W and T medaka under four environments: (A) high food availability, predation absent; (B) high food availability, predation present; (C) low food availability, predation absent; and (D) low food availability, predation present. Overall, T females were more fecund than W, and fecundity was highest in Environment B. Offspring of TW and WT crosses had higher survival to sexual maturity than offspring of two W parents. Fish in Environment A reached sexual maturity sooner than fish in all other environments. W males had a mating advantage in Environments B and C. Finally, we observed gene flow in populations of T and W medaka in Environments A-D for 210 days. The final transgene frequency in Environment A was greater than in Environments C or D. We parameterized a demographic model with fitness trait values collected under the same environments, which predicted that transgene frequency in Environment A would be the highest, but also overestimated transgene frequency compared to observed results. Predicted transgene frequencies overlapped with observations in Environments B and C but not in the more extreme Environments A and D. Our results suggest that risk assessment of gene flow from T to W fish ought to consider the impact of limiting environmental factors on fitness components. Before using models to inform ecological risk assessments, predictions should be confirmed with data collected under relevant environmental conditions.
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    Genetic diversity, structure, and hybridization in a harvested gray wolf (Canis lupus) population in Minnesota
    (2015-12) Rick, Jessica
    The demographic, social, and genetic effects of harvest-based management practices are not fully understood, especially in social carnivore species. Minnesota was one of several states that instituted a public hunting and trapping season to manage gray wolves (Canis lupus) following the delisting of wolves from the Endangered Species Act in 2012. Hunters and trappers harvested 413 wolves in Minnesota in 2012, about three times the average number of wolves removed annually under depredation control in previous years. Using tissue from wolves harvested during the 2012 and 2013 seasons in Minnesota, I assessed the population genetic consequences of this increase in anthropogenic mortality to determine if the harvest led to changes in population genetic structure and diversity in the first post-harvest year. I also sequenced a portion of the mitochondrial DNA (mtDNA) control region to assess the extent of gray wolf-eastern wolf (C. lycaon) and gray wolf-coyote (C. latrans) hybrid ancestry in Minnesota wolves. I found no significant difference in genetic diversity indices or mtDNA haplotype frequencies between years; however, population genetic structure and effective gene flow among the sampled wolves changed from 2012 to 2013. These analyses provide a baseline to determine variation in structure between years is normal for Minnesota wolves and how changes in genetic structure positively or negatively impact wolf populations. Baseline population genetic analysis at the beginning of managed harvest enabled my analysis of initial genetic responses to harvest, and will allow for comparisons with the population genetic structure of historical and future wolf populations in Minnesota.
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    Moving up: Using climate, physiology, and gene flow to characterize current and future geographic range limits in montane salamanders
    (2017-12) Lyons, Marta
    What causes, maintains, and changes species’ geographic ranges are central questions in ecology and evolution. Geographic ranges are a complex product of both ecological and evolutionary processes, reflecting current biotic and abiotic conditions as well as gene flow, drift, adaptation, and history. It is only through understanding the factors that influence species past and present distributions that we can begin to accurately predict how these distributions will change in the future. Anthropogenic climate change poses a major threat to native biodiversity around the world, but especially in montane systems. Understanding the dynamics at these lower elevation range limits is of particular importance. My dissertation has sought to elucidate why adaptation fails at the range edge and how that influences current and future species distributions. For this work, I focused on mountaintop, terrestrial, lungless salamanders of the genus Plethodon. A commonly invoked hypothesis for the inhibition of range expansion centers around the idea that asymmetrical gene flow from a densely populated range center prevents local adaptation at the range periphery. In Chapter 1, I quantified gene flow and effective population size along a bidirectional elevation transect in the Smoky Mountains, for the species Plethodon jordani. I found evidence for downslope biased gene flow and more dense mountaintop populations. In Chapter 3, I further explored the potential for asymmetric gene flow to limit adaptation by assessing both gene flow and phenotypic differentiation in the species Plethodon ouachitae in the Ouachita Mountains. Unlike my findings in the Smoky Mountains, in the Ouachitas, there was no indication of asymmetrically biased downslope gene flow, even though population density appears to diminish at low elevation. On the majority of transects movement appeared to be biased upslope. Within a single mountain, I found sampling sites were connected by gene flow supporting a single panmictic population within a mountain. Between mountains, I found an overall signature of genetic structure with populations segregating by mountain, supporting prior work that indicated unique mitochondrial lineages on each mountain. Correlative niche models built on occurrence records for each individual mountain indicate that the abiotic conditions occupied by populations on each mountain are different. These same metrics have been used in other work to indicate niche divergence between species and as indication of niche adaptation. However, I found neither differentiation in metabolic rate thermal sensitivity nor differentiation in acclimation ability between populations on different mountains and populations at different elevations. These findings support that mountaintop endemic Plethodon, even in the absence of gene flow shows conservation in these ecophysiological traits. In Chapter 2, I used this species-specific physiology to predict shifts in future distributions for four montane Plethodon in the Southern Appalachians. I was able to predict current range limits with high accuracy using both correlative and mechanistic distribution models for the three mountaintop species. Neither model was able to accurately predict the distribution of the one lower elevation generalist species, most likely because these limits are determined by biotic interactions as well as climate. As hypothesized the mechanistic model forecasted more suitable habitat under almost all future climate scenarios for the three mountaintop species. The choice of global circulation model had an order of magnitude influence on how much suitable habitat was predicted for both distribution modeling methods. All models indicate that these animals will be quickly contracting their distributions upslope.
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    Phenotypic And Molecular Insight Into Genetic Differentiation, Introgression And Selection In Quercus Rubra At A Fine Spatial Scale
    (2021-07) Gomez Quijano, Maria Jose
    The massive scale and cold temperature of Lake Superior creates unique microclimates in coastal terrestrial environments resulting in cooler summers, an extended fall season, warmer winters, and a reduced risk of spring frost. This gives rise to a steep climate gradient from coastal to inland regions that could lead to genetic differentiation among populations. To test this hypothesis, we studied Northern red oak (Quercus rubra L.) to examine phenotypic and molecular differentiation among populations ranging from 1–160 km from the lake shore. In a common garden experiment, we found 30% of germination and juvenile traits differed significantly from expectation. We also used restriction site associated DNA sequencing (RAD-seq) to examine population structure and genomic signatures of selection in these populations. Our results suggest that, in contrast to quantitative traits, Q. rubra populations are not differentiated at neutral genetic markers according to their distance from Lake Superior. However, unexpectedly, we also found evidence of increasing levels of introgression from the closely related species Quercus ellipsoidalis E.J. Hill into Q. rubra as species overlap and population distance from the lake increased. Our scan for selection and environmental association analysis identified one outlier locus in common, and this locus is associated with the precipitation of the wettest month. Overall, despite the lack of molecular population structure, the common garden experiment revealed that Q. rubra populations differ for key phenotypic traits. This, in combination with the genomic scans for selection, suggests the influence of natural selection driven by climate heterogeneity with increasing distance from the lake. Moreover, this is the first study that has jointly leveraged quantitative and molecular genetics to dissect signatures of selection in Q. rubra across a fine geographical scale.