Browsing by Subject "hybridization"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Devising superconvergent HDG methods by M-decompositions
    (2016-05) Fu, Guosheng
    In this thesis, we develop the concept of an M-decomposition as an effective tool for devising high-order accurate hybridizable discontinuous Galerkin methods and hybridized mixed methods that superconverge on unstructured meshes of shape-regular polyhedral elements for three linear elliptic partial differential equations, namely, the (steady-state) diffusion equation, the equations for linear elasticity, and the equations for incompressible Stokes flow.
  • Thumbnail Image
    Item
    How Salamander Species Can Hybridize Extensively Yet Remain Distinct: Insights from Habitat Data, Molecules, and Behavior
    (2016-07) Lowe, Benjamin
    This project explores a situation where two distinctive species hybridize extensively at zones of contact yet appear not to be collapsing into a single species. Lack of impending merger is inferred when regions made up of organisms of mixed ancestry (‘hybrid zones’) are not increasing in extent but instead are stable. There is growing recognition that this phenomenon is common nature. Several forces have been proposed to function in preventing lineage merger in these situations. Selection for different ecological conditions (‘exogenous selection’) is widely acknowledged to maintain species limits, especially when the contacting lineages are associated with different habitats. Genome incompatibilities (when hybridization leads to the breakdown of co-adapted gene complexes, or ‘endogenous selection’) have also been cited as contributing to hybrid zone stability. Positive assortative mating, where individuals preferentially mate with similar individuals, has also been put forward as a process that could prevent the merger of species. Two species of lungless salamanders, Plethodon shermani and P. teyahalee, have parapatric distributions in the southern Appalachian Mountains and form hybrid zones where their distributions meet. I investigated hybrid zone stability and potential factors maintaining species limits between these salamanders. In Chapter 1, I use coalescent simulations to identify a lower bound on the timing of secondary contact, which in turn leads to an expected hybrid zone extent under a model of neutral diffusion. By comparing observed and expected hybrid zone extent, I show that the two species are not in the process of freely merging despite extensive introgression of molecular markers. In Chapter 2, I evaluate predictions of ex- and endogenous selection using ground-level temperature data and character clines fitted to molecular and morphological data. I find evidence for exogenous selection but not for endogenous selection. In Chapter 3 I present data from courtship trials performed in the laboratory that reveal that despite frequent interspecific hybridization, these two species show a preference for conspecifics. These findings shed light on Plethodon hybrid zone dynamics and the maintenance of species limits for hybridizing species.
  • Thumbnail Image
    Item
    Human Impacts on Minnesota Prairie Genetics: Salted Environments, Echinacea Hybrids, and Local Seed Sourcing
    (2018-12) Goldsmith, Nicholas
    Humans are modifying various aspects of the environment, from building roadways, to moving species beyond their range, to purposefully reconstructing plant communities. These actions affect both the current distribution of populations and the potential for populations to persist. In this dissertation, I examine two human-caused impacts to plant populations and one aspect of efforts to support native plant communities. In chapter one, I focus on the impact of sodium chloride, a road de-icing agent. Such agents can damage plants and change dominant species along roadsides. I carried out two experiments, planting a pedigreed population of the native prairie legume Chamaecrista fasciculata into a roadside environment and into four greenhouse salinity treatments. I tracked their survival and reproduction. Using Aster models, I detected potential to adapt both to roadside salinity and to low salinity in the greenhouse. I also detected gene-by-environment interactions in both experiments. These results indicate a potential to adapt, but a potential which may be slowed by gene-by-environment interactions. In chapter two, I focus on the interaction of Echinacea pallida, introduced outside of its range, on local populations of E. angustifolia. I used controlled crosses and monitored their seed set and the survival of the progeny over five years. Crossing of the two species produces offspring capable of surviving multiple years. Comparing conspecific and heterospecific crosses, I found that conspecific crosses of E. angustifolia resulted in lower pollen compatibility and survival to year four than did conspecific crosses with E. pallida or heterospecific crosses. These results demonstrate a risk to E. angustifolia populations by E. pallida populations planted nearby. In chapter three, I focus on efforts to remediate human impacts through restoration of Minnesota prairie plant communities, which depends on the production and use of source-identified seeds. Restoration practice often emphasizes use of seeds sourced from populations near the restoration site, but demand frequently outstrips supply. I conducted focus group interviews with groups of producers and users of locally-sourced seeds to identify strengths and weaknesses with current practices. Participants discussed continued increases in production and use of these plant materials but also identified aspects where improvement is needed.
  • Thumbnail Image
    Item
    Mixed-source reintroductions lead to outbreeding depression in second-generation descendents of a native North American fish
    (2011) Huff, David, D.; Miller, Loren, M.; Chizinski, Christopher, J.; Vondracek, Bruce
    Reintroductions are commonly employed to preserve intraspecific biodiversity in fragmented landscapes. However, reintroduced populations are frequently smaller and more geographically isolated than native populations. Mixing genetically, divergent sources are often proposed to attenuate potentially low genetic diversity in reintroduced populations that may result from small effective population sizes. However, a possible negative tradeoff for mixing sources is outbreeding depression in hybrid offspring. We examined the consequences of mixed-source reintroductions on several fitness surrogates at nine slimy sculpin (Cottus cognatus) reintroduction sites in south-east Minnesota. We inferred the relative fitness of each crosstype in the reintroduced populations by comparing their growth rate, length, weight, body condition and persistence in reintroduced populations. Pure strain descendents from a single source population persisted in a greater proportion than expected in the reintroduced populations, whereas all other crosstypes occurred in a lesser proportion. Length, weight and growth rate were lower for second-generation intra-population hybrid descendents than for pure strain and first-generation hybrids. In the predominant pure strain, young-of the-year size was significantly greater than any other crosstype. Our results suggested that differences in fitness surrogates among crosstypes were consistent with disrupted co-adapted gene complexes associated with beneficial adaptations in these reintroduced populations. Future reintroductions may be improved by evaluating the potential for local adaptation in source populations or by avoiding the use of mixed sources by default when information on local adaptations or other genetic characteristics is lacking.
  • Thumbnail Image
    Item
    Seed sourcing for ecological restoration in an era of climate change: Impacts of source latitude and hybridization
    (2022-11) Rushing, Naomi
    In Minnesota, tallgrass prairie ecosystems currently occupy less than 1% of their former range. The importance of maintaining and restoring this dwindling ecosystem is well recognized but the ecological restoration process is complex, particularly in the current era of climate change. Successful establishment and persistence of restoration populations depends in large part on seed source selection. Previous research and discussion have explored the importance of maintaining local adaptation and genetic diversity. There has also been discussion of intentionally translocating populations in specific directions in response to ongoing climate change. In an effort to inform seed sourcing guidelines, the research presented here investigates (1) the implications for restoration of translocating populations across latitudes, (2) the phenological and fitness outcomes of hybridization between distinct populations, and (3) genetic effects contributing to differences between divergent populations. Chapter 1 focuses on the phenological and fitness impacts of translocation along a latitudinal gradient within the state of Minnesota using a common garden style approach and three perennial prairie species. Chapters 2 and 3 expand upon this work and investigates the impact of translocation on an annual prairie species sampled across a latitudinal span from Minnesota to Missouri, as well as investigating the outcome of hybridization between these divergent populations. Our results highlight the importance of latitude of origin to both phenology and fitness of translocated populations, as plants from more northern locations tended to have earlier timing of flowering and fruiting in the common gardens, as well as higher fitness for all of our study species. In addition, Chapters 2 and 3 demonstrate the potential positive impacts of hybridization across a range of geographic distances with no indication of outbreeding depression, as hybrid generations tended to have higher mean fitness in the common gardens than the parental generations. However, phenological mismatch between seed source and planting site in populations translocated across large latitudinal distances can result in low fitness and limit hybridization with local populations. Taken together, these results highlight the benefits of hybridization between populations, while demonstrating the potential drawbacks of translocating populations across large latitudinal distances.