Browsing by Subject "Hybridization"
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Item Attempted hybridization between Chara rusbyana and related species(Texas Tech University, 1965-08) McCracken, Michael DwayneNot availableItem Biochemical genetic investigations of introgressive hybridization and systematic relationships in the spadefoot toads, genus Scaphiopus(Texas Tech University, 1978-12) Sattler, Paul W.The primary purpose of this study is to more thoroughly document hybridization and possible introgression between the spadefoot toads (Scaphiopus bombifrons and S_. multiplicatus, using starch gel electrophoresis. Analysis of mating call recordings (Blair, 1955; Bogert, 1960) first suggested the possibility of hybridization between these species. This possibility was further investigated in northwestern Texas oy Forester (1973). On the basis of mating call analysis he classified 6.3% of the animals as natural hybrids and 10.9% as backcross progeny. The two forms have also been found to be compatible in experimental crosses. Interspecific crosses were 78-97% as successful as intraspecific crosses (Littlejohn, 1959; Wasserman, 1964; H. Brown, 1967; Forester, 1969). Forester (1969) found laboratory raised F, hybrid males to exhibit an average fertility of 61.9% as compared with controls.Item Experimental hybridization between three populations of the lizard, Uta stansburiana(Texas Tech University, 1966-05) McKinney, Charles OranNot availableItem Hybridization and the Typological Paradigm(2012-02-14) Carlson, CharlesThe presence of parasites in a population has an impact on mate choice and has substantial evolutionary significance. A relatively unexplored aspect of this dynamic is whether or not the presence of parasites increases the likelihood of hybridization events, which also have a significant role in ecological adaptation. One explanation of increased hybridization in some areas and not others is that stress from parasites results in selection for an increase of novel genotypes. Two swordtail species Xiphophorus birchmanni and Xiphophorus malinche maintain an active hybrid zone. The patterns of hybridization are unique in that they do not match up directly with expectations. We set out to test whether or not individuals can sense, using chemical cues, whether conspecifics in their immediate vicinity have high parasite loads and also whether this has an effect on mating and association behavior toward both conspecific and hybrid mates. Our hypothesis being that females will have greater association times with hybrid/heterospecific mates if conscpecifics are heavily parasitized. We found that females exposed to parasitized males had a weaker preference for conspecific odor than those exposed to unparasitized males, both relative to a water control and relative to hybrids. The empirical investigation described above is coupled with a historical and philosophical discussion of some of the issues surrounding the acceptance and understanding of the concept of hybridization. This discussion takes as its major themes: an analysis of the role that social views have on the formation of scientific hypothesis; the lag between epochal change in the scientific community and the assimilation of the consequences into social beliefs; the survival of hierarchical and teleological thinking in our concept of species and purity; and the failures of contemporary evolutionary theory to provide satisfactory explanations about the meaning and upshot of hybridization. Two specific misconceptions about hybridization are addressed. First, that hybridization clashes with the belief in kinds/types/species having separate and pure identities. Secondly, the teleological view that reads purpose into nature and places all instances of variation on a hierarchical scale; the top and bottom of which are determined by estimated closeness to the predetermined perfection of a type. < <Item Implications of hybridization between the Rio Grande ground squirrel (Ictidomys parvidens) and the thirteen-lined ground squirrel (I. tridecemlineatus)(2013-05) Thompson, Cody.; Bradley, Robert D.; Baker, Robert J.; Densmore, Llewellyn D.; Strauss, Richard E.; Stangl, Frederick B.The primary objective of this study was to apply a multifaceted approach to understand the historical and contemporary aspects of hybridization between 2 species of ground squirrels (Ictidomys). Genetic and ecological data were used to determine the influence of historical biogeography on hybridization, the extent of contemporary hybridization, and the role the environment plays in determining locations of contact and potential hybridization. In Chapter I, the subject of hybridization and hybrid zones and its part in the speciation process was introduced. In addition, literature relevant to hybridization in mammals was discussed. Relevant to this dissertation, hybridization between the Rio Grande ground squirrel (I. parvidens) and the thirteen-lined ground squirrel (I. tridecemlineatus) was examined. In Chapter II, the historical contribution to hybridization between I. parvidens and I. tridecemlineatus was evaluated. Given the genetic data incorporated in this study, these species likely have undergone an ancient hybridization event, leading to mitochondrial capture in areas of previous sympatry. In Chapter III, the extent of hybridization at areas previously identified to have such was determined. By combining sequence data used in Chapter II with a genome-wide scan, hybridization was limited to small populations, with hybrids in a mosaic spatial pattern. In Chapter IV, the contributions of climate and anthropogenic changes to habitat were assessed. Through ecological niche modeling, it was determined that climate contributed the most to distributional patterns of both species. However, recent habitat modifications might have had an additive effect on both species’ distributions. Concluding remarks are provided in Chapter V.Item Late Pleistocene Neandertal-Early Modern Human Population Dynamics: The Dental Evidence(2013-04-11) Springer, Victoria SuzanneRecent genetic studies have confirmed that there was admixture between African early modern humans and archaic populations throughout the Old World. In this dissertation, I examine European early modern human dental morphology to assess the evidence for Neandertal-human admixture. The focus of this study is not on the question of taxonomic designations of Late Pleistocene Homo, but rather on the interactions of these populations in Europe. This focus on gene flow itself redefines the Neandertal question. Rather than asking if Neandertals are a different species from H. sapiens, I focus on the nature of the interactions between archaic and modern populations, which is essential to understanding the history of modern H. sapiens regardless of species definitions. I recorded dental metric measurements and morphology observations on 85 fossil Neandertals and early modern humans and a recent modern human comparative sample of 330 Native Americans and Spaniards. I examined each trait distribution individually and through the use of Mahalanobis D2, mean measure of divergence, principle components analysis, discriminant function analysis, k-means cluster analysis, and a population genetics program, structure. Through these methods, I found evidence of admixture in the dental trait distributions of European early modern humans. However, it is not evident in traditional distance measures or cluster analyses. The earliest European modern humans do not follow the trend of dental reduction found throughout the Pleistocene and into the Holocene and do not uniformly classify with any fossil population in discriminant function analysis of metric traits. The non-metric trait sample size is too small to make any definitive conclusions, but a mosaic pattern of trait frequencies also suggests admixture. The recent modern human sample shows that while increased variation and a mosaic of non-metric traits persist through many generations after admixture has ceased, traditional methods of distance analysis cannot detect low levels of admixture within 200 years. The program structure is effective in finding patterns of variation within and among populations using morphological data. It will be useful for future analyses of dental traits and other fossil data, given the ability to use it with an incomplete data set.Item Mate choice and hybridization within swordtail fishes (Xiphophorus spp.) and wood warblers (family Parulidae)(2011-05) Willis, Pamela Margaret; Ryan, Michael J. (Michael Joseph), 1953-; Bolnick, Daniel I.; Mueller, Ulrich G.; Rosenthal, Gil G.; Singer, Michael C.Behavioral isolation is an important barrier to gene flow, contributing to the formation and maintenance of animal species. Nevertheless, hybridization occurs more commonly than is generally recognized, occurring in over ten percent of animal species in the wild. Although the genetic consequences of hybridization are of considerable interest given their evolutionary implications, the reasons that animals choose to mate with other species are less clear. I apply mate choice theory to the question of hybridization, using wood warblers (family Parulidae) and swordtail fishes (genus Xiphophorus) as study systems. Over half of the 45 species of North American wood warbler have produced hybrids. Using comparative methods, I address the questions: Do ecological and demographic factors predict hybridization in this family? Similarly, how do phylogeny, song similarity, and sympatry with congeners correlate with hybridization? As with North American wood warblers, behavioral isolation is also considered of primary importance in isolating sympatric species of swordtail fishes. Two species, X. birchmanni and X. malinche, hybridize in several locations in the wild. Through experimentation with these and other Xiphophorus species, I investigate some of the factors that cause female mate choice to vary, possibly contributing to hybridization. Specifically, I address the following questions: Do females become less choosy when predation risk is high, or encounter rates with conspecifics are low? Are female preferences for conspecifics innate, or can they be modified by experience? And, do female preferences for conspecifics vary among species, populations, or experiments? These studies illustrate the utility of treating hybridization as just another possible outcome of variation in mate choice. I find that warbler hybridization correlates with ecological and other variables, that female swordtails become more responsive to heterospecifics when mate choice is costly, and that female preferences for conspecifics are species- and context-dependent. As animal hybridization can have important evolutionary consequences, studying the factors that contribute to this variation can enhance our understanding of the evolutionary process.Item Phylogenetic relationships and arbuscular mycorrhizal diversity of Tolpis Adans. (Asteraceae), with special reference to island endemism and biogeography(2013-12) Gruenstaeudl, Michael; Jansen, Robert K., 1954-The plant genus Tolpis (Asteraceae) is a predominantly insular plant lineage. It inhabits four of the five archipelagoes that comprise the Atlantic region of Macaronesia and also occurs in Mediterranean Europe and North Africa. Twelve species are currently recognized in Tolpis, of which ten are insular and two continental. The majority of the insular species inhabit the five western Canarian islands, where they constitute endemics to specific ecological habitats. A comprehensive molecular phylogeny of Tolpis is generated via DNA sequences of one nuclear ribosomal and two low-copy nuclear DNA markers. Considerable phylogenetic uncertainty among inferred tree topologies is detected, and incongruence between these topologies is resolved via statistical hypotheses testing. The extant diversity of the genus is identified to be the result of two independent colonization pathways and adaptive radiations on several islands. Moreover, potential hybridization is detected between species that inhabit different islands and archipelagoes, indicating a more widespread historical distribution of the genus. Details of the biogeographic history of Tolpis are inferred via ancestral area reconstructions under parsimony and likelihood optimality criteria. The hypothesis that Tolpis may have undergone a back-dispersal from an island to a continental habitat is also tested. Uncertainty in taxon cladograms owing to the presence of hybrid or allopolyploid taxa is characterized and a potential adjustment strategy evaluated. Averaging reconstruction results over all optimal phylogenetic trees and the manual pruning of cloned DNA sequences are found potential adjustment strategies against the impact of topological uncertainty owning to hybrid or allopolyploid taxa. Adjusted ancestral area reconstructions in Tolpis do not support the scenario that the genus has undergone a reverse colonization of the continent. In addition to the phylogenetic and biogeographic history of the genus, the diversity of symbiotic mycorrhizal fungi associated with Tolpis is characterized. A molecular survey using two nuclear ribosomal DNA markers and 454 pyrosequencing is performed. Particular emphasis is placed on the quality filtering of resulting fungal DNA sequences, the generation of operational taxonomic units, and their taxonomic assignment via similarity searches against DNA sequence databases. Numerous potentially novel fungal genotypes are identified.Item Sequence differences between Candida albicans and Candida dubliniensis(Texas Tech University, 2001-05) Stevens, Natalie KNot availableItem Some Philosophical Origins of an Ecological Sensibility(2012-10-19) Carlson, CharlesThis dissertation is centered on problems within the history and philosophy of biology. The project identifies the philosophical roots of the current ecological movement and shows how a version of philosophical naturalism might be put to use within contemporary ethical issues in biology, and aid in the development of research programs. The approach is historically informed, but has application for current dilemmas. The traditions from which I primarily draw include classical American philosophy, particularly C.S. Peirce and John Dewey, as well as thinkers associated with the German Naturphilosophie movement, such as Goethe and Schopenhauer. There are deep, but often overlooked, resonances between these seemingly disparate traditions and contemporary biology that are located in the conflict between the developing organism and the ever-fluctuating environment. The dissertation makes the case for a shared description of nature among these traditions and proposes applications to burgeoning contemporary ecological interpretations of issues such as hybridization and epigenetics.Item Temporal genetic structure of feral honey bees (Hymenoptera: Apidae) in a coastal prairie habitat of southern Texas: impact of Africanization(Texas A&M University, 2004-09-30) Pinto, Maria AliceThe goal of this study was to examine the impact of Africanization on the genetic structure of the Welder Wildlife Refuge feral honey bee population by scoring mtDNA and microsatellite polymorphisms. Adult honey bee workers, collected between 1991 and 2001, were screened for mtDNA using the cytochrome b/BglII, ls rRNA/EcoRI, and COI/HinfI PCR-based assays. The procedure allowed identification of four mitotypes: eastern European, western European, A. m. lamarckii, and A. m. scutellata. The relative frequencies of the four mitotypes changed radically during the 11-year period. Prior to immigration of Africanized honey bees, the resident population was essentially of eastern European maternal ancestry. The first colony of A. m. scutellata mitotype was detected in 1993. Between 1995 and 1996 there was a mitotype turnover in the population from predominantly eastern European to predominantly A. m. scutellata. From 1997 onward, most colonies (69 %) were of A. m. scutellata mitotype. The temporal change in mtDNA was paralleled by nuclear DNA. The 12 microsatellite loci analyzed indicated (1) the mechanism of Africanization of the Welder population involved both maternal and paternal bi-directional gene flow (hybridization) between European and Africanized honey bees; and (2) the resident panmitic European population was replaced by panmitic asymmetrical admixtures of A. m. scutellata and European genes. The steepest increase in the proportion of introgressed A. m. scutellata nuclear alleles occurred between 1994 and 1997. The post-Africanization gene pool was composed of a diverse array of recombinant classes with a substantial European genetic contribution (mean proportion of European-derived alleles was 37 % as given by mR estimator or 25 % as given by mY estimator, for 1998-2001). If European genes continue to be retained at moderate frequencies, then the Africanized population is best viewed as a "hybrid swarm" instead of "pure African". The most radical change in the genetic structure of the Welder Wildlife Refuge feral honey bee population (observed between 1995 and 1997) coincided with arrival of the parasitic Varroa mite. We suggest that Varroa likely hastened the demise of European honey bees and had a major role in restructuring the Welder Wildlife Refuge feral honey bee population.Item The heterotic effects of dwarf A lines in hybrid sudangrass(Texas Tech University, 1967-05) Clement, Edward LeonThe purpose of this study was to compare the various heights of the male-sterile Rhodesian sudangrass lines, with their respective number of genes for dvrarfness, from the following points of view. 1. To determine the effects of the various dvrarf A lines on the forage yield of their respective hybrids. 2. To determine the effects of the various dwarf A lines on the leaf-stem ratio of their respective hybrids. 3. To determine the effects of the various dwarf A lines on the percent protein content of their respective hybrids. 4. To compare the performance of the hybrids, A lines, and the H line (Tift). 5. To compare the performance of the Lubbock planting and the Beaumont planting in order to determine the climatic effects on the hybrids, A lines, and the R line (Tift).Item The Hybridization between the Endangered Gambusia nobilis and Introduced Gambusia geiseri in Texas(2017-07-14) Rodriguez, Victoria; Hargrave, Chad W.Introduced species are a major cause of biodiversity loss because of predation, competition for limited resources and space, and hybridization with native taxa. Hybridization poses the greatest risk for native taxa when the non-native and native taxa are closely related. This can compromise the genetic structure of native populations and drive those taxa to extinction. Moreover, the extinction risk to native taxa by hybridization with non-native is greatest when native taxa are rare (e.g., endangered or threatened) because rare taxa often lack the genetic variation necessary mitigate ongoing hybridization events. Herein, we provide morphological and genetic evidence to suggest that the introduced Largespring Gambusia (Gambusia geiseri) and endangered Pecos Gambusia (Gambusia nobilis) are hybridizing within the San Solomon Spring complex, Reeves, Co. Texas. We inferred hybridization and gene flow from data collected on seven morphometric characters, nine meristic measurements, and five molecular markers (the mitochondrial gene Cytb; nuclear genes Rag 1, Rag 2, and RPS7; and one microsatellite) from the two species and the putative hybrid. The results support morphological intermediacy and mixed genetic heritage of Gambusia nobilis and Gambusia geiseri in some individuals. In addition, we were able to infer extensive hybridization and introgression over several generations. Thus, alternate conservation efforts may be needed to counteract the effects hybridization on the endangered Pecos Gambusia.Item Wide Hybridization, Genomic, and Overwintering Characterization of High-Biomass Sorghum Spp. Feedstocks(2012-10-19) Whitmire, David KyleThe federally mandated 36 billion gallons a year production goal for "advanced biofuels" by 2022 has created a demand for lignocellulosic feedstocks that are inexpensive to produce. The current lack of market development for lignocellulosic feedstocks incentivizes the development of versatile biomass products with greater end-use possibilities, as in either a forage or bioenergy system. High-biomass, perennial grasses offer dual-use potential in either forage or biofuel systems. In 2009 and 2010 controlled pollinations were made to evaluate the efficiency of producing interspecific hybrids between homozygous recessive iap/iap and Iap/- Sorghum bicolor (L.) Moench, cultivated sorghum, and three S. halepense (L.) Pers., johnsongrass, genotypes. The iap/iap genotype removes reproductive barriers to alien pollen in S. bicolor and aids in wide hybridization. Total seed set, germinable seed set, and hybrid production were significantly higher using the iap/iap genotype. The iap/iap S. bicolor genotype is a valuable tool available to plant breeders for the creation of wide hybrids with S. halepense. In a related study a bulked segregant analysis was conducted using bulked samples of S. bicolor, typical flowering S. halepense, non-flowering S. halepense, and putative triploid hybrids of the two species to identify unique markers for each bulk and to evaluate S. bicolor genetic material introgression into the non-flowering S. halepense genome. Thirty-nine and 23 markers were found to be unique to the S. bicolor and typical flowering S. halepense bulks, respectively. These unique markers could be used in a breeding program to identify interspecific hybrids. Alleles at fifteen markers were found in both the S. bicolor and non-flowering S. halepense bulks but not in typical flowering S. halepense and may help explain the non-flowering phenotype. In 2010 and 2011 a study was conducted to investigate the rhizome composition of 11 genotypes of Sorghum species and its relationship to overwintering. Genotype, environment, and sampling date had significant effects on rhizome metabolite concentrations. Overwintering capacity was related to fructans and crude protein concentrations and NIRS (Near Infrared Spectroscopy) was effective at estimating these values. This information can be used to screen for stronger perennial parents to be used in future breeding programs.