Browsing by Subject "Species"
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Analytical, computational, and statistical approaches to studying speciation(2007) Lemmon, Alan Richard, 1976-; Kirkpatrick, Mark, 1956-; Hillis, David M., 1958-Two of the most challenging goals of evolutionary biology are to reconstruct the evolutionary relationships among all extant species and to understand the process by which new species form. Accomplishing these goals will require accurate computational methods for reconstructing phylogenetic trees, general analytic models of speciation, and powerful statistical tools for studying the process of speciation in natural systems. In the first chapter, I study the effects of improper model assumption on estimates of phylogeny. Using DNA sequence data simulated under a variety of models of sequence evolution, I demonstrate that use of oversimplified models can result in erroneous phylogeny estimates. This result suggests that if the models currently utilized are oversimplified then current estimates of phylogeny may be inaccurate and more complex models need to be developed and employed. In the second and third chapters, I study one process thought to be important in completing the final stages of speciation: reinforcement. Using simulations of a hybrid zone, I show that the process of reinforcement can result in patterns other than reproductive character displacement. I also show that speciation by reinforcement is more likely when the genes involved in reproductive isolation are sex-linked. In the fourth chapter, I develop a statistical method of quantifying the degree of isolation between species undergoing divergence. Using genotype data obtained from natural hybrid zones, this novel method can be used to estimate the fitness of hybrids during different stages of their life cycle. This approach offers a new approach to empirical biologists studying extrinsic postzygotic isolation in natural systems.Item Combining direct methods (PIT tags and radio-telemetry) with an indirect method (mtDNA) to measure movement and dispersal at different scales in North American tarantulas (Aphonopelma spp.).(Texas Tech University, 2008-05) Hamilton, Donna E.; Densmore, Llewellyn D.; McIntyre, Nancy E.; Reichling, Steve; Strauss, Richard E.; Deslippe, Richard J.Despite their conspicuousness and importance as predators in arid and semi-arid ecosystems, almost nothing is known about the behavioral ecology and genetic structure of populations of North American tarantulas (Araneae, Theraphosidae). Additionally, two members of this genus are threatened and listed on CITES Appendix II. We used three methods of measuring movement and dispersal in these animals –the direct methods of radio-telemetry and passive integrated transponders and the indirect method of mitochondrial DNA analysis. We radio-telemetered 18 adult female tarantulas, Aphonopelma hollyi, in order to gather information regarding their time budgets, the effect of environmental factors on behavior, interactions between colonial females, and individuality in behavior between tarantulas. Date and cloud cover were the only environmental factors measured that affected activity levels in the tarantulas. Equilibrium behavior frequencies indicate time budgets that indicate the spiders spend more than 96% of their time inside the burrow, even in their peak activity season. We introduce a novel method for measuring the individuality of behavior between animals by comparing individual equilibrium behavioral frequencies with the frequencies estimated for the entire study group. We found no indications of individuality in behavior in the tarantulas monitored. We used Passive Integrated Transponders (PIT tags) as permanent, internal markers in order to monitor burrow fidelity and movement within a colony of the tarantula Aphonopelma hollyi over the span of 14 months. We used two data sets of weather variables in the analyses; one collected at the study site and the other collected 9.75 km from the study site. All the variables were statistically the same between the data sets except for days of measurable precipitation per month. These data were significantly different with t = 3.318; df = 13 and p = 0.0028. To determine how typical the period of the study was in relation to the previous ten years, we performed an ANOVA on data that included the past 10 years and there was no significantly different year found in the eleven years tested (p = 0.1543; df = 49). Over the span of the fourteen months of the study, all sixteen tagged females abandoned their burrows. Using multiple regression we determined the model including maximum air temperature, cumulative monthly precipitation and days of precipitation per month accounted for 48.82% of the variance explaining the percentage of PIT tagged females remaining in their burrow at each monthly time interval. The p value was 0.096 and so not quite significant for the model as a whole. Days of measurable precipitation were the only variable that was found to make a significant contribution (p = 0.018) to the model. Because North American tarantulas are relatively unique in their natural history when compared to other spiders, even member of the same family, diversity studies previously published are not generally applicable to members of the genus Aphonoplema. Here we present the first data (16S) that can be used to evaluate specimens within the genus Aphonopelma for hierarchical structure in genetic diversity in order understand the long-term patterns of movement and dispersal in these animals. We were able to isolate contiguous 16S sequences from 27 animals that were 430 base pairs in length. We were able identify a total of 9 haplotyes present in the 27 animals analyzed and there were 28 polymorphic nucleotides found in the 27 16S sequences analyzed (6.4%). The only significant FST values were found at the generic level of analysis (FST = 0.546). There was no apparent relationship between geographic and genetic distance within the genus; although there are three clear divisions apparent in the neighbor-joining network, which we believe to represent natural species divisions. Our analyses show a pattern of divergence that is consistent with the presence of three species: A. hentzi, A. hollyi and an unidentified species A. sp. And there was an average of 4.42% difference between species. We found no evidence of regionally selective pressures on the 16S gene.Item Conceptualizing vertebrate faunal dynamics : new perspectives from the Triassic and Eocene of Western North America(2013-05) Stocker, Michelle Renae; Bell, Christopher J., 1966-Conceptualizations of actual biological patterns as preserved in the fossil record must accommodate the results of biotic and abiotic drivers of faunal dynamics. However, those conceptualizations also may reflect cognitive biases resulting from foundational philosophical stances. Whether fossils are conceptualized as the remains of biological entities or as geological objects will affect both taxonomic identifications and secondary inferences derived from those identifications. In addition, operational research bias centered on relativistic views of ‘importance’ of particular components (i.e., taxonomic or skeletal region) of the assemblage results in preferential documentation of some taxa and marginalization of others. I explored the consequences of those specific cognitive and operational biases through examination of Triassic and Eocene faunal assemblages in western North America. For the Triassic I focused on taxonomic and systematic treatments of Paleorhinus, a group of phytosaurs important for the establishment of biochronologic correlations. Specimen-level reexamination of Paleorhinus supported a restricted usage of Paleorhinus as a clade, dissolved a biochronologic connection between terrestrial and marine deposits, and indicated a prior compression of the early part of the Late Triassic as a result of previous conceptualizations of species. I reexamined the Otis Chalk tetrapod assemblage in light of new specimens and modern phylogenetic frameworks. My examination supported a restricted usage of the Otischalkian for biochronologic correlation of the Late Triassic, and emphasized the importance of apomorphic character-based specimen examinations in conjunction with detailed lithostratigraphy prior to the development of biochronologic schema. For the Eocene I focused on undocumented terrestrial reptiles from the late Uintan fauna of West Texas. Specifically I discovered new taxa and new geographic occurrences of amphisbaenians and caimanine crocodylians. The amphisbaenians represent the southernmost record of the clade in the North American Paleogene, and, when combined with other amphisbaenian records, document that the clade responded to late Paleogene climatic changes in ways different from the inferred mammalian response. The new taxon of caimanine crocodylian represents a new geographic and temporal record of that clade. That new record indicates that the biogeographic range of extant caimans represents a climate-driven restriction from a formerly more expansive range, and suggests that the previous geographic and temporal gap in paleodistribution data is related to sampling biases and is not a solely a biological phenomenon. These data indicate that reliable characterization of vertebrate faunal dynamics requires open acknowledgment and appropriate documentation of cognitive and operational biases that affect interpretations of paleontological data.Item 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. < <