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- Title
- Dispersal, Gene Flow, and Adaptive Evolution During Invasion: Testing Range-Limit Theory with the Asian Tiger Mosquito.
- Creator
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Medley, Kimberly, Jenkins, David, Quintana-Ascencio, Pedro, Hoffman, Eric, Lounibos, Phil, University of Central Florida
- Abstract / Description
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Understanding the factors that make non-native species successful invaders is an important step towards mitigating spread. At the same time, species invasions can serve as natural experiments to test range-limit theory. Range-limit theory postulates declines in local abundance (abundant center model) and genetic diversity (central-peripheral hypothesis) towards range edges because of underlying environmental gradients. Such declines constrain adaptation to marginal habitats via gene swamping....
Show moreUnderstanding the factors that make non-native species successful invaders is an important step towards mitigating spread. At the same time, species invasions can serve as natural experiments to test range-limit theory. Range-limit theory postulates declines in local abundance (abundant center model) and genetic diversity (central-peripheral hypothesis) towards range edges because of underlying environmental gradients. Such declines constrain adaptation to marginal habitats via gene swamping. However, broader evolutionary theory predicts intermediate rates of immigration into range-edge populations can relieve genetic drift and improve adaptive potential. I tested hypotheses generated from theory while illuminating aspects affecting of the invasion of the Asian tiger mosquito (Aedes albopictus Skuse) into the US. Using reciprocal distribution modeling, I found US populations occupied significantly different climate and habitat than in their native range (SE Asia). Most inconsistencies were found in the northern US range, where Ae. albopictus has recently crept northward, providing an opportunity to test range-limit theory as the range reaches its limit. Because of its limited natural dispersal ability, rapid spread after the 1985 US introduction pointed to human-aided dispersal. I tested the current role of human-aided versus natural dispersal using a landscape genetics framework, and found that natural dispersal dominated current patterns. Some distant localities were highly genetically similar, indicating potential human-aided transport in limited cases. Asymmetric gene flow from core to edge localities supported the abundant center model, but uniformly high genetic diversity contrasted with the central-marginal hypothesis. I detected a significant signature of local adaptation by overwintering diapause-induced eggs in multiple field sites using reciprocal transplants. Surprisingly, most genotypes from throughout the range produced large offspring when overwintered at the range edge. Relative offspring mass between home and away winters peaked at an intermediate immigration rate. These results show that rapid adaptation has occurred in US populations of Ae. albopictus and highlight the potential for further spread. Genetic admixture from multiple introductions may explain high genetic diversity throughout the US range and contribute to high offspring size for all genotypes overwintered at the range edge. Finally, my work highlights the need for a better understanding of contemporary ecological and evolutionary processes leading to range-limits (or expansion) to more accurately reflect processes occurring in a human-dominated world.
Show less - Date Issued
- 2012
- Identifier
- CFE0004635, ucf:49891
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004635
- Title
- Beyond building a tree: Phylogeny of pitvipers and exploration of evolutionary patterns.
- Creator
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Fenwick, Allyson, Parkinson, Christopher, Hoffman, Eric, Crampton, William, Wiens, John, University of Central Florida
- Abstract / Description
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As generic and higher-scale evolutionary relationships are increasingly well understood, systematists move research in two directions: 1) understanding species-level relationships with dense taxon sampling, and 2) evaluating evolutionary patterns using phylogeny. In this study I address both foci of systematic research using pitvipers, subfamily Crotalinae. For direction one, I evaluate the relationships of 96% of pitvipers by combining independent sets of molecular and phenotypic data. I...
Show moreAs generic and higher-scale evolutionary relationships are increasingly well understood, systematists move research in two directions: 1) understanding species-level relationships with dense taxon sampling, and 2) evaluating evolutionary patterns using phylogeny. In this study I address both foci of systematic research using pitvipers, subfamily Crotalinae. For direction one, I evaluate the relationships of 96% of pitvipers by combining independent sets of molecular and phenotypic data. I find the inclusion of species with low numbers of informative characters (i.e. less than 100) negatively impacts resolution of the phylogeny, and the addition of independent datasets has no effect on or a small benefit to confidence in estimated evolutionary relationships. Combined evidence is extremely useful in evaluating taxonomy; I use it with South American bothropoid pitvipers. Previous work found the genus Bothrops paraphyletic, but no study had included enough species to propose a taxonomic resolution. I resolve the relationships of 90% of bothropoid pitvipers, and support the paraphyly of Bothrops as previously defined, but find it consists of three well-supported clades distinguished by distinct habitats and geographic ranges. I propose the division of Bothrops sensu lato into three genera.To address research direction two, I investigate the change in reproductive mode from egg-laying (oviparity) to livebearing (viviparity) in vipers, as well as the expansion of pitvipers through South America. I resolve the phylogeny and the divergence times for subgroups of interest then use model comparison and ancestral character state or geographic range estimation to trace the evolution of reproductive mode or geographic range across evolutionary history. For vertebrates, the predominant explanation for the evolution of reproductive mode is Dollo's Law of unidirectional evolution. This law has been challenged for a number of characters in different systems, but the phylogenetic methods that found those violations were criticized. I find support for unidirectional evolution in two analyses and rejection of it in others, and therefore do not reject Dollo's Law for the evolution of reproductive mode in vipers. In the case of geographic range, dozens of hypotheses have been proposed to explain the great biodiversity in South America, but tests of these hypotheses are lacking. I define specific time- and space-based predictions for seven hypotheses based on geological and climatic events (-) uplift of the Andes Mountains, saltwater inundation of inland areas, change in river flow, and Pleistocene climate changes. I find some support for half of the hypotheses, including one allopatric, one parapatric, and one based on climate change. I conclude that the evolution of South American pitvipers is extremely complex. Through fulfillment of both systematic research directions, I generated new knowledge about pitvipers and evolutionary processes. My methods of evaluating evolutionary patterns provide frameworks for different research questions in these areas, and I suggest that other researchers apply similar techniques to evaluate other portions of the Tree of Life.
Show less - Date Issued
- 2012
- Identifier
- CFE0004535, ucf:49236
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0004535
- Title
- GENETIC AND PHENOTYPIC EVOLUTION IN THE ORNATE CHORUS FROG (PSEUDACRIS ORNATA): TESTING THE RELATIVE ROLES OF NATURAL SELECTION, MIGRATION, AND GENETIC DRIFT.
- Creator
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Degner, Jacob, Hoffman, Eric, University of Central Florida
- Abstract / Description
-
Understanding how migration, genetic drift, and natural selection interact to maintain the genetic and phenotypic variation we observe in natural populations is a central goal of population genetics. Amphibians provide excellent model organisms for investigating the interplay between these evolutionary forces because amphibians are generally characterized by limited dispersal abilities, high philopatry, and are obligately associated with the areas around suitable habitats (e.g. breeding ponds...
Show moreUnderstanding how migration, genetic drift, and natural selection interact to maintain the genetic and phenotypic variation we observe in natural populations is a central goal of population genetics. Amphibians provide excellent model organisms for investigating the interplay between these evolutionary forces because amphibians are generally characterized by limited dispersal abilities, high philopatry, and are obligately associated with the areas around suitable habitats (e.g. breeding ponds). Thus, on relatively small geographic scales, the relative effects of all of these evolutionary forces can be studied together. Here, we study the interaction of migration, genetic drift, natural selection, and historical process in the ornate chorus frog (Pseudacris ornata). We report the development and characterization of 10 polymorphic microsatellite genetic markers. Number of alleles per locus ranged from 2 to 21 averaging 9.2 and expected heterozygosities ranged from 0.10 to 0.97 averaging 0.52. However, in an analysis of two populations, three locus-by-population comparisons exhibited significant heterozygote deficiencies and indicated that null alleles may be present some loci. Furthermore, we characterized genetic structure and historical biogeographic patterns in P. ornata using these microsatellite markers along with mitochondrial DNA sequence data. Our data indicate that in these frogs, migration may play a large role in determining population structure as pairwise estimates of FST were relatively small ranging from 0.04 to 0.12 (global FST = 0.083). Additionally, we observed an overall pattern of isolation-by-distance in neutral genetic markers across the species range. Moreover, our data suggest that the Apalachicola River basin does not impede gene flow in P. ornata as it does in many vertebrate taxa. Interestingly, we identified significant genetic structure between populations separated by only 6 km. However, this fine scale genetic structure was only present in the more urbanized of two widespread sampling localities. Finally, in this study, we demonstrated that there was a significant correlation between the frequency of green frogs and latitude. There was a higher frequency of green frogs in southern samples and a lower frequency of green frogs in northern samples. However, when we interpreted this phenotypic cline in light of the overall pattern of isolation-by-distance, it was apparent that the neutral evolutionary forces of genetic drift and migration could explain the cline, and the invocation of natural selection was not necessary.
Show less - Date Issued
- 2007
- Identifier
- CFE0001721, ucf:47319
- Format
- Document (PDF)
- PURL
- http://purl.flvc.org/ucf/fd/CFE0001721