Browsing by Subject "Conservation genetics"

Now showing 1 - 3 of 3
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    Evolution and the climatic niche: Using genomics and niche modeling to explore how climate impacts evolutionary processes
    (2022-02) Weaver, Samuel
    Climate shapes the distributions of and interactions among species and thus influences many evolutionary processes related to the generation and maintenance of biodiversity. Oscillations in climatic regimes have played an important role in shaping the patterns of diversity by driving speciation events when previously connected populations become allopatrically isolated in different environments. Changing climates also are associated with extinction events when populations are unable to track their climatic niche or adapt to novel conditions. The rapid climate change caused by human activity emphasizes the need to understand the role climate plays in mediating species interactions and distributions. This work combines the use of climatic and genomic data across a variety of vertebrate systems to explore how climate has shaped the processes of speciation and evolution, and how climate may threaten the continued persistence of both recognized and unrecognized diversity. The evolution of a species’ climatic niche, or the climatic conditions under which a species occurs, plays a central role in generating diversity and adaptation to new environmental conditions. Faster rates of climatic niche evolution are associated with increased diversification rates, suggesting that the exploration of novel climate space can facilitate isolation and subsequent diversification. The evolution of traits that may increase or decrease rates of climate niche evolution, then, may play an important role in the colonization of novel environments and the formation of species. In my first chapter, I show that the evolution of a short aquatic larval stage in Desmognathus salamanders led to an increase in the rate of climatic niche evolution, which may have played a central role in the adaptive radiation of this group. Changes in climate have the potential to bring long-isolated species into contact with one another. Oftentimes, these species can produce viable offspring with one another and form hybrid zones. These hybrid zones often form along ecological gradients, with hybrids occurring in habitats intermediate to the climatic conditions occupied by the pure parental populations. In the Southern Appalachian Mountains, Plethodon shermani and Plethodon teyahalee hybridize extensively along an elevational gradient. P. shermani occurs on different mountaintop isolates, and P. teyahalee is distributed in between them at lower elevations. In my second chapter, I explore the genomic evidence for hybridization between these two species and whether climatic variation associated with elevation maintains species boundaries in this system. All surveyed parental P. shermani populations have experienced some degree of introgression from P. teyahalee, and multiple lines of evidence suggest that selection for P. teyahalee alleles drives asummetric introgression from P. teyahalee into P. shermani. We identify no intrinsic genetic barriers to gene flow, suggesting that these hybrid zones are regulated by ecological, rather than intrinsic factors. These findings suggest that all P. shermani populations are in danger of swamping by P. teyahalee as conditions in the Appalachians become warmer and drier. Genomics and niche modeling are powerful tools for identifying cryptic lineages of conservation concern within widespread species. In addition to identifying lineages, these approaches can inform managing agencies about threats to population persistence such as climate change-induced habitat loss and inbreeding. In my final chapter, I assess patterns of genomic and environmental differentiation among populations of Kinosternon hirtipes. Within this group, we identified multiple evolutionarily distinct lineages, many of which correspond to described subspecies. Genetic and ecological differentiation among these lineages appears to be due to vicariance associated with the Trans-Mexican Volcanic Belt. Northern populations exhibit low genetic diversity, high levels of inbreeding, and may lose over 85% of climatically suitable habitat to climate change, raising concern over their long-term viability.
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    Examining genetic diversity, outbreeding depression, and local adaptation in a native fish local adaptation in a native fish reintroduction program.
    (2010-05) Huff, David Derland
    Reintroductions are a common approach for preserving intraspecific biodiversity in fragmented landscapes; however, reintroduced populations are often smaller and more geographically isolated than native populations. Reintroductions may therefore exacerbate the reduction in genetic variability initially caused by population fragmentation due to the small effective population size of the reintroduced populations. Mixing genetically divergent sources is assumed to alleviate this issue by increasing genetic diversity, but the effects on genetic diversity are often not monitored and there are potential negative tradeoffs for mixing genetically distinct sources. I examined the consequences of mixed-source reintroductions on the ancestral composition, genetic variation and fitness of a small stream fish, the slimy sculpin (Cottus cognatus), from three source populations at nine reintroduction sites in southeast Minnesota. I used microsatellite markers to evaluate allelic richness and heterozygosity in the reintroduced populations relative to computer simulated expectations. I then inferred the fitness of each crosstype in the reintroduced populations by comparing their overall persistence, growth rates, and relative body conditions. Finally, I modeled the response of fitness related variables in the reintroduced populations to variation in habitat using a combination of regression and ordination methods. Ancestry analysis revealed that one of the three sources had more ancestors than the other two sources at most reintroduction sites. Sculpins in reintroduced populations exhibited higher levels of heterozygosity and allelic richness than the sources, but only slightly higher than the most genetically diverse source population. Simulations of maximum genetic variation indicated only a modest expected increase over the most diverse source. Growth rate, body size, and relative body condition suggest significantly reduced fitness in second generation hybrids. I detected evidence of local adaptation in the source populations based on greater predicted fitness for each source in its respective habitat. This local adaptation is strongly associated with a gradient in winter water temperatures. My study indicates that using more than one source for reintroductions may not substantially enhance genetic diversity. Furthermore, using multiple sources risks disruption of important adaptations and may cause outbreeding depression. Future reintroductions may be improved by evaluating the potential for local adaptation in ongoing reintroduction programs.
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    Patterns of ancestry and genetic diversity in reintroduced populations of the slimy sculpin: implications for conservation
    (2010-02-11) Huff, David, D.; Miller, Loren, M.; Vondracek, Bruce
    Reintroductions are a common approach for preserving intraspecific biodiversity in fragmented landscapes. However, they may exacerbate the reduction in genetic diversity initially caused by population fragmentation because the effective population size of reintroduced populations is often smaller and reintroduced populations also tend to be more geographically isolated than native populations. Mixing genetically divergent sources for reintroduction purposes is a practice intended to increase genetic diversity. We documented the outcome of reintroductions from three mixed sources on the ancestral composition and genetic variation of a North American fish, the slimy sculpin (Cottus cognatus). We used microsatellite markers to evaluate allelic richness and heterozygosity in the reintroduced populations relative to computer simulated expectations. Sculpins in reintroduced populations exhibited higher levels of heterozygosity and allelic richness than any single source, but only slightly higher than the single most genetically diverse source population. Simulations intended to mimic an ideal scenario for maximizing genetic variation in the reintroduced populations also predicted increases, but they were only moderately greater than the most variable source population. We found that a single source contributed more than the other two sources at most reintroduction sites. We urge caution when choosing whether to mix source populations in reintroduction programs. Genetic characteristics of candidate source populations should be evaluated prior to reintroduction if feasible. When combined with knowledge of the degree of genetic distinction among sources, simulations may allow the genetic diversity benefits of mixing populations to be weighed against the risks of outbreeding depression in reintroduced and nearby populations.