RSS 1.0Biological Sciences
For Marine Biology, see the Marine Sciences collection.
Recent Submissions
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Factors affecting nest and brood survival of rock ptarmigan (Lagopus muta) in Interior AlaskaRock ptarmigan (Lagopus muta) are a circumpolar species endemic to high elevations and latitudes of North America and are common throughout Alaska. The r- selected life history of ptarmigan indicates that reproduction and specifically nest and brood survival is the most important component of population growth. However, factors affecting these population parameters have not been studied extensively or intensively, since there have only been three studies done in Alaska. Rock ptarmigan exhibit population fluctuations, which may be caused by changes in reproduction and survival due to predation and weather events. Warming climatic patterns and shifts in the range of their food resources may also be impacting rock ptarmigan populations. Previous research on rock ptarmigan in Alaska was completed five decades ago and methods of assessing their populations have improved. Therefore, a better understanding of factors affecting nest and brood survival is essential for understanding factors limiting population growth, particularly in a rapidly changing environment. In this study, we investigated whether variations in hen age, weather, timing of nest initiation, and nesting habitat affected nest and brood survival across two study sites. We focused this study on previously studied alpine populations of rock ptarmigan at Eagle Summit and Denali Highway sites in Interior Alaska from spring through summer in 2018 and 2019. Hens outfitted with transmitters were monitored weekly to determine the status of their nest or brood. We found canopy cover around the nest had the most effect on nest survival. Survival of nests with a closed canopy was more than five times higher than those with an open canopy at the Eagle Summit site and nearly two times higher at the Denali Highway site. Ptarmigan at Eagle Summit had higher brood survival than ptarmigan at the Denali Highway site. Our modeling indicated that survival of nests and broods was not affected by fluctuations in seasonal weather (e.g., minimum temperature and maximum precipitation). Establishing a basis for understanding temporal and spatial trends in population ecology is essential for effective management in a rapidly changing environment and these findings may improve the management of rock ptarmigan.
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Strontium isotope movement modeling of modern and ancient megafauna in AlaskaStrontium isotope analysis is a technique that can be used to infer the geographic origin of biological materials. The strontium isotope ratios (87Sr/86Sr) of biological tissues can be matched to locations on a modeled strontium geographic distribution (“isoscape”) with similar 87Sr/86Sr. In this dissertation, I measured 87Sr/86Sr and other stable isotopes along the length of a mammoth tusk to model its lifetime movement and infer details about its food sources and nutritional status. I then adapted this modeling method to caribou tooth enamel to compare modern and premodern caribou space use in interior Alaska and built a new 87Sr/86Sr isoscape of interior Alaska and western Yukon with 87Sr/86Sr data from analyses of small rodent teeth. Finally, I added vegetation measurements to the isoscape model in northern Alaska, showing that vascular and non-vascular plants do not differ in 87Sr/86Sr in this region, and argued that further improvement of the isoscape of the region is necessary. Overall, the research completed in this dissertation expanded on the use of 87Sr/86Sr in reconstructing the movement of large mammals, and improved the potential for this proxy to be used in broader provenance and mobility studies in Alaska.
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Molecular survey of Leptospira spp. and Bartonella spp. in Alaskan volesLeptospira spp. and Bartonella spp. are two Gram-negative bacterial genera responsible for important zoonotic diseases worldwide, yet they remain poorly studied in northern ecosystems. Out objective was to assess Bartonella and Leptospira prevalence in vole populations in Interior Alaska and examine potential associations between prevalence and human activities (landscape and resource modification from sled dog kennels and reindeer farms). I surveyed for Bartonella and Leptospira in three vole species, Clethrionomys rutilis, Microtus pennsylvanicus, and Alexandronomys oeconomus, collected from three different areas in Interior Alaska in the summer of 2024. Using conventional PCR, I targeted the 16S rRNA gene for Leptospira spp. and the 16S-23S internal transcribed spacer (ITS) region for Bartonella spp. While no voles were found positive for Leptospira, Bartonella DNA was detected in 38 of 229 voles. Five species of Bartonella were identified: B. henselae, B. grahamii, B. doshiae, B. rochalimae, and B. heixiaziensis. This is the first study to identify B. grahamii, B. doshiae, B. rochalimae, B. henselae, and B. heixiaziensis in Alaska, and the third to identify Bartonella in Alaskan voles. Bartonella prevalence varied significantly across all three areas, with an areawide prevalence of 16.5%. While Bartonella prevalence varied significantly on a geographical scale, anthropogenic disturbance was not found to be correlated with prevalence. These findings suggest that ecological and population-level factors may play an influential role in the transmission dynamics of Bartonella in small mammal populations. This study contributes to the understanding of bacterial pathogens in northern small mammal populations.
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Relationships between deer and vegetation on Coronation Island, southeastern AlaskaRelationships between Sitka black-tailed deer (Odocoileus hemionus sitkensis) and their forage were assessed on Coronation Island in southeastern Alaska. I compared plant abundance, species richness, and deer body size with results from an earlier study by Klein (1965, Ecol. Monogr. 35:259-284). Wolves were introduced, flourished, and then died out between these studies. The deer population rebounded after the wolf-induced low. Deer were significantly larger and plants more abundant and speciose in my study. Forbs, graminoids, and shrubs predominated in summer deer feces, similar to other sites in southeastern Alaska, whereas conifers composed 73% of winter feces; a much greater percentage of conifers than in feces from other sites. Estimated metabolizable energy in all summer diets was sufficient for maintenance and reproduction. Winter diet on Coronation provided less than half the energy believed necessary for maintenance. Different intensities of use of vegetation by deer appear responsible for these differences.
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Aspects of vocal behavior of the raven (Corvus corax) in interior AlaskaThe vocal behavior of the Common Raven (Corvus corax principalis) was studied near Fairbanks, Alaska. Observations were made throughout the year on aggregations at feeding sites, soaring groups, nesting birds and birds en route to communal roost. Over 30 distinct call categories are distinguished on the basis of audible and audiospectrographic characteristics. Visual components of display which accompany the vocalizations are described for over 20 of the call categories. Kaww and Koww calls were the most frequently given vocalizations and were extremely variable within the population. Disyllabic calls (Kukwik, Kikkoo, Kulkulk) and multisyllabic calls (Kowulkulkulk and Kukuk) were the most stereotyped calls within the population. Visual components of display for disyllabic and multisyllabic calls were more stereotyped than visual components of display associated with monosyllabic calls. The highly evolved social organization of ravens and the plasticity of instinctive behavior patterns may account for its large and varied repertoire of acoustic signals.
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From the sea to the classroom: harmful algal blooms, northern sea otters, and engaging curriculumHarmful Algal Blooms (HAB) consist of a myriad of phytoplankton that can produce multiple potentially lethal biotoxins, which are ingested by shellfish as they consume algae in their diet. HAB events can occur when sunlight, nutrients, temperature, and turbidity conditions combine optimally. These bloom events are expected to increase as ocean temperatures continue to rise. The present study takes a multifaceted approach to evaluate the concentrations of paralytic shellfish toxins (PST), in northern sea otters (Enhydra lutris kenyoni), and provides a curriculum for students in grades 9-12 to support student’s conceptualization of microscopic phytoplankton and their roles in coastal ecosystems. The first aspect of the project evaluates PST congeners in northern sea otter stomach contents and body fluids using high-performance liquid chromatography post column oxidation from samples that were collected in Icy Strait from subsistence hunters near Gustavus, Alaska. The predominant stomach content species identified include butter clams (Saxidomous gigantea; n=7), horse clams (Tresus capax; n=16), horse mussels (Modiolus modiolus; n=14), pink neck clams (Leukoma staminea; n=2), and softshell clams (Mya arenaria; n=3). Body fluids analyzed were from 2015 samples, and included serum (n=5), whole blood (n=3), stomach fluid (n=5), and urine (n=5). The second aspect of the project includes the creation of a curriculum that consists of ecosystem-based discussions, field collection, laboratory safety, microscopy, and concludes with a creative evaluation. Students are evaluated using a creative media/method to explain how phytoplankton have the potential to negatively impact ecosystems and how such impacts may evolve in coming years, decades, or generations. This curriculum is geared towards non-traditional classrooms, Tribal or coastal communities, field courses, and multi-generational gatherings. Developing climate-focused curricula alongside traditional academic laboratory techniques increases accessibility to various user groups and supports fostering students who will go on to make climate-focused decisions in their daily lives, communities, and future careers.
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Vegetation analysis and mapping in evolving ice-wedge-polygon terrain Prudhoe Bay Region, AlaskaThe Arctic is warming at an accelerating pace, and within the past few decades, ice-rich regions of the Arctic have undergone systemic changes. The subsidence of ground over degraded ice wedges has created new drainage networks and ponds within previously perpetually inundated areas, fundamentally altering ice-wedge-polygon landscape dynamics. Understanding the nature and distribution of these changes is crucial to determining potential impacts on climate, wildlife, and human society. We focus on an accessible and data-rich region within Prudhoe Bay. Although the changes caused by this shift in moisture regime are multi-faceted, we use vegetation as an easily measured proxy for multiple factors. Within this thesis, we delineate and describe the post-regime-shift vegetation at the study site along with corresponding environmental data. Following vegetation description, we map this vegetation at a very fine spatial scale (<1-m) using an automated approach suitable for efficient spatial and temporal repetition. Our results show that vegetation is strongly influenced by soil moisture, and consequently microrelief, making it a suitable indicator of inundation or drainage following permafrost subsidence. Moreover, novel vegetation types have been identified in both newly inundated and newly drained areas. Mapping results show that distribution of vegetation types is strongly influenced by surficial geology, and consequently ice richness. Older surfaces with thicker ice wedges have a higher cover of dry and moist vegetation types on drained polygon centers in addition to transitional aquatic vegetation within thermokarst ponds. Younger surfaces with thinner or absent ice wedges remain inundated, and have a higher cover of wet vegetation in addition to shallow, sparsely-vegetated lakes and ponds. We recommend further vegetation sampling at the study site to support development of a pan-Arctic vegetation classification, and additionally to better understand vegetation dynamics in enriched areas within close proximity to oil field infrastructure. We also recommend temporal repetition of the mapping approach in order to identify continued landscape changes over time.
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An exploration of panarctic lake formation and methane emission since the Last Glacial MaximumPolar ice cores show that atmospheric methane concentrations nearly doubled in response to rapid climate warming over the last deglacial transition. Since concentrations of this potent greenhouse gas are tightly coupled to the Earth’s climate system, understanding the climate ecosystem interactions that precipitated this event may help predict feedbacks to current and future warming. This work reconstructs panarctic lake areas and methane emissions to assess their contribution to global atmospheric methane budgets since the Last Glacial Maximum. In the first two chapters of my dissertation, I show that climate warming and deglaciation caused widespread lake formation across land surfaces poised toward this trajectory by glaciation. Thermokarst (thaw) lake formation that accelerated in response to climate warming released methane from a mixture of radiocarbon-depleted permafrost soils and contemporary carbon sources, creating a positive climate feedback that helped sustain early Holocene temperature increases. Younger, albeit ultimately larger sources of methane from more extensive glacial lakes, lagged those from thermokarst lakes but were more than twice their magnitude throughout most of the Holocene. These findings are consistent with top-down polar ice core ¹⁴CH₄ constraints. Not included in my initial analysis were exceptionally large proglacial lakes dammed by continental ice sheets. These proglacial lakes, which had never been explored as a methane source in the literature, were the focus of my third dissertation chapter. I found that within a single large proglacial lake, Lake Agassiz, lake lowering and subsequent re-expansion into shallow aquatic and subaerial environments provided the most significant opportunity for methane production, which was otherwise limited by substantial water depth. Since it is unlikely that projected warming will cause extensive lake formation on the order of that observed during last deglacial, much of the 21st century permafrost carbon feedback will ultimately depend on how many new lakes the landscape can support. Over geologic timescales, the function of northern lakes as a carbon source could be unique to early interglacial stages due to the inevitability that lake drainage and terrestrialization will transform these features into climate stabilizing carbon sinks.
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Seasonal habitat relationships of adult female deer on Kodiak Island, AlaskaMovements of adult female deer (Odocoileus hemionus sitkensis) were monitored using radio-collars (n = 21) in a region lacking old-growth conifer forest on Kodiak Island, Alaska, from 17 July 1990 to 8 July 1991. Mean distance between seasonal ranges for 7 deer that migrated from the study area during winter was 22 km (SD = 10.2 km), whereas < 5 km separated seasonal ranges of 14 deer that remained in the study area throughout the year. Mean movement date to winter range was 30 October (SD = 38 days), and to summer range, 29 May (SD = 18 days). Overall habitat use differed significantly (P < 0.001) between seasons. Habitats used more than available (P ≤ 0.01) were tall shrub closed in summer and tall shrub open in winter. Using the 95% adaptive kernel method (Worton 1989), mean summer home range (454 ha, n = 11, range 134 - 819 ha, SD = 227 ha) was larger (P < 0.001)than the mean winter home range (107 ha, n = 9, range 67-217 ha, SD = 56 ha).
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Plant architecture and forage selection by mooseThe effects of plant architecture on browse selection and the extent of use of Salix alaxensis and Salix plantifolia by moose foraging in winter in Interior Alaska were studied during 1997 and 1998. Three sampling techniques were employed to estimate forage availability and utilization. Sampling forage availability prior to use (in autumn) provided the best estimates of forage use in spring. In Salix plantifolia, selection of current annual growth (CAG) twigs was significantly related to basal diameter of CAG, diameter of nearest neighbor, distance to nearest neighbor, and number of leaders per cluster. In contrast, CAG selection in Salix alaxensis was related only to basal diameter. The proportion of CAG biomass removed from stems of either species was not related to any measured plant architecture variables. Because plant architecture affects browse use by moose, it is an important factor in determining food availability, and thereby in assessing moose habitat
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Comparative habitat and diet selection of muskoxen and reindeer on the Seward Peninsula, western AlaskaFactors influencing choice of feeding sites, cratering microsites and diets of reindeer (Rangifer tarandus) and reintroduced muskoxen (Ovibos moschatos) were examined on the Seward Peninsula, western Alaska, during late winters of 1996 and 1997. Both ungulates foraged primarily in upland habitats with low snow depth, relatively high occurrence of lichens and low occurrence of graminoids. Both selected against snow depth when choosing feeding sites and against snow depth and hardness when selecting cratering areas within feeding sites. Diet selection differed between species. Reindeer selected mainly lichens while muskoxen selected more sedge and moss. Few behavioral interactions between species were observed, and none seemed to result in displacement of either species. Despite similar use of late winter feeding sites, competition between muskoxen and reindeer in the study area is not likely at the moment, but may occur if severe snow conditions or increasing densities of either species restrict available winter habitat
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Distribution and behavior of barren-ground caribou in relation to weather and parasitic insectsRelationships between weather and the activity of mosquitoes (Culicidae) and oestrid flies (Oestridae), and responses by caribou (Rangifer tarandus) to insect harassment, were examined near Milne Point, Alaska. Weather conditions were usually unfavorable for insects within 20 km of the Beaufort Sea, and were least favorable within 1-3 km of the eoast. Weather affected the occurrence more than the level of insect activity. Mosquitoes were rarely active within 1 km of the coast; maritime weather conditions had little effect on oestrids. Weather conditions and insect activity were more variable through time than through space： this necessitated models predicting: (1) the presence of insects, and (2) levels of insect activity when insects were present. Insect harassment caused caribou to travel rapidly to coastal areas at the expense of feeding and lying, and form large, mixed groups. Insect activity was most highly correlated with caribou rate of travel and behavior.
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Nesting habitat relationships of four species of alcids at Fish Island, AlaskaTufted Puffins, Horned Puffins, Parakeet Auklets, and Pigeon Guillemots were studied at Fish Island, Alaska, 59°52, N, 147°25, W, to determine if nesting habitat relationships indicated nest separa- tion or competition. The timing of early stages of breeding and daily activity patterns overlapped broadly among all species. Aggressive interactions occurred among all species. Tufted Puffins nested in cliff edges and grassy slopes; all species used rocky slopes and cliff faces. Tufted Puffin nests in rocks differed from Pigeon Guillemot and Parakeet Auklet nests in having larger entrance height and area, and they were placed farther from the high tide line. These dif- ferences related to body size and take-off ability, and may be indica- tions of past competition for nest sites. Interspecific interactions and site use by more than one species indicated some competition may have occurred for certain sites. Overall, most evidence indicated competition had little influence on nest site use among species.
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A range extension for Carex sartwellii in Interior AlaskaMean annual temperatures and growing season length have been increasing in northern latitudes. This has impacted permafrost thaw and the water balance of northern regions, resulting in a pattern of drying lakes in the Yukon Flats, Alaska. As lakes dry, they expose lake sediments to colonization by terrestrial vegetation. Recent interest in the terrestrial response to climate change and its effects on ecosystem services led to the formation of the Yukon River Basin project. As a part of this project, we studied plant succession and diversity in the drying lake basins. In the course of our field work we encountered a sedge we believed to be previously undocumented in Alaska. Our documentation of Sartwell’s Sedge, Carex sartwellii, on nine drying lakes during fieldwork in the central Yukon Flats, Alaska, represents a range extension for this species. Previously, its range extended as far northwest as Yukon, Canada, with a reported, but lost collection, from Alaska in 1895. Two earlier collections from the Yukon Flats have been verified; one was misidentified as Carex praegracilis until 2007. Carex sartwellii’s assumed absence from Alaska and Yukon flora, misidentification of an earlier collection, and the remoteness of the Yukon Flats may have contributed to the rarity of its collection. In Alaska this species is morphologically similar to C. praegracilis, but can be distinguished using traits of the perigynia, leaf sheaths, and the production of true vegetative culms. This sedge was found extensively in alkaline drying lake basins, which are similar environments to those found during the Pleistocene. Many of the species that occurred with C. sartwellii in lake basin plant communities have been documented in paleo reconstructions of plants from the Beringian steppe. The Yukon Flats are botanically understudied as a region in Alaska and further research should focus on identifying these unique relict plant communities in the Yukon Flats and their distribution along historic Beringia into Yukon. This would likely lead to more collections of C. sartwellii and expand our knowledge of its distribution and ecology.
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Effects of juvenile mass on reproduction and calf survival in a low-density moose populationMoose (Alces alces) are a valuable big game species in Alaska and serve as a critical food source for residents. Near Nome, Alaska, the local moose population has remained at low densities for decades, and there is strong public interest in investigating the cause behind the population's failure to increase in abundance. Compared to other moose populations in Alaska, the population of moose near Nome does not appear to be nutritionally limited or close to carrying capacity. I sought to explore how juvenile mass, a widely used metric to assess moose nutritional status in Alaska, influences reproductive output and subsequent calf survival rates in the moose population in Game Management Units 22C and 22D near Nome by estimating calving rates of collared known-age and known-mass female moose and then monitoring their calves. I found that female moose that were heavier as juveniles had a higher probability of calving for the first time at age 2 or 3 and a higher probability of twinning. I found low calf survival rates (18%) through the first year of life and did not find a significant relationship between any maternal or calf characteristics and calf survival. Overall, it appears that this moose population is defined by low calf survival rates but high reproductive rates and high survival after the first year of life. Additionally, the metric of juvenile mass and primiparity as indicators of nutritional status appears to be variable within populations among years and may not be a reliable management tool. Additional research is warranted to further explore the effect of environmental factors on driving variation in primiparity probability.
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Unveiling soil microbial communities and resistomes in northern Alaska National Wildlife RefugesMicrobial communities residing in pristine high-latitude soils play a critical role in ecosystem function, but also harbor potential threats such as acting as reservoirs of antimicrobial resistance (AMR) genes. Current knowledge about these microbial communities and the resistance genes they carry presents limits to the ability to predict how these ecosystems will respond to climate change. This knowledge gap is particularly concerning in light of the potential public health threat posed by antimicrobial resistance harbored within these communities as antibiotic-resistant human infections continue to increase. This study investigated the microbial communities and details the antimicrobial resistance gene reservoirs in previously unsurveyed soils of three northern Alaska National Wildlife Refuges representing three distinct high-latitude biomes. I used a combination of 16S rRNA gene sequencing and metagenomic sequencing to characterize microbial community diversity and composition, as well as the AMR gene resistome. Also, I analyzed soil chemical components to evaluate their potential role in shaping these communities. My findings reveal significant geographic structure in microbial communities likely driven by differences in soil properties and dispersal limitation. Additionally, I found variation in pH significantly explained differences in alpha diversity, with slightly acidic soils harboring the highest diversity. The pattern of resistome structure matched the pattern of community structure, with microbial communities within the same refuge showing less variation than communities between refuges. Additionally, the data revealed significantly fewer AMR genes in the Selawik National Wildlife Refuge than in the other refuges. I found that variation in pH and in phosphorus concentrations significantly explained variation in AMR gene abundance with higher pH and higher phosphorus resulting in more AMR genes detected. My analysis identified that over 60% of AMR genes encoded resistance to lastresort glycopeptide antibiotics. My findings reveal that soil chemistry, particularly pH, plays a key role in shaping both microbial communities and AMR gene reservoirs in these pristine high-latitude soils. This study's characterization provides a crucial foundation for understanding how climate change and human activities might impact these ecosystems. Understanding the presence and distribution of AMR genes within microbial communities of pristine soils is essential for conserving these ecosystems and mitigating public health risks, including those associated with the spread of antibiotic resistance genes, especially those encoding resistance to last-resort antibiotics.
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Adaptive strategies and energetic profiles of bacteria in permafrost and temperate environments: a comparative studyExploring microbial life in extreme conditions has not only challenged our definition of habitability but is expanding our understanding of where extraterrestrial life may occur. Permafrost, which covers approximately 27% of Earth’s surface, offers a unique window into microbial resilience in an extreme sub-zero environment, which is considered analogous to environments found on icy planets like Mars. Despite such harsh conditions, permafrost sustains diverse and active microbial communities. However, the energy dynamics and genomic adaptations that enable their survival remain largely unexplored. Here, we compare the maintenance energy requirements and genomic traits of permafrost-derived bacteria with bacteria from temperate environments to gain a better understanding of how these microbes survive in permafrost. We find that permafrost bacteria maintain stable maintenance energy levels as temperatures decrease, suggesting the presence of energy-use efficiency adaptations. Further genomic analysis of permafrost bacteria identified distinct gene adaptations related to stress response and resource acquisition, highlighting increased gene copies in pathways such as transporters and folding proteins. These results not only challenge previous assumptions about microbial energy dynamics but also provide insights into the complex mechanisms enabling microbial life to thrive under some of the most extreme conditions on Earth.
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Body condition of Pacific common eiders breeding along the Beaufort Sea coast of AlaskaPacific common eiders (Somateria mollissima v-nigrum; common eiders) are capital breeding seaducks that fast throughout their ~26 day incubation period. The incubation fast includes three metabolic phases: (I) a transition from feeding to using energy stored during the pre-breeding season, (II) the use of stored lipids for energy, and (III) the use of stored protein for energy as lipid reserves near depletion. With limited energy reserves for incubation, common eiders are more vulnerable to factors that increase the metabolic demands of reproduction, such as climate change or disturbance. We assessed the following metrics of body condition: mass, packed-cell volume, β-hydroxybutyrate, uric acid, and triacylglycerol, to estimate fasting phase of incubating common eiders. Our primary goal was to understand if common eiders breeding along the Beaufort Sea coast of Alaska entered phase III of fasting and, if so, at what point during incubation. We analyzed blood samples throughout incubation from 230 common eiders captured between Spy Island, west of Prudhoe Bay, and the U.S.-Canada Border from 2014 to 2019. Mass and packed-cell volume decreased throughout incubation which was expected as females lose up to 45% of their body mass while fasting. Serum β-hydroxybutyrate increased during incubation, indicating an increased use of stored lipids, typical during phase II of fasting. Serum uric acid decreased during incubation, also suggesting common eiders remained in phase II of fasting and were effective at protein sparing. On average, serum triacylglycerol initially decreased during incubation, consistent with phase II of fasting, then increased towards the end suggesting that some females may be feeding to augment the metabolic needs of incubation. Our body condition analysis suggests that the majority of common eiders breeding along the Beaufort Sea coast of Alaska are primarily using lipids for energy, sparing protein, and finishing incubation in phase II of fasting.
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The effect of permafrost thaw on merucry- and methane-cycling microbes and their potential interactionsIn this study, I investigated potential interactions between methane and mercury cycles in boreal forest soils. Additionally, I examined the changes in these cycles relative to shifts in soil moisture along an environmental soil moisture gradient. This investigation is pertinent due to the escalating rate of permafrost thaw driven by climate change in Arctic and subarctic ecosystems. Permafrost thaw leads to increased soil moisture, fostering favorable conditions for anaerobic microbial processes such as mercury methylation, methanogenesis, and anaerobic methanotrophy. Microbial mercury methylation creates monomethylmercury, a neurotoxin that accumulates in aquatic food webs. Methane cycling results in the production of greenhouse gases that can create a climate-warming feedback loop. In this study, I explored the mercury and methane cycles and analyzed the microbial communities involved in these cycles along an environmental soil moisture gradient. Microbial communities were analyzed by quantifying the relative abundance of taxonomic groups and by quantifying functional genes associated with mercury methylation, methanogenesis, and anaerobic methanotrophy. The relationship between soil water content and functional gene quantities was not significant. However, my findings did reveal a significant relationship between relative beta diversity and gravimetric water content along the environmental soil moisture gradient. The functional potential was predicted by quantifying net methane and net monomethylmercury production through incubations designed to measure total production in completely saturated, anoxic conditions I found that total mercury increases as soil moisture increases, methane efflux increases as soil moisture increases, and carbon dioxide efflux increases as soil moisture increases. This suggests that the activity of the mercury and methane cycles may change as permafrost continues to thaw and soil moisture content increases. In a changing climate, continuing to monitor these cycles in Alaska is pertinent due to its robust fishing industry, indigenous communities, subsistence fishing practices.
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Divergence and adaptation in Beringian birdsBeringia is a high-latitude hotspot of avian divergence and speciation. The unique biogeography of Beringia impacted avian speciation in two ways: through the cyclic appearance of the land bridge between the Asian and North American continents and through glacial refugia. These cyclic processes repeatedly split and connected avian populations, alternately reducing and increasing opportunities for gene flow between populations. In this thesis, I examine how this dynamic system impacted Beringian avian taxa using population genomic analyses. First, I examine broad patterns of divergence and gene flow across 11 lineages of birds using ultraconserved elements (UCEs), which are a multi-locus subsampling of the nuclear genome. These bird lineages contain two or more sister taxa at the population, subspecies, or species level that were likely impacted by the Bering land bridge and/or by glacial refugia. I tested models that provided key demographic information, such as population size, gene flow, and divergence time estimates. Demographic modeling showed gene flow in all cases at a wide range of rates between pairwise comparisons, and all inferred models included a divergence event during the Quaternary. Next, I focus on one species, the Song Sparrow (Melospiza melodia), in the Beringian part of its range. Five subspecies of the Song Sparrow reside in southern Alaska, from the Aleutian Islands to southeast Alaska, and have a wide range of body sizes. Using whole- genomic sequencing and morphology, I examine the phenotypic and genomic differences in these subspecies. I quantified the morphological differences, showing that the western subspecies are significantly larger than the eastern subspecies. I then determined that two candidate genes are under positive selection in the most isolated subspecies, M. m. maxima. Finally, I reconstructed a phylogeny and found that M. m. maxima is sister to the other M. melodia subspecies. These results highlight how the unique biogeography of Beringia impacted the generation of avian diversity in the region.
