RSS 1.0Biological Sciences
For Marine Biology, see the Marine Sciences collection.
Recent Submissions
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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.
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Lessons from the old school: phenological responses of the horsetail Equisetum arvense to experimental air and soil warming in Interior Alaskan boreal forestAlthough there are many studies on plant phenological shifts due to climate change, few of them focus on the phenological responses of seedless vascular plant species to warming climate. The boreal forest biome contains ~ 30% of the carbon stored by forests globally and horsetails with their circumboreal distribution are abundant in the boreal forest. Understanding the phenological response of horsetails to warming air and the timing of ground thaw is an important component for understanding how much carbon will be fixed by plants in the boreal biome in the future warmer climate. To examine the effects of air and soil warming on the phenology of Equisetum arvense L. in interior Alaskan boreal forest near Fairbanks, Alaska, we carried out a two-by-two full factorial warming experiment using open topped warming chambers (air warming) and snow removals to advance ground thaw (soil warming). Warming soil by 1 °C caused E. arvense to emerge sooner, and warming air by 0.7 °C caused E. arvense to grow faster and advance to photosynthetic activity sooner. Warmed E. arvense stems also entered senescence earlier than stems in un-warmed control plots, but the advance was greater in the spring, leading to an overall maximum extension of their growing season by 6%, or 6.7 days, for plants that were exposed to both air and soil warming. This is double the average growing season extension of 3% (1.5 days) documented in similar warming experiments of arctic seed plants, and more than the mean growing season extension per decade for seed plants in Europe (4.8 days) and China (6.2 days). Such season expansion at relatively low temperature increases suggests that E. arvense has potential to fix more carbon in future boreal forests.
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Survival, harvest, and abundance of waterfowl populations using tag-recoveries, harvest data, and Bayesian estimationAnnual harvest, survival, and abundance are three of the most monitored vital rates of waterfowl populations in North America. Annual harvest and survival probabilities are estimated from harvest tag-recovery data, which is a form of capture-mark-recapture data, while abundance estimation varies with species. While tag-recovery models were parameterized over 30 years ago, modern applications of these models often estimate harvest and survival probabilities as random effects drawn from Normal distributions. We evaluated tag-recovery models for reliable parameter estimation relative to different 1) monitoring scenarios varying by total individuals tagged annually, 2) prior distributions for the standard deviations of random effects, and 3) life history traits. When sample sizes of tag-recovery datasets were modest, hierarchical mean estimates of harvest and survival probability were reliably estimated but annual estimates of these parameters tended to underestimate true variation due to parameter shrinkage. The sample sizes required to capture true parameter variation with tag-recovery models likely only exist for a few species like mallards (Anas platyrhynchos) and lesser snow geese (Anser caerulescens caerulescens). Abundance of waterfowl populations is increasingly monitored using Lincoln’s index, which estimates annual abundance by dividing annual harvest count data by annual harvest probability. We demonstrated that harvest probabilities estimated from tag-recovery models can be used with Lincoln’s method, which improves the certainty of parameter estimates and increases the power to evaluate different hypotheses about harvest vulnerability within tagged samples. Our work indicates tag-recovery models should be used to assess for different harvest vulnerabilities between recently tagged individuals and individuals alive for at least one year after being tagged. If unmodeled heterogeneity in the form of different harvest vulnerabilities exist within a tagged sample and are not accounted for, inference about annual harvest, survival, and Lincoln’s abundance index will be biased.
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Towards reciprocity in common ravens, corvus corax, near anthropogenic food sources in interior Alaska during winterRavens, Corvus corax, and other corvids are intelligent birds that are the focus of many studies, such as in-depth dives into potential facial recognition and tool use to name a few. Despite these numerous behavioral studies, ravens lack an accessible basic universal ethogram and have rarely been observed in their undisturbed, natural state. Due to this, my study focuses on free-roaming common raven behavior in Fairbanks, Alaska, for which I utilize exploratory analysis to identify patterns in collected data. In doing so, I show how data mining and machine learning can further support behavior research with a systems perspective in the Anthropocene using pattern recognition. Using an ethogram and machine learning techniques on open access data for two winter seasons, I examine what factors affect common raven behavior around human-subsidized food sources in Fairbanks, Alaska by answering: 1) What consistent reactions do wild ravens communities show to objects, people, and other organisms (typically small songbirds or dogs) and 2) Do other factors, such as daylight or location, contribute to differing raven behaviors? I found that ravens exhibit predictable responses that vary based on urbanization level. In addition, I found an unusual pattern in raven behavior that indicates that ravens adjust their behavior based on hourly and daily human activity, indicating that raven behavior is scheduled. These results provide evidence that merging modern and classic techniques into behavioral research reveals patterns that may be missed by traditional methods alone.
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Differential use of willow species by moose in AlaskaPatterns of differential winter utilization of willow by moose in Interior Alaska and the Kenai Peninsula were studied during 1977 and 1978. Knowledge of such patterns is important to the wildlife manager who must evaluate the relative importance of different habitat types for moose. The study areas were composed of sites dominated by mature and seral habitat types.
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Effects of hunting pressure on the spatial dynamics of a subarctic caribou herdIndirect effects of hunting can have important ecological and hunt management implications, and little has been done to quantify these indirect effects on caribou (Rangifer tarandus). To assess effects of hunting pressure on caribou spatial dynamics, we used GPS locations that spanned fall and winter 2010-2022 from the semi-migratory Fortymile caribou herd in interior Alaska. We analyzed these locations using integrated step selection analysis to evaluate step lengths (i.e., movement rates) and selection of distance to roads and trails, and forest cover across 3 hunting pressure levels (none, low, and high) as well as road crossings during hunting compared to non-hunting periods. We found that the caribou response to hunting pressure varied by season and, within the fall season, by hunting pressure level. Relative to no hunting pressure, caribou in fall showed a very strong avoidance of roads at high hunting pressure and a lower avoidance at low hunting pressure. Similarly, caribou in fall showed an avoidance of trails at high hunting pressure although, unlike roads, the avoidance continued at low hunting pressure. Conversely, relative to no hunting pressure, caribou did not change their selection of forest cover in either season nor did they alter their selection of roads or trails in winter. Furthermore, in both seasons, changes in step lengths in response to hunting pressure were less than we expected. Last, caribou avoided road crossings more during hunting compared to non-hunting periods in both seasons. Overall, caribou response to hunting pressure could have implications for caribou availability to hunters, especially during the fall season, as well as caribou distribution in relation to roads across both seasons. Hunt managers and public stakeholders could use our results to inform how changes to caribou harvest management might indirectly impact caribou movements and hunter opportunity.
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Biogeographic history of the world's marmots and the genetic basis of melanism in an Alaskan population of hoary marmotsThis dissertation addresses questions related to the phylogenetics, molting phenology, and genetic basis of melanism in marmots. Marmots (genus Marmota) are large, diurnal ground squirrels that hibernate for 7-8 months each year and have a broad Holarctic distribution. In Chapter 1, I use ultraconserved elements from all 15 extant species to better resolve the phylogeny of Marmota and shed light on the biogeographic history of marmots. The results indicate marmots originated in North America ~16.3 Ma and crossed the Bering Land Bridge into Eurasia ~3-4 Ma. In addition, the Woodchuck (M. monax) and the Alaska Marmot (M. broweri) are more closely related to Eurasian species than to other North American species, and the Hoary Marmot (M. caligata) may be paraphyletic with respect to the Vancouver Island Marmot (M. vancouverensis) and the Olympic Marmot (M. olympus). Chapter 2 is a review of molt phenology in mammals, with a primary emphasis on marmots. Molting is a metabolically expensive process that is generally timed around other costly events such as lactation, parturition, and dispersal. In this chapter I summarize what is known of molting phenology in marmots, which may be particularly informative as to how precise control over molt timing evolved because of the short active period over which molting and all other costly life history events must occur. In addition, I present evidence that the Olympic Marmot only molts once annually, in contrast to other reports that it is the only biannually molting marmot. Chapter 3 is an investigation of melanism in the Hoary Marmot, which is observed in this species only in SE Alaska. I show that melanism is at least partially caused by a gain-of-function mutation in melanocortin-1-receptor (MC1R), a gene that affects melanin deposition in the skin and hair. The mutation affects hair agouti banding such that the middle light band is reduced in length relative to the brown base and black tip, resulting in the melanistic phenotype.
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Changes in benthic prey availability and quality suggest less favorable foraging conditions for threatened Steller's eiders (Polysticta stelleri) molting at Izembek Lagoon, AlaskaIzembek Lagoon, located in the Alaskan southern Bering Sea, is designated as critical molting and wintering habitat for the Alaska-breeding population of Steller's eiders (Polysticta stelleri), listed as Threatened under the United States Endangered Species Act. During the nonbreeding season, the lagoon also hosts a large proportion of the Pacific population of Steller's eiders that nest along the coast of northeastern Russia, and the lagoon is an important stopover site for many other species of migratory water birds. Since the early 1980s, there has been a decline of Steller's eiders in their known nonbreeding range in the southern Bering Sea, but especially in Izembek Lagoon during their remigial molt in the fall. The cause of this decline is unknown; however, in recent years, higher sea temperatures have been observed in Izembek Lagoon and warming ocean temperatures have been associated with shifts in benthic community structure elsewhere. If forage conditions are less favorable in Izembek Lagoon, Steller's eiders may need to redistribute to other locations, or the population at Izembek Lagoon may decline due to reduced survival. To determine if forage conditions have changed, we replicated a 1998 benthic sampling effort in fall of 2018 and 2019 to understand if prey availability has become less favorable to Steller's eiders during their molt in Izembek Lagoon. We compared forage conditions based on the relative biomass (%), overall biomass (g/m2), and size (mm) of organisms belonging to the marine benthic groups: Bivalvia, Gastropoda, Crustacea, and Polychaeta between the two time points. The results suggest a shift in these taxa with an associated change in their biomass and size. The community shifted from being dominated by bivalves in 1998 to more predominantly polychaetes in 2018 and 2019. In addition to a significant reduction of bivalve and crustacean biomass in 2019 as compared to 1998 (p = 0.04, p = 0.02, respectively), bivalves and gastropods were significantly smaller (p < 0.01, p < 0.01, respectively). The decline of Steller's eiders' use of this critical habitat may reflect shifting benthic prey availability. As it has been suggested that Steller's eiders may prefer hard-shelled prey (e.g., bivalves, gastropods) and larger sized bivalves during the molt period specifically, contemporary foraging conditions at Izembek Lagoon may be less favorable or insufficient for supporting historical numbers of Steller's eiders during an energetically taxing time in their annual cycle. Therefore, the molting Steller's eider population at Izembek Lagoon may have difficulty recovering to historical numbers if available forage conditions are of inadequate quality and abundance.
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Controls over visitation rates to mineral licks by snowshoe hares (Lepus americanus) in Northern AlaskaGeophagy, or soil consumption, is a common behavior of several avian and mammalian herbivore species. This activity has been attributed to providing essential nutrients and improving digestion of forage high in plant secondary metabolites. Recently, this behavior has been observed in snowshoe hares (Lepus americanus) and is thought to influence both their nutritional ecology and population dynamics. The purpose of this study was to examine the possible ecological controls over snowshoe hare visitation rates to mineral licks using a camera trap study at four sites near Wiseman, AK, from 2017 to 2020. Data visualization and modeling showed hare activity was strongly influenced by season and time of day, with visitation rates being significantly higher during the summer and at night. Vegetation cover was linked to higher visitation at some sites, however, the pattern was not consistent across all licks. Knowing that mineral licks influence the distribution and movement of hares, these habitat features may similarly influence the movements of hare predators. Thus, this study provides valuable insights into the complex relationships between snowshoe hares, mineral soil, and the broader ecosystem.
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Geochemical variation in the muscle of Aleutian Steller Sea Lion preyBody tissue chemistry has been extensively utilized as biomarkers about the cryptic life histories of Steller sea lions (Eumetopias jubatus) in the western and central Aleutian Islands, Alaska, specifically tissue total mercury concentrations and stable isotope ratios of carbon and nitrogen. As patterns in these biomarkers can be associated with either trophic dynamics or environmental conditions, I examined spatiotemporal and biological variability of bulk carbon and nitrogen stable isotope ratios and total mercury concentrations in the muscle tissue of ten fishes and two cephalopods found in Steller sea lion diets. I hypothesized that the complex bathymetry and oceanography of the region associated with deep-water "oceanic passes" separating islands may limit movement of these species between island groups, compartmentalizing communities in a manner to create distinct geochemical groups. In my first chapter, I found that several oceanic passes act as break points in an east to west decrease in carbon and nitrogen stable isotope ratios in most species sampled, suggesting island groups of the Aleutian Islands have distinct environmental baseline chemistry and/or primary production dynamics. In my second chapter, I found that total mercury concentrations in muscle tissues decrease with distance from the Rat Island group. When this spatial variation was accounted for and species were grouped by feeding guild, benthic invertebrate consumers had the highest mercury concentrations, followed by piscivores and then zooplankton consumers. Multiple species-specific relationships between length and each of these trophic biomarkers provided additional insight into trophic dynamics of these prey species in addition to spatial variation. Considered together, trophic biomarker patterns in Steller sea lion prey suggest trophic networks in the Aleutian Islands are spatially compartmentalized, and variation in sea lion tissue biochemistry will depend on where and what they forage upon in remarkably nuanced manners.
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Influence of fire on boreal stream metabolismWildfires are becoming more severe, frequent, and intense in the boreal forest, which has large repercussions for ecosystem processes, such as carbon and nutrient cycling. Combustion of terrestrial soils and biomass can propagate to influence streams, including increased nutrient inputs, flashier discharge, and changes to the light regime. Due to a warming climate, fire regimes are changing in concert with precipitation regimes, including more frequent and larger storms, which can scour primary producers and remove poorly attached detritus. Changing physicochemical attributes of streams resulting from fire and precipitation could influence metabolic processes that in turn influence carbon (C) storage and flux to the atmosphere. I modeled rates of gross primary production (GPP) and ecosystem respiration (ER) during the ice-free period in nine boreal streams of Interior Alaska that drained watersheds varying in fire history and across up to four years that varied in timing and magnitude of precipitation. Gross primary production and ER increased with watershed size. Average rates of GPP and ER were greater in streams of unburned compared to burned watersheds while controlling for watershed size. Streams were typically heterotrophic and net ecosystem production (NEP, GPP - ∎ER∎) was greater in burned than in unburned watersheds. GPP was correlated with physicochemical attributes including water temperature, whereas ER was unrelated to measured attributes of streams. Temporal patterns in GPP were explained by precipitation at seasonal and daily timescales, with reduced cumulative GPP in the year of greatest cumulative precipitation. Gross primary production declined and remained low following storms that occurred in late summer, but returned to pre-storm rates when storms occurred earlier in the open-water season. Increases in frequency of wildfire are expected to decrease the contribution of aquatic metabolism to CO₂ emissions from streams of the boreal forest due to higher rates of NEP, whereas increased precipitation will likely increase C emissions by suppressing GPP.
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Smoke without fire: wildfire smoke affects phenolic composition of wild blueberry fruits (Vaccinium uliginosum)Wildfire smoke can induce changes in plant growth, phenology, and chemical composition. The frequency and intensity of wildfires have increased over the last thirty years in Alaska, and smoke has the potential to affect important wild fruit plants, such as bog blueberry (Vaccinium uliginosum L.), a food source for many Alaskans and wild animals. We exposed bog blueberry plants to wood smoke at different stages in fruit development: early-season when the plants were flowering ("early-smoked"), mid-season when fruits were unripe ("mid-smoked"), and late-season when fruits were fully ripe ("late-smoked"). We measured anthocyanins, proanthocyanidins, and total phenolics in the ripe fruits, as well as branch growth, leaf anthocyanin levels, fruit set, and flower, fruit, and leaf phenology. Impact of smoke exposure on anthocyanins depended on fruit developmental state: fruits exposed late in the season had no changes in anthocyanin concentration, while early- and mid-smoked fruits showed increases in anthocyanins. Changes in proanthocyanidins followed a similar pattern to anthocyanins, but differences between treatments were not statistically significant. Total phenolic compounds were not different across treatments. Leaf anthocyanins from mid-smoked and late-smoked plants were higher than the control, while early-smoked leaves were unaffected. Early-smoked plants had lower fruit set than the control, but there was no effect of smoke exposure on mid- and late-smoked fruit abundance. Smoke caused treated plants to lose leaves at a faster rate than control plants, but did not change the timing of leaf color change. Smoke did not affect branch growth or flower and fruit phenology. Our study shows that smoke has immediate effects on bog blueberry in the increase of anthocyanins in leaves and fruits, and seasonal effects in lower leaf longevity and limited fruit set in plants exposed while flowering. These results indicate higher stress levels in smoke-exposed plants that might result in higher fruit quality due to the health benefits of anthocyanins, but at the expense of fruit abundance.
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Effects of desformylflustrabromine on compulsive-like and social behaviors in mouse models of OCD and autismObsessive-Compulsive Disorder (OCD) and autism spectrum disorders (ASD) share a number of similar deficits, including altered cholinergic activity in the central nervous system (CNS), manifestation of repetitive, restricted, and compulsive-like patterns of behavior, and frequent co-morbid presentation. Desformylflustrabromine is a novel positive allosteric modulator of α4β2 nicotinic acetylcholine receptors, which has recently been shown to be able to reduce compulsive-like behavior in a non-induced mouse model of OCD. In this study, I attempted to replicate the compulsive-like behavior-reducing effects of desformylflustrabromine in the mouse model of OCD, as well as expose the model to a novel assessment; social behavior, as measured by the 3-Chamber Social test. Furthermore, I altered the model with prenatal exposure to valproic acid to induce an ASD-like construct. This ASD animal model has been used extensively to study the social deficits and neurochemistry of ASD, although limited data exists on co-morbid models. By exposing the OCD model to valproic acid, I attempted to establish two additional models; a comorbid OCD / ASD model in the compulsive-like high-activity (HA) strain and an ASD model in the non-compulsive-like low-activity (LA) strain. All mouse models and controls participated in a battery of behavioral tests quantifying compulsive-, anxiety-, and depression-like behaviors, as well as the 3-chamber social test to quantify social preference behaviors. The ASD model was not strongly established, and the desformylflustrabromine appeared to be inactive in all strains and models. I assessed potential reasons for the failure to establish a robust ASD construct in the OCD mouse model, and the failure of desformylflustrabromine to have any significant effect, in contrast with previous research using the drug in the OCD mouse model.
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Microplastics in spotted seal stomachs from the Bering and Chukchi Seas in 2012 and 2020Microplastics pose a significant threat to marine ecosystems across multiple trophic levels. Spotted seals (Phoca largha) are piscivorous and occupy one of the higher trophic positions in the Bering and Chukchi seas, putting them at risk of ingesting microplastics through prey. This project aimed to determine if microplastics are present in the stomachs of spotted seals harvested for subsistence purposes and compare their presence spatially between two harvest locations, Gambell and Shishmaref, AK. Microplastics are predicted to increase in the Arctic over time due to climate warming and subsequent deposition of microplastics from melting sea ice. Therefore, we examined stomachs from 2012 and 2020 to explore temporal changes. Furthermore, as spotted seal pups (<1 yr of age) and non-pups forage differently, we expected a difference in microplastic ingestion between age classes. We processed stomachs using enzymatic digestion and vacuum filtration. Use of the enzyme digestion method enabled microplastic detection while preserving the hard parts of prey items (e.g., fish otoliths and shrimp carapaces) for diet analysis. We then examined filters with a stereomicroscope, and calculated microplastic frequency of occurrence (FO). A total of 34 (16 from 2012 and 18 from 2020) stomachs from Gambell and Shishmaref have been examined, and a total of 211 microplastic particles were isolated from 33 stomachs (97.1% FO), containing 1 to 23 particles per stomach. Our analysis showed no significant difference in FO between pups and non-pups, between the two harvesting locations, or between harvest years. Additionally, there was no significant difference in the microplastic concentration among the spotted seal stomachs examined in this study. Our data indicate that microplastic ingestion has not changed in frequency between age class, harvest location, or year. This baseline study was successful in isolating microplastics in the stomachs of spotted seals and showed that microplastics have been ingested consistently by spotted seals for at least the past decade. Furthermore, we found increased microplastic abundance in spotted seal stomachs when seals consumed prey at higher trophic levels and prey from benthic zones. Continued study of microplastic ingestion, including absorption and accumulations of the contaminants, is needed to assess potential impacts on the health of spotted seals and other ice-associated pinnipeds, who serve as indicators of ecosystem health in the Bering and Chukchi seas.
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Avian divergence and speciation across Beringia examined using comparative mitogenomicsAccurate knowledge of divergence and speciation processes is critical for understanding key aspects of biodiversity. As a well-known, speciose group of vertebrates, an increased understanding of how birds diverge and speciate allows us to better manage extant avian diversity and understand how it develops over time. Additionally, birds often exhibit complex and variable patterns of divergence, resulting in complexes of taxonomic uncertainty. Filling gaps in our knowledge of divergence across time and space increases our ability to correctly identify and understand not just avian diversity but clade-level patterns in speciation processes. These higher-order findings give us tools to compare and understand biodiversity more broadly across a wide range of taxa. In this thesis, I investigated both temporal and spatial elements of avian divergence, with an emphasis on the high-latitude system of Beringia, which is of particular interest for speciation due to its position at the meeting point of the Eurasian and American continental avifaunas. Chapter 1 describes my investigation of the temporal dynamics of Beringian divergence. The cyclic opening and closing of the Bering Strait due to glacial cycles intermittently isolated and reunited Asia and North America during the Pleistocene (2.6 Mya to 10 Kya). This was hypothesized to produce an uncertain number of associated 'pulses' of avian divergence events spanning that time period. I used a pairwise sampling approach among 39 taxa and a mitogenomic dataset under Bayesian modeling and found no statistical evidence for multiple vicariance events. Instead, divergence times were spread fairly evenly across a large period of time, appearing as a single vicariance event. This is biologically unusual given the system and the cyclic nature of the most likely abiotic driver (glacial cycles) and may be the result of multiple overlaid periods of divergence and gene flow in taxa with older divergence dates. In Chapter 2, I examine the relative contributions of phenotypic and genetic divergence in pairwise comparisons of diverging bird lineages in high- versus low-latitude systems in Beringia and the Philippines. Phenotypic divergence in birds is assumed to be largely due to selection (Price 2008), with genetic divergence assumed to be more driven by time in isolation. I hypothesize that the Beringian system should have less divergence overall than the Philippines, but that a greater proportion of the divergence should be phenotypic, due in part to increased population connectivity in high-latitude systems as a result of larger long- term range fluctuations as a result of Pleistocene glacial cycles. Increased connectivity should be particularly effective in removing neutral, rather than phenotypic, divergence, where selection may be in operation, in part due to a nonlinear, inverse relationship between gene flow and neutral divergence. To test this, I used standardized measures of phenetic and genetic divergence and used linear regressions to quantify the relationship between divergence metrics and the rates of divergence in each system. Beringia showed lower levels of genetic and phenotypic divergence than the Philippines, but the relationship between data types was stronger and the rate of divergence higher than in the Philippine system. I suggest that this is a result of decreased time spent in allopatry in high-latitude systems, but recognize that an increased rate of phenotypic divergence, possibly due to increased selection pressure at high latitudes, also might play a role.
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The effect of cold exposure and activity on skeletal muscle physiology: a study of human and animal modelsEnvironmental factors and physical activity have the potential to modulate skeletal muscle physiology in beneficial ways. Cold exposure and endurance exercise, specifically, may improve aerobic capacity and atrophy resistance. I utilized three models to examine the effect of cold exposure and activity level on skeletal muscle physiology: quantitation of body composition and energy expenditure estimates in humans participating in a transmountain race, comparative proteomic analysis of skeletal muscle in hibernating and summer active American black bears (Ursus americanus), and an experimental study of the combined effects of cold exposure and endurance training on white adipose tissue, and gastrocnemius and soleus muscles in Sprague-Dawley rats. Body composition analysis of participants of the transmountain race revealed significant fat but not lean body mass loss despite significant caloric deficit. Proteomic analysis of American black bear skeletal muscle revealed an upregulation of glycolytic, inflammatory, immune response, and lipid transport proteins, and a decrease of lipid, and amino acid catabolism proteins during hibernation. Modulation of metabolism and the immune system during hibernation appears to mitigate skeletal muscle atrophy, despite prolonged inactivity and fasting. In Sprague-Dawley rats, cold or exercise alone have similar effects on body composition but exert unique effects on oxidative and glycolytic skeletal muscles that overall supports enhanced aerobic capacity. When combined, cold and exercise appear to improve oxygen diffusion via reduced cross-sectional area of some fiber types in oxidative skeletal muscle but have opposing effects in glycolytic muscles. In summary, skeletal muscle is highly plastic and perturbations such as cold, fasting, and endurance training result in cellular remodeling and changes in protein expression that improves aerobic capacity and conserves skeletal muscle mass across species.
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Cross-seasonal effects in a sea ice-associated sea duck: do winter conditions affect breeding spectacled eiders?Climate change in the Arctic is more rapid than anywhere on the globe and changes in the marine environment can impact the distribution and abundance of Arctic and sub-Arctic species. Understanding how a species responds to climate change can aid conservation planning and recovery. Spectacled eiders (Somateria fischeri), sea ducks listed as "threatened" under the Endangered Species Act, winter at the Bering Sea and nest along the coastal areas of Alaska and Arctic Russia. Severity of winter conditions in the Bering Sea have been associated with both reduced annual survival and reduced breeding abundance and may have sublethal effects during the breeding season. In this study, we used 24 years of nesting data from Kigigak Island, a sub-Arctic site on the Yukon-Kuskokwim Delta, and 10 years from Utqiaġvik, on the Arctic Coastal Plain, to examine the hypothesis that winter conditions in the Bering Sea influence the reproductive performance of eiders in the following breeding season. For both sites, we examined the effects of winter ice conditions and spring temperature and wind on nest initiation date, clutch size, and nest survival. Nest initiation date was not strongly associated with conditions experienced prior to the breeding season. Estimates of nest initiation date following extreme high and extreme low winter ice conditions differed by only 2 days. In contrast, the difference in mean initiation dates between sites was 20 days. We found no evidence that winter and spring conditions preceding the breeding season explained variation in clutch size (mean clutch size = 4.8, 95% CI: 4.7, 4.8), suggesting that breeding propensity may buffer against variation in clutch size. Nest survival varied among years; annual estimates ranged from 0.11 (95% CI: -0.02, 0.24) to 0.95 (95% CI: 0.92, 0.98) at Kigigak Island and 0.40 (95% CI: 0.16, 0.63) to 0.83 (95% CI: 0.66, 0.99) at Utqiaġvik. At both sites, low days of high ice during winter were associated with lower nest survival and moderate to high counts of high ice cover conditions during winter were associated with higher nest survival. After accounting for the effect of days of high ice during winter, nest survival was higher at Utqiaġvik than Kigigak Island, potentially related to later nest initiation in the Arctic. We concluded that for breeding spectacled eiders, low sea ice winters are associated with reduced nest survival through reduced body condition, and we speculate that following winters with high sea ice more individuals may possibly decide not to breed. Delayed nest initiation at Arctic breeding sites may provide additional time for spectacled eiders to recover from low ice winters and contribute to higher nest survival at Utqiaġvik compared to the sub-Arctic breeding site. Associations between changing ice conditions on multiple demographic rates may lead to future population declines for spectacled eiders at rates higher than previously predicted.
