Theses and Dissertations

Permanent URI for this collection

https://hdl.handle.net/10217/100356

Browse

Now showing 1 - 20 of 128

Open Access
Determinants of habitat use and community structure of rodents in northern shortgrass steppe
(Colorado State University. Libraries, 1996) Stapp, Paul T., author; Van Horne, Beatrice, advisor; Bjostad, Louis Benjamin, committee member; Wiens, John A., committee member; Wunder, Bruce A., committee member
Patterns of distribution and abundance of small mammals reflect the responses of individuals to the spatial and temporal availability of resources and abiotic conditions, as well as interactions with conspecifics and other species. I examined habitat selection of two rodents, the deer mouse (Peromyscus maniculatus) and the northern grasshopper mouse (Onychomys leucogaster), on shortgrass steppe in north-central Colorado. Both species consume arthropods when these resources are plentiful, but grasshopper mice prey on other rodents and thus may have both competitive and predatory effects on deer mice. To examine these interactions, I conducted a removal experiment to determine the effect of grasshopper mice on microhabitat use, diet, and abundance of deer mice, and an odor-response experiment to determine whether olfactory cues mediate interactions between these species. Deer mice preferred shrubs at both individual and population levels, presumably to reduce predation risk. Mice oriented movements toward shrubs and traveled under shrubs more often than expected based on the density of shrubs on study plots. Population density also increased with increasing shrub density and aggregation. The response of mice to shrub cover was non-linear. Thresholds in the selective use of shrubs, movement patterns, and abundance occurred over a narrow range of shrub cover where shrubs were most aggregated, underscoring the importance of both shrub density and dispersion. Mice tended to accumulate in areas where their movements were most tortuous, suggesting that it is possible to generate testable predictions about patterns of abundance from individual movements. In contrast, grasshopper mice showed no affinity for shrub microhabitats, and instead oriented movements towards rodent burrows and disturbances created by pocket gophers (Thomomys talpoides). Results from pitfall trapping in different microhabitat types suggested that grasshopper mice used gopher mounds and burrows because of the concentration of insect prey in these microhabitats. The abundance of these microhabitats also was a better predictor of grasshopper-mouse abundance than were broad-scale, qualitative descriptors of macrohabitat type. The significance of these microhabitats across scales demonstrates the importance of spatial and temporal availability of prey to grasshopper mice. Even though grasshopper mice and deer mice show different habitat affinities, grasshopper mice may affect the surface activity and abundance of deer mice in areas where they co-occur. Deer mice decreased in number throughout the removal experiment on both control and removal sites, but the decline was greatest on controls, where grasshopper-mouse numbers increased. No shifts in microhabitat use were detected on removal sites, but deer mice increased their use of shrubs on control sites when grasshopper mice were most abundant. Because diets of deer mice did not differ between control and removal sites during the experiment, grasshopper mice apparently influenced the behavior and populations of deer mice through predation or interference rather than resource competition. Increases in the abundance of granivorous rodents on removal sites support this conclusion, and suggest that grasshopper mice, when abundant, can impact the composition of local assemblages on shortgrass steppe. However, if deer mice actively avoid contact with grasshopper mice, it is unlikely that this interaction is mediated by olfactory cues. When presented with odors of grasshopper mice, harvest mice, and clean cotton, deer mice showed no avoidance of grasshopper-mouse odors, regardless of season, sex or reproductive condition of respondents, or history of contact with grasshopper mice.
Open Access
Genetic analysis of a black-tailed prairie dog (Cynomys ludovicianus) metapopulation within shortgrass steppe
(Colorado State University. Libraries, 1999) Roach, Jen L., author; Van Horne, Beatrice, advisor; Antolin, Michael F., advisor; Wilson, Kenneth R. (Kenneth Ray), committee member
Black-tailed prairie dogs (Cynomys ludovicianus) in shortgrass steppe currently exist as a metapopulation. Habitat alteration, recreational shooting, agricultural control, and most recently, the introduction of sylvatic plague (Yersinia pestis) have contributed to local colony extinction and a steady decline of C. ludovicianus from its large and continuous historical range. Difficulties in quantifying dispersal have complicated efforts to document the degree of connectedness between isolated colonies. However, patterns of genetic similarity among populations, as measured by neutral molecular markers, provide an estimate of the degree of linkage within a metapopulation. We sampled 13 black-tailed prairie dog colonies in shortgrass steppe in Weld County, Colorado. The history of extinctions and recolonizations of the 13 colonies during the past 18 years is known. We examined 153 prairie dogs for variation at seven microsatelite loci and found moderate levels of genetic differentiation among prairie-dog populations (FST = 0.118). Akaike's Information Criterion was used to model prairie-dog dispersal as a function of genetic distance. Pairwise genetic distances between populations were related to both the distances along drainages (potential dispersal corridors), and to the relative ages of the populations. Cluster analysis revealed that prairie-dog populations are not more closely related to nearest neighbors than to other populations, indicating that populations are not in genetic drift-migration equilibrium and that prairie dogs are likely to disperse among all populations.
Open Access
Cattle use of prairie dog towns on the Shortgrass Steppe of Colorado
(Colorado State University. Libraries, 2000) Guenther, Debra A., author; Detling, James K., advisor; Rittenhouse, L. R. (Larry Ronald), 1940-, committee member; Steingraeber, David Allen, 1953-, committee member
Studies on the mixed-grass prairie have found that native large herbivores preferentially graze on prairie dog towns. I investigated the use of prairie dog towns by cattle (Bos taurus) in northeast Colorado by conducting surveys of cattle and vegetation on the Shortgrass Steppe Long Term Ecological Research Site from June-August, 1999. Twelve pastures containing 15 black-tailed prairie dog (Cynomys ludovicianus) towns were surveyed three times a week, and the number of cattle on the towns and their behavior were recorded. A subset of three pastures was intensively surveyed twice weekly wherein the habitat and activity of a randomly chosen focal animal was recorded every six minutes for 3.5 hours. Bite and step counts of other individuals were recorded for five-minute intervals. Vegetation height and cover data were collected monthly on each of the six habitat types. Resource selection functions for driving survey data indicated no significant difference between prairie dog town use and availability. Regression analysis showed no correlation between rain events and prairie dog town use by cattle. The intensively surveyed pastures yielded similar results: i.e., cattle did not significantly prefer or avoid the prairie dog towns. Cattle spent 60% of their time grazing, 13% resting, and 15% traveling when present on prairie dog towns. These percentages were not significantly different from most other habitat types. There were no significant differences in the number of bites per step taken by cattle on towns compared to off town swales, Atriplex canescens terraces, and crested wheatgrass (Agropyron cristatum) strips. Five plant species palatable to cattle occurred in relatively high frequencies (36-65%) on prairie dog towns. In general, bare ground, litter, and vegetation cover on prairie dog towns did not significantly differ from most other habitat types. Vegetation on prairie dog towns was however significantly shorter on (mean= 6.7cm) than that off (mean= 11.9cm) prairie dog towns. This research indicates that cattle on the shortgrass steppe use prairie dog towns randomly and do not avoid them despite the shorter vegetation on prairie dog towns. However, cattle do not prefer to graze on prairie dog towns as bison (Bison bison) do on the mixed-grass prairie.
Open Access
Mouths wide open: yawning as a communicative behavior in dogs
(Colorado State University. Libraries, 2001) Hoff, Anna E., author; Nash, Donald J., advisor; Ackley, Steven R., committee member; Granger, Ben P., committee member
Yawning is an action humans are very familiar with, yet this behavior is not unique to our species. Most vertebrate animals demonstrate yawning behavior. The cause of yawning is still uncertain, but yawns across vertebrate species seem to be concentrated around transitions between sleep and activity. Our most popular companion animal, Canis familiaris, also has periods of yawning before and after sleep. Dogs are naturally social living creatures and rely extensively on body language as a form of communication between group members. Behaviorists have suggested that some dog yawns are part of this visual communication system. The object of this observational study was to confirm that dogs have two main yawn types: a "rest" yawn that occurs between sleep-activity transitions, and a "social" yawn occurring during social interactions. Social interactions in this study referred to both dog-dog and human-dog interactions. Communicative yawning is performed to displace anxiety in an individual dog or to pacify aggression or excitement in other individuals. The frequency of rest yawns was predicted to be higher than that of social yawns. Both yawn types were morphologically the same, so the context of a yawn was used to indicate whether the yawn occurred for rest or communication. Even when recording the context of a yawn, distinguishing between displacement and pacification intentions was very difficult. Therefore, yawns motivated by displacement or pacification were collectively considered social in function. Because social yawns only occur in the presence of other individuals, dogs were observed in the social settings of dog daycare and obedience classes. Individual dogs were observed for 15-20 minutes. Some observations were videotaped, but the majority were taken in real time. Behaviors immediately preceding and following a yawn were recorded using an ethogram tailored to rest, displacement, and pacification behaviors. This study indicated that the majority of dog yawns occur during social interactions and not during sleep transitions. Using the yawn as a gauge to indicate if a dog is anxious or relaxed is one step towards more effective communication between dogs and humans. A yawn can act as a behavioral cue for dog handlers, trainers, owners and anyone concerned with canine welfare.
Open Access
Regulation of copper transport into and within Arabidopsis thaliana chloroplasts: a focus on copper transport proteins
(Colorado State University. Libraries, 2007) Gogolin, Kathryn Amy, author; Pilon, Marinus, advisor
Copper is an essential micronutrient that is required for the biological processes of photosynthesis and respiration. Nutrients, such as copper, must travel long distances through several organs and across many membranes before they are incorporated into target enzymes. Plastocyanin is a small, copper containing protein that is located within the thylakoid lumen and is vital for photosynthetic activity in higher plants. In addition chloroplasts contain a second target for copper, the superoxide dismutase enzyme CSD2. Although copper is essential it can also be toxic to the cell, therefore there is tight regulation of ion transport. The objective of the research conducted here is to develop a better understanding of copper homeostasis in plant cells. By focusing on the proteins that are involved in the transport of copper new insight can be gained on the delivery pathways of this metal. In this dissertation, I further characterize P-type ATPase of Arabidopsis 1 (PAA1) and P-type ATPase of Arabidopsis 2 (PAA2). An Arabidopsis Copper Chaperone for Cu,Zn Superoxide dimustase (CCS) is identified as a functional homolog of the yeast copper chaperone for Cu,Zn superoxide dimustase (Ccs1/Lys7). I study the effects of altered CCS expression on copper homeostasis in a plant system and I determine that the Heavy Metal Associated 1 transporter functions to transport a metal other than Cu(I) across the chloroplast envelope which affects photosynthetic activity. Finally, I completed a comprehensive analysis of copper transport protein-protein interactions in Arabidopsis studied by the yeast two-hybrid system. With the data gathered here, I propose several new models for copper homeostasis in Arabidopsis. I suggest that there is regulation of Fe Superoxide Dismutase (FeSOD), CCS, and CSD2 in the chloroplast which is controlled by metal cofactor availability, specifically copper. By utilizing the yeast two-hybrid technique, I have identified two new possible delivery pathways for copper. I believe that CCS can deliver copper to Heavy Metal Associated 5 to aid in cell detoxification or possible long distance transport of the ion. Additionally, I propose that copper is transported directly from PAA1 to PAA2 in the chloroplast for delivery to plastocyanin.
Open Access
New roles for calcium channel beta subunits in early zebrafish development
(Colorado State University. Libraries, 2008) Ebert, Alicia Marie, author; Garrity, Deborah, advisor
Voltage-gated calcium channels are present on pre-synaptic terminals and at neuromuscular junctions in the adult. In embryos, the channel is primarily expressed in the developing heart. The auxiliary β subunit is responsible for trafficking the pore-forming α subunit to the membrane, and regulating the calcium channel kinetics. In non-canonical roles, the β subunit regulates gene silencing, vesicle docking, and calcium release from pancreatic cells. We report here the cloning and expression of two zebrafish β2 genes and two β4 genes. Morpholino inhibition of the β4 subunit slowed or blocked the morphogenetic movements of gastrulation, causing the blastoderm to retract and the embryos to assume dorsalized phenotypes. The nuclei of the extra-embryonic yolk syncytial layer (YSL) contained extra centrosomes, which led to formation of abnormal mitotic spindle. Microtubule arrays in the yolk were disrupted or absent. In 48 hpf embryos, the axis of the embryo was expanded mediolaterally and shorter anteroposteriorly. Gastrulation defects were present as early as shield formation. These data combined support the hypothesis for a novel role of the β4 subunit in early zebrafish development.
Open Access
The role of CpNifS in selenium and sulfur plant metabolism: implications for phytoremediation and photosynthesis
(Colorado State University. Libraries, 2008) Van Hoewyk, Doug, author; Pilon, Marinus, advisor; Pilon-Smits, Elizabeth, advisor
NifS-like proteins are a conserved group of proteins that can cleave the sulfur-containing amino acid cysteine in alanine and elemental sulfur (S), and selenocysteine alanine and selenium (Se). In yeast and bacteria, NifS-like proteins are essential for survival because they provide the S for iron(Fe)-S clusters, a prosthetic group that is inserted into various FeS proteins that have a role in electron transfer. Furthermore, NifS-proteins are an essential part of Se metabolism in organisms that require this trace element. The goal of this research was to characterize the function of a chloroplastic NifS-like protein in Arabidopsis thaliana, designated AtCpNifS. As described in this dissertation, overexpression of CpNifS increases plant tolerance to selenate and accumulation of Se. Increased levels of CpNifS prevents toxic incorporation of selenocysteine into proteins, and thus enhances Se tolerance. This may benefit phytoremediation-the use of plants to naturally clean polluted soils and groundwater. In an effort to further the field of phytoremediation, a transcriptome experiment was performed in order to identify other genes and pathways that are involved in responding to Se stress. However, as divulged, plants likely do not require Se for essential metabolism, and the true function of CpNifS is more likely in the maturation of FeS clusters. The knockdown of CpNifS proteins in Arabidopsis using an inducible RNAi approach revealed that chloroplast function and structure became impaired, and that levels of all tested FeS proteins decreased. Consequently, the rate of photosynthetic electron transport, which is dependent on FeS proteins, diminished, and plants became chlorotic and eventually died. Therefore, CpNifS is required for FeS proteins, and is essential for proper photosynthesis and plant growth.
Open Access
Regulation of copper homeostasis in plants: a focus on chloroplastic superoxide dismutases and copper delivery mechanisms
(Colorado State University. Libraries, 2009) Cohu, Christopher Michael, author; Pilon, Marinus, advisor
Copper (Cu) is an essential micronutrient for higher plant growth and is found in proteins that are important in photosynthesis and respiration. As a cofactor, this trace element is associated with many proteins including plastocyanin, Cu/Zn superoxide dismutase (Cu/ZnSOD), and mitochondrial cytochrome- c oxidase. Due to its redox-active role, Cu is essential for plant life, yet Cu is also dangerous as a free cellular ion and even toxic if in excess. Therefore, delivery and sequestration of Cu must be tightly regulated. The research of this dissertation indicates that sensory mechanisms and signaling pathways exist to coordinate Cu transport and target protein expression based on Cu status. For Arabidopsis and crop species, chloroplastic Cu/ZnSOD is down-regulated during limited Cu availability while at the same time FeSOD is up-regulated. During Cu-limited growth, when Cu/ZnSOD is down-regulated, plastocyanin levels do not change. We suggest that this reduction in Cu/ZnSOD allows for preferential Cu delivery to plastocyanin, which is essential for photosynthesis, while also maintaining chloroplast SOD activity. Cu delivery to Cu/ZnSOD is accomplished by the Cu Chaperone for SOD (CCS). When a CCS loss of function mutant was grown on Cu supplemented soil Cu/ZnSOD and FeSOD activity was not detected. Chloroplast did not exhibit an observable phenotype or photosynthetic deficiencies, even after high light stress treatments. Recent studies have shown that Cu/ZnSODs in the cytosol and chloroplast, along with other Cu proteins, are regulated by Cu via microRNA directed cleavage of Cu protein mRNA. It has also been determined that during Cu-limited growth the SPL7 transcription factor plays a central role in activating Cu-microRNAs and possibly Cu transporters. The research of this dissertation indicates that CCS is also regulated by Cu, mediated by microRNA398, which was not previously predicted by bioinformatic algorithms. Furthermore, data is presented to suggest that SPL7 likely regulates the promoter of FeSOD by activating transcription during limited Cu availability.
Open Access
Pathogen persistence in wildlife populations: case studies of plague in prairie dogs and rabies in bats
(Colorado State University. Libraries, 2009) George, Dylan, author; Webb, Colleen, advisor
Disease ecology focuses, in part, on how pathogens persist within host wildlife populations For my dissertation my colleagues and I investigated pathogen persistence mechanisms in two host-pathogen systems: Yersinia pestis (plague) in prairie dogs and rabies virus in bats. Plague, caused by the bacterium Yersinia pestis, recently spread into the range of black-tailed prairie dogs (Cynomys ludovicianus) in North America, and has caused drastic and rapid reduction in local prairie dog populations which have generated a metapopulation dynamic for prairie dogs. We developed a stochastic patch occupancy model to determine if prairie dog populations could persist long-term given the effects of plague. Our model demonstrates that metapopulation dynamics can allow prairie dog persistence. Town extinction in this system is caused by plague. Thus, town extinction and plague colonization are two sides of the same coin, which allows to us to interpret plague dynamics implicit within the prairie dog metapopulation. Long-term metapopulation dynamics indicate plague persists within the system and does not require the involvement of additional reservoir hosts (i.e., other resistant rodent species). Bats are a natural reservoir for rabies, and an increasing number of emerging zoonotic viruses. Little is known about mechanisms that generate unique seasonal patterns and allow enzootic pathogen persistence in bat populations. We propose that life history characteristics unique to many bat species coupled with viral adaptations allow for rabies persistence. First, we developed a statistical model to investigate seasonal patterns of rabies cases in bats. Second, we used data from a five-year study of rabies in big brown bats (Eptesicus fuscus) to parameterize a dynamic disease model that elucidates pathogen persistence mechanisms. We show rabies persists in two distinct ways, (1) through effects on bat population viability, and (2) through effects on viral persistence within a viable bat population. Mortality rates vary across seasons, and low rates during hibernation allow long-term bat population viability. Within a viable bat population, viral persistence occurs because of a lengthy incubation period, enhanced by the metabolic effects of host torpor. The mechanisms we identify may be operating in a similar manner for other bat-borne diseases.
Open Access
Colorado cytospora canker complex on Populus tremuloides Michx.
(Colorado State University. Libraries, 2009) Kepley, Jeff B., author; Reeves, F. Brent, advisor
Cytospora canker is a serious fungal disease affecting aspen in natural and commercial forests as well as urban sites. In Colorado the causal organism responsible for this canker disease is typically reported to be Cytospora chrysosperma (Pers.) Fr. However, a thorough understanding of the species of Cytospora attacking aspen in Colorado is lacking. Fungal identification has been based upon morphological characteristics of fruiting/vegetative structures despite the plasticity known to occur in such diagnostic features. Examinations of cankers on aspen stems in Colorado revealed a morphologically distinct Cytospora-like fungus that frequently co-occurs with C. chrysosperma. This fungus is a new species and is closely associated with and superficially resembles C. chrysosperma. Based on these findings Cytospora canker on aspen in Colorado is a complex of fungi, contrary to what is typically reported in the literature. Isoenzyme analysis was employed as an initial step to determine the genetic/biochemical differences that occur among and between C. chrysosperma and the new non-C. chrysosperma isolates. Of the twelve enzyme systems initially screened only three, viz., alpha esterase, amylase, and glucose-6-phosphate dehydrogenase, provided good resolution for all isolates. Following cluster analysis, two major clades well-delineated the two taxa. Phylogenetic analyses of ITS1-5.8S-ITS2 rDNA and EF-1α sequences produced phylogenetic trees in which non- C. chrysosperma isolates formed a monophyletic clade (with strong bootstrap support and high posterior probability) within a Cytospora spp. phylogeny. Based on these results the non-C. chrysosperma isolates from aspen in Colorado are considered a new Cytospora species. External morphological features of the ascostromata and conidiomata (natural specimens) as well as histological sections of the new Cytospora sp. reveal conceptacles and conceptacle-like tissues which gives fruit bodies a unique target-like appearance. Cultures are darkly pigmented and display robust (large diameter) bead-like hyphae; many hyphal tips from young cultures lyse. Pycnidia produced in vitro do not enclose a multi-lobed locular structure; rather they have indentations/pockets with conidiophores lining these invaginations as well as pycnidial surfaces. In addition to the Cytospora anamorph a Phialocephala-like synanamorph is produced by some isolates. Descriptions of the new Cytospora species and C. chrysosperma, occurring on aspen in Colorado, are provided.
Open Access
Understanding adaptive regulation of skeletal muscle physiology in the Weddell seal: a proteomics approach
(Colorado State University. Libraries, 2010) Cable, Amber E. (Amber Elizabeth), author; Kanatous, Shane, advisor; Florant, Gregory L., committee member; Mykles, Donald L., committee member; Bell, Christopher, committee member
Air-breathing, diving vertebrates foster unique adaptations to exercise; namely, these animals are able to exercise for prolonged periods of time while "holding" their breath. Weddell seals (Leptonychotes weddellii) routinely undergo progressive hypoxia and ischemia throughout the course of diving activity. In essence, this unique animal has overcome problems that are considered to be otherwise pathological in terrestrial vertebrates. The goal of this project was to verify the use of cross-species analysis and develop a proteomics protocol for use in diving mammals. These steps are necessary in order to ultimately use proteomics to identify age class protein signatures and better understand the molecular regulation of the physiological changes that couple the development of inactive Weddell seal pups into elite diving adults. Proteins from the primary swimming muscle (M. longissimus dorsi) of two distinct age classes, pups (3-5 weeks/nondivers) and adults (7+ years/expert divers), were visualized using two dimensional gel electrophoresis (2DE), quantified, and identified. This study validated the use of cross-species analysis, which was of paramount importance due to the fact that the pinniped genome is largely unidentified, and established a 2DE protocol tailored to suit the unique properties of diving mammal skeletal muscle tissue. To our knowledge, this was the first study in which proteomics was applied to study the proteome of a diving mammal. Understanding the control of these adaptations in the Weddell seal, which develops its ability to endure hypoxia associated with breath-hold exercise rather than being born ready to dive, has considerable potential for pharmacological implications for treating various human diseases, specifically those that involve hypoxic conditions such as cardiovascular and pulmonary diseases.
Open Access
The role of CACNβ4 in zebrafish development
(Colorado State University. Libraries, 2010) Harrell, Cory Jean, author; Garrity, Deborah M., advisor; Mykles, Donald L., committee member; DeLuca, Jennifer G., committee member
The calcium channel β4 subunit (CACNβ4) is an intracellular auxiliary protein of voltage-gated calcium channels. It is a member of the membrane-associated guanylate kinase (MAGUK) family of proteins. Mutations in the CACNβ4 subunit are associated with ataxia and seizures in mice and with epilepsy in humans. Since known mutant alleles of CACNβ4 are not embryonic lethal in mammals, the developmental functions of the protein are unclear. The best characterized role for the β4 subunit is to facilitate the translocation of the calcium channel α subunit to the plasma membrane and the modulation of the channel gating. Recently, additional roles have been proposed for the β subunits including facilitation of vesicle docking, attenuation of gene silencing and transcriptional regulation of calcium channel turnover. In studying the functional roles of the CACNβ4 gene, we unexpectedly discovered that targeted knockdown of CACNβ4 genes in zebrafish led to arrest or delay of epiboly and the subsequent death of the early embryo. Embryonic death can be rescued by co-injection with full-length RNA of human CACNβ4 (homologue). In this study we investigated the sub-cellular localization and critical domains of the β4 proteins. Upon injection of a construct with GFP-tagged β4 gene under the control of the β-actin promoter we observed that the β4 protein is present in the nucleus in higher concentrations than in the rest of the cell. We determined via rescue experiments with truncated RNA constructs that the N-terminus and the chromoshadow binding element (CBE) are necessary for CACNβ4's function during gastrulation. Our findings suggest that CACNβ4 has a nuclear role, potentially interacting with chromobox family proteins, which is necessary for early zebrafish development.
Open Access
Habitat use, territoriality, and parental behavior of orange-crowned warblers (Oreothlypis celata)
(Colorado State University. Libraries, 2010) Yoon, Jongmin, author; Ghalambor, Cameron K., advisor; Angeloni, Lisa Marie, committee member; Doherty, Paul F., 1970-, committee member; Sillett, Terence Scott, 1966-, committee member
To view the abstract, please see the full text of the document.
Open Access
Meiotic recombination and synapsis in wild-type and asynaptic mutants of tomato (Solanum lycopersicum)
(Colorado State University. Libraries, 2010) Qiao, Huanyu, author; Anderson, Lorinda K., advisor; Stack, Stephen M., committee member; Bedinger, Patricia A., committee member; Ranu, Rajinder Singh, committee member
Recombination nodules (RNs) and synaptonemal complexes (SCs) are meiosis-specific structures that play important roles in crossing over. During pachytene, RNs mark crossover sites along SCs. MLH1, a mismatch repair protein, promotes crossing over and is a component of most RNs. In wild-type tomato, each bivalent has one, two or three crossovers (=chiasmata), and the number and distribution of these crossovers is affected by crossover interference (the tendency for one crossover to reduce the likelihood of another crossover nearby). Although the phenomenon of genetic interference was discovered nearly one hundred years ago, its molecular basis is still unknown. SCs occur between pairs of homologous chromosomes (bivalents) during prophase I and consist of two parallel rod-like lateral elements held together by transverse fibers. Each lateral element is associated with the two sister chromatids of one of the homologous chromosomes. Cohesin complexes consisting of four proteins (SMC1, SMC3, SYN1/REC8 and SCC3) are found in lateral elements and link sister chromatids together. My research addressed the question of how synapsis (SC formation) is related to the frequency and control of crossing over using tomato, particularly the as1 meiotic mutant, as a model system. Meiocytes from tomato plants homozygous for the mutation as1 do not complete chromosome synapsis and have few chiasmate bivalents, resulting in unbalanced chromosome segregation and sterility. We found a severe delay of prophase I in the as1 mutant compared to wild-type tomato using an in vivo BrdU labeling method, which may be related to the asynaptic phenotype. The asynapsis and delay in the as1 mutant are not likely to be due to a defect in the early steps of recombination, since the frequency and distribution of early recombination proteins (MRE11, RAD50, and RAD51) are similar in wild-type and in the as1 mutant. EM immunolabeling demonstrated that MLH1, a late recombination protein, is present in a subset of RNs in as1, an observation similar to that in wild-type. However, RNs in as1 are larger than those in wild-type. Previous work by other researchers showed a normal level of crossovers in several genetic intervals of the as1 mutant, which was unexpected based on the high degree of asynapsis observed at the cytological level. To evaluate crossing over in the as1 mutant, we examined the immunolabeling patterns of MLH1 foci that mark crossover sites. In as1 meiocytes, we observed that most MLH1 foci were associated with SC segments between two homologous chromosomes. We found that the number of MLH1 foci per micrometer is higher in the as1 mutant compared to wild-type. In addition, interference between MLH1 foci was lower in the mutant than in wild-type tomato. The weakened genetic interference in the as1 mutant may be due to a defect of the medium of interference, since early events of the recombination pathway in as1 seem normal, and MLH1 foci representing crossovers, the last step of the recombination pathway, are still present in the mutant. A good candidate to transmit interference is the cohesin complex that makes up a part of lateral elements. Compared to wild-type, we observed reduced immunofluorescence for the cohesins SMC1, SYN1, and SCC3, but not SMC3 in the as1 mutant. Although we do not yet know the specific mutation of as1 in tomato, we have shown that the asynaptic phenotype is accompanied by alterations in cohesin proteins in AE/LEs and in the distribution of MLH1 foci compared to wild-type. To our knowledge, this is the first report of an association between cohesin proteins and crossover interference regulation in any organism. This discovery represents a significant advance in our efforts to understand the molecular basis of crossover interference.
Open Access
Three guanylyl cyclases in the green shore crab, carcinus maenas: cDNA cloning and effects of molt stage on expression in molting gland (Y-organ)
(Colorado State University. Libraries, 2010) Gunderson, Jennifer L., author; Mykles, Donald L., advisor; Reddy, Anireddy N., committee member; Tjalkens, Ronald B., committee member
YO ecdysteroidogensis is suppressed by molt-inhibiting hormone (MIH) and the pleiotropic neuropeptide crustacean hyperglycemic hormone (CHH) with these neuropeptides being produced in the X-organ of the eyestalk (ES) ganglia. CHH signaling is mediated by a membrane receptor guanylyl cyclase (GC), while MIH signaling may involve a soluble NO-sensitive GC. Here we report the cloning of cDNA sequences encompassing the catalytic domain of the~ subunit of a soluble NO-sensitive GC ( Cm-GC-I ß), membrane receptor GC ( Cm-GC-II), and soluble NO-insensitive GC (Cm-GC-III) from the European green crab, Carcinus maenas, using RT-PCR and RACE. Adult C. maenas occur as two color morphs that differ in growth traits; the "green" morphs molt more frequently than the "red" morphs. These data suggest that YOs in red morphs are less active than the YOs in green morphs, and that the red morphs are refractory to molt induction by eyestalk ablation (ESA). We tested the effects of ESA on the expression of NO synthase ( Cm-NOS), Cm-GC-I ß, Cm-GC-II, and Cm-GC-III in the YOs from green and red morphs using quantitative PCR. Elongation factor-2 (Cm- EF2) served as a constitutively expressed control. ESA caused a small, transient increase in hemolymph ecdysteroid titers in both morphs, with the increase occurring at 3 days post-ESA in green morphs and at 14 days post-ESA in red morphs. ESA had no significant effect on the expression of Cm-EF2, Cm-NOS, Cm-GC-II, and Cm-GC-III, which were not correlated with hemolymph ecdysteroid titers. ESA caused a significant decrease in Cm-GC-I ß expression in red morphs, but had no significant effect in green morphs. Expression was also quantified in green morphs undergoing spontaneous natural molting. There was no significant difference in the expression of Cm-EF2, Cm-NOS, Cm- GC-II, and Cm-GC-II in YOs from intermolt, premolt, and postmolt animals. By contrast, Cm-GC-III mRNA was about 2-fold greater in YOs from postmolt animals than in intermolt and premolt animals. The results show that both color morphs are resistant to ESA and that molting has little effect on NOS and GC expression.
Open Access
Fine-scale habitat use by black-footed ferrets (Mustela nigripes) released on black-tailed prairie dog (Cynomys ludovicianus) colonies in New Mexico
(Colorado State University. Libraries, 2010) Chipault, Jennifer G., author; Detling, James K., advisor; Biggins, Dean E., advisor; Reich, Robin M., committee member
Black-footed ferrets (Mustela nigripes) are among the most endangered animals in North America. The dependency of ferrets on diminishing prairie dog {Cynomys spp.) colonies for prey and shelter has been detrimental to their persistence in the wild. Reintroductions of captive-born ferrets into remaining prairie dog complexes have become crucial to the conservation of the species. Gaps in knowledge of ferret behavior hinder the success of these reintroductions. In this study, fine-scale prairie dog burrow density use by captive-born ferret kits was analyzed to inform future management. In September 2007, captive-born ferrets were released on a black-tailed prairie dog (C. ludovicianus) colony on the Vermejo Park Ranch in northern New Mexico. Locations {n = 46) from 16 ferret kits experimentally released in areas of comparatively low and high prairie dog burrow densities were obtained via spotlight surveys. Ten kits were subsequently translocated to low and high burrow density areas on other Vermejo colonies and located thereafter (« = 53). For two months, habitat use was quantified by mapping all burrow openings within a 30 m radius of where ferrets were located. Spatial autoregressive models and spatially-explicit t-tests were used to account for autocorrelation in the used burrow densities. It was hypothesized that ferrets released in, or translocated to, areas of low burrow densities would move so as to increase their localized burrow densities as they spent more nights in the wild. It was also hypothesized that ferrets released in, or translocated to, high burrow density areas would maintain high used burrow densities. There was an inverse relationship between used prairie dog burrow densities and nights in the wild for ferrets released in high burrow density areas. For ferrets translocated to high burrow density areas, a pattern was not detected in burrow densities over time, which does not contradict the hypothesis for these ferrets. However, burrow densities used by ferrets released in, and translocated to, low burrow density areas did not increase over time as expected. With the number of nights in the wild converted to release or translocation burrow densities versus ferret-used burrow densities, average used burrow densities increased for ferrets placed in low burrow density areas, and average used densities decreased for ferrets placed in high burrow density areas. Used burrow densities on most inhabited colonies were similar to available densities, except for one colony, where used densities were lower than available densities. Because newly-released ferrets in this study used burrow densities similar to densities available at the colony level, releasing ferrets on colonies offering overall high burrow densities might increase reintroduction success rates. Furthermore, burrow densities directly correlated with prey densities in this study. Ferrets used higher burrow densities before midnight; future research on ferret habitat use should consider within night variation. Other studies on ferret habitat use after release are necessary; kits monitored for more than two months, or with experience in the wild at a younger age, might select high burrow density areas within colonies as predicted.
Open Access
Hormonal controls of obesity in feeding and fasting hibernating mammals
(Colorado State University. Libraries, 2010) Healy, Jessica, author; Florant, Gregory L., advisor; Kanatous, Shane B., 1968-, advisor; Ghalambor, Cameron K., committee member; Irlbeck, Nancy A., committee member
Mammals that hibernate (hibernators) are intriguing models for the study of controls of food intake and adiposity due to their robust circannual cycle of obesity and anorexia. The pathways controlling these cycles in hibernators have not been fully elucidated. In order to clarify the relationships between various hormones, enzymes and metabolic factors, I examined endogenous and experimentally manipulated levels of several factors in hibernators kept under various physiological conditions, including short-term fasting in summer, long-term fasting in winter, and at low and high body temperature. I compared orexigenic factors (such as the hormone ghrelin and the enzyme AMP-activated protein kinase (AMPK)) with anorexigenic compounds (such as leptin and the enzyme acetyl CoA carboxylase (ACC)) at various times of the year and under experimentally manipulated conditions. Ghrelin is an orexigenic hormone produced by the stomach which increases food intake. Leptin is an anorexigenic hormone produced by white adipose tissue (WAT) which decreases food intake. Both of these hormones impact AMPK, a cellular-energy sensing enzyme that increases food intake and fatty acid oxidation through its inactivation of ACC. I found distinct seasonal profiles of these enzymes and hormones that correlated well with the observed life history characteristics of one species of hibernator, the golden-mantled ground squirrel (GMGS, Callospermophilus lateralis). In spring and summer, when GMGS are normophagic and lipogenic, the hormone profile of hibernators was much like non-hibernating rodents--AMPK and ghrelin increased with fasting, and injected ghrelin caused an increase in food intake with an associated increase in the active form of AMPK (pAMPK). In autumn, when GMGS are hyperphagic and lipogenic, circulating ghrelin concentrations were higher than at other times of the year, and release of leptin from WAT lagged behind fat mass to allow hyperphagic animals to become obese before hibernation. In winter, when GMGS were aphagic and lipolytic, AMPK and ACC activation were higher in torpid than in euthermic animals, circulating leptin concentrations were once again coupled with fat mass, ghrelin was still circulating in the blood, but at lower concentrations than during normophagic seasons, and circulating ghrelin was higher in euthermic than in torpid GMGS. This was the first published investigation of the hormone ghrelin in a true hibernator, and provides a potential explanation of the dramatic seasonal changes in food intake seen in mammals that hibernate.
Open Access
Ecological interactions involving plant selenium hyperaccumulation
(Colorado State University. Libraries, 2010) Quinn, Colin Francis, author; Pilon-Smits, Elizabeth, advisor; Paschke, Mark, committee member; Seshadri, Arathi, committee member; Steingraeber, David, committee member
To view the abstract, please see the full text of the document.
Open Access
Reproductive ecology of the island scrub-jay (Aphelocoma insularis)
(Colorado State University. Libraries, 2010) Caldwell, Luke, author; Angeloni, Lisa M., advisor; Sillett, T. Scott, committee member; Savidge, Julie A., committee member
The small population size and limited range of the Island Scrub-Jay make it a species of conservation concern, yet its reproductive ecology is poorly known. From 2008 - 2010 I investigated factors influencing nest success, quantified annual fecundity per pair, and documented breeding behavior. Nest predation was the major factor influencing nest success, accounting for 92 percent of documented nest failures. Nests that were initiated earlier in the breeding season, nests that were higher and more concealed, and nests of breeding pairs that had smaller home ranges had higher daily nest survival. Despite a low estimated daily nest survival rate of 0.945 ± 0.004 SE, the high frequency of renesting allowed pairs to maintain a mean fecundity of 1.13 ± 0.15 SE. Island Scrub-Jays may benefit from an increase in breeding habitat and lower nest predation from the ongoing regeneration of woody vegetation and understory structure following the removal of exotic herbivores on Santa Cruz Island.
Open Access
Impacts of thawing permafrost on nematode populations and soil habitat characteristics in an Antarctic polar desert ecosystem
(Colorado State University. Libraries, 2011) Smith, Tracy Elise, author; Wall, Diana H., advisor; Hogg, Ian D., advisor; Knapp, Alan K., 1956-, committee member; Conant, Richard T., committee member
Global climatic changes are altering ecosystem dynamics at unprecedented rates and degrees. Given this, studying the controls on species distribution and functioning within ecosystems, as well as how they are impacted by such changes, is timely. Polar deserts such as those in the McMurdo Dry Valleys, Antarctica (MDV) have been exposed to long-term cooling over the last two decades as well as increased frequency of seasonal warming events, and may also be exposed to a warming trend within the next several decades. Each of these changes can lead to substantial shifts in ecosystem characteristics, affecting habitat conditions for biota. I examined these issues with a specific focus on how nematode communities, the dominant fauna in the extremely cold and arid environment of the MDV, responded to a warming event that led to inundation of moisture from thawing permafrost. I took samples to the depth of the ice-cemented soil layer in seeps of permafrost thaw and compared nematode community structure to dry soils not affected by thaw. I also assessed potential alterations to soil properties that determine suitability of nematode habitats, measuring soil pH, salinity, and texture. I observed a gradient in impacts on each of these soil properties, which were consistent with the pattern of the degree of moisture increase. I additionally observed a response by nematode populations that similarly followed these patterns. My results suggest that warming and the resulting moisture increases from thawing permafrost can have profound negative effects on nematode abundance and distribution.