No description available.

I studied four areas in south Mississippi from 2009-2010 to examine habitat conditions and faunal communities associated with presence of black pine snakes (Pituophis melanoleucus lodingi), a candidate for federal listing. Field studies included vegetation sampling, small vertebrates trapping, and fire ant (Solenopsis invicta) mound densities estimation. Areas that supported black pine snakes exhibited vegetation communities that differed from areas that did not support pine snakes. Presence of black pine snakes was influenced by ground cover vegetation and stump hole densities. Greatest densities of ant mounds were detected in areas that supported pine snakes and gopher tortoises (Gopherus polyphemus). Species associates of black pine snakes included coachwhips (Coluber flagellum flagellum), scarlet snakes (Cemophora coccinea), six lined race runners (Aspidoscelis sexlineata sexlineata), and gopher tortoises. Findings of my study are being used to address creation of habitat corridors for black pine snakes and species associates within the Mississippi longleaf pine belt.

No description available.

No description available.

Flying snakes possess a sophisticated gliding ability with a unique aerial behavior, in which they flatten their body to make a roughly triangular cross-sectional shape to produce lift and gain horizontal acceleration. Also, the snakes assume an S-like posture and start to undulate by sending traveling waves down the body. The present study aims to answer how the snakes are able to control their glide trajectory and remain stable without any specialized flight surfaces. Undulation is the most prominent behavior of flying snakes and is likely to influence their dynamics and stability. To examine the effects of undulation, a number of theoretical models were used. First, only the longitudinal dynamics were considered with simple two-dimensional models, in which the snake was approximated as a number of connected airfoils. Previously measured force coefficients were used to model aerodynamic forces, and undulation was considered as periodic changes in the mass and area of the airfoils. The model was shown to be passively unstable, but it could be stabilized with a restoring pitching moment. Next, a three-dimensional model was developed, with the snake modeled as a chain of airfoils connected through revolute joints, and undulation was considered as periodic changes in the joint angles. It was shown that undulation, when added to a linearization-based closed-loop control, could increase the size of the basin of stability. Our theoretical results suggested that the snakes need some extent of closed-loop control in spite of the clear contribution of undulation to the stability of glide. Next, we considered the effects of aerodynamic interactions between the fore and the aft body on the aerodynamic performance of flying snakes. Two-dimensional anatomically accurate airfoils were used in a water tunnel. Lift and drag forces were measured by load cells, and the flow field data were obtained using digital particle image velocimetry. The results confirmed strong dependence of the aerodynamic performance on the tandem arrangement. Flow fields around the airfoils were obtained to show how the tandem arrangement modified the separated flow and the wake; therefore altering the pressure field and resulting in changes in the lift and drag. / Ph. D.

While nocturnal basal snakes have rod-dominant retinae, diurnal garter snakes have all-cone retinae. Previous work from the Chang lab identified three visual pigments expressed in the photoreceptors of Thamnophis proximus: SWS1, LWS and RH1. I further characterized T. proximus photoreceptors using electron microscopy, immunohistochemistry, and in vitro protein expression. T. proximus have four types of morphological cones: double cones, large single cones, small single cones, and very small single cones. Some small single cones have rod-like features, such as rod-like outer-segment membranes and a lack of micro-droplets. Immunohistochemistry showed that rod-specific transducin is expressed in some T. proximus photoreceptors. In vitro expression of T. proximus RH1 produced a functional rhodopsin with λmax at 485nm, which corresponds to microspectrophotometry measurement from some small single cones. Current results suggest that small single cones of T. proximus may have evolved from ancestral rods, and secondarily acquired a cone-like morphology as adaptation to diurnality.

Pathogenic fungi are increasingly associated with epidemics in wildlife populations and represent a significant threat to global biodiversity. Snake fungal disease is an emerging disease caused by the fungus, Ophidiomyces ophiodiicola, and appears to be widespread in the eastern United States. Yet an evaluation of field diagnostics, and an understanding of the population-level consequences of the disease, are lacking. First, I evaluated the use of clinical signs to predict the presence of O. ophiodiicola across season and snake habitat affiliation (aquatic or terrestrial) and I compared two sampling methods to see if collection method impacts PCR result. Overall, snakes with clinical signs had a higher probability of testing positive regardless of season or habitat association. However, terrestrial snakes had a lower overall probability of testing positive for O. ophiodiicola compared to aquatic snakes. I found no significant difference between sampling methods. Second, I used Passive Integrated Transponder (PIT) telemetry, and multistate capture-mark-recapture modelling to determine if SFD affects the short-term survival, movement, and behavior of wild snakes. I found no difference in short-term survival for snakes with SFD. Snakes with SFD spend more time surface-active and have lower permanent emigration and temporary immigration rates than snakes without SFD.

Environmental cues such as day length and temperature contribute to timing of biological rhythms in seasonal breeders. Life-history transitions such as spring emergence from hibernation, migration, or mating must be coordinated with environmental conditions or survival is compromised. Therefore, there must be chemical signaling pathways in the brain that transduce seasonally-changing sensory inputs into signals that initiate a hormonal cascade, culminating in reproductive behavior. The relative importance of environmental cues to reproductive timing varies with species, time of year, and sex, and the mechanisms driving these differences remain unknown. The role of photoperiod in regulating reproductive behavior has been explored in birds and mammals, but much less is known about the role of so-called supplementary cues such as temperature, which is crucial in the timing of ectotherm reproduction. This is a critical gap in our knowledge, because shifts in seasonal temperatures due to climate change could create a mismatch between peak reproductive behavior and resources necessary for gestation and offspring survival. Deiodinase 2 (DIO2) enzyme is a critical component of the pathway that mediates reproduction in photoperiod-activated seasonal breeders, but whether deiodinase 2 is sensitive to seasonal changes in environmental temperature is unknown. In this study, we used an ectothermic vertebrate known to be a temperature-activated seasonal breeder, the red-sided garter snake (Thamnophis sirtalis parietalis), to investigate changes in hypothalamic DIO2 in response to hibernation at 4°C and 12°C. We captured male and female snakes in Manitoba, Canada as they returned to their winter den site from summer feeding grounds. Snakes were hibernated in complete darkness at either 4°C or 12°C for up to 16 weeks. A subset of each sex and temperature group were euthanized at intervals, and the brains collected and processed for DIO2 immunohistochemistry. DIO2-specific staining was found in the anterior hypothalamus, in the periventricular hypothalamic nucleus and ventral pre-optic area, along the longitudinally central region of the olfactory tract, in the bed nucleus of the stria terminalis, caudally in the cortex and optic tectum, and in the lateral septal nucleus. DIO2-stained area in the anterior hypothalamus was quantified. Male T. sirtalis in both the 4°C and 12°C groups were found to have an increase in DIO2-specific staining in the anterior hypothalamus after 8 weeks in hibernation. Female T. sirtalis were found to have an increase in DIO2-specific staining in the anterior hypothalamus after 8 weeks in the 12°C group only. These findings shed light on the neuroendocrine pathway through which environmental cues other than photoperiod influence the timing of seasonal reproduction, and support the hypothesis that at least some components of this pathway are conserved across seasonal breeders.

Astragalus oniciformis Barneby is a xerophyte of the sagebrush deserts of central Idaho. It is a narrow endemic of the upper Snake River Plains where it inhabits stabilized, aeolian sand deposits over Quaternary basalt flows. The objective of this study was to determine the levels and distribution of genetic differentiation within and among populations of Astragalus oniciformis. Fifteen individuals from each of eight populations, chosen from throughout the range of the species, were selected for their accessibility, density of individuals, and large population size. Two disjunct eastern populations selected for this study have been separated from the continuous western populations for 3600 years by an eight-mile wide, inhospitable lava flow. Inter-simple sequence repeats (ISSR) were chosen as the marker to assess genetic differentiation. Two primers were selected that yielded 40 loci, all of which were polymorphic in A. oniciformis. In an analysis of molecular variance (AMOVA), 88.69 percent of the variation was significantly attributed to variation within populations. The differentiation between the two disjunct populations and the western populations was insignificant. High gene flow (Nm=3.91-3.93) and a low percent deviation from Hardy-Weinberg equilibrium due to population subdivision (G[subscript st]=0.113-0.1134) were found among populations of A. oniciformis. These results suggest that current threats to this species, ranging from plant community changes due to changing fire patterns, habitat alteration from livestock grazing, and habitat loss from agricultural development have not yet affected the genetic diversity of this species. Preservation of the numerous, large populations and the high gene flow will help insure that the levels of genetic diversity found in Astragalus oniciformis will not decrease. / Graduation date: 2002

Roads are significant objects of an infrastructure and the extraction of roads from aerial and satellite images are important for different applications such as automated map generation and change detection. Roads are also important to detect other structures such as buildings and urban areas. In this thesis, the road extraction approach is based on Active Contour Models for 1- meter resolution gray level images. Active Contour Models contains Snake Approach. During applications, the road structure was separated as salient-roads, non-salient roads and crossings and extraction of these is provided by using Ribbon Snake and Ziplock Snake methods. These methods are derived from traditional snake model. Finally, various experimental results were presented. Ribbon and Ziplock Snake methods were compared for both salient and non-salient roads. Also these methods were used to extract roads in an image. While Ribbon snake is described for extraction of salient roads in an image, Ziplock snake is applied for extraction of non-salient roads. Beside these, some constant variables in literature were redefined and expressed in a formula as depending on snake approach and a new approach for extraction of crossroads were described and tried.