After partial denervation of mature muscle, the remaining motoneurons grow terminal sprouts, which reinnervate denervated muscle fibers. In neonatal rat soleus muscle however, not only do the remaining motoneurons fail to reinnervate nearby muscle fibers, but they also display clear morphological and physiological evidence of terminal disruption. My ultimate aim is to attain a better understanding of this disruption by performing repeated in vivo observations of individually identified terminals in transgenic mice expressing fluorescent proteins in their motoneurons. For technical reasons, these in vivo imaging studies would ideally be conducted on CFP mouse sternomastoid (SM) muscle. I therefore tested whether neonatal partial denervation of CFP mouse SM muscle also causes terminal disruption. Two to five days after neonatal partial denervation, I fluorescently labeled nerve terminals and acetylcholine receptors (AChRs) to assess the effect on terminal morphology. Terminal disruption after partial denervation did not occur as extensively in CFP mouse SM muscle (a fast-twitch muscle) as it did in rat soleus muscle (a slow-twitch muscle). This relative absence of terminal disruption in CFP mouse SM suggested that the extent/occurrence of terminal disruption after neonatal partial denervation could depend on either the species being studied or muscle fiber type. To distinguish between these possibilities, I investigated terminal disruption after partial denervation of rat SM muscle. In both soleus and sternomastoid muscles of rats, neonatal partial denervation resulted in disruption of about half of the terminals, whereas in SM muscles from CFP mice only 8% of terminals showed evidence of disruption. Therefore, it appears that the nature of terminal disruption that takes place after partial denervation of neonatal muscles is not related to muscle fiber type but may be species-specific.

A series of static toxicity tests were conducted to determine the tolerance of yellow perch to ammonia and nitrite on larvae, juvenile and adult fish. Toxicity tests on adults were conducted at 18, 22, and 25 C. The tests on larvae showed highly varible results and were ultimately inconclusive. The 96h LC50 for ammonia and nitrite to juveniles were 0.77 mg/L as NH3-N and 78.24 mg/l as NO2-N, respectively. Adult and juvenile yellow perch had similiar tolerance levels. lc50 values for ammonia and nitrite varied with temperature and were 0.64 mg/l as NH3-N and 65.8 mg/l as NO2-N, respectively at 22 C. Lower water temeprature reduced the toxicity of ammonia and nitrite to yellow perch adults significantly. At 18 C, the LC50 values and nitrite were 59% higher (1.02 mg/l as NH3-N) and 34% higher (88.5 mg/l as NO2-N), respectively than the values at 22 C.

Subadult red drum Sciaenops ocellatus are ecologically and economically important in North Carolina, but little is known about factors influencing their mortality and distribution in estuaries. I first assessed the effect of fishing on red drum abundance using 24 years of tagging data. The tag-return model incorporated all first returns from fish caught-and-released and accounted for age-dependent selectivities that varied by fate of the fish. Estimated fishing mortality rates (F) were high and variable before regulation changes in 1991, but decreased in magnitude and variability after 1991. A dome-shaped selectivity pattern was estimated to account for migration of older fish into coastal waters. To quantify the natural mortality rate and seasonal Fs for red drum, I conducted the first field test of a combined telemetry â tag return approach. Estimated Fs were similar in seasonal pattern and magnitude between tagging and telemetry, but joint estimates were influenced primarily by tagging. Natural mortality rate was low and influenced primarily by telemetry. The combined approach provides a new tool to estimate mortality rates for myriad fish species. Next, habitat use of subadult red drum was quantified with a combination of fishery-independent sampling, telemetry, and generalized additive models. At a large scale, red drum were associated with shallow, nearshore waters, sometimes with seagrass. To determine the influence of prey, I examined red drum stomachs and used generalized additive models to relate physicochemical and prey attributes to telemetered red drum at a small scale. Telemetered red drum were negatively related to salinity and positively related to dissolved oxygen and total prey. Last, I used tagging and telemetry to quantify the large- and small-scale movements of subadult red drum. Movement rates and directions were influenced by age of fish and region and season of tagging, and suggest that the spatial scale of management and regulations currently employed in North Carolina are appropriate. Tagging and fishery-independent surveys have provided valuable information to improve red drum management.

The euryhaline tilapia, Oreochromis mossambicus, has the ability to live in both freshwater (FW) and saltwater (SW) environments. Prolactin (PRL) is the most critical hormone to promoting life in FW, and without it tilapia loses the capacity to osmoregulate in hypotonic environments. Consistent with PRLâs actions in FW adaptation, pituitary PRL synthesis, content, secretion, and cell activity are all elevated in FW compared to SW acclimated tilapia We found that the PRL region of a FW tilapia pituitary has a 3-fold larger volume than the PRL region of a SW pituitary. It is unclear whether this increased tissue volume is due to larger cells (hypertrophy) or more cells (hyperplasia). Therefore, we evaluated if PRL cell proliferation and apoptosis might be sensitive to salinity and could account for the greater abundance of PRL in FW versus SW fish. Freshwater tilapia were transferred to either SW or sham transferred to FW and SW fish were moved to either FW or SW over a time course of 7 days. Pituitaries were sampled over the course of salinity challenge and triple stained for determination of lactotroph cell density (nuclei staining with Hoescht dye), proliferation (BrdU labeling) and apoptosis (TUNEL assay). Lactotrophs were identified by immunostaining using tilapia specific PRL antisera. Lactotroph cell densities were 40% lower in FW than SW fish and declined when fish were transferred from SW to FW (P < 0.001). The larger volume of the PRL cell region within the pituitary area combined with lower number of lactotrophs per unit area suggests that the cells are larger in FW than SW acclimated fish. There were negligible levels of apoptosis in lactotrophs and salinity was ineffective in regulating programmed cell death. By contrast, we found a dramatic effect of salinity on lactotroph cell proliferation. The pituitaries of FW tilapia show a higher rate of PRL cell proliferation than those of SW fish. During transfer from SW to FW proliferation increased by almost 20-fold compared with controls (P < 0.001). When fish were transferred from FW to SW, proliferation declined within 1 day to levels observed in sham transferred SW fish. The enhanced proliferation combined with increased volume of the pituitary PRL cell region, decline in lactotroph cell density, and presumed increase in cell volume, suggests that the tilapia lactotroph undergoes hypertrophy and hyperplasia in FW environments. Apoptosis appears to play little role in regulating lactotroph density under different salinities. Overall, these results suggest that the elevated production and content of PRL critical to life in FW is mediated, in part, through enhanced lactotroph proliferation and hypertrophy.

Natural mortality has always been a challenging quantity to estimate in harvested populations. The most common approaches to estimation include a regression model based on life history parameters and more recently tag-return models. In recent years, Bayesian methods have been increasingly implemented in ecological models due to their ability to handle increased model complexity and auxiliary datasets. In this dissertation, I explore the implementation of Bayesian methods to analyze tag-return data focusing on natural mortality. Chapter 1 is focused on the addition of two components to the tag-return model framework: random effects and auxiliary data. Auxiliary information on the instantaneous rate of natural mortality is provided through Hoenig's equation relating lifespan to natural mortality, and also implemented through a hierarchical prior. A simulation study validates the performance of the model while an analysis of the classic Cayuga Lake trout dataset demonstrates its use. Chapter 2 adds a change-point allowing for the estimation of two levels of natural mortality and the timing of the discrete-time shift in mortality. Analysis is focused on a Chesapeake Bay striped bass tagging dataset of fish tagged at six years of age and older from 1991-2002. Results show the ability to account for shift in timing. Contrasting with Jiang et al.'s study on the same striped bass dataset, the timing of the change-point was different between the two studies, likely because the Jiang study assumed a fixed tag-reporting probability of 0.43 whereas estimates seem to indicate it may be closer to 0.3. Chapter 3 introduces a change-point allowing for a shift in the tag-reporting probability while assuming a constant natural mortality rate. High reward tags are included in a subset of the data time-series to improve estimation. A factorial simulation design was used to investigate the model performance with different reporting rate and high reward tag scenarios. In general, the model performed very well with little bias except in the case of no high-reward tags. The model performed surprisingly well in a six year study. The results suggest the importance of high reporting rates and/ or auxiliary data sources such as high reward tags.

Habitat characteristics influencing growth of fishes often affect habitat selection because behaviors leading to rapid growth are under selective pressure. For pelagic piscivores such as striped bass Morone saxatilis stocked into southern reservoirs, temperature and prey density will likely be the most important factors influencing growth and spatial distribution. The traditional paradigm used to understand reservoir striped bass has focused on unsuitable physical conditions that may develop during summer stratification when hypolimnetic hypoxia forces fish into warm epilimnetic water. This study investigates how forage availability modifies the effects of physical conditions on this species. Striped bass in Badin Lake, NC, tagged with temperature-sensing transmitters tolerated temperatures above 27 degrees Celcius for two months to avoid hypolimnetic hypoxia but still displayed rapid growth. Bioenergetics models showed that high consumption rates allowed these fish to allocate energy to growth even during the summer and to grow rapidly during the fall as temperatures cooled. In contrast, striped bass in Lake Norman, NC, had slower growth despite experiencing warm summer temperatures for two to four weeks less. Lake Norman striped bass had lower consumption rates, and bioenergetics model simulations in which habitat conditions were exchanged between the reservoirs indicated that differences in forage availability had a greater relative effect on growth of striped bass than differences in thermal regime. These results suggest that criteria for determining the suitability of reservoirs for striped bass should incorporate a measure of prey availability. As with growth, habitat selection of Badin Lake striped bass was not solely dependent on temperature. Growth rate potential (the rate of growth of a predator occupying a particular location characterized by temperature and forage fish density) provided a better explanation of the spatial distribution of striped bass than did temperature or forage fish density alone. These results suggest growth rate potential can help us understand how fish integrate information on temperature and forage fish density, but it is important to note that growth rate potential was not a perfect predictor of the spatial distribution of striped bass so we cannot assume fish will optimize their patch choice with respect to this variable under all circumstances.

The movement of individuals is one of the fundamental components of contemporary ecological problems such as metapopulation theory, epidemic models, competitive coexistence, and invasion dynamics. Advection-diffusion models, sometimes with a reaction term, have been usefully applied to such problems. For this dissertation, I broadened this approach by seeking to understand the effects of certain biotic and abiotic factors on movement ecology, and asking how to incorporate flexible behavioral responses into classical advection-diffusion models. I asked how resources, competitive environment, and habitat structure, interacting with body size or not, affect the movement behaviors of two coexisting invasive snails (Melanoides tuberculata and Tarebia granifera), and whether including the behavioral response to these factors improves advection-diffusion models of movement. I also made natural history observations regarding the snail system to provide a biological context for my empirical work. To address these questions, I conducted replicated experiments and observational studies, extended advection-diffusion models, and arbitrated among candidate models using AIC (Akaike?s Information Criterion) model selection. Specific studies included (1) behavioral response to phenotypic and resource heterogeneities, and their interaction, (2) behavioral response to intraspecific and interspecific competition, and (3) behavioral response to spatially uniform versus spatially heterogeneous environments. In summary, this dissertation provides insights into modeling movement behaviors, using two coexisting invasive snails as the model system. I advocate for a behaviorally informed modeling framework that integrates sentient responses of individuals in terms of movement, improving our ability to accurately model ecological processes that depend on movement ecology.

Seed dispersal mutualisms are important ecological interactions that can shape plant communities by influencing species distributions, community composition, and the regeneration of populations following a disturbance. Considering the fundamental role seed dispersal mutualisms play in many plant communities, it is important to understand, both generally and for individual seed dispersal mutualisms, what determines when animal partners successfully disperse seeds and when they do not. Myrmecochory, the dispersal of seeds by ants, is the most common form of zoochory in Western Australia. Myrmecochore plant diversity is richest in the Kwongan sandplains of the south-west, where ant-dispersed species can make up as much as 36% of the plant community. Here, I studied the determinants of seed dispersal rates to understand local variation in myrmecochorous seed dispersal rates. At a series of 30 sites, we sampled the ant and plant communities, measured aspects of the community structure (vegetation height, openness, topography, soil), measured seed removal rates and observed ant-seed interactions. The most significant factor that governed seed removal rates was the presence of the ant species Rhytidoponera violacea. Additionally, during seed dispersal observation trials, R. violacea removed 95% of all seeds taken. To better understand the fate of Acacia blakelyi seeds dispersed by R. violacea, we simulated variable seed burial depths and elaiosome removal by ants, followed by a bushfire to stimulate germination. Seed burial depth had a significant effect on seedling emergence, with the proportion of emerged seedlings declining with burial depth. The effect of depth was due to the strength of a fire-cue (heat) declining with depth. Seed burial depth also had a fitness cost, with a greater proportion of ârobustâ seedlings emerging from seeds buried closer to the surface. Seeds buried too deep to receive fire-cues remained dormant, adding to a long-lived soil seed bank.

Claudin-5 is an important member of the claudin gene family. The expression of claudin-5 in the heart of Xenopus laevis was determined by whole mount in situ hybridization. RNA over expression and knock down experiments demonstrated that claudin-5 is critical for heart development. Meanwhile, claudin-5 down regulated bone morphogenetic protein 4 (BMP4) expression in early stage through upregulating chordin (chd). In addition, other pathways such as estrogen hormone and transforming growth factor-β (TGF-β) may also affect claudin-5 activity. The results show that claudin-5 plays an important role in heart development and is involved in a complex pathway of gene regulation. The mRNA expression of claudin-12, another member of claudin protein family was also determined from cleavage stage to tadpole stage by whole mount in situ hybridization.

The common dolphin (<I>Coryphaena hippurus</I>) supports economically important fisheries along the east coast of the United States. In recent years, landings of dolphin from the United States Atlantic have increased dramatically. For example, recreational landings in the US South Atlantic Bight have increased from 162,000 dolphin in the 1960s to over 1.3 million dolphin in recent years. The last age and growth study of North Carolina dolphin was conducted in the early 1960s. It is hypothesized that life history parameters may have changed due to increased exploitation. Age, growth and reproduction were studied on dolphin (n=802; size range=89 to 1451 mm FL) collected between May 2002 and May 2004 from commercial and recreational catches in North Carolina. Annual increments from scales (n=541) and daily increments from sagittal otoliths (n=126) were examined; estimated von Bertalanffy parameters were L&#8734 = 1299 mm FL and k = 1.08 yr ^-1. The maximum age observed was 3 years. No major change in length at age has occurred since the early 1960s. Daily growth increments for age-0 dolphin reduced much of the variability in length-at-age values for age-0 dolphin and provided an average growth rate of 3.78 mm/day in the first six months, which is extremely fast for a teleost fish. Growth of North Carolina dolphin is similar to that found in Florida and the Mediterranean, but differs from observed growth in the Caribbean and Gulf of Mexico. Age at 50% maturity was around 4 months for female dolphin and 6 months for male dolphin. Monthly length-adjusted gonadal weights suggest that peak spawning occurs from April through July off North Carolina; back-calculated hatch dates from age-0 dolphin along with prior studies on the east coast of Florida suggest that dolphin spawning occurs year round with highest levels from January through June. This study provides an updated and improved (year-round sampling and otolith daily ages) age-length function for dolphin caught off the coast of North Carolina using both scale annuli and daily growth increments and provides some of the first comprehensive data on North Carolina dolphin reproduction. The life history of dolphin, including fast growth and early maturity, allows for high levels of exploitation.