No description available.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [139]-165).

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2009. / Härtill 5 uppsatser.

The integument is the body organ interfacing between the internal and external environments of a lizard. This study explores aspects of its structure, texture, and coloration, relating them to survival strategies of horned lizards. The dermal chromatophore structure of Phrynosoma modestum is described. Color change depends on two cell types, melanophores and iridophores. This cellular arrangement may be typical of lizards utilizing color change for thermoregulation. Color pigment cells (xanthophores and erythrophores) function in pattern formation and background color matching. Experiments on the regulation of color change revealed that (1) -MSH is the prime skin darkening agent, (2) - and -adrenergic receptors also play a role in color change, and (3) temperature is a factor in in vitro and in vivo darkening and lightening responses. Apparently the primary role of color change is thermoregulation. Intraepidermal mechanoreceptors on dorsal body, limb, and head scales were studied, their ultrastructure is described, and their role in defense and survival is explored. The use of the integument for "rain-harvesting" of drinking water by P. cornutum is described, including stereotyped behavior, stereoscopic SEM examination of interscalar channels, experiments on capillary water flow, and an evaluation of micro-ornamentation. Comparisons are made with the putative use of the integument for the collection of rain, fog, or dew for drinking by Moloch and Phrynocephalus. A stereotypic behavior that utilizes positioning of occipital horns and dorsal scale armament is described and hypothesized to be an ophidian antipredator defense. Attacks by Onychomys torridus on P. cornutum and P. modestum were studied to further evaluate the role of occipital horns, dorsal scalation, and dermal collagen as antipredator defenses. Attack behaviors of the grasshopper mice and defense behaviors of the lizards are detailed. The use of color pattern, integumental structures, and mimetic behavior by P. modestum in avoidance of predator detection, through "stone-mimicry," is hypothesized and supported. Aspects of social communication in four species were studied. The importance of olfaction for intraspecific communication and lack of visual color signals is related to the need for chromatic crypticity in order to avoid detection by predators.

No description available.

No description available.

The chytridiomycete Batrachochytrium dendrobatidis (Bd) is a parasite which has been blamed for amphibian declines across the world. This study was designed to investigate the effects of Bd on natterjack toads (Bufo calamita), following the discovery of Bd populations of this species in the UK. The effect of Bd on natterjack toads was assessed by fieldwork and experiments. Wild adult natterjacks were tagged and repeatedly tested for Bd during 2009-2011. Captive adults and juveniles from infected populations were also tested in response to changes in environmental conditions. Swabs were used to collect Bd DNA from the skin of study animals. Swabbing did not reliably diagnose infection but the quantity of Bd DNA in swabs (Bd score) provided an indication of infection activity. Immersion in water appeared to trigger Bd zoospore emergence from the skin, resulting in an increase in the likelihood of Bd detection and increases in Bd score. Bd dynamics in natterjack populations were also influenced by salinity. Natterjacks in the UK are found mainly in coastal habitat, where ponds are often inundated by high tides. Adults captured in brackish water were less likely to test positive than those caught in fresh water. Bd isolated from coastal natterjacks was killed in vitro by a salinity equivalent to 50% seawater. The isolate grew fastest at low salinities, suggesting that it may have become adapted to brackish conditions. Despite this adaptation, tidal inundation may be sufficient to disinfect ponds and limit Bd transmission. Capture-mark-recapture (CMR) data from adult natterjacks revealed a weak negative correlation between Bd score and survival in the wild. Males had higher Bd scores than females but survival did not differ between sexes and there was no correlation between Bd score and growth. An experiment showed BD could kill natterjacks if infection activity was boosted by wet conditions. However only 6% of wild adults recorded Bd scores in excess of a mortality threshold derived from this experiment. Many adults and juvenile natterjacks can tolerate Bd infection and act as reservoirs of this pathogen. Despite detection of Bd in at least 14 UK natterjack populations by 2011, no mass mortalities of adult natterjacks have been reported and spawning has continued at all sites. Bd does not appear to have a major effect on natterjacks but this situation may not persist and vigilance should be maintained. Bd isolated from natterjack toads in this study belomgs to a global panzootic lineage (GPL) of Bd which Farrer et al (2011) claim has achieved a global distribution as a result of human activities.

Three aspects of renal function were measured in the toad, Bufo marinus (N=lO): (1) effect of rate of blood volume expansion on renal functions (UFR; GFR; urine and plasma ion concentrations; and ion excretion rates), (2) effect of hypo- and hyperosmotic blood volume expansions on renal functions, and (3) role of GFR and tubular processes in the differential response of UFR under different osmotic expansion stresses. Renal responses to differential rates of blood volume expansion have not been investigated in amphibians. Rate responses will be analyzed considering effects: ( 1) during infusion (neural, or, short term regulation of extracellular fluid volume) and (2) post infusion (hormonal, or, long term regulation of extracellular fluid volume). Volume expansions were administered with hypoosmotic (0.4%) saline and hyperosmotic (1.4%) saline, and ranged in rate from 4.0 to 20.6 ml/kg/min. This protocol is designed to present volume regulatory mechanisms with increased volume stimuli and different osmotic stimuli. Overall, infusion rate had no significant effects on renal responses measured: urine flow rate (UFR); glomerular filtration rate (GFR); urine and plasma ion concentrations; natriuresis; or kaliuresis. This was true for the infusion period and for the observed post infusion period (90 min). Rate was correlated with GFR in the hypoosmotic group (r=0.30, p=0.04) and natriuresis in the hyperosmotic group (r=0.34, p=0.03). A significant positive correlation was observed between UFR and GFR. Relative to treatment, UFR differed significantly; GFR response was inherently similar despite differences at individual intervals, indicating UFR differences between the treatments is due to tubular processes. Responses to hypoosmotic infusion included a significant diuresis, natriuresis, and a decreased urine sodium concentration, relative to hyperosmotic infusion. At low UFRs the hyperosmotic group produced urine relatively concentrated in sodium. Urine sodium concentration and UFR were positively correlated in the hypoosmotic infusion group -- at high UFRs, kidneys were unable to produce a dilute urine.

Diss. (sammanfattning) Uppsala : Uppsala universitet, 2009. / Härtill 5 uppsatser.

Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.