The first quantitative studies of pulmonary and cutaneous respiration in the amphibians were made on Rana esculenta and Rana temporaria by Krogh (1904). He inserted a cannula connected to an air pump into the trachea and analyzed separately the air forced through the lungs by the pump and the air surrounding the frog. He was able to show that in R. temporaria the lungs and skin are both important in respiratory exchange but in somewhat different ways. Oxygen enters through the lungs whereas carbon dioxide is excreted through the skin. Oxygen intake through the skin is determined solely by physical limitation while carbon dioxide excretion may vary with environmental charges. Krogh concluded that in R. temporaria the lungs dominate in oxygen consumption over the skin in a ratio of 3:1. In R. esculenta the ratio was 1:1. This probably correlated with the more aquatic habitat of R. esculenta. In the salamander, Ambystoma maculatum, Hutchison (1963) found that not only is eighty percent of the carbon dioxide produced released through the skin but the skin is also responsible for more than fifty percent of the total oxygen uptake at 15°C and below. Rana catesbeiana tadpoles were used in these experiments. They were obtained from the Mokelumne River on Highway 88, two miles west of Clements, California The function of the lungs in Rana catesbeiana tadpoles was studied.

The widespread use and subsequent release of pesticides into aquatic environments have sparked concerns about how organisms within these aquatic systems are affected by pesticide pollution. While many studies have examined the effects of pesticides on individual organisms, in a series of experiments, I investigated the effects of a pesticide mixture on members of a complex host-parasite system and on host susceptibility to infection. In my first experiment in the laboratory, I examined changes in survivorship when trematode parasites (Echinostoma trivolvis) and their first intermediate host, Planorbella trivolvis snails, were exposed to a low concentration (10 ppb: 15 ppb) and high concentration (85 ppb: 100 ppb) mixture of atrazine and metolachlor, respectively. There was a significant decline in parasite survivorship in the high concentration treatment at 14 hours, while snail survivorship was unaffected across all treatments. In my second experiment, prior to infection, I exposed the parasites and/or second intermediate hosts, Rana clamitans and Rana sylvatica tadpoles, to the pesticide mixtures and examined subsequent infection levels in the tadpoles. The atrazine and metolachlor mixtures had no significant effects on parasite load in the laboratory. Newly shed parasites were more likely than 10 hours old parasites to infect tadpoles, regardless of pesticide exposure. In my final experiment, I utilized outdoor mesocosms to expose parasites, snail hosts, and Rana sylvatica tadpoles to the pesticide mixture, and I examined differences in parasite load within the tadpoles after two weeks. The pesticides had no significant effect on parasite loads in the field. Overall, my findings suggest the atrazine and metolachlor mixtures used in this study had no significant effects on disease dynamics in a system involving Echinostome parasites, snails, and tadpoles. / Master of Science

本研究選取香港十二個淡水濕地，在二零零九年六月至二零一零年六月間調查其環境特性、蝌蚪及其相關的捕食者的種類和數量，以瞭解重要的環境因素如何影響蝌蚪在淡水濕地的多樣性及數量。三種蝌蚪（澤蛙、斑腿泛樹蛙及沼蛙）被選為研究對象，比較蝌蚪面對不同捕食者（中國鬥魚、食蚊魚、日本真龍虱及偉蜓科稚蟲）的外觀及行為反應，以瞭解蝌蚪的分佈與其面對捕食者的反應的關係，及調查捕食者的捕食效率。 / 在十二個淡水濕地的調查記錄了十一種兩棲類、十六種淡水魚類、三十一種蜻蜓（二十四種差翅亞目及七種束翅亞目）、四種鞘翅目及三種半翅目。沼蛙蝌蚪分佈最廣，出現在永久性及季節性濕地。斑腿泛樹蛙蝌蚪傾向出現於沒有捕食者的季節性濕地，澤蛙則傾向出現在沒有捕食者但水文週期較長的濕地。食蚊魚及狹腹灰蜻是數量最多及分佈最廣的淡水魚類和蜻蜓品種。 / 環境特性對蝌蚪在濕地的種類及數量的影響大於捕食者。水文週期與濕地的環境特性及捕食者種類關連，是最具影響力的環境因素。蝌蚪的多樣性於季節性濕地最高，而蜻蜓的多樣性則與水文週期長度成正相關。其他環境特性如基質，水位及植被覆蓋率對個別蝌蚪品種的數量有影響。 / 澤蛙、斑腿泛樹蛙及沼蛙能夠分辨不同種類的捕食者，並對魚類和無脊椎捕食者作出不同的外觀及行為反應。與無脊椎捕食者並存時，斑腿泛樹蛙蝌蚪在身體與尾部的交接處發展出較大而明顯的白斑，發展出較大尾部的蝌蚪的生長速度比對照組慢。與捕食者並存時，斑腿泛樹蛙及沼蛙蝌蚪的尾部顏色改變。斑腿泛樹蛙蝌蚪的游泳速度與身體形態相關，澤蛙及沼蛙蝌蚪則與體型大小相關。當面對捕食者時，三種蝌蚪均減少活動時間，游泳距離及速度。對比面對魚類時，在無脊椎捕食者之下，沼蛙蝌蚪的低活躍程度的維持時間較長。蝌蚪面對捕食者的反應的多樣性和蝌蚪與捕食者的相遇機率成正相關。 / 在田野調查中，發現魚類對蝌蚪數量的影響比蜻蜓稚蟲大，而鞘翅目及半翅目的數量則與蝌蚪數量沒有關連，由此推斷後兩者非蝌蚪的主要捕食者。中國鬥魚是最具效率的蝌蚪捕食者，相比之下食蚊魚雖捕食較少數量的蝌蚪，但憑其捕食習慣及野外數量之多足以導致蝌蚪種群數量下降。蜻蜓稚蟲也是具效率的蝌蚪捕食者，但因為蜻蜓稚蟲的羽化時間與兩棲類的繁殖時間同步（即稚蟲離開水體而蝌蚪進入水體時間基本重疊），總體上對蝌蚪構成較低的捕食風險。 / Environmental characteristics, larval amphibian assemblages and associated predators in twelve freshwater wetlands in Hong Kong were investigated from June 2009 to June 2010, in order to identify the key environmental characteristic(s) affecting the richness and abundance of tadpoles in freshwater wetlands in Hong Kong. Predator induced changes in morphology and behavior of three tadpole species (Fejervarya limnocharis, Polypedates megacephalus and Rana guentheri) were examined under the presence of Paradise Fish (Macropodus opercularis), Mosquito Fish (Gambusia affinis), Cybister and dragonfly naiads (Aeshnid) in order to investigate predator inducible defense(s) in local tadpoles and its relation to tadpoles’ distribution and effectiveness of local predators. / Fauna assemblages in 12 freshwater wetlands included 11 amphibian, 16 fish, 31 odonate (24 Anisoptera and 7 Zygoptera), four coleopteran and three hemipteran species. R. guentheri was the most widespread species and occupied both permanent and temporary wetlands. P. megacephalus were most commonly found in temporary wetlands without predators and F. limnocharis were common in wetlands with longer hydroperiod but without predators. Mosquito fish and Orthetrum sabina sabina were the most abundant and widespread fish and dragonfly species, respectively. / Abundance and occurrence of individual tadpole species were more attributable to environmental characteristics than to predators. Wetland hydroperiod was the most influential factor that correlated with environmental characteristics and occurrence of predator species. Larval amphibian richness was highest in temporary wetlands while dragonfly richness increased with habitat permanence. Other environmental characteristics such as substrate types, water depth and vegetation coverage also affected abundance of individual amphibian species. / Three tadpole species were capable of recognizing predators and exhibiting differential inducible changes when exposed to invertebrate and fish predators. P. megacephalus exhibited a large and prominent white spot at the body-tail intersection in the presence of invertebrate predators, and exhibited a growth cost in maintaining an enlarged tail. Tail coloration changed in P. megacephalus and R. guentheri in the presence of predators. Burst swimming performance was associated with body shape in P. megacephalus and to body size in R. guentheri and F. limnocharis. All three tadpole species showed a reduction in active time, travel distance and swimming speed in the presence of predators. R. guentheri reduced activity level for a longer time period after sensing invertebrate predation cues than after sensing fish cues. The variations in plasticity of predator-induced traits increased with predator encounter rate. / Fish caused a greater impact on tadpole abundance than dragonflies in field study, while coleopterans and hemipterans were probably not the major predators of tadpoles as no negative correlation with tadpoles were found. Efficiency of predation varied among fish species. The Paradise Fish was an efficient predator of tadpoles. Mosquito fish consumed fewer tadpoles and yet could cause a significant decline in tadpole populations by its foraging behavior and abundance in local freshwater wetlands. Dragonflies were efficient predator of tadpoles, however, the predation risk to tadpoles could be alleviated by synchronized timing of naiad emergence and amphibian breeding, along with predator-induced defenses of the tadpoles. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Wong, Chuk Kwan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 199-215). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / Abstracts --- p.i / Acknowledgements --- p.vii / of Contents --- p.ix / List of Tables --- p.xii / List of Figures --- p.xv / List of Plates --- p.xvii / Chapter Chapter 1 --- Introduction --- p.1 / Chapter 1.1 --- Wetlands --- p.1 / Chapter 1.1.1 --- Definition --- p.1 / Chapter 1.1.2 --- Wetland functions --- p.2 / Chapter 1.1.3 --- Hydrology and hydroperiod --- p.3 / Chapter 1.1.4 --- Predation and inducible defenses --- p.5 / Chapter 1.1.5 --- Predictions on inducible defenses --- p.7 / Chapter 1.2 --- Hong Kong Situations --- p.9 / Chapter 1.2.1 --- Climates in Hong Kong --- p.9 / Chapter 1.2.2 --- Amphibians diversity and habitats --- p.11 / Chapter 1.2.3 --- Habitat loss in Hong Kong and neighboring regions --- p.12 / Chapter 1.2.4 --- Wetland conservation policy in Hong Kong --- p.14 / Chapter 1.3 --- Knowledge Gap and Significance --- p.17 / Chapter 1.4 --- Objectives --- p.19 / Chapter 1.5 --- Thesis Layout --- p.19 / Chapter Chapter 2 --- Assemblages of larval amphibians and associated predators in freshwater wetlands in Hong Kong --- p.21 / Chapter 2.1 --- Introduction --- p.21 / Chapter 2.2 --- Materials and Methods --- p.24 / Chapter 2.2.1 --- Study sites --- p.24 / Chapter 2.2.1.1 --- Fauna survey --- p.24 / Chapter 2.2.1.2 --- Hydroperiod estimation --- p.29 / Chapter 2.2.1.3 --- Environmental characteristics --- p.31 / Chapter 2.2.1.4 --- Water quality --- p.31 / Chapter 2.2.2 --- Data analysis --- p.33 / Chapter 2.2.2.1 --- Multivariate analysis --- p.33 / Chapter 2.2.2.2 --- Data transformation --- p.34 / Chapter 2.3 --- Results --- p.39 / Chapter 2.3.1 --- Site characteristics --- p.39 / Chapter 2.3.1.1 --- Environmental characteristics --- p.39 / Chapter 2.3.1.2 --- Seasonal variation in water quality and wetness score --- p.43 / Chapter 2.3.1.3 --- Seasonal variation in water quality in four wetland types --- p.46 / Chapter 2.3.2 --- Species assemblages in local wetlands --- p.47 / Chapter 2.3.2.1 --- Tadpoles --- p.48 / Chapter 2.3.2.2 --- Dragonflies --- p.53 / Chapter 2.3.2.3 --- Damselflies --- p.53 / Chapter 2.3.2.4 --- Freshwater fish --- p.54 / Chapter 2.3.2.5 --- Coleopterans and hemipterans --- p.54 / Chapter 2.3.2.6 --- Seasonal variations in species assemblages --- p.55 / Chapter 2.3.3 --- Biodiversity of study sites --- p.58 / Chapter 2.3.3.1 --- Species richness in study sites --- p.58 / Chapter 2.3.3.2 --- Species abundance in study sites --- p.63 / Chapter 2.3.4 --- Multivariate analysis --- p.64 / Chapter 2.3.4.1 --- Global approach --- p.64 / Chapter 2.3.4.2 --- Independent approach --- p.76 / Chapter 2.3.4.3 --- Predator approach --- p.81 / Chapter 2.3.5 --- Hydroperiod and faunal assemblages --- p.92 / Chapter 2.3.5.1 --- Effect of hydroperiod on wetland diversity --- p.92 / Chapter 2.3.5.2 --- Effects of hydroperiod on faunal groups --- p.94 / Chapter 2.3.5.3 --- Effects of hydroperiod on species composition --- p.96 / Chapter 2.3.5.4 --- Comparison with other explanatory variables --- p.98 / Chapter 2.3.6 --- Hydroperiod, environmental characteristics and predation --- p.98 / Chapter 2.3.6.1 --- Effects of hydroperiod on environmental characteristics --- p.98 / Chapter 2.3.6.2 --- Effects of environmental characteristics on tadpoles --- p.99 / Chapter 2.3.6.3 --- Effects of predation on tadpoles --- p.99 / Chapter 2.3.6.4 --- Relative importance of environmental characteristics and predation --- p.100 / Chapter 2.3.7 --- Tadpole traits, wetland permanence and predation pressure --- p.100 / Chapter 2.4 --- Discussion --- p.104 / Chapter 2.5 --- Conclusions --- p.112 / Chapter Chapter 3 --- Predator-induced plasticity in tadpoles and its effect on survivorship under the presence of different groups of predator --- p.113 / Chapter 3.1 --- Introduction --- p.113 / Chapter 3.2 --- Materials and Methods --- p.117 / Chapter 3.2.1 --- Egg collection --- p.117 / Chapter 3.2.1 --- Predator collection --- p.118 / Chapter 3.2.2 --- Experimental design --- p.119 / Chapter 3.2.2.1 --- Predator induced plasticity in tadpoles --- p.119 / Chapter 3.2.2.2 --- Predation experiment --- p.126 / Chapter 3.2.3 --- Data analysis --- p.128 / Chapter 3.3 --- Results --- p.130 / Chapter 3.3.1 --- Morphological responses --- p.131 / Chapter 3.3.2 --- Tail coloration --- p.135 / Chapter 3.3.3 --- Burst swimming performance --- p.144 / Chapter 3.3.4 --- Life history --- p.149 / Chapter 3.3.5 --- Activity test --- p.153 / Chapter 3.3.5.1 --- Predator effects on activity level of Paddy Frog tadpoles --- p.153 / Chapter 3.3.5.2 --- Predator effects on activity level of Brown Tree Frog tadpoles --- p.157 / Chapter 3.3.5.3 --- Predator effects on activity level of Guenther’s Frog tadpoles --- p.160 / Chapter 3.3.6 --- Predation experiment --- p.164 / Chapter 3.4 --- Discussion --- p.174 / Chapter 3.4.1 --- Inducible changes in Paddy Frog tadpoles --- p.174 / Chapter 3.4.2 --- Inducible changes in Brown Tree Frog tadpoles --- p.175 / Chapter 3.4.3 --- Inducible response to rarely encountered fish --- p.178 / Chapter 3.4.4 --- Inducible changes in Guenther’s Frog tadpoles --- p.179 / Chapter 3.4.5 --- Effect of inducible defenses on tadpole survival --- p.180 / Chapter 3.4.6 --- Predator inducible changes and hydroperiod gradient --- p.181 / Chapter 3.4.7 --- Predator strength --- p.183 / Chapter 3.4.8 --- Importance of predation on tadpole assemblages --- p.185 / Chapter 3.5 --- Conclusions --- p.186 / Chapter Chapter 4 --- General Conclusions --- p.187 / Chapter 4.1 --- Summary --- p.187 / Chapter 4.2 --- Applications --- p.189 / Chapter 4.2.1 --- Mitigation wetlands --- p.189 / Chapter 4.2.1.1 --- Design --- p.189 / Chapter 4.2.1.2 --- Placement --- p.192 / Chapter 4.2.1.3 --- Management practices --- p.192 / Chapter 4.2.1.4 --- Natural model of temporary wetland --- p.194 / Chapter 4.2.2 --- Wetland conservation --- p.195 / Chapter 4.3 --- Further studies --- p.197 / References --- p.199 / Appendices --- p.216

Closely related species at the same trophic level are often considered to be ecologically equivalent. However, it is clear that individuals species can have unique functional roles that drive community and ecosystem processes. In this study we examine the growth responses of two Neotropical hylid tadpole species, Agalychnis callidryas and Dendropsophus ebraccatus, to intraspecific and interspecific competition. We also look at density-dependent effects of each on phytoplankton, periphyton and zooplankton, as well as their responses to a caged dragonfly predator through ontogeny. Intraspecific competition affected both species similarly, and their effects on resources were qualitatively similar but quantitatively different. Predators affected resource levels and interspecific competition. Predator effects on tadpole size varied in both magnitude and direction through ontogeny for both species. This study shows that closely related species at the same trophic level can have different ecological roles and that tadpoles are more functionally unique than previously thought.

A intervenção das atividades antrópicas ao meio ambiente tem repercutido na estrutura e funções dos ecossistemas, sendo que o uso de aditivos químicos, como agrotóxicos e fertilizantes, destacam-se pela parcela de responsabilidade que assumem diante desses desequilíbrios. O agrotóxico Vertimec® 18CE, cuja toxicidade para diversas taxóns já é conhecida, é amplamente utilizado em lavouras agrícolas, e têm-se conhecimento a respeito das intensas práticas de manuseio, muitas vezes irregulares, o que pode fazer com que concentrações muito maiores do que as previstas atinjam o ambiente aquático. Um dos grupos que nos últimos anos vem se destacando pelo declínio crescente associado ao uso destes produtos são os anfíbios. Os anfíbios possuem papel central na cadeia alimentar, e muitos estudos relatam o desequilíbrio ecológico causado pelo declínio desse grupo em relação a adição de contaminantes, incluindo os agrotóxicos. No presente estudo foram desenvolvidos testes laboratoriais a fim de determinar o estágio dos girinos de Lithobates catesbeianus mais suscetível à intervenção do agrotóxico e à concentração capaz de causar mortalidade em 50% dos indivíduos (CL50, 96h). A partir desses resultados, experimentos in situ (mesocosmos) com girinos no estágio mais avançado (25 da tabela de Gosner) foram desenvolvidos com o intuito de comparar as diferenças de toxicidade do Vertimec® 18CE quando manipulado em campo e laboratório, e quais os efeitos causados por uma única aplicação do produto e por aplicações múltiplas. Os testes laboratoriais demonstraram que os girinos em estágios mais precoce (21G) foram mais sensíveis ao agrotóxico Vertimec® 18CE do que àqueles mais avançados (25G). O experimento em campo indicou que a CL50, 96h para L. catesbeianus (25G) foi muito mais agressiva quando próxima às condições naturais, causando a mortalidade de todos os indivíduos no mesmo estágio de desenvolvimento em um período inferior a 24 horas. Entretanto, a concentração inferior à CL50, 96h (0,002 ml de Vertimec.L-1) quando ministrada em campo, assim como no laboratório, não causou mortalidade, mas implicou em atraso no desenvolvimento e maior período larval do que àqueles organismos que não estiveram em contato com o agrotóxico, já que atingiu os recursos disponíveis, promovendo um efeito indireto no sucesso dessa espécie. Não foi possível observar diferença entre as aplicações única e múltipla do Vertimec® 18CE, em decorrência da morte dos girinos do tratamento em dosagem múltipla, porém observou-se desequilíbrio das condições limnológicas do sistema ao sofrer nova intervenção do Vertimec® 18CE. Diante dos resultados obtidos é possível concluir que o Vertimec® 18CE é capaz de afetar diretamente (mortalidade, estágios de desenvolvimento e comportamento) e indiretamente (redução de recursos alimentares) a população de Lithobates catesbeianus, contribuindo para o declínio de anfíbios nos sistemas naturais. / The intervention of anthropogenic activities to the environment has reflected in the structure and functions of ecosystems and the use of chemical additives, such as pesticides and fertilizers, has contributed for the disequilibrium. The Vertimec® 18EC, whose toxicity is described to different taxa, is widely used in agricultural crops, and it has been known about the intense handling practices, often irregular, which can reach higher concentrations than those expected in the aquatic environment. One group that has been highlighted in recent years by the increasing decline associated with the use of these products is the amphibians. Amphibians plays a central role in the food chain and several studies have related the ecological disequilibrium caused by the decline of this group due to the addition of contaminants, including pesticides. In this study, laboratory bioassays were developed to determine the more susceptible stage and the LC50,96h of Lithobates catesbeianus to Vertimec® 18EC. From these results, in situ experiments (mesocosms) were conducted with tadpoles in more advanced stage (25 of Gosner table) in order to compare the differences in toxicity of Vertimec® 18EC when manipulated both in field and in laboratory. Also, the effects caused by a single and multiple application of the pesticides were evaluated. The laboratorial results showed that earlier stages (21G) were more sensitive than more developing tadpoles (25G), and the effects of the pesticide were more aggressive under natural conditions (mesocoms), with 100% of mortality before 24 hours, at the same developmental stage. The results of laboratorial and in situ bioassays indicated that the lower concentration (0.002 ml Vertimec.L-1) didn\'t cause mortality, but alterations on development stage and larval period time were observed, indicating indirect effects (available resources) on the success of this species. On the other hand, no difference was found between the single and multiple applications of Vertimec® 18EC because all organisms died in the unique dosage treatment, but it was possible to verify limnological alterations after the second application of the pesticide. Considering the results obtained we conclude that Vertimec® 18EC can affect directly (mortality, development stages and behavior) and indirectly (food reduction) the population of Lithobates catesbeianus, contributing to the decline of amphibians in the natural systems.

This study resulted from the identification of gaps in the literature pertaining to the morphological descriptions of the tadpoles occurring at high altitudes in the Drakensberg Mountains in South Africa. These tadpoles are exposed to low temperatures, high desiccation risk, elevated ultraviolet radiation, competition, and predation and inhabit the clear, flowing streams and marsh areas of the mountain. Highly varying environmental conditions caused tadpoles to have considerable intraspecific variation. The high degree of plasticity necessitated extensive descriptive studies of tadpole morphology in order to document intraspecific variation and set up reliable keys for species identification. Specified adaptations to the extreme montane conditions are present in tadpoles of certain species. An especially interesting adaptation is the elygium, a hemispherical pigmented area above the eye, which apparently protects the retina from harmful ultraviolet radiation. There are no known studies of elygium plasticity in tadpole eyes in relation to variation in ultraviolet radiation. Particular attention was given to the functionality and cytology of this structure. Detailed measurements of tadpoles of six frog species of the high altitude Drakensberg Mountains were made. Morphological adaptations were described on the basis of these measurements. The cytological origin of the elygium of Amietia vertebralis was revealed through histological and cellular ultrastructure studies. The change in elygium morphology over time was studied as a function of ultraviolet intensity by exposing tadpoles to different levels of ultraviolet radiation. From the detailed morphological descriptions a more reliable binomial key was constructed, which made it possible to distinguish between Amietia umbraculata and A. vertebralis. A new amended definition of the epidermal elygium can now be given as an area of melanophores originating from the pigmented epithelium of the retina, forming a hemispherical shape from the dorsal margin of the iris. It is positioned in such a way as to protect the retina when light enters directly from above. This empirical study of the functional significance of the elygium showed that elygium morphology was considerably plastic, and that there were differences in elygium area and base length in the presence or absence of UVB radiation. In the presence of high UV radiation tadpoles produced an elygium with a broader base rather than longer elygia with a larger area. A wider elygium base shaded the pupil more effectively, thus protecting the retina from harmful UV radiation. The presence of a ventral elygium was also discovered. / Thesis (M.Sc. (Environmental Science))--North-West University, Potchefstroom Campus, 2011.

This study resulted from the identification of gaps in the literature pertaining to the morphological descriptions of the tadpoles occurring at high altitudes in the Drakensberg Mountains in South Africa. These tadpoles are exposed to low temperatures, high desiccation risk, elevated ultraviolet radiation, competition, and predation and inhabit the clear, flowing streams and marsh areas of the mountain. Highly varying environmental conditions caused tadpoles to have considerable intraspecific variation. The high degree of plasticity necessitated extensive descriptive studies of tadpole morphology in order to document intraspecific variation and set up reliable keys for species identification. Specified adaptations to the extreme montane conditions are present in tadpoles of certain species. An especially interesting adaptation is the elygium, a hemispherical pigmented area above the eye, which apparently protects the retina from harmful ultraviolet radiation. There are no known studies of elygium plasticity in tadpole eyes in relation to variation in ultraviolet radiation. Particular attention was given to the functionality and cytology of this structure. Detailed measurements of tadpoles of six frog species of the high altitude Drakensberg Mountains were made. Morphological adaptations were described on the basis of these measurements. The cytological origin of the elygium of Amietia vertebralis was revealed through histological and cellular ultrastructure studies. The change in elygium morphology over time was studied as a function of ultraviolet intensity by exposing tadpoles to different levels of ultraviolet radiation. From the detailed morphological descriptions a more reliable binomial key was constructed, which made it possible to distinguish between Amietia umbraculata and A. vertebralis. A new amended definition of the epidermal elygium can now be given as an area of melanophores originating from the pigmented epithelium of the retina, forming a hemispherical shape from the dorsal margin of the iris. It is positioned in such a way as to protect the retina when light enters directly from above. This empirical study of the functional significance of the elygium showed that elygium morphology was considerably plastic, and that there were differences in elygium area and base length in the presence or absence of UVB radiation. In the presence of high UV radiation tadpoles produced an elygium with a broader base rather than longer elygia with a larger area. A wider elygium base shaded the pupil more effectively, thus protecting the retina from harmful UV radiation. The presence of a ventral elygium was also discovered. / Thesis (M.Sc. (Environmental Science))--North-West University, Potchefstroom Campus, 2011.

Thesis (Ph. D.)--Oregon State University, 2009. / Printout. Includes bibliographical references (leaves 115-128). Also available on the World Wide Web.

Thesis (Ph. D.) -- University of Tennessee, Knoxville, 2005. / Title from title page screen (viewed on Sept. 6, 2005). Thesis advisor: Arthur C. Echternacht. Thesis advisior: Christine R. B. Boake. Document formatted into pages (xvi, 151 p. : ill. (some col.)). Vita. Includes bibliographical references.

Thesis (Ph. D.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 147-169). Also available on the World Wide Web.