Thesis advisor: Sarah K. McMenamin / Thesis advisor: Vicki Losick / Proper bone development requires coordination and timing of specific morphogenetic events, and relative shifts in these temporal processes can change morphology. Thyroid hormone (TH) plays an important role in regulating the timing of vertebrate skeletogenesis, and the hormone induces the profound skeletal shape changes that occur during amphibian metamorphosis. Like humans, zebrafish do not undergo an ecological metamorphosis; yet TH is essential in coordinating postembryonic developmental processes. In particular, several elements of the craniofacial skeleton that continue to ossify and remodel during later stages of development are sensitive to TH titer. My aims focus on the role of TH in regulating skeletal growth and shape changes in zebrafish. To examine changes in the entire zebrafish skeleton during normal postembryonic development, I generated a skeletal reference of microCT scans of zebrafish ranging from early juvenile through adult stages (Chapter 2). After defining the normal changes that wild-type zebrafish undergo, I hypothesized that TH coordinates the developmental shape changes and determined the role of TH in stimulating developmental shape change in zebrafish skulls and its effects on skeletogenic cell populations (Chapter 3). Finally, I investigated whether phenotypes induced by altered TH levels mirror some of the evolutionary diversity seen across Danioninae craniofacial skeletons (Chapter 4). My research elucidates the role of TH in the regulation of bone growth and shape change in a vertebrate system and provides new insights into the natural craniofacial diversity of Danioninae. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Biology.

Cloudina foi o primeiro fóssil de um organismo biomineralizado encontrado no final do Ediacarano. Também figuram nesse período Corumbella, Namacalathus, Sinotubulites e Namapoikia entre a biota esquelética. No Grupo Corumbá (MS), em carbonatos e pelitos da Formação Tamengo, ocorrem os fósseis de Cloudina e Corumbella, respectivamente. Este trabalho teve como objetivo analisar questões paleobiológicas referentes ao fóssil esquelético Cloudina, como seu contexto tafonômico, taxonômico e paleoecológico. Análises geoquímicas e de microestrutura foram realizadas para permitir melhor compreensão da esqueletogênese desse fóssil. Para tanto, foram utilizadas técnicas paleométricas, como: Espectroscopia Raman, Energia Dispersiva de Raios-x (EDS), Fluorescência de Raios-x por Energia Dispersiva (EDXRF) e Fluorescência de Raios-x Sincrotron (XRF-SRS) - para as análises de composição química e mineralógica; e Microscopia Eletrônica de Varredura (MEV) e Microtomografia Computadorizada (MicroCT) - para imageamento de microestruturas e feições morfológicas não visíveis na superfície, respectivamente. As análises tafonômicas de orientação revelaram padrões NNE-SSW e NE-SW, assim como WNW-ESSE, sugerindo correntes que variaram desde quase paralelas, até, possivelmente, perpendiculares com relação à linha de costa. As alterações tafonômicas encontradas incluem fragmentação das porções externas da concha, deformação plástica, neomorfismo, dissolução da parede e presença de calcita eodiagenética entre as abas dos funis. Esse contexto tafonômico indica uma deposição por retrabalhamento dos bioclastos e sugere que informações morfológicas, como diâmetro, são alteradas tafonomicamente. A análise biométrica das amostras alóctones indicou bimodalidades para populações estatísticas de Cloudina considerando 1, 2, 3 ou 4 camadas em corte transversal, e conjuntamente com a distribuição de tamanho normal para uma assembleia autóctone sugere uma mistura de populações originais de tamanhos diferentes. Esses resultados trazem implicações para a taxonomia de Cloudina para esses depósitos, definindo C. lucianoi como tafotáxon. A análise da amostra autóctone demonstra a ocorrência de Cloudina com biolaminitos e microfósseis e fortalecem a interpretação de que esse metazoário vivia em habitats associados com microbialitos. A presença de goethita e calcita eodiagenética entre as abas de Cloudina, assim como microesferas silicificadas sugerem a presença de uma matéria orgânica nessas porções externas do organismo que podem estar relacionadas com o desenvolvimento de possíveis biofilmes simbiontes. A posição de vida horizontal verificada para Cloudina na amostra autóctone indica a versatilidade de modo de vida dessa organismo quando comparada a ocorrências de espécimes verticais em outras localidades. Nessa mesma amostra, indivíduos com mudanças na direção de crescimento podem ser resultantes da proximidade com outros espécimes, o que sugere capacidade sensoriais que auxiliariam na ocupação do substrato. Os resultados de MEV demonstraram que geralmente a microestrutura não está preservada, mas em alguns casos pode-se notar microgrânulos de calcita e um padrão reticulado. Conjuntamente com MEV, em análises petrográficas foram observadas duas camadas formando a parede de Cloudina. As análises geoquímicas de EDS e Raman demonstraram a presença de carbono na concha e corroboram trabalhos anteriores que postularam uma concha rica em matéria orgânica. As quantidades de Mg% e MgO% verificadas por EDS caracterizaram os fósseis da Formação Tamengo como de baixo teor de magnésio e fitting de bandas de calcita em espectros Raman fortalecem essa interpretação. Mesmo assim, alterações diagenéticas de estabilização por perda de Mg podem ter ocorrido. Os resultados de XRF-SRS mostraram que não há variação de Sr maior que 1000 ppm entre o fóssil e a rocha, indicando que, pelo menos, a mineralogia da concha não era aragonítica. Sendo assim, o presente trabalho traz novos cenários para a paleobiologia de Cloudina da Fm. Tamengo: Cloudina lucianoi é considerado como tafotáxon pelo contexto tafonômico e análise biométrica, indica ambientes de vida associados com microbialitos e possíveis cianobactérias, relações simbióticas podem ter ocorrido entre esse metazoário e biofilmes, é inferido modo de vida horizontal a sub-horizontal, é sugerido comportamentos de competição por espaço, a esqueletogênese de Cloudina é caracterizada por funis compostos por uma parede com duas camadas, rica em matéria orgânica e com microgrânulos de calcita. / Cloudina was the first fossil of a biomineralized organism found in latest Ediacaran. Also in this period, there was Corumbella, Namacalathus, Sinotubulites and Namapoikia within the skeletal biota. In the Corumbá Group (MS), in carbonates and pelites of Tamengo Formation, occur the fossils of Cloudina and Corumbella, respectively. This work aims to analyze paleobiological questions regarding Cloudina, such as its taphonomical, taxonomical and paleoecological context. Geochemical and microstructural analyses were performed to better understand the skeletogenesis of this fossil. For this, were utilized paleometrical techniques, such: Raman Spectroscopy, Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Fluorescence Synchrotron based (XRF-SRS) - for chemical and mineralogical analyses; and Scanning Electron Microscopy (SEM) and Computerized Microtomography (MicroCT) - for imaging of non-visible surficial microstructures and morphological attributes. The taphonomical analyses of orientation revealed NNE-SSW and NE-SW, as well as WNW-ESSE patterns, indicating currents that varied from almost parallel, to, possibly, perpendicular with relation to the ancient coastline. The taphonomical alterations include fragmentation of the external portions of the flares, plastic deformation, neomorphism, dissolution of the wall and the presence of eodiagenetic calcite between the flares of the funnels. This taphonomical context suggests a deposition by reworking and indicates that morphological information, such as diameter, is taphonomical altered. The biometrical analysis for the allochthonous specimens indicated bimodality for the statistical populations of Cloudina considering one, two, three or four layers in cross section, and together with the normal size distribution for the autochthonous assemblage suggest a mixture of original populations of different sizes. These results bring implications to the taxonomy of Cloudina, defining C. lucianoi as a taphotaxon. The study of the autochthonous assemblage demonstrated the occurrence of Cloudina with biolaminites and microfossils, and strengthens the interpretation that this metazoan lived in habitats associated with microbialites. The presence of goethite and eodiagenetic calcite between the flares of Cloudina, as well as silicified microspheres suggest the presence of organic matter in these external portions of the organism that can be related to de development of possibly symbiotic biofilms. The horizontal life position verified for Cloudina in the autochthonous assemblage together with occurrences in other localities of vertical specimens indicates the versatility of the life modes of this organism. Also in this sample, individuals with changes in the growing direction could be resultant of the proximity with other specimens, suggesting sensorial capacities, which assisted in the occupation of the substrate. SEM results demonstrated that often the microstructure is not preserved, but in some cases can be noted microgranules of calcite and a reticulate pattern. Allied with SEM, in petrographic sections were observed two layers forming the wall of Cloudina. EDS and Raman analysis showed the presence of carbon in the carapace and corroborate previous studies that postulated a shell with high amount of organic matter. Quantities of Mg% and MgO% verified by EDS characterized the fossils as low-magnesian calcites and fitting of calcite bands from Raman spectra strengthen this interpretation. Nevertheless, diagenetical alterations of stabilization by loss of Mg could have occurred. The results from XRF-SRS showed that there is no great variation in the Sr content between the fossil and the rock matrix, indicating that the mineralogy was not aragonitic. Thus, this work brings new scenarios for the paleobiology of Cloudina from the Tamengo Fm: Cloudina lucianoi is considered as a taphotaxon by the taphonomical and biometrical results, indicates habitats associated with microbialites and possible cyanobacteria, symbiotic relations could have occurred between this metazoan and biofilms, is inferred a horizontal to sub-horizontal life position and behaviors for space competition, the skeletogenesis of Cloudina is characterized by funnels composed of a wall with two layers, rich in organic matter and with microgranules of calcite.

Biomineralização é o processo em que organismos precipitam materiais sólidos para a formação de estruturas esqueléticas. Nos Echinodermata o esqueleto é composto por CaCO3, com uma organização e morfologia variável entre as classes do filo. Nos Echinoidea, onde o processo de calcificação tem sido mais estudado, os sítios de formação do esqueleto aparentemente são vacúolos sinciciais dos esclerócitos. Pouco tem sido estudado sobre calcificação nas demais classes dos Echinodermata, principalmente em Holothuroidea, onde os elementos esqueléticos têm uma distribuição esparsa, sem a mineralização densa encontrada nas demais classes. Neste grupo os ossículos se encontram em sua maioria agrupados em projeções da superfície corporal, ou papilas, cujas exatas funções na biologia do animal ainda são discutidas. Para um estudo mais detalhado da função destas estruturas e dos mecanismos envolvidos na calcificação, a manutenção das células em ambiente controlado, onde possam ser acompanhadas e manipuladas, seria de grande importância. O conhecimento, no entanto, ainda é bastante restrito, e não existem linhagens celulares estabelecidas de equinodermos. Neste trabalho foram realizados: a descrição morfológica e funcional da estrutura que conecta os ossículos dentro das papilas de Chiridota rotífera; análises da matriz orgânica dos ossículos, envolvidas na calcificação de Holothuria grisea, Synaptula hydriformis e Chiridota rotífera; e desenvolvidos protocolos adequados para manutenção das células de organismos da classe Holothuroidea em cultura. / Biomineralization is a process that organisms precipitate solid materials to the formation of skeletal structures. In Echinodermata the skeleton is composed by CaCO3, with an organization and variable morphology among phylum classes. In Echinoidea, where the calcification process has been hardly studied, apparently the sites of skeleton formation are vacuolar syncytia of sclerocytes. Little is known about calcification process in other Echinodermata classes, mainly in Holothuroidea, where skeletal parts are random distributed, without thick mineralization found in other classes. In this group, ossicles are found in clusters of papillae, that dont have defined functions for biology to animal. To a more specific and detailed study of the structures and mechanisms involved with calcification, it is necessary cell maintenance in a controlled environment, once these points can be accompanied and manipulated. However, the knowledge is extremely restricted and there is no cell lineages established of echinoderms. In this present study was performed the morphological and functional description of the structure that is responsible for the ossicles connection inside papillae of Chiridota rotífera; analyze of ossicles organic matrix involved with the Holothuria grisea, Synaptula hydriformis e Chiridota rotífera calcification, and development of adequate culture protocols to the maintenance of cell from Holothuroidea Class organisms.

One of the most fundamental and critical functions of embryological development is the control and regulation of differential genes and gene networks. The study of the gene networks involved in development is a mechanism for understanding the developmental process at its most basic level. An evolutionary change in a morphological feature or features must depend on a reorganization or co-option of one or more developmental gene regulatory network just as retention of an ancestral morphological trait must rely on retention of a common gene regulatory network. Studying two closely related classes in the same phylum with the same essential morphological feature yet with unique developmental characteristics provides insight into the evolution of these evolutionarily resolute gene regulatory networks. We have developed a new model system using brittle stars to further these studies. In this investigation I have identified key genes of the gene regulatory network (GRN) found in embryonic endo-mesoderm development in the sea urchin, responsible for embryonic skeletogenesis, and compared these key genes with homologues in the brittle star. From the examination of two closely related gene regulatory networks found in two related classes of Echinoderms insight can be gained into the foundation of morphological change over time.

xvii, 125 p. : ill. (some col.) A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / MicroRNAs are small regulatory RNAs that control various developmental and physiological processes in animals and plants. To study the involvement of microRNAs in skeletal development, I manipulated the expression of miR-140, which is strongly expressed in the developing skeleton, and miR-196, which is located among the body patterning Hox cluster genes. I found that miR-140 regulates zebrafish palate formation by interfering with neural crest cell migration through the inhibition of the expression of the platelet derived growth factor receptor alpha ( pdgfra ) gene. I also found that miR196 regulates zebrafish pectoral fin initiation by regulating the expression of the retinoic acid receptor alpha b ( rarab ) gene and that miR-196 is involved in the patterning of zebrafish pharyngeal arches and vertebrae. These results illuminate previously unknown regulatory mechanisms of skeletal development. I also reviewed current knowledge concerning microRNAs in skeletal development and evolution and discussed potential relationships between microRNAs and skeletal disease. This dissertation includes previously published and unpublished coauthored material. / Committee in charge: Judith Eisen, Chairperson, Biology; John Postlethwait, Advisor, Biology; Charles Kimmel, Member, Biology; William Cresko, Member, Biology; J. Andrew Berglund, Outside Member, Chemistry

Biomineralização é o processo em que organismos precipitam materiais sólidos para a formação de estruturas esqueléticas. Nos Echinodermata o esqueleto é composto por CaCO3, com uma organização e morfologia variável entre as classes do filo. Nos Echinoidea, onde o processo de calcificação tem sido mais estudado, os sítios de formação do esqueleto aparentemente são vacúolos sinciciais dos esclerócitos. Pouco tem sido estudado sobre calcificação nas demais classes dos Echinodermata, principalmente em Holothuroidea, onde os elementos esqueléticos têm uma distribuição esparsa, sem a mineralização densa encontrada nas demais classes. Neste grupo os ossículos se encontram em sua maioria agrupados em projeções da superfície corporal, ou papilas, cujas exatas funções na biologia do animal ainda são discutidas. Para um estudo mais detalhado da função destas estruturas e dos mecanismos envolvidos na calcificação, a manutenção das células em ambiente controlado, onde possam ser acompanhadas e manipuladas, seria de grande importância. O conhecimento, no entanto, ainda é bastante restrito, e não existem linhagens celulares estabelecidas de equinodermos. Neste trabalho foram realizados: a descrição morfológica e funcional da estrutura que conecta os ossículos dentro das papilas de Chiridota rotífera; análises da matriz orgânica dos ossículos, envolvidas na calcificação de Holothuria grisea, Synaptula hydriformis e Chiridota rotífera; e desenvolvidos protocolos adequados para manutenção das células de organismos da classe Holothuroidea em cultura. / Biomineralization is a process that organisms precipitate solid materials to the formation of skeletal structures. In Echinodermata the skeleton is composed by CaCO3, with an organization and variable morphology among phylum classes. In Echinoidea, where the calcification process has been hardly studied, apparently the sites of skeleton formation are vacuolar syncytia of sclerocytes. Little is known about calcification process in other Echinodermata classes, mainly in Holothuroidea, where skeletal parts are random distributed, without thick mineralization found in other classes. In this group, ossicles are found in clusters of papillae, that dont have defined functions for biology to animal. To a more specific and detailed study of the structures and mechanisms involved with calcification, it is necessary cell maintenance in a controlled environment, once these points can be accompanied and manipulated. However, the knowledge is extremely restricted and there is no cell lineages established of echinoderms. In this present study was performed the morphological and functional description of the structure that is responsible for the ossicles connection inside papillae of Chiridota rotífera; analyze of ossicles organic matrix involved with the Holothuria grisea, Synaptula hydriformis e Chiridota rotífera calcification, and development of adequate culture protocols to the maintenance of cell from Holothuroidea Class organisms.

Cloudina foi o primeiro fóssil de um organismo biomineralizado encontrado no final do Ediacarano. Também figuram nesse período Corumbella, Namacalathus, Sinotubulites e Namapoikia entre a biota esquelética. No Grupo Corumbá (MS), em carbonatos e pelitos da Formação Tamengo, ocorrem os fósseis de Cloudina e Corumbella, respectivamente. Este trabalho teve como objetivo analisar questões paleobiológicas referentes ao fóssil esquelético Cloudina, como seu contexto tafonômico, taxonômico e paleoecológico. Análises geoquímicas e de microestrutura foram realizadas para permitir melhor compreensão da esqueletogênese desse fóssil. Para tanto, foram utilizadas técnicas paleométricas, como: Espectroscopia Raman, Energia Dispersiva de Raios-x (EDS), Fluorescência de Raios-x por Energia Dispersiva (EDXRF) e Fluorescência de Raios-x Sincrotron (XRF-SRS) - para as análises de composição química e mineralógica; e Microscopia Eletrônica de Varredura (MEV) e Microtomografia Computadorizada (MicroCT) - para imageamento de microestruturas e feições morfológicas não visíveis na superfície, respectivamente. As análises tafonômicas de orientação revelaram padrões NNE-SSW e NE-SW, assim como WNW-ESSE, sugerindo correntes que variaram desde quase paralelas, até, possivelmente, perpendiculares com relação à linha de costa. As alterações tafonômicas encontradas incluem fragmentação das porções externas da concha, deformação plástica, neomorfismo, dissolução da parede e presença de calcita eodiagenética entre as abas dos funis. Esse contexto tafonômico indica uma deposição por retrabalhamento dos bioclastos e sugere que informações morfológicas, como diâmetro, são alteradas tafonomicamente. A análise biométrica das amostras alóctones indicou bimodalidades para populações estatísticas de Cloudina considerando 1, 2, 3 ou 4 camadas em corte transversal, e conjuntamente com a distribuição de tamanho normal para uma assembleia autóctone sugere uma mistura de populações originais de tamanhos diferentes. Esses resultados trazem implicações para a taxonomia de Cloudina para esses depósitos, definindo C. lucianoi como tafotáxon. A análise da amostra autóctone demonstra a ocorrência de Cloudina com biolaminitos e microfósseis e fortalecem a interpretação de que esse metazoário vivia em habitats associados com microbialitos. A presença de goethita e calcita eodiagenética entre as abas de Cloudina, assim como microesferas silicificadas sugerem a presença de uma matéria orgânica nessas porções externas do organismo que podem estar relacionadas com o desenvolvimento de possíveis biofilmes simbiontes. A posição de vida horizontal verificada para Cloudina na amostra autóctone indica a versatilidade de modo de vida dessa organismo quando comparada a ocorrências de espécimes verticais em outras localidades. Nessa mesma amostra, indivíduos com mudanças na direção de crescimento podem ser resultantes da proximidade com outros espécimes, o que sugere capacidade sensoriais que auxiliariam na ocupação do substrato. Os resultados de MEV demonstraram que geralmente a microestrutura não está preservada, mas em alguns casos pode-se notar microgrânulos de calcita e um padrão reticulado. Conjuntamente com MEV, em análises petrográficas foram observadas duas camadas formando a parede de Cloudina. As análises geoquímicas de EDS e Raman demonstraram a presença de carbono na concha e corroboram trabalhos anteriores que postularam uma concha rica em matéria orgânica. As quantidades de Mg% e MgO% verificadas por EDS caracterizaram os fósseis da Formação Tamengo como de baixo teor de magnésio e fitting de bandas de calcita em espectros Raman fortalecem essa interpretação. Mesmo assim, alterações diagenéticas de estabilização por perda de Mg podem ter ocorrido. Os resultados de XRF-SRS mostraram que não há variação de Sr maior que 1000 ppm entre o fóssil e a rocha, indicando que, pelo menos, a mineralogia da concha não era aragonítica. Sendo assim, o presente trabalho traz novos cenários para a paleobiologia de Cloudina da Fm. Tamengo: Cloudina lucianoi é considerado como tafotáxon pelo contexto tafonômico e análise biométrica, indica ambientes de vida associados com microbialitos e possíveis cianobactérias, relações simbióticas podem ter ocorrido entre esse metazoário e biofilmes, é inferido modo de vida horizontal a sub-horizontal, é sugerido comportamentos de competição por espaço, a esqueletogênese de Cloudina é caracterizada por funis compostos por uma parede com duas camadas, rica em matéria orgânica e com microgrânulos de calcita. / Cloudina was the first fossil of a biomineralized organism found in latest Ediacaran. Also in this period, there was Corumbella, Namacalathus, Sinotubulites and Namapoikia within the skeletal biota. In the Corumbá Group (MS), in carbonates and pelites of Tamengo Formation, occur the fossils of Cloudina and Corumbella, respectively. This work aims to analyze paleobiological questions regarding Cloudina, such as its taphonomical, taxonomical and paleoecological context. Geochemical and microstructural analyses were performed to better understand the skeletogenesis of this fossil. For this, were utilized paleometrical techniques, such: Raman Spectroscopy, Energy-Dispersive X-ray Spectroscopy (EDS), X-ray Fluorescence Synchrotron based (XRF-SRS) - for chemical and mineralogical analyses; and Scanning Electron Microscopy (SEM) and Computerized Microtomography (MicroCT) - for imaging of non-visible surficial microstructures and morphological attributes. The taphonomical analyses of orientation revealed NNE-SSW and NE-SW, as well as WNW-ESSE patterns, indicating currents that varied from almost parallel, to, possibly, perpendicular with relation to the ancient coastline. The taphonomical alterations include fragmentation of the external portions of the flares, plastic deformation, neomorphism, dissolution of the wall and the presence of eodiagenetic calcite between the flares of the funnels. This taphonomical context suggests a deposition by reworking and indicates that morphological information, such as diameter, is taphonomical altered. The biometrical analysis for the allochthonous specimens indicated bimodality for the statistical populations of Cloudina considering one, two, three or four layers in cross section, and together with the normal size distribution for the autochthonous assemblage suggest a mixture of original populations of different sizes. These results bring implications to the taxonomy of Cloudina, defining C. lucianoi as a taphotaxon. The study of the autochthonous assemblage demonstrated the occurrence of Cloudina with biolaminites and microfossils, and strengthens the interpretation that this metazoan lived in habitats associated with microbialites. The presence of goethite and eodiagenetic calcite between the flares of Cloudina, as well as silicified microspheres suggest the presence of organic matter in these external portions of the organism that can be related to de development of possibly symbiotic biofilms. The horizontal life position verified for Cloudina in the autochthonous assemblage together with occurrences in other localities of vertical specimens indicates the versatility of the life modes of this organism. Also in this sample, individuals with changes in the growing direction could be resultant of the proximity with other specimens, suggesting sensorial capacities, which assisted in the occupation of the substrate. SEM results demonstrated that often the microstructure is not preserved, but in some cases can be noted microgranules of calcite and a reticulate pattern. Allied with SEM, in petrographic sections were observed two layers forming the wall of Cloudina. EDS and Raman analysis showed the presence of carbon in the carapace and corroborate previous studies that postulated a shell with high amount of organic matter. Quantities of Mg% and MgO% verified by EDS characterized the fossils as low-magnesian calcites and fitting of calcite bands from Raman spectra strengthen this interpretation. Nevertheless, diagenetical alterations of stabilization by loss of Mg could have occurred. The results from XRF-SRS showed that there is no great variation in the Sr content between the fossil and the rock matrix, indicating that the mineralogy was not aragonitic. Thus, this work brings new scenarios for the paleobiology of Cloudina from the Tamengo Fm: Cloudina lucianoi is considered as a taphotaxon by the taphonomical and biometrical results, indicates habitats associated with microbialites and possible cyanobacteria, symbiotic relations could have occurred between this metazoan and biofilms, is inferred a horizontal to sub-horizontal life position and behaviors for space competition, the skeletogenesis of Cloudina is characterized by funnels composed of a wall with two layers, rich in organic matter and with microgranules of calcite.

The mineralized eggshell of Reptilia was a major innovation in the evolution of the amniotic egg. Inorganic components strengthen the eggshell and are a potential source of nutrients to developing embryos. Embryos of oviparous reptiles do extract calcium from eggshells but vary interspecifically in exploitation of this resource. The pattern of embryonic calcium nutrition of the corn snake, Pantherophis guttatus, is similar to a diversity of squamate species: embryos obtain most calcium from yolk, yet also mobilize calcium from the eggshell. We tested the hypothesis that embryonic development is not dependent on eggshell calcium by manipulating calcium availability. We peeled away the outer calcareous layer of the eggshell of recently oviposited eggs; control eggs were left intact. Eggs were sampled periodically and calcium content of egg compartments (embryo, yolk, eggshell) was measured. We also analyzed skeletal development and size of hatchlings. There was no difference in survivorship or length of incubation between treatments. However, hatchlings from intact eggs contained more calcium and were larger in mass and length than siblings from peeled eggs. There were no observable differences in ossification but hatchlings from intact eggs had larger skeletal elements (skull, vertebrae). Our results indicate that mobilization of eggshell calcium is not a requirement for embryonic development of P. guttatus and that embryos augment yolk calcium by extracting calcium from the eggshell. This pattern of embryonic calcium nutrition would favor embryos with a greater capacity to mobilize calcium from the eggshell by promoting growth and thereby potentially enhancing hatchling fitness.

Thesis advisor: Sarah McMenamin / Pectoral fins are evolutionarily homologous to tetrapod limbs and can serve as useful models for studying the genetic and hormonal factors regulating appendage development. To test the roles of thyroid hormone (TH) in the development of these appendages, we examined the morphogenesis of zebrafish pectoral fins under euthyroid (EuTH) or hypothyroid (hypoTH) conditions. TH plays an important role in modulating the development of the pectoral fin endoskeleton, as well as the proximo-distal patterning of the fin rays. Additionally, in HypoTH fish, shh was expressed in the same domains, but at ~50% of WT expression levels. Nuclear TH acts by binding to dual-action receptors, including Thrab, which represses or activates expression depending on interaction with the TH ligand. When Thrab was absent in HypoTH fish, we found that many elements of the HypoTH phenotype were rescued, suggesting TH relieves Thrab- mediated repression. We also found that TH modulates the development of the musculature surrounding the pectoral fin. Lastly, we generated CRISPR-Mediated knockouts of dio1 and dio3b, to learn how the deiodination of TH may be affecting the development of the pectoral fin. / Thesis (BS) — Boston College, 2023. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Departmental Honors. / Discipline: Biology.

No description available.