Gotowa bibliografia na temat „Tadpoles”

We used high-speed videography of staged encounters between tadpoles of either Bufo americanus Holbrook, 1836 or Rana sylvatica LeConte, 1825 and Echinostoma Rudolphi, 1809 cercariae to understand why echinostomatoid trematodes, such as species from the genera Echinostoma and Ribeiroia Travassos, 1939 (implicated in anuran limb deformities), attack specific anatomical regions of tadpoles. Bufo and Rana tadpoles can shed cercariae on their skin from some parts of their body more easily than others. In particular, cercariae that enter the "dead-water zone" at the junction of a tadpole's body and tail appear particularly difficult for tadpoles to brush off. Cercariae that reach this recess can easily enter the inguinal region of tadpoles (as do Ribeiroia spp.) or ascend the tadpole's cloaca (as do Echinostoma spp.). When tadpoles sense cercariae contacting their skin they make explosive movements to shed those parasites. Factors that reduce tadpoles' activity, such as predator threat or certain pesticides, may increase a tadpole's susceptibility to echinostomatoid infection. Because Bufo tadpoles are unpalatable to many predators, they can afford to make more conspicuous evasive maneuvers than Rana tadpoles, and do so in the laboratory. Bufo tadpoles in the field also have a lower rate and different anatomical distribution pattern of Ribeiroia infection than Rana tadpoles. Factors that reduce tadpole activity in the field may act synergistically to increase parasite loads and subsequent deformities in anurans.

All living creatures, whether plants or animals depend on the food available in the system for nourishment and energy necessary for the completion of their life cycle. Feeding constituents are always been the important aspect of biology of tadpoles, which is the main target of this study. Available dietary resources in the ecosystem is especially important in tadpoles because they need to attend the early stage in very short-lived aquatic environments i.e. temporal ponds and tadpoles need to consume food that will ensure their metamorphosis prior to drying up the pond. Tadpoles of Polypedates maculatus were collected from temporary ponds of northern Odisha. The guts of tadpoles were dissected out and analysed for the qualitative and quantitative analysis of food consumed. Diet is basically composed of microalgae and relatively low amount of detritus. The algae belonging to class Chlorophyceae, Bacillariophyceae, Cyanophyceae and Euglenophyceae were recorded. The numeric frequency (NF%) and frequency of occurrence (FO%) of different food items show the species richness and abundance, which is consumed by tadpole. Huge diversity of algal flora as tadpole’s food items are determined by the two diversity indices i.e. Simposon and Shannon-Weiner. Niche breadth of the tadpole was analysed through Levin’s measure. The physicochemical parameters of water signifies the pollution free tadpole’s habitat, which the support the growth and metamorphosis of tadpoles. The diet preference and choice of algae as food indicates that the conservation of habitat in terms of algal diversity is essential for survival and completion of their life cycle of the tadpoles for successful survival of anurans.

AbstractAlsodes gargola is an endemic species from northwest Patagonia, Argentina. Its tadpoles inhabit oligotrophic high altitude lakes and mountain streams from their sources. Tadpole diet is an important yet still unknown feature of its biology. This study analyzes alimentary tract content from A. gargola tadpoles collected from several of the species' typical habitats. For each group of items eaten, frequency of occurrence and its importance in the diet according to biovolume was calculated. Tadpole feeding behavior was also observed. The most common items were periphyton and plant material. The predominant algae were diatoms (typically periphytic), chlorophytes (periphytic and some planktonic) and a few cyanobacteria. Planktonic components were found in low proportion in all samples. The animal component (mainly from periphyton) was represented by ciliates, flagellates and amoebae, and varied according to the habitats, as did vascular plant fragments. There was a wide size range of ingested particles (from 10 to 400 μm) and a wide variety of components, according to the features of each habitat. These results suggest that tadpole of A. gargola are grazers of the periphytic community and detritus gatherers. The larval diet matches the tadpole's morphological and structural adaptations to a lotic-benthic habitat (depressed body, ventral subterminal oral disc capable of adherence, dorsal eyes, low, subparallel fins) and direct observation of behavior in natural environments (slow-swimming bottom-dwelling tadpoles in still water or streams with slow-flowing microhabitats). We discuss the ecological role of slow-developing tadpoles (regulation of periphyton development), which attain large biomass in their particular ecosystems, where they are the only aquatic vertebrates.

Herein we describe the tadpole of Hypsiboas latistriatus from its type-locality and an adjacent, higher elevation pond. The tadpole is similar to the known tadpoles of other species of the H. pulchellus group. The tadpoles of H. latistriatus can be distinguished from other species group tadpoles by their oral formula [2(1,2)/ 3(1)] allied with a rounded lateral profile of the tail fins, instead of taper. The overall morphology is congruent with bentonic tadpoles. The tadpoles of H. latistriatus are usually found in Highland grass fields above 2000 m.a.s.l. in clear slow-flowing water bodies. Almost all tadpoles used in this study presented highly whitened mouthparts suggesting the presence of the fungal pathogen Batrachochytrium dendrobatidis.

Shortly after hatching, Xenopus laevis tadpoles fill their lungs with air. We examined the role played by early lung use in these organisms, since they are able to respire with both their lungs and their gills. We investigated the effect on X. laevis development when the larvae were prevented from inflating their lungs, and whether early lung use influenced the size of the lungs or the tadpole's ability to metamorphose. Tadpoles that were denied access to air had lungs one-half the size of those of controls. This difference in lung size was too large to be explained merely by a stretching of the lung due to inflation. The longer tadpoles were denied access to air, the longer they took to metamorphose, and their probability of completing metamorphosis diminished. One tadpole raised throughout its larval life without access to air successfully metamorphosed but had abnormal, solidified lungs and an enlarged heart. Collectively, these experiments demonstrate that early lung use in tadpoles is important in determining both ultimate lung size and the probability of successfully metamorphosing. Lung use during early larval development in X. laevis is not absolutely necessary for survival through metamorphosis, but its absence severely handicaps growth.

The relative susceptibility of two closely associated herbivorous tadpole species (Uperodon taprobanicus and Duttaphrynus melanostictus) to their natural carnivorous predatory tadpole, Hoplobatrachus tigerinus and the significance of refugia in predator avoidance was studied in the laboratory. In a total of 50 trials, 10 tadpoles each of U. taprobanicus and D. melanostictus of comparable sizes were exposed to starved H. tigerinus. Twenty-five trials included refugia while 25 did not. The results of this study showed that in both the presence and absence of refugia, D. melanostictus tadpoles fell prey to H. tigerinus more frequently than U. taprobanicus tadpoles. A key difference between the two prey species is the speed of swimming; Vmax of D. melanostictus (13.58 cm/s) tadpoles is significantly lower than that of U. taprobanicus (24.89 cm/s) tadpoles. This is likely to be the main reason why more D. melanostictus tadpoles were preyed upon than were U. taprobanicus tadpoles. It is important to note that the Vmax of the predator (60.21 cm/s) is much greater than those of the two prey species. However, predation risk of both prey tadpole species was affected significantly by the presence of refugia. The susceptibility of both prey tadpole species was lower where refugia were available. The present study clearly demonstrates that the more efficient avoidance of predation by U. taprobanicus tadpoles could be due to better use of refugia and their faster rate of movement.

Our purpose was to determine how nonlethal prey injury and habitat complexity mediate the dynamics of a predator–prey system. We assessed rates of predation by the crayfish Procambarus acutus acutus on Hyla chrysoscelis tadpoles with four levels of tail loss (0, 25, 50, and 75% total tail length removed), and in habitats of three levels of complexity (zero, low, and high density of screen) in a 4 × 3 factorial design. We also examined the effects of tail loss on tadpole sprint velocity and distance traveled. Tadpoles with 75% tail loss were preyed upon significantly more often than tadpoles in the other tail-loss treatments. Habitat complexity did not affect tadpole survival. In addition, there was no interaction between tail loss and habitat complexity. Tail loss significantly affected both tadpole swimming velocity and sprint distance traveled. Tadpoles with 75% tail loss had slower sprint speed and swam a shorter distance than tadpoles with 0 and 25% tail loss, and tadpoles with 50% tail loss had slower sprint speed and swam a shorter distance than tadpoles in the 0% tail loss treatment. Although tadpoles generally rely on short bursts of speed, generated by the tail, to escape predators, tail injury and apparently reduced swimming performance did not increase vulnerability to predation in a simple linear fashion.

The comparative vulnerability of two co-existing tadpole species (Indosylvirana temporalis and Clinotarsus curtipes) to their common predator, water scorpions (Laccotrephes sp.; Hemiptera: Nepidae), and the importance of refugia in predator avoidance were studied in the laboratory. In a total of 60 experimental trials, 10 tadpoles each of I. temporalis and C. curtipes of comparable body sizes were exposed to water scorpions (starved for 48 h). Thirty trials included refugia while 30 did not. The results of this study showed that in both the absence and the presence of refugia C. curtipes tadpoles fell prey to water scorpions more frequently than I. temporalis tadpoles. A main difference between the two species is the speed of swimming; Vmax of C. curtipes (24.73 cm/s) tadpoles is lower than that of I. temporalis (30.78 cm/s) tadpoles. This is likely to be the reason why more C. curtipes tadpoles were preyed upon than were I. temporalis tadpoles. Predation risk of tadpoles of both species was affected significantly by the presence of refuge sites. The vulnerability of both tadpole species was lower where refuge sites were available. The present study clearly shows that I. temporalis tadpoles avoid predation by water scorpions more effectively than do C. curtipes tadpoles.

The mechanism of food detection in tadpoles of Polypedates maculatus was experimentally tested. We used a rectangular glass test tank with stimulus zones in opposite ends to provide visual and/or chemical food. For visual cues, boiled spinach was placed inside a glass container, and for chemical cues boiled spinach was placed in a mesh cage. Each tadpole of P. maculatus (either at an early or medium developmental stage) was held at the center of the test tank for acclimation. The tadpole was released, and we recorded whether it approached or did not approach the caged food. Tadpoles of all stages failed to detect food using visual cues. Tadpoles of all stages detected food using chemical cues. In tests using chemical cues, they spent the majority of their time (69.3% by early stage tadpoles and 87.3% by medium-stage tadpoles) near the container with food than in the end with no containers or with only visual food cues. Tadpoles in medium stages spent more time near food (18.1% of total time) than tadpoles in early stages. These findings indicate that tadpoles of P. maculatus detect food by chemical sensory mechanisms rather than visual ones. Tadpoles in medium stages spent more time near food than tadpoles in early stages indicating that time spent foraging increases as tadpoles grow.

We assessed the role of habitat structure in the outcome of predation by measuring how aquatic vegetation influences predation rates of water bugs (Belostoma oxyurum (Dufour, 1863), Hemiptera, Belostomatidae) on tadpoles of Dendropsophus minutus (Peters, 1872) and Scinax curicica Pugliese, Pombal, and Sazima, 2004 (Anura, Hylidae). Considering that previous studies have shown that some tadpole species preferentially use microhabitats with aquatic vegetation at sites in southeastern Brazil, we hypothesized that these tadpoles may select such complex microhabitats because they can offer some protection against co-occurring predatory aquatic insects. We used field enclosures containing tadpoles of D. minutus and S. curicica and one predator (B. oxyurum), placed on natural substrata in sites both with and without aquatic vegetation, according to treatment. We measured the combined effects of predation and habitat structure on the survivorship of tadpoles, monitoring each enclosure daily during 10 days to survey surviving tadpoles. Treatments with predators reduced tadpole survivorship significantly in relation to controls for both tadpole species. The interaction between predator and vegetation was also significant, predation rates being lower when vegetation was present.

The investigation of new threats to amphibian conservation is a priority of researchers and wildlife managers. Emerging infectious diseases are one of the most threatening processes to wildlife around the world including amphibians. Australian frogs have suffered large scale declines and extinctions from pathogens such as chytrid fungus (Batrochochytrium dendrobatidis). The once overly abundant Green and golden bell frog (Litoria aurea) has declined over 90% of its range with disease listed as a key threat. A routine pathogen screen of tadpoles from a captive breeding population of Green and golden bell frogs found an unknown parasitic infection in the brains, bile ducts and gallbladders of tadpoles (later confirmed as Myxosporea). It was this preliminary identification that was the impetus for my thesis. Myxosporean parasites found in Australian frog gallbladders were thought to be Cystodiscus immersus from Central and South America. The parasite was assumed to have been introduced to Australia with the Cane toad (Rhinella marina, syn. Bufo marinus) in 1935. Cystodiscus immersus was supposed to have translocated with the Cane toad from native Brazil and was infecting a broad range of Australian frog species with no apparent host impact. The aim of this thesis was to challenge all aspects of this assumption, to establish the true myxosporean species present in Australian frogs, if it was an exotic infection, if it was an emerging pathogen and what threat did it pose to hosts. The parasite found in Australian frogs and tadpoles was examined using histological and ultrastructural morphology as well as molecular identification. This revealed there was in fact two myxosporean species in multiple species of frogs and tadpoles. Sequencing of partial small iv subunit and large subunit as well as the internal transcribed spacers (ITS1 and ITS2) of ribosomal DNA regions confirmed these were distinct species (differing 9%, 7%, 34% and 37% at each region respectively). They were in fact separate species infecting multiple Australian host species,samples of C. immersus from Brazil were compared to establish if either of these was the exotic C. immersus. We found instead that these were completely unrelated despite sharing similar spore morphology. In addition the Brazil material revealed the cryptic diversity of myxosporea in frog gallbladders around the world and the ambiguous identity of Cystodiscus immersus. To determine if the parasites were emerging, the presence of these parasites in 130 years was established using voucher specimens. Four native species and the exotic Cane toad were examined for gallbladder myxospores from 1879 to 2009, the first positive was in 1966 in Green tree frog outside of Sydney. The prevalence of myxosporea increased in both native and exotic species over the last 40 years including the threatened Green and golden bell frog. The emergence of these parasites is a cause for concern, especially when found in endangered species. Close scrutiny of these parasites prompted the formal description of Cystodiscus axonis and Cystodiscus australis, resurrecting the original genus name proposed by Lutz in 1889. The description revealed diagnostic features previously unknown for frog gallbladder myxosporea species. Scanning electron microscopy revealed filiform polar appendages on the myxospores of C. axonis, absent in C. australis. In addition, histological examination showed unique developmental stages in the nervous tissue of tadpoles and frog hosts infected with C. axonis, these stages are only found in hosts infected with this parasite. The use of development stages as a species diagnostic character has not been previously reported for any amphibian myxosporea as yet. The genetic and morphological differences between C. axonis and C. australis prompted the development of a species specific multiplex PCR using ITS1, 5.8S and ITS2 ribosomal DNA. Multifaceted diagnostic tools (morphology and species specific PCR) demonstrated significant disease associated with these pathogens in native and exotic frog species. Seven host species were morphologically examined for Cystodiscus infection showing endangered species to have significant disease associated with infection. Cystodiscus axonis was linked to neurological signs,haemorrhage, necrosis and gliosis in Southern bell frogs (Litoria raniformis), Green and golden bell frogs (Litoria aurea), Booroolong frogs (Litoria booroolongensis), and the recently rediscovered Yellow spotted bell frogs (Litoria castanea). Cystodiscus spp. infection in the bile ducts of tadpoles was associated with biliary hyperplasia, loss of hepatocytes and inflammation. These lesions were statistically associated with the presence of infection in the Green and golden bell frog. This research disproved an assumption about myxosporean parasites that had held for 25 years. The disease found with Cystodiscus parasite infection in Australian frogs and tadpoles, as well as the previously unknown biodiversity in this cryptic species complex, highlight a number of areas in need of further research. This work has provided insight into the importance of multifaceted approaches to species identification and amphibian pathogen surveillance which uncovered a threat to endangered Australian amphibians, now listed as one of the key disease threats to frogs by the Department of Environment and Health (Australia) in 2011.

Mutations of Drosophila bagpipe, an NK3 class homeobox gene, result in failure of visceral mesoderm to differentiate into stomach tissue. Thus bagpipe, in association with other factors, is a good candidate for specification of visceral mesoderm in Drosophila. The cloning and characterisation of a Xenopus bagpipe homologue was therefore of great interest. This study describes the isolation of a full length Xenopus cDNA clone that on the basis of database analysis and sequence comparisons has been assigned as Xenopus bagpipe (XBap). Previous studies had revealed that the majority of homeoproteins recognise DNA sites with a 5'-TAAT-3' core but the NK class of homeoproteins had been shown to bind specifically to sites containing a 5'-CAAG-3' core. Experiments described here, however, show the XBap DNA binding site to be an even more divergent, 5'-TTAAGTGG-- TTAAGTGG-3'. A series of mutant oligonucleotides revealed that the `T' of the 5'- T_{1}A_{2}A_{3}G_{4}-3' core, as well as the presence of two such cores, are indeed essential for optimal XBap DNA binding. The murine NK3 class homeoproteins, Nkx-3.1 and Bapxl, are demonstrated to have the same requirements for optimal DNA binding as XBap. Drosophila Bagpipe, however, was found to have a less stringent requirement for a `T' at position one of the core, binding equally well to a 'C' in this position, but the presence of two such cores is still necessary for optimal DNA binding. Preliminary studies using site directed mutagenesis attempted to define the amino acids responsible for the differences. The effect of XBap on transcription was studied using a Xenopus oocyte assay and two cell transfection assays. XBap was not found to act as a transcriptional activator in any of these assays but evidence was obtained to suggest that a C-terminal truncation of XBap could act as a repressor of transcription.

Methylmercury (MeHg) is a toxic heavy metal and a health threat to wildlife and humans, however nothing is known about its effects on amphibians. MeHg is produced from inorganic Hg in the aquatic environment, and bioaccumulates in the food chain. This exposes tadpoles to elevated levels of MeHg in their diet, and may pose a risk to development. Tadpoles of the North American species Bufo americanus and Rana pipiens as well as the African frog model species Xenopus tropicalis were subchronically exposed to dietary McHg ranging in concentration from 1ng/g to 1000 ng/g to determine LC50s and species sensitivity differences. A developmental differences study was also performed with B. americanus. The 33-day LC50 estimates indicate that Gosner stage 25 tadpoles of both B. americanus and R. pipiens were the most sensitive, and they exhibited a similar sensitivity to McHg toxicity. The X. tropicales LC50 estimate is significantly higher (p=0.05) than those calculated for B. americanus and R. pipiens Gosner stage 25, and the developmentally advanced B. americanus Gosner stage 27-30 LC50 estimate is also significantly higher (p=0.05) than the B. americanus Gosner stage 25 LC50. (Abstract shortened by UMI.)

This work centered on the tadpoles in a temporaray pond in the middle of Kenilworth racecourse, Cape Town, South Africa. Trapping was carried out over two wet seasons and five species were found. The racecourse was selected to investigate the tadpole community occupying temporary winter pools. The main focus of this study was the community of tadpoles that occur in the ephemeral ponds in the centre of Kenilworth Racecourse. This study was a very broad insight into tadpole ecology in the Western Cape.

“Issues on tadpoles and vacuum redefinitions in String Theory” Marco Nicolosi Questa Tesi di dottorato è dedicata al problema dei “tadpoles” di NS-NS, funzioni ad un punto di campi bosonici assorbiti dal vuoto che tipicamente emergono nella Teoria delle Stringhe in seguito alla rottura della supersimmetria. Queste teorie contengono campi bosonici in due settori, quello di NS-NS e quello di R-R. Mentre i “tadpoles” di R-R tipicamente segnalano un’inconsistenza, come la presenza di anomalie quantistiche nel caso di spazi interni compatti, e quindi in generale devono essere cancellati, i “tadpoles” di NS-NS sono associati ad una ridefinizione del vuoto, come indicato per la prima volta da Fischler e Susskind negli anni ottanta. In particolare, nella stringa di Tipo I i “tadpoles” di NS-NS emergono già a livello del disco e, da un punto di vista spazio temporale, corrispondono a una configurazione di D-brane e piani di orientifold con tensione non nulla che danno luogo ad una netta attrazione gravitazionale che curva lo spazio tempo di “background”. Fino ad oggi siamo capaci di fare calcoli di stringa in maniera efficiente solo nel “background” piatto di Minkowski, un caso che è permesso e protetto dalla supersimmetria. Quindi, le divergenze infrarosse che emergono nelle ampiezze di stringa (canale chiuso) dopo la rottura della supersimmetria, dovute alla propagazione di stati non massivi di NS-NS che sono assorbiti dai “tadpoles” a impulso nullo, sono proprio il segnale che il “background” piatto di Minkowski non è più un vuoto della teoria. In questo contesto la nostra proposta è di continuare a quantizzare la stringa nel “background” di Minkowski e recuperare il risultato corretto risommando opportunamente i “tadpoles” in modo da cancellare le divergenze infrarosse. Questa procedura è comunque molto difficile da attuare nella Teoria delle Stringhe, perché le correzioni di “tadpoles” di ordine più grande corrispondono a superfici di Riemann di genere crescente, mentre si riescono a fare calcoli di stringa essenzialmente fino a genere uno (ampiezze ad un “loop”). Inoltre, nella maggior parte dei modelli che realizzano la rottura di supersimmetria, i “tadpoles” emergono già a livello del disco, e quindi, perfino in una regione perturbativa di piccola costante di accoppiamento di stringa, le prime correzioni di “tadpole” possono essere grandi. Pertanto, è interessante cercare modelli con “tadpoles” piccoli. Esempi di questo tipo sembrano essere forniti da modelli con opportuni flussi interni, per i quali risultati perturbativi credibili possono essere ottenuti considerando solo le prime correzioni di “tadpole”. Un’altra linea che si può perseguire è quella di cercare quantità che sono protette dalle divergenze infrarosse. Un esempio di questo tipo è dato dalle correzioni di stringa ad un “loop” alle costanti di accoppiamento di “gauge”, comunemente conosciute come “correzioni di soglia”, per modelli con supersimmetria rotta e con brane parallele, un caso che è stato ampiamente discusso in questa Tesi. Questa Tesi è organizzata nel seguente modo. Iniziamo con un’Introduzione generale sulla Teoria delle Stringhe, dove riportiamo le principale idee della Teoria, provando ad evidenziarne successi e problemi. Nel primo Capitolo richiamiamo le proprietà di base degli spettri di stringa e discutiamo qualche semplice esempio di compattificazione toroidale e di “orbifold”. Il secondo Capitolo è dedicato a riassumere differenti meccanismi di rottura di supersimmetria. Nel terzo Capitolo iniziamo ad analizzare il nostro programma di risommazione per diversi modelli giocattolo in Teoria dei Campi, provando a recuperare i giusti risultati, almeno a livello classico, a partire da un “vuoto sbagliato”. I casi di potenziale cubico e quartico sono semplici ed interessanti e mostrano alcune caratteristiche generali riguardanti le risommazioni dei “tadpoles” e i domini di convergenza intorno ai punti di flesso del potenziale, dove l’espansione nei “tadpoles” viene meno. La nostra analisi mostra che, partendo da un valore iniziale arbitrario del campo, la risommazione dei “tadpoles” a livello classico tipicamente guida le quantità che stiamo calcolando verso un estremo del potenziale, non necessariamente un minimo. Inoltre, nel caso del potenziale quartico troviamo alcuni punti molto speciali di “non-rinormalizzazione” per i quali tutte le correzioni di “tadpole” di ordine superiore si cancellano. Analizziamo poi la nostra procedura per un modello giocattolo inspirato dalla Teoria delle Stringhe, con “tadpoles” localizzati su D-brane di dimensione più bassa, calcolando le risommazioni esplicitamente. L’introduzione della gravità, che dovrebbe introdurre ulteriori complicazioni legate al termine di massa del gravitone, sembra non alterare sostanzialmente il nostro programma, ed infatti le risommazioni dei “tadpoles” continuano a funzionare ancora anche in questo caso. In fine, nel quarto Capitolo, iniziamo a trattare il problema dei “tadpoles” nella Teoria delle Stringhe. Nel primo Paragrafo, descriviamo un esempio dove la ridefinizione del vuoto può essere capita non solo a livello della teoria effettiva di bassa energia, ma anche a livello della stringa. In particolare, mostriamo che il vuoto di un “orientifold” di un modello di Tipo II con una dimensione compatta e “tadpoles” locali è un orientifold di Tipo 0 senza dimensioni compatte. Questi risultati sono contenuti in un articolo pubblicato in Nuclear Physics B. In fine, nell’ultimo Paragrafo, iniziamo l’analisi delle “correzioni di soglia” ad un “loop” in diversi modelli con rottura di supersimmetria e brane parallele, privi di tachioni chiusi che si propagano nel “bulk”. Il risultato è che le “correzioni di soglia” ad un “loop” in tutti questi casi sono sempre finite nell’infrarosso (canale chiuso), nonostante la presenza dei “tadpoles” di NS-NS. Questi risultati saranno inclusi in un articolo attualmente in preparazione.
“Issues on tadpoles and vacuum redefinitions in String Theory” M. Nicolosi This Thesis is devoted to the problem of NS-NS tadpoles, bosonic one-point functions going into the vacuum that typically emerge in String Theory after supersymmetry breaking. These theories contain bosonic fields in two sectors, commonly denoted with NS-NS and R-R. While R-R tadpoles typically signal an inconsistency, like the presence of quantum anomalies in the case of a compact internal space, and thus in general must be cancelled, NS-NS tadpoles are associated to redefinitions of the background, as first stressed by Fischler and Susskind in the eighties. In particular, in Type I String Theory NS-NS tadpoles emerge already at the disk level and, from a space-time viewpoint, correspond to configurations of D-branes and orientifold planes with a non-vanishing tension giving rise to a net gravitational attraction that curves the background space-time. Up to now one is able to perform efficient string computations only in a flat Minkowski background, a case that is allowed and protected by supersymmetry. Hence, the (closed) infrared divergences emerging after supersymmetry breaking in string amplitudes, due to the propagation of NS-NS massless states that are absorbed by tadpoles at vanishing momentum, are just the signal that the flat Minkowski background is no more a vacuum of the theory. In this context our proposal is to keep quantizing the string around the Minkowski background, recovering the proper results after suitable tadpole resummations that cancel the infrared divergences. This procedure is still very difficult to carry out in String Theory, because the higher-order tadpole corrections correspond to Riemann surfaces of increasing genus, and efficient calculations can be only carried out up to genus one (one-loop amplitudes). Moreover, in most models that realize supersymmetry breaking, tadpoles arise already at the disk level, and thus, even in a perturbative region of small string coupling, the first tadpole corrections can be large. Hence, it is interesting to search for models with “small” tadpoles. Examples of this kind seem are provided by models with suitable internal fluxes, for which reliable perturbative results can be recovered just considering the first tadpole corrections. Another line that one can pursue is to search for quantities that are protected against the infrared divergences. An example of this kind is provided by the one-loop string corrections to gauge couplings, commonly known as threshold corrections, for supersymmetry breaking models with parallel branes, a case that we have widely discussed in this Thesis. The Thesis is organized in the following way. There is a general Introduction to String Theory, where we summarize the main ideas of the Theory, trying to underline its successes and its open problems. Then in the first Chapter we recall the basic properties of string spectra and discuss some simple examples of toroidal and orbifold compactifications. The second Chapter is devoted to reviewing a number of different mechanisms to break supersymmetry. In the third Chapter we begin to analyze our resummation program in a number of field theory toy models, trying to recover the right results, at least at the classical level, starting from a “wrong vacuum”. The cases of cubic and quartic potentials are simple and interesting, and display some general features concerning tadpole resummations and convergence domains around inflection points of the potential, where the tadpole expansion breaks down. Our analysis shows that, starting from an arbitrary initial value of the field, classical tadpole resummations typically drive the quantities we are computing towards an extremum of the potential, not necessary a minimum. In addition, for the case of a quartic potential we find some very special “non-renormalization” points for which all higher order tadpole corrections cancel. We then analyze our procedure for a sting-inspired toy model with tadpoles localized on lower dimensional D-branes, performing explicitly the resummations. We also consider the introduction of gravity, that should give further complications related to the graviton mass terms, but seems to not affect substantially our program, and indeed tadpole resummations prove still to work in this case. Finally, in Chapter four we begin to face the tadpole problem in String Theory itself. In the first Section, we describe an example where the vacuum redefinition can be understood not only at the level of the low energy effective field theory, but also at the full string theory level. In particular, we show that the vacuum of a Type II orientifold with a compact dimension and local tadpoles is a Type 0 orientifold without compact dimensions. These results are contained in a paper to appear in Nuclear Physics B. Finally, in the last Section we begin the analysis of one-loop threshold corrections in a number of models with supersymmetry breaking with parallel branes and no closed tachyons propagating in the bulk. The result is that the one-loop threshold corrections in all these cases are always (closed) infrared finite, in spite of the presence of NS-NS tadpoles. These computations will be included in a paper that is currently in preparation.

Besides fish there are a lot of animals can swim effectively in the water, such as tadpole. Different from fishes using multiple fins to swim, tadpole has only one tail. It is well known that most fish employ the caudal fin to generate thrust, and use the pectoral fin, pelvic fin, etc. to balance the body and control its moving direction. However, the tadpole fulfilled all these tasks by the tail only. Hence, it is interesting to build a robot tadpole and study its motion. In this paper, a robot tadpole is designed. It has a blunt head and a tail. The control system, power supply and actuator are inside the head. The tail is a novel wire driven flapping propeller. The tail has a serpentine backbone with 7 joints, which are controlled by just one actuator. A prototype is built. The overall length of the robot tadpole is 328cm. Experiment results show that the robot tadpole can swim freely in the water. Its speed is affected by the flapping amplitude and frequency. In the experiments, the tadpole’s speed can reach 0.413 body length per second (BL/s), which matches the prediction from the propulsion model.

Once common and widespread in Southern California, California red-legged frogs (Rana draytonii) began declining sometime in the middle of the 20th century. They were listed as threatened under the Endangered Species Act in 1996. Three small and isolated populations remained in Los Angeles and Ventura Counties by the start of the 21st century. The nearest population of California red-legged frogs to Santa Monica Mountains National Recreation Area is critically small, located 15 km to the north, yet there is evidence of persistence, including successful reproduction each year it has been measured. A potential solution to alleviate small population size and isolation is to reintroduce a species back to habitable historical locations nearby. In 2011, we initiated a project to reintroduce California red-legged frogs back to the Santa Monica Mountains, where historical records showed they were once widespread. We developed a procedure to transfer partial egg masses into tadpole rearing pens located within streams determined to be suitable for the species. This translocation protocol outlines our procedure and results for the first five years of the project. It is our hope that this protocol will guide and inform similar conservation efforts for California red-legged frogs in other parts of their range as well as other amphibian conservation efforts throughout the world.