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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Stable Isotopes and the Ecology and Physiology of Reptiles

Durso, Andrew M. 01 May 2016 (has links)
Animals trade-off limited resources among competing demands. Trade-offs are difficult to quantify because it is challenging to measure investment into disparate physiological systems using a common scale. Additionally, biologists desire methods to more precisely measure energy status in wild animals. I used stable isotopes to help solve both of these problems. I examined natural spatial and temporal variation in stable isotope signatures of wild lizards and found significant variation. In the lab, I was able to demonstrate the utility of nitrogen stable isotope ratios of uric acid pellets for measuring nutritional stress. By tracing labeled amino acids through the bodies of gravid female lizards, I demonstrated that vitellogenesis and wound healing compete for amino acids and quantified the direction and magnitude of the trade-offs. I showed that reproductive-immune trade-offs vary based on reproductive stage and energy availability, have effects on metabolism and immune function, and are influenced by hormonal mechanisms. My findings shed light on the interconnectedness of stable isotope endpoints and key physiological systems in animals. I showed that isotopic signatures of physiological stress can be reflected at a large scale in natural populations, and I made novel measurements of the size and direction of trade-offs, which were formerly limited to physiological and performance outcomes.
2

Invertebrate life-history trade-offs and dispersal across a pond-permanence gradient

Galatowitsch, Mark Louis January 2014 (has links)
Flexible life-history traits and dispersal may allow generalist populations to persist across a range of habitats despite experiencing contrasting selection pressures. Invertebrates exploiting temporary ponds must develop quickly and disperse as adults, or have wide environmental tolerances. Conversely, permanent-pond invertebrates must avoid a suite of predators (e.g., fish and dragonflies). This gradient of pond permanence can result in life-history trade-offs that influence fitness, population dynamics, and genetic structure. In addition, recruitment between habitats may balance juvenile life-history trade-offs and be crucial to sustain generalist invertebrate populations in ponds with unpredictable hydrology. Through a multi-year survey of three pond complexes in the Canterbury high-country and a series of mesocosm experiments using two generalist pond invertebrates, Xanthocnemis zealandica damselflies and Sigara arguta waterboatmen, I found these two species had alternative life-history strategies that influenced their distributions across the pond-permanence gradient. With longer juvenile development, X. zealandica benefited from flexible life-history traits: temporary-pond X. zealandica had accelerated development and short-term desiccation tolerance, but were excluded from ponds with long dry periods, whereas, permanent-pond X. zealandica had extended development and predator avoidance behaviours (e.g., reduced movement and refuge-use). In contrast, S. arguta had an opportunistic life-history strategy with a fixed, rapid development response that allowed them to inhabit more temporary ponds, but they were intolerant of drying and limited to permanent ponds that contained shallow refuges from fish. These results illustrate how alternative life-history strategies enabled two generalist species to achieve broad realised niches. Recruitment between habitats also appeared to be important for balancing trade-offs and maintaining meta-populations across the pond-permanence gradient. To evaluate the importance of X. zealandica dispersal among and within pond complexes I used microsatellite analyses. While there was unique genetic population structure between the North and South Islands, at lower spatial scales there was little variability in genetic diversity and limited genetic structure in populations, likely due to gene flow among different habitat types. Overall, this work shows how an interaction of juvenile strategies and adult dispersal could reduce life-history trade-offs, resulting in weak selection pressures across an unpredictable disturbance gradient. Whether increasingly unpredictable hydrological patterns under climate-warming favour generalist species will likely depend on how well generalist life-history traits and dispersal allow exploitation of a range of habitat types and resilience to variable selection pressures. Higher mean summer rainfall in New Zealand may allow both species to exploit more temporary ponds, whereas longer dry periods between extreme precipitation events could limit X. zealandica distributions. Thus, species with generalist strategies are likely to be favoured under warming, but their specific life-history strategies will likely promote or limit their ability to exploit more unpredictable habitats.
3

Causes and consequences of oxidative stress in a cooperatively breeding bird

Cram, Dominic Laurence January 2013 (has links)
Oxidative stress has recently been highlighted as a potential physiological mechanism underpinning life-history trade-offs in animals. While the role of oxidative stress in mediating such trade-offs is receiving increasing attention, its importance in wild populations remains poorly understood. In this thesis, I use a wild population of cooperatively breeding white-browed sparrow weavers (Plocepasser mahali) to investigate the role that oxidative stress plays in mediating the costs of reproduction and immune defence. Cooperative animal societies offer a unique opportunity to investigate the costs of reproduction, because dominants frequently monopolise breeding opportunities (exhibiting higher reproductive effort than subordinates), and subordinate cooperative contributions frequently lighten reproductive workloads. My findings reveal, first, that dominants’ reproductive monopolies do not arise because they exhibit superior oxidative balance, as no such rank-related differences in oxidative state exist prior to breeding (Chapter 2). However, the higher reproductive effort of dominant females may underpin their differential declines in antioxidant protection after the breeding season (Chapter 2). Second, experimental manipulation of reproductive effort reveals marked oxidative damage and body mass costs incurred during reproduction. However, these costs are entirely mitigated in large social groups, suggesting that the cooperative contributions of helpers may offset the costs of reproduction for all group members (Chapter 3). While this represents rare evidence of an oxidative stress cost of reproduction in the wild, longitudinal data suggests that these costs do not endure after the breeding season (Chapter 4), highlighting that circulating markers of oxidative balance are unlikely to mediate long-term costs of reproduction. Finally, an immune activation experiment reveals that, while mounting an immune response causes no net change in oxidative balance, the scale of the response can be adjusted according to baseline antioxidant protection in an oxidative-condition-dependent manner (Chapter 5). Together my results provide support for the role of oxidative stress in shaping life histories in the wild. Furthermore, evidence of rank-related disparities in oxidative balance and the avoidance of reproductive costs in large social groups may have important implications for our understanding of both the evolution of cooperative breeding and the patterns of health and ageing in societies.
4

Avian malaria, life-history trade-offs and interspecific competition in Ficedula flycatchers

Kulma, Katarzyna January 2013 (has links)
This thesis investigates the impact of avian malaria (Haemosporidia) parasites on the outcome of interspecific competition between two closely related bird species, pied (Ficedula hypoleuca) and collared (F. albicollis) flycatchers. I further investigated how variation in timing of breeding, life history strategies and immune competence genes (MHC genes) modulate the fitness effects of malaria parasites in one of the two species i.e. collared flycatchers. Collared flycatchers colonized the Baltic island Öland in the late 1950-ties and has since then been expanding their breeding range while competitively excluding pied flycatchers from the favourable habitats (deciduous forests). I investigated the underlying mechanisms behind this exclusion by combining detailed long-term breeding data with modern molecular genetic techniques identifying both the presence/absence and lineage specificity of haemosporidian blood parasites. I found that the rapid decline of pied flycatchers can be explained by the combined effects of competition over nestling sites, hybridization and haemosporidian infections. Haemosporidian infections have a negative impact on survival of pied flycatcher females but no detectable effect on collared flycatchers’ longevity or reproductive success. This may be due to the fact that collared flycatchers carry (and are potentially exposed to) a higher diversity of parasites than pied flycatchers, which in turn may select for a higher diversity of MHC genes and hence a better overall protection from the negative impact of parasites. Indeed, functional MHC diversity correlates negatively with malaria prevalence among collared flycatchers from Gotland. Moreover, I found that both, malaria infection intensity and immunoglobulin level influences how infected collared flycatchers respond to increased nestling food-demands. The latter results mean that there is variation in allocation strategies (i.e. in resource allocation between reproductive effort and immune competence) within the collared flycatcher population. Hence, this population has the ability to respond to novel selection pressures in terms of optimal allocation of resources into immune functions. In summary, my results show that local parasites may facilitate the expansion of a new colonizer. This is important in the context of global climate change that will probably increase the colonization rate of southern species and lead to novel host-parasite interactions.
5

An Examination of Possible Maternal Effects due to Parasite and Density Stress on the Mealworm Beetle, Tenebrio molitor

Bennell, Maria C. 01 December 2011 (has links)
Few empirical studies examine the influence that the maternal parasite environment can have on offspring fitness (maternal effects) in invertebrates. Several recent studies have found that mothers can adjust offspring phenotype to counter the negative effects of parasite infection. In this thesis I subjected the parental generation of the host species, Tenebrio molitor (Insecta: Coleoptera), to a high parasite, high density, or control treatment. Offspring were subsequently subjected to either the same stress, the alternate stress, or to the control, and fitness-related life history traits were measured in both generations. The results from this thesis do not support the hypothesis that T. molitor mothers influence offspring fitness in a positive way. Instead, maternal effects led to a reduction in offspring fitness under both types of stress. At least under some environmental conditions, females invest in their fitness at the expense of their offspring.
6

An Examination of Possible Maternal Effects due to Parasite and Density Stress on the Mealworm Beetle, Tenebrio molitor

Bennell, Maria C. 01 December 2011 (has links)
Few empirical studies examine the influence that the maternal parasite environment can have on offspring fitness (maternal effects) in invertebrates. Several recent studies have found that mothers can adjust offspring phenotype to counter the negative effects of parasite infection. In this thesis I subjected the parental generation of the host species, Tenebrio molitor (Insecta: Coleoptera), to a high parasite, high density, or control treatment. Offspring were subsequently subjected to either the same stress, the alternate stress, or to the control, and fitness-related life history traits were measured in both generations. The results from this thesis do not support the hypothesis that T. molitor mothers influence offspring fitness in a positive way. Instead, maternal effects led to a reduction in offspring fitness under both types of stress. At least under some environmental conditions, females invest in their fitness at the expense of their offspring.
7

The Stability of Lytic Sulfolobus Viruses

Gazi, Khaled S. January 2017 (has links)
No description available.
8

The effects of nutritional and social environment on ovarian dynamics and life history strategy in Nauphoeta cinerea

Barrett, Emma Louise Beverley January 2009 (has links)
The trade-off between gametes and soma is central to life-history evolution. Oosorption has been proposed as a mechanism that can mediate this trade-off. When conditions are not conducive to successful reproduction, females are expected to be able to recoup nutrients from unfertilized oocytes and reinvest them into the somatic processes that promote survival and hence future reproduction. Although positive correlations between oocyte degradation and lifespan have been documented in oviparous insects, the adaptive significance of this process in species with more complex reproductive biology has not been explored. Oocyte degradation via apoptosis (programmed cell death) occurs in response to enforced virginity in females of the ovoviviparous cockroach, Nauphoeta cinerea. Observed apoptosis may represent oosorption, however, an alternative but not mutually exclusive argument is that oocyte apoptosis may represent oocyte ageing and clearance in order to maintain reproductive synchrony. The aim of this thesis was to test the hypothesis that the function of oocyte apoptosis is oosorption in N. cinerea. I found that in addition to enforced virginity, starvation induces oocyte apoptosis. However, the life history outcome following one form of stress is the opposite of the other. Hence, the functional role of oocyte apoptosis appears to be different depending on whether apoptosis is induced through starvation or age. Following a period of starvation-induced apoptosis females exhibit the increase in survival and future reproduction predicted by oosorption. Whereas, following a period of age-induced apoptosis females suffer fecundity and longevity cuts. However, age-induced apoptosis does not appear to simply be cellular ageing and clearance. In conjugation with age-induced apoptosis, ovariole number declines whilst the size of surviving oocytes increases. Hence, it appears that resources from sacrificed oocytes are being recycled into the survivors, and that this reinvestment in current reproduction trade-offs with future reproductive capacity. My thesis shows the importance of studying proximal mechanisms alongside more traditional measures of life history, as the relationship between isolated biological levels is not always clear.
9

Effet maternels et compromis évolutifs chez une espèce à reproduction coopérative, le Républicain social (Philetairus socius) / Maternal investment and life history trade-offs in a cooperative breeding bird, the Sociable weaver, Philetairus socius

Paquet, Matthieu 18 December 2013 (has links)
Maximiser le nombre de copies de gènes transmises aux générations suivantes implique une série de compromis. Chez les espèces à reproduction coopérative, des individus ne se reproduisent pas mais participent aux soins des jeunes d'autres individus reproducteurs. Ces assistants sont particulièrement intéressants dans le contexte des traits d'histoire de vie car ils forment un environnement prédictible favorable pour la reproduction, et leur présence peut aussi influencer les compromis évolutifs chez les reproducteurs. Un compromis évolutif majeur mais sous-étudié dans le cadre de la reproduction coopérative est l'allocation maternelle notamment via des effets maternels qui sont des modifications épigénétiques du phénotype de la descendance. Nous avons étudié l'existence d'effets maternels associés à la présence d'assistants et leurs possibles conséquences sur les femelles et leurs descendants chez un oiseau colonial et coopératif du sud de l'Afrique, le Républicain social Philetairus socius. Nos résultats montrent que les femelles pondent des œufs plus légers en présence d'assistants et que ces œufs sont moins concentrés en corticostérone et testostérone. Nos résultats montent aussi une plus grande probabilité de survie pour les femelles se reproduisant en groupe pouvant être en partie due à leur plus faible investissement dans les œufs. De plus, l'étude de la température dans les nids en fonction de la taille des groupes a permis de suggérer d'autres bénéfices pour les parents et assistants, en particulier via une réduction des coûts de thermorégulation qui pourrait aussi permettre de garder de l'énergie pour la survie. Pour comprendre les conséquences de la présence d'assistants et de l'allocation différentielle pour les poussins, une expérience d'adoption croisée a été réalisée. Elle a révélé que les œufs pondus par les femelles avec plus d'assistants produisent des poussins qui quémandent moins, montrant que des effets maternels pourraient influencer le comportement des poussins. Enfin nous avons étudié la survie des poussins après l'envol à l'aide d'analyses de captures recaptures et avons trouvé de manière surprenante que les poussins à l'envol ont une probabilité de survie plus faible lorsqu'ils sont élevés présence d'assistants. Ces résultats dans leur ensemble démontrent l'importance d'étudier les effets maternels chez les espèces coopératives et ouvrent de nombreuses perspectives de recherche sur les conflits familiaux et de compromis évolutifs associés à la présence d'assistants. / Maximizing of the number copies of genes that are transmitted to the next generations involves a series of tradeoffs. In cooperatively breeding species some sexually mature individuals do not breed but instead help other individuals to raise their offspring. These helpers are particularly interesting in a life history context as they create a predictably favorable breeding environment and their presence can thus influence evolutionary trade-offs. A major evolutionary trade-off that is often neglected in studies on cooperative breeding is maternal allocation, notably through maternal effects that are epigenetic modifications of offspring phenotype. Here we investigate whether there are maternal effects induced by the presence of helpers and their possible consequences on females and their offspring in a colonial cooperative breeder of southern Africa, the sociable weaver Philetairus socius. Our results show that females lay smaller eggs in the presence of helpers and in addition these eggs have lower corticosterone and testosterone concentrations. Our results also show a higher survival probability of females breeding in groups, which may be partially due to their lower investment in eggs. In addition, a study of roosting chamber temperatures in relation to group size suggests further benefits for parents and helpers, particularly through lower costs of thermoregulation that could also allow energy savings for survival. To start understanding the consequences of helpers presence and differential maternal allocation for offspring we conducted a cross fostering experiment. Our results show that eggs produced by females breeding in larger groups produce chicks that beg at a lower rate, showing that maternal effects may influence chicks' behavior. Finally, we investigated post-fledging survival through capture-recapture analyses and, surprisingly, found that fledglings have a lower survival probability when raised with helpers. Taken together, these results demonstrate the importance of studying maternal effects on cooperative breeders and open several research prospects on family conflicts and life history trade-offs according to the presence of helpers.
10

Links between avian botulism outbreaks in waterfowl, hatching asynchrony, and life history trade-offs of prefledgling Franklin's gulls (<i>larus pipixcan</i>)

Soos, Catherine 01 December 2004
This study investigated factors associated with two mortality events: avian botulism in waterfowl and mortality associated with hatching asynchrony in prefledgling Franklins gulls (Larus pipixcan). The initial focus of my research was on the spatiotemporal relationship between mortality of Franklins gulls and the onset of botulism outbreaks in waterfowl, and the suitability of gull carcasses for proliferation and toxigenesis of Clostridium botulinum. From 1999 to 2001, dead hatch-year Franklins gulls were by far the most abundant carcasses, and the only source of toxin-laden maggots found on transects prior to the occurrence of avian botulism in waterfowl. Nest density was a significant predictor of hatch-year gull carcass density. High density of toxic material from gull carcasses prior to the onset of botulism in waterfowl coincided with high densities of susceptible birds; hence, mortality of Franklins gulls has the potential to be a major initiating factor for botulism outbreaks at Eyebrow Lake, Saskatchewan. The causes of gull mortality were conditions or diseases associated with starvation, stress, or immunosuppression, and most mortality occurred in third-hatched chicks. To separate effects of laying order from effects of hatching asynchrony on prefledgling survival, a cross-fostering experiment was conducted to create clutches containing asynchronously hatching eggs of the same laying order, and of similar egg mass, egg volume, and female quality. Hatching order, independent of laying order, significantly affected survival to fledging, whereas laying order had no observable effect, indicating that intraclutch variation in egg quality does not predetermine the fate of prefledglings, and may be less important than hatching asynchrony for survival of prefledgling Franklins gulls. Relationships among hatching asynchrony, laying order, mass, corticosterone, immune function, growth, and survival at two stages of development were complex. Hatching asynchrony significantly affected early and late prefledgling survival, and was directly or indirectly associated with mass, corticosterone level, and cell-mediated immune responses at early and later stages of development. Both hatching asynchrony and mass appeared to play key roles in mediating life history trade-offs among cell-mediated immune function, growth, and survival. In contrast to cell-mediated immune responses, primary humoral immune response was not directly affected by hatching order or mass, nor was it associated with survival to fledging. Rather, it was associated with laying order, neonatal testosterone, corticosterone at 2 weeks, growth of leg length, and clutch initiation date, illustrating the importance of examining more than one branch of the immune system in studies of life history trade-offs. This study is a step toward using a multipronged and multidisciplinary approach to demonstrate interactions and trade-offs among life history traits, the physiological mechanisms that produce these relationships, and how these relationships may change depending on stage of development.

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