Post-Meiotic Intra-Testicular Sperm Senescence in a Wild Vertebrate

There is growing interest in sperm senescence, both in its underlying mechanisms and evolutionary consequences, because it can impact the evolution of numerous life history traits. Previous studies have documented various types of sperm senescence, but evidence of post-meiotic intra-testicular sperm senescence in wild animals is lacking. To assess such senescence, we studied within-season changes in sperm motility in the common toad (Bufo bufo), where males produce all sperm prior to the breeding season. We found that males exposed to experimentally induced re-hibernation at the start of the breeding season, that is to experimentally lowered metabolic rates, stored sperm of significantly higher motility than males that were kept under seminatural conditions without females throughout the breeding season. This finding indicates that re-hibernation slows normal rates of sperm ageing and constitutes the first evidence to our knowledge of post-meiotic intra-testicular sperm senescence in a wild vertebrate. We also found that in males kept in seminatural conditions, sperm motility was positively related to the number of matings a male achieved. Thus, our results suggest that post-meiotic intratesticular sperm senescence does not have a genetically fixed rate and may be modulated by temperature and possibly by mating opportunities

Bayesian Analysis of Intratumoural Oxygen Data

There is now ample evidence to support the notion that a lack of oxygen (hypoxia) within the tumour adversely affects the outcome of radiotherapy and whether a patient is able to remain disease free. Thus, there is increasing interest in accurately determining oxygen concentration levels within a tumour. Hypoxic regions arise naturally in cancerous tumours because of their abnormal vasculature and it is believed that oxygen is necessary in order for radiation to be effective in killing cancer cells. One method of measuring oxygen concentration within a tumour is the Eppendorf polarographic needle electrode; a method that is favored by many clinical researchers because it is the only device that is inserted directly into the tumour, and reports its findings in terms of oxygen partial pressure (PO2). Unfortunately, there are often anomalous readings in the Eppendorf measurements (negative and extremely high values) and there is little consensus as to how best to interpret the data. In this thesis, Bayesian methods are applied to estimate two measures commonly used to quantify oxygen content within a tumour in the current literature: the median PO2, and Hypoxic Proportion (HP5), the percentage of readings less than 5mmHg. The results will show that Bayesian methods of parameter estimation are able to reproduce the standard estimate for HP5 while providing an additional piece of information, the error bar, that quantifies how uncertain we believe our estimate to be. Furthermore, using the principle of Maximum Entropy, we will estimate the true median PO2 of the distribution instead of simply relying on the sample median, a value which may or may not be an accurate indication of the actual median PO2 inside the tumour. The advantage of the Bayesian method is that it takes advantage of probability theory and presents its results in the form of probability density functions. These probability density functions provide us with more information about the desired quantity than the single number that is produced in the current literature and allows us to make more accurate and informative statements about the measure of hypoxia that we are trying to estimate

The Effects of Extrinsic and Intrinsic Noise on a Tumour and a Proposed Metastasis Model

Cancer is a ubiquitous disease that afflicts millions of people worldwide and we will undoubtedly encounter it at some point in our lives, whether it be random strangers on the news, or someone much closer. As such, research into cancer (and cures for cancer) has been an intense area of focus. Malignant tumours show three main characteristics: 1) aggressive and uncontrolled growth, 2) invasion into surrounding tissue, and 3) the ability to leave the primary tumour site and invade another organ (metastasis). Mathematical models of these three aspects began in earnest about half a century ago, for example with Laird\cite{gompertz} in 1964 proposing that tumour growth was gompertzian. With the advent of the modern computer, complex partial differential equation (PDE) models of tumour growth which incorporate the other two features of malignant tumours have become accessible to the average researcher. Utilizing a mixture of both analytical and numerical methods, this thesis aims to add to the schema of cancer research by examining the effects of noise on a well established model of tumour growth, and a promising model for mitosis that we hope to eventually adapt to describe metastasis. The tumour model that we will examine is a single species reaction-diffusion model that captures the first two aspects of tumour growth. The reaction part determines how fast the tumour grows and the diffusion part describes how quickly the cancer cells spread within the domain. Adding noise to the model is a method of describing the disorder that is in a typical tumour, and allows us to determine error bounds on the tumour size and survival time, which gives us a sense of how accurate the estimates of those two quantities are. This method of estimating the uncertainty in survival time also allows us to further determine how modifications to the model (such as changing the diffusivity or adding chemotherapy) affects the error in the system. Our model of mitosis is an excitable system that admits a traveling wave as a possible solution. Mitosis is a process that occurs in a very spatially specific manner within the embryo and this model describes how a signal propagates from the centre of the embryo outwards. When we allow noise to perturb the system we will see that the model allows noise induced traveling waves in what would normally be a stable system in a deterministic setting. This means that the parameter range under which signalling can occur is relaxed and traveling waves occur more readily than expected. In terms of metastasis, where the tumour microenvironment is especially noisy and chaotic, that might explain why metastasis is so prevalent in malignant tumours. Adding noise to well established PDE models gives it an extra layer of fidelity that allows us to extract additional information from the model not available in the traditional deterministic setting. Using both a numerical and an analytical approach, this thesis develops and demonstrates general methods for estimating the uncertainty in the model outputs and also a method for calculating when a system might admit a noise induced instability in an otherwise stable system. More specifically, the error bounds in the estimates of tumour size and survival time in the tumour growth model may be of future use to doctors treating patients, and the noise induced effects of the mitosis model helps us to understand further how metastasis arises out of a developing tumour

The effect of social connections on the discovery of multiple hidden food patches in a bird species

Social foraging is thought to provide the possibility of information transmission between individuals, but this advantage has been proved only in a handful of species and contexts. We investigated how social connections in captive flocks of house sparrows (Passer domesticus) affected the discovery of (i.e. feeding for the first time from) two hidden food patches in the presence of informed flock-mates. At the first-discovered and most-exploited food patch social connections between birds affected the order of discovery and presumably contributed to a greater exploitation of this patch. However, social connections did not affect discovery at the second food patch despite its close spatial proximity. Males discovered the food sources sooner than females, while feeding activity was negatively related to patch discovery. Age had no effect on the order of discovery. Birds that first discovered and fed at the food patches were characterized by higher level of social indifference, i.e. followed others less frequently than other birds in an independent context. Our findings provide experimental evidence for the importance of variable social connections during social foraging in house sparrow flocks, and suggest that social attraction can contribute differently to the exploitation of different patches when multiple food sources are present

Experimental evidence for beneficial effects of projected climate change on hibernating amphibians

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Host response to cuckoo song is predicted by the future risk of brood parasitism

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Introduction: Risk assessment occurs over different temporal and spatial scales and is selected for when individuals show an adaptive response to a threat. Here, we test if birds respond to the threat of brood parasitism using the acoustical cues of brood parasites in the absence of visual stimuli. We broadcast the playback of song of three brood parasites (Chalcites cuckoo species) and a sympatric non-parasite (striated thornbill, Acanthiza lineata) in the territories of superb fairy-wrens (Malurus cyaneus) during the peak breeding period and opportunistic breeding period. The three cuckoo species differ in brood parasite prevalence and the probability of detection by the host, which we used to rank the risk of parasitism (high risk, moderate risk, low risk). Results: Host birds showed the strongest response to the threat of cuckoo parasitism in accordance with the risk of parasitism. Resident wrens had many alarm calls and close and rapid approach to the playback speaker that was broadcasting song of the high risk brood parasite (Horsfield’s bronze-cuckoo, C. basalis) across the year (peak and opportunistic breeding period), some response to the moderate risk brood parasite (shining bronze-cuckoo, C. lucidus) during the peak breeding period, and the weakest response to the low risk brood parasite (little bronzecuckoo, C. minutillus). Playback of the familiar control stimulus in wren territories evoked the least response. Conclusion: Host response to the threat of cuckoo parasitism was assessed using vocal cues of the cuckoo and was predicted by the risk of future parasitism

Songbirds use scent cues to relocate to feeding sites after displacement: An experiment in great tits (Parus major)

Air-borne chemicals are highly abundant sensory cues and their use in navigation might be one of the major evolutionary mechanisms explaining the development of olfaction in animals. Despite solid evidence for the importance of olfaction in avian life (e.g., foraging or mating), the importance of chemical cues in avian orientation remains controversial. In particular, songbirds are sorely neglected models, despite their remarkable orientation skills. Here we show that great tits (Parus major) require olfactory cues to orientate toward winter-feeding sites within their home range after displacement. Birds that received an olfaction-depriving treatment were impaired in homing. However, the return rates between olfaction-deprived and control individuals did not differ. Birds with decreased perception of olfactory cues required more time to return to the winter feeding sites. This effect became apparent when the distance between the releasing and capture sites was greater. Our results indicate that even in a familiar environment with possible visual landmarks, scent cues might serve as an important source of information for orientation

BMC Zoology – a home for all zoological research in the BMC series

This editorial accompanies the launch of BMC Zoology, a new open access, peer-reviewed journal within the BMC series that considers manuscripts on all aspects of zoology. BMC Zoology will increase and disseminate zoological knowledge through the publication of original research, methodology, database, software and debate articles. With the launch of BMC Zoology, the BMC series closes a gap in its portfolio of subject-specific research journals and is now able to cover all aspects of animal research together with BMC Ecology, BMC Evolutionary Biology and BMC Veterinary Research