1,721,268 research outputs found
Living on the edge : daily, seasonal and annual body temperature patterns of Arabian Oryx in Saudi Arabia
Full text linkHeterothermy, the ability to allow body temperature (Tb) to fluctuate, has been proposed as an adaptive mechanism that enables large ungulates to cope with the high environmental temperatures and lack of free water experienced in arid environments. By storing heat during the daytime and dissipating it during the night, arid-adapted ungulates may reduce evaporative water loss and conserve water. Adaptive heterothermy in large ungulates should be particularly pronounced in hot environments with severely limited access to free water. In the current study we investigated the effects of environmental temperature (ambient, Ta and soil, Ts) and water stress on the Tb of wild, free-ranging Arabian oryx (Oryx leucoryx) in two different sites in Saudi Arabia, Mahazat as-Sayd (MS) and Uruq Bani Ma’arid (UBM). Using implanted data loggers wet took continuous Tb readings every 10 minutes for an entire calendar year and determined the Tb amplitude as well as the heterothermy index (HI). Both differed significantly between sites but contrary to our expectations they were greater in MS despite its lower environmental temperatures and higher rainfall. This may be partially attributable to a higher activity in an unfamiliar environment for translocated animals in UBM. As expected Tb amplitude and HI were greatest during summer. Only minor sex differences were apparent that may be attributable to sex-specific investment into reproduction (e.g. male-male competition) during rut. Our results suggest that the degree of heterothermy is not only driven by extrinsic factors (e.g. environmental temperatures and water availability), but may also be affected by intrinsic factors (e.g. sex and/or behaviour).National Program Saudi Arabia and the National Research Foundation, South AfricaThis xls file contains: Streicher et al. Body temp data Mahazat, Streicher et al. Body temp data UBM, Streicher et al. Climate data, Streicher et al. Heterothermy index and Streicher et al. Table S1 overview of oryx body mass
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Environmental effects on the circadian systems of a diurnal ( rhabdomys dilectus) and noctural (micaelamys namaquensis) rodent species with specific reference to light pollution
Full text linkDissertation (MSc)--University of Pretoria, 2019.The presence of artificial light at night (ALAN) is one of many contributing factors to global change today. The spectral range of ALAN can also alter the potential effects of light pollution in certain contexts which creates an exceptionally complex cascade of impacts. The purpose of this thesis was to examine the interactions of various environmental factors including ALAN on biological variables, locomotor activity and corticosterone concentration, of two species of rodent. This was accomplished by manipulating the environmental factors; environmental enrichment, temperature and lighting in captivity. A pilot field study was also conducted in order to test the future feasibility of incorporating information garnered from the laboratory study into larger scale real world experiments. The two species were collected from the field and was subsequently subjected to various light cycles, during which locomotor activity was monitored and urinary corticosterone stress hormone was assessed. Results showed that Micaelamys namaquensis, a nocturnal species, reacted favourably to the addition of enrichment by increasing activity levels whereas Rhabdomys dilectus, a diurnal species decreased activity levels while improving the strength of entrainment. Both M. namaquensis and R. dilectus decreased activity during a light cycle which simulated natural dawn and dusk patterns of light. The two species reacted differently when a 24hr
ambient temperature cycle was introduced, with M. namaquensis increasing its locomotor activity and R. dilectus decreasing overall activity. M. namaquensis decreased its average activity in response to ALAN and did not show any difference in reaction towards different types of light at night. R. dilectus on the other hand increased its activity under ALAN but also showed no preference between different spectra of light at night. While corticosterone concentrations were monitored during all the environmental factor experiments, fluctuations in hormone concentrations were noted, however found to be statistically non-significant. Thus, only speculations could be made regarding the impacts of the various environmental factors on the stress physiology of M. namaquensis and R. dilectus. These results highlight the importance of considering species specific outcomes even under virtually identical circumstances. Understanding the impacts of environmental factors is crucial in order to extrapolate laboratory-based findings into real world experiments. This work can be used to further understand the impacts of different environmental factors on the circadian systems of nocturnal and diurnal rodent species as well as the potential implication of ALAN under various environmental conditions. In future, this can be combined into a large-scale field experiment in order to monitor the impacts of light pollution using the methodology elucidated during the pilot study. The results of this study show that the impacts of ALAN can be incredibly diverse and specific to the species in which they are examined.Zoology and EntomologyMScUnrestricte
The relationship between immunocompetence, parasite load and reproductive effort in the highveld mole-rat (Cryptomys hottentotus pretoriae) Roberts 1913.
Full text linkDissertation (MSc)--University of Pretoria, 2011.Life-history theory is based on the notion that resources are generally limited in nature, and that organisms have to allocate these resources amongst different physiological systems to maximise their survival and fitness. Therefore life-history traits such as maintenance, growth and fecundity are very often negatively associated with each other. Since the immune system plays a prominent role in fitness and survival of an organism it often features in life-history trade-offs particularly with respect to reproductive effort. This thesis focused predominantly on the interactions between immune function and reproductive effort in the highveld mole-rat, Cryptomys hottentotus hottentotus as well as other factors that may influence these two vital systems.
In the first chapter interactions between reproductive effort and immune function in 22 female highveld mole-rats (5 reproductive females and 17 non-reproductive females) is investigated by stimulating reproductive competition amongst females within colonies and monitoring hormonal and haematological parameters. Behavioural observations focusing on agonistic, grooming and sexual behaviour is also included in this chapter mostly as tool to identify reproductive competition amongst females.
The second chapter deals specifically with the effect of the season, gender and reproductive status on a febrile response to an exogenously administered pyrogen. Lipopolysaccharide, a protein produced by gram negative bacteria, was used to induce fever in 37 mole-rats during both winter and summer months. The final chapter explored the relationships between parasite infestation and host gender and reproductive status while concurrently identifying some of the parasites associated with the highveld mole-rat. A total of 46 mole-rats were assessed for intensity of gastrointestinal parasites, 131 for prevelance of cestodes by faecal examination and 85 for intensity and prevalence of ectoparasites. A possible relationship between host group size and intensity of parasitism is explored. Seasonal patterns of the parasites found is also investigated and related to possible seasonal variation in immune function.Zoology and EntomologyUnrestricte
The effect of temperature and photoperiod on selected male reproductive characteristics in two seanonally breeding ( Cryptomys hottentotus hottentotus and Cryptomys hottentotus pretoriae ) and one aseasonally breeding mole-rat species ( Cryptomys damarensis )
Full text linkDissertation (MSc)--University of Pretoria, 2005.Please read the abstract in the section 00front of this documentZoology and EntomologyUnrestricte
Reproductive regulation in female Damaraland mole-rats, Cryptomuys damarensis : physiological and neuroendocrine mechanisms
Full text linkDissertation (MSc (Zoology))--University of Pretoria, 1999.The aim of this study was to elucidate the proximate mechanisms, both social and physiological, responsible for the anovulation observed in non-reproductive, female Damaraland mole-rats (Cryptomys damarensis). To identify the social cues involved in the inhibition of fertility, the histological and endocrine response of the female reproductive axis to different social environments, was investigated. The presence of corpora lutea and increased circulating progesterone concentrations indicates that nonreproductive females ovulate spontaneously when they are housed in the absence of the breeding pair. Since anovulation is due to the inhibition of fertility rather than a lack of copulatory stimulation, it has the potential to play a role in maintaining reproductive skew. The endocrine and neuroendocrine mechanisms responsible for anovulation were also investigated. In comparison to reproductive females (RF), the pituitaries of nonreproductive females (NRF) were found to be desensitised to exogenous gonadotrophin-releasing hormone (GnRH) and contained less luteinizing hormone. However, GnRH priming did not increase pituitary sensitivity. Although there was no apparent difference in the distribution and morphology of GnRH-immunoreactive structures in the brain, a significantly greater concentration of GnRH was found in the brains of NRF compared to RF. This supports the hypothesis that an inhibition of GnRH release, and consequent desensitisation of the pituitary, is responsible for infertility in NRF. Differences in pituitary sensitivity between RF and NRF were apparent following hystero-ovariectomy, in the absence of gonadal steroids. Cortisol concentrations did not differ between RF and NRF. Thus, a gonadal steroid independent pathway, that does not involve the negative effects of stress, appears to be responsible for the inhibition of gonadotrophin secretion. A non-steroidal mechanism does not appear to be mediated through an increased activity of endogenous opioid peptides, since the opioid antagonist, naloxone, had no effect on LH secretion. This study shows that many of the pathways leading to anovulation are common to different forms of natural infertility.Zoology and EntomologyMSc (Zoology)Unrestricte
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Aspects of memory in the Damaraland mole-rat, Cryptomys damarensis : spatial learning and kin recognition
Full text linkDissertation (MSc (Zoology))--University of Pretoria, 2007.African mole-rats (Bathyergidae) exhibit a wide range of social structures ranging from solitary to eusocial. This allows for studies looking at links between sociality and measurable characteristics such as spatial learning and kin-recognition. Furthermore, the existence of species with differing level of sociality allows for comparison between the highly social species and the solitary species. The existence of differences in spatial learning ability and memory between the sexes has long been debated. Eusocial Damaraland mole-rats (Cryptomys damarensis) and solitary Cape mole-rats (Georychus capensis) were tested to see if there were sex or species differences in the ability to locate food in an artificial maze task with the express purpose of investigating spatial learning and memory. Measurements of the time taken to complete the task, the distance travelled, wrong turns taken, and the average velocity at which animals travelled were used to compare performance between animals. Both sexes in each of the species exhibited learning and a decay in memory over time. The Damaraland mole-rat exhibited superior learning and memory retention when compared to the Cape mole-rat. Male Cape mole-rats had superior learning and longer term memory retention when compared to females of the same species. There was no significant difference in learning curves between male and female Damaraland mole-rats, but this species did exhibit a tendency for females to show better medium term memory retention while males performed better on long term memory trials. Species differences are likely to be linked to social organization and possibly the resultant burrow-structure in the natural environment, while sex-differences may be due to differing life histories. Kin-recognition is important in maintaining the social structure and hierarchy in the eusocial species of African mole-rat, Cryptomys damarensis. Opposite sex sibling pairs from reproductively quiescent colonies were tested to see if exposure to colony urine odour would reinforce recognition of opposite sex siblings and the concomitant incest avoidance. Control sibling pairs from the same colonies were exposed to water. Mating, social, and non-social behaviours were measured in all sibling pairs. In addition, urinary levels of cortisol, progesterone and testosterone were measured to examine the interaction between four factors: colony olfactory cues (urinary odour), hormone levels, mating behaviour and relatedness. Exposure to urinary odour reinforced recognition and was correlated to a decrease in mating behaviour. Hormonal assays suggest that female hormone levels are modified based on exposure to colony urine odour, while males are not affected. Olfactory cues such as colony urinary odour is linked to the alteration and correlation of hormone levels and mating behaviour. The Damaraland mole-rat and other species in the family Bathyergidae provide a useful system for investigating aspects of learning and memory, as well as the potential correlation between cognitive processes and sociality.Zoology and Entomologyunrestricte
Personality, hormonal correlates and parasite load in the eastern rock elephant shrew
Full text linkDissertation (MSc)--University of Pretoria, 2014.Inter-individual variation in behaviour, or as it has now come to be known, personality, has been shown to affect many different components of fitness in animals. A concept that used to be thought of as background ‘noise’ has come to explain much of the variation we observe within populations and between individuals. The personality of an animal can affect how an animal utilises its environment. In a heterogeneous environment this may increase the potential to find limiting resources, such as mates. However, it may also result in different risks experienced by the animal, such as the number of parasites in may be exposed to. To date, links between personality and parasites have rarely been studied although it is a commonly held concept that more exploratory, bolder individuals should have greater parasite loads. As with individual differences in behaviour, individuals may differ in their circulating hormone profiles. Hence it has been proposed that personality can potentially be shaped by these circulating hormone concentrations with shyer individuals having higher corticosteroid (i.e. cortisol and corticosterone) concentrations while bolder ones may have higher testosterone levels. However, corticosteroids may also be elevated by stressors such as parasites. Similarly, animals that produce more testosterone may have reduced immune-abilities as suggested by the immunocompetence handicap hypothesis. These animals would also protect larger territories and fight rather than flee from potential conspecifics. Consequently, correlations between personality with both parasitic infestation and hormone concentrations have been suggested. In the current study we examined this relationship in the eastern rock sengi (Elephantulus myurus) or elephant shrew that is endemic to southern Africa. They are monogamous, sexually monomorphic and both sexes maintain and defend home ranges year-round. In the wild these animals also have large diversity of ectoparasites with two tick, one mite and one louse species being the most important. Burdens of these varied seasonally but not with sex. Personality was highly correlated across time and contexts suggesting a behavioural syndrome with reactive (more exploratory, bold and aggressive) and reactive (less exploratory, shy and submissive) types for E. myurus. In addition, personality was repeatable within individuals captured over a long term period. Personality scores suggested increasing reactivity with increasing body condition. At the same time only one of the four main ectoparasite species was affected by personality with burdens increasing with increasing reactivity. This suggests that correlations between personality and parasites may depend on the parasite species and that more studies should be done with multiple parasites when evaluating this relationship. We found consistently high levels of urinary C and low T throughout the study with no correlations of either hormone with our personality measures. The former may in part be due to the large abundances of ectoparasites while the monogamous mating system and year-round territorial defense by both sexes could account for low T. Consequently, the current study does not support some of the frequently assumed links between personality and other traits but highlights the need to explicitly consider mating system and multiple parasite species when addressing similar questions.DST-NRF SARChI Chair of Behavioural Ecology and PhysiologyZoology and EntomologyMScUnrestricte
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