UWCScholar :: Browsing by Author "Couldridge, Vanessa"

Browsing by Author "Couldridge, Vanessa"

Now showing 1 - 14 of 14

Acoustic signalling in bladder grasshoppers (orthoptera: pneumoridae)
(University of the Western Cape, 2022) Lagaa, Sasya; Couldridge, Vanessa
Sound plays a vital communicative role in many Orthopteran insect species. Acoustic signals are often used during courtship behaviour and mate location. The Pneumoridae, commonly referred to as bladder grasshoppers, are a family of insects native to southern and eastern Africa. They are highly adapted for long-distance sound communication, with the males emitting very loud advertisement calls that are typically distinctive to each species. However, relatively few previous studies have examined sound communication within the entire family, and little is known about interspecific variation in signals and how this relates to evolutionary history. The aim of this study was to compare acoustic signal characteristics, as well as the morphology of the sound-producing structures, across multiple species in order to better understand morphological constraints on sound production.
An acoustic, genetic and morphological review of the genus Bullacris (Orthoptera; Pneumoridae)
(University of the Western Cape, 2017) Gordon, Mikhaila Leigh; Couldridge, Vanessa
Bladder grasshoppers (Orthoptera: Pneumoridae) are nocturnal African herbivores that are endemic to the coastal regions of southern Africa. They rely heavily on sound communication for mate location and have a unique body structure, with an inflated abdomen seen only in males that aids in sound production. They have a continuous distribution that extends along the coast of South Africa from Namibia, into the eastern regions of Mozambique and beyond, as far as Uganda. Bullacris is the largest genus within the Pneumoridae family. Members of this genus are mostly found within South Africa and inhabit different vegetation biomes, namely the Succulent- Karoo, Fynbos and Savannah biomes. There are currently seven described species within the genus, based solely on morphological differences. However, these morphological differences are not well defined for all species pairs, leading to some degree of uncertainty in species delineation.
The behaviour and feeding ecology of extralimital giraffe within Albany Thicket vegetation in the Little Karoo, South Africa
(University of the Western Cape, 2018) Paulse, Jamie; Couldridge, Vanessa; Cupido, Clement; Deacon, Francois
Due to their popularity for tourism, giraffes are being introduced into Thicket areas within the Little Karoo region of the Western Cape. However, information regarding the activity budgets and diet selection of these giraffes is lacking. Therefore, this study aimed to achieve three objectives; to determine the diurnal activity budget, diet composition and browsing levels, and the estimated browsing capacities of extralimital giraffe. The study was conducted on two privately owned farms, namely Kareesbos Private Game Reserve and Tsumkwe Private Game Reserves. Observations were completed on both study sites using the interval scan method, whereby observations were conducted on all visible individuals from 6 am – 6 pm for four days every 3 months (winter, spring, summer and autumn). Observations found browsing to be the most dominant activity displayed by both populations, with walking and rumination being the second and third most dominant activity. Females browsed more than males in both study sites. Dietary observations showed four species (Pappea capensis, Portulacaria afra, Euclea undulata and Searsia longispina) and five species (Searsia longispina, Euclea undulata, Pappea capensis, Vachellia karroo and Grewia robusta) to comprise approximately 90% and 80% of their diet in Kareesbos and Tsumkwe respectively. The importance of flower bearing species (Lycium spp. and Rhigozhum obovatum) increased during the spring and summer seasons in both study sites. In addition to the diet selection, browsing by both giraffe populations was shown to occur mostly below 2 m. Estimated browsing capacities for Kareesbos and Tsumkwe were 25 and 21, and 107 and 88 ha per giraffe, respectively, for the respective browse height strata of less than two metres and five metres. It is suggested that browsing capacities of less than two metres be considered when stocking giraffe and the number of individuals adjusted accordingly on each farm, due to the continuous low browsing of giraffe at less than two metres. Furthermore, results indicate that these giraffes have adapted to take advantage of forage available in ecosystems outside their natural ranges. Low foraging heights suggests possible niche overlap with other browsers, which may result in increased competition for food when it becomes limited. Long term ecological monitoring of extralimital populations and appropriate management procedures are therefore required to avoid the displacement and degradation of indigenous fauna and flora within the Little Karoo, and possible mortalities amongst the giraffe populations.
Blood cell histology of Homopus areolatus: effects of season and cohort
(University of the Western Cape, 2015) Sparks, Sharna; Hofmeyr, Emer. Margaretha D.; Couldridge, Vanessa
Homopus areolatus is an endemic terrestrial tortoise that resides in a Mediterranean type of climate, which is characterised by winter rainfall and mild winter temperatures. Within ectotherms, such as H. areolatus, physiological changes are elicited by changes in the ambient temperature. These physiological changes are evident in the blood profile of reptiles. I described the morphology of immature and mature erythrocytes, leukocytes as well as thrombocytes of H. areolatus. Additionally, I evaluated erythrocytes, leukocytes and thrombocytes to assess the effects of season and cohort on these cells. Blood samples were collected in 2000 and 2001 at Elandsberg Nature Reserve in the Western Cape from H. areolatus cohorts (female, male, juvenile) in all seasons (spring, summer, autumn, winter). Blood smears were made and stained with modified Giemsa stain. SigmaStat was used for all statistical analysis. Immature erythrocyte types within H. areolatus included basophilic rubricytes, polychromatophilic rubricytes and polychromatophilic erythrocytes. Upon my evaluation, I encountered evidence to suggest that small and large immature erythrocytes possibly developed from two distinctive lineages. Further research is required to discern which lineage gave rise to which immature erythrocyte type. Cohort had no effect upon immature erythrocytes. Erythropoiesis was most prevalent during winter and spring within H. areolatus. Aberrant features of erythrocytes appeared to be more prevalent during autumn, which signified the driest season with limited food and water. Mature erythrocytes play a huge role in oxygen transport and metabolism in individuals. Factors such as size and shape are relevant since small, mature, ellipsoidal erythrocytes transport oxygen more efficiently than large, spherical erythrocytes. In H. areolatus small, mature, ellipsoidal erythrocytes appeared to be most prevalent during spring and summer. During winter however, large, spherical erythrocytes appeared to be most prevalent. Thrombocytes and seven types of leukocytes were observed within H. areolatus, namely heterophils, lymphocytes, eosinophils, basophils, monocytes, plasma cells and azurophils. Among cohort and season heterophils were most prevalent overall, followed by lymphocytes and eosinophils respectively. Basophils, monocytes, plasma cells and azurophils were present but overall, were relatively few. H. areolatus appeared to be healthy, and leukocyte counts as well as its dimensions appeared to be in accordance with other reptilian studies. This study serves as the first baseline haematological reference forH. areolatus. The study forms the second of its kind on South African tortoises, only one other haematological study has been done namely, P. geometricus which is a sympatric species to H. areolatus.
The diurnal activity budgets of extralimital giraffe (Giraffa camelopardalis giraffa) in the Western Cape Province, South Africa
(Wiley, 2023) Paulse, Jamie; Couldridge, Vanessa; Cupido, Clement
Despite being an extralimital species in the region, South African giraffes (Giraffa camelopardalis giraffa, Schreber 1784) are continuously being introduced into the Albany Thicket Biome of the Western Cape Province of South Africa. This study aimed to determine the diurnal activity budgets of two extralimital giraffe populations in the Western Cape of South Africa. Diurnal activity budgets are important to provide baseline information on the adaptability of species in newly introduced areas and for more detailed ecological studies such as those relating to habitat suitability, animal–plant interactions and interactions with other resident animals.
Ecology and diet of the caracal (Caracal caracal) on lethal and non-lethal control farms in the Karoo
(University of the Western Cape, 2020) Jooste, Erin Cecilia; Couldridge, Vanessa
Human-wildlife conflict is an ongoing issue worldwide. Within South Africa, human-carnivore conflict (HCC) as a result of carnivore depredation on small-livestock causes large-scale losses, and promotes the use of predator management tools by farmers. Despite being one of the major offenders involved in HCC, caracals, and their ecology in particular, are understudied. This is mainly due to high levels of persecution, coupled with their elusive nature. Within the Karoo region of South Africa, pastoralists make use of large-scale lethal predator controls in an attempt to remove the offenders, or non-lethal predator controls to protect livestock and deter predators. However, the effects of these various predator control techniques on caracal ecology have not been widely tested. Therefore, the aims of this thesis were, firstly, to assess caracal diet on lethal and non-lethal treatment farms in the Karoo; secondly, to investigate the drivers of caracal habitat selection on a non-lethal farm in the Karoo; and finally, to evaluate caracal activity patterns on the non-lethal farm. To do this, I made use of two non-invasive techniques (i.e. scat analysis and camera trapping). Caracals appeared to favour natural prey across all sites, with livestock remains only found in scats collected at the lethal treatment farm. Caracals had the broadest dietary breadth on the non-lethal treatment site, and the narrowest on the lethal treatment site. The main components of caracal diet included small mammals, lagomorphs, rock hyraxes (Procavia capensis), wild ungulates and arthropods. Caracal habitat selection was explained by resource dispersion and environmental features Interestingly, the presence of livestock was not a major consideration in caracal habitat selection. Caracals were mainly nocturnal but became increasingly crepuscular during winter. In addition, caracal activity overlapped significantly with black-backed jackals (Canis mesomelas), lagomorphs and common duikers (Sylvicapra grimmia). Caracals showed plasticity in their activity patterns based on seasonal temperature fluctuations, and partially human avoidance. This study contributes to understanding how caracal ecology differs on differently managed livestock farms. Throughout this study, the importance of both a natural prey base, as well as natural lands to caracal survival have been revealed. These findings can contribute to caracal conservation in HCC areas.
Ecology and diet of the caracal (Caracal caracal) on lethal and non-lethal control farms in the Karoo
(University of the Western Cape, 2020) Jooste, Erin Cecilia; Couldridge, Vanessa
Human-wildlife conflict is an ongoing issue worldwide. Within South Africa, human-carnivore conflict (HCC) as a result of carnivore depredation on small-livestock causes large-scale losses, and promotes the use of predator management tools by farmers. Despite being one of the major offenders involved in HCC, caracals, and their ecology in particular, are understudied. This is mainly due to high levels of persecution, coupled with their elusive nature. Within the Karoo region of South Africa, pastoralists make use of large-scale lethal predator controls in an attempt to remove the offenders, or non-lethal predator controls to protect livestock and deter predators. However, the effects of these various predator control techniques on caracal ecology have not been widely tested. Therefore, the aims of this thesis were, firstly, to assess caracal diet on lethal and non-lethal treatment farms in the Karoo; secondly, to investigate the drivers of caracal habitat selection on a non-lethal farm in the Karoo; and finally, to evaluate caracal activity patterns on the non-lethal farm.
The effect of anthropogenic noise and weather conditions on male calls in the bladder grasshopper Bullacris unicolor
(Taylor and Francis Group, 2021) Sathyan, Rekha; Couldridge, Vanessa
Acoustic communication in animals relies upon specificcontextsandenvironments for effective signal transmission. Increasing anthropo-genic noise pollution and different weather conditions can disruptacoustic communication. In this study, we investigated call parameterdifferences in the bladder grasshopperBullacris unicolorinhabitingtwo sites in close proximity to each other that differed in their noiselevels. Calling activity was monitored via passive acoustic recorders.Weather conditions, including wind speed, temperature and humid-ity, were also recorded. We found that the interval between succes-sive calls increased with higher noise levels at both sites, and the peakfrequency became lower. The total number of calls detected alsodecreased with anthropogenic noise, but this relationship was onlyevident at the noisier site. In addition, grasshoppers shifted the timingof their calls to later in the night at the noisier site, possibly to takeadvantage of relatively lower noise levels.
Genetic and morphological comparisons within the orthopteran family Pneumoridae
(University of the Western Cape, 2019) Laubscher, Maxine; Couldridge, Vanessa
Bladder grasshoppers belong to the order Orthoptera, ancient family Pneumoridae and Superfamily Pneumoroidea. This small group of grasshoppers are sound producing, nocturnal, herbivorous grasshoppers endemic to the coastal regions of southern Africa. Very little genetic work has been done on these grasshoppers, and there is some taxonomic confusion regarding the validity of some species descriptions. The aim of this study was to provide much needed clarity on the true taxonomic diversity and polymorphic attributes within the Pneumoridae, focusing on selected taxa of uncertain status. Bladder grasshoppers show distinct discontinuous polymorphism, resulting in two clearly different male morphs utilizing two different mating strategies. Primary males make use of acoustic communication for mate location. Secondary males (alternate males) are significantly smaller and employ a “sneaker” or satellite strategy where they exploit the calling between duetting couples to locate the females before the primary male. Three species of bladder grasshoppers have been described (Parabullacris vansoni, Paraphysemacris spinosus and Pneumoracris browni) that only have an alternate male morph. The validity of these species descriptions has come into question with the discovery of alternate male morphs in at least three other species (Bullacris discolor, B. membracioides and B. obliqua). Thus, the species described by Dirsh (1963) may simply be alternate males of existing species. However, to date there have been no studies looking at the genetics of alternate males, which would definitively establish whether they are conspecific with primary males.
Intra- and inter-population variation in the bladder grasshopper Bullacris unicolor
(University of the Western Cape, 2014) Sathyan, Rekha; Couldridge, Vanessa
Although the processes that promote biodiversity and speciation remain poorly understood, ecological factors are thought to be one of the causal agents responsible for promoting variation. Bladder grasshoppers (Orthoptera; Pneumoroidea) are a group of endemic southern African insects that provide an ideal model system to study the role of ecology in speciation. All species rely on acoustic communication for mate location, with males producing an extremely loud advertisement call that is highly species specific. Any alteration to the male call would thus likely have implications for species integrity. In this study, I examined geographic variation as well as potential ecological drivers of biological diversity within Bullacris unicolor, a variable and wide-ranging species of bladder grasshopper. The main aims of the study were to characterise the extent of acoustic and morphological variation among individuals sampled from five geographic locations and to correlate this variation with environmental data and host plant use. At the inter-population level, I found significant differences between populations with respect to both morphological and acoustic characters. Results of multivariate analyses showed significant differences in the body length, pronotum length and head width of males and in the pronotum length, abdomen width and head width of females. Similarly, the acoustic signals of males from the five populations differed significantly in both temporal and frequency components, with all but one variable (peak frequency of the introductory syllables) showing a significant difference. However, there was no correlation between morphological and acoustic variables among populations, and acoustic characters showed far greater divergence among populations than did morphology. In both males and females, the morphological variables that differed among populations were negatively correlated with mean annual temperature, indicating that grasshoppers are larger in areas with lower temperatures. Also, some of the call characteristics of males were correlated with temperature, precipitation, altitude, and slope. Although grasshoppers were observed feeding on a range of host plant species, neither morphology nor signal characteristics were found to vary according to host plant. At the intra-population level, multivariate analyses revealed that all acoustic characters differed significantly among individuals. Morphology may be influencing signal properties within a population to some extent as there were significant correlations between some of the call characters and both abdomen width and tibia length, with lengths of these two morphological variables being positively correlated with temporal components of the call and abdomen width being negatively correlated with frequency components. I also found a significant difference in the carrier frequency of male calls, as well as in some of the morphological characters of males and females, according to host plant. This indicates that host plant use has a greater effect on variation at the intra-population level than at the interpopulation level. In conclusion, the results of my study reveal significant variation in the morphology and acoustic signals of B. unicolor, both within and among populations, and suggest that this variation is at least partially related to ecological factors.
The invasive guttural toad, Amietophrynus gutturalis
(University of the Western Cape, 2015) Telford, Nicolas S.; Couldridge, Vanessa; Channing, Alan
The guttural toad, Amietophrynus gutturalis, Power 1927, is a common toad with a broad geographic range through much of temperate, sub-tropical and tropical southern and central Africa. Introduced to the islands of Mauritius and Reunion in the 1960’s, and subsequently to Cape Town in the 1990’s, the species has become invasive in its extra-limital ranges. Determining the invasion history of a species provides valuable information for conservation biologists and managers and it is fundamentally important for improving our understanding of the underlying processes of biological invasions. This study aimed to determine the source populations of the extra-limital populations from Mauritius and Cape Town. Furthermore, studies investigating genetic diversity and demographics of African Bufonidae are largely absent from the literature. Understanding the evolutionary history of the species may also assist with determining their invasive ability and identifying similar features in other bufonids such as Amietophrynus regularis and A. xeros. Using mtDNA sequence data from the 16S and ND2 markers four geographically distinct clades were identified through Bayesian phylogenies and haplotype networks. However, a spatial analysis of molecular variance (SAMOVA) indicated a grouping structure of three clades. A total of 16 haplotypes were identified from 53 samples for the 16S marker and 22 haplotypes were identified from 43 samples for the ND2 marker. Both the Mauritius and Cape Town invasive populations were found to have originated from the eastern clade. However, they matched the common haplotype from this region which was found across a vast area that spans the KwaZulu-Natal province and into the Mpumulanga and Limpopo provinces. This did not allow for identifying a more precise region for the origin of the founder populations. The presence of haplotypes unique to the Cape Town invasive population, which group with the eastern clade, indicates that there has potentially been more than one introduction event. Demographic analysis revealed a recent population expansion in both the northern (Fs = -2.92) and the eastern clades (Fs = -5.03). Significant genetic variation was found among groups (93.92%), with low variation among populations and among populations within groups. Population pairwise differences were found to be significantly different between all clades except between the central and the southern clade. There was a negligible difference in the genetic diversity of the invasive populations when compared to the eastern clade. The eastern clades’ genetic diversity was low compared to the two other clades and demographic analysis revealed that this region has undergone the most recent population expansion. The negligible difference between the eastern clades’ genetic diversity and both invasive populations indicate that founder effects and genetic bottlenecking should have no impact on the invasive populations.
Revealing the factors that promote divergence in the Bladder Grasshopper Bullacris unicolor (Orthoptera; Pneumoroidea)
(University of the Western Cape, 2019) Sathyan, Rekha; Couldridge, Vanessa; Engelbrecht, Adriaan
Variation in sympatric and allopatric populations is believed to be a precursor to eventual speciation. The dispersion of genes from one gene pool into another is prevented by various processes, including the founder effect, sexual selection, ecological differences and random genetic divergence. Examining patterns of intraspecific variation in phenotypic and genotypic traits may thus provide valuable insights into the processes that govern species origination. Bladder grasshoppers (Orthoptera; Pneumoroidea) are an ideal model system to investigate patterns of geographic and ecological divergence due to their high host plant specificity, low dispersal and distinctive acoustic signals. This dissertation investigates intraspecific diversification in the bladder grasshopper Bullacris unicolor (Orthoptera: Pneumoroidea). Recent research on this species has shown significant intra- and inter-population variation in male advertisement calls and morphological characters. However, the exact cause of this variation has remained unclear. Furthermore, a previous study showed that the calls of B. unicolor from one particular population are highly differentiated from other populations, possibly due to the effects of anthropogenic noise. Here we aim to examine the drivers of diversity within Bullacris unicolor by embracing a multidisciplinary approach that encompasses the effects of environmental factors, genetics, anthropogenic noise and host plant associated divergence.
Species recognition and reproductive isolation in Malawi cichlid fishes, Metriaclima estherae and M. callainos (Teleostei: Cichlidae)
(University of the Western Cape, 2019) Nyalungu, Nonhlanhla Precotia; Couldridge, Vanessa; Engelbrecht, Adriaan
Cichlids are one of the most diverse groups of fishes in the world. The highest concentration of cichlids is found in Lake Malawi, where over 1500 species are recorded to occur, which are dominated by the haplochromine tribe. Several authors proposed that sexual selection has been a major contributor in the high rate of speciation of haplochromine cichlids. However, sexual selection alone may not be sufficient to fully explain high speciation rates among cichlids. Many closely related cichlids in Lake Malawi differ only in coloration, yet occur in sympatry. It is still not fully understood how they remain reproductively isolated. Previous studies suggest that visual cues are primarily used for reproductive isolation and species recognition. In the current study, visual, chemical and acoustic cues were investigated to observe how they may potentially influence species recognition and reproductive isolation between two closely related species, Metriaclima estherae and M. callainos, as well as between alternate colour morphs of M. estherae.
Tonic immobility in two species of Southern African catsharks
(University of Western Cape, 2020) Sebastian, Lemόne Margeaux; Couldridge, Vanessa
Tonic immobility (TI) can be defined as an unlearned behavioural response described by a physical state of immobility. This behaviour can last from a few seconds up to several hours. Tonic immobility in sharks has not been investigated extensively, despite being observed and used widely. Due to this limited research, there is still uncertainty about the significance of this response, especially in smaller shark species. Anecdotal evidence suggests that females may enter a tonic state during courtship, but this has never been scientifically investigated. Alternatively, tonic immobility may function as an anti-predator response. The aim of this study was thus to examine the behaviour and physiology associated with tonic immobility in two closely related species of catshark, Haploblepharus edwardsii and Haploblepharus pictus, and to test for differences between males and females (if the evolutionary significance of TI was related to courtship), and between the two species (if TI evolved in response to species-specific drivers).

Browsing by Author "Couldridge, Vanessa"

Results Per Page

Sort Options