UWCScholar :: Browsing by Author "Hofmeyr, Margaretha D."

Browsing by Author "Hofmeyr, Margaretha D."

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Accurate automated quantitative imaging of tortoise erythrocytes using the NIS image analysis system
(Taylor & Francis, 2013) Walton, S.; Hofmeyr, Margaretha D.; van der Horst, Gerhard
The standard method for assessing blood cell characteristics using an ocular micrometer is time-consuming and limited. We used the Nikon NIS Elements imaging software and May-Grünwald-Giemsa staining to determine whether automated image analysis is suitable for rapid and accurate quantitative morphometry of erythrocytes. Blood was collected during four seasons from 126 geometric tortoises and the blood smears were evaluated for cell (C) and nuclear (N) characteristics of the erythrocytes. We measured area, length (L), width (W), perimeter, elongation and pixelation intensity, and calculated L/W and N/C areas. Erythrocyte size differed among cohorts; females, the larger sex, had smaller erythrocytes than either males or juveniles. Males had more elongated erythrocytes than females and erythrocytes of adults were more elongated than those of juveniles. Erythrocyte size and shape influence the efficiency of gas exchange owing to surface area to volume ratios, which are greater for small, elongated cells than for large, round cells. The high N/C ratio and low pixelation intensities of males and juveniles indicate that they may have had more immature erythrocytes in their circulation than females. The use of pixelation intensity to indicate the presence of immature erythrocytes was validated by seasonal differences that corresponded to the biology of the tortoises. Pixelation intensity was lowest in winter. We found that automated image analysis is a rapid and reliable method for determining cell size and shape, and it offers the potential for distinguishing among developmental stages that differ in staining intensity. The method should be useful for rapid health assessments, particularly of threatened species, and for comparative studies among different vertebrates.
Body of evidence: forensic use of baseline health assessments to convict wildlife poachers
(CSIRO Publishing, 2013) Henen, Brian T.; Hofmeyr, Margaretha D.; Baard, Ernst H. W.
CONTEXT. Given the immense impact of wildlife trade, disease and repatriations on populations, health assessments can" "provide powerful forensic material to help convict wildlife poachers and minimise risks of releasing unhealthy wildlife." AIMS. We aimed to use reference ranges to assess the health of conﬁscated tortoises, to illustrate forensic application of these ranges, and to advance analyses for future applications." METHODS. We used analyses of variance (ANOVA) and covariance (ANCOVA), and composite indices, to compare wild and conﬁscate tortoise body condition, haematocrit and haemoglobin concentration of males and females of three tortoise species. Subsequently, we used multivariate statistics (e.g. discriminant analyses) to evaluate the relative importance of species, sex and group (wild or conﬁscate) on tortoise condition and haematology." KEY RESULTS. Our initial statistical tests demonstrated, at P < 0.05 to P < 0.0005, that conﬁscate body condition and haematology were compromised compared with that of wild tortoises. Subsequently, discriminant analyses strongly discriminated between most wild and conﬁscate groups (P < 0.0001), correctly classiﬁed individual health as wild or conﬁscate 80–90% of the time, indicated that species and sex effects were stronger than was the wild-conﬁscate category, and provided discriminant functions for use on other taxa and studies." CONCLUSIONS. The health assessments discriminated well between wild and conﬁscate tortoises. The results had considerable forensic value, being relevant, quickly generated using portable ﬁeld equipment, reliable, accurate, easy to explain and convey in terms of likelihood in a court of law, synergistically consistent among variables and groups, a strong rebuttal to the poachers’ speciﬁc statements, and consistent with other types of evidence. Multivariate analyses were consistent with, and more prudent and powerful than, the original statistical analyses. Discriminant functions can be applied in future studies and on other chelonian species, and should be developed for other wildlife species." IMPLICATIONS. Reference ranges provide considerable value for forensics, diagnostics and treatment. Given the disease risks resulting from the massive scale of wildlife trade and release, reference ranges should be developed for more species."
Ecology and morphology of the Kalahari tent tortoise, Psammobates oculifer, in a semi-arid environment
(University of the Western Cape, 2012) Keswick, Tobias; Hofmeyr, Margaretha D.; Faculty of Science
Southern Africa harbours one-third of the world's Testudinid species, many of which inhabit arid or semi-arid areas, but ecological information on these species is scant. I studied the habitat, morphology and ecology of Kalahari tent tortoises over 13 months in semi-arid Savanna at Benfontein farm, Northern Cape Province, South Africa. In order to allow continuous monitoring of individuals, I attached radiotransmitters to males and females, split equally between two habitats, sites E (east) and W (west), with apparent differences in vegetation structure. Results of the study were based on data obtained from 27 telemetered tortoises and 161 individuals encountered opportunistically. Female Kalahari tent tortoises were larger than males and the sex ratio did not differ from 1:1. Based on person-hours to capture tortoises, the population appeared to have a low density, with more time required to capture a juvenile (35 hours) than an adult (10-11 hours). The frequency distribution of body size ranges was indicative of recruitment. Relative age, based on annuli counts, suggested that males were younger than females, perhaps because males as the smaller sex are more predation-prone than females. Linear relationships between annuli counts and shell volume indicated that, after reaching sexual maturity, female body size increased faster in volume than did male body size, possibly because a larger volume may enhance female reproductive success. Body condition differed between sites, sexes and among seasons. The hot and dry summer may account for low summer body condition, whereas vegetation differences and size effects, respectively, may account for the low body condition of tortoises in site W and in males. Site E was sandy with grasses, particularly Schmidtia pappophoroides, being the prevalent growth form. This habitat resembled a Savanna vegetation type Schmidtia pappophoroides – Acacia erioloba described for a neighbouring reserve. Site W was stonier, dominated by shrubs, and was reminiscent of Northern Upper Karoo vegetation (NKu3). Neither site resembled Kimberley Thornveld (SVk4), the designated vegetation type of the area. Differences in substrate and grazing intensity may have contributed to site vegetation differences. Rainfall had an important influence on seasonal vegetation. Short grass abundance correlated with rainfall and annual plants sprouted after spring rain. Refuge use changed according to season and sex. Males selected denser refuges than females did, perhaps because males were smaller and more vulnerable to predation and solar heat. Tortoises selected sparse, short grass as refuges in cool months, probably to maximise basking whilst remaining in protective cover. During hot periods, mammal burrows were preferred to vegetation as refugia. The smaller males spent more time in cover than females, which may be related to predator avoidance or thermoregulation. Females spent more time basking than males, perhaps due to their larger size and to facilitate reproductive processes. Tortoises did not brumate, but through a combination of basking, and orientation relative to the sun in their refuges, managed to attain body temperatures that allowed small bouts of activity. Body temperature for active tortoises was similar among seasons, and was higher for more specialised active behaviours, such as feeding and socialising, than for walking. Increased activity by males in spring could relate to mating behaviour while females were more active in autumn, when they foraged more than males, perhaps due to the high cost of seasonal reproductive requirements. Males displaced further per day than did females, but home range estimates did not differ between sexes. Annual home range estimates varied substantially among individuals: 0.7–306 ha for minimum convex polygons and 0.7–181 ha for 95% fixed kernel estimates. The ability to cover large areas would assist tortoises in finding resources, e.g., food, in an area where resource distribution may be patchy. Differences among seasonal home ranges and movements probably reflect seasonal climatic change; activity areas shrinking when temperatures were extreme. In order to assess the effects of a semi-arid environment on the morphology of P. oculifer, I compared its morphology to that of its ‘cool-adapted’ sister taxon Psammobates geometricus, using live and museum specimens. Both P. oculifer and P. geometricus are sexually dimorphic and differences between the two species could indicate environmental or sexual selection effects, or a combination of the two. The shorter bridge length, which allowed more leg space, and wider front feet in P. oculifer cohorts probably represent traits for manoeuvring in a sandy habitat, while wider heads in P. oculifer possibly relate to interspecific differences in diet. The flatter shell in female P. oculifer, relative to P. geometricus, may represent a trade-off between space for reproductive structures, e.g., eggs, and the need to fit into small refuges, e.g., mammal burrows. Male P. oculifer had wider shells, more space around their hind legs, and wider hind feet than P. geometricus males had, all characteristics which may assist males to fight and mate in a sandy environment.
Effects of season and cohort on the haematology of the geometric tortoise Psammobates geometricus.
(University of the Western Cape, 2012) Walton, Shasheen; Hofmeyr, Margaretha D.
The geometric tortoise is one of the world‟s rarest terrestrial tortoises and is endemic to the Southwestern Cape, South Africa. There has been cause for conservation concern for Psammobates geometricus, yet as is common for many species, quantitative physiological research has been lacking. Considering the important role of red blood cells in oxygen circulation, and the role of white blood cells in immune resistance, blood profiles have been used across taxa as a reliable indicator of health status and physiological processes. Forming part of a larger chelonian conservation programme in South Africa, I studied the haematological changes in P. geometricus, to better understand their physiological responses to changes in climatic conditions. Sampled peripheral blood from males, females and juveniles of the largest known wild geometric tortoise population over four seasons (spring, summer, autumn and winter) from August 2000 to June 2001. Blood samples were used to make smears and determine red cell count (RCC), packed cell volume (PCV), haemoglobi concentration (Hb), red cell indices and differential white cell counts. Digital imaging analysis was used for the histological evaluation of stained blood smears, including descriptions of red and white blood cell morphologies, as well as erythrocyte developmental stages. In the cooler periods, geometric tortoises showed low Hb and mean cell haemoglobin concentration values. Erythrocytes were larger and rounder in winter and spring, which were likely due to hydration states. In addition, increased numbers of immature erythrocytes in circulation suggested an erythropoietic response in winter and spring. This regenerative response is common in reptiles emerging from periods of limited activity and is associated with increasing primary production following rainfall events. In the following summer and autumn, increased mean cell haemoglobin concentrations suggested elevated metabolic rates influenced by rising temperatures. This would seem pertinent to meet the extra physical demands associated with foraging effort in the season characterised with limited water and food supply, and mating behaviour, which occurs in the summer. Low body conditions across all cohorts provided evidence for nutrition stress, while erythrocyte size, shape and degenerative responses indicated dehydration stress. Physiological responses to seasonal influences are specific to growth or reproductive demands and differed for each cohort. Males experienced increased Hb, PCV, RCC, and erythrocyte sizes in summer and autumn, which relate to the erythropoieticstimulating effects of androgens. Female erythropoietic cycles in spring accommodate the increased metabolic demands of increased foraging needed for a larger body size and egg production, and again in autumn again for vitellogenesis. Juvenile tortoises showed minimal differences, and could indicate species-specific responses to environmental changes. A spring-related erythropoiesis was observed in juveniles while during summer and autumn, juveniles showed less evidence for dehydration stress than in adults. No haemoparasites were observed in peripheral blood. Seven leukocyte types were identified and included heterophils, eosinophils, basophils, lymphocytes, plasma cells, monocytes and azurophils, in addition to thrombocytes. Heterophils were the most abundant leukocyte, followed by lymphocytes and eosinophils while monocytes and basophils were equally low; plasma cells and azurophils were rare. Heterophil counts were higher in spring than in summer and autumn, and in summer, were more abundant in females than in juveniles. Eosinophil counts were low in spring for all cohorts, and additionally, female and juvenile counts were low in summer. Eosinophils in juveniles were significantly lower than in adults in winter and spring. Lymphocyte numbers increased in autumn for all cohorts, while summer counts were higher in juveniles than in adults. Basophils and monocytes showed minimal seasonal changes, although basophil counts in females in winter tended to be high. Thrombocytes were lowest in spring for all cohorts. Understanding the physiological responses associated with seasonal changes and for each cohort is critical for effective chelonian conservation management. Results obtained from this study indicate a clinically healthy population of Psammobates geometricus and represented the first of this kind to establish baseline haematological reference data for this Critically Endangered tortoise species.
How many species of angulate tortoises occur in Southern Africa? (Testudines: Testudinidae: Chersina)
(Wiley-Blackwell, 2020) Hofmeyr, Margaretha D.; Spitzweg, Cäcilia; Vamberger, Melita
Using range-wide sampling and 1,143 bp of mtDNA (cytochrome b gene) and 14 microsatellite loci, we examined genetic differentiation in the widely distributed Southern African angulate tortoise (Chersina angulata). We found evidence for two genealogical lineages that differ in both genetic marker systems and their preferred habitat conditions. According to a fossil-calibrated molecular clock for all African tortoise lineages using 1,870 bp mitochondrial and 1,416 bp nuclear DNA, the two lineages of C. angulata diverged in the Pliocene (approx. 3.8 million years ago). Species distribution models reveal that the ranges of the two lineages shifted little since the Last Glacial Maximum, which is in agreement with the demographic population descriptors suggestive of stationary populations that did not experience expansion. One lineage occurs in the west, and the other in the south of the extant distribution range. In the geographic contact zone, the two lineages hybridize extensively, providing evidence for their conspecificity under the biological species concept. Each lineage could be recognized as a distinct subspecies, but the ill-defined geographic origins of the type material of the available names prevent their identification with any taxon.
In quest of contact: phylogeography of helmeted terrapins (Pelomedusa galeata, P. subrufa sensu stricto)
(PeerJ, 2018) Vamberger, Melita; Hofmeyr, Margaretha D.; Ihlow, Flora; Fritz, Uwe
Based on rangewide sampling and three mitochondrial and two nuclear markers (together up to 1,850 bp and 1,840 bp, respectively), we examine the phylogeography of two helmeted terrapin species (Pelomedusa galeata and P. subrufa sensu stricto) and infer shifts of climatically suitable spaces since the Last Glacial Maximum using a modeling approach. Whilst P. galeata displays significant phylogeographic structuring across its range and consists of two deeply divergent lineages that could represent distinct species, P. subrufa shows no obvious phylogeographic differentiation. This seems to be related to historically stable or fluctuating ranges. One of the lineages within P. galeata appears to be confined to the westernmost, winter-rainfall region of South Africa and deserves special conservational attention due to the scarcity of surface water. The other lineage is distributed further east and is differentiated in three weakly supported subclades with parapatric distribution; one occurring inland, and two along the south and east coasts, respectively. As far as is known, P. subrufa occurs in South Africa only in the northeast of the country (Limpopo, Mpumalanga) and we report the species for the first time from the Lapalala Wilderness Area in the Waterberg region (Limpopo), approximately 350 km further west than previously recorded. We confirmed the occurrence of P. galeata only 80 km south of Lapalala. Thus, a sympatric occurrence of P. galeata and P. subrufa is possible. Another putative contact zone, for the two lineages within P. galeata, must be located in the Western Cape region, and further contact zones are likely for the eastern subclades within P. galeata. The nuclear loci provided no evidence for gene flow across taxa or genetic clusters within taxa. Future investigations should use denser sampling from putative contact zones and more nuclear markers to re-examine this situation. Despite few phylogeographic studies published for southern African biota, it seems likely that differentiation follows general rules, and that climate and physiographic barriers (e.g., the Great Escarpment) have shaped phylogeographic patterns.
Leopard tortoises in southern Africa have greater genetic diversity in the north than in the south (Testudinidae)
(Wiley, 2018) Spitzweg, Cäcilia; Hofmeyr, Margaretha D.; Fritz, Uwe; Vamberger, Melita
In contrast to mammals, little is known about the phylogeographic structuring of widely distributed African reptile species. With the present study, we contribute data for the leopard tortoise (Stigmochelys pardalis). It ranges from the Horn of Africa southward to South Africa and westwards to southern Angola. However, its natural occurrence is disputed for some southern regions. To clarify the situation, we used mtDNA sequences and 14 microsatellite loci from 204 individuals mainly from southern Africa. Our results retrieved five mitochondrial clades; one in the south and two in the north-west and north-east of southern Africa, respectively, plus two distributed further north. Using microsatellites, the southern clade matched with a well-defined southern nuclear cluster, whilst the two northern clades from southern Africa corresponded to another nuclear cluster with three subclusters. One subcluster had a western and central distribution, another occurred mostly in the north-east, and the third in a small eastern region (Maputaland), which forms part of a biodiversity hotspot. Genetic diversity was low in the south and high in the north of our study region, particularly in the north-east. Our results refuted that translocations influenced the genetic structure of leopard tortoises substantially. We propose that Pleistocene climatic fluctuations caused leopard tortoises to retract to distinct refugia in southern and northern regions and ascribe the high genetic diversity in the north of southern Africa to genetic structuring caused by the survival in three refuges and subsequent admixture, whereas tortoises in the south seem to have survived in only one continuous coastal refuge
Population ecology of Psammobates oculifer in a semi-arid environment
(Taylor & Francis and UNISA Press, 2013) Keswick, Toby; Hofmeyr, Margaretha D.
We studied the ecology of Psammobates oculifer over 13 months near Kimberley, South Africa, to ascertain if the population’s life history traits conform to chelonian patterns in arid environments. Capture rates were highest in spring and lowest in winter when environmental conditions were respectively most and least favourable for tortoise activity. Body condition did not change from autumn to spring, but reached lower values during the summer drought. Capture effort averaged 5 hours/tortoise, which corresponds closely to that of species with low population densities in arid regions. Population size structure was skewed towards adults, indicative of low recruitment and/or low juvenile survivorship. Females were larger and heavier than males, confirming sexual dimorphism in this species. Body size of cohorts scaled to annuli counts, indicating a close correspondence between body size and age. Telemetered adults deposited one or no growth ring in the year of study; consequently, annuli counts could underestimate adult age. Regression analyses showed that male and female growth rates did not differ, but males matured at a smaller size and younger age than females. The smallest male showing reproductive behaviour had 12 annuli and a shell volume of 157 cm3, while similar measures for females were 14 annuli and 185 cm3. The sex ratio of the population did not differ from 1:1 but the bias towards males in spring, and towards females in autumn, indicates that studies limited to particular seasons can misrepresent life history traits of populations. We concluded that the life history of P. oculifer conforms to chelonian patterns in arid regions.
Seasonal effects on the feeding ecology and habitat of Chersina Angulata in the South Western Cape
(University of the Western Cape, 2008) Joshua, Quinton Ignatius; Hofmeyr, Margaretha D.; Henen, Brian T.
Nearly one-third of the world’s tortoises live in South Africa, but little is known about their habitat requirements and feeding ecology. Chersina angulata, the angulate tortoise, is endemic to southern Africa, with a wide distribution along the western and southern coasts. Because this tortoise occupies a number of different habitat types, it has always been considered a generalist herbivore, although little is known about its diet and other needs. This study evaluates the habitat characteristics and feeding ecology of C. angulata at two study sites in the southwestern Cape, the West Coast National Park (WCNP) and Dassen Island (DI). The WCNP is a large conserved area in the Fynbos biome, along the southwestern coast of South Africa, whereas DI is a small offshore island with low floral and faunal diversity, just south of the WCNP. The efficacy of three methods used to study the feeding ecology of herbivores, focal observations, macroscopic faecal analysis and histological analysis of scats, was evaluated. Plant cover, species diversity, and the variety of growth forms were substantially larger at the WCNP than on DI. In the WCNP, shrubs and grasses were the dominant growth forms but the vegetation also included herbs, succulents, restios, sedges and parasitic plants. A few perennial species such as the grass Ehrharta villosa, shrubs such as Helichrysum niveum, Nylandtia spinosa and Rhus spp., and succulents such as Carpobrotus edulis and Ruschia spp., provided most of the plant cover. DI had a depauperate flora, consisting of succulents and herbs, and ephemeral plants contributed more than perennials did to plant cover throughout the year. The succulents Mesembryanthemum crystallinum and Tetragonia fruticosa provided most of the cover on DI. Angulate tortoises are herbivores and 72 diet plants in 32 plant families were identified to the species or genus level. Several diet species, however, could not be identified. In addition to angiosperms, the tortoises’ diet included mosses, mushrooms, insects,snails and animal faeces. The most important growth forms in the diet were herbs and grasses. The diet of the WCNP tortoises was more diverse than the diet of DI tortoises, but the number of principal food items in the diet did not differ between the two sites. Over an annual cycle, WCNP tortoises had four principal food plants while DI tortoises had five principal food plants. At both sites, principal food plants changed with the season and few plants remained principal food items in more than one season. Cynodon dactylon was a principal food item in three of the four seasons in the WCNP, whereas Trachyandra divaricata was a principal food plant each season on DI. Most principal food plants were grass or herb species but the sedge Ficinia nigrescens, and a succulent that could be identified only to the family level (Aizoaceae), featured strongly in the spring diets of DI and WCNP tortoises, respectively. The three study methods did not provide the same type or quality of information about the feeding ecology of angulate tortoises. The small size and wary nature of angulate tortoises compromised focal studies because it was often not possible to see what the tortoises ate. This method, however, provided the interesting observation that rabbit faecal pellets contributed nearly 30% to summer and autumn diets on DI when food was scarce. Rabbit faeces may not only provide a source of nutrients but may also supplement the microflora, required to digest cellulose, in the tortoises’ guts. Macroscopic evaluation of the tortoises’ scats appeared to be an ineffective method to identify diet plants, and the bulk of the scat mass could not be identified. This indicates that angulate tortoises either selected food low in fibrous content or that the digestive system of the tortoises dealt efficiently with tough plant material. The macroscopic method was the only method that highlighted the large contribution of fruits / seeds to the diet of angulate tortoises. Since the tortoises digested many seeds only partially, or not at all, C. angulata is potentially an important agent of seed dispersal in the southwestern Cape. The macroscopic study showed that on DI, sand made up 28% of the scat mass in spring, whereas sand never made a substantial contribution to the scat composition of WCNP tortoises. Lithophagy may be an important strategy in a depauperate habitat, such as DI, because the abrasive action of sand may help with the digestion of tough plants, or the sand may provide the tortoises with important minerals that are deficient in their food plants.The histological analysis of scats provided the most comprehensive diet list for C. angulata. Selection indices based on data from the histological analysis indicated that angulate tortoises were highly selective in their food choice. Most of the principal food items were selected out of proportion to their availability and the tortoises avoided the most abundant plants in their habitats. Several factors, such as palatability, accessibility and profitability, may have influenced their food choice. The proportional similarity indices for WCNP and DI tortoises, respectively, were 0.31 and 0.16, confirming that C. angulata is a food specialist and not a food generalist as was previously thought. This factor should be considered in the management of this species and in future conservation planning of its habitat.
Seasonal movement and activity patterns of the endangered geometric tortoise, psammobates geometricus
(University of the Western Cape, 2005) Van Bloemestein, Ulric Patrick; Hofmeyr, Margaretha D.; Henen, Brian T.; Dept. of Biodiversity and Conservation Biology; Faculty of Science
Due to the critical status of Psammobates geometricus and the vulnerability of their habitat, there is a need to allocate areas for their protection. The aim of this study was to provide information on the space requirements and activity level of geometric tortoises to facilitate future conservation efforts. The thread-and-spool method was used to compare short-term movements, habitat utilisation, and activity patterns of male and female tortoises over 15 and 20 days respectively, in autumn and spring. Through radiotelemetry, the long-term movements of 10 male and 11 female tortoises were evaluated from April 2002 to April 2003. Locality data for the short-term and long-term studies were used to calculate the size of activity areas and home ranges as minimum convex polygons and fixed kernel estimates. Male and female geometric tortoises were active throughout the year, and maintained a high level of activity in autumn and in spring. However, females were more active than males were in spring. Females may require more resources, particularly food, in spring when they produce eggs. Although males and females travelled similar distances in autumn and in spring, males displaced further than females displaced in both seasons. The movement path for males was often linear, perhaps because this path may enhance their opportunities to encounter females. Geometric tortoise males were substantially smaller than females, which may explain why the distances that males moved and displaced in spring were negatively correlated to environmental temperature. In autumn, when temperatures were lower than in spring, the distance travelled by males was not correlated to temperature. However, in autumn female displacement showed a positive correlation with environmental temperature. Geometric tortoises showed large inter-individual variation in home range size, which may contribute to the fact that home range size did not differ among the three different habitat types: mature renosterveld, burned renosterveld and the old agricultural fields. Average home range size was 11.5 ha for 95% fixed kernel estimates, and 7.0 ha for minimum convex polygon estimates. Body size influenced the home range size of female geometric tortoises, but had no effect on the home range size of male tortoises. Females had larger home ranges than male tortoises had, possibly because females were larger, but reproductive requirements of females may have played a role. During the dry season, home range size increased when compared to the wet season. The larger home range during the dry season, which is associated with high temperatures, may be related to a reduction in resource availability. The fewer resources available, the greater the distance the tortoises would need to travel in order to acquire the necessary resources. The small home range in the wet season may indicate an abundance of resources, but it may also be that large pools of standing water restrict the movements of tortoises. Understanding the spatial and habitat requirements of P. geometricus will help to assess the viability of populations in disturbed and highly fragmented areas, and contribute to the conservation efforts for this endangered species.
Too hot to nest? In a hot summer the tortoise Chersina Angulata can switch from nesting to facultative viviparity
(Frontiers Media, 2022) Kuchling, Gerald; Hofmeyr, Margaretha D.
In a captive colony of Chersina angulata in Cape Town, South Africa, we observed in 2015/16 retention of the last egg clutch inside the female until the hatching stage was reached, conforming to the generally accepted definition of viviparity. Retrospective climatic analysis indicates egg retention until the hatching stage co-occurred with unusually hot summer weather: the average air temperatures in December 2015 and January and February 2016 were higher than during the preceding five and the following 5 years when facultative viviparity could not be observed. Late December and January appears to be the critical period for females to either deposit their last clutch of the nesting season into a nest, or to retain the last clutch for embryonic development inside the female. Over the 28 December to 24 January period the minimum, average and maximum air temperatures in 2015–16 were about 3◦C higher than in the five following years.
Unraveling the diversification and systematic puzzle of the highly polymorphic Psammobates tentorius (Bell, 1828) complex (Reptilia: Testudinidae) through phylogenetic analyses and species delimitation approaches
(Wiley-Blackwell, 2020) Hofmeyr, Margaretha D.; Zhao, Zhongning; Heideman, Neil J.L.
The high level of phenotypic diversity in southern African tent tortoises (Psammobates tentorius complex) has for decades prevented systematists from developing a stable taxonomy for the group. Here, we used a comprehensive DNA sequence dataset (mtDNA: Cytb, ND4, ND4 adjacent tRNA-His, and tRNA-Ser, 12S, 16S; and nDNA: PRLR gene) of 455 specimens, and the latest phylogenetic and species delimitation analytical procedures, to unravel the long-standing P. tentorius complex systematic puzzle. Our results for mtDNA and nDNA were incongruent, with the poorly supported nDNA phylogeny differentiating the three recognized subspecies, and showing potential hybridization in some regions. In contrast, the concatenated mtDNA phylogeny identified seven operational taxonomic units, with strong support. Clades 1, 4, 5, and 7 corresponded to tortoises identified as P. t. tentorius, clade 3 to P. t. trimeni, and clades 2 and 6 to P. t. verroxii. Our analyses showed conflicting topologies for the placement of C6 (P. t. verroxii north of the Orange River), with stronger support for it being sister to C2 + C3 than to the other clades. Clades 1, 2, and 6 had significantly higher genetic diversity than clades 3, 4, 5, and 7, perhaps because these clades inhabit substantially larger areas.
Variation in the daily activity, movement and refugia of Critically Endangered geometric tortoises, Psammobates geometricus, in autumn and spring
(Taylor & Francis, 2017) Henen, Brian T.; van Bloemestein, Ulric P.; Hofmeyr, Margaretha D.; Weatherby, Craig A.
To help assess habitat requirements of Critically Endangered geometric tortoises, we used thread-trailing to measure daily activity, movements and refugia of adult Psammobates geometricus in autumn and spring 2002. We found strong differences between seasons, and effects of weather, individuals and sex. The high activity was consistent with mild weather during autumn and spring. However, daily temperatures limited female movements on cool autumn days and male movements on warm spring days, a pattern consistent with sexual size dimorphism (large females and small males). The long movements in autumn probably helped tortoises find food plants that grow quickly after autumn rains; both sexes recover body condition from autumn lows, and females begin egg production in late-autumn and winter. These movements may also help males mate with females before they ovulate. The high activity of females in spring should help them forage and sustain their vitellogenesis, egg production and nesting in spring. Male paths tended to be more linear than female paths in both seasons, so this sexual difference is likely not linked to food consumption. Males may move long, linear paths to engage females and avoid other males. Males may have been thermally-challenged in spring. Their movements decreased with increased ground temperatures (in the sun), they used denser refugia in spring than in autumn, and in spring used denser refugia than females used. Geometric tortoises typically used different refugia on consecutive nights, a type of predator avoidance mechanism.

Browsing by Author "Hofmeyr, Margaretha D."

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