Etosha National Park Research Articles

Unraveling the Effects of Selection and Demography on Immune Gene Variation in Free-Ranging Plains Zebra (Equus quagga) Populations

Demography, migration and natural selection are predominant processes affecting the distribution of genetic variation among natural populations. Many studies use neutral genetic markers to make inferences about population history. However, the investigation of functional coding loci, which directly reflect fitness, is critical to our understanding of species' ecology and evolution. Immune genes, such as those of the Major Histocompatibility Complex (MHC), play an important role in pathogen recognition and provide a potent model system for studying selection. We contrasted diversity patterns of neutral data with MHC loci, ELA-DRA and -DQA, in two southern African plains zebra (Equus quagga) populations: Etosha National Park, Namibia, and Kruger National Park, South Africa. Results from neutrality tests, along with observations of elevated diversity and low differentiation across populations, supported previous genus-level evidence for balancing selection at these loci. Despite being low, MHC divergence across populations was significant and may be attributed to drift effects typical of geographically separated populations experiencing little to no gene flow, or alternatively to shifting allele frequency distributions driven by spatially variable and fluctuating pathogen communities. At the DRA, zebra exhibited geographic differentiation concordant with microsatellites and reduced levels of diversity in Etosha due to highly skewed allele frequencies that could not be explained by demography, suggestive of spatially heterogeneous selection and local adaptation. This study highlights the complexity in which selection affects immune gene diversity and warrants the need for further research on the ecological mechanisms shaping patterns of adaptive variation among natural populations.

Double SET point: G9a makes its mark in adipogenesis

EMBO J (2013) 32 1, 45–59 doi:10.1038/emboj.2012.306; published online November232012 Sequence-specific DNA-binding transcription factors (TFs) bind throughout the genome to orchestrate the process of adipocyte differentiation in an exquisitely timed and precise manner. TF binding recruits histone-modifying enzymes, resulting in dynamic epigenomic modifications that correlate with extensive gene expression changes. In this issue of The EMBO Journal, Wang et al (2012) demonstrate a critical role for the SET-containing histone methyltransferase G9a in generating repressive chromatin marks that are lost in the process of adipogenesis.

Development of 11 microsatellite markers for Giraffa camelopardalis through 454 pyrosequencing, with primer options for an additional 458 microsatellites

Many wild giraffe populations are declining across Africa, with two subspecies listed by the IUCN as Endangered in the past 4 years. We developed 11 microsatellite markers from Giraffa camelopardalis angolensis in Etosha National Park, Namibia using 454 sequencing. In 70 individuals, the loci showed 2-4 alleles per locus and expected heterozygosities of 0. 082-0. 711. There were no significant deviations from Hardy-Weinberg equilibrium for any of the loci. Null allele frequencies were low (<3 %) across all loci. We present primer options for an additional 458 microsatellites. This new set of microsatellite markers and primer options will benefit conservation, population and quantitative genetics studies of giraffe populations.

BLACK-BACKED JACKAL EXPOSURE TO RABIES VIRUS, CANINE DISTEMPER VIRUS, AND BACILLUS ANTHRACIS IN ETOSHA NATIONAL PARK, NAMIBIA

Canine distemper virus (CDV) and rabies virus (RABV) occur worldwide in wild carnivore and domestic dog populations and pose threats to wildlife conservation and public health. In Etosha National Park (ENP), Namibia, anthrax is endemic and generates carcasses frequently fed on by an unusually dense population of black-backed jackals (Canis mesomelas). Using serology, phylogenetic analyses (on samples obtained from February 2009-July 2010), and historical mortality records (1975-2011), we assessed jackal exposure to Bacillus anthracis (BA; the causal bacterial agent of anthrax), CDV, and RABV. Prevalence of antibodies against BA (95%, n = 86) and CDV (71%, n = 80) was relatively high, while that of antibodies against RABV was low (9%, n = 81). Exposure to BA increased significantly with age, and all animals >6 mo old were antibody-positive. As with BA, prevalence of antibodies against CDV increased significantly with age, with similar age-specific trends during both years of the study. No significant effect of age was found on the prevalence of antibodies against RABV. Three of the seven animals with antibodies against RABV were monitored for more than 1 yr after sampling and showed no signs of active infection. Mortality records revealed that rabid animals are destroyed nearly every year inside the ENP tourist camps. Phylogenetic analyses demonstrated that jackal RABV in ENP is part of the same transmission cycle as other dog-jackal RABV cycles in Namibia.

Distribution and Molecular Evolution of Bacillus anthracis Genotypes in Namibia

The recent development of genetic markers for Bacillus anthracis has made it possible to monitor the spread and distribution of this pathogen during and between anthrax outbreaks. In Namibia, anthrax outbreaks occur annually in the Etosha National Park (ENP) and on private game and livestock farms. We genotyped 384 B. anthracis isolates collected between 1983–2010 to identify the possible epidemiological correlations of anthrax outbreaks within and outside the ENP and to analyze genetic relationships between isolates from domestic and wild animals. The isolates came from 20 animal species and from the environment and were genotyped using a 31-marker multi-locus-VNTR-analysis (MLVA) and, in part, by twelve single nucleotide polymorphism (SNP) markers and four single nucleotide repeat (SNR) markers. A total of 37 genotypes (GT) were identified by MLVA, belonging to four SNP-groups. All GTs belonged to the A-branch in the cluster- and SNP-analyses. Thirteen GTs were found only outside the ENP, 18 only within the ENP and 6 both inside and outside. Genetic distances between isolates increased with increasing time between isolations. However, genetic distance between isolates at the beginning and end of the study period was relatively small, indicating that while the majority of GTs were only found sporadically, three genetically close GTs, accounting for more than four fifths of all the ENP isolates, appeared dominant throughout the study period. Genetic distances among isolates were significantly greater for isolates from different host species, but this effect was small, suggesting that while species-specific ecological factors may affect exposure processes, transmission cycles in different host species are still highly interrelated. The MLVA data were further used to establish a model of the probable evolution of GTs within the endemic region of the ENP. SNR-analysis was helpful in correlating an isolate with its source but did not elucidate epidemiological relationships.

Male African elephants (Loxodonta africana) queue when the stakes are high

Linear dominance hierarchies are thought to form within groups of social animals to minimize conflict over access to resources. Dominance in both male and female African elephants (Loxodonta africana) is based mostly on intrinsic factors relating to age, and dominance hierarchies have been described within and between family groups of females. Very little is reported about male elephant social structure and dominance has only been described at the level of one-on-one contests. We test the hypothesis that male African elephants form linear hierarchies when resources are limited by monitoring a known group of elephants in Etosha National Park, Namibia, and measuring dominance interactions between males (outside the context of reproduction) during the dry season of 4 consecutive years. We show that males form a stable linear dominance hierarchy under normal arid conditions (in 2005 and 2007) when water is limited and resource competition is high. In unusually wet years with increased water availability (in 2006 and 2008), there is no linearity to the dominance hierarchy, less interaction between individuals and more agonistic behaviors exhibited, particularly in lower ranking individuals. This is the first study to quantify the existence of a linear dominance hierarchy in male African elephants as well as the effect of climatic fluctuations on dominance from year to year.

Exploring the use of acoustics as a tool in male elephant/human conflict mitigation

Elephant/human conflict mitigation solutions have been explored with varying degrees of success. We present findings on a potential acoustic tool to reduce negative outcomes of male elephants entering agricultural areas in the region northeast of Etosha National Park, Namibia. We monitored elephant traffic within and outside the park boundary using GPS collars on five male elephants with known hormonal status as well as information on the frequency and location of fence breaks. Male elephants in the hormonal state of musth have an increased range, often extending outside the protected area. We explored the feasibility of attracting musth males away from potential conflict areas noninvasively, using estrus calls. We played back estrus calls to known individual subadult (n = 9) and adult musth (n = 9) and nonmusth (n = 6) male elephants and show that adult musth and subadult nonmusth males were much more likely to respond and approach the source than nonmusth adult males (p = 0.029 and p = 0.009, respectively) with an equal level of intensity (p = 0.822). Our findings suggest that the use of acoustics may serve as an effective tool in noninvasive male elephant/human conflict mitigation, depending on the age and hormonal status.

Conservation genetics of the black rhinoceros, Diceros bicornis bicornis, in Namibia

Poaching and habitat destruction across sub-Saharan Africa brought the black rhinoceros (Diceros bicornis) close to extinction. Over the past few decades, however, one of four subspecies, D. b. bicornis, has experienced a significant population increase as a consequence of its protection within Etosha National Park (ENP), Namibia. We report here on the level and spatial distribution of black rhinoceros genetic diversity within ENP. Using nine microsatellite loci, genetic variation was assessed from 144 individuals. Our results are consistent with the observation of lower levels of genetic diversity in D. b. bicornis, when compared to D. b. michaeli, but greater diversity when compared to D. b. minor. We also showed that ENP’s black rhino genetic diversity is well represented in Waterberg National Park, originally founded with ENP individuals. We found no genetic signature of a recent bottleneck in ENP, however, suggesting that the genetic diversity within ENP has not been adversely affected by the recent severe population decline. Using Bayesian clustering methods, we observed no significant population structure within ENP, but positive spatial genetic correlation is observed at distances up to 25 km. This relationship exists in females but not males, suggesting reduced dispersal among females, the first evidence of limited female dispersal or philopatry in any species of rhinoceros.

EFFECTS OF RAINFALL, HOST DEMOGRAPHY, AND MUSTH ON STRONGYLE FECAL EGG COUNTS IN AFRICAN ELEPHANTS (LOXODONTA AFRICANA) IN NAMIBIA

Wild African elephants (Loxodonta africana) are commonly infected with intestinal strongyle parasites. Our objective was to determine baseline fecal strongyle egg counts for elephants in the northeast region of Etosha National Park, Namibia and determine if these numbers were affected by annual rainfall, elephant demography (age of individuals and composition of groups), and hormonal state of males. We found that matriarchal family group members have significantly higher fecal egg counts than male elephants (bulls). Among family group members, strongyle egg counts increased with age, whereas among bulls, strongyle egg counts decreased with age. Years of higher rainfall were correlated with decreased numbers of strongyle eggs among bulls. Finally, bulls were not affected by their physiologic (hormonal) status (musth vs. nonmusth). These results suggest that infection by strongyle parasites in Namibian African elephants is a dynamic process affected by intrinsic and extrinsic factors including host demography and rainfall.

Biomass transformation webs provide a unified approach to consumer–resource modelling

An approach to modelling food web biomass flows among live and dead compartments within and among species is formulated using metaphysiological principles that characterise population growth in terms of basal metabolism, feeding, senescence and exploitation. This leads to a unified approach to modelling interactions among plants, herbivores, carnivores, scavengers, parasites and their resources. Also, dichotomising sessile miners from mobile gatherers of resources, with relevance to feeding and starvation time scales, suggests a new classification scheme involving 10 primary categories of consumer types. These types, in various combinations, rigorously distinguish scavenger from parasite, herbivory from phytophagy and detritivore from decomposer. Application of the approach to particular consumer-resource interactions is demonstrated, culminating in the construction of an anthrax-centred food web model, with parameters applicable to Etosha National Park, Namibia, where deaths of elephants and zebra from the bacterial pathogen, Bacillus anthracis, provide significant subsidies to jackals, vultures and other scavengers.

SEASONAL AND DEMOGRAPHIC FACTORS INFLUENCING GASTROINTESTINAL PARASITISM IN UNGULATES OF ETOSHA NATIONAL PARK

Host-parasite dynamics can be strongly affected by seasonality and age-related host immune responses. We investigated how observed variation in the prevalence and intensity of parasite egg or oocyst shedding in four co-occurring ungulate species may reflect underlying seasonal variation in transmission and host immunity. This study was conducted July 2005-October 2006 in Etosha National Park, Namibia, using indices of parasitism recorded from 1,022 fecal samples collected from plains zebra (Equus quagga), springbok (Antidorcas marsupialis), blue wildebeest (Connochaetes taurinus), and gemsbok (Oryx gazella). The presence and intensity of strongyle nematodes, Strongyloides spp. and Eimeria spp. parasites, were strongly seasonal for most host-parasite combinations, with more hosts infected in the wet season than the dry season. Strongyle intensity in zebra was significantly lower in juveniles than adults, and in springbok hosts, Eimeria spp. intensity was significantly greater in juveniles than adults. These results provide evidence that acquired immunity is less protective against strongyle nematodes than Eimeria spp. infections. The seasonal patterns in parasitism further indicate that the long dry season may limit development and survival of parasite stages in the environment and, as a result, host contact and parasite transmission.

Understanding the effects of rainfall on elephant–vegetation interactions around waterholes

The distribution of surface water affects herbivore–vegetation interactions in arid and semi-arid regions. Limited access to surface water typically results in the emergence of vegetation gradients around natural and artificial water sources. In particular, African elephants can create large-scale gradients of woody vegetation. Understanding the dynamics of these gradients is of particular importance for the conservation of other, less mobile herbivores that depend on woody vegetation in areas close to water. While rainfall is known to be a key determinant of herbivore–vegetation interactions in dry areas, we only have limited understanding on how it impacts woody vegetation gradients around waterholes. To address this problem, we developed a deterministic simulation model that describes the interplay of rainfall, elephants and woody vegetation in the vicinity of waterholes. The model is based on elephant telemetry data and the ecological conditions in Etosha National Park (ENP), Namibia. We found that decreasing amounts of rainfall led to an increased degradation of woody vegetation, which was particularly severe in areas close to water. Based on this result we conclude that low rainfall was an important driver of recently observed patterns of vegetation degradation in ENP. More generally, rainfall appears to be a key factor that determines elephant–vegetation interactions and thus dynamics of woody vegetation gradients around waterholes. Using long-term rainfall data from ENP, we also demonstrate that an increase in the number of water sources during periods of low rainfall can mitigate the destructive impact of elephants in areas close to water. However, more research is required to assess the sustainability and effectiveness of rainfall-adapted strategies of artificial water provisioning in more detail. In particular it is important to investigate potential effects on elephant population dynamics.

Habitat use and spatial organisation of relocated black rhinos in Namibia

Abstract In this study we systematically examined species-specific exploration behaviour and behavioural acclimatisation of a black rhino Diceros bicornis founder group post-translocation. The study was carried out in a fenced region, approximately 350 km2 in size and directly adjacent to Etosha National Park in Namibia. Rhinos were radio-tracked and movement data were complemented by detailed habitat descriptions at the centres of rhino activity with vegetation plot sampling. Rhinos used both geological formations of the study area: Otavi dolomite and Etosha calcrete substrate. The latter was dominated by Acacia spp. due to former land use for livestock farming. The size of total and seasonal home ranges and core areas, as well as home range establishment patterns and habitat use, are highly variable among individual rhinos. Home ranges of most individuals from our study are among the largest recorded for the species. We found age class specific patterns of home range establishment, typical mating and social behaviour, seasonal changes of home range and core area size, and clear shifts in spatial behaviour over time. The results provide our best estimate to date for the natural exploration behaviour and behavioural acclimatisation of black rhinos in a semi-arid savannah ecosystem.

Prey selection and prey preferences of spotted hyenas Crocuta crocuta in the Etosha National Park, Namibia

AbstractThe feeding ecology of the spotted hyena Crocuta crocuta was studied in the central and eastern part of the Etosha National Park, Namibia. Hyenas mainly hunted migratory ungulates such as springbok Antidorcas marsupialis, zebra Equus burchelli, and blue wildebeest Connochaetes taurinus, but also resident species such as the greater kudu Tragelaphus strepsiceros and gemsbok Oryx gazella. There were, however, major differences in the species most frequently killed by hyenas in central and eastern Etosha. The preferred prey species of spotted hyenas in central Etosha was springbok, whereas regarding the abundance of zebra and wildebeest, these two species were rather avoided. In contrast, the prey species preferred by hyenas in eastern Etosha was kudu. Zebra and gemsbok were taken in proportion to their abundance, whereas wildebeest and springbok seemed to be rather avoided. Differences in prey selection and preferences were also reflected in differences in hunting group sizes. In eastern Etosha, where spotted hyenas frequently hunted larger prey, hunting group sizes were significantly larger compared to those in the center of the park.

Cover Caption

Cover description: Gemsbok (Oryx gazella) at a water hole in the Etosha National Park, Namibia. Adding new individuals to small populations of translocated grazing mammals increases per capita growth rates and aids their establishment. Photo credit: Rudi van Aarde

Breaking down fences: Recoupling social–ecological systems for biodiversity conservation in Namibia

Herero communities in northern Namibia recently formed the Ehi-rovipuka Conservancy under a national Community-Based Natural Resource Management Programme (CBNRM) that has received international acclaim for wildlife conservation and poverty alleviation. Nearly a century ago ancestors of the Herero were ousted from Etosha National Park, contiguous to the Ehi-rovipuka Conservancy. The communities have been denied access ever since. Participatory Rural Appraisal (PRA) methods were employed to elucidate relationships of the Herero and their communal conservancy with the Etosha National Park. Memory mapping and villager interviews revealed a profound sense of lost traditional territory inside Etosha and a strong desire to return to the Park, not to harvest wildlife but to restore cultural practices and reap certain benefits from the Park. We term the separation of the communities from their traditional territory as a ‘decoupling’ of people from their local environment. We further suggest that the potential benefits that villagers identify from the Park represent mechanisms for ‘recoupling’ local social–ecological systems, requiring the literal and figurative breakdown of the Park fence. We describe a model to illustrate decoupling and recoupling mechanisms, and argue that recoupled social–ecological systems are necessary for long-term conservation of biodiversity. We further suggest a collaborative landscape model for biodiversity conservation featuring institutional linkages and integration between community-conserved areas, integrated conservation corridors for connectivity, and dynamic, mobile reserves collaboratively integrated with national parks management. This model may have applicability in Namibia and similar regions elsewhere with low population densities, high species endemism and prevailing or emerging threats to biodiversity.

Genetic structure of two populations of the Namibian giraffe, Giraffa camelopardalis angolensis

AbstractTwo geographically distinct populations of giraffe (Giraffa camelopardalis) were sampled for this study, the northern Namib Desert and Etosha National Park. Population genetic parameters and relationships within subpopulations were estimated to better understand the genetic architecture of this isolated subspecies. Gene flow between the geographically separated populations can be attributed to recent translocation of giraffe between the two populations. Inbreeding estimates in the six subpopulations studied were low though we found evidence that genetic drift may be affecting the genetic diversity of the isolated populations in northern Namibia. Population dynamics of the sampling locations was inferred with relationship coefficient analyses. Recent molecular systematics of the Namibian giraffe populations indicates that they are distinct from the subspecies Giraffa camelopardalis giraffa and classified as G. c. angolensis. Based on genetic analyses, these giraffe populations of northern Namibia, the desert‐dwelling giraffe and those protected in Etosha National Park, are a distinct subspecies from that previously assumed; thus we add data on G. c. angolensis to our scientific knowledge of this giraffe of southern Africa.

A keystone predator at risk? Density and distribution of the spotted hyena (Crocuta crocuta) in the Etosha National Park, Namibia

For wildlife management and conservation biology, it is important to be able to estimate the status and distribution of animals and to monitor their population trends. In the Etosha National Park, Namibia, there is a lack of knowledge about numbers and distribution of spotted hyenas ( Crocuta crocuta (Erxleben, 1777)) and factors regulating their population. To estimate hyena density and distribution, tape-recorded vocalizations (call-ups) were performed to attract hyenas in the central and eastern parts of Etosha. Eighty-five adult and subadult hyenas responded to the calls, with most of them responding in an area with high density of migratory ungulates, principally springbok ( Antidorcas marsupialis (Zimmermann, 1780)), wildebeest ( Connochaetes taurinus (Burchell, 1823)), and Burchell’s zebra ( Equus burchelli (Gray, 1824)). These migratory species are the main prey of spotted hyenas in Etosha. There was a strong spatial relationship between hyena density and migratory prey biomass. Based on this mathematical correlation, I estimated 203 ± 79 hyenas, i.e., 2.7 ± 1.1 hyenas/100 km2, in the central and eastern parts of Etosha. Applying this correlation to the western part of the park, it was possible to estimate 339 ± 176 spotted hyenas, corresponding to an overall density of 2.1 ± 1.0 hyenas/100 km2, in the whole Etosha National Park.

African Acrostics: A Word in Edgeways (review)

Reviewed by: African Acrostics: A Word in Edgeways Deborah Stevenson Harley, Avis . African Acrostics: A Word in Edgeways; illus. with photographs by Deborah Noyes. Candlewick, 2009 [40p]. ISBN 978-0-7636-3621-0$17.99 Reviewed from galleys R Gr. 4-6 Acrostics, poems wherein the first letters of each line make up a relevant word or phrase when read vertically, are some of the most accessible of formal poems, and Harley offers nearly a score of lively examples. Each poem treats an African animal, from crocodile to zebra, including both classic literary subjects (elephant and giraffe) and less common stars (African wild cat and kudu). The poems are nimble and crafty, demonstrating that acrostics can actually be effective verse as well as technical achievements. Harley tucks in rhymes, alliteration, and poetic tropes and seasons her verse with a playful sensibility ("But/ Even so, I know/ A rhino when I / See one, and this is the time not/ To"), making them entertaining to read across as well as down, perhaps even out loud. The layout is actually on the young side for the poetry, following the big print/colored background/portrait photo format familiar from many early verse collections, but the photos, taken in Namibia's Etosha National Park, are vivid close-ups. Young wordsmiths will itch to try their hands at the verse form after reading this; it would also make a useful complement to Janeczko's A Kick in the Head (BCCB 4/05) in discussing poetic forms and structure. A concluding spread offers more information about acrostics, including advanced versions such as double and multiple acrostics; another spread offers natural-history notes on the featured animals, while a statement from the photographer gives some insight into Namibia. Copyright © 2009 The Board of Trustees of the University of Illinois

Black Rhinoceros (Diceros bicornis) Populations in Northwestern Namibia Are Apparently Not Infected with Piroplasms

Babesiosis is a potentially fatal disease in black rhinoceroses. Blood specimens collected from black rhinoceroses from Etosha National Park (n = 29) and Damaraland (n = 22), Namibia, were subjected to polymerase chain reaction using Theileria and Babesia genus-specific primers and reverse line blot, with negative results. The animals were sparsely infested with ticks. In the absence of suitable prophylactic measures, naïve rhinoceroses would be at risk if translocated to Babesia-endemic areas.