Zebra Equus Research Articles

Non‐invasive physiological markers demonstrate link between habitat quality, adult sex ratio and poor population growth rate in a vulnerable species, the Cape mountain zebra

Abstract Effective conservation and species management require an understanding of the causes of poor population growth. Conservation physiology uses biomarkers to identify factors that contribute to low individual fitness and population declines. Building on this, macrophysiology can use the same markers to assess how individual physiology varies with different ecological or demographic factors over large temporal and spatial scales. Here, we use a macrophysiological approach to identify the ecological and demographic correlates of poor population growth rates in the Cape mountain zebra metapopulation. We use two non‐invasive biomarkers: faecal glucocorticoids as a measure of chronic stress, and faecal androgens as an indicator of male physiological status. We found that faecal glucocorticoid concentrations were highest in the spring prior to summer rainfall, and were elevated in individuals from populations associated with low‐quality habitat (lower grass abundance). In addition, faecal androgen concentrations were higher in populations with a high proportion of non‐breeding stallions (where male:female adult sex ratios exceed 2:1) suggesting sex ratio imbalances may intensify male competition. Finally, population growth rate was negatively associated with faecal glucocorticoid concentrations and female fecundity was negatively associated with faecal androgens, indicating a relationship between hormone profiles and fitness. Together, our results provide cross‐population evidence for how poor population growth rates in Cape mountain zebra can be linked to individual physiological biomarkers. More broadly, we advocate physiological biomarkers as indicators of population viability, and as a way to evaluate the impact of variable ecological and demographic factors. In addition, conservation physiology can be used to assess the efficacy of management interventions for this subspecies, and this approach could inform models of species’ responses to future environmental change. A plain language summary is available for this article.

Adaptive Governance of Cape Mountain Zebra, Can It Work?

Adaptive governance and network governance theory provide a useful conceptual framework to guide the conservation of threatened species in complex multi-actor, multijurisdictional social ecological systems. We use principles from this theory to assess strengths and weaknesses in (1) national legislation, and (2) the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) Regulations applicable to the conservation of the Cape mountain zebra (Equus zebra zebra) (CMZ) in South Africa. A legislated conservation tool, Biodiversity Management Plans for Species (BMP-S), establishes a collaborative network of role players and facilitates the important principles of collaborative learning and adaptation. Effective governance of this network is critical to success, but challenging because of a mandate gap and limited capacity in government to provide essential network-level competencies. National regulations governing human use of CMZ (Threatened or Protected Species (TOPS) Regulations) accords with the principles of (1) being developed in consultation with stakeholders and (2) open to revision and adaptation. CITES Regulations also provide adequately for adaptation. Poor alignment of regulations between different regulatory authorities in South Africa and limited capacity for implementation of regulations seriously constrain learning and adaptation.

Temporal dynamics in microbial soil communities at anthrax carcass sites

BackgroundAnthrax is a globally distributed disease affecting primarily herbivorous mammals. It is caused by the soil-dwelling and spore-forming bacterium Bacillus anthracis. The dormant B. anthracis spores become vegetative after ingestion by grazing mammals. After killing the host, B. anthracis cells return to the soil where they sporulate, completing the lifecycle of the bacterium. Here we present the first study describing temporal microbial soil community changes in Etosha National Park, Namibia, after decomposition of two plains zebra (Equus quagga) anthrax carcasses. To circumvent state-associated-challenges (i.e. vegetative cells/spores) we monitored B. anthracis throughout the period using cultivation, qPCR and shotgun metagenomic sequencing.ResultsThe combined results suggest that abundance estimation of spore-forming bacteria in their natural habitat by DNA-based approaches alone is insufficient due to poor recovery of DNA from spores. However, our combined approached allowed us to follow B. anthracis population dynamics (vegetative cells and spores) in the soil, along with closely related organisms from the B. cereus group, despite their high sequence similarity. Vegetative B. anthracis abundance peaked early in the time-series and then dropped when cells either sporulated or died. The time-series revealed that after carcass deposition, the typical semi-arid soil community (e.g. Frankiales and Rhizobiales species) becomes temporarily dominated by the orders Bacillales and Pseudomonadales, known to contain plant growth-promoting species.ConclusionOur work indicates that complementing DNA based approaches with cultivation may give a more complete picture of the ecology of spore forming pathogens. Furthermore, the results suggests that the increased vegetation biomass production found at carcass sites is due to both added nutrients and the proliferation of microbial taxa that can be beneficial for plant growth. Thus, future B. anthracis transmission events at carcass sites may be indirectly facilitated by the recruitment of plant-beneficial bacteria.

DESCRIPTION OF GASTRIC ULCERS AND OF THEIR SUSPECTED, ASSOCIATED RISK FACTORS IN DECEASED WILD EQUIDS AT THE RÉSERVE AFRICAINE DE SIGEAN, FRANCE (2010-2016).

Gastric ulcers are common in domestic horses and foals, affecting at least 90% of unmedicated racehorses in active training. Despite these high prevalences in domestic horses, literature about this condition in wild equids is almost nonexistent. The presence of gastric ulcers was evaluated at necropsy in six species of wild equids that died at the Réserve Africane de Sigean, a safari park in the south of France from 2010 to 2016. Among the 55 individuals that died during that period, a description of the gastric mucosa was available in 82% (45/55) of cases. Considering the cases for which a description of the gastric mucosa was available, the prevalence of gastric ulcers was 64% (29/45). The highest prevalences were noted in Grant's zebra (Equus quagga boehmi) and Hartmann's mountain zebra (Equus zebra hartmannae) at 83% and 100%, respectively. In contrast to what is reported in domestic foals, gastric ulcerations were only diagnosed in one foal (out of 11 foals necropsied). The higher prevalence was noted in young individuals (3-36 mo old) at 93% (14/15); the lesions observed consisted mainly of single to multiple, superficial lesions, of which, only the mucosa was missing; these superficial lesions are often considered not clinically significant. The prevalence was lower for adults (74%; 14/19), but lesions were deeper or with a hyperemic or inflammatory appearance. All the lesions observed were located in the gastric, nonglandular, stratified squamous mucosa, along the margo plicatus. No statistical correlation could be found between the development of gastric ulcers and an ongoing, chronic pathologic process or a digestive tract pathology. The detection of gastric ulcers was, therefore, significantly greater in wild equids isolated in smaller enclosures. Nevertheless, additional larger-scale research is needed to point out predisposing factors in equids under human care.

Equine behavioral enrichment toys as tools for non-invasive recovery of viral and host DNA.

Direct collection of samples from wildlife can be difficult and sometimes impossible. Non-invasive remote sampling for the purpose of DNA extraction is a potential tool for monitoring the presence of wildlife at the individual level, and for identifying the pathogens shed by wildlife. Equine herpesviruses (EHV) are common pathogens of equids that can be fatal if transmitted to other mammals. Transmission usually occurs by nasal aerosol discharge from virus-shedding individuals. The aim of this study was to validate a simple, non-invasive method to track EHV shedding in zebras and to establish an efficient protocol for genotyping individual zebras from environmental DNA (eDNA). A commercially available horse enrichment toy was deployed in captive Grévy's, mountain, and plains zebra enclosures and swabbed after 4-24 hr. Using eDNA extracted from these swabs four EHV strains (EHV-1, EHV-7, wild ass herpesvirus and zebra herpesvirus) were detected by PCR and confirmed by sequencing, and 12 of 16 zebras present in the enclosures were identified as having interacted with the enrichment toy by mitochondrial DNA amplification and sequencing. We conclude that, when direct sampling is difficult or prohibited, non-invasive sampling of eDNA can be a useful tool to determine the genetics of individuals or populations and for detecting pathogen shedding in captive wildlife.

Ungulates rely less on visual cues, but more on adapting movement behaviour, when searching for forage.

Finding suitable forage patches in a heterogeneous landscape, where patches change dynamically both spatially and temporally could be challenging to large herbivores, especially if they have no a priori knowledge of the location of the patches. We tested whether three large grazing herbivores with a variety of different traits improve their efficiency when foraging at a heterogeneous habitat patch scale by using visual cues to gain a priori knowledge about potential higher value foraging patches. For each species (zebra (Equus burchelli), red hartebeest (Alcelaphus buselaphus subspecies camaa) and eland (Tragelaphus oryx)), we used step lengths and directionality of movement to infer whether they were using visual cues to find suitable forage patches at a habitat patch scale. Step lengths were significantly longer for all species when moving to non-visible patches than to visible patches, but all movements showed little directionality. Of the three species, zebra movements were the most directional. Red hartebeest had the shortest step lengths and zebra the longest. We conclude that these large grazing herbivores may not exclusively use visual cues when foraging at a habitat patch scale, but would rather adapt their movement behaviour, mainly step length, to the heterogeneity of the specific landscape.

Evidence of African horse sickness virus infection of Equus zebra hartmannae in the south-western Khomas Region, Namibia.

Equine mortalities suspected to be due to African horse sickness (AHS) were reported from the arid Khomas Region, Namibia, in 2008. The area was previously considered a localized AHS-free area. Hartmann's mountain zebra (Equus zebra hartmannae), a potential but unconfirmed reservoir host of African horse sickness virus (AHSV), occurs in the region. Between 2009 and 2010 serum, blood and tissue samples from 31 culled E.z.hartmannae were analysed by reverse transcription-polymerase chain reaction(RT-PCR) (n=31) and enzyme-linked immunosorbent assay (ELISA) (n=18) to determine the presence of AHSV and/or antibodies against AHSV. The presence of antibodies against AHSV was demonstrated in all 18 samples assayed, and AHSV double stranded RNA was detected in 26% of the animals. This is evidence that E.z.hartmannae can become infected with AHSV.

Hiding in Plain Sight: Evidence of Hybridization between Cape Mountain Zebra (Equus zebra zebra) and Plains Zebra (Equus quagga burchelli)

Historically, Cape mountain zebras (Equus zebra zebra) were widely distributed along mountain ranges in the Eastern and Western Cape provinces of South Africa (Boshoff, Landman & Kerley, 2015). By the 1930s, excessive hunting and habitat loss resulted in a reduction in Cape mountain zebra numbers with populations being confined to only five localities. Two of these subpopulations subsequently became extinct. Three relic populations currently exist; the population in the Cradock district,was formally protected in 1937 by the proclamation of the Mountain Zebra National Park (MZNP; Lloyd 1984). The two other populations in the Kammanassie and Gamka Mountains, have been protected since 1923 and 1971, respectively. Cape mountain zebra numbers increased steadily from their critical status of fewer than 80 individuals in the 1950s, to an estimated minimum of 4791 individuals by 2015 (Hrabar & Kerley, 2015). Plains zebra (Equus quagga burchelli) were subsequently introduced, in sympatry with Cape mountain zebra into four formally protected areas, including the MZNP in 1999 and Karoo National Park in 1998. Until recently no cases of hybridization between plains zebra and Cape mountain zebra were known. Hybridization was not of great concern as a threat to Cape mountain zebra populations as fertile hybrids were thought to be unlikely, due to the relatively large difference in the number of chromosomal pairs between the two species (44 versus 32 in plains zebra and Cape mountain zebra, respectively; Ryder, Epel & Benirschke, 1978; Cordingley et al., 2009; Hrabar & Kerley, 2013). By 2013, the plains zebra population had increased substantially in the MZNP (estimated at 769 Cape mountain zebra and 124 plains zebra by aerial census (unpublished aerial census data, 2013) and were potentially competing with Cape mountain zebra for resources. A decision was thus taken to remove the plains zebra. This intervention resulted in a disruption in the social structure, and some of the small, fragmented groups or plains zebra individuals joined Cape mountain zebra herds. In addition, conservation officials observed ‘Cape mountain zebra’ with plains zebra characteristics. These included slight shadow striping, stripes extending all the way down to the ventral midline of the chest and abdomen, and, although they did have the reddish muzzle of mountain zebra, they did not have the characteristic mountain zebra gridiron pattern on their rumps (Fig. 1), but rather had absent or distorted patterns on the rump. They exhibited the distinct dewlap of the Cape mountain zebra and ear shapes were similar to plains zebra. This raised concerns of possible hybridization between the two species. Here, we report on a molecular evaluation using maternal, paternal and biparental markers to identify suspected hybrid Cape mountain and plains zebra in MZNP and Karoo National Park, South Africa.

Retention of solute and particle markers in the digestive tract of captive Somali wild asses (Equus africanus somaliensis)

In contrast to the domestic horse, whose digestive physiology has been thoroughly investigated, knowledge on the digestive physiology of wild equids is scarce. Comparisons between the domestic horse and the domestic donkey suggest that wild asses might achieve higher digestibilities. This could derive from longer retention times or a greater difference in the mean retention time (MRT) of particles vs. fluid (the selectivity factor (SF)). Here, we measured MRT of a solute (fluid; MRTsolute) and a particle (<2 mm; MRTparticle) marker in five captive male Somali wild asses (Equus africanus somaliensis) fed a diet of 95% grass hay. At a mean dry matter intake of 94 ± 3 g kg−0.75 day−1, MRTsolute was 33.3 ± 5.4 h and MRTparticle 39.6 ± 3.9 h, resulting in a SF of 1.21 ± 0.14. For their food intake, Somali wild asses appeared to have slightly higher MRTparticle than expected based on domestic equid data, in contrast to Grevy zebras (Equus grevyi), potentially indicating higher capacities of the digestive tract. However, considering data on domestic horses, donkeys, and zebra, there was no evident difference in the SF of wild equids compared to domestic ones. Together with an absence of reported anatomical differences in the digestive tract of wild and domestic equids, the data suggest a general similarity in the digestive physiology of equid species that contrasts with the diversity in the digestive physiology of ruminants, and that might be one contributing factor to a lack of sympatric, niche-differentiated equid species.

Placentation in the plains zebra (Equus quagga).

The placenta and fetal gonads of 12 pregnant plains zebra (Equus quagga), estimated to be between 81 and 239 days of gestation, were examined. The diffuse, microcotyledonary zebra placenta appeared, developmentally, to be 3-4 weeks behind its counterpart in horse pregnancy and this, together with the presence of small and long-lived endometrial cups, low levels of zebra chorionic gonadotrophin in maternal serum and few accessory corpora lutea in the maternal ovaries during the first half of gestation, made zebra pregnancy more similar to donkey than horse pregnancy. Zebra fetal gonads enlarged after 80 days of gestation and their interstitial cells stained positively for 3β hydroxysteroid dehydrogenase and 17,20 lyase steroid enzymes while the trophoblast stained for aromatase. This confirmed that zebra fetal gonads, like those of the horse and donkey, can synthesise C19 androgens, which can then be aromatised by the placenta to C18 oestrogens. It is remarkable that such unusual feto-placental mechanisms of production of gonadotrophic and steroid hormones has persisted unchanged within the genus Equus despite the many physical adaptations and the considerable loss of chromosomes that have occurred during the evolution of its member species.

Contrasting results from molecular and pedigree-based population diversity measures in captive zebra highlight challenges facing genetic management of zoo populations.

Zoo conservation breeding programs manage the retention of population genetic diversity through analysis of pedigree records. The range of demographic and genetic indices determined through pedigree analysis programs allows the conservation of diversity to be monitored relative to the particular founder population for a species. Such approaches are based on a number of well-documented founder assumptions, however without knowledge of actual molecular genetic diversity there is a risk that pedigree-based measures will be misinterpreted and population genetic diversity misunderstood. We examined the genetic diversity of the captive populations of Grevy's zebra, Hartmann's mountain zebra and plains zebra in Japan and the United Kingdom through analysis of mitochondrial DNA sequences. Very low nucleotide variability was observed in Grevy's zebra. The results were evaluated with respect to current and historic diversity in the wild, and indicate that low genetic diversity in the captive population is likely a result of low founder diversity, which in turn suggests relatively low wild genetic diversity prior to recent population declines. Comparison of molecular genetic diversity measures with analogous diversity indices generated from the studbook data for Grevy's zebra and Hartmann's mountain zebra show contrasting patterns, with Grevy's zebra displaying markedly less molecular diversity than mountain zebra, despite studbook analysis indicating that the Grevy's zebra population has substantially more founders, greater effective population size, lower mean kinship, and has suffered less loss of gene diversity. These findings emphasize the need to validate theoretical estimates of genetic diversity in captive breeding programs with empirical molecular genetic data. Zoo Biol. 36:87-94, 2017. © 2016 Wiley Periodicals, Inc.

Effectiveness of electro-fencing for restricting the ranging behaviour of wildlife: a case study in the degazetted parts of Akagera National Park

Several national parks on the African continent have been fenced to mitigate human–wildlife conflict, but the effectiveness of different fencing strategies seems to vary between regions. Here, we assessed the effectiveness of electro-fencing for restricting movement patterns of several wild ungulates in Akagera National Park (NP), Rwanda. Following the turmoil of the Rwandan genocide and civil war (1991–1995), large numbers of returning war refugees brought about an increasing pressure on land use, after which considerable parts of the western Akagera NP and adjacent Mutara Game Reserve were degazetted, followed by the construction of an electric fence in 2013 and a helicopter-based game-drive of ungulates into the modern park. We conducted distance sampling of wildlife and domestic livestock in the Uruhita plain – now no longer part of Akagera NP but bordering the modern Akagera NP to the west – for extended periods of time (2010–2015) before and after fencing. For abundant species population densities could be calculated, whereas for other species encounter frequencies are reported. We report on continuously high cattle densities, and increasing encounter frequencies of sheep/goats in the Uruhita plain. We found decreasing densities of zebra (Equus quagga) and decreasing encounter frequencies of waterbuck (Kobus ellipsiprymnus), stagnant encounter frequencies in the case of topi (Damaliscus lunatus jimela) and stagnant densities of impala (Aepyceros melampus). The latter species can jump fences, and we argue that competitive release and reduced predation may be the prime factors leading impala to (temporarily) exploit grasslands outside the modern national park.

A SEROLOGIC AND POLYMERASE CHAIN REACTION SURVEY OF EQUINE HERPESVIRUS IN BURCHELL'S ZEBRAS (EQUUS QUAGGA), HARTMANN'S MOUNTAIN ZEBRAS (EQUUS ZEBRA HARTMANNAE), AND THOMSON'S GAZELLES (EUDORCAS THOMSONII) IN A MIXED SPECIES SAVANNAH EXHIBIT.

Reports of equine herpesvirus (EHV) 1 and EHV-9 causing clinical disease in a wide range of species have been well documented in the literature. It is thought that zebras are the natural hosts of EHV-9 both in the wild and in captive collections. Concerns about potential interspecies transmission of EHV-1 and EHV-9 in a mixed species savannah exhibit prompted serologic and polymerase chain reaction surveys. Eighteen Burchell's zebras ( Equus quagga ), 11 Hartmann's mountain zebras ( Equus zebra hartmannae), and 14 Thomson's gazelles ( Eudorcas thomsonii ) cohabitating the same exhibit were examined for EHV-1 virus neutralization titers, and evidence of virus via EHV 1-5 polymerase chain reactions. None of the animals had previous exposure to vaccination with EHV-1 or EHV-4. All tested zebras had positive EHV-1 titers, ranging from 4 to 384. All zebras and Thomson's gazelles had negative polymerase chain reaction results for all targeted equine herpesviruses. EHV-9-specific assays are not available but EHV-1, EHV-4, and EHV-9 cross-react serologically. Positive serology results indicate a potential latent equine herpesvirus in the zebra population, which prompted initiation of an equine herpesvirus vaccine protocol, changes in pregnant zebra mare management, and equine herpesvirus polymerase chain reaction screening prior to shipment to or from the study site.

International trade in endangered species: the challenges and successes of the 17th conference of parties to the convention on international trade in endangered species of wild fauna and flora (CITES)

International trade in endangered species: the challenges and successes of the 17th conference of parties to the convention on international trade in endangered species of wild fauna and flora (CITES)

Recognition and management of ecological refugees: A case study of the Cape mountain zebra

Anthropogenic activities have led to long-term range contraction in many species, creating isolated populations in ecologically marginal and suboptimal habitats. ‘Refugee’ species have a current distribution completely restricted to suboptimal habitat. However, it is likely that many species are partial refugees, where one or more populations are managed in ecologically unsuitable habitat. Here, we develop a framework to assess potential refugee populations in marginal habitats using a model species: the Cape mountain zebra. We assessed habitat quality by the abundance and palatability of grass and diet quality using proximate nutrient and element analysis. High grass abundance was associated with higher population growth rates and zebra density and less skewed adult sex ratios. Furthermore, faecal nutrient and dietary element quality was also positively associated with grass abundance. Our results show that poorly performing populations were characterised by suboptimal habitat, supporting the hypothesis that the Cape mountain zebra has refugee populations. In addition, we found more variance in sex ratio and population growth rates in smaller populations suggesting they may be more at risk for random stochastic effects, such as a biased sex ratio, compounding poor performance. We show how the ‘refugee’ concept can be applied more generally when managing species with fragmented populations occurring across marginal habitats. More broadly, the results presented herein highlight the importance of recognizing the range of habitats historically occupied by a species when assessing ecological suitability. Identifying and mitigating against refugee, relict and gap populations is especially critical in the face of on-going environmental change.

The vegetation of the farms Jurisdam and Zeekoegat of the Mountain Zebra National Park, Eastern Cape

The vegetation of the farms Jurisdam and Zeekoegat of the Mountain Zebra National Park, Eastern Cape

Fossil hair in brown hyaena (Parahyaena brunnea) coprolites from Middle Pleistocene deposits at Gladysvale Cave, South Africa

Based on fossil hair identified from brown hyaena (Parahyaena brunnea) coprolites from Middle Pleistocene deposits at Gladysvale Cave in the Sterkfontein valley, South Africa, the scale pattern and cross-sectional morphology of fossil hair conclusively established that brown hyaenas shared the Sterkfontein valley with humans, warthog (Phacochoerus aethiopicus), impala (Aepyceros melampus), Burchell’s zebra (Equus quagga, formerly burchelli), greater kudu (Tragelaphus strepsiceros) and black wildebeest (Connochaetes gnou). These animals are associated with mixed savanna biomes. Even though it cannot be attributed to which hominin species the fossil hair belong, they, however, lived in a mixed savanna environment.

Namibian Farmland Cheetahs (Acinonyx jubatus) Demonstrate Seronegativity for Antibodies Against Bacillus anthracis

The cheetah (Acinonyx jubatus) is a vulnerable species, with estimates of only 6700 animals left in the wild. Namibia, an anthrax-endemic country, is home to the world's largest and most viable free-ranging population (~3000 animals), which predominantly resides on unprotected private farmlands (Durant, 2015). For over 170 years, anthrax has been reported in African wildlife species with sporadic outbreaks across Namibia (Beyer et al., 2012). Anthrax is regularly reported from zebra (Equus quagga), hartebeest (Alcelaphus buselaphus), springbok (Antidorcas marsupialis) and kudu (Tragelaphus strepsiceros) (Turner et al., 2014; Wafula, Patrick & Charles, 2007); all cheetah prey species. Anthrax epidemics occur annually in Namibia's Etosha National Park (ENP), whereas the establishment of a government mandated livestock vaccination programme in 1973 reduced the occurrence of anthrax on the surrounding farmlands (Bellanet al., 2012; Schneider, 1994; Turner et al., 2013). However, sporadic epidemics still occur on private farmlands throughout Namibia (Shaanika, 2013).

Population genetic diversity and hybrid detection in captive zebras.

Zebras are members of the horse family. There are three species of zebras: the plains zebra Equus quagga, the Grevy’s zebra E. grevyi and the mountain zebra E. zebra. The Grevy’s zebra and the mountain zebra are endangered, and hybridization between the Grevy’s zebra and the plains zebra has been documented, leading to a requirement for conservation genetic management within and between the species. We characterized 28 microsatellite markers in Grevy’s zebra and assessed cross-amplification in plains zebra and two of its subspecies, as well as mountain zebra. A range of standard indices were employed to examine population genetic diversity and hybrid populations between Grevy’s and plains zebra were simulated to investigate subspecies and hybrid detection. Microsatellite marker polymorphism was conserved across species with sufficient variation to enable individual identification in all populations. Comparative diversity estimates indicated greater genetic variation in plains zebra and its subspecies than Grevy’s zebra, despite potential ascertainment bias. Species and subspecies differentiation were clearly demonstrated and F1 and F2 hybrids were correctly identified. These findings provide insights into captive population genetic diversity in zebras and support the use of these markers for identifying hybrids, including the known hybrid issue in the endangered Grevy’s zebra.

Androgen receptor gene polymorphism in zebra species

Androgen receptor genes (AR) have been found to have associations with reproductive development, behavioral traits, and disorders in humans. However, the influence of similar genetic effects on the behavior of other animals is scarce. We examined the loci AR glutamine repeat (ARQ) in 44 Grevy's zebras, 23 plains zebras, and three mountain zebras, and compared them with those of domesticated horses. We observed polymorphism among zebra species and between zebra and horse. As androgens such as testosterone influence aggressiveness, AR polymorphism among equid species may be associated with differences in levels of aggression and tameness. Our findings indicate that it would be useful to conduct further studies focusing on the potential association between AR and personality traits, and to understand domestication of equid species.