Spotted hyena (Crocuta crocuta) coexisting at high density with people in Wukro district,northern Ethiopia

We surveyed density and abundance of spotted hyena (Crocuta crocuta) in the highly degraded and prey depleted Wukro district, northern Ethiopia, with a human population density of 98 persons per square kilometer. A total of 117 spotted hyenas responded to callups, giving a hyena density of 52 hyenas per 100 km² or a total population of 535 hyenas in the district. We quantified the economic impact of spotted hyena predation on livestock using semi structured interviews with randomly selected households. Respondents indicated a total loss of 203 domestic animals to hyena depredation over the past five years. Average annual depredation per household was 0.13 livestock worth US$ 6.1. The diet of spotted hyenas was assessed in three sub-districts by scat analysis and showed 99% prey items of domestic origin, only three of 211 scat contained hair of Ethiopian hare (Lepus fagani) and porcupine (Hystrix cristata). We conclude that hyenas in northern Ethiopia live at high density and eat almost exclusively anthropogenic food and are not dependent on conservation areas.     

Long-Read Genome Sequencing Provides Molecular Insights into Scavenging and Societal Complexity in Spotted Hyena Crocuta crocuta

The spotted hyena (Crocuta crocuta) is a large and unique terrestrial carnivore. It is a particularly fascinating species due to its distinct phenotypic traits, especially its complex social structure and scavenging lifestyle, with associated high dietary exposure to microbial pathogens. However, the underlying molecular mechanisms related to these phenotypes remain elusive. Here, we sequenced and assembled a high-quality long-read genome of the spotted hyena, with a contig N50 length of ∼13.75 Mb. Based on comparative genomics, immunoglobulin family members (e.g., IGKV4-1) showed significant adaptive duplications in the spotted hyena and striped hyena. Furthermore, immune-related genes (e.g., CD8A, LAG3, and TLR3) experienced species-specific positive selection in the spotted hyena lineage. These results suggest that immune tolerance between the spotted hyena and closely related striped hyena has undergone adaptive divergence to cope with prolonged dietary exposure to microbial pathogens from scavenging. Furthermore, we provided the potential genetic insights underlying social complexity, hinting at social behavior and cognition. Specifically, the RECNE-associated genes (e.g., UGP2 and ACTR2) in the spotted hyena genome are involved in regulation of social communication. Taken together, our genomic analyses provide molecular insights into the scavenging lifestyle and societal complexity of spotted hyenas.     

Ancient mitochondrial genomes from Chinese cave hyenas provide insights into the evolutionary history of the genus Crocuta

Cave hyenas (genus Crocuta) are extinct bone-cracking carnivores from the family Hyaenidae and are generally split into two taxa that correspond to a European/Eurasian and an (East) Asian lineage. They are close relatives of the extant African spotted hyenas, the only extant member of the genus Crocuta. Cave hyenas inhabited a wide range across Eurasia during the Pleistocene, but became extinct at the end of the Late Pleistocene. Using genetic and genomic datasets, previous studies have proposed different scenarios about the evolutionary history of Crocuta. However, causes of the extinction of cave hyenas are widely speculative and samples from China are severely understudied. In this study, we assembled near-complete mitochondrial genomes from two cave hyenas from northeastern China dating to 20 240 and 20 253 calBP, representing the youngest directly dated fossils of Crocuta in Asia. Phylogenetic analyses suggest a monophyletic clade of these two samples within a deeply diverging mitochondrial haplogroup of Crocuta. Bayesian analyses suggest that the split of this Asian cave hyena mitochondrial lineage from their European and African relatives occurred approximately 1.85 Ma (95% CI 1.62–2.09 Ma), which is broadly concordant with the earliest Eurasian Crocuta fossil dating to approximately 2 Ma. Comparisons of mean genetic distance indicate that cave hyenas harboured higher genetic diversity than extant spotted hyenas, brown hyenas and aardwolves, but this is probably at least partially due to the fact that their mitochondrial lineages do not represent a monophyletic group, although this is also true for extant spotted hyenas. Moreover, the joint female effective population size of Crocuta (both cave hyenas and extant spotted hyenas) has sustained two declines during the Late Pleistocene. Combining this mitochondrial phylogeny, previous nuclear findings and fossil records, we discuss the possible relationship of fossil Crocuta in China and the extinction of cave hyenas.     

Pleistocene Chinese cave hyenas and the recent Eurasian history of the spotted hyena,Crocuta crocuta

The living hyena species (spotted, brown, striped and aardwolf) are remnants of a formerly diverse group of more than 80 fossil species, which peaked in diversity in the Late Miocene (about 7–8 Ma). The fossil history indicates an African origin, and morphological and ancient DNA data have confirmed that living spotted hyenas (Crocuta crocuta) of Africa were closely related to extinct Late Pleistocene cave hyenas from Europe and Asia. The current model used to explain the origins of Eurasian cave hyena populations invokes multiple migrations out of Africa between 3.5–0.35 Ma. We used mitochondrial DNA sequences from radiocarbon‐dated Chinese Pleistocene hyena specimens to examine the origin of Asian populations, and temporally calibrate the evolutionary history of spotted hyenas. Our results support a far more recent evolutionary timescale (430–163 kya) and suggest that extinct and living spotted hyena populations originated from a widespread Eurasian population in the Late Pleistocene, which was only subsequently restricted to Africa. We developed statistical tests of the contrasting population models and their fit to the fossil record. Coalescent simulations and Bayes Factor analysis support the new radiocarbon‐calibrated timescale and Eurasian origins model. The new Eurasian biogeographic scenario proposed for the hyena emphasizes the role of the vast steppe grasslands of Eurasia in contrast to models only involving Africa. The new methodology for combining genetic and geological data to test contrasting models of population history will be useful for a wide range of taxa where ancient and historic genetic data are available.     

A survey for Echinococcus spp. of carnivores in six wildlife conservation areas in Kenya

To investigate the presence of Echinococcus spp. in wild mammals of Kenya, 832 faecal samples from wild carnivores (lions, leopards, spotted hyenas, wild dogs and silver-backed jackals) were collected in six different conservation areas of Kenya (Meru, Nairobi, Tsavo West and Tsavo East National Parks, Samburu and Maasai Mara National Reserves). Taeniid eggs were found in 120 samples (14.4%). In total, 1160 eggs were isolated and further analysed using RFLP-PCR of the nad1 gene and sequencing. 38 of these samples contained eggs of Echinococcus spp., which were identified as either Echinococcus felidis (n = 27) or Echinococcus granulosus sensu stricto (n = 12); one sample contained eggs from both taxa. E. felidis was found in faeces from lions (n = 20) and hyenas (n = 5) while E. granulosus in faeces from lions (n = 8), leopards (n = 1) and hyenas (n = 3). The host species for two samples containing E. felidis could not be identified with certainty. As the majority of isolated eggs could not be analysed with the methods used (no amplification), we do not attempt to give estimates of faecal prevalences. Both taxa of Echinococcus were found in all conservation areas except Meru (only E. felidis) and Tsavo West (only E. granulosus). Host species identification for environmental faecal samples, based on field signs, was found to be unreliable. All samples with taeniid eggs were subjected to a confirmatory host species RLFP-PCR of the cytochrome B gene. 60% had been correctly identified in the field. Frequently, hyena faeces were mistaken for lion and vice versa, and none of the samples from jackals and wild dogs could be confirmed in the tested sub-sample. This is the first molecular study on the distribution of Echinococcus spp. in Kenyan wildlife. The presence of E. felidis is confirmed for lions and newly reported for spotted hyenas. Lions and hyenas are newly recognized hosts for E. granulosus s.s., while the role of leopards remains uncertain. These data provide the basis for further studies on the lifecycles and the possible link between wild and domestic cycles of cystic echinococcosis in eastern Africa.     

Conditions Favorable for the Somatic Embryogenesis in Carrot Cell Culture Enhance Expression of the roIC Promoter-GUS Fusion Gene

We obtained carrot (Daucus carota) cells possessing the 5′-noncoding sequence of the ORF12 gene (roIC) of TL-DNA of the Ri plasmid and a structural gene of bacterial β-glucuronidase by Agrobacterium-mediated transformation. When such cells were cultured in medium containing 2,4-dichlorophenoxyacetic acid, substantial reduction in β-glucuronidase activity was observed. Upon transferring the cells from a 2,4-D-containing medium to one devoid of 2,4-dichlorophenoxyacetic acid, enhanced expression of β-glucuronidase in somatic embryo development was recorded. Activation by gibberillic acid and suppression by abscisic acid of β-glucuronidase activities, in concord with embryogenesis, were also noted.     

Apparent TRANS Control of Murine βglucuronidase Synthesis by a Temporal Genetic Element

A difference in the heat-inactivation kinetics between the β-glucuronidases of C3HeB/FeJ and C57Bl/6J mice was utilized to assess the mode of action of a temporal genetic element in controlling the expression of the β-glucuronidase structural gene Gus. The heat-inactivation kinetics of liver and kidney β-glucuronidase from F₁ C3HeB/FeJ x C57Bl/6J animals were intermediate with respect to the parental enzyme patterns, suggesting that equal concentrations of the two allelic products were present in β-glucuronidase tetramers of F₁ progeny. β-glucuronidase heteropolymers assembled in vivo under conditions where equal concentrations of the two structural alleles of the enzyme were known to be present also exhibited intermediate heat-inactivation kinetics. These observations are consistent with a trans mode of action of a genetic element that controls the rate of murine β-glucuronidase synthesis.     

Environmental factors influencing spotted hyena and lion population biomass across Africa

The spotted hyena (Crocuta crocuta Erxleben) and the lion (Panthera leo Linnaeus) are two of the most abundant and charismatic large mammalian carnivores in Africa and yet both are experiencing declining populations and significant pressures from environmental change. However, with few exceptions, most studies have focused on influences upon spotted hyena and lion populations within individual sites, rather than synthesizing data from multiple locations. This has impeded the identification of over‐arching trends behind the changing biomass of these large predators. Using partial least squares regression models, influences upon population biomass were therefore investigated, focusing upon prey biomass, temperature, precipitation, and vegetation cover. Additionally, as both species are in competition with one other for food, the influence of competition and evidence of environmental partitioning were assessed. Our results indicate that spotted hyena biomass is more strongly influenced by environmental conditions than lion, with larger hyena populations in areas with warmer winters, cooler summers, less drought, and more semi‐open vegetation cover. Competition was found to have a negligible influence upon spotted hyena and lion populations, and environmental partitioning is suggested, with spotted hyena population biomass greater in areas with more semi‐open vegetation cover. Moreover, spotted hyena is most heavily influenced by the availability of medium‐sized prey biomass, whereas lion is influenced more by large size prey biomass. Given the influences identified upon spotted hyena populations in particular, the results of this study could be used to highlight populations potentially at greatest risk of decline, such as in areas with warming summers and increasingly arid conditions.     

Characterization of spotted hyena,Crocuta crocuta microsatellite loci

We have isolated 10 polymorphic microsatellite loci in the spotted hyena, Crocuta crocuta. The loci displayed between eight and 14 alleles in a minimum of 12 individuals tested. These loci will be used to investigate relatedness within social groups, the genetic structure of populations, sexual selection, and mate choice in spotted hyenas.     

Markedly Elevated Antibody Responses in Wild versus Captive Spotted Hyenas Show that Environmental and Ecological Factors Are Important Modulators of Immunity

Evolutionary processes have shaped the vertebrate immune system over time, but proximal mechanisms control the onset, duration, and intensity of immune responses. Based on testing of the hygiene hypothesis, it is now well known that microbial exposure is important for proper development and regulation of the immune system. However, few studies have examined the differences between wild animals in their natural environments, in which they are typically exposed to a wide array of potential pathogens, and their conspecifics living in captivity. Wild spotted hyenas (Crocuta crocuta) are regularly exposed to myriad pathogens, but there is little evidence of disease-induced mortality in wild hyena populations, suggesting that immune defenses are robust in this species. Here we assessed differences in immune defenses between wild spotted hyenas that inhabit their natural savanna environment and captive hyenas that inhabit a captive environment where pathogen control programs are implemented. Importantly, the captive population of spotted hyenas was derived directly from the wild population and has been in captivity for less than four generations. Our results show that wild hyenas have significantly higher serum antibody concentrations, including total IgG and IgM, natural antibodies, and autoantibodies than do captive hyenas; there was no difference in the bacterial killing capacity of sera collected from captive and wild hyenas. The striking differences in serum antibody concentrations observed here suggest that complementing traditional immunology studies, with comparative studies of wild animals in their natural environment may help to uncover links between environment and immune function, and facilitate progress towards answering immunological questions associated with the hygiene hypothesis.     

Patterns of livestock depredation and cost‐effectiveness of fortified livestock enclosures in northern Tanzania

Human–carnivore conflicts and retaliatory killings contribute to carnivore populations' declines around the world. Strategies to mitigate conflicts have been developed, but their efficacy is rarely assessed in a randomized case–control design. Further, the economic costs prevent the adoption and wide use of conflict mitigation strategies by pastoralists in rural Africa. We examined carnivore (African lion [Panthera leo], leopard [Panthera pardus], spotted hyena [Crocuta crocuta], jackal [Canis mesomelas], and cheetah [Acinonyx jubatus]) raids on fortified (n = 45, total 631 monthly visits) and unfortified (traditional, n = 45, total 521 monthly visits) livestock enclosures (“bomas”) in northern Tanzania. The study aimed to (a) assess the extent of retaliatory killings of major carnivore species due to livestock depredation, (b) describe the spatiotemporal characteristics of carnivore raids on livestock enclosures, (c) analyze whether spatial covariates influenced livestock depredation risk in livestock enclosures, and (d) examine the cost‐effectiveness of livestock enclosure fortification. Results suggest that (a) majority of boma raids by carnivores were caused by spotted hyenas (nearly 90% of all raids), but retaliatory killings mainly targeted lions, (b) carnivore raid attempts were rare at individual households (0.081 raid attempts/month in fortified enclosures and 0.102 raid attempts/month in unfortified enclosures), and (c) spotted hyena raid attempts increased in the wet season compared with the dry season, and owners of fortified bomas reported less hyena raid attempts than owners of unfortified bomas. Landscape and habitat variables tested, did not strongly drive the spatial patterns of spotted hyena raids in livestock bomas. Carnivore raids varied randomly both spatially (village to village) and temporally (year to year). The cost‐benefit analysis suggest that investing in boma fortification yielded positive net present values after two to three years. Thus, enclosure fortification is a cost‐effective strategy to promote coexistence of carnivores and humans.     

The lysosomal membrane complex. Focal point of primary steroid hormone action

At short intervals after the intravenous administration of oestradiol-17β, diethylstilboestrol, testosterone or saline control solution to ovariectomized rats, highly purified lysosome samples were prepared in substantial yield from preputial glands, sex accessory organs rich in these organelles. The preparations were essentially devoid of mitochondrial contamination. Exposure in vivo to doses of these hormones varying from 0.1 to 5μg/100g body wt. provoked dose-dependent labilization of the lysosomal membrane surface, as evidenced by significantly diminished structural latency of several characteristic acid hydrolases, including acid phosphatase, β-glucuronidase and acid ribonuclease II, when such preparations were subsequently challenged in vitro with autolytic conditions, detergent or mechanical stress. Enhanced lytic susceptibility induced by hormone pretreatment was occasionally detectable in the initial preparation without further provocative stimuli in vitro. Comparable results were obtained with the corresponding fractions of uterus, despite the more limited concentration of lysosomes in this steroidal target organ. By the present criteria oestradiol-17α was essentially inert, even in a dose 25 times that effective for its active β-epimer (<0.1μg/100g body wt.). Pretreatment with diethylstilboestrol exerted substantial membrane-destabilizing influence in preputial-gland lysosome samples from orchidectomized rats. Moreover, administration of testosterone to gonadectomized animals resulted in essentially equivalent dose-dependent augmentation of lysosomal enzyme release in preputial-gland preparations of either sex. The membrane stability of lysosome-enriched preparations from uterus, on the other hand, was unaffected by testosterone pretreatment. The sensitivity, specificity and selectivity of the lysosomal response to sex steroids provide evidence for the physiological significance of this phenomenon as a general mechanism for mediation of secondary biochemical transformations in the hormone-stimulated target cell.     

Prey selection and prey preferences of spotted hyenas <Emphasis Type="Italic">Crocuta crocuta</Emphasis> in the Etosha National Park,Namibia

The 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.     

Ecological Specialization and Evolutionary Reticulation in Extant Hyaenidae

During the Miocene, Hyaenidae was a highly diverse family of Carnivora that has since been severely reduced to four species: the bone-cracking spotted, striped, and brown hyenas, and the specialized insectivorous aardwolf. Previous studies investigated the evolutionary histories of the spotted and brown hyenas, but little is known about the remaining two species. Moreover, the genomic underpinnings of scavenging and insectivory, defining traits of the extant species, remain elusive. Here, we generated an aardwolf genome and analyzed it together with the remaining three species to reveal their evolutionary relationships, genomic underpinnings of their scavenging and insectivorous lifestyles, and their respective genetic diversities and demographic histories. High levels of phylogenetic discordance suggest gene flow between the aardwolf lineage and the ancestral brown/striped hyena lineage. Genes related to immunity and digestion in the bone-cracking hyenas and craniofacial development in the aardwolf showed the strongest signals of selection, suggesting putative key adaptations to carrion and termite feeding, respectively. A family-wide expansion in olfactory receptor genes suggests that an acute sense of smell was a key early adaptation. Finally, we report very low levels of genetic diversity within the brown and striped hyenas despite no signs of inbreeding, putatively linked to their similarly slow decline in effective population size over the last ∼2 million years. High levels of genetic diversity and more stable population sizes through time are seen in the spotted hyena and aardwolf. Taken together, our findings highlight how ecological specialization can impact the evolutionary history, demographics, and adaptive genetic changes of an evolutionary lineage.     

Penicillium ochrochloron MTCC 517 chitinase: An effective tool in commercial enzyme cocktail for production and regeneration of protoplasts from various fungi

Penicillium ochrochloron MTCC 517 is a potent producer of chitinolytic enzymes. Novozyme 234, traditional enzyme cocktail for protoplast generation is not available in the market. So, new enzyme cocktail is prepared for protoplast formation from various filamentous fungi which consists of 5 mg ml⁻¹ lysing enzymes from Trichoderma harzianum, 0.06 mg ml⁻¹ β-glucuronidase from Helix pomatia and 1 mg ml⁻¹P. ochrochloron chitinase. The greatest number of protoplasts could be produced from most of the fungi in 0.8 M sorbitol and by incubation for about 2 h at 37 °C, but the number was decreased by incubation for more than 3 h. About twice as many protoplasts were produced from different species of fungi by involvement of P. ochrochloron chitinase than with combined commercial enzymes.     

aguA, the Gene Encoding an Extracellular α-Glucuronidase from Aspergillus tubingensis, Is Specifically Induced on Xylose and Not on Glucuronic Acid

An extracellular α-glucuronidase was purified and characterized from a commercial Aspergillus preparation and from culture filtrate of Aspergillus tubingensis. The enzyme has a molecular mass of 107 kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and 112 kDa as determined by mass spectrometry, has a determined pI just below 5.2, and is stable at pH 6.0 for prolonged times. The pH optimum for the enzyme is between 4.5 and 6.0, and the temperature optimum is 70°C. The α-glucuronidase is active mainly on small substituted xylo-oligomers but is also able to release a small amount of 4-O-methylglucuronic acid from birchwood xylan. The enzyme acts synergistically with endoxylanases and β-xylosidase in the hydrolysis of xylan. The enzyme is N glycosylated and contains 14 putative N-glycosylation sites. The gene encoding this α-glucuronidase (aguA) was cloned from A. tubingensis. It consists of an open reading frame of 2,523 bp and contains no introns. The gene codes for a protein of 841 amino acids, containing a eukaryotic signal sequence of 20 amino acids. The mature protein has a predicted molecular mass of 91,790 Da and a calculated pI of 5.13. Multiple copies of the gene were introduced in A. tubingensis, and expression was studied in a highly overproducing transformant. The aguA gene was expressed on xylose, xylobiose, and xylan, similarly to genes encoding endoxylanases, suggesting a coordinate regulation of expression of xylanases and α-glucuronidase. Glucuronic acid did not induce the expression of aguA and also did not modulate the expression on xylose. Addition of glucose prevented expression of aguA on xylan but only reduced the expression on xylose.     

R. J. Gordon’s Discovery of the Spotted Hyena’s Extraordinary Genitalia in 1777

In the history of zoology the English anatomist Morrison Watson (1845–1885) is considered to be the discoverer of the masculinized sexual organs of the spotted hyena. Beginning in 1877, Watson had published a series of anatomical studies on the spotted hyena (Watson, 1877, 1878, 1881, Watson and Young, 1879), in which he, in which he for the first time made public the anatomical peculiarities of the female spotted hyena’s genitalia. This scientific achievement is well documented. But now we can also state that a hundred years before Watson the Dutch amateur zoologist Robert Jacob Gordon (1743–1795), while serving in the Scots Brigades at the Cape of Good Hope, had already made the same discovery and merely unfortunate personal circumstances prevented publication. During his stay at the Cape, Gordon had studied spotted hyenas intensively and recorded his observations in accurate drawings and comments. These drawings have been preserved as part of a large collection of animal drawings entitled Gordon Atlas. With his discovery, Gordon actually was the first to provide empirical evidence of a “curious and inexplicable case of dimorphism” (Darwin on a beetle) in mammalians, long before étienne Geoffrey Saint-Hilaire (Cours de l’histoire naturelle des mammifères, 1829) started examining masculinized sexual organs in the mole or Darwin recognized the importance of sexual dimorphism (Descent of Man, 1871). In this paper we reproduce for the first time all hyena drawings from the Gordon Atlas, including Gordon’s handwritten notes in the margins in the original Dutch and in translation. Additionally, we briefly delineate the knowledge about the South African spotted hyena in Gordon’s time and indicate that we doubt Watson’s explanation for the age-old confusion about the hyena.     

Selection of Astaxanthin-Overproducing Mutants of Phaffia rhodozyma with β-Ionone

β-Ionone, an end ring analog of β-carotene, inhibits astaxanthin production in the red yeast Phaffia rhodozyma. Astaxanthin-overproducing mutants of this yeast are easily spotted on β-ionone-containing yeast malt agar plates. β-Ionone appears to block astaxanthin synthesis at the β-carotene level.     

Sexual differentiation in three unconventional mammals: spotted hyenas, elephants and tammar wallabies

The present review explores sexual differentiation in three non-conventional species: the spotted hyena, the elephant and the tammar wallaby, selected because of the natural challenges they present for contemporary understanding of sexual differentiation. According to the prevailing view of mammalian sexual differentiation, originally proposed by Alfred Jost, secretion of androgen and anti-Mullerian hormone (AMH) by the fetal testes during critical stages of development accounts for the full range of sexually dimorphic urogenital traits observed at birth. Jost's concept was subsequently expanded to encompass sexual differentiation of the brain and behavior. Although the central focus of this review involves urogenital development, we assume that the novel mechanisms described in this article have potentially significant implications for sexual differentiation of brain and behavior, a transposition with precedent in the history of this field. Contrary to the "specific" requirements of Jost's formulation, female spotted hyenas and elephants initially develop male-type external genitalia prior to gonadal differentiation. In addition, the administration of anti-androgens to pregnant female spotted hyenas does not prevent the formation of a scrotum, pseudoscrotum, penis or penile clitoris in the offspring of treated females, although it is not yet clear whether the creation of masculine genitalia involves other steroids or whether there is a genetic mechanism bypassing a hormonal mediator. Wallabies, where sexual differentiation occurs in the pouch after birth, provide the most conclusive evidence for direct genetic control of sexual dimorphism, with the scrotum developing only in males and the pouch and mammary glands only in females, before differentiation of the gonads. The development of the pouch and mammary gland in females and the scrotum in males is controlled by genes on the X chromosome. In keeping with the "expanded" version of Jost's formulation, secretion of androgens by the fetal testes provides the best current account of a broad array of sex differences in reproductive morphology and endocrinology of the spotted hyena, and androgens are essential for development of the prostate and penis of the wallaby. But the essential circulating androgen in the male wallaby is 5alpha androstanediol, locally converted in target tissues to DHT, while in the pregnant female hyena, androstenedione, secreted by the maternal ovary, is converted by the placenta to testosterone (and estradiol) and transferred to the developing fetus. Testicular testosterone certainly seems to be responsible for the behavioral phenomenon of musth in male elephants. Both spotted hyenas and elephants display matrilineal social organization, and, in both species, female genital morphology requires feminine cooperation for successful copulation. We conclude that not all aspects of sexual differentiation have been delegated to testicular hormones in these mammals. In addition, we suggest that research on urogenital development in these non-traditional species directs attention to processes that may well be operating during the sexual differentiation of morphology and behavior in more common laboratory mammals, albeit in less dramatic fashion.     

Post-weaning maternal effects and the evolution of female dominance in the spotted hyena

Mammalian societies in which females dominate males are rare, and the factors favouring the evolution of female dominance have yet to be clearly identified. We propose a new hypothesis for the evolution of female dominance and test its predictions with empirical data from the spotted hyena (Crocuta crocuta), a well-studied species characterized by female dominance. We suggest that constraints imposed by the development of a feeding apparatus specialized for bone cracking, in combination with the intensive feeding competition characteristic of spotted hyenas, led to the evolution of female dominance. Specifically, we propose that protracted development of the feeding apparatus in young hyenas led to selection for increased aggressiveness in females as a compensatory mechanism for mothers to secure food access for their young after weaning. Our analyses yielded results consistent with this hypothesis. Morphological and behavioural measurements indicate that skull development is indeed protracted in this species; spotted hyenas do not achieve adult skull size or feeding performance capabilities until after sexual maturity. The period between weaning and completed skull development is particularly challenging, as indicated by high mortality. Finally, maternal presence between weaning and full skull maturity, as well as the relative ability of females to aggressively displace conspecifics from food, are important determinants of offspring survival.