Hippopotamus Research Articles

T. S. Eliot’s ‘The Hippopotamus’ and the Bible

T. S. Eliot’s ‘The Hippopotamus’ and the Bible

Common hippopotamus in Nigeria: New census data and literature review confirm the conservation importance of sites outside protected areas

AbstractOnce abundant across Africa, the common hippopotamus is threatened owing to habitat degradation and loss, hunting, and negative human–wildlife interactions. West African populations are notably small and fragmented and therefore at greatest risk.In Nigeria, Africa's most populous nation, the IUCN estimates that only 100 hippos remain. They occur in protected areas, such as national parks and game reserves, and outside protected areas in estuarine habitats, inland rivers, lakes, and reservoirs. However, the status of hippos in most sites is poorly known. Reliable data are needed to better ascertain the status of this species in Nigeria.Over five days in December 2018 and May 2019, motorized boats were used to conduct a census of the hippo population in Kiri Dam reservoir, a large‐dam reservoir along the Gongola River, a major tributary of the Benue River, in north‐eastern Nigeria. These findings were compared with data on hippo abundance from several sites across Nigeria and the Benue River basin in North Cameroon.A minimum of 56 hippos (51 adults and 5 calves) were recorded, predominantly in the transitional zone of the reservoir. Based on available data, hippos in Kiri reservoir currently represent the largest recorded population in Nigeria, exceeding individual populations in official protected areas.Research and conservation efforts for hippos in Nigeria should focus on assessing their status and improving protection in key sites and increasing connectivity among populations. Special attention should be paid to populations within the Benue River basin, which is emerging as critical for hippopotamus conservation in west‐central Africa.

Reproductive cycle and pregnancy monitoring in the common hippopotamus (Hippopotamus amphibius) through salivary steroid analyses and trans-abdominal ultrasonography.

The use of an enzyme immunoassay (EIA) was validated to monitor progestogens in common hippopotamus Hippopotamus amphibius saliva and transabdominal ultrasonography was used to diagnose and monitor pregnancy in this species. Both faecal and saliva extracts contained elevated progestogens indicative of luteal phases and gestation. Faecal and saliva progestogen concentrations of six adult female hippos revealed a strong positive correlation between the two sample types (r=0.60–0.85). Salivary and faecal progestogen analysis revealed a cycle length of 31.8±6.9 days and 33.4±2.9 days and average non-pregnant luteal phase duration of 17.3±1.5 days and 14.0±1.5 days, respectively. Progestogen concentrations (faecal and saliva samples collected ~days 0 to 90) from a full-term pregnancy (saliva: 1,167.1±1,269.4 pg/ml; faecal: 2,812.4±1,657.5 ng/g) were higher on average than luteal phase concentrations (saliva: 335.0±358.1 pg/ml; faecal: 1,399.5±613.0 ng/g). Comparatively, progestogen concentrations (saliva samples collected days 0 to 181; faecal samples collected ~days 120 to 181) of a pre-term (premature live birth ~181 days) pregnancy (saliva: 244.3±155.2 pg/ml; faecal: 501.7±492.2 ng/g) were on average lower than concentrations observed during the full-term pregnancy and/or luteal phase. The nulliparous female that gave birth pre-maturely was trained for voluntary transabdominal ultrasound exams conducted weekly. Intrauterine fluid and foetal tissue were observed 79 days following last confirmed mating. Foetal spine, rib cage, beating heart and internal organs were visible at 156 days. In summary, salivary progestogen monitoring and transabdominal ultrasonography appear suitable for tracking reproductive activity and diagnosing and monitoring pregnancy in the common hippo.

Multiscale drivers of hippopotamus distribution in the St Lucia Estuary, South Africa

This study provides preliminary data on predictors of Hippopotamus amphibius (Linnaeus, 1758; hippo) distribution in St Lucia Estuary, the largest estuarine system in Africa and a key habitat for one of South Africa’s largest hippo populations. We use binary logistic regression models to evaluate selected habitat features as predictors of hippo occurrence at two spatial scales and a negative binomial model with log-link function to evaluate predictors of frequency of use at a fine spatial scale. At the scale of the whole estuary, models indicate that hippos preferentially select diurnal refuge sites that are closer to river inlets and farther from human settlements. At a fine scale (within the Narrows in which more than 50% of the population resides), occurrence and frequency of use models suggested that hippos preferentially settle in sites with water depths between 0.5 and 1.49 m, that are farther from human settlements, closest to natural wetland vegetation and near neighbouring groups. Preliminary data on habitat variables influencing hippo distribution highlights the necessity to manage water levels, restore wetland floodplains, protect wetland vegetation and halt human settlement encroachment in order to ensure the viability of this UNESCO site and its hippo population.

Looking the River Horse in the Mouth: New Insights on Incisors, Canine Curvatures and Mulling the Molars

Tooth numbers, types, eruption patterns, occlusion, and timing of tooth replacement in the living hippopotamus species, Hippopotamus amphibius (common or Nile hippo) and Choeropsis liberiensis (pygmy hippo), were examined. We discovered inaccuracies in the published dental formula of H. amphibius, and present the corrected dental formula in this study. By examining crania and mandibles ranging in chronological age from late fetal or neonatal to aged adult hippos, we also identified the relative timing of tooth eruption and growth rates for both deciduous and permanent dentitions. Living hippos have ever‐growing incisors and canines that shape the anterior rostrum for foraging and intraspecific competition. Despite their highly differential use of the canines, with H. amphibius using these teeth for intraspecific aggression and display while pygmy hippos use them in foraging, the canine teeth of both living taxa are greatly enlarged in comparison to other components of the dentitions. In fact, Hippopotamus amphibius has some of the largest canine teeth among mammals. In addition to thegosis, or wear caused by tooth‐tooth contact, foraging behavior and tongue wear cause incisor attrition, albeit deriving from different species‐specific tooth usage. As individuals of H. amphibius grow, the erupting canines show lateral displacement, which correlates with anterior rostral elongation. This dramatic change in both length and width of the face in H. amphibius allows the roots of the enlarging canine teeth to occupy increased space in the maxilla and mandible. Despite facial elongation, enlargement of the recurved roots of the ever‐growing canines drastically reduces space for the alveolus of the first and sometimes the second premolar. In some cases this results in the elimination of one or more premolars from the adult dentition. These losses may not be symmetrical in either maxilla or mandible. In other cases, all deciduous premolars may be retained into adulthood, resulting in the published conclusion that the number of premolars in H. amphibius is variable, a phenomenon that is rare among mammals. In contrast, in C. liberiensis the canines enlarge to a relatively lesser degree and do not displace the deciduous premolars; therefore pygmy hippos retain the full premolar complement, explaining the dichotomy in dental formulae between the two species. This study also expands a previous rubric for chronological age determination in H. amphibius, wherein mandibles were divided into twenty stages to include characterization of the dentitions of the correlated skulls (N = 34). The crania examined represented thirteen of twenty H. amphibius age classes. These specimens are housed in the osteological collections of the Smithsonian Institution (USNM) and the Field Museum of Natural History (FMNH). This chronological aging method was also adapted to provide a relative age of skulls and mandibles (N = 15) representing ten of the twenty age classes of C. liberiensis from the same collections. Observations reveal that an increased time interval between successive molar eruptions in H. amphibius may reflect adaptation to a lifespan of up to sixty years, a phenomenon not seen in C. liberiensis.Support or Funding InformationNot applicable

Reconciling Landscape Fragmentation and Hippopotamuses Population Decrease in Virunga National Park Wetland

Wetlands have been noted to be beneficial worldwide. Despite wetlands being a natural asset that is of great significance to the human community, they are threatened by human and natural events. In Virunga National Park (VNP) wetlands are the habitat of Hippopotamus (Hippopotamus amphibius) which are among the animal species threatened by extinction in VNP since the past few decades. As shown by the last studies the number of Hippos population declined for 96% for the period of less than 40 years. This study evaluated landscape fragmentation status and its implication on the decline of the hippos population in VNP wetland for the period from 1990 to 2018. This study’s land cover data was obtained using remote sensing techniques with the help of software package ERDAS IMAGINE v16.6 and ArcGIS v10.3. It was mapped and classified using the maximum likelihood supervised classification technique. The landscape was classified into seven classes, which included Cropland, Forest, grassland, wetland, scrubland, bare area, and water. Satellite data (Landsat) was used to evaluate NDVI and NDWI and finally the landscape patterns in the study were analyzed using Fragstats 4.2, which was also used to calculate landscape indices for the respective periods. The results obtained from the LULC, NDVI, NDWI and the landscape metrics showed that during the period of our study the VNP wetland was fragmented. A strong negative correlation between the number of hippos and the wetland’s LFI (Landscape Fragmentation Index) values showed that wetland fragmentation was one of the reasons of the decline of Hippos in the park.

Spatial ecology of male hippopotamus in a changing watershed

The obligate dependency of the common hippopotamus, Hippopotamus amphibius, on water makes them particularly vulnerable to hydrological disturbances. Despite the threats facing this at-risk species, there is a lack of information regarding H. amphibius spatial ecology. We used high-resolution tracking data of male H. amphibius to assess home range size, movement mode (e.g. residency and migratory movements), and resource selection patterns. We compared these results across seasons to understand how hydrological variability influences H. amphibius movement. Our study watershed has been severely impacted by anthropogenic water abstraction causing the river to stop flowing for prolonged periods. We observed H. amphibius movements to be highly constrained to the river course with grassy floodplains being their preferred habitat. Dominant and small sub-adult males displayed year-round residency in/near river pools and had smaller home ranges compared to large sub-adults. During the dry season, large sub-adult males made significant (~15 km) upstream movements. The larger home range size of large sub-adults can be attributed to the elevated levels of migratory and exploratory activities to limit conspecific aggression as the river dries. Our observations provide insight into how future changes in water flow may influence male H. amphibius movements and populations through density-dependent effects.

Detection of Bacillus anthracis in animal tissues using InBios active anthrax detect rapid test lateral flow immunoassay.

The Active Anthrax Detect (AAD) Rapid Test lateral flow immunoassay is a point-of-care assay that was under investigational use for detecting Bacillus anthracis capsular polypeptide (polyglutamic acid) in human blood, serum and plasma. Small sample volumes, rapid results and no refrigeration required allow for easy use in either the field or laboratory. Although the test was developed for use in suspect cases of human inhalation anthrax, its features also make it a potentially powerful tool for testing suspect animal cases. We tested animal tissue samples that were confirmed or ruled out for B. anthracis. The AAD Rapid Tests were also deployed in the field, testing animal carcasses during an anthrax outbreak in hippopotami (Hippopotamus amphibius) and Cape buffalo (Syncerus caffer) in Namibia. Evaluation of all samples showed a specificity of 82% and sensitivity of 98%. However, when the assay was used on specimens from only fresh carcasses (dead for <24h), the specificity increased to 96%. The AAD Rapid Test is a rapid and simple screening assay, but confirmatory testing needs to be done, especially when the age of the sample (days animal has been deceased) is unknown. SIGNIFICANCE AND IMPACT OF THE STUDY: In countries where anthrax is endemic, many human outbreaks are often caused by epizootics. Earlier detection of infected animals may allow for identification of exposed people, early implementation of prevention and control methods, and ultimately lessen the number of people and animals affected. Detection of Bacillus anthracis in animal tissues using a simple, rapid and field-deployable method would allow for faster outbreak response. We evaluated a simple sample collection and processing method for use with the Active Anthrax Detect Rapid Test lateral flow immunoassay to screen dead animals for anthrax.

The functional roles of mammals in ecosystems

The diverse functional roles of over 6,000 species of extant mammals that range in body size across eight orders of magnitude, from blue whales (Balaenoptera musculus) to tiny Etruscan shrews (Suncus etruscus), contribute to shaping Earth's ecosystems. Large mammalian herbivores (e.g., African elephants [Loxodonta africana], American bison [Bison bison], hippopotamuses [Hippopotamus amphibius]) and carnivores (e.g., wolves [Canis lupus], pumas [Puma concolor], sea otters [Enhydra lutris]) often have significant effects on primary producers in terrestrial, aquatic, and marine systems through nutrient cycling, energy flow, and the exertion of bottom-up and top-down processes. Small mammals, like bats, are important pollinators, dispersers of fruits, and consumers of arthropods, and others, especially rodents and primates, are important predators and dispersers of seeds. Many of these mammal-mediated processes occur simultaneously in the same ecosystem, and have significant effects on community structure of primary producers that in turn alter communities of other vertebrates and invertebrates. Many mammals also are ecosystem engineers (e.g., elephants, American beavers [Castor canadensis], porcupines [Erithezon dorsatum], prairie dogs [Cynomys spp.]) that create, significantly modify, or destroy habitat, and by doing so, they alter ecosystem structure and function and increase habitat heterogeneity and biodiversity. The extensive influence mammals have on ecosystems results in important services that contribute to human well-being, such as pollination, insect pest control, and bioturbation of soils. The rapid declines in abundance of many mammal populations and the associated increase in extinction risk raise conservation concerns for mammals. To maintain mammalian diversity and the critical ecosystem processes they provide, scientists need to mobilize concern for their status and strive for more effective and comprehensive conservation action. We provide insights and synthesis on the ecological role of mammals and highlight key research questions and future directions for their conservation.

War-induced collapse and asymmetric recovery of large-mammal populations in Gorongosa National Park, Mozambique.

How do large-mammal communities reassemble after being pushed to the brink of extinction? Few data are available to answer this question, as it is rarely possible to document both the decline and recovery of wildlife populations. Here we present the first in-depth quantitative account of war-induced collapse and postwar recovery in a diverse assemblage of large herbivores. In Mozambique’s Gorongosa National Park, we assembled data from 15 aerial wildlife counts conducted before (1968–1972) and after (1994–2018) the Mozambican Civil War (1977–1992). Pre-war total biomass density exceeded 9,000 kg km-2, but populations declined by >90% during the war. Since 1994, total biomass has substantially recovered, but species composition has shifted dramatically. Formerly dominant large herbivores—including elephant (Loxodonta africana), hippo (Hippopotamus amphibius), buffalo (Syncerus caffer), zebra (Equus quagga), and wildebeest (Connochaetes taurinus)—are now outnumbered by waterbuck (Kobus ellipsiprymnus) and other small to mid-sized antelopes. Waterbuck abundance has increased by an order of magnitude, with >55,000 individuals accounting for >74% of large-herbivore biomass in 2018. By contrast, elephant, hippo, and buffalo, which totaled 89% of pre-war biomass, now comprise just 23%. These trends mostly reflect natural population growth following the resumption of protection under the Gorongosa Restoration Project; reintroductions (465 animals of 7 species) accounted for a comparatively small fraction of the total numerical increase. Waterbuck are growing logistically, apparently as-yet unchecked by interspecific competition or predation (apex-carnivore abundance has been low throughout the post-war interval), suggesting a community still in flux. Most other herbivore populations have increased post-war, albeit at differing rates. Armed conflict remains a poorly understood driver of ecological change; our results demonstrate the potential for rapid post-war recovery of large-herbivore biomass, given sound protected-area management, but also suggest that restoration of community structure takes longer and may require active intervention.

Biochronological framework for the late Galerian and early-middle Aurelian Mammal Ages of peninsular Italy

Following a recent chronostratigraphic revision of 17 fossiliferous sites hosting assemblages constituting local faunas of the Aurelian Mammal Age for peninsular Italy, we provide a re-structured biochronological framework and discuss the current validity and significance of the middle Pleistocene Faunal Units (FU) for this region. Contrasting with the previous model of a wide faunal renewal during Marine Isotope Stage (MIS) 9 (∼330ka), the First Occurrences (FO) of several species of the Torre in Pietra FU are significantly backdated and referred to the Fontana Ranuccio FU (530–400ka). We show that the faunal renewal was more gradual and occurred earlier than previously assumed. Many taxa that are typical of the late Pleistocene register their FO in the Fontana Ranuccio FU, latest Galerian, which is characterized by the almost total disappearance of Villafranchian taxa and by the persistence of typical Galerian taxa such as Dama clactoniana, Bison schoetensacki and Ursus deningeri, and by the FO of Stephanorhinus kirchbergensis, S. hemitoechus, Hippopotamus amphibius, Cervus elaphus eostepahnoceros, Ursus spelaeus, Canis lupus, and Vulpes vulpes. The next Torre in Pietra FU is characterized only by the FO of Megaloceros giganteus and Mustela putorius. However, we observe that MIS 9 marks the actual moment when the faunal assemblages of this region are represented only by those taxa characterizing the late middle Pleistocene and late Pleistocene. For this reason, we propose to still consider the Torre in Pietra (lower levels) local fauna as a conventional boundary for the Galerian-Aurelian transition. Finally, we remark that the strong faunal renewal in MIS 13, with five FOs, coincides with the temperate climatic conditions due to the absence of marked glacial periods that could have favored the FO and the subsequent spread of these taxa.

A Comparison of Common Hippopotamus (Artiodactyla) and Mysticete (Cetacea) Nostrils: An Open and Shut Case

Hippos are considered the closest living relatives to cetaceans and they have some similar adaptations for aquatic living, such as a modified respiratory tract. Behavioral observations of male and female common hippos (Hippopotamus amphibius) at Disney's Animal Kingdom® and the Adventure Aquarium were conducted to describe and examine movements of the nostrils during respiration (inspiration, expiration, and inter-breath interval). The hippo nostril is a crescent shaped opening with lateral and medial aspects that are mobile and can be adducted and abducted to regulate the nostril opening. Notably, the default (resting) position of the nostrils is closed during the inter-breath interval, even when hippos are resting in water and their heads are not submerged. Similar to cetaceans, this aquatic adaptation protects the respiratory tract from an accidental incursion of water that can occur even when the nostrils are above water. Dissection of a deceased captive common hippo suggests there are separate muscles that pull the medial and lateral aspects for abduction. The internal nasal passage has a nasal plug that is similar in shape but less pronounced than the nasal plugs of two baleen whale species studied (minke whale Balaenoptera acutorostrata, fin whale Balaenoptera physalus). Examination of the musculature suggests fibers attach from the premaxillae and extend caudally to retract the plug to open the nasal passage. We discuss similarities and differences of the nostrils/blowholes of fully aquatic, semi-aquatic, and terrestrial species to assess adaptations related to environmental conditions that may be convergent or derived from a common ancestor. Anat Rec, 2018. © 2018 Wiley Periodicals, Inc. Anat Rec, 302:693-702, 2019. © 2018 Wiley Periodicals, Inc.

100 Reproductive cycle and pregnancy monitoring in the common hippopotamus (Hippopotamus amphibius) through salivary steroid analyses and transabdominal ultrasonography

The common hippopotamus (Hippopotamus amphibius) is listed as vulnerable to extinction by the IUCN due to a significant decrease in population size, caused by habitat loss and poaching. Ex situ populations can help ensure against species loss, but careful reproductive management is essential to maintain sustainable populations. Hormone monitoring allows for characterisation of the reproductive cycle and gestation, offering insight into timing of receptivity and conception and facilitating pregnancy diagnosis and estimation of parturition date. Fecal steroid analysis has been validated for measuring progestogens in hippos. However, hippos are often housed in groups and frequently defecate in the water, making sample collection and source identification difficult. Salivary steroid analysis has been employed for monitoring reproductive activity in several species, but has not been tested in hippos. Additionally, transabdominal ultrasonography has proven valuable in diagnosing and monitoring pregnancy in many large mammals, but efficacy in the common hippo is unknown. The goals of this project were to (1) validate the use of an enzyme immunoassay to monitor progestogens in hippo saliva, (2) confirm that salivary progestogen profiles accurately reflect reproductive activity, (3) determine if transabdominal ultrasonography can be used to diagnose pregnancy, and, if so, (4) monitor and characterise fetal development via weekly examinations. Saliva (4-7 per week) and fecal (2-7 per week) samples were collected from 7 adult female hippos housed at 3 USA facilities over 3-7 months. Saliva and fecal samples were extracted in ethanol and extracts diluted (1:2 to 1:10 and 1:25 to 1:500, respectively) before evaluation by enzyme immunoassay (Progesterone mini-kit; Arbor Assays). Parallelism was confirmed between serially diluted fecal (r2=0.993) and saliva (r2=0.990) samples and the standard curve. Inter- and intra-assay coefficients of variation were maintained at &amp;lt;10%. Comparison of fecal and saliva progestogen concentrations revealed a strong correlation between the 2 sample types (r2=0.848) and suggested that saliva offers a comparable alternative. Both fecal and saliva extracts exhibited elevated progestogens during luteal phases and gestation. One nulliparous female housed at the Cincinnati Zoo &amp;amp; Botanical Garden (Cincinnati, OH, USA) was trained for voluntary transabdominal ultrasound exams. An Ibex Pro portable ultrasound machine (E.I. Medical Imaging, Loveland, CO, USA) with curvilinear probe (5-2.5MHz) was used at a scanning depth of 17.8 and 23.4cm. Intrauterine fluid and possible fetal tissue were observed 79 days following the last confirmed mating. Spine, rib cage, and beating heart were clearly visible at ~156 days of gestation. Ultrasound procedures were continued until the premature birth of a calf at ~181 days (normal hippo gestation ~231 days). Salivary progestogen monitoring and transabdominal ultrasonography appear suitable for tracking reproductive activity and diagnosing and monitoring pregnancy in the common hippo.

UAS imagery reveals new survey opportunities for counting hippos.

IntroductionThe common hippopotamus Hippopotamus amphibius L. is a vulnerable species that requires efficient methods to monitor its populations for conservation purposes. Rapid evolution of civil drones provides new opportunities but survey protocols still need development. This study aims to determine the optimal flight parameters for accurate population estimates. A second objective is to evaluate the effects of three environmental factors: wind speed, sun reflection and cloud cover.MethodWe estimated the population of two main hippo schools (Dungu and Wilibadi II) located in Garamba National Park in Democratic republic of Congo. Eight observers reviewed 252 photos taken over the Dungu school, representing a total of 2016 experimental units. A detection rate and a level of certainty were associated with each experimental unit, and five parameters were related to each count: flight height, three environmental parameters (sun reflection on water surface, cloud cover, and wind speed), and observers’ experience.ResultsFlight height reduced the observers’ confidence in their detection ability, rather than the detection itself. For accurate counts of large groups an average height of 150 m was shown to be a good compromise between animal detection without zooming in and the area covered in one frame. Wind speed had little influence on the counts, but it affected the performance of the UAS. Sun reflection reduced the detection rate of hippos and increased level of certainty, while cloud cover reduced detection rates slightly. Therefore, we recommend flying when the sun is still low on the horizon and when there is little cloud, or when cloud cover is light and even. This last point reinforces our recommendation for flights early in the day. The counts also showed large differences between groups of inexperienced and experienced observers. Experienced observers achieved better detection rates and were generally more confident in their detection. Experienced observers detected 86.5% of the hippos on average (confidence interval = ±0.76%). When applied to data from the second site, the detection was 84.3% (confidence interval = ±1.84%). Two correction factors were then calculated, as the inverse of the detection rate, based on the estimated number of hippos present during one flight (Factor 1) or in the general population respectively (Factor 2). Factor 2 especially was consistent with previous studies using traditional aerial counts (1.22 vs 1.25). Factor 2 was found to be appropriate for use by experienced observers. These results confirm the use of correction factor 2 for hippo surveys, regardless of the study site, as it accounts for hippo behavior. Optimum counting and cost efficiency were achieved with two trained observers counting 7 pictures.ConclusionThis study is a promising approach for routine surveys of the hippopotamus which is a species usually ignored in wildlife counts. Drone technology is expected to improve rapidly; therefore UAS could become a very useful and affordable survey tool for other species requiring specific monitoring.

Morphological Studies of Developmental Stages of Oculotrema hippopotami (Monogenea: Polystomatidae) Infecting the Eye of Hippopotamus amphibius (Mammalia: Hippopotamidae) Using SEM and EDXA with Notes on Histopathology.

The present study was performed to observe histopathological effects of Oculotrema hippopotami Stunkard, 1924 infection in the eye of Hippopotamus amphibius, as well as to reveal new details of morphology and structural features of this monogenean and its comparison between 2 age stages of the parasite. This was done using both light and scanning electron microscopy, energy dispersive X-ray analysis (EDXA) and histopathology. The presence of a mixture of different generations (adult and sub-adult) in one host individual is common for Oculotrema Stunkard, 1924 in contrast to Polystoma Zeder, 1800. New metrical and graphical information obtained for adults and sub-adults compared with the previous studies. Here we show the presence of genital papillae in adults, metrical data on the distal part of the vas deferens. SEM micrographs of sperm ejaculatory structures and information about the flattened dorsal side of the body provided for the first time. Histopathological changes, such as necrosis and hemorrhage in host tissues as a result of O. hippopotami attachment structures are described. Structural analysis of different body parts of O. hippopotami of both age groups are also included. We show qualitative differences in the presence of hardening ions (S, P, Ca) in attachment structures (oral and haptor suckers) that increase with the age of the worm. The presence of sub-adults and adults on the same host, together with high levels of infection without high pathogenicity may account for Oculotrema being one of the most successful parasites among the Monogenea.

Skull Bone Anatomy of the Young Common Hippopotamus (Hippopotamus Amphibius)

Abstract Hippopotamidae family is nowadays represented by two species within two different genera: pygmy hippopotamus (Choeropsis liberiensis) and common hippopotamus (Hippopotamus amphibius). The common hippopotamus has a very unique anatomy, and the shape of the body, especially the head is adapted for a semi-aquatic life style. The morphological examination and description of the gross anatomical features of the hippopotamus skull is described in this paper. The shape of the skull is adapted for the amphibian way of life. Their eyes, ears and nostrils are placed high on the roof of the skull which allows these organs to remain above the surface of the water while the animal is being submerged underwater. The skull is massive, but the brain case (neurocranium) is extremely small compared with the splanchnocranium and complete head. The dental formula of the common hippopotamus is: incisors (I) 2/2, canines (C) 1/1, premolars (P) 3-4/3-4 and molars (M) 3/3. Incisors and canine teeth are formed in the shape of tusks and are used for threat or “demonstration of power” among animals when vigorously fi ghting. Incisor teeth grow continuously and are twice bigger in males than in females.

Diverse effects of the common hippopotamus on plant communities and soil chemistry.

The ecological importance of the common hippopotamus (Hippopotamus amphibius) in aquatic ecosystems is becoming increasingly well known. These unique megaherbivores are also likely to have a formative influence on the terrestrial ecosystems in which they forage. In this study, we employed a novel exclosure design to exclude H. amphibius from experimental plots on near-river grasslands. Our three-year implementation of this experiment revealed a substantial influence of H. amphibius removal on both plant communities and soil chemistry. H. amphibius significantly reduced grassland canopy height, increased the leafiness of common grasses, reduced woody plant abundance and size, and increased the concentrations of several soil elements. Many of the soil chemistry changes that we experimentally induced by exclusion of H. amphibius were mirrored in the soil chemistry differences between naturally occurring habitats of frequent (grazing lawns) and infrequent (shrub forest) use by H. amphibius and other grazing herbivores. In contrast to existing hypotheses regarding grazing species, we found that H. amphibius had little effect on local plant species richness. Simultaneous observations of exclosures designed to remove all large herbivores revealed that H. amphibius removal had ecologically significant impacts, but that the removal of all species of large herbivores generated more pronounced impacts than the removal of H. amphibius alone. In aggregate, our results suggest that H. amphibius have myriad effects on their terrestrial habitats that likely improve the quality of forage available for other herbivores. We suggest that ongoing losses of this vulnerable megaherbivore are likely to cause significant ecological change.

Metastatic oral squamous cell carcinoma in a captive common hippopotamus (Hippopotamus amphibius)

Metastatic oral squamous cell carcinoma in a captive common hippopotamus (Hippopotamus amphibius)

Trophic structure of an African savanna river and organic matter inputs by large terrestrial herbivores: A stable isotope approach

Abstract Knowledge of trophic structure is important to understand sources and pathways of energy resources in community ecology and to identify determinants of ecosystem changes. Yet, little is known from rivers of African savanna receiving large inputs of terrestrial organic matter and nutrients by large mammalian herbivores. We used Stable Isotope (δ13C and δ15N) Bayesian Ellipses in R (SIBER) and Layman's community‐wide metrics to describe seasonal variation in trophic niches and trophic structures in midorder river reaches in the Mara River (Kenya) that differed in environmental conditions (agricultural vs. forested) and amounts of organic matter and nutrients (low vs. high inputs by livestock and hippopotami, Hippopotamus amphibius). These analyses were supplemented with data on the trophic diversity of macroinvertebrate functional feeding groups (FFGs) and fish trophic guilds. The δ13C and δ15N of basal resources and consumers differed between sites and changed with seasons. Sites in agricultural areas that were utilised by livestock and a site with hippopotami had higher δ13C than the forested site due to the presence of C4 carbon from egestion and excretion by the grazers. The forested site recorded the most taxon‐rich and trophic‐diverse invertebrate community, suggesting both autochthonous and allochthonous sources of energy were available. Agricultural sites and the site with hippopotami recorded high abundances of collector taxa in response to large inputs of organic matter. Fish trophic guilds were less diverse and were dominated by insectivores. The food web at the forested site had the widest trophic niche size and highest isotopic trophic diversity compared to sites in areas with large mammalian herbivores. Invertebrate and fish trophic niche sizes changed according to food resources varying with space and time. Invertebrates had higher δ13C values during the dry season. In contrast, fish showed higher δ13C values during the wet season, and trophic niche sizes were constricted and considerably overlapping, suggesting feeding on a narrow range of food sources with high trophic redundancy. This study showed that increased terrestrial organic matter by large mammalian herbivores affected trophic diversity and niche sizes for aquatic consumers in rivers draining the African savanna. Linking the density of terrestrial large mammalian herbivores to aquatic ecosystem structure and function could help manage their populations sustainably.

Comparative Anatomy of the Larynx in Pinnipeds (Seal, Sea lion, Walrus)

Pinnipeds (e.g., seal, sea lion, walrus) are marine mammals that spend time both in and out of the water. All are able to vocalize in air using the pneumatically driven vocal fold vibrations, a mechanism common to terrestrial mammals. This is no surprise, as their ancestors were once terrestrial mammals. Pinnipeds, however, are also able to vocalize underwater. It is not known how they generate or transmit these sounds. This study explores pinniped laryngeal anatomy in: harbor seal (Phoca vitulina), gray seal (Halichoerus grypus), elephant seal (Mirounga angustirostris), California sea lion (Zalophus californianus), and walrus (Odobenus rosmarus). Comparisons were made with the laryngeal anatomy of several closely related terrestrial species including: dog (Canis familiaris) and black bear (Ursus americanus), and several semiaquatic species including: polar bear (Ursus maritimus), sea otter (Enhydra lutris), river otter (Lontra canadensis), beaver (Castor canadensis), muskrat (Ondatra zibethicus), and hippo (Hippopotamus amphibius). Comparisons were also made to fully aquatic mammals that can vocalize underwater including: manatee (Trichechus manatus), baleen whales (Caperea marginata, Balaena glacialis, Megaptera novaeangliae, Balaenoptera musculus, B. physalus, B. borealis, B. acutorostrata), and over 20 species of toothed whales (including sperm whales, beaked whales, dolphins, and porpoises). Results indicate that the harbor and gray seals have an unremarkable larynx that appears grossly similar to that of most other mammals. Elephant seal, sea lion, and walrus larynges, however, were unusual in having arytenoid cartilages that are extremely large and rounded on their rostral surface. The arytenoids form a valve across approximately half of the laryngeal lumen. Interestingly, this feature also occurs in sea otters. The corniculate and cuneiform cartilages are difficult to detect in the elephant seal, sea lion, and walrus. The epiglottic cartilage is very short in the sea lion and walrus, similar to the manatee, but robust in the elephant seal. The vestibular fold of the elephant seal is very prominent, and appears connected to the arytenoid cartilage. Harbor seal, gray seal, and walrus vocal folds are oriented perpendicular to airflow, as in other terrestrial mammals. Elephant seal and sea lion vocal folds are rotated, compared with other terrestrial mammals, with the ventral attachment located more rostrally. Their vocal folds are thus positioned near the ventral aspect of the larynx. This orientation is similar to those of the hippo, baleen whales, and toothed whales. None of the pinnipeds have vocal folds resembling the smooth sloped vocal folds of the manatee, or the thickened vocal folds of the polar bear. The unusual arytenoid size and vocal fold orientation in some pinnipeds may indicate evolutionary convergence with other underwater laryngeal vocalizers (e.g., hippo, baleen whales). It is unclear whether laryngeal morphologies of elephant seal, sea lion, and walrus are functional adaptations representing autapomorphies (uniquely derived features) of these species. Further work should be directed towards understanding whether laryngeal specializations may relate to variations in underwater sounds or in‐air vocalizations. More pinniped species need to be studied, particularly deep diving seals that are very vocal (e.g., Weddell seal) or fur seals (having external morphology and behaviors very similar to sea lions).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.