Quantitative Macroscopic Digestive Tract Anatomy of the Beira
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Research article Quantitative macroscopic digestive tract anatomy of the beira (Dorcatragus megalotis) Cathrine Sauer1,2, Catrin Hammer3,4, Mads F. Bertelsen1, Thomas Tütken5, Marcus Clauss6* and Sven Hammer3,4 1Center for Zoo and Wild Animal Health, Copenhagen Zoo, Roskildevej 38, DK-2000 Frederiksberg, Denmark. 2Present address: North of England Zoological Society, Chester Zoo, Chester, CH2 1LH, United Kingdom 3Al Wabra Wildlife Preservation, Al Wabra Wildlife Preservation, P.O. Box 44069, Doha, State of Qatar 4Present address: Naturschutz-Tierpark Görlitz, Zittauerstr. 43, D-02826 Görlitz, Germany 5Analytical Palaeontology, Institute for Geoscience, Johannes Gutenberg University, J.-J.-Becher-Weg 21, 55128 Mainz Germany 6Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, CH-8057 Zurich, Switzerland. JZAR Research article Research JZAR * Correspondence: Marcus Clauss; [email protected] Keywords: Abstract abomasum, intestine, gazelle, omasum, The digestive system of the beira (Dorcatragus megalotis), a small East African antelope, has not been reticulum, rumen, salivary glands described previously. We present anatomical data collected from the only known captive population of the species, allowing for a first understanding of the morphophysiological ‘type’ of this species. Article history: The gastrointestinal anatomy was quantified by weights, dimensions and areas, measured in a total Received: 4 January 2016 of 19 beiras (ranging in body mass from 3.5 to 13.5 kg; not all measures taken in all animals). These Accepted: 27 September 2016 characteristics were then evaluated against a comparative dataset consisting of data from both Published online: 3 November 2016 browsing and grazing ruminants. Overall, for example, in terms of reticular crest height, masseter mass and omasal laminar surface area, the beira digestive tract resembled that of the browsing ‘moose- type’ ruminants. A diet of dicotyledonous plant material was further supported by the carbon isotope 13 composition (δ C = -27.5‰) typical for C3 plants of a faecal sample collected from a wild specimen, as well as the limited ecological information available for the species. OPEN ACCESS Introduction new species to the catalogue is welcome in order to increase the power of future investigations of convergence. Here, we The digestive anatomy of ruminants has been an object used the opportunity of access to digestive tracts of beira of continuous attention, due to the enormous diversity in antelope (Dorcatragus megalotis) for the description of the morphological details across species (Garrod 1877; Neuville macroscopic digestive anatomy of the species. and Derscheid 1929; Langer 1973). While much of this work was The beira is a small antelope from East Africa, with an area of motivated by the aim of inferring phylogenetic relationships distribution from the southern coast of the Gulf of Aden to the (reviewed by Clauss 2014), it was the work of Hofmann (1968, Horn of Africa in the east, to the borders of Somalia, Ethiopia 1973, 1988, 1989) that introduced the potential of digestive and Djibouti in the west, and to the Marmar Mountains in tract characteristics for studies of convergence, by linking the north-eastern Ethiopia (Künzel and Künzel 1998; Nowak variation of a large number of morphological details with the 1999; Heckel et al. 2008; Giotto et al. 2009). So far, only one three feeding types of browser, intermediate feeder and grazer. population of beira antelopes has been maintained in captivity Convergence was more recently formally confirmed for several (Hammer 2011). The scarce information on the species derives of these details (e.g. Hofmann et al. 2008; Clauss et al. 2010a). from limited observations in the wild and extensive study of In order to enhance the clarity of the concept of comparing this captive group (Hammer and Hammer 2005; Giotto et al. morphology on the one hand to the natural diet on the other 2008; Giotto et al. 2009; Hammer 2011). In their review of hand, the terms ‘moose-type’ and ‘cattle-type’ were coined as diets of African bovids, Gagnon and Chew (2000) estimated descriptors of anatomy and physiology that can be juxtaposed that beira consume 90% of dicot material, 5% fruit and only to the botany-focused descriptors of the natural diet (browser 5% grass in their natural diet, but considered the underlying vs intermediate feeders and grazers) (Clauss et al. 2010b). information inadequate and hence the estimation unreliable. While a varying number of morphological details have been During sporadic observations, Giotto et al. (2008) recorded published for up to 90 ruminant species, the addition of any a list of 19 dicot and one monocot plant species that were 174 Journal of Zoo and Aquarium Research 4(4) 2016 Beira digestive anatomy ingested by beiras. Based on the literature cited, we hypothesised to standard dissection protocols as described in other species that the anatomical characteristics of the digestive tract should (e.g. Sauer et al. 2016b), including the dissection of the masseter place the beira among the ‘moose-type’ ruminants. muscle (Axmacher and Hofmann 1988; Clauss et al. 2008), the parotid gland (Hofmann et al. 2008), and the tongue (Meier et al. Methods 2016). Depending on the status of the animals and the necessary pathological investigations, not all measurements could be taken Data were collected from 19 beiras (six males and 13 females, in all animals. The number of animals available for each measure body mass [BM] range 3.5–13.5 kg) housed at the Al Wabra is indicated in the tables. All dissections and measurements were Wildlife Preservation (AWWP, Qatar). At AWWP, beiras were kept performed by the same investigator (M. Clauss). Terms were used on a diet of browse and fresh lucerne supplemented with pelleted in agreement with the Nomina Anatomica Veterinaria (I.C.V.G.A.N. feeds, vegetables and mineral supplements (Hammer 2011). After 2012). a period in which it prospered, the captive population suffered A single faecal sample of a free-ranging beira was collected during from an epidemic of Mycoplasma that led to a drastic decline a field trip to Djibouti in 2003. A homogenised aliquot of the faecal in population size (Hammer 2011; Müller et al. 2013; Gull et al. sample was analysed for its carbon isotope composition–13C/12C 2014). Most animals investigated in the present study originated expressed as δ13C value versus Vienna Pee Dee Belemnite (Coplen from that pool of deceased animals. The beiras were submitted 1994), following standard procedures using an elemental analyser coupled to a continuous flow isotope ratio mass spectrometer (Codron et al. 2007). As faecal δ13C values reflect the composition of ingested plants (Codron et al. 2007), the proportion of C3 (mainly dicot) and C4 (monocot) plants in the beira diet, i.e. the percentage of leaves and grass, could be estimated from this faecal sample. For a comparative evaluation of the anatomical measures of beiras, current data were plotted against literature data on forestomach anatomy and salivary gland weight of other ruminant species, classified as having either a ‘moose-type’ or ‘cattle-type’ digestive tract (for species and literature sources, see Sauer et al. 2016a), with additional comparative data on tongue anatomy from Meier et al. (2016). Figure 2. Internal aspect of a reticulorumen of a beira antelope (Dorcotragus megalotis). Abbreviations: D = dorsal rumen, A = Atrium ruminis, R = reticulum. Figure 1. Digestive tract of the beira antelope (Dorcotragus megalotis). Abbreviations: DR = dorsal rumen, VR = ventral rumen, RE = reticulum, O = omasum, A = abomasum, SI = small intestine, CE = caecum, and LI = Figure 3. Internal aspect of a reticulum of a beira antelope (Dorcotragus large intestine. megalotis). Journal of Zoo and Aquarium Research 4(4) 2016 175 Sauer et al. Table 1. Regression equations (y = α * xβ; with 95% confidence intervals for parameter estimates) for the relationship of rumen and reticulum size measures to body mass (BM) in beira antelope (Dorcotragus megalotis). Measure n BM (kg) Mean ± SD BM effect α β R2 Reticulorumen tissue weight g 13 4.0–13.5 165.0 ± 55.9 p < 0.001 34.91 [21.24; 57.37] 0.73 [0.50; 0.97] 0.81 Rumen height cm 12 4.0–13.5 20.3 ± 2.5 p = 0.050 14.56 [10.44; 20.30] 0.16 [0.00; 0.33] 0.33 Dorsal rumen length cm 12 4.0–13.5 18.0 ± 2.0 p = 0.089 13.61 [9.76; 18.99] 0.14 [-0.03; 0.30] 0.26 Ventral rumen length cm 12 4.0–13.5 17.3 ± 2.1x p = 0.094 12.85 [9.01; 18.31] 0.15 [-0.03; 0.32] 0.25 Total rumen diagonal cm 9 4.0–13.5 20.6 ± 3.1 p = 0.048 13.54 [8.95; 20.48] 0.22 [0.00; 0.43] 0.45 Reticulum height cm 13 4.0–13.5 9.6 ± 2.0x p < 0.001 4.05 [2.76; 5.96] 0.42 [0.23; 0.61] 0.69 Reticulum length cm 12 4.0–13.5 5.0 ± 1.3x p = 0.051 2.35 [1.13; 4.89] 0.36 [-0.00; 0.72] 0.33 Reticular crest height mm 14 4.0–13.5 1.0 ± 0.3 p = 0.223 0.59 [0.25; 1.38] 0.24 [-0.17; 0.65] 0.12 Cranial rumen pillar thickness mm 15 4.0–13.5 3.8 ± 1.0 p = 0.014 1.36 [0.63; 2.95] 0.49 [0.11; 0.86] 0.38 Caudal rumen pillar thickness mm 15 4.0–13.5 4.9 ± 1.5 p = 0.341 3.08 [1.21; 7.84] 0.21 [-0.25; 0.66] 0.07 To determine the relation between BM and anatomical measures the expected isometric value in the 95% CI of the BM exponent in the beiras, data were ln-transformed and linear regression (Tables 1–4).