Publications by authors named "Daryl Codron"

43 Publications

Less need for differentiation? Intestinal length of reptiles as compared to mammals.

PLoS One 2021 2;16(7):e0253182. Epub 2021 Jul 2.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.

Although relationships between intestinal morphology between trophic groups in reptiles are widely assumed and represent a cornerstone of ecomorphological narratives, few comparative approaches actually tested this hypothesis on a larger scale. We collected data on lengths of intestinal sections of 205 reptile species for which either body mass (BM), snout-vent-length (SVL) or carapax length (CL) was recorded, transforming SVL or CL into BM if the latter was not given, and analyzed scaling patterns with BM and SVL, accounting for phylogeny, comparing three trophic guilds (faunivores, omnivores, herbivores), and comparing with a mammal dataset. Length-BM relationships in reptiles were stronger for the small than the large intestine, suggesting that for the latter, additional factors might be relevant. Adding trophic level did not consistently improve model fit; only when controlling for phylogeny, models indicated a longer large intestine in herbivores, due to a corresponding pattern in lizards. Trophic level effects were highly susceptible to sample sizes, and not considered strong. Models that linked BM to intestine length had better support than models using SVL, due to the deviating body shape of snakes. At comparable BM, reptiles had shorter intestines than mammals. While the latter finding corresponds to findings of lower tissue masses for the digestive tract and other organs in reptiles as well as our understanding of differences in energetic requirements between the classes, they raise the hitherto unanswered question what it is that reptiles of similar BM have more than mammals. A lesser effect of trophic level on intestine lengths in reptiles compared to mammals may stem from lesser selective pressures on differentiation between trophic guilds, related to the generally lower food intake and different movement patterns of reptiles, which may not similarly escalate evolutionary arms races tuned to optimal agility as between mammalian predators and prey.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0253182PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8253402PMC
July 2021

Dental microwear texture gradients in guinea pigs reveal that material properties of the diet affect chewing behaviour.

J Exp Biol 2021 Jul 12;224(13). Epub 2021 Jul 12.

Applied and Analytical Palaeontology, Institute of Geosciences, Johannes Gutenberg University, J.-J.-Becher-Weg 21, 55128 Mainz, Germany.

Dental microwear texture analysis (DMTA) is widely used for diet inferences in extant and extinct vertebrates. Often, a reference tooth position is analysed in extant specimens, while isolated teeth are lumped together in fossil datasets. It is therefore important to test whether dental microwear texture (DMT) is tooth position specific and, if so, what causes the differences in wear. Here, we present results from controlled feeding experiments with 72 guinea pigs, which received either fresh or dried natural plant diets of different phytolith content (lucerne, grass, bamboo) or pelleted diets with and without mineral abrasives (frequently encountered by herbivorous mammals in natural habitats). We tested for gradients in dental microwear texture along the upper cheek tooth row. Regardless of abrasive content, guinea pigs on pelleted diets displayed an increase in surface roughness along the tooth row, indicating that posterior tooth positions experience more wear compared with anterior teeth. Guinea pigs feedings on plants of low phytolith content and low abrasiveness (fresh and dry lucerne, fresh grass) showed almost no DMT differences between tooth positions, while individuals feeding on more abrasive plants (dry grass, fresh and dry bamboo) showed a gradient of decreasing surface roughness along the tooth row. We suggest that plant feeding involves continuous intake and comminution by grinding, resulting in posterior tooth positions mainly processing food already partly comminuted and moistened. Pelleted diets require crushing, which exerts higher loads, especially on posterior tooth positions, where bite forces are highest. These differences in chewing behaviour result in opposing wear gradients for plant versus pelleted diets.
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http://dx.doi.org/10.1242/jeb.242446DOI Listing
July 2021

Tooth wear, growth and height in rabbits (Oryctolagus cuniculus) fed pelleted or extruded diets with or without added abrasives.

J Anim Physiol Anim Nutr (Berl) 2021 May 12. Epub 2021 May 12.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.

Among the different factors thought to affect dental wear, dietary consistency is possibly the least investigated. To understand tooth wear of herbivorous animals consuming different dietary consistencies with different abrasive potential, we fed 14 rabbits (Oryctolagus cuniculus) exclusively with a timothy grassmeal-based diet in either pelleted or extruded form, or the same diets with an addition of 5% fine sand abrasives (mean size 130 µm). First, we offered the rabbits the pelleted and extruded diets as well as the pelleted control and pelleted abrasive diet in a two-stage preference experiment. Then, the rabbits received each diet for 2 weeks in a randomised serial feeding experiment, where each animal served as its own control. Tooth measurements for wear, growth and height were achieved using a manual calliper, endoscopic examination and CT scans. The analysis of the diets as fed showed almost identical mean particle size, but the extruded diet had a lower density (volume/mass) and softer consistency compared to the pelleted one and was favoured by most rabbits. The rabbits selected against the diet with sand during the preference experiment, possibly because it caused more tooth wear, especially on the teeth most exposed to wear along the upper tooth row (upper P4 and M1). The maxillary teeth also showed evidence of an increased chewing laterality by the end of the experiment. The extruded diet led to a significantly lower cheek teeth height than the pelleted diet, potentially due to the higher chewing effort needed for a similar dry matter intake. The results suggest that dietary hardness alone is a poor predictor of dental wear. The regrowth of the teeth matched wear consistently.
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http://dx.doi.org/10.1111/jpn.13565DOI Listing
May 2021

Mammalian intestinal allometry, phylogeny, trophic level and climate.

Proc Biol Sci 2021 02 10;288(1944):20202888. Epub 2021 Feb 10.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland.

An often-stated ecomorphological assumption that has the status of 'textbook knowledge' is that the dimensions of the digestive tract correlate with diet, where herbivores-consuming diets of lower digestibility-have longer intestinal tracts than faunivores-consuming diets of higher digestibility. However, statistical approaches have so far failed to demonstrate this link. Here, we collated data on the length of intestinal sections and body mass of 519 mammal species, and test for various relationships with trophic, climatic and other biological characteristics. All models showed a strong phylogenetic signal. Scaling relationships with body mass showed positive allometry at exponents greater than 0.33, except for the caecum, which is particularly large in smaller species. Body mass was more tightly linked to small intestine than to large intestine length. Adding a diet proxy to the relationships increased model fit for all intestinal sections, except for the small intestine when accounting for phylogeny. Thus, the diet has a main effect on the components of the large intestine, with longer measures in herbivores. Additionally, measures of habitat aridity had a positive relationship with large intestine length. The small intestine was longer in species from colder habitats at higher latitudes, possibly facilitating the processing of peak intake rates during the growing season. This study corroborates intuitive expectations on digestive tract anatomy, while the dependence of significant results on large sample sizes and inclusion of specific taxonomic groups indicates that the relationships cannot be considered fixed biological laws.
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http://dx.doi.org/10.1098/rspb.2020.2888DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7893215PMC
February 2021

Chewing, dental morphology and wear in tapirs (Tapirus spp.) and a comparison of free-ranging and captive specimens.

PLoS One 2020 15;15(6):e0234826. Epub 2020 Jun 15.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.

Feeding practice in herbivorous mammals can impact their dental wear, due to excessive or irregular abrasion. Previous studies indicated that browsing species display more wear when kept in zoos compared to natural habitats. Comparable analyses in tapirs do not exist, as their dental anatomy and chewing kinematics are assumed to prevent the use of macroscopic wear proxies such as mesowear. We aimed at describing tapir chewing, dental anatomy and wear, to develop a system allowing comparison of free-ranging and captive specimens even in the absence of known age. Video analyses suggest that in contrast to other perissodactyls, tapirs have an orthal (and no lateral) chewing movement. Analysing cheek teeth from 74 museum specimens, we quantified dental anatomy, determined the sequence of dental wear along the tooth row, and established several morphometric measures of wear. In doing so, we showcase that tapir maxillary teeth distinctively change their morphology during wear, developing a height differential between less worn buccal and more worn lingual cusps, and that quantitative wear corresponds to the eruption sequence. We demonstrate that mesowear scoring shows a stable signal during initial wear stages but results in a rather high mesowear score compared to other browsing herbivores. Zoo specimens had lesser or equal mesowear scores as specimens from the wild; additionally, for the same level of third molar wear, premolars and other molars of zoo specimens showed similar or less wear compared specimens from the wild. While this might be due to the traditional use of non-roughage diet items in zoo tapirs, these results indicate that in contrast to the situation in other browsers, excessive tooth wear appears to be no relevant concern in ex situ tapir management.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0234826PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7295239PMC
September 2020

Confirmation of a wear-compensation mechanism in dental roots of ruminants.

Anat Rec (Hoboken) 2021 02 15;304(2):425-436. Epub 2020 May 15.

Vetsuisse Faculty, Clinic for Zoo Animals, Exotic Pets and Wildlife, University of Zurich, Zurich, Switzerland.

Diet affects many factors of an animal's anatomy, but teeth are a specific focus of dietary research, as their durability lends them to record information on a large variety of scales. Abrasive diets like those of grazing herbivores are known to wear down teeth, but how that wear affects tooth growth and the relations between its different morphological components is rarely investigated. Seven pelleted diets varying in abrasive size and concentration were fed over a 17-month period to 49 sheep (Ovis aries), of which n = 39 qualified for morphology measurements. Using computed tomography, scans of the skulls were made over the course of the experiment, and the impact of diet-related wear was observed on tooth volume and morphology, including the position of dental burr marks, over time. Digital caliper measurements were applied to 3D renderings of the teeth, and the volume of crown and root segments were investigated separately. We aimed to detect a signal of root growth compensating for wear, and test if this mechanism would be affected by dietary abrasives. Crown-segment volume loss was correlated to root-segment volume gain. Height and burr mark measurements indicated a much higher experimental tooth wear than that previously reported for free-ranging animals. The reason for this is unclear. There was no relationship between tooth height and dentine basin depth. For all parameters, there was no effect of diet; hence, while the measurements corroborate general understanding of tooth wear and compensatory processes, these methods appear not suitable to assess subtle differences between feeding regimes.
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http://dx.doi.org/10.1002/ar.24402DOI Listing
February 2021

'Remote' behavioural ecology: do megaherbivores consume vegetation in proportion to its presence in the landscape?

PeerJ 2020 19;8:e8622. Epub 2020 Feb 19.

Department of Classics and Archaeology, University of Nottingham, Nottingham, UK.

Examination of the feeding habits of mammalian species such as the African elephant () that range over large seasonally dynamic areas is exceptionally challenging using field-based methods alone. Although much is known of their feeding preferences from field studies, conclusions, especially in relation to differing habits in wet and dry seasons, are often contradictory. Here, two remote approaches, stable carbon isotope analysis and remote sensing, were combined to investigate dietary changes in relation to tree and grass abundances to better understand elephant dietary choice in the Kruger National Park, South Africa. A composited pair of Landsat Enhanced Thematic Mapper satellite images characterising flushed and senescent vegetation states, typical of wet and dry seasons respectively, were used to generate land-cover maps focusing on the forest to grassland gradient. Stable carbon isotope analysis of elephant faecal samples identified the proportion of C (typically browse)/C (typically grass) in elephant diets in the 1-2 days prior to faecal deposition. The proportion of surrounding C land-cover was extracted using concentric buffers centred on faecal sample locations, and related to the faecal %C content. Results indicate that elephants consume C vegetation in proportion to its availability in the surrounding area during the dry season, but during the rainy season there was less of a relationship between C intake and availability, as elephants targeted grasses in these periods. This study illustrates the utility of coupling isotope and cost-free remote sensing data to conduct complementary landscape analysis at highly-detailed, biologically meaningful resolutions, offering an improved ability to monitor animal behavioural patterns at broad geographical scales. This is increasingly important due to potential impacts of climate change and woody encroachment on broad-scale landscape habitat composition, allowing the tracking of shifts in species utilisation of these changing landscapes in a way impractical using field based methods alone.
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http://dx.doi.org/10.7717/peerj.8622DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7035871PMC
February 2020

The uneven weight distribution between predators and prey: Comparing gut fill between terrestrial herbivores and carnivores.

Comp Biochem Physiol A Mol Integr Physiol 2020 05 22;243:110683. Epub 2020 Feb 22.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland. Electronic address:

The general observation that secondary consumers ingest highly digestible food and have simple short guts and small abdominal cavities intuitively results in the assumption that mammalian carnivores carry less digesta in their gut compared to herbivores. Due to logistic constraints, this assumption has not been tested quantitatively so far. In this contribution, we estimated the dry matter gut contents (DMC) for 25 species of the order Carnivora (including two strictly herbivorous ones, the giant and the red panda) using the physical 'Occupancy Principle', based on a literature data collection on dry matter intake (DMI), apparent dry matter digestibility (aD DM) and retention time (RT), and compared the results to an existing collection for herbivores. Scaling exponents with body mass (BM) for both carnivores and herbivores were in the same range with DMI ~ BM; aD DM ~ BM; RT ~ BM and DMC ~ BM. The trophic level (carnivore vs herbivore) significantly affected all digestive physiology parameters except for RT. Numerically, the carnivore DMI level reached 77%, the RT 32% and DMC only 29% of the corresponding herbivore values, whereas the herbivore aD DM only reached 82% of that of carnivores. Thus, we quantitatively show that carnivores carry less inert mass or gut content compared to herbivores, which putatively benefits them in predator-prey interactions and might have contributed to the evolution towards unguligradism in herbivores. As expected, the two panda species appeared as outliers in the dataset with low aD DM and RT for a herbivore but extremely high DMI values, resulting in DMC in the lower part of the herbivore range. Whereas the difference in DMI and DMC scaling in herbivores might allow larger herbivores to compensate for lower diet quality by ingesting more, this difference may allow larger carnivores not to go for less digestible prey parts, but mainly to increase meal intervals, i.e. not having to hunt on a daily basis.
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http://dx.doi.org/10.1016/j.cbpa.2020.110683DOI Listing
May 2020

The way wear goes: phytolith-based wear on the dentine-enamel system in guinea pigs ().

Proc Biol Sci 2019 10 9;286(1912):20191921. Epub 2019 Oct 9.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich 8057, Switzerland.

The effect of phytoliths on tooth wear and function has been contested in studies of animal-plant interactions. For herbivores whose occlusal chewing surface consists of enamel ridges and dentine tissue, the phytoliths might particularly erode the softer dentine, exposing the enamel ridges to different occlusal forces and thus contributing to enamel wear. To test this hypothesis, we fed guinea pigs (; = 36 in six groups) for three weeks exclusively on dry or fresh forage of low (lucerne), moderate (fresh timothy grass) or very high (bamboo leaves) silica content representing corresponding levels of phytoliths. We quantified the effect of these treatments with measurements from micro-computed tomography scans. Tooth height indicated extreme wear due to the bamboo diet that apparently brought maxillary incisors and molars close to the minimum required for functionality. There were negative relationships between a cheek tooth's height and the depth of its dentine basin, corroborating the hypothesis that dentine erosion plays an important role in herbivore tooth wear. In spite of lower body mass, bamboo-fed animals paradoxically had longer cheek tooth rows and larger occlusal surfaces. Because ever-growing teeth can only change in shape from the base upwards, this is a strong indication that failure to compensate for wear by dental height-growth additionally triggered general expansive growth of the tooth bases. The results suggest that enamel wear may intensify after enamel has been exposed due to a faster wear of the surrounding dentine tissue (and not the other way around), and illustrate a surprising plasticity in the reactivity of this rodent's system that adjusts tooth growth to wear.
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http://dx.doi.org/10.1098/rspb.2019.1921DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6790768PMC
October 2019

Seasonal and habitat effects on the nutritional properties of savanna vegetation: Potential implications for early hominin dietary ecology.

J Hum Evol 2019 08 27;133:99-107. Epub 2019 Jun 27.

Department of Anthropology, University of Colorado Boulder, Boulder, CO, 80309, USA.

The African savannas that many early hominins occupied likely experienced stark seasonality and contained mosaic habitats (i.e., combinations of woodlands, wetlands, grasslands, etc.). Most would agree that the bulk of dietary calories obtained by taxa such as Australopithecus and Paranthropus came from the consumption of vegetation growing across these landscapes. It is also likely that many early hominins were selective feeders that consumed particular plants/plant parts (e.g., leaves, fruit, storage organs) depending on the habitat and season within which they were foraging. Thus, improving our understanding of how the nutritional properties of potential hominin plant foods growing in modern African savanna ecosystems respond to season and vary by habitat will improve our ability to model early hominin dietary behavior. Here, we present nutritional analyses (crude protein and acid detergent fiber) of plants growing in eastern and southern African savanna habitats across both wet and dry seasons. We find that many assumptions about savanna vegetation are warranted. For instance, plants growing in our woodland habitats have higher average protein/fiber ratios than those growing in our wetland and grassland transects. However, we find that the effects of season and habitat are complex, an example being the unexpectedly higher protein levels we observe in the grasses and sedges growing in our Amboseli wetlands during the dry season. Also, we find significant differences between the vegetation growing in our eastern and southern African field sites, particularly among plants using the C photosynthetic pathway. This may have implications for the differences we see between the stable carbon isotope compositions and dental microwear patterns of eastern and southern African Paranthropus species, despite their shared, highly derived craniodental anatomy.
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http://dx.doi.org/10.1016/j.jhevol.2019.01.003DOI Listing
August 2019

Gross intestinal morphometry and allometry in ruminants.

J Morphol 2019 09 26;280(9):1254-1266. Epub 2019 Jun 26.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.

While some descriptions of ruminants' dietary adaptations suggest that the length of the intestinal tract reflects the proportion of grass or browse in the diet, this assumption has been questioned. We collated data on body mass (BM), as well as small intestine, caecum, colon/rectum, large and total intestine length in 68 ruminant species, and, while accounting for the phylogenetic structure of the dataset, evaluated both allometric scaling and the potential influence of diet, digestive physiology or climate proxies on measures of intestine length. Intestinal length generally scaled to BM at an exponent higher than the 0.33 expected due to geometry. Diet or digestive physiology proxies did not have an influence on any intestinal length measures, though some proxies indicating more arid natural habitats were positively correlated with measures of the large intestine. The relative size of a forestomach compartment, the omasum, was negatively correlated with intestine length. The results indicate that intestine length measures provide little indication of feeding type or digestive physiology, but rather indicate adaptations to aridity. Higher-than-geometry scaling of intestinal length may be related to the necessity of maintaining geometric (or metabolic) scaling of intestinal surface area while keeping gut diameter, and hence the diffusion distances, small. The way in which space trade-offs determine the macroanatomy of different organs in the abdominal cavity, such as the omasum and the intestine, deserves further investigation.
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http://dx.doi.org/10.1002/jmor.21028DOI Listing
September 2019

Digesta passage in nondomestic ruminants: Separation mechanisms in 'moose-type' and 'cattle-type' species, and seemingly atypical browsers.

Comp Biochem Physiol A Mol Integr Physiol 2019 09 18;235:180-192. Epub 2019 Jun 18.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland. Electronic address:

Ruminants have been classified as having a 'moose-type' or 'cattle-type' digestive physiology. 'Cattle-type' ruminants have a clear difference in the mean retention time (MRT) of fluid vs. small particles in the reticulorumen (RR), with a high 'selectivity factor' (SF = MRT/ MRT, >1.80), and are typically grazers and intermediate feeders. 'Moose-type' ruminants have lower SF (<1.80), possibly because of defensive salivary proteins that constrain amounts of (high-viscosity) saliva, and are typically restricted to browsing. To further contribute to testing this physiology-diet correlation, we performed 55 individual passage measurements in 4/6 species that have/have not been investigated previously, respectively. Co-EDTA was used as a solute (fluid) and Cr-mordanted hay particles (<2 mm) as particle markers. Results are related to the percentage of grass in the natural diet taken from the literature. Moose (Alces alces, n = 4 on 4 to 5 diets each and n = 2 on a single diet, 5% grass, SF 1.46 ± 0.22) and giraffe (Giraffa camelopardalis, n = 3 on 3 to 5 diets each, 1%, 1.42 ± 0.23) as classical 'moose-type', and cattle (Bos taurus, n = 2, 70%, 2.04) as classical 'cattle-type' ruminants yielded results similar to those previously published, as did waterbuck (Kobus ellipsiprymnus, n = 5, 84%, 2.46 ± 0.49), corroborating that the SF represents, to a large extent, a species-specific characteristic. Results in oryx (Oryx leucoryx, n = 1, 75%, 2.60) and sitatunga (Tragelaphus spekii, n = 4, 68%, 1.81 ± 0.21) correspond to the concept of 'cattle-type' ruminants being grazers or intermediate feeders. However, European bison (Bison bonasus, n = 1, 10%, 2.74), nyala (T. angasii, n = 6, 20%, 1.95 ± 0.25), bongo (T. eurycerus, n = 3, 13%, 2.39 ± 0.54) and gerenuk (Litocranius walleri, n = 1, 0%, 2.25) appear as 'cattle-type' ruminants, yet have a browse-dominated diet. While the results do not challenge the view that a 'moose-type' digestive physiology is an adaptation to browse diets, they indicate that it may not be the only adaptation that enables ruminants to use browse. Apparently, a 'cattle-type' digestive physiology with a high SF does not necessarily preclude a browsing diet niche. High-SF browsers might have the benefit of an increased harvest of RR microbiota and grit removal prior to rumination; how they defend themselves against secondary plant compounds in browse remains to be investigated.
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http://dx.doi.org/10.1016/j.cbpa.2019.06.010DOI Listing
September 2019

Dietary Evolution: The Panda Paradox.

Curr Biol 2019 06;29(11):R417-R419

Department of Zoology and Entomology, University of the Free State, PO BOX 339, Bloemfontein, South Africa.

Giant pandas are specialized herbivores that digest little of the bamboo they consume. A new study argues that pandas, like carnivores, get most of their energy from protein, explaining their carnivore-like guts and poor digestion. This may have facilitated their ancestors' transition to herbivory.
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http://dx.doi.org/10.1016/j.cub.2019.04.045DOI Listing
June 2019

The ecomorphology of southern African rodent incisors: Potential applications to the hominin fossil record.

PLoS One 2019 20;14(2):e0205476. Epub 2019 Feb 20.

Department of Anthropology, University of Colorado Boulder, Boulder, Colorado, United States of America.

The taxonomic identification of mammalian fauna within fossil assemblages is a well-established component of paleoenvironmental reconstructions. However, many fragmentary specimens recovered from fossil sites are often disregarded as they can be difficult to identify with the precision required for taxonomic methods. For this reason, the large numbers of isolated rodent incisors that are often recovered from hominin fossil bearing sites are generally regarded as offering little interpretive value. Ecomorphological analysis, often referred to as a "taxon-free" method, can potentially circumvent this problem by focusing on the adaptive, rather than the taxonomic significance of rodent incisor morphology. Here, we determine if the morphology of the upper incisors of modern southern African rodents reflects dietary behavior using discriminant function analysis. Our model suggests that a strong ecomorphological signal exists in our modern sample and we apply these results to two samples of isolated incisors from the hominin fossil bearing sites, Sterkfontein and Swartkrans.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0205476PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6382097PMC
November 2019

Comparative omasum anatomy in ruminants: Relationships with natural diet, digestive physiology, and general considerations on allometric investigations.

J Morphol 2019 02 7;280(2):259-277. Epub 2019 Jan 7.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.

The omasum is the third forestomach compartment of pecoran ruminants. It is assumed that the re-absorption of fluid present in the forestomach digesta (that facilitates particle sorting, digestion, and harvest of microbes) is its main function, so that less diluted digesta is submitted to enzymatic digestion in the lower digestive tract. Here, we evaluate measures of omasum size (representing 84 ruminant species in the largest data set) against body mass and proxies of the natural diet (%grass) or forestomach physiology (fluid throughput), using phylogenetically controlled models. The origin of specimens (free-ranging or captive) did not have an effect in the data set. Models with the best support invariably either included %grass or a physiology proxy in addition to body mass. These effects were not necessarily additive (affecting the intercept of the allometric regression), but often indicated a change in the allometric body mass-exponent with diet or physiology. Only models that allowed an influence on the allometric exponent yielded basic exponents compatible with predictions derived from geometry. Species that include more grass in their natural diet, or that have a "cattle-type" physiology marked by a high forestomach fluid throughput, generally have larger omasa. However, the existence of outliers, as well as the overall data pattern, suggest that this is not an obligatory morphophysiological condition. Circumstantial evidence is presented leading to the hypothesis that the comparatively small and less complex omasa of "moose-type" species do not necessarily represent an "original" state, but may be derived from more complex states by ontogenetic reduction and fusion of omasal laminae.
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http://dx.doi.org/10.1002/jmor.20942DOI Listing
February 2019

Within trophic level shifts in collagen-carbonate stable carbon isotope spacing are propagated by diet and digestive physiology in large mammal herbivores.

Ecol Evol 2018 Apr 25;8(8):3983-3995. Epub 2018 Mar 25.

Institut für Geowissenschaften AG für Angewandte und Analytische Paläontologie Johannes Gutenberg-Universität Mainz Mainz Germany.

Stable carbon isotope analyses of vertebrate hard tissues such as bones, teeth, and tusks provide information about animal diets in ecological, archeological, and paleontological contexts. There is debate about how carbon isotope compositions of collagen and apatite carbonate differ in terms of their relationship to diet, and to each other. We evaluated relationships between δC and δC among free-ranging southern African mammals to test predictions about the influences of dietary and physiological differences between species. Whereas the slopes of δC-δC relationships among carnivores are ≤1, herbivore δC increases with increasing dietary δC at a slower rate than does δC, resulting in regression slopes >1. This outcome is consistent with predictions that herbivore δC is biased against low protein diet components (C-enriched C grasses in these environments), and δC is C-enriched due to release of C-depleted methane as a by-product of microbial fermentation in the digestive tract. As methane emission is constrained by plant secondary metabolites in browse, the latter effect becomes more pronounced with higher levels of C grass in the diet. Increases in δC are also larger in ruminants than nonruminants. Accordingly, we show that ΔC- spacing is not constant within herbivores, but increases by up to 5 ‰ across species with different diets and physiologies. Such large variation, often assumed to be negligible within trophic levels, clearly cannot be ignored in carbon isotope-based diet reconstructions.
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http://dx.doi.org/10.1002/ece3.3786DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5916294PMC
April 2018

Grass leaves as potential hominin dietary resources.

J Hum Evol 2018 04 27;117:44-52. Epub 2018 Feb 27.

Department of Anthropology, University of Colorado Boulder, Boulder, CO 80309, USA.

Discussions about early hominin diets have generally excluded grass leaves as a staple food resource, despite their ubiquity in most early hominin habitats. In particular, stable carbon isotope studies have shown a prevalent C component in the diets of most taxa, and grass leaves are the single most abundant C resource in African savannas. Grass leaves are typically portrayed as having little nutritional value (e.g., low in protein and high in fiber) for hominins lacking specialized digestive systems. It has also been argued that they present mechanical challenges (i.e., high toughness) for hominins with bunodont dentition. Here, we compare the nutritional and mechanical properties of grass leaves with the plants growing alongside them in African savanna habitats. We also compare grass leaves to the leaves consumed by other hominoids and demonstrate that many, though by no means all, compare favorably with the nutritional and mechanical properties of known primate foods. Our data reveal that grass leaves exhibit tremendous variation and suggest that future reconstructions of hominin dietary ecology take a more nuanced approach when considering grass leaves as a potential hominin dietary resource.
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http://dx.doi.org/10.1016/j.jhevol.2017.10.013DOI Listing
April 2018

Carnivore stable carbon isotope niches reflect predator-prey size relationships in African savannas.

Integr Zool 2018 Mar;13(2):166-179

Florisbad Quaternary Research Department, National Museum, Bloemfontein, South Africa.

Predator-prey size relationships are among the most important patterns underlying the structure and function of ecological communities. Indeed, these relationships have already been shown to be important for understanding patterns of macroevolution and differential extinction in the terrestrial vertebrate fossil record. Stable isotope analysis (SIA) is a powerful remote approach to examining animal diets and paleodiets. The approach is based on the principle that isotope compositions of consumer tissues reflect those of their prey. In systems where resource isotope compositions are distributed along a body size gradient, SIA could be used to reconstruct predator-prey size relationships. We analyzed stable carbon isotope distributions amongst mammalian herbivores in extant and Plio-Pleistocene African savanna assemblages, and show that the range of δ C values among mammalian prey species (herbivores and rodents) increases with body mass (BM), because C plant feeding (essentially grazing) is more common among larger taxa. Consequently, δ C values of mammalian carnivores in these systems are related to species' BM, reflecting a higher average C prey component in the diets of larger-bodied carnivores. This pattern likely emerges because only the largest carnivores in these systems have regular access to the C prey base, whereas smaller carnivores do not. The δ C-BM relationship observed in mammalian carnivores is a potentially powerful approach for reconstructing and parameterizing predator-prey size relationships in contemporary and fossil savanna assemblages, and for interpreting how various behavioral, ecological and environmental factors influence prey size selection.
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http://dx.doi.org/10.1111/1749-4877.12290DOI Listing
March 2018

Growth rate and stable carbon and nitrogen isotope trophic discrimination factors of lion and leopard whiskers.

Rapid Commun Mass Spectrom 2018 Jan;32(1):33-47

Florisbad Quaternary Research Department, National Museum, PO Box 266, Bloemfontein, 9300, South Africa.

Rationale: Stable isotope analysis (SIA) of whiskers has been used to identify temporal feeding habits, intra-population diet variation, as well as individual dietary specialisation of marine and terrestrial carnivores. However, the potential of the method to disclose such dietary information for large wild felids is hampered by lack of information on species-specific whisker growth rates, whisker growth patterns and whisker-diet trophic discrimination factors (TDFs).

Methods: Whisker growth rates and growth patterns were measured for four lions (Panthera leo) and one leopard (Panthera pardus) held at the National Zoological Gardens, Pretoria, South Africa. Actively growing whiskers of the felids were 'marked' four times over 185 days using C-depleted, C -based giraffe (Giraffa camelopardalis) meat. The periods with low δ C values, identified following serial sectioning of the regrown whiskers at 1 mm intervals and isotopic analysis, were then correlated to specific giraffe meat feeding bouts and hence growth periods. δ C and δ N whisker-diet TDFs were estimated for five lions whose diet remained consistent over multiple years.

Results: The whisker growth rates of three lionesses and the leopard were similar (mean = 0.65 mm day ), despite species, sex and age differences. There was a decrease in whisker growth rate over time, suggesting a non-linear whisker growth pattern. However, linear and non-linear growth simulations showed slight differences between the two growth patterns for the proximal ~50 mm of whiskers. δ C and δ N lion whisker-diet TDFs were also similar amongst individuals (mean = 2.7 ± 0.12 ‰ for δ C values and 2.5 ± 0.08 ‰ for δ N values), irrespective of age and sex.

Conclusions: The whisker growth rate and δ C and δ N lion whisker-diet TDFs obtained in this study can be applied in future studies to assign dietary information contained in analysed felid whiskers to the correct time period and improve deductions of prey species consumed by wild felids.
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http://dx.doi.org/10.1002/rcm.8003DOI Listing
January 2018

Intrinsic factors, adrenal gland morphology, and disease burden in captive cheetahs (Acinonyx jubatus) in South Africa.

Zoo Biol 2017 Jan 27;36(1):40-49. Epub 2016 Dec 27.

National Zoological Gardens of South Africa, Pretoria, South Africa.

Adrenal gland weight (AW) and corticomedullary ratio (ACMR) are used as indicators of stress in animals. Captive cheetahs (Acinonyx jubatus) have higher ACMRs than free-ranging ones and stress has been linked to gastritis, amyloidosis, glomerulosclerosis, and myocardial fibrosis. We reviewed age, sex, body weight (BW), kidney weight (KW), and left AW and ACMR with necropsy findings in 51 South African captive cheetahs. Eleven common histopathologic lesions were counted for each animal as measure of its disease burden. Adrenal corticomedullary hyperplasia was significantly correlated with left AW and ACMR. Males had significantly higher AWs than females; other parameters showed no difference between the sexes. Disease burden, gastritis, and myocardial fibrosis were moderately correlated with adrenal morphology supporting prior evidence that gastritis and myocardial fibrosis are linked to stress. Glomerulosclerosis was not correlated with adrenal morphology and neither kidney nor liver amyloidosis contributed significantly to variation in AW or ACMR on multivariate analyses. Interstitial nephritis showed much stronger correlations with kidney and liver amyloidosis than gastritis. All three adrenal parameters were correlated with age; age was the only significant variable affecting ACMR on the multivariate analyses; and disease burden as well as systemic amyloidosis and kidney disease (except for fibrosis) showed moderate correlations with age. Age may, therefore, be important in the pathogenesis of disease in captive cheetahs, particularly of amyloidosis and kidney disease. None of the intrinsic measurements or adrenal parameters were sufficiently closely linked to disease to be used as ante-mortem proxies for disease burden or specific diseases. Zoo Biol. 36:40-49, 2017. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/zoo.21341DOI Listing
January 2017

Breeding Young as a Survival Strategy during Earth's Greatest Mass Extinction.

Sci Rep 2016 Apr 5;6:24053. Epub 2016 Apr 5.

School of Life Sciences, University of Lincoln, Lincoln LN6 7DL, UK.

Studies of the effects of mass extinctions on ancient ecosystems have focused on changes in taxic diversity, morphological disparity, abundance, behaviour and resource availability as key determinants of group survival. Crucially, the contribution of life history traits to survival during terrestrial mass extinctions has not been investigated, despite the critical role of such traits for population viability. We use bone microstructure and body size data to investigate the palaeoecological implications of changes in life history strategies in the therapsid forerunners of mammals before and after the Permo-Triassic Mass Extinction (PTME), the most catastrophic crisis in Phanerozoic history. Our results are consistent with truncated development, shortened life expectancies, elevated mortality rates and higher extinction risks amongst post-extinction species. Various simulations of ecological dynamics indicate that an earlier onset of reproduction leading to shortened generation times could explain the persistence of therapsids in the unpredictable, resource-limited Early Triassic environments, and help explain observed body size distributions of some disaster taxa (e.g., Lystrosaurus). Our study accounts for differential survival in mammal ancestors after the PTME and provides a methodological framework for quantifying survival strategies in other vertebrates during major biotic crises.
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http://dx.doi.org/10.1038/srep24053DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4820772PMC
April 2016

Geometric factors influencing the diet of vertebrate predators in marine and terrestrial environments.

Ecol Lett 2014 Dec 30;17(12):1553-9. Epub 2014 Sep 30.

Institute of Zoology, Zoological Society of London, Regent's Park, London, NW1 4RY, UK.

Predator-prey relationships are vital to ecosystem function and there is a need for greater predictive understanding of these interactions. We develop a geometric foraging model predicting minimum prey size scaling in marine and terrestrial vertebrate predators taking into account habitat dimensionality and biological traits. Our model predicts positive predator-prey size relationships on land but negative relationships in the sea. To test the model, we compiled data on diets of 794 predators (mammals, snakes, sharks and rays). Consistent with predictions, both terrestrial endotherm and ectotherm predators have significantly positive predator-prey size relationships. Marine predators, however, exhibit greater variation. Some of the largest predators specialise on small invertebrates while others are large vertebrate specialists. Prey-predator mass ratios were generally higher for ectothermic than endothermic predators, although dietary patterns were similar. Model-based simulations of predator-prey relationships were consistent with observed relationships, suggesting that our approach provides insights into both trends and diversity in predator-prey interactions.
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http://dx.doi.org/10.1111/ele.12375DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284001PMC
December 2014

Diet and diet-related disorders in captive ruminants at the national zoological gardens of South Africa.

Zoo Biol 2014 Sep-Oct;33(5):426-32. Epub 2014 Jul 24.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.

Although diet-related disorders have received much attention in the zoo literature, evidence-based results on relationships between diet and disease are still rare, often due to a lack of quantitative dietary information that can be linked to clinical or necropsy reports. We investigated 24 species of captive ruminants from one facility for which quantitative feeding instructions and necropsy reports between 1991 and 2012 were available. Species were classified as grazer (GR), intermediate feeder (IM), or browser (BR). Feeding type and body mass were significantly correlated to the diet fed, with smaller and BR species receiving higher proportions of non-roughage diet items. There were no significant differences between feeding types in the occurrence of parakeratosis/ruminitis/acidosis (PRA) at necropsy, but in body condition score, with BR more often in poor and less often in excellent body condition at necropsy. While there was no direct correlation between the proportion of non-roughage diet items and PRA across species, there was a significant effect of the proportion of non-roughage diet items on PRA when body mass was also taken into account: larger species, and those that received more non-roughage diet items, had higher prevalence of PRA. The results underline that diet and lack of structured feed items can be associated with the disease complex of acidosis in ruminants, but also suggest that this is modified by factors related to animal size. These latter may include susceptibility to acidosis, or husbandry-related opportunities to monopolize non-roughage feeds and ingest higher proportions than intended by feeding instructions.
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http://dx.doi.org/10.1002/zoo.21150DOI Listing
June 2015

Growth and wear of incisor and cheek teeth in domestic rabbits (Oryctolagus cuniculus) fed diets of different abrasiveness.

J Exp Zool A Ecol Genet Physiol 2014 Jun 2;321(5):283-98. Epub 2014 Apr 2.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.

Although patterns of tooth wear are crucial in palaeo-reconstructions, and dental wear abnormalities are important in veterinary medicine, experimental investigations on the relationship between diet abrasiveness and tooth wear are rare. Here, we investigated the effect of four different pelleted diets of increasing abrasiveness (due to both internal [phytoliths] and external abrasives [sand]) or whole grass hay fed for 2 weeks each in random order to 16 rabbits (Oryctolagus cuniculus) on incisor and premolar growth and wear, and incisor and cheek tooth length. Wear and tooth length differed between diets, with significant effects of both internal and external abrasives. While diet abrasiveness was linked to tooth length for all tooth positions, whole forage had an additional effect on upper incisor length only. Tooth growth was strongly related to tooth wear and differed correspondingly between diets and tooth positions. At 1.4-3.2 mm/week, the growth of cheek teeth measured in this study was higher than previously reported for rabbits. Dental abnormalities were most distinct on the diet with sand. This study demonstrates that concepts of constant tooth growth in rabbits requiring consistent wear are inappropriate, and that diet form (whole vs. pelleted) does not necessarily affect cheek teeth. Irrespective of the strong effect of external abrasives, internal abrasives have the potential to induce wear and hence exert selective pressure in evolution. Detailed differences in wear effects between tooth positions allow inferences about the mastication process. Elucidating feedback mechanisms that link growth to tooth-specific wear represents a promising area of future research.
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http://dx.doi.org/10.1002/jez.1864DOI Listing
June 2014

Detecting inter-cusp and inter-tooth wear patterns in rhinocerotids.

PLoS One 2013 3;8(12):e80921. Epub 2013 Dec 3.

Bristol Conservation and Science Foundation, c/o Bristol Zoo Gardens, Bristol, United Kingdom ; School of Biological Sciences, University of Bristol, Bristol, United Kingdom.

Extant rhinos are the largest extant herbivores exhibiting dietary specialisations for both browse and grass. However, the adaptive value of the wear-induced tooth morphology in rhinos has not been widely studied, and data on individual cusp and tooth positions have rarely been published. We evaluated upper cheek dentition of browsing Diceros bicornis and Rhinoceros sondaicus, mixed-feeding R. unicornis and grazing Ceratotherium simum using an extended mesowear method adapted for rhinos. We included single cusp scoring (EM(R)-S) to investigate inter-cusp and inter-tooth wear patterns. In accordance with previous reports, general mesowear patterns in D. bicornis and R. sondaicus were attrition-dominated and C. simum abrasion-dominated, reflecting their respective diets. Mesowear patterns for R. unicornis were more attrition-dominated than anticipated by the grass-dominated diet, which may indicate a low intake of environmental abrasives. EM(R)-S increased differentiation power compared to classical mesowear, with significant inter-cusp and inter-tooth differences detected. In D. bicornis, the anterior cusp was consistently more abrasion-dominated than the posterior. Wear differences in cusp position may relate to morphological adaptations to dietary regimes. Heterogeneous occlusal surfaces may facilitate the comminution of heterogeneous browse, whereas uniform, broad grinding surfaces may enhance the comminution of physically more homogeneous grass. A negative tooth wear gradient was found in D. bicornis, R. sondaicus and R. unicornis, with wear patterns becoming less abrasion-dominated from premolars to molars. No such gradients were evident in C. simum which displayed a uniform wear pattern. In browsers, premolars may be exposed to higher relative grit loads, which may result in the development of wear gradients. The second premolar may also have a role in food cropping. In grazers, high absolute amounts of ingested abrasives may override other signals, leading to a uniform wear pattern and dental function along the tooth row, which could relate to the observed evolution towards homodonty.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0080921PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3849094PMC
August 2014

Ecological interactions in dinosaur communities: influences of small offspring and complex ontogenetic life histories.

PLoS One 2013 30;8(10):e77110. Epub 2013 Oct 30.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zürich, Zürich, Switzerland ; Florisbad Quaternary Research, National Museum, Bloemfontein, South Africa ; School of Biological and Conservation Sciences, University of KwaZulu-Natal, Pietermaritzburg, South Africa ; Department of Anthropology, University of Colorado at Boulder, Boulder, Colorado, United States of America.

Because egg-laying meant that even the largest dinosaurs gave birth to very small offspring, they had to pass through multiple ontogenetic life stages to adulthood. Dinosaurs' successors as the dominant terrestrial vertebrate life form, the mammals, give birth to live young, and have much larger offspring and less complex ontogenetic histories. The larger number of juveniles in dinosaur as compared to mammal ecosystems represents both a greater diversity of food available to predators, and competitors for similar-sized individuals of sympatric species. Models of population abundances across different-sized species of dinosaurs and mammals, based on simulated ecological life tables, are employed to investigate how differences in predation and competition pressure influenced dinosaur communities. Higher small- to medium-sized prey availability leads to a normal body mass-species richness (M-S) distribution of carnivorous dinosaurs (as found in the theropod fossil record), in contrast to the right-skewed M-S distribution of carnivorous mammals (as found living members of the order Carnivora). Higher levels of interspecific competition leads to a left-skewed M-S distribution in herbivorous dinosaurs (as found in sauropods and ornithopods), in contrast to the normal M-S distribution of large herbivorous mammals. Thus, our models suggest that differences in reproductive strategy, and consequently ontogeny, explain observed differences in community structure between dinosaur and mammal faunas. Models also show that the largest dinosaurian predators could have subsisted on similar-sized prey by including younger life stages of the largest herbivore species, but that large predators likely avoided prey much smaller than themselves because, despite predicted higher abundances of smaller than larger-bodied prey, contributions of small prey to biomass intake would be insufficient to satisfy meat requirements. A lack of large carnivores feeding on small prey exists in mammals larger than 21.5 kg, and it seems a similar minimum prey-size threshold could have affected dinosaurs as well.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0077110PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3812983PMC
August 2014

Herbivory and body size: allometries of diet quality and gastrointestinal physiology, and implications for herbivore ecology and dinosaur gigantism.

PLoS One 2013 30;8(10):e68714. Epub 2013 Oct 30.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.

Digestive physiology has played a prominent role in explanations for terrestrial herbivore body size evolution and size-driven diversification and niche differentiation. This is based on the association of increasing body mass (BM) with diets of lower quality, and with putative mechanisms by which a higher BM could translate into a higher digestive efficiency. Such concepts, however, often do not match empirical data. Here, we review concepts and data on terrestrial herbivore BM, diet quality, digestive physiology and metabolism, and in doing so give examples for problems in using allometric analyses and extrapolations. A digestive advantage of larger BM is not corroborated by conceptual or empirical approaches. We suggest that explanatory models should shift from physiological to ecological scenarios based on the association of forage quality and biomass availability, and the association between BM and feeding selectivity. These associations mostly (but not exclusively) allow large herbivores to use low quality forage only, whereas they allow small herbivores the use of any forage they can physically manage. Examples of small herbivores able to subsist on lower quality diets are rare but exist. We speculate that this could be explained by evolutionary adaptations to the ecological opportunity of selective feeding in smaller animals, rather than by a physiologic or metabolic necessity linked to BM. For gigantic herbivores such as sauropod dinosaurs, other factors than digestive physiology appear more promising candidates to explain evolutionary drives towards extreme BM.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0068714PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3812987PMC
August 2014

Comparison of fluid types for resuscitation in acute hemorrhagic shock and evaluation of gastric luminal and transcutaneous Pco2 in Leghorn chickens.

J Avian Med Surg 2013 Jun;27(2):109-19

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 260, 8052 Zurich, Switzerland.

The objective of this study was to compare the effects of 3 different fluid types for resuscitation after experimentally induced hemorrhagic shock in anesthetized chickens and to evaluate partial pressures of carbon dioxide measured in arterial blood (Paco2), with a transcutaneous monitor (TcPco2), with a gastric intraluminal monitor (GiPco2), and by end tidal measurements (Etco2) under stable conditions and after induced hemorrhagic shock. Hemorrhagic shock was induced in 40 white leghorn chickens by removing 50% of blood volume by phlebotomy under general anesthesia. Birds were divided into 4 groups: untreated (control group) and treated with intravenous hetastarch (haes group), with a hemoglobin-based oxygen carrier (hemospan group), or by autotransfusion (blood group). Respiratory rates, heart rates, and systolic arterial blood pressure (SAP) were compared at 8 time points (baseline [T0]; at the loss of 10% [T10%], 20% [T20%], 30% [T30%], 40% [T40%], and 50% [T50%] of blood volume; at the end of resuscitation [RES]; and at the end of anesthesia [END]). Packed cell volume (PCV) and blood hemoglobin content were compared at 6 time points (T0, T50%, RES, and 1, 3, and 7 days after induced hemorrhagic shock). Measurements of Paco2, TcPco2, GiPco2, and Etco2 were evaluated at 2 time points (T0 and T50%), and venous lactic acid concentrations were evaluated at 3 time points (T0, T50%, and END). No significant differences were found in mortality, respiratory rate, heart rate, PCV, or hemoglobin values among the 4 groups. Birds given fluid resuscitation had significantly higher SAPs after fluid administration than did birds in the control group. In all groups, PCV and hemoglobin concentrations began to rise by day 3 after phlebotomy, and baseline values were reached 7 days after blood removal. At T0, TcPco2 did not differ significantly from Paco2, but GiPco2 and Etco2 differed significantly from Paco2. After hemorrhagic shock, GiPco2 and TcPco2 differed significantly from Paco2. The TcPco2 or GiPco2 values did not differ significantly at any time point in birds that survived or died in any of the groups and across all groups. These results showed no difference in mortality in leghorn chickens treated with fluid resuscitation after hemorrhagic shock and that the PCV and hemoglobin concentrations increased by 3 days after acute hemorrhage with or without treatment. The different CO2 measurements document changes in CO2-values consistent with poor perfusion and may prove useful for serial evaluation of responses to shock and shock treatment.
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http://dx.doi.org/10.1647/2012-018DOI Listing
June 2013

Ecological modelling, size distributions and taphonomic size bias in dinosaur faunas: reply to Brown et al.

Biol Lett 2013 Feb;9(1):20120922

Clinic for Zoo Animals, Exotic Pets and Wildlife, University of Zurich, Zurich, Switzerland.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3565508PMC
http://dx.doi.org/10.1098/rsbl.2012.0922DOI Listing
February 2013

Assessing the Jarman-Bell Principle: Scaling of intake, digestibility, retention time and gut fill with body mass in mammalian herbivores.

Comp Biochem Physiol A Mol Integr Physiol 2013 Jan 6;164(1):129-40. Epub 2012 Oct 6.

Clinic for Zoo Animals, Exotic Pets and Wildlife, Vetsuisse Faculty, University of Zurich, Winterthurerstr. 260, 8057 Zurich, Switzerland.

Differences in allometric scaling of physiological characters have the appeal to explain species diversification and niche differentiation along a body mass (BM) gradient - because they lead to different combinations of physiological properties, and thus may facilitate different adaptive strategies. An important argument in physiological ecology is built on the allometries of gut fill (assumed to scale to BM(1.0)) and energy requirements/intake (assumed to scale to BM(0.75)) in mammalian herbivores. From the difference in exponents, it has been postulated that the mean retention time (MRT) of digesta should scale to BM(1.0-0.75)=BM(0.25). This has been used to argue that larger animals have an advantage in digestive efficiency and hence can tolerate lower-quality diets. However, empirical data does not support the BM(0.25) scaling of MRT, and the deduction of MRT scaling implies, according to physical principles, no scaling of digestibility; basing assumptions on digestive efficiency on the thus-derived MRT scaling amounts to circular reasoning. An alternative explanation considers a higher scaling exponent for food intake than for metabolism, allowing larger animals to eat more of a lower quality food without having to increase digestive efficiency; to date, this concept has only been explored in ruminants. Here, using data for 77 species in which intake, digestibility and MRT were measured (allowing the calculation of the dry matter gut contents (DMC)), we show that the unexpected shallow scaling of MRT is common in herbivores and may result from deviations of other scaling exponents from expectations. Notably, DMC have a lower scaling exponent than 1.0, and the 95% confidence intervals of the scaling exponents for intake and DMC generally overlap. Differences in the scaling of wet gut contents and dry matter gut contents confirm a previous finding that the dry matter concentration of gut contents decreases with body mass, possibly compensating for the less favorable volume-surface ratio in the guts of larger organisms. These findings suggest that traditional explanations for herbivore niche differentiation along a BM gradient should not be based on allometries of digestive physiology. In contrast, they support the recent interpretation that larger species can tolerate lower-quality diets because their intake has a higher allometric scaling than their basal metabolism, allowing them to eat relatively more of a lower quality food without having to increase digestive efficiency.
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http://dx.doi.org/10.1016/j.cbpa.2012.09.018DOI Listing
January 2013