Publications by authors named "Amanda McGrosky"

6 Publications

  • Page 1 of 1

Mammalian intestinal allometry, phylogeny, trophic level and climate.

Proc Biol Sci 2021 Feb 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
February 2021

A comprehensive survey of Retzius periodicities in fossil hominins and great apes.

J Hum Evol 2020 12 15;149:102896. Epub 2020 Oct 15.

Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University, Tempe, AZ 85287, USA.

Recent studies have provided great insight into hominin life history evolution by utilizing incremental lines found in dental tissues to reconstruct and compare the growth records of extant and extinct humans versus other ape taxa. Among the hominins, studies that have examined Retzius periodicity (RP) variation have come to contradictory conclusions in some instances. To clarify RP variation among hominins and better place this variation in its broader evolutionary context, we conduct the most comprehensive analysis of published RP values for hominins and great apes to date. We gathered all available data from the literature on RP data from extant humans, great apes, and fossil hominins and assessed their variation using parametric and nonparametric analyses of variance. We also performed phylogenetic generalized least-squares regressions of RP data for these taxa as well as a larger set of hominoids for which RP data have been published against data for body mass, encephalization, and mean semicircular canal radius (a proxy for metabolic rate). Our results show that modern humans have a mean RP significantly differing from that of other hominins. Pongo also is significantly different from nearly all other taxa in all analyses. Our results also demonstrate that RP variation among hominins scales with respect to body mass, encephalization, and semicircular canal radius similarly to other hominids but that modern humans and Pongo stand out in this regard. Operating within the hypothesis that RP reflects autonomic biorhythms that regulate multiple life history variables, our results reinforce the idea that Homo sapiens has evolved a life history distinct from other hominins, even from other members of Homo, and suggest that many of these life history differences may be driven by hypothalamic output from the brain.
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http://dx.doi.org/10.1016/j.jhevol.2020.102896DOI Listing
December 2020

Fracture mechanics, enamel thickness and the evolution of molar form in hominins.

Biol Lett 2020 01 22;16(1):20190671. Epub 2020 Jan 22.

Department of Anthropology, Washington University in St Louis, St Louis, MO, USA.

As the tissue most directly responsible for breaking down food in the oral cavity, the form and function of enamel is obviously of evolutionary significance in humans, non-human primates and other vertebrates. Accordingly, a standard metric, relative enamel thickness (RET), has been used for many decades to provide insights into vertebrate and human palaeobiology. Relatively thick enamel has evolved many times in vertebrates including hominoids (the group to which living humans and fossil hominins belong), and this pattern is thought to provide information about taxonomy, phylogeny, functional anatomy and diet. In particular, relatively thick enamel is thought to make tooth crowns strong so that they resist fractures associated with eating mechanically resistant foods. Here, we use current models of tooth biomechanics to show that RET is at best only moderately informative of function and diet in living hominoids and fossil hominins, and at worst provides misleading information. We propose a new metric, absolute crown strength, to assess the resistance of teeth to fracture, and identify what may be a novel characteristic of tooth strength in fossil hominins.
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http://dx.doi.org/10.1098/rsbl.2019.0671DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7013474PMC
January 2020

Gross intestinal morphometry and allometry in primates.

Am J Primatol 2019 08 18;81(8):e23035. Epub 2019 Jul 18.

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

Although it is generally assumed that among mammals and within mammal groups, those species that rely on diets consisting of greater amounts of plant fiber have larger gastrointestinal tracts (GIT), statistical evidence for this simple claim is largely lacking. We compiled a dataset on the length of the small intestine, caecum, and colon in 42 strepsirrhine, platyrrhine, and catarrhine primate species, using specimens with known body mass (BM). We tested the scaling of intestine length with BM, and whether dietary proxies (percentage of leaves and a diet quality index) were significant covariates in these scaling relationships, using two sets of models: one that did not account for the phylogenetic structure of the data, and one that did. Intestine length mainly scaled geometrically at exponents that included 0.33 in the confidence interval; Strepsirrhini exhibited particularly long caeca, while those of Catarrhini were comparatively short. Diet proxies were only significant for the colon and the total large intestine (but not for the small intestine or the caecum), and only in conventional statistics (but not when accounting for phylogeny), indicating the pattern occurred across but not within clades. Compared to terrestrial Carnivora, primates have similar small intestine lengths, but longer large intestines. The data on intestine lengths presented here corroborate recent results on GIT complexity, suggesting that diet, as currently described, does not exhaustively explain GIT anatomy within primate clades.
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http://dx.doi.org/10.1002/ajp.23035DOI 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

Biology by the Bay.

Authors:
Amanda McGrosky

Evol Anthropol 2018 Mar 6;27(2):78-79. Epub 2018 Apr 6.

School of Human Evolution and Social Change, Arizona State University, Tempe, AZ, 85281.

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http://dx.doi.org/10.1002/evan.21583DOI Listing
March 2018