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Meghan M. Eastman

Bio: Meghan M. Eastman is an academic researcher from University of Notre Dame. The author has contributed to research in topics: Masticatory force & Australopithecus. The author has an hindex of 5, co-authored 5 publications receiving 146 citations.

Papers
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Journal ArticleDOI
TL;DR: It is shown that hard-object feeding cannot explain the extreme morphology of Paranthropus boisei, and analysis of long-term dietary plasticity in an animal model suggests year-round reliance on tough foods requiring prolonged postcanine processing in P. boISEi.
Abstract: The robust jaws and large, thick-enameled molars of the Plio–Pleistocene hominins Australopithecus and Paranthropus have long been interpreted as adaptations for hard-object feeding. Recent studies of dental microwear indicate that only Paranthropus robustus regularly ate hard items, suggesting that the dentognathic anatomy of other australopiths reflects rare, seasonal exploitation of hard fallback foods. Here, we show that hard-object feeding cannot explain the extreme morphology of Paranthropus boisei. Rather, analysis of long-term dietary plasticity in an animal model suggests year-round reliance on tough foods requiring prolonged postcanine processing in P. boisei. Increased consumption of such items may have marked the earlier transition from Ardipithecus to Australopithecus, with routine hard-object feeding in P. robustus representing a novel behaviour.

83 citations

Journal ArticleDOI
TL;DR: The authors used experimental diet manipulation to examine the life-history trajectory of plasticity in the feeding complex of a model organism, the white rabbit (Oryctolagus cuniculus), and demonstrated that the jaws of weanlings and young adults exhibit similar increases in relative bone cross-sectional areas in response to the introduction of mechanically challenging foods into their diets.
Abstract: Many organisms exhibit a decrease in the ability to modify their phenotypes in response to shifts in environmental conditions as they mature. Such age-dependent plasticity has important implications in a variety of evolutionary and ecological contexts, particularly with respect to understanding adaptive responses to heterogeneous environments. In this study, we used experimental diet manipulation to examine the life-history trajectory of plasticity in the feeding complex of a model organism, the white rabbit (Oryctolagus cuniculus). We demonstrate that, contrary to expectations derived from previous cross-sectional studies of skeletal plasticity, the jaws of weanlings and young adults exhibit similar increases in relative bone cross-sectional areas in response to the introduction of mechanically challenging foods into their diets. Furthermore, we present evidence that sensitivity to loading patterns persists well into adulthood in some regions of the masticatory apparatus in rabbits, indicating that there is an extended window of opportunity to respond to changes in dietary properties during an animal’s life span. We conclude that certain aspects of the facial skeleton of rabbits, and perhaps mammals in general, are sensitive to environmental stimuli long after skeletal maturity is achieved, highlighting the importance of plasticity as a source of adaptive variation at later life-history stages.

29 citations

Journal ArticleDOI
TL;DR: Varying osteogenic responses in the arch suggests that skeletal adaptation, and corresponding variation in performance, may reside differentially at one level of bony architecture, and it is possible that phenotypic diversity in the mammalian zygoma is due more singularly to natural selection (vs. plasticity).
Abstract: The zygomatic arch is morphologically complex, providing a key interface between the viscerocranium and neurocranium. It also serves as an attachment site for masticatory muscles, thereby linking it to the feeding apparatus. Though morphological variation related to differential loading is well known for many craniomandibular elements, the adaptive osteogenic response of the zygomatic arch remains to be investigated. Here, experimental data are presented that address the naturalistic influence of masticatory loading on the postweaning development of the zygoma and other cranial elements. Given the similarity of bone-strain levels among the zygoma and maxillomandibular elements, a rabbit and pig model were used to test the hypothesis that variation in cortical bone formation and biomineralization along the zygomatic arch and masticatory structures are linked to increased stresses. It was also hypothesized that neurocranial structures would be minimally affected by varying loads. Rabbits and pigs were raised for 48 weeks and 8 weeks, respectively. In both experimental models, CT analyses indicated that elevated masticatory loading did not induce differences in cortical bone thickness of the zygomatic arch, though biomineralization was positively affected. Hypotheses were supported regarding bone formation for maxillomandibular and neurocranial elements. Varying osteogenic responses in the arch suggests that skeletal adaptation, and corresponding variation in performance, may reside differentially at one level of bony architecture. Thus, it is possible that phenotypic diversity in the mammalian zygoma is due more singularly to natural selection (vs. plasticity). These findings underscore the complexity of the zygomatic arch and, more generally, determinants of skull form. Anat Rec, 299:1646–1660, 2016. © 2016 Wiley Periodicals, Inc.

24 citations

Journal ArticleDOI
16 Mar 2017-Zoology
TL;DR: Varying osteogenic responses in masticatory elements suggest that physiological adaptation, and corresponding variation in skeletal performance, may reside differentially at one level of bony architecture, potentially affecting the accuracy of behavioral and in silico reconstructions.

14 citations

01 Jan 2014
TL;DR: It is concluded that certain aspects of the facial skeleton of rabbits, and perhaps mammals in general, are sensitive to environmental stimuli long after skeletal maturity is achieved, highlighting the importance of plasticity as a source of adaptive variation at later life-history stages.
Abstract: Many organisms exhibit a decrease in the ability to modify their phenotypes in response to shifts in environmental conditions as they mature. Such age-dependent plasticity has important implications in a variety of evolutionary and ecological contexts, particularly with respect to understanding adaptive responses to heterogeneous environments. In this study, we used experimental diet manipulation to examine the life-history trajectory of plasticity in the feeding complex of a model organism, the white rabbit (Oryctolagus cuniculus). We demonstrate that, contrary to expectations derived from previous cross-sectional studies of skeletal plasticity, the jaws of weanlings and young adults exhibit similar increases in relative bone cross-sectional areas in response to the introduction of mechanically challenging foods into their diets. Furthermore, we present evidence that sensitivity to loading patterns persists well into adulthood in some regions of the masticatory apparatus in rabbits, indicating that there is an extended window of opportunity to respond to changes in dietary properties during an animal's life span. We conclude that certain aspects of the facial skeleton of rabbits, and perhaps mammals in general, are sensitive to environmental stimuli long after skeletal maturity is achieved, highlighting the importance of plasticity as a source of adaptive variation at later life-history stages.

5 citations


Cited by
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Journal ArticleDOI
08 Oct 2004-Science

836 citations

Journal ArticleDOI
01 Aug 2018-Genetics
TL;DR: It is argued that it is not sufficient to accommodate developmental bias into evolutionary theory merely as a constraint on evolutionary adaptation, and recent theory on regulatory networks that explains why the influence of genetic and environmental perturbation on phenotypes is typically not uniform, and may even be biased toward adaptive phenotypic variation is described.
Abstract: Phenotypic variation is generated by the processes of development, with some variants arising more readily than others-a phenomenon known as "developmental bias." Developmental bias and natural selection have often been portrayed as alternative explanations, but this is a false dichotomy: developmental bias can evolve through natural selection, and bias and selection jointly influence phenotypic evolution. Here, we briefly review the evidence for developmental bias and illustrate how it is studied empirically. We describe recent theory on regulatory networks that explains why the influence of genetic and environmental perturbation on phenotypes is typically not uniform, and may even be biased toward adaptive phenotypic variation. We show how bias produced by developmental processes constitutes an evolving property able to impose direction on adaptive evolution and influence patterns of taxonomic and phenotypic diversity. Taking these considerations together, we argue that it is not sufficient to accommodate developmental bias into evolutionary theory merely as a constraint on evolutionary adaptation. The influence of natural selection in shaping developmental bias, and conversely, the influence of developmental bias in shaping subsequent opportunities for adaptation, requires mechanistic models of development to be expanded and incorporated into evolutionary theory. A regulatory network perspective on phenotypic evolution thus helps to integrate the generation of phenotypic variation with natural selection, leaving evolutionary biology better placed to explain how organisms adapt and diversify.

140 citations

Journal ArticleDOI
TL;DR: The variables that influence primate feeding preference: food availability, chemical defense, and nutrient content are explored and it is concluded that “fallback” is not an intrinsic state of the food or the consumer and that this conclusion complicates the application of this concept to feeding models.
Abstract: Eating is a risky affair. All animals have to offset risks of feeding such as exposure to plant toxins, increased vulnerability to predation, or conspecific aggression with a food's energetic and nutritional return. What, when, and where an individual eats can impact fitness and, ultimately, species-level adaptations. Here, we explore the variables that influence primate feeding preference: food availability, chemical defense, and nutrient content. We present information demonstrating that consumers manipulate nutrient and energy intake, indicating that what may be a less-than-optimal food for one state of an animal's phenotype may not be for another. This evidence suggests that factors previously assumed to be constraints in Optimal Foraging Theory, Functional Response, and—recently—Fallback Food feeding models would be better categorized as variables. We conclude that “fallback” is not an intrinsic state of the food or the consumer and that this conclusion complicates the application of this concept to ...

115 citations

Journal ArticleDOI
09 Jul 2018-Nature
TL;DR: The observed changes in the hydroclimate of southeastern Africa—both in terms of its long-term state and marked precessional variability—could have had a role in the evolution of early hominins, particularly in the extinction of Paranthropus robustus.
Abstract: The past two million years of eastern African climate variability is currently poorly constrained, despite interest in understanding its assumed role in early human evolution1–4. Rare palaeoclimate records from northeastern Africa suggest progressively drier conditions2,5 or a stable hydroclimate6. By contrast, records from Lake Malawi in tropical southeastern Africa reveal a trend of a progressively wetter climate over the past 1.3 million years7,8. The climatic forcings that controlled these past hydrological changes are also a matter of debate. Some studies suggest a dominant local insolation forcing on hydrological changes9–11, whereas others infer a potential influence of sea surface temperature changes in the Indian Ocean8,12,13. Here we show that the hydroclimate in southeastern Africa (20–25° S) is controlled by interplay between low-latitude insolation forcing (precession and eccentricity) and changes in ice volume at high latitudes. Our results are based on a multiple-proxy reconstruction of hydrological changes in the Limpopo River catchment, combined with a reconstruction of sea surface temperature in the southwestern Indian Ocean for the past 2.14 million years. We find a long-term aridification in the Limpopo catchment between around 1 and 0.6 million years ago, opposite to the hydroclimatic evolution suggested by records from Lake Malawi. Our results, together with evidence of wetting at Lake Malawi, imply that the rainbelt contracted toward the Equator in response to increased ice volume at high latitudes. By reducing the extent of woodland or wetlands in terrestrial ecosystems, the observed changes in the hydroclimate of southeastern Africa—both in terms of its long-term state and marked precessional variability—could have had a role in the evolution of early hominins, particularly in the extinction of Paranthropus robustus.

69 citations