Award Abstract # 1627206
Collaborative Research: Integrative analysis of ingestive biomechanics and dental microwear in evolutionary and ecological context

NSF Org: BCS
Division of Behavioral and Cognitive Sciences
Recipient: WASHINGTON UNIVERSITY, THE
Initial Amendment Date: May 3, 2016
Latest Amendment Date: May 3, 2016
Award Number: 1627206
Award Instrument: Standard Grant
Program Manager: Rebecca Ferrell
rferrell@nsf.gov
 (703)292-7850
BCS
 Division of Behavioral and Cognitive Sciences
SBE
 Directorate for Social, Behavioral and Economic Sciences
Start Date: July 1, 2015
End Date: August 31, 2019 (Estimated)
Total Intended Award Amount: $73,751.00
Total Awarded Amount to Date: $73,751.00
Funds Obligated to Date: FY 2014 = $73,751.00
History of Investigator:
  • David Strait (Principal Investigator)
    dstrait@wustl.edu
Recipient Sponsored Research Office: Washington University
1 BROOKINGS DR
SAINT LOUIS
MO  US  63130-4862
(314)747-4134
Sponsor Congressional District: 01
Primary Place of Performance: Washington University
Saint Louis
MO  US  63130-4899
Primary Place of Performance
Congressional District:
01
Unique Entity Identifier (UEI): L6NFUM28LQM5
Parent UEI:
NSF Program(s): Biological Anthropology
Primary Program Source: 01001415DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s): 1392, 7298, 9179
Program Element Code(s): 139200
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.075

ABSTRACT

Modern humans exhibit small teeth, lightly built jaws and weak chewing muscles - anatomical features which have been shaped by evolutionary processes related to dietary intake and the processing of foods. The fossil record demonstrates that our morphology stands in contrast to that of our ancestors, who evolved to have large, strong teeth, massive jaws and powerful chewing muscles. Evolutionary explanations for this change include competing hypotheses as to how natural selection on diet drove adaptation over the course of human evolution. These hypotheses suggest that the presence or absence of either very hard or very tough foods may have been a critical factor influencing the evolution of our ancestors. Alternatively, the hardness or toughness of foods may have been less important than the behaviors (i.e., biting, puncturing, crushing, twisting, grinding) used to process foods of various shape and size with the jaws and teeth. This project will provide evidence to differentiate between these selective scenarios, thereby contributing to a fuller understanding of the evolutionary processes that have shaped this important aspect of modern human anatomy.

This research will require focus on a primate model, South American capuchins, which exhibit the relevant diversity in musculoskeletal anatomy and diet requisite to testing hypotheses regarding how food properties (i.e., hardness, toughness) or feeding behaviors influence the evolution of feeding adaptations. The study integrates observations of capuchin feeding behavior in the wild with laboratory experiments, advanced computer modeling using engineering methods, examination of the microscopic damage done to teeth by food and other items (i.e., dental microwear), the determination of the material properties (i.e., hardness, toughness) of food resources in the wild, and the collection and analysis of abrasive particles adhering to those foods (that might be influencing microwear patterns). Collectively, these data in capuchins will allow us to evaluate the assumptions underlying our interpretations of the interrelationships between dietary behavior, food resources, and the biology of our human ancestors, thereby transforming our understanding of human evolutionary history.

The broader impacts of this research are considerable. In relation to the public understanding of science, the research provides information that will address a topic of great public interest; namely, our own evolutionary history. As a related benefit, the project illustrates how ecological factors affecting other animals may be equally relevant and impactful for our own species. In terms of STEM training, research training opportunities are provided for high school students, undergraduates, graduate students, and postdoctoral fellows, many of whom are expected (based on past history at the collaborating institutions) to be young female scientists. The project also contributes to environmental awareness by collecting basic ecological data relevant to rainforest conservation. In the process of doing so, it further develops collaborative ties with international counterparts and institutions. Lastly, the project illustrates to the engineering community how their methods can be used to answer evolutionary questions.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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Baumgarten, S. E., Smith, A. L., Wright, K. A., Wright, B. A., Scott R. S., Ross C. F., Strait, D. S. "Biomechanical correlates of premolar root variation in robust and gracile capuchins." American Journal of Physical Anthropology , v.165 , 2018 , p.21
Laird MF, Granatosky MC, Wall CE, Taylor AB, Ross CF. "Quantifying energy costs in the primate feeding system." American Journal of Physical Anthropology , v.165 , 2018
Scott, R.S., B.W. Wright, K.A. Wright, C. Ross, A. Van Casteren, M. Fogaça, D.M. Fragaszy, Claire Marcil & D.S. Strait. "Food toughness and dental microwear anisotropy." American Journal of Physical Anthropology , v.162 , 2017 , p.352
Wright, B.W., Wright, K.A., Strait, D.S., Ross, C.F., Laird, M.F., van Casteren, A., Scott, R "Taking a big bite: working together to better understand the evolution of feeding in primates." American Journal of Primatology , v.81 , 2019 , p.e22981
Wright KA, Rivera AO, Wright BW, Fogaca M, Van Casteren A, Fragaszy D, Scott RS, Strait DS, Ross CF, Larid MF "How do food material properties affect ingestive behavior?" American Journal of Physical Anthropology , v.165 , 2018 , p.305

PROJECT OUTCOMES REPORT

Disclaimer

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

Our study combined behavioral, experimental, imaging, and engineering methods to test two sets of hypotheses about feeding adaptations in living primates that are relevant to understanding human evolution.  First, we sought to understand whether or not ingestion is a behavior that significantly impacts the form, function and evolution of the parts of the skull involved in feeding.  Ingestion refers to the behaviors that bring food into the mouth, including taking bite-sized portions of large food items.  To date, most studies of feeding in primates have assumed that mastication (chewing), rather than ingestion, is the most important variable in driving dietary adaptation, so our project is opening a new avenue of study.  Second, we sought to understand the degree to which variation in primate dental microwear (the microscopic damage done to tooth surfaces by items in the mouth) reflects either variation in the material properties (i.e., hardness, toughness) of the foods being consumed, or variation in the mineral grit being ingested along with those foods.  Conventional wisdom suggests that dental microwear provides information about the foods eaten by primates (including fossil humans) but a debate has developed concerning whether or not the size, shape and hardness of grit particles are, in fact, the primary influence on microwear signals.  We chose to test these hypotheses in capuchins, South American monkeys known to differ in their diets and whose populations are spread across a variety of habitats.

We found compelling evidence that ingestion may be an adaptively important behavior. Capuchins spend roughly as much time engaging in ingestion as mastication, and process the most mechanically challenging tissues during ingestion.  The jaws of robust capuchins, who ingest very hard and tough foods, are mechanically stronger than those of gracile capuchins, who avoid ingesting the hardest and toughest foods.  These findings are compatible with the hypothesis that anatomical differences between these capuchins are functionally related to these differences in feeding.

 We also found that contrary to expectations, the capuchin populations that fed on the hardest foods did not have the most complex (i.e., pitted) dental microwear. This is consistent with the possibility that grit rather than food hardness or toughness is most responsible for affecting dental microwear patterns.  Indeed, we found quartz on most types of capuchin foods in multiple types of habitats.  The density and size of quartz particles varied in ways that might affect microwear, and this phenomenon needs to be studied more extensively.

Some early human ancestors exhibit massively large jaws and molar teeth that have traditionally been interpreted as being adaptations for chewing hard foods, and yet exhibit dental microwear that, lacking pits, seemingly does not preserve evidence of hard object feeding.  Here we show using a primate model that we should also consider the possibilities that the absence of pitted microwear does not necessarily indicate the absence of hard foods in the diet, and that their dental and skeletal traits may be adaptations for ingestion rather than mastication.

Our project has 1) fostered international collaborations between American, Brazillian and Surinamese scientists, 2) supported the research and/or training of female scientists at the undergraduate, graduate, postdoctoral, and early- and mid-career faculty levels, 3) aided in the informed management and conservation of the capuchins at our study sites, and 4) integrated engineering methods into evolutionary anthropology.

 


Last Modified: 12/23/2019
Modified by: David S Strait

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