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Calibration of test diameter and area as proxies for body size in the planktonic foraminifer Globoconella puncticulata

Calibration of test diameter and area as proxies for body size in the planktonic foraminifer Globoconella puncticulata
Calibration of test diameter and area as proxies for body size in the planktonic foraminifer Globoconella puncticulata
Body size is one of the most commonly measured traits in ecology and evolution because it covaries with environmental (e.g., temperature, latitude, degree of population isolation) and life-history (e.g., metabolic rate, generation time) traits. However, the driving mechanisms of body size variation in the distant geological past are poorly known and complicated by partial specimen recovery, limited population-level sampling, and the use of linear measurements as proxies for three-dimensional volumetric-size data. How much information are we missing by using approximate metrics of body size? Here we examine this question in an evolving lineage of planktonic foraminifera. We measure test diameter and surface area of over 500 individuals of the species Globoconella puncticulata using two-dimensional images. These results are compared with measurements of test volume of the same individuals as measured by a recently developed high-throughput method for analysing three-dimensional morphometrics as well as high-resolution three-dimensional computed tomography scanning. Our results show that even in a lineage showing substantial morphological change, a cross-sectional test area can provide a consistent proxy for body volume. Approximating body volume with one-dimensional (linear) size measurements is more problematic as it systematically over- and underestimates the smallest and largest tests, respectively. In our study, shape (here measured as shell-aspect ratio) only explained marginally more variation when included in the regressions. The use of 3D light microscopy introduces a small degree of scatter in the data, but the number of individuals necessary to detect trends in body size with sufficient statistical power is comparable to the sample size required for other traits. These results imply that even in an evolving lineage undergoing substantial morphological change, cross-sectional area can provide a consistent proxy for body size.
0096-1191
241-245
Brombacher, Anieke
2a4bbb84-4743-4a36-973b-4ad2bf743154
Elder, Leanne E.
98ac4665-b68a-4fc0-896b-6fd2beca8f40
Hull, Pincelli M.
071e549a-6172-448b-b339-9359c495c03c
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Ezard, Thomas H.G.
a143a893-07d0-4673-a2dd-cea2cd7e1374
Brombacher, Anieke
2a4bbb84-4743-4a36-973b-4ad2bf743154
Elder, Leanne E.
98ac4665-b68a-4fc0-896b-6fd2beca8f40
Hull, Pincelli M.
071e549a-6172-448b-b339-9359c495c03c
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Ezard, Thomas H.G.
a143a893-07d0-4673-a2dd-cea2cd7e1374

Brombacher, Anieke, Elder, Leanne E., Hull, Pincelli M., Wilson, Paul A. and Ezard, Thomas H.G. (2018) Calibration of test diameter and area as proxies for body size in the planktonic foraminifer Globoconella puncticulata. Journal of Foraminiferal Research, 48 (3), 241-245. (doi:10.2113/gsjfr.48.3.241).

Record type: Article

Abstract

Body size is one of the most commonly measured traits in ecology and evolution because it covaries with environmental (e.g., temperature, latitude, degree of population isolation) and life-history (e.g., metabolic rate, generation time) traits. However, the driving mechanisms of body size variation in the distant geological past are poorly known and complicated by partial specimen recovery, limited population-level sampling, and the use of linear measurements as proxies for three-dimensional volumetric-size data. How much information are we missing by using approximate metrics of body size? Here we examine this question in an evolving lineage of planktonic foraminifera. We measure test diameter and surface area of over 500 individuals of the species Globoconella puncticulata using two-dimensional images. These results are compared with measurements of test volume of the same individuals as measured by a recently developed high-throughput method for analysing three-dimensional morphometrics as well as high-resolution three-dimensional computed tomography scanning. Our results show that even in a lineage showing substantial morphological change, a cross-sectional test area can provide a consistent proxy for body volume. Approximating body volume with one-dimensional (linear) size measurements is more problematic as it systematically over- and underestimates the smallest and largest tests, respectively. In our study, shape (here measured as shell-aspect ratio) only explained marginally more variation when included in the regressions. The use of 3D light microscopy introduces a small degree of scatter in the data, but the number of individuals necessary to detect trends in body size with sufficient statistical power is comparable to the sample size required for other traits. These results imply that even in an evolving lineage undergoing substantial morphological change, cross-sectional area can provide a consistent proxy for body size.

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Accepted/In Press date: 6 February 2018
e-pub ahead of print date: 2 July 2018

Identifiers

Local EPrints ID: 421136
URI: http://eprints.soton.ac.uk/id/eprint/421136
ISSN: 0096-1191
PURE UUID: 67574e93-2944-40fc-b10b-f59cd3617cf2
ORCID for Thomas H.G. Ezard: ORCID iD orcid.org/0000-0001-8305-6605

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Date deposited: 23 May 2018 16:30
Last modified: 06 Jan 2020 17:32

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