Is shape in the eye of the beholder? Assessing landmarking error in geometric morphometric analyses on live fish
Geometric morphometrics is widely used to quantify morphological variation between biological specimens, but the fundamental influence of operator bias on data reproducibility is rarely considered, particularly in studies using photographs of live animals taken under field conditions. We examined th...
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ftdoajarticles:oai:doaj.org/article:6152a6e8ec5f40aeb3716041724eb169 2023-09-05T13:18:14+02:00 Is shape in the eye of the beholder? Assessing landmarking error in geometric morphometric analyses on live fish Paolo Moccetti Jessica R. Rodger Jonathan D. Bolland Phoebe Kaiser-Wilks Rowan Smith Andy D. Nunn Colin E. Adams Jen A. Bright Hannele M. Honkanen Angus J. Lothian Matthew Newton Domino A. Joyce 2023-08-01T00:00:00Z https://doi.org/10.7717/peerj.15545 https://doaj.org/article/6152a6e8ec5f40aeb3716041724eb169 EN eng PeerJ Inc. https://peerj.com/articles/15545.pdf https://peerj.com/articles/15545/ https://doaj.org/toc/2167-8359 doi:10.7717/peerj.15545 2167-8359 https://doaj.org/article/6152a6e8ec5f40aeb3716041724eb169 PeerJ, Vol 11, p e15545 (2023) Measurement error Bias Landmarks Morphometrics Replication crisis Reproducibility Medicine R article 2023 ftdoajarticles https://doi.org/10.7717/peerj.15545 2023-08-20T00:33:41Z Geometric morphometrics is widely used to quantify morphological variation between biological specimens, but the fundamental influence of operator bias on data reproducibility is rarely considered, particularly in studies using photographs of live animals taken under field conditions. We examined this using four independent operators that applied an identical landmarking scheme to replicate photographs of 291 live Atlantic salmon (Salmo salar L.) from two rivers. Using repeated measures tests, we found significant inter-operator differences in mean body shape, suggesting that the operators introduced a systematic error despite following the same landmarking scheme. No significant differences were detected when the landmarking process was repeated by the same operator on a random subset of photographs. Importantly, in spite of significant operator bias, small but statistically significant morphological differences between fish from the two rivers were found consistently by all operators. Pairwise tests of angles of vectors of shape change showed that these between-river differences in body shape were analogous across operator datasets, suggesting a general reproducibility of findings obtained by geometric morphometric studies. In contrast, merging landmark data when fish from each river are digitised by different operators had a significant impact on downstream analyses, highlighting an intrinsic risk of bias. Overall, we show that, even when significant inter-operator error is introduced during digitisation, following an identical landmarking scheme can identify morphological differences between populations. This study indicates that operators digitising at least a sub-set of all data groups of interest may be an effective way of mitigating inter-operator error and potentially enabling data sharing. Article in Journal/Newspaper Atlantic salmon Salmo salar Directory of Open Access Journals: DOAJ Articles PeerJ 11 e15545 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Measurement error Bias Landmarks Morphometrics Replication crisis Reproducibility Medicine R |
spellingShingle |
Measurement error Bias Landmarks Morphometrics Replication crisis Reproducibility Medicine R Paolo Moccetti Jessica R. Rodger Jonathan D. Bolland Phoebe Kaiser-Wilks Rowan Smith Andy D. Nunn Colin E. Adams Jen A. Bright Hannele M. Honkanen Angus J. Lothian Matthew Newton Domino A. Joyce Is shape in the eye of the beholder? Assessing landmarking error in geometric morphometric analyses on live fish |
topic_facet |
Measurement error Bias Landmarks Morphometrics Replication crisis Reproducibility Medicine R |
description |
Geometric morphometrics is widely used to quantify morphological variation between biological specimens, but the fundamental influence of operator bias on data reproducibility is rarely considered, particularly in studies using photographs of live animals taken under field conditions. We examined this using four independent operators that applied an identical landmarking scheme to replicate photographs of 291 live Atlantic salmon (Salmo salar L.) from two rivers. Using repeated measures tests, we found significant inter-operator differences in mean body shape, suggesting that the operators introduced a systematic error despite following the same landmarking scheme. No significant differences were detected when the landmarking process was repeated by the same operator on a random subset of photographs. Importantly, in spite of significant operator bias, small but statistically significant morphological differences between fish from the two rivers were found consistently by all operators. Pairwise tests of angles of vectors of shape change showed that these between-river differences in body shape were analogous across operator datasets, suggesting a general reproducibility of findings obtained by geometric morphometric studies. In contrast, merging landmark data when fish from each river are digitised by different operators had a significant impact on downstream analyses, highlighting an intrinsic risk of bias. Overall, we show that, even when significant inter-operator error is introduced during digitisation, following an identical landmarking scheme can identify morphological differences between populations. This study indicates that operators digitising at least a sub-set of all data groups of interest may be an effective way of mitigating inter-operator error and potentially enabling data sharing. |
format |
Article in Journal/Newspaper |
author |
Paolo Moccetti Jessica R. Rodger Jonathan D. Bolland Phoebe Kaiser-Wilks Rowan Smith Andy D. Nunn Colin E. Adams Jen A. Bright Hannele M. Honkanen Angus J. Lothian Matthew Newton Domino A. Joyce |
author_facet |
Paolo Moccetti Jessica R. Rodger Jonathan D. Bolland Phoebe Kaiser-Wilks Rowan Smith Andy D. Nunn Colin E. Adams Jen A. Bright Hannele M. Honkanen Angus J. Lothian Matthew Newton Domino A. Joyce |
author_sort |
Paolo Moccetti |
title |
Is shape in the eye of the beholder? Assessing landmarking error in geometric morphometric analyses on live fish |
title_short |
Is shape in the eye of the beholder? Assessing landmarking error in geometric morphometric analyses on live fish |
title_full |
Is shape in the eye of the beholder? Assessing landmarking error in geometric morphometric analyses on live fish |
title_fullStr |
Is shape in the eye of the beholder? Assessing landmarking error in geometric morphometric analyses on live fish |
title_full_unstemmed |
Is shape in the eye of the beholder? Assessing landmarking error in geometric morphometric analyses on live fish |
title_sort |
is shape in the eye of the beholder? assessing landmarking error in geometric morphometric analyses on live fish |
publisher |
PeerJ Inc. |
publishDate |
2023 |
url |
https://doi.org/10.7717/peerj.15545 https://doaj.org/article/6152a6e8ec5f40aeb3716041724eb169 |
genre |
Atlantic salmon Salmo salar |
genre_facet |
Atlantic salmon Salmo salar |
op_source |
PeerJ, Vol 11, p e15545 (2023) |
op_relation |
https://peerj.com/articles/15545.pdf https://peerj.com/articles/15545/ https://doaj.org/toc/2167-8359 doi:10.7717/peerj.15545 2167-8359 https://doaj.org/article/6152a6e8ec5f40aeb3716041724eb169 |
op_doi |
https://doi.org/10.7717/peerj.15545 |
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PeerJ |
container_volume |
11 |
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e15545 |
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