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Endocranial asymmetry in New World monkeys: a comparative phylogenetic analysis of morphometric data

Abstract

Brain lateralization is a widespread phenomenon although its expression across primates is still controversial due to the reduced number of species analyzed and the disparity of methods used. To gain insight into the diversification of neuroanatomical asymmetries in non-human primates we analyze the endocasts, as a proxy of external brain morphology, of a large sample of New World monkeys and test the effect of brain size, home range and group sizes in the pattern and magnitude of shape asymmetry. Digital endocasts from 26 species were obtained from MicroCT scans and a set of 3D coordinates was digitized on endocast surfaces. Results indicate that Ateles, Brachyteles, Callicebus and Cacajao tend to have a rightward frontal and a leftward occipital lobe asymmetry, whereas Aotus, Callitrichinae and Cebinae have either the opposite pattern or no directional asymmetry. Such differences in the pattern of asymmetry were associated with group and home range sizes. Conversely, its magnitude was significantly associated with brain size, with larger-brained species showing higher inter-hemispheric differences. These findings support the hypothesis that reduction in inter-hemispheric connectivity in larger brains favors the lateralization and increases the structural asymmetries, whereas the patterns of shape asymmetry might be driven by socio-ecological differences among species.

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Availability of data and material

All data generated and analyzed during this study are included in this published article (Supplementary Tables S1 and S2).

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Code available upon request.

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Acknowledgements

We thank two anonymous reviewers for the comments that helped to improve the clarity of this article.

Funding

This work is supported by Universidad Nacional de La Plata Grant # 911 to S.I.P. and P.N.G. (4113), FAPESP (2017/17357-0) to S.F.d.R.

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Authors and Affiliations

Authors

Contributions

PNG: study conception and design, analysis and interpretation of data, drafting of manuscript, critical revision. MVA: study conception and design, analysis and interpretation of data, critical revision. LA: acquisition of data, analysis and interpretation of data, critical revision. RTL: acquisition of data, critical revision. SFR: acquisition of data, critical revision. SIP: study conception and design, acquisition of data, analysis and interpretation of data, drafting of manuscript, critical revision.

Corresponding author

Correspondence to Paula N. Gonzalez.

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The authors declare no conflict of interest.

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Supplementary Information

Below is the link to the electronic supplementary material.

429_2021_2371_MOESM1_ESM.pdf

Supplementary Fig. S1. Distribution of specimens along the first two principal components (PC1 and PC2) obtained from the asymmetric shape component (PDF 43 kb)

429_2021_2371_MOESM2_ESM.xlsx

Supplementary Table S1. List of specimens included in this study. The information about the genus, species, specimen ID, endocranial volume and sex is provided (XLSX 11 kb)

429_2021_2371_MOESM3_ESM.csv

Supplementary Table S2. Morphometric and socio-ecological variables used for the comparative phylogenetic analyses (CSV 4 kb)

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Gonzalez, P.N., Vallejo-Azar, M., Aristide, L. et al. Endocranial asymmetry in New World monkeys: a comparative phylogenetic analysis of morphometric data. Brain Struct Funct 227, 469–477 (2022). https://doi.org/10.1007/s00429-021-02371-z

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  • DOI: https://doi.org/10.1007/s00429-021-02371-z

Keywords

  • Brain lateralization
  • Endocranial shape
  • Geometric morphometrics
  • Home range size
  • Group size
  • Primates