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Article: Functional integration for enrolment constrains evolutionary variation of phacopid trilobites despite developmental modularity

Palaeontology - Vol 62, Part 5 - Cover Image
Publication: Palaeontology
Volume: 62
Part: 5
Publication Date: September 2019
Page(s): 805 821
Author(s): Morgane Oudot, Pascal Neige, Rémi Laffont, Nicolas Navarro, Ahmed Yacine Khaldi, and Catherine Crônier
Addition Information

How to Cite

OUDOT, M., NEIGE, P., LAFFONT, R., NAVARRO, N., KHALDI, A.Y., CRôNIER, C. 2019. . Palaeontology, 62, 5, 805-821. DOI: /doi/10.1111/pala.12428

Author Information

  • Morgane Oudot - Biogéosciences UMR CNRS 6282 Université Bourgogne Franche‐Comté 6 boulevard Gabriel 21000 Dijon France
  • Pascal Neige - Biogéosciences UMR CNRS 6282 Université Bourgogne Franche‐Comté 6 boulevard Gabriel 21000 Dijon France
  • Rémi Laffont - Biogéosciences UMR CNRS 6282 Université Bourgogne Franche‐Comté 6 boulevard Gabriel 21000 Dijon France
  • Nicolas Navarro - Biogéosciences UMR CNRS 6282 Université Bourgogne Franche‐Comté 6 boulevard Gabriel 21000 Dijon France
  • Nicolas Navarro - EPHE PSL University 21000 Dijon France
  • Ahmed Yacine Khaldi - Laboratoire de Paléontologie Stratigraphique et Paléo‐Environnements Université d'Oran boîte postale 1524, El‐M'naouer 31000 Oran Algérie
  • Catherine Crônier - Université de Lille CNRS UMR 8198–Evo‐Eco‐Paléo F‐59000 Lille France

Publication History

  • Issue published online: 29 August 2019
  • Manuscript Accepted: 17 January 2019
  • Manuscript Received: 18 April 2018

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Abstract

Modularity and integration are variational properties expressed at various levels of the biological hierarchy. Mismatches among these levels, for example developmental modules that are integrated in a functional unit, could be informative of how evolutionary processes and trade‐offs have shaped organismal morphologies as well as clade diversification. In the present study, we explored the full, integrated and modular spaces of two developmental modules in phacopid trilobites, the cephalon and the pygidium, and highlight some differences among them. Such contrasts reveal firstly that evolutionary processes operating in the modular spaces are stronger in the cephalon, probably due to a complex regime of selection related to the numerous functions ensured by this module. Secondly, we demonstrate that the same pattern of covariation is shared among species, which also differentiate along this common functional integration. This common pattern might be the result of stabilizing selection acting on the enrolment and implying a coordinate variation between the cephalon and the pygidium in a certain direction of the morphospace. Finally, we noticed that Austerops legrandi differs slightly from other species in that its integration is partly restructured in the way the two modules interact. Such a divergence can result from the involvement of the cephalon in several vital functions that may have constrained the response of the features involved in enrolment and reorganized the covariation of the pygidium with the cephalon. Therefore, it is possible that important evolutionary trade‐offs between enrolment and other functions on the cephalon might have partly shaped the diversification of trilobites.

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