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Genetic assimilation in the fossil record: phenotypic plasticity and later accommodation in Cambrian arthropods
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Genetic assimilation is a hypothesised process in which an initially plastic developmental phenotypic response of an organism to the environment is fixed genetically, i.e. assimilated into its genome 1,2. One central prediction of genetic assimilation is that “phenotypic accommodation can precede, rather than follow, genetic change, in adaptive evolution”3. Here we test this prediction in the fossil record. Agnostus pisiformis, a Cambrian Series 3 trilobite-like arthropod, has been shown to exhibit subtly different patterns of pygidial morphological variation across coeval assemblages4, varying chiefly in the degree to which the axial lobe dominates the pygidium. We demonstrate that this morphological variation as well as that of the slightly younger closely related Homagnostus obesus is significantly correlated with geochemical indicators of dysoxia/euxinia and thus stressed environments5-7. In addition, the variances of high and low-stress assemblages also differ significantly, suggesting that the morphological variability of the different assemblages is induced by environmental stress and can be understood as a reaction norm8. We include in our analysis the younger relative Trilobagnostus holmi and interpret its morphology, which has a strongly reduced variance, as representing a more canalized9 or stabilized1 stage of the assimilation process. Thus our data contain all stages of adaptation via phenotypic plasticity and genetic assimilation10 and support the main predictions of the ‘Extended Evolutionary Synthesis’3.

National Category
Evolutionary Biology
Identifiers
URN: urn:nbn:se:uu:diva-319484OAI: oai:DiVA.org:uu-319484DiVA: diva2:1087695
Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2017-04-19
In thesis
1. Morphometric analysis of Cambrian fossils and its evolutionary significance
Open this publication in new window or tab >>Morphometric analysis of Cambrian fossils and its evolutionary significance
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Extended Evolutionary Synthesis (EES) is currently emerging as a theoretical alternative to the Modern Synthesis (MS) in which to frame evolutionary observations and interpretations. These alternative frameworks differ fundamentally in their understanding of the relative roles of the genotype, phenotype, development and environment in evolutionary processes and patterns. While the MS represents a gene-centred view of evolution, the EES instead emphasizes the interactions between organism, development and environment. This novel theoretical framework has generated a number of evolutionary predictions that are mutually incompatible with the equivalent of the MS. While research and empirical testing has begun on a number of these in a neontological context, the field of palaeontology has yet to contribute meaningfully to this endeavour. One of the reasons for this is a lack of methodological approaches capable of investigating relevant evolutionary patterns in the fossil record. In this thesis morphometric methods capable of providing relevant data are developed and employed in the analysis of Cambrian fossils. Results of these analyses provide empirical support for the process of evolution through phenotypic plasticity and genetic assimilation hypothesized by the EES. Furthermore, theoretical revision to the species concept in a palaeontological context is suggested. Finally, predictions of the EES specific to the fossil record are made explicit and promising directions of future research are outlined.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 63 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1506
Keyword
Extended Evolutionary Synthesis, phenotypic plasticity, genetic assimilation, phenotypic accommodation, Agnostus pisiformis, Mackinnonia, elliptical fourier analysis, species concept
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-319487 (URN)978-91-554-9894-8 (ISBN)
Public defence
2017-06-02, Norrlands 1 & 2, Villavägen 16, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2017-05-12 Created: 2017-04-10 Last updated: 2017-05-16

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Citation style
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