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Morphometric analysis of Cambrian fossils and its evolutionary significance
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Palaeobiology.
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 [en]
Extended Evolutionary Synthesis, phenotypic plasticity, genetic assimilation, phenotypic accommodation, Agnostus pisiformis, Mackinnonia, elliptical fourier analysis, species concept
National Category
Evolutionary Biology
Identifiers
URN: urn:nbn:se:uu:diva-319487ISBN: 978-91-554-9894-8 (print)OAI: oai:DiVA.org:uu-319487DiVA: diva2:1087708
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
List of papers
1. Intraspecific morphological variation of Agnostus pisiformis, a Cambrian Series 3 trilobite-like arthropod
Open this publication in new window or tab >>Intraspecific morphological variation of Agnostus pisiformis, a Cambrian Series 3 trilobite-like arthropod
(English)In: Lethaia: an international journal of palaeontology and stratigraphy, ISSN 0024-1164, E-ISSN 1502-3931Article in journal (Refereed) Epub ahead of print
Abstract [en]

The study of evolution in a palaeontological context is chiefly the study of change in shape and form. This requires data sets that quantify morphology and morphological variation. Historically morphology has been described using discrete characters or more recently using various morphometric approaches. Elliptical Fourier analysis (EFA) is an approach to quantifying morphology that results in the production of large data sets of elliptical Fourier descriptors (EFDs), which are highly suitable to multivariate analysis. EFA is used in this paper to quantify the shape and describe the ontogeny of Agnostus pisiformis (Wahlenberg 1818: Nova Acta Regiae Societatis Scientiarum Upsaliensis 8, 1), a trilobite-like arthropod of Cambrian Series 3, from three coeval localities in Sweden. An ontogenetic difference was detected between geographically distant populations from Västergötland and Skåne in Sweden. These differences are probably the result of environmental dysoxic stress leading to increasing phenotypic variation. These findings illustrate the utility of EFA applied to the study of fossil organisms; permitting studies of such high resolution that multiple assemblages of the same species can be comparatively studied to achieve a more detailed understanding of their morphological and ontogenetic variation.

Keyword
Agnostus pisiformis, Alum Shale, elliptical Fourier analysis, intraspecific variation, morphometrics
National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-319483 (URN)10.1111/let.12201 (DOI)
Available from: 2017-04-05 Created: 2017-04-05 Last updated: 2017-04-12Bibliographically approved
2. Morphometric Analysis of the Early Cambrian mollusc Mackinnonia and the Incipient Species Concept
Open this publication in new window or tab >>Morphometric Analysis of the Early Cambrian mollusc Mackinnonia and the Incipient Species Concept
(English)In: Palaeontology, ISSN 0031-0239, E-ISSN 1475-4983Article in journal (Other academic) Submitted
Abstract [en]

Phylogenetic relationships within the helcionelloids have been difficult to establish. One of the reasons for this is that qualitative approaches to investigating morphological variation in this group have struggled to identify clear patterns. An alternative method of identifying these patterns is to study these organisms quantitatively. Here we exemplify this approach by employing morphometric methods to investigate patterns of subtle morphological variation in two species of Mackinnonia Runnegar in Bengtson et al. Specifically, we conduct a combination of elliptical Fourier and multivariate analyses to study intra- and interspecific variation in protoconch form and variation in ontogenetic trajectory of two species of Mackinnonia. The material we use consists of two assemblages of Mackinnonia rostrata (Zhou & Xiao), from the Shackleton Limestone of Antarctica and Ajax Limestone of Australia, and an assemblage of Mackinnonia taconica (Landing & Bartowski) from the Bastion Formation of Greenland. Results of our study show significant (p=<0.0001) differences in protoconch shape between all three groups. Ontogenetic sequences of outline curves truncated at successive rugae significantly (p=<0.05) discriminate between M. rostrata and M. taconica. We discuss the uncovered significant intraspecific morphological variation of disparate assemblages of M. rostrata despite shared qualitative features and develop a conceptual framework for understanding such patterns of variation. We define the incipient species concept using Mackinnonia as an empirical example.

National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-319485 (URN)
Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2017-04-19
3. Genetic assimilation in the fossil record: phenotypic plasticity and later accommodation in Cambrian arthropods
Open this publication in new window or tab >>Genetic assimilation in the fossil record: phenotypic plasticity and later accommodation in Cambrian arthropods
(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:nbn:se:uu:diva-319484 (URN)
Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2017-04-19
4. The Extended Evolutionary Synthesis in the fossil record
Open this publication in new window or tab >>The Extended Evolutionary Synthesis in the fossil record
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The Extended Evolutionary Synthesis (EES) has recently emerged as a theoretical alternative or complement to the Modern Synthesis (MS) in which to frame evolutionary observations and interpretations. The theoretical framework of the EES places a greater evolutionary significance on a number of controversial hypotheses and processes, such as phenotypic plasticity and genetic assimilation, and makes a number of empirical predictions based thereon. Investigation and empirical exploration of these predictions has begun in a neontological context yet the field of palaeontology has not yet been instrumental in developing or testing these predictions. Here the hypothetical process of evolution via phenotypic plasticity and genetic assimilation is explained and contextualised to the fossil record. A prediction of the EES specific to palaeontological data is formulated and methods suitable for its empirical testing are suggested.

National Category
Evolutionary Biology
Identifiers
urn:nbn:se:uu:diva-319486 (URN)
Available from: 2017-04-10 Created: 2017-04-10 Last updated: 2017-04-15

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