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Placental morphology and the cellular brain in mammalian evolution

Lewitus, E.; (2011) Placental morphology and the cellular brain in mammalian evolution. Doctoral thesis, UCL (University College London). Green open access

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Abstract

A major focus of evolutionary neurobiology has been on whether different regions of the eutherian brain evolve in concert, and how free the brain is to evolve independently of body plans. Since the eutherian brain is loosely modularized, such that one region is rarely isolated for specialization at the expense of others, but the design of modularization itself can be adapted by tweaking developmental programs, the degree to which brain regions must evolve in concert and can evolve independently may carry a deep phylogenetic signal. Using data collected from preserved brain tissue of 37 primate, 21 carnivore, and 15 other eutherian species (spanning 11 orders), I examined the phylogenetic level at which the proliferation of neurons and glia in the primary visual cortex and hippocampus proper, as well as granular layer volumes of the dentate gyrus and cerebellum, may be constrained by conserved developmental programs. In doing so, I was able to test for cellular signatures of (1) evolutionary changes in metabolic activity, (2) phylogenetic divergences, (3) specializations in behavior, and (4) developmental constraints. The degree to which disparate brain regions evolve in concert is shown to be generally conserved in Eutheria, although a derived ability to evolve regions independently is observed along the primate lineage. Using a separate dataset on placental and life-histroy character states, a comprehensive comparative phylogenetic approach was used to resolve relationships among five aspects of placental structure and to identify syndromes of placental morphology with life-history variables. My results support two discrete biological phenotypes of placental morphology and life-history, which are shown to have an evolutionary affect on allocortical, but not neocortical, brain organization. I have provided a new perspective on exploring how developmental constraints – acting both within and without the brain – may affect brain organization at the cellular level, and the extent to which those constraints have been adapted along certain eutherian lineages.

Type:Thesis (Doctoral)
Title:Placental morphology and the cellular brain in mammalian evolution
Open access status:An open access version is available from UCL Discovery
Language:English
UCL classification:UCL > School of Arts and Social Sciences > Faculty of Social and Historical Sciences > Anthropology

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