Iwaniuk, Andrew

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https://opus.uleth.ca/handle/10133/4634

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Browsing Iwaniuk, Andrew by Subject "Allometry"

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    The cerebellar anatomy of red junglefowl and white leghorn chickens: insights into the effects of domestication on the cerebellum
    (Royal Society, 2021) Racicot, Kelsey J.; Popic, Christina; Cunha, Felipe; Wright, Dominic; Henriksen, Christina; Iwaniuk, Andrew N.
    Domestication is the process by which wild organisms become adapted for human use. Many phenotypic changes are associated with animal domestication, including decreases in brain and brain region sizes. In contrast with this general pattern, the chicken has a larger cerebellum compared with the wild red junglefowl, but what neuroanatomical changes are responsible for this difference have yet to be investigated. Here, we quantified cell layer volumes, neuron numbers and neuron sizes in the cerebella of chickens and junglefowl. Chickens have larger, more folded cerebella with more and larger granule cells than junglefowl, but neuron numbers and cerebellar folding were proportional to cerebellum size. However, chickens do have relatively larger granule cell layer volumes and relatively larger granule cells than junglefowl. Thus, the chicken cerebellum can be considered a scaled-up version of the junglefowl cerebellum, but with enlarged granule cells. The combination of scaling neuron number and disproportionate enlargement of cell bodies partially supports a recent theory that domestication does not affect neuronal density within brain regions. Whether the neuroanatomical changes we observed are typical of domestication or not requires similar quantitative analyses in other domesticated species and across multiple brain regions.
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    The evolution of mammalian brain size
    (American Association for Advancement of Science, 2021) Smaers, J. B.; Rothman, R. S.; Hudson, D. R.; Balanoff, A. M.; Beatty, B.; Dechmann, D. K. N.; de Vries, D.; Dunn, J. C.; Fleagle, J. G.; Gilbert, C. C.; Goswami, A.; Iwaniuk, Andrew N.; Jungers, W. L.; Kerney, M.; Ksepka, D. T.; Manger, P. R.; Mongle, C. S.; Rohlf, F. J.; Smith, N. A.; Soligo, C.; Weisbecker, V.; Safi, K.
    Relative brain size has long been considered a reflection of cognitive capacities and has played a fundamental role in developing core theories in the life sciences. Yet, the notion that relative brain size validly represents selection on brain size relies on the untested assumptions that brain-body allometry is restrained to a stable scaling relationship across species and that any deviation from this slope is due to selection on brain size. Using the largest fossil and extant dataset yet assembled, we find that shifts in allometric slope underpin major transitions in mammalian evolution and are often primarily characterized by marked changes in body size. Our results reveal that the largest-brained mammals achieved large relative brain sizes by highly divergent paths. These findings prompt a reevaluation of the traditional paradigm of relative brain size and open new opportunities to improve our understanding of the genetic and developmental mechanisms that influence brain size.