Browsing by Author "Parker, William"

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    Evolution of bacteria in the human gut in response to changing environments: an invisible player in the game of health
    (Elsevier B.V., 2021-01) Venkatakrishnan, Aarushi; Holzknecht, Zoie E.; Holzknecht, Rob; Bowles, Dawn E.; Kotzé, Sanet H.; Modliszewski, Jennifer L.; Parker, William
    Several factors in Western society, including widespread use of antibiotics, chronic inflammation, and loss of complex eukaryotic symbionts such as helminths, have a dramatic impact on the ecosystem of the gut, affecting the microbiota hosted there. In addition, reductions in dietary fiber are profoundly impactful on the microbiota, causing extensive destruction of the niche space that supports the normally diverse microbial community in the gut. Abundant evidence now supports the view that, following dramatic alterations in the gut ecosystem, microorganisms undergo rapid change via Darwinian evolution. Such evolutionary change creates functionally distinct bacteria that may potentially have properties of pathogens but yet are difficult to distinguish from their benign predecessors.
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    Multiple independent appearances of the cecal appendix in mammalian evolution and an investigation of related ecological and anatomical factors
    (Elsevier, 2013) Smith, Heather F.; Parker, William; Kotze, Sanet H.; Laurin, Michel
    Although the cecal appendix has been widely viewed as a vestige with no known function or a remnant of a formerly utilized digestive organ, the evolutionary history of this anatomical structure is currently unresolved. A database was compiled for 361 mammalian species, and appendix characters were mapped onto a consensus phylogeny along with other gastrointestinal and behavioral characters. No correlation was found between appearance of an appendix and evolutionary changes in diet, fermentation strategy, coprophagia, social group size, activity pattern, cecal shape, or colonic separation mechanism. Appendix presence and size are positively correlated with cecum and colon size, even though this relationship rests largely on the larger size of cecum and colon in taxa that have an appendix. The appendix has evolved minimally 32 times, but was lost fewer than seven times, indicating that it either has a positive fitness value or is closely associated with another character that does. These results, together with immunological and medical evidence, refute some of Darwin's hypotheses and suggest that the appendix is adaptive but has not evolved as a response to any particular dietary or social factor evaluated here.