Browsing by Author "Holland, Barbara R."

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    The Emergence of Predators in Early Life: There was No Garden of Eden
    (PLoS One, 2009-06-03) de Nooijer, Silvester; Holland, Barbara R.; Penny, David
    Background: Eukaryote cells are suggested to arise somewhere between 0.85 similar to 2.7 billion years ago. However, in the present world of unicellular organisms, cells that derive their food and metabolic energy from larger cells engulfing smaller cells (phagocytosis) are almost exclusively eukaryotic. Combining these propositions, that eukaryotes were the first phagocytotic predators and that they arose only 0.85 similar to 2.7 billion years ago, leads to an unexpected prediction of a long period (similar to 1-3 billion years) with no phagocytotes - a veritable Garden of Eden. Methodology: We test whether such a long period is reasonable by simulating a population of very simple unicellular organisms - given only basic physical, biological and ecological principles. Under a wide range of initial conditions, cellular specialization occurs early in evolution; we find a range of cell types from small specialized primary producers to larger opportunistic or specialized predators. Conclusions: Both strategies, specialized smaller cells and phagocytotic larger cells are apparently fundamental biological strategies that are expected to arise early in cellular evolution. Such early predators could have been 'prokaryotes', but if the earliest cells on the eukaryote lineage were predators then this explains most of their characteristic features.
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    Testing the Effect of Metabolic Rate on DNA Variability at the Intra-Specific Level
    (PLoS One, 2010-03-15) McGaughran, Angela; Holland, Barbara R.
    We tested the metabolic rate hypothesis (whereby rates of mtDNA evolution are postulated to be mediated primarily by mutagenic by-products of respiration) by examining whether mass-specific metabolic rate was correlated with root-to-tip distance on a set of mtDNA trees for the springtail Cryptopygus antarcticus travei from sub-Antarctic Marion Island. Using Bayesian analyses and a novel application of the comparative phylogenetic method, we did not find significant evidence that contemporary metabolic rates directly correlate with mutation rate (i.e., root-to-tip distance) once the underlying phylogeny is taken into account. However, we did find significant evidence that metabolic rate is dependent on the underlying mtDNA tree, or in other words, lineages with related mtDNA also have similar metabolic rates. We anticipate that future analyses which apply this methodology to datasets with longer sequences, more taxa, or greater variability will have more power to detect a significant direct correlation between metabolic rate and mutation rate. We conclude with suggestions for future analyses that would extend the preliminary approach applied here, in particular highlighting ways to tease apart oxidative stress effects from the effects of population size and/or selection coefficients operating on the molecular evolutionary rate.