UBC Theses and Dissertations
Using phylogenetic data to investigate how interspecific interactions affect diversification dynamics Kaur, Katrina Minasha
The causes of the diversity differences that are apparent across taxonomic groups in the tree of life remain a key question in biology. This question has been investigated from the perspective of antagonistic, competitive, and mutualistic interactions. The evidence of macroevolutionary implications of mutualistic interspecific interactions, in which two species benefit from each other, has been based on differing methodologies, and some methods have been later shown to be prone to error. In my thesis I investigated how mutualistic interactions can affect the processes of speciation and extinction and consequently diversification (the difference between speciation and extinction). In Chapter 2, I used a variety of phylogenetic trees from different taxonomic groups with known mutualisms and several phylogenetic comparative approaches to assess if and how mutualism influenced diversification. I found that mutualism tends to have no effect or a positive effect on diversification, with only a few cases showing a negative effect; the pattern may be context dependent or influenced by the type of mutualism and how dependent partners are on each other. Chapter 3 also considered a mutualistic interaction, but in this case, I specifically focused on the interaction between a host and its microbial partners to assess if host-microbe mutualisms, where symbionts live within a host, also influence diversification. Using sister group comparisons, I found that engaging with a host partner decreased diversification on a large-scale bacterial phylogeny suggesting that mutualism hinders diversification or that host-microbe interactions behave differently than other mutualisms. In Chapter 4, I use ancestry-based approaches and apply them outside of species interactions, to the interaction between an antibody and antigen to ask if trees can be used to delimit antibody clonal families based on their diversification histories from one ancestral clone. I suggest that ancestry-based approaches can be used in the study of antibody clones to reconstruct ancestors but there are limitations to using tree-based methods to classify clonal families. Overall, my thesis demonstrates how mutualisms likely do not have a consistent influence on the macroevolutionary trajectories of the interacting species and the difference in how similarity-based and ancestry-based approaches classify antibody clones into families.
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