Evolution has traditionally been seen as an open-ended, adirectional process. However, the ubiquity of convergent evolution instead suggests that a hierarchy of physical and biological constraints shape evolution. This thesis examines the empirical evidence for convergent evolution’s impact on macroevolutionary patterns. One corollary of convergent evolution is the tendency for animal groups to reach maximum morphological disparity early in their evolutionary histories. An analysis of plants confirms that bottom heavy disparity profiles (Centre of Gravity < 0.5) are not unique to animals. This pattern is most easily explained by character exhaustion, with repetition of character states becoming increasingly probable as evolutionary time increases. However, in a sample of 93 extinct clades, no correlation between character exhaustion and disparity profile shape was found. Instead, ecological or genetic constraints likely limit organism form.Convergent evolution can introduce noise to morphological phylogenies. Anecodotal evidence in mammals shows molecular phylogenies are more congruent with biogeography than their morphological forbears, suggesting ecological constraint could be driving morphological convergence which confounds phylogeny. Similar patterns are common in other clades. In a systematic study of 48 plant and animal clades, the significant majority (70%) of molecular trees were more consilient with biogeographical distributions than their morphological counterparts. Genetic constraint might also limit evolutionary possibility and drive convergent evolution. If so, genome duplications, by introducing genetic redundancy, are expected to be associated with evolutionary novelty and diversification. An analysis of 356 sister clade pairs shows polyploids contain significantly more species than their non-polyploid counterparts. Whilst a direct link between morphological and genetic constraints has yet to be identified genetic constraints are likely to play an important role in the diversification of species. Finally, the importance of these findings for the study of convergent evolution and evolutionary processes in general is discussed, along with future lines of research.
|Date of Award||23 May 2018|
|Sponsors||John Templeton Foundation|
|Supervisor||Matthew Wills (Supervisor) & Mark Wilkinson (Supervisor)|
- convergent evolution