January 17 2019

5:00 pm 1100 TLSB

EcoEvoPub Series

Graduate Student Presentations


Mark Juhn
Department of Ecology and Evolutionary Biology, UCLA

Title: Exploring Macroevolutionary Ratchets as a Potential Driver of Clades in Decline

Diversity declines are well documented and widespread in the fossil record, but the mechanisms that drive the observed dynamics remain unclear. Macroevolutionary ratchets have been proposed as a potential driver of decline, where selection favors the loss of early generalized forms, which results in more vulnerable specialized forms late in the history of the clade. We used simulations to explore the relationship between trait evolution, extinction, and clade decline under macroevolutionary ratchet-type scenarios. Our simulations confirm that a macroevolutionary ratchet-type scenario will lead to a diversity decline trajectory. However, the diversity trajectory after peak diversity is not always unidirectional, suggesting that clades may be able to recover from short periods of decline. Additionally, clades where the relationship between trait value and extinction was high were unable to generate enough diversity in the rise phase in order to experience decline. Inferences from these simulations can be used to detect the signature of the macroevolutionary ratchet in empirical clades. Our results clarify how trait evolution can drive decline under a range of parameter values and provides additional insights on a mechanistic hypothesis of clade decline.

Elizabeth Karan
Department of Ecology and Evolutionary Biology, UCLA
Title: Evolution of False Eyespots in Butterflyfishes: Testing Eye Camouflage and Mimicry as Anti-predator Adaptations

Many species of butterflyfish (Chaetodontidae) exhibit false eyespots (circular regions with dark pigment on the posterior body) but the factors underlying the phylogenetic distribution of this trait remain poorly understood. False eyespots are hypothesized to play a role in predator avoidance and may function to distract predators away from the true eye and head to the posterior of the body to facilitate escape. Concealment of the eye, most commonly by a vertical stripe, is thought to camouflage the eye from predators, although alternative hypotheses suggest that patterns like eye bars may play a role in reducing glare. Eye coverage commonly co-occurs with false eyespots and the two patterns are hypothesized to complement each other in reducing the conspicuousness of the true eye. We assembled a phylogeny for 95 species of butterflyfish and scored each for the presence/absence of eyespots as well as a suite of other traits related to body coloration. A comparative multivariate analysis revealed a strong association between false eyespots and eye coverage thus supporting the hypothesis that false eyespots have evolved to distract predators from the true eye. A comparative phylogenetic approach was used to test how color patterns evolve to minimize predation, providing a framework for studying how different factors shape color pattern diversity across fishes.

























































































































































































































































































































































































































































































































































































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