November 19 2015

5:00 pm 154 BSRB

Julia Notar
Department of Ecology and Evolutionary Biology, UCLA

A comparative study of sea urchin visual ecology


Sea urchin behavioral reactions to light are more complex than previously thought. These animals have a diffuse photoreceptive system with at least two types of opsins expressed throughout their epidermis. Essentially, each urchin functions as a large compound eye. Their dermal light sense facilitates behavioral tasks that even include coarse spatial vision. This is novel, as diffuse dermal photoreception is generally assumed to mediate non-visual tasks. It has been suggested that urchins inhabiting rocky reefs use spatial vision to locate dark crevices to hide from predators. It is commonly thought that animals have photoreceptive and visual abilities that correlate to the complexity of their light-guided behaviors. The goal of this investigation was to determine the thresholds of urchin photoreception and spatial vision in the context of environmental relevance. Laboratory behavioral trials were conducted to establish the lower limits of intensity required for spatial tasks, action spectra, and image resolution of several Southern California urchin species that vary in depth range and habitat. Results indicate that each species has visual abilities relatively suited to its environment. Describing the function of the urchin as a compound eye allows us to understand how these animals perceive their environments and make choices based on visual cues.

Lei Dai
Departments of Molecular and Medical Pharmacology and Ecology and Evolutionary Biology, UCLA

The adaptive potential of an RNA virus with increasing selection pressure.


The spectra of beneficial mutations, as the raw materials of adaptation, are crucial for a quantitative understanding of how pathogens may evolve to acquire drug resistance. Most empirical studies on the fitness effects of beneficial mutations, however, are potentially biased by the sparse sampling of single mutations (i.e. a small subset of constructed or isolated mutants). Here we systematically quantified the relative fitness of all single-site amino acid point mutations (86 amino acids, 1634 variants) in the drug-targeted region of nonstructural protein 5A (NS5A) of Hepatitis C Virus under different concentrations of a potent NS5A inhibitor Daclatasvir. As the selection pressure increases, the distribution of fitness effects of beneficial mutations shifts from an exponential distribution to a Frechet-type distribution characterized by a heavy tail of a few exceptionally fit mutants. Moreover, the number of available beneficial mutations and the selection coefficient are both found to increase at higher levels of Daclatasvir. A simple pharmacodynamics model describing viral fitness as a function of drug concentration (i.e. phenotype-fitness map) helps elucidate the changing spectra of beneficial mutations as well as the role of selection pressure in modulating the adaptive potential of drug resistance.











































































































































































































































































































































































































































































































































































































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