The source of organismal diversity and the link between genotype and phenotype are key questions for understanding evolution. The evolutionary mechanisms that shape phenotypes depend on population size, the complexity of genetic networks underlying traits, and the relative role of genetics versus the environment in shaping traits. In this proposal, we examine the genetic basis of opsin gene expression, which determines visual sensitivities. We choose African cichlid fishes as they have significant variation in visual sensitivity. They also have small population sizes, comparable to humans, and will help identify the types of evolutionary mechanisms that might be important in small populations. African cichlid fishes have seven cone opsin genes, with species differing in which subsets of the genes are expressed. Typically, genes are expressed in three combinations, which we call the short, medium, and long visual palettes. To some degree, the optimal palette depends on the foraging style and the water clarity where species live. For the proposed work, we have made three crosses between species that differ in opsin palette: short x medium, short x long and medium x long. These three crosses will enable us to identify the key transcription factors that shift opsin expression between these genetically determined palettes. In addition, we will study two crosses that differ in whether environmental factors, such as light spectrum, contribute to opsin expression variation. By identifying factors which control both differences between the palettes and environmental plasticity, we can determine whether these two kinds of factors are the same or different. Further, we can use RNAseq from retinal and other transcriptomes to calculate the genetic network controlling opsin expression and see how these two types of factors are distributed in that network. We predict that factors controlling fixed genetic differences will be more central to the network, while factors involved in environmental responses will be more peripheral.

Public Health Relevance

Phenotypes can be determined by both genotypes and environmental input. Understanding how genotypes and the environment influence phenotypes is critical to our ability to unravel the genetic basis of human health traits, such as disease susceptibility. This proposal will focus on the genetic and environmental inputs to gene expression in the fish retina.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Genetic Variation and Evolution Study Section (GVE)
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Neuhold, Lisa
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University of Maryland College Park
Earth Sciences/Resources
College Park
United States
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Escobar-Camacho, Daniel; Ramos, Erica; Martins, Cesar et al. (2016) The Opsin Genes of Amazonian Cichlids. Mol Ecol :
Carleton, Karen L; Dalton, Brian E; Escobar-Camacho, Daniel et al. (2016) Proximate and ultimate causes of variable visual sensitivities: Insights from cichlid fish radiations. Genesis 54:299-325
Phillips, Genevieve A C; Carleton, Karen L; Marshall, N Justin (2016) Multiple Genetic Mechanisms Contribute to Visual Sensitivity Variation in the Labridae. Mol Biol Evol 33:201-15
Dalton, Brian E; Lu, Jessica; Leips, Jeff et al. (2015) Variable light environments induce plastic spectral tuning by regional opsin coexpression in the African cichlid fish, Metriaclima zebra. Mol Ecol 24:4193-204
Escobar-Camacho, Daniel; Carleton, Karen L (2015) Sensory modalities in cichlid fish behavior. Curr Opin Behav Sci 6:115-124