The roles of exaptive and adaptive co-option in eye evolution

Iowa State University, Ames IA

Investigators

Abstract

A basic question in biology asks: Where do new complex traits, such as eyes, come from, and in particular, where do the genes that encode them come from? Despite the many different eye types possessed by animals from jellyfish to humans, the genes affecting how light is transformed into the chemical signals of seeing are similar across eyes. Interestingly, some of these genes necessary for light-sensing in eyes are also found in organs not used for vision. Therefore, it may be that the light-sensing machinery used in eyes came from a non-eye origin. This project looks at how genes can be turned on and off in a new place in the body or at different times during development to generate eyes. In doing so it will help us more generally to understand how organisms can evolve to repurpose their genes to create entirely new organs. The work will produce new genome sequences that can be used by commercial and governmental agencies in aquaculture development for economically important species, like scallops, oysters, and clams. It will also improve 7-12th grade educators' understanding of evolution to help them achieve the Next Generation Science Standards goals. This will be done by training them to better teach molecular evolution, and creating and disseminating novel lesson plans for teaching molecular evolution to high school students. The research will also provide training opportunities in cutting edge fields of genomics and bioinformatics to postdoctoral researchers and undergraduate students. This will increase the skills of the next generation of workers in using DNA-based tools and analyses. Understanding the evolutionary origin of eyes is of great interest to biologists because eyes provide insight into how complex phenotypes can arise through redeployment and elaboration of genetic pathways. Yet, previous studies have not utilized closely related taxa that possess a diversity of eye types. This work will examine five separate origins of eyes in a group of closely related bivalves in the Pteriomorphia. Using a combination of tissue-specific transcriptomes and genome assembly, the researchers will identify genes involved in phototransduction across species spanning the taxonomic and ocular diversity of the Pteriomorphia and analyze these in a phylogenetic framework to understand how changes to either the location or timing of gene expression has played a role in the evolution of pteriomorphian eye type diversity. The work will address the following questions: 1) Are lineages with eyes associated with gene family expansions of the phototransduction pathway members? 2) What is the degree of similarity of the phototransduction genes between the different photoreceptive structures within and among species? and 3) Do eyes acquire their phototransduction pathways using the same evolutionary process or does each eye have a unique evolutionary trajectory to photoreception? This work is the first phylogenetic investigation of eye evolution in bivalves, and builds on the PIs' research, recently available genomic resources, and new data on phototransduction pathway evolution. The project will thus advance knowledge of how sensory systems evolve. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.