The Genomic Basis of Electric Signal Diversity

Michigan State University, East Lansing MI

Investigators

Abstract

Communication signals are important in the evolution of new species, as evidenced by many groups of species with elaborate variation in songs, color patterns, and pheromones. In many of these systems, the mechanisms that produce this variation are poorly understood, limiting the ability to understand how selection acts on communication signals to facilitate the speciation process. Electric fish, such as mormyrid fishes from Africa, produce weak electric fields for the purposes of communication and navigation through their environments. There are more than 200 species of mormyrid electric fish; most species have a specific electric discharge, and the mechanisms underlying the production are well understood. In this project, the researchers seek to identify the genetic basis of electric signal diversity by leveraging the recent discovery of a "hybrid zone" between populations of mormyrid electric fish with distinct electric signals to identify genes responsible for differences in electric signals. The project will draw on next-generation genomic sequencing technologies, as well the development of new transgenic techniques in electric fish. This research is important because electric discharges are critical in species recognition, and identifying genes responsible for behavioral differences within species will ultimately help biologists understand how changes in behavior can facilitate, or perhaps cause, one species to become multiple species. In connection with this work, this project will establish a new educational outreach program, focusing on "forms of energy," to middle school students in Olivet, MI. The more than 200 nominal species of mormyrids produce easily measured and quantified electric discharge signals (EODs), which have a discrete anatomical and physiological basis. EOD signals are typically species-specific and have been demonstrated to be a necessary component of courtship behavior, particularly for a rapidly evolved "species flock" of mormyrids in the genus Paramormyrops. Recent work has focused on linking these macroevolutionary patterns of electric signal diversity to population-level processes. Recent discoveries have identified a population level polymorphism in EOD signals within the species Paramormyrops kingsleyae that reflects macroevolutionary patterns of EOD diversity in Paramormyrops and other mormyrids. The objective of this project is to determine the genetic basis of divergent signals in P. kingsleyae. The researchers will achieve this objective by completing three specific aims. The first aim is to determine the divergent genomic regions between sympatric, polymorphic species of electric fish by assembling a reference P. kingsleyae genome, and then align low-coverage whole genome resequencing data from individuals with divergent EOD types. The hypothesis is that these divergent genomic regions between populations are responsible for differences in EOD complexity. The second aim is to identify patterns of gene expression correlated with EOD complexity among closely related Paramormyrops species. The hypothesis is that differences in EOD complexity will be associated with changes in expression of genes relating to electrocyte cell shape and structure. The third aim is to test the putative effects of candidate genomic regions and/or changes in gene expression identified by interfering with gene function in vivo. By achieving these three aims, this project will provide the first demonstration of the genetic basis of a vertebrate communication behavior. EOD diversity is maintained by P. kingsleyae despite the fact that both signal types are maintained in sympatric, fully interbreeding populations. These differences represent the same EOD characteristics that have been strongly implicated in the evolution of reproductive isolation between species and genera. The outcomes of this project will contribute broadly to understanding how evolutionary novelty arises in natural populations, a substrate for speciation. This project will enhance infrastructure for research by constructing web-based tools for exchanging phenotypic and genomic data in electric fish on the website http://efishgenomics.zoology.msu.edu. The international component of this research is supported in part by the National Science Foundation's Office of International Science and Engineering.