Abstract
ABSTRACTUnderstanding how speciation occurs and how reproductive barriers contribute to population structure at a genomic scale requires elucidating the genetic architecture of reproductive isolating barriers. In particular, it is crucial to determine if loci underlying reproductive isolation are genetically linked or if they are located on sex chromosomes, which have unique inheritance and population genetic properties. Bluefin killifish (Lucania goodei) and rainwater killifish (L. parva) are closely related species that have diverged across a salinity gradient and are reproductively isolated by assortative mating, hybrid male infertility, viability of hybrid offspring at high salinities, as well as reduced overall fitness of F2 offspring and backcrosses toL. goodei. We conducted QTL mapping in backcrosses betweenL. parvaandL. goodeito determine the genetic architecture of sex determination, mate attractiveness, fertility, and salinity tolerance. We find that the sex locus appears to be male determining and located on a chromosome that has undergone a Robertsonian fusion inL. parvarelative toL. goodei. We find that the sex locus on the fused chromosome is involved in several genomic incompatibilities, which affect the survival of backcrossed offspring. Among the backcrossed offspring that survived to adulthood, we find that one QTL for male attractiveness toL. goodeifemales is closely linked to this sex locus on chromosome 1. Males homozygous forL. goodeialleles at the sex locus laid more eggs withL. goodeifemales. QTL associated with salinity tolerance were spread across the genome but did not tend to co-localize with reproductive isolation. Thus, speciation in this system appears to be driven by reinforcement and indirect selection against hybrids rather than direct natural selection for salinity tolerance. Our work adds to growing evidence that sex chromosome evolution may contribute to speciation.
Publisher
Cold Spring Harbor Laboratory