Dimensions US-China: Allosomes: An Unexplored Dimension of Biodiversity

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Despite more than 150 years of scientific study, our understanding of the mechanisms of speciation is still incomplete. Early work emphasized the importance of geographic isolation to limit gene flow among populations. Without gene flow, populations might then evolve into new species over long periods of time. More recent work has focused on the role of natural selection in accelerating the evolution of species, with or without gene flow among populations. This project tests a new idea, that the rapid evolution of new allosomes can accelerate the rate of speciation in some lineages. The researchers will focus on the exceptionally diverse lineage of cichlid fishes found in tropical areas around the world. More than 2,000 species of cichlid fishes are known, making them the most rapidly speciating lineage of extant vertebrates. Recent work has revealed unexpected diversity in the allosomes of these fishes. This diversity may be due to a unique behavior in which females mouthbrood eggs and larvae for periods of up to three weeks. The associated differences in behavior and physiology between males and females causes different genetic changes to be favored in males and females. This pattern is known as genetic conflict. This project will test the hypothesis that these genetic conflicts are responsible for the rapid evolution of new allosomes. In turn, this rapid evolution is thought to be important in the rapid rate of speciation in this group. The project will promote scientific exchange between the U.S., Europe, China and Brazil. It will also provide research training opportunities for undergraduate students at University of Maryland. The researchers will use genomic techniques to characterize allosomes in cichlid fishes from Africa and South America. Regions of genetic differentiation between males and females will be identified using whole-genome DNA sequencing. Long-read sequencing technology will be used to characterize changes in the sequence and structure of chromosomes during the early stages of allosome evolution. Comparative phylogenetic analysis will be used to determine whether high rates of allosome turnover are associated with life history traits. The specific focal trait is female mouthbrooding, which correlates with antagonistic selection between males and females. To determine whether evolutionary changes in allosomes create genetic incompatibilities the researchers will measure the fitness of hybrids between species with different allosomes. These data will allow theoretical predictions about the mechanisms of allosome evolution to be tested.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.