NSFDEB-NERC: The origin of reproductive parasitism in the Amazon Molly

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This project will examine how complex traits evolve by exploring an apparent reproductive paradox. The vast majority of species have two sexes and both are needed to reproduce. But one mode of reproduction, gynogenesis, seems to combine a seemingly impossible combination of traits. In this mode, eggs have to be fertilized by males of a different species, but the genes provided by males are not incorporated into the offspring so that the resulting offspring are genetically identical to their mothers. This reproductive mode requires the evolution of several important evolutionary changes: rejection of the father's DNA, the loss of males, and the formation of diploid eggs. Large transitions in a single evolutionary step is highly unlikely, but this is the prevailing explanation. In the proposed project, the researchers will form a synthetic gynogenetic species by replicating the evolutionary pathway that led to the origin of the fish, the Amazon molly. Mathematical models will guide experiments that cross existing species and their hybrids. This research also will provide outreach to the public via workshops and training opportunities for multiple young scientists.The research will artificially form a gynogenetic species through hybridization of two existing species, determining the most likely evolutionary pathway from one to the other. The existing species are from Texas and Mexico, and the new species resulted from a natural hybridization event. To retrace the evolution of this species, the research team will use several mathematical techniques, including differential equations and Monte-Carlo simulations to model the most likely pathway for the evolution of a unique set of traits, including unisexuality, formation of unreduced eggs, and clonality. Current thinking hypothesizes that all of these changes happened in one evolutionary step, but this seems unlikely. Guided by the models, a large-scale crossing experiment will be conducted to actually form a gynogenetic species in the laboratory. This experiment will involve crossing sexual fishes, the resulting F1 individuals amongst each other, and backcrosses. Every unique cross will further be characterized genomically, genetically, and morphologically.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.