QTL Mapping of Reproductive Isolation in Louisiana Irises

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0074159ArnoldThe evolution of reproductive isolation is critically important in the speciation process, because it is cessation of gene flow that definitively places diverging lineages onto separate evolutionary paths towards becoming new species. How speciation and reproductive isolation occur depends on the number of genes conferring isolation and the relative importance of pre- vs. post-zygotic reproductive barriers. Identifying the number and magnitude of genes involved can also elucidate both the time and strength of natural selection needed for speciation.We will study the genetic basis of reproductive isolation in the Louisiana Irises, a species complex has been a focus of ecological, genetic and evolutionary studies for almost a century. We will construct a QTL (quantitative trait loci) map of reproductive isolating mechanisms separating two species, Iris fulva and I. brevicaulis. Our analysis will locate QTLs that have the largest effect on the expression of both pre-mating and post-mating barriers to reproduction. The traits associated with the pre-mating barriers include floral differences that cause bumblebees to preferentially visit I. brevicaulis and hummingbirds to preferentially visit I. fulva (e.g., flowering time, flower color, nectar guide shape, nectar sugar concentration). The traits associated with post-mating barriers include (i) gamete competition (i.e., conspecific pollen tubes grow more quickly and thus fertilize ovules more efficiently than do pollen tubes from the alternate species) and (ii) pollen fertility of hybrids formed between the two species.