Ecological Genomics of Adaptation and Incipient Speciation
The ecological genetic and genomic mechanisms controlling the early phases of population divergence are essential for understanding how speciation is initiated in the face of gene flow. Moreover, theory suggests that stable genetic correlations among independent forms of reproductive isolation are necessary for differentiation to persist despite gene flow. However, the genomic changes responsible for incipient species formation are poorly understood. In this area of our research, we use complementary approaches to identify the genomic regions contributing to early-acting reproductive isolation and to measure the strength of divergent selection on these loci.
We have used field and greenhouse experiments to quantify the strength of multiple reproductive barriers between two ecotypes of Mimulus aurantiacus in southern Califrornia. Premating barriers (ecogeographic and pollinator isolation) are strong, but incomplete. However, postmating barriers are weak to absent, providing the opportunity for gene flow between the ecotypes. Nevertheless, premating barriers are sufficient to maintain differentiation (Sobel and Streisfeld 2015). Recent studies have investigated the traits associated with these two forms of isolation and how they are maintained in nature despite gene flow (Stankowski et al. in review; Sobel et al. in review).
We are also using next-generation sequencing to survey the M. aurantiacus genome for signatures of divergent selection contributing to this ecotypic divergence. In doing so, we will develop an integrated set of genomic resources that will aid in future studies of evolutionary ecology and molecular evolution within M. aurantiacus and across the entire genus Mimulus. We are also using QTL and functional approaches to determine the types of genetic correlations responsible for maintaining associations between traits or independent isolating barriers. Finally, we will tie both of these approaches together with field experiments to estimate the strength of divergent selection on target loci across multiple life history stages. We anticipate that the results from these studies will provide novel insights into the characteristics of genome structure and mechanisms of natural selection that contribute to the formation of incipient species.
We have used field and greenhouse experiments to quantify the strength of multiple reproductive barriers between two ecotypes of Mimulus aurantiacus in southern Califrornia. Premating barriers (ecogeographic and pollinator isolation) are strong, but incomplete. However, postmating barriers are weak to absent, providing the opportunity for gene flow between the ecotypes. Nevertheless, premating barriers are sufficient to maintain differentiation (Sobel and Streisfeld 2015). Recent studies have investigated the traits associated with these two forms of isolation and how they are maintained in nature despite gene flow (Stankowski et al. in review; Sobel et al. in review).
We are also using next-generation sequencing to survey the M. aurantiacus genome for signatures of divergent selection contributing to this ecotypic divergence. In doing so, we will develop an integrated set of genomic resources that will aid in future studies of evolutionary ecology and molecular evolution within M. aurantiacus and across the entire genus Mimulus. We are also using QTL and functional approaches to determine the types of genetic correlations responsible for maintaining associations between traits or independent isolating barriers. Finally, we will tie both of these approaches together with field experiments to estimate the strength of divergent selection on target loci across multiple life history stages. We anticipate that the results from these studies will provide novel insights into the characteristics of genome structure and mechanisms of natural selection that contribute to the formation of incipient species.