Assistant Professor, Department of Biology, Texas State University, San Marcos, TX 78666
The Martin lab is concerned with understanding the origin and maintenance of biological diversity. While diversification certainly results from a variety of evolutionary forces such as natural selection and genetic drift, ultimately the process of speciation involves the evolution of reproductive isolation. To this end, we have been primarily focused on identifying reproductive barriers that are important in preventing interspecific gene flow, determining the degree to which individual barriers restrict gene flow in natural populations, and identifying the genetic architecture underlying a diverse array of prezygotic and postzygotic isolating barriers. We utilize intensive ecological field studies and forward genetic approaches (e.g. QTL mapping) in a newly emerging model system for studying plant speciation and introgressive hybridization, Louisiana Iris.
The four species in the Louisiana Iris species complex (I. fulva, I. hexagona, I. brevicaulis, and I. nelsonii) have a number of advantages as a model system: all four species are highly interfertile and self compatible, allowing for the creation of a diverse array of experimental hybrids. They are perennial and clonal, enabling us to place replicates of the same individuals into a wide array of habitats and monitor them over several (often very different) growing seasons. Several populations occur in sympatry with one another, and natural hybridization is common, often resulting in very complex and stable hybrid zones. Though reproductive isolation is clearly not complete, a number of prezygotic and postzygotic barriers between the four species have been identified, reducing the chance for gene flow, and by utilizing a QTL mapping approach (in experiments conducted entirely in natural field conditions), we have examined (and are examining) the genetic architecture of a number of those barriers including habitat isolation, temporal isolation, pollinator isolation, hybrid inviability, and hybrid sterility.
Some of the funded projects were are actively pursuing utilizing Louisiana Iris : 1) Building off our work examining the genetic architecture of these diverse barriers, our lab is collaborating with Mike Arnold at the University of Georgia to determine whether QTLs responsible for effecting reproductive isolation are predictive of patterns of introgression (at QTL-linked markers) in natural hybrid zones. 2) I. nelsonii is a purported stabilized homoploid hybrid species (between I. fulva, I. hexagona, and I. brevicaulis). Our lab is developing a genetic linkage map of I. nelsonii, and using population genetic approaches, we are determining the genomic origin of each mapped marker. Furthermore, we are identifying important prezygotic and postzygotic barriers between I. nelsonii and its progenitor species, and utilizing a QTL mapping approach to determine the genetic architecture of most identified barriers. 3) We also are initiating a project examining the genetic basis of resistance and tolerance to herbivore attack in Louisiana Iris species and their hybrids. We actively seek interested collaborators in any and all listed projects.