Noland Martin, Ph.D.
Curriculum Vitae (PDF)
Ph.D., 2004, Duke University
M.S., 2000, University of Oregon
B.S., 1996, University of Texas
Genetics (BIO 2450)
Evolution (BIO 4301)
The primary focus in the lab centers around the ecological genetics of speciation and natural hybridization. How are populations transformed into new species? What are the evolutionary consequences of natural hybridization? These are two of the most fundamental and interrelated questions in evolutionary biology, and with new ecological, molecular and statistical genomic techniques, answering them is a distinct possibility. The evolution of new species is generally thought to be a consequence of genetic divergence between populations ultimately resulting in complete reproductive isolation. However, reproductive isolation is often incomplete and hybridization may occur between genetically divergent taxa. While the mere existence of hybrids often fuels debate as to the usefulness of long- standing species concepts, naturally hybridizing taxa provide unique opportunities to study speciation "as it happens" before the process has been completed. To understand hybridization and speciation in both a genetic and ecological context, I use large-scale field studies, greenhouse experiments, and genomic-scale analyses in Louisiana Iris. Evolutionary biology requires the integration of such diverse types of data, and my research program illustrates the potential for using these data to ask a broad range of questions about the origin of species and the long-term consequences of natural hybridization.
The primary study system that we work on is Louisiana Iris. The Louisiana Iris species complex consists of three geographically widespread species: Iris brevicaulis, Iris, fulva, and Iris hexagona. All species are found sympatrically in southern Louisiana where natural hybrid zones can frequently be encountered. We are interested in the consequences of such natural hybridization, which can include adaptive introgression and even hybrid speciation. We have utilized QTL mapping to examine the genetic architecture of reproductive isolating barriers between Louisiana Iris species, which has also resulted in the identification of genomic regions responsible for adaptive introgression. We are now using high-throughput “next-generation” sequencing technologies to not only produce high-density genetic linkage maps for QTL mapping, but also to quantify introgression patterns and perform admixture mapping in natural hybrid zones.
A fourth Louisiana Iris species, Iris nelsonii has a very small geographic distribution and occurs only in a single Parish in Southern Louisiana. This unique species, however, has been documented to be of homoploid hybrid origin – a product of hybridization between all three of the more widespread Louisiana Iris species. Molecular evidence reveals that a large portion of the I. nelsonii genome is derived from I. fulva with a minority of the genome consisting of small introgressed regions that originated from I. hexagona and I. brevicaulis. When experimental crosses are made between I. nelsonii and its progenitors, the resulting hybrids are viable and quite fertile, suggesting that intrinsic postzygotic isolation contributes little to the total isolation observed between these species. Instead, it is likely that ecological isolation played a primary role in the origin (and current maintenance) of I. nelsonii. Another primary research focus in the lab thus focuses on integrating genomic and experimental approaches to examine ecological isolation in this species. Furthermore, because Iris nelsonii is rare and geographically restricted, the Louisiana Department of Wildlife and Fisheries (LDWF) have identified it as a “species of concern”. As such, we have an ongoing collaboration with LDWF whereby our work on the ecological requirements of I. nelsonii directly informs conservation planning for this unique species.
Arnold, M.L., A.N. Brothers, J.A.P. Hamlin, S.J. Taylor, and N.H. Martin. 2015. Divergence with gene flow: what humans and other animals got up to in reticulate evolution: symbiosis, lateral gene transfer, hybridization, and infectious heredity. Interdisciplinary Evolution Research 3: 255-296.
Martin, N.H. and S.J. Taylor. 2013. Floral preference, flower constancy, and pollen transfer efficiency of the ruby-throated hummingbird (Archilochus colubris) in mixed arrays of Iris nelsonii and Iris fulva. Evolutionary Ecology Research 15: 783-792.
Taylor, S.J., L.D. Rojas, S.W. Ho, and N.H. Martin. 2013. Genomic collinearity and the genetic architecture of floral differences between the homoploid hybrid species Iris nelsonii and one of its progenitors, Iris hexagona. Heredity 110: 63-70.
Benedict, B.G., Modliszewski, J.L., A.L. Sweigart, N.H. Martin, and J.H. Willis. 2012. Mimulus sookensis (Phrymaceae), a new allotetraploid species derived from Mimulus guttatus and Mimulus nasutus. Madroño 59: 29-43.
Ballerini, E.A., A.N. Brothers, S. Tang, S.J. Knapp, A. Bouck, S.J. Taylor, M.L. Arnold and N.H. Martin. 2012. QTL mapping reveals the genetic architecture of loci affecting pre- and postzygotic isolating barriers in Louisiana Iris. BMC Plant Biology 12: 91.
Taylor, S.J., K.J. AuBuchon, and N.H. Martin. 2012. Identification of floral visitors of Iris nelsonii. Southeastern Naturalist: 11: 141-144.
Dobson, M.C., S.J. Taylor, M.L. Arnold and N.H. Martin. 2011. Patterns of herbivory and fungal infection in experimental Louisiana Iris hybrids. Evolutionary Ecology Research 13: 543-552.
Taylor, S.J., R.W. Willard, J.P. Shaw, M.C. Dobson, and N.H. Martin. 2011. Differential response of the homoploid hybrid species Iris nelsonii (Iridaceae) and its progenitors to abiotic habitat conditions. American Journal of Botany 98: 1309-1316.
Martin N.H. 2011. A scientist’s perspective on national funding for science. Irises: The Bulletin of the American Iris Society 92: 17-23.
Martin, N.H. and J.H. Willis. 2010. Geographic variation in postzygotic isolation and its genetic basis within and between two Mimulus species. Philosophical Transactions of the Royal Society B: Biological Sciences 365: 2469-2478.
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