Community phylogeography of alpine “sky islands”
Mountains inspired Humboldt to synthesize his thoughts about how species diversity changes across space, yet we know relatively little about the diversity of multi-species assemblages within and among alpine regions. In these remote and understudied areas, evolutionary history can be particularly useful for providing insights into macro-ecological and evolutionary processes driving diversity in the absence of detailed information on functional traits.
To understand what drives diversity at the limits of plant life, I've been exploring floristic patterns across alpine summits in the remote Sawtooth Nation Forest in Central Idaho, and the Écrins National Park, France (in collaboration with Dr. Sébastien Lavergne). I combine field-based floristic plant collections, publically available data repositories, and advances in sequencing technologies to describe diversity. I used bioclimatic variables to evaluate environmental drivers of phylogenetic diversity patterns, and reconstructions of the glacial extent during the last maximum to assess the imprint of history on community phylogenetic diversity patterns (Marx et al. 2017). With novel models and statistical approaches, we are beginning to unravel dominant processes shaping alpine plant communities at regional scales.
Marx HE, Richards M, Johnson GM & Tank DC. 2019. Increasing phylogenetic stochasticity at high elevations on summits across a remote North American wilderness. American Journal of Botany.106(7): 958-970. DOI: 10.1002/ajb2.1328 GitHub Dryad Data
Marx HE, Dentant C, Renaud J, Delunel R, Tank DC & Lavergne S. 2017. Riders in the sky (islands): using a mega-phylogenetic approach to understand plant species distribution and coexistence at the altitudinal limits of angiosperm plant life. Journal of Biogeography. DOI: 10.1111/jbi.13073 GitHub Dryad Data
Metatranscriptomics and community plasticity
Predicting how species respond to environmental change is of critical importance, but quantifying ecological responses over biogeographic scales remains challenging. The ability to produce different phenotypes in heterogeneous environments—phenotypic plasticity—can be essential for responding successfully to change. Short-term (seasonal) plasticity might reflect a broad physiological niche that is adaptive in the long-term. There is recent evidence from experimental studies that plasticity at the level of gene expression can be adaptive under changing environments, but genomic plasticity has not been connected with ecological success in nature.
Working with Drs. Mike Barker and Katrina Dlugosch at the University of Arizona, I am developing an approach to use genomic plasticity to track community-wide responses to environmental change. Follow the progress of our community plasticity reserach at the Harvard Forest NEON site here!
Yang Y, Moore MJ, Brockington SF, Timoneda-Monfort A, Feng T, Marx HE, Walker JF, Smith SA. 2017. An efficient field and laboratory workflow for plant phylotranscriptomic projects. Applications in Plant Sciences . DOI: 10.3732/apps.1600128
Invasion dynamics on oceanic islands
Species introductions provide a unique opportunity to address diversity dynamics in nature, particularly within insular island systems. As alien species continue to accumulate across the globe, it is increasingly important to predict their future spread and impact. Darwin was one of the first to note the potential for species introductions for understanding the distributions we observe, predicting the success of alien species would depend on their similarity to the native community they invade. Since then, invaded communities have become an important study system for understanding community assembly and eco-evolutionary feedbacks in natural systems due to the replication of invasions at different scales.
To estimate evolutionary relationships between species within an ecological community, I developed a bioinformatic workflow to mine publicly available sequence data from GenBank in a consistent, comparative phylogenetic framework (Marx et al. 2016). This approach is illuminating biogeographic trends in island invasions, and I am interested in continuing to incorporate other anthropogenic, biogeographic, and climatic parameters to predict the spread of alien species given phylogenetic structure.
Lu-Irving P, Marx HE, Dlugosch K. 2018. Leveraging contemporary species invasions to test phylogenetic hypotheses of trait evolution. Current Opinion in Plant Biology. 42: 95–102. DOI: 10.1016/j.pbi.2018.04.011
Marx HE., Giblin DE, Dunwiddie PW, Tank DC. 2016. Deconstructing Darwin’s Naturalization Hypothesis in the San Juan Islands using community phylogenetics and functional traits. Diversity and Distributions. 22: 318–331. DOI: 10.1111/ddi.12401. GitHub Dryad Data
(Plant) phylogenetics & systematics
The tree of life provides a context to test ecological and evolutionary hypotheses. I have always been interested in developing new approaches for understanding how species are related to one another, and the processes that have generated the great diversity of life on our planet.
Landis JB, Soltis DE, Li Z, Marx HE, Barker MS, Tank DC, Soltis PS. 2018. Impact of wholegenome duplication events on diversification rates in angiosperms. American Journal of Botany–Special Issue: Using and Navigating the Plant Tree of Life. 105(3): 348–363. DOI: 10.1002/ajb2.1060
Goldberg CS, Tank DC, Uribe-Convers S, Bosworth WR, Marx HE, Waits LP. Species designation of the Bruneau Dune tiger beetle (Cicindela waynei) is supported by phylogenetic analysis of mitochondrial DNA sequence data. Conservation Genetics. Conservation Genetics. 13: 373–380. DOI: 10.1007/s10592-011-0295-9
Marx HE, O'Leary N, Yuan YW, Lu-Irving P, Tank DC, Múlgura ME, Olmstead RG. 2010. A molecular phylogeny and classification of Verbenaceae. American Journal of Botany. 97(10): 1647-1663. DOI: 10.3732/ajb.1000144
Yuan YW, Liu C, Marx HE, Olmstead RG. 2010. An empirical demonstration of using PPR (pentatricopeptide repeat) genes as phylogenetic tools: phylogeny of Verbenaceae and the Verbena complex. Molecular Phylogentics and Evolution. 54: 23-35. DOI: 10.1016/j.ympev.2009.08.029
Yuan YW, Liu C, Marx HE, Olmstead RG. 2009. The PPR (pentatricopeptide repeat) gene family, a tremendous resource for plant phylogenetic studies. New Phytologist. 182: 272-283. DOI: 10.1111/j.1469-8137.2008.02739.x
Few localities can claim to be a Lagerstätte—a fossil site with exceptional preservation. The Miocene fossil beds in Clarkia, Idaho are one of them. In this ancient lake sediment, anoxic preservation compressed leaf tissues before they were able to decompose. Today, you can open blocks of this lakebed and watch leaves change from green to black before your eyes. While extracting ancient DNA remains challenging, I am intrigued by the idea of comparing genetic variation of 15 million year old sub-tropical plant communities with the coniferous forest that has since replaced it. Watch a video of us lifting leaves that fell from tress during the Miocene below!