Professor and Associate Chair
Dr. Ashman received her Ph.D. in 1991 with M.L. Stanton at the University of California at Davis, performed her postdoctoral studies with DJ Schoen at McGill University, and joined the Department in 1994.
Current work in the lab revolves around three major foci: 1) Extending the ecological study of the evolution of dioecy to that of sex chromosomes, 2) Understanding how biotic and abiotic elements of plant communities shape the evolution of floral phenotypes, and 3) Understanding the role of polyploidy in adaptation, range expansion and sexual dimorphism.
What is the nature of the evolving sex chromosome?
Despite numerous studies in a wide range of organisms, the very earliest step in sex chromosome evolution -- from two linked but recombining loci to suppression of recombination between them (and thus the transition from subdioecy to dioecy) --remains unexplored. We are merging genetic, genomic and bioinformatic approaches with ecology and phylogeny to test hypotheses regarding recombination suppression, sequence divergence and selection for sexually antagonistic genes linked to sex. We are utilizing several species within the sexually variable clade of Fragaria (Figure 1) to gain transformative insight into early sex chromosome evolution, as well as the unique roles of hybridization and polyploidy in the transition from hermaphroditism to separate sexes.
How does biodiversity affect plant-plant-pollinator interactions and pollination sufficiency?
Understanding the nature of plant-plant-pollinator interactions (i.e., whether plants compete for pollinators or facilitate each other’s pollination) and how they translate into pollination sufficiency and ultimately plant population persistence is central to our understanding of the generation and maintenance of diverse plant communities. We are determining how increasing plant community diversity affects pollinator diversity and abundance, conspecific and heterospecific pollen transfer, post-pollination interactions, and thus both quantity and quality aspects of pollen limitation. We are using meta-analysis and an internationally coordinated research effort (in three biodiversity hotspots: Spain, California and the Yucatan) to gain universally relevant knowledge of pattern and process that will inform conservation strategies of wild flora in the face of modern threats such as pollinator decline, habitat fragmentation, and climate change.
What drives floral trait evolution and plant speciation?
A common theme of the research in the Ashman lab is to determine how the floral phenotype is shaped by selection through mutualists, enemies and/or the abiotic environment (Figure 2). We often explore this in the context of sexual dimorphism because the sex morphs provide an elegant natural comparison. However, we are also interested in evolution of floral variation in general, and especially in terms of less well-studied characters, such as floral fragrance, longevity, reward chemistry, and ultra-violet color patterns. Each of these has been implicated in mediating interactions with pollinators but also may be under selection via a variety of other agents (herbivores, pathogens, mycorrhizal fungi, soil chemistry) either directly or indirectly, and understanding how these interactions lead to evolution of floral phenotype, mating system and reproductive isolation is a main agenda in the lab.
How is polyploidy a driver of biodiversity?
All flowering plants are ancient and/or recent polyploids (possessing two or more copies of every chromosome as a result of whole genome duplication). This phenomenon is thought to be a main driver of plant speciation, biological adaptation, expansion and sexual dimorphism. Yet exactly how genome doubling contributes to biodiversity, and which genomic mechanisms or functional traits underlie the success of polyploids, remain unanswered questions.
The Ashman lab is leading an international collolaboration to address these questions using wild strawberry (Fragaria) that has centers of diversity in China and North America. Strawberries possess numerous features (small genome size, amenity to replicated experiments through clonal propagation, availability of synthetic neopolyploids, susceptibility to climate change due to early-spring flowering and northern latitude or high elevation distribution) that make them an outstanding model system to resolve uncertainty concerning the manner in which genome doubling contributes to biodiversity. By targeting seven triplets –a polyploid and its diploid progenitors—and using phylogenetic, population genomic and transcriptomic approaches we will determine whether similarities in functional diversity and ecological amplitude of polyploid species are the result of the same patterns (‘rules’) of genetic diversity, chromosome structure or gene expression in a polyploid genome or whether multiple genetic and genomic pathways could lead to successful responses to environmental change.
Govindarajulu, R., A. Liston and T-L. Ashman. In press. Sex-determining chromosomes and sexual dimorphism: insights from genetic mapping of sex expression in a natural hybrid Fragaria ×ananassa subsp. cuneifolia. Heredity
Njuguna, W. A. Liston, R. Cronn, T-L. Ashman and N. Bassil. (2012) Phylogeny of Fragaria based on whole chloroplast genome sequencing. Molecular Phylogenetics and Evolution http://dx.doi.org/10.1016/j.ympev.2012.08.026
Li, J. M. Koski, and T-L. Ashman. 2012. Functional analysis of gynodioecy in Fragaria vesca ssp. bracteata. Annals of Botany 109:545- 552.
Otto, S.P., J. Pannell, C. L. Peichel, T-L Ashman, D. Charlesworth, A. K. Chippendale, L. F. Delph, R. F. Guerrero, S. V. Scarpino and B. F. McAllister. (2011) About PAR: The distinct evolutionary dynamics of the Pseudoautosomal Region. Trends in Genetics 27(9):358-367
Alonso, C., C. M. Herrera, and T-L. Ashman. (2012) A piece of the puzzle: A method for comparing pollination quality and quantity across multiple species and reproductive events. New Phytologist 193:532-542
Gomez, G. A. and T-L. Ashman. (2011) Heterospecific pollen deposition: Does diversity alter the consequences? New Phytologist 192(3): 738-746
Spigler, R. B. and T-L. Ashman. (2012) Gynodioecy to dioecy: Are we there yet? Special issue on 'Plant Mating' of Annals of Botany 109:531- 543
Burns, J.H., T.L. Ashman, J.A. Steets, A. Harmon-Threatt, and T.M. Knight (2011) A phylogenetically controlled analysis of the roles of reproductive traits in plant invasions. Oecologia : 166:1009-1017
Spigler, R.B., and T.L. Ashman (2011) Sex ratio and subdioecy in Fragaria virginiana: the roles of plasticity and gene flow examined. New Phytol : 190(4):158-168.
Shulaev, V., D.J. Sargent, R.N. Crowhurst, T.C. Mockler, O. Folkerts, A.L. Delcher, P. Jaiswal, K. Mockaitis, A. Liston, S.P. Mane, P. Burns, T.M. Davis, J.P. Slovin, N. Bassil, R.P. Hellens, C. Evans, T. Harkins, C. Kodira, B. Desany, O.R. Crasta, R.V. Jensen, A.C. Allan, T.P. Michael, J.C. Setubal, J.M. Celton, D.J. Rees, K.P. Williams, S.H. Holt, J.J. Ruiz Rojas, M. Chatterjee, B. Liu, H. Silva, L. Meisel, A. Adato, S.A. Filichkin, M. Troggio, R. Viola, T.L. Ashman, H. Wang, P. Dharmawardhana, J. Elser, R. Raja, H.D. Priest, J.r. Bryant DW, S.E. Fox, S.A. Givan, L.J. Wilhelm, S. Naithani, A. Christoffels, D.Y. Salama, J. Carter, E. Lopez Girona, A. Zdepski, W. Wang, R.A. Kerstetter, W. Schwab, S.S. Korban, J. Davik, A. Monfort, B. Denoyes-Rothan, P. Arus, R. Mittler, B. Flinn, A. Aharoni, J.L. Bennetzen, S.L. Salzberg, A.W. Dickerman, R. Velasco, M. Borodovsky, R.E. Veilleux, and K.M... Folta (2011) The genome of woodland strawberry (Fragaria vesca). Nat Genet 43:109-116
Spigler, R.B., K.S. Lewers, and T.L. Ashman (2011) Genetic architecture of sexual dimorphism in a subdioecious plant with a proto-sex chromosome. Evolution 65:1114-1126
Collin, C.L., and T.-L. Ashman (2010) Root fungi in wild strawberry root colonization depends on host inbreeding. Evol Ecol Res 12:477-490
Goldberg, M.T., R.B. Spigler, and T.L. Ashman (2010) Comparative genetic mapping points to different sex chromosomes in sibling species of wild strawberry (Fragaria). Genetics 186:1425-1433
Steets, J.A., and T.-L. Ashman (2010) Maternal effects of herbivory in Impatiens capensis. Int. J. Plant Sci. 171(5):509-518.
Spigler, R.B., K.S. Lewers, A. Johnson, and T.-L. Ashman (2010) Comparative mapping reveals autosomal origin of sex chromosome in octoploid Fragaria virginiana. J. Heredity 101:S107-S117
Bishop, E., R.B. Spigler, and T.-L. Ashman (2010) Sex-allocation plasticity in hermaphrodites of sexually dimorphic Fragaria virginiana (Rosaceae). Botany 88:231-240
Alonso, C., J. Vamosi, T.M. Knight, J. Steets, and T.-L. Ashman (2010) Is reproduction of endemic plant species particularly pollen limited in biodiversity hotspots? Oikos 119:1192-1200
Rohde, A.S., and T.-L. Ashman (2010) The effects of florivory and inbreeding on reproduction in hermaphrodites of the wild strawberry, Fragaria virginiana. Int. J. Plant Sci. 171:175-184
Case, A.L., and T.-L. Ashman (2009) Resources and pollinators contribute to population sex ratio bias and pollen limitation in gynodioecious wild strawberry (Fragaria virginiana). Oikos 118:1250-1260
Burd, M., T.-L. Ashman, D.R. Campbell, M.R. Dudash, M.O. Johnson, T.M. Knight, S.J. Mazer, R.J. Mitchell, J.A. Steets, and J.C. Vamosi (2009) Ovule number per flower in a world of unpredictable pollination. Am. J. Bot. 96:1159-1167
Ashman, T.-L. (2009) Sniffing out patterns of sexual dimorphism in floral scent. Functional Ecol. 23:852-862
Majetic, C.J., R. Raguso, and T.-L. Ashman (2009) The sweet smell of success: Floral scent affects pollinator attraction and seed fitness in Hesperis matronalis (Brassicaceae). Func. Ecol. 3:480-487
- Gerardo Arceo Gomez, Graduate Student
- Rajanikanth Govindarajulu, Post Doc
- Matthew Koski, Graduate Student
- George Meindl, Graduate Student
- Katherine Shuller, Staff
- Kathryn LeCroy, Graduate Student
- Alannie-Grace Grant, HMB Post baccalaureate Student
- Rebecca Dalton, Undergraduate student
- Isabella Salamone, Undergraduate student
- Lauren Stanley, Undergraduate student
- Kyle DeHart, Undergraduate student