Our Research Emphases
Pollination in biodiversity hotspots and urban jungles
Adaptation to changing environments
Drivers of sexual system and floral evolution
Plant-plant-pollinator interactions (i.e., whether plants interfere or facilitate each other's pollination) translate into pollination sufficiency and ultimately plant population persistence, and thus are central to our understanding of the generation and maintenance of diverse plant communities.
Plant-microbe & plant-virus interactions Shared pollinators also mediate interactions within flowers that lead to direct and indirect interactions with floral microbes and viruses that can affect plant fitness both positively and negatively.
Work in both of these areas is even more relevant in the Anthropocene as native pollinator-plant interactions are at risk from land-use and climate change, and as species invasions reshape interaction networks. One current emphasis of the lab is to understand how pre- and post-pollination interactions contribute to plant community assembly and coexistence, and how pollinator networks that include intentional and spontaneous plants lead to novel plant-pathogen interactions and/or disrupt microbial mutualisms.
Our focus on post-pollination interactions has elucidated novel heterospecific-conspecific pollen interactions as well as pollen-pistil ones that we are continuing to explore. We also are keenly focused on how novel interactions created by plant invasions and phenological shifts in both native and urban habitats affect both aspects of the pollination process. We are using phylogenetically informed meta-analysis and an internationally coordinated research efforts (California, Hawaii, the Yucatan, and urban sites in Pittsburgh; and Leipzig Germany, see collaborators) to gain universally relevant knowledge of pattern and process that will inform conservation strategies of wild flora in the face of modern threats. Along these lines, the Ashman lab maintains a worldwide perspective on the causes and consequences of pollen limitation of plant reproduction; see collaborators), and is deeply engaged understanding the global drivers of pollen limitation.
Floral phenotypes are all traditionally thought to have evolved in response to pollinator-mediated selection. However, recent work has shown the whole suite of interacting agents that can shape the evolution of these traits. Work in the Ashman lab strives for a holistic perspective on floral evolution. In doing so, we have explored the interface of plant phenotype and many types of selective agents, including pollinators, herbviores, florivores, mycorrhizae, and the abiotic environment. We are especially interested in traits that have traditionally been overlooked--but mediate these important interactions and evolve in response to them-- such as floral longevity, floral scent, and ultraviolet floral patterning. We are also interested in how these interactions affect mating system evolution, and thus study how they directly or indirectly affect mating system expression, as well as components of mating system evolution (e.g., inbreeding depression, autonomous selfing).
Separate sexes evolve from hermaphroditism in nearly half of all flowering plant families, yet few dioecious species have evolved sex chromosomes from autosomes. The Ashman lab has combined phylogenetic and observational approaches with manipulative experiments in specific groups (e.g., Fragaria) test mechanistic hypotheses concerning the forces influencing sexual system evolution, either toward or away from dioecy. We are exploring the very earliest steps in sex chromosome evolution by 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 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
Polyploidy (possessing two or more copies of every chromosome as a result of whole genome duplication) and hybridization (mating between two species) are thought to be a main drivers of biological adaptation, range expansion and speciation. Yet exactly how they contribute to biodiversity, and which genomic mechanisms, functional traits or biotic associations underlie success, remain unanswered questions. The Ashman lab is exploring how polyploidy contributes to ecological and evolutionary success in several species. In the genus of wild strawberry (Fragaria) we aim to resolve uncertainty concerning the manner in which genome doubling contributes to functional diversity and ecological amplitude of polyploid species (see collaborations). We use phylogenetic, population genomic and transcriptomic approaches to evaluate 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. We are also interested in how polyploidy affects species interactions including those that facilitate plant success across resource gradients and in competitive conditions. For instance we are exploring how genome doubling enhances plant-rhizobia symbioses. We are keenly interested in the effects of polyploidization on pollinator and pollen-pollen interactions.
We also are interested in whether hybridization generates phenotypic novelty, cyto-nuclear mismatches and opportunities for new mutualistic partners. In particular, how the plant microbiome contributes to abiotic stress tolerance and how it may mediate other species interactions.