Michelle M Mcmahon
Associate Professor, Ecology and Evolutionary Biology
Associate Research Professor
Curator, Herbarium
Primary Department
Department Affiliations
(520) 621-7243
Research Interest
Research in Dr. McMahon's lab focuses on the analysis of biological diversity, particularly through phylogenetic systematics of plants. Lab-based work includes comparative molecular sequencing, aimed at inferring evolutionary relationships among lineages in the legume family (Fabaceae), and using the resulting phylogenies to infer historical rates and modes of floral morphological evolution. Computational research includes testing data from public molecular sequence databases for the ability to construct large-scale phylogenetic trees for all 1.7 million known species, investigating theoretical limits to phylogenetic inference, and developing software for analyzing the effects of fragmentation in phylogenetic and phylogenomic data sets


Marazzi, B., Conti, E., Sanderson, M. J., McMahon, M. M., & Bronstein, J. -. (2013). Diversity and evolution of a trait mediating ant-plant interactions: Insights from extrafloral nectaries in Senna (Leguminosae). Annals of Botany, 111, 1263–1275.
BIO5 Collaborators
Judith Bronstein, Michelle M Mcmahon
Hufford, L., McMahon, M. M., Sherwood, A. M., Reeves, G., & Chase, M. W. (2003). The major clades of Loasaceae: Phylogenetic analysis using the plastid matK and trnL-trnF regions. American Journal of Botany, 90(8), 1215-1228.

PMID: 21659222;Abstract:

Phylogenetic analyses of Loasaceae that apply DNA sequence data from the plastid trnL-trnF region and matK gene in both maximum-parsimony and maximum-likelihood searches are presented. The results place subfamily Loasoideae as the sister of a subfamily Gronovioideae-Mentzelia clade. Schismocarpus is the sister of the Loasoideae-Gronovioideae-Mentzelia clade. The Schismocarpus-Loasoideae-Gronovioideae-Mentzelia clade is the sister of Eucnide. Several clades in Loasoideae receive strong support, providing insights on generic circumscription problems. Within Mentzelia, several major clades receive strong support, which clarifies relationships among previously circumscribed sections. Prior taxonomic and phylogenetic hypotheses are modeled using topology constraints in parsimony and likelihood analyses; tree lengths and likelihoods, respectively, are compared from constrained and unconstrained analyses to evaluate the relative support for various hypotheses. We use the Shimodaira-Hasegawa (SH) test to establish the significance of the differences between constrained and unconstrained topologies. The SH test rejects topologies based on hypotheses for (1) the placement of gronovioids as the sister of the rest of Loasaceae, (2) the monophyly of subfamily Mentzelioideae as well as Gronovioideae and Loasoideae, (3) the monophyly of Loasa sensu lato as circumscribed by Urban and Gilg, and (4) the monophyly of Mentzelia torreyi and Mentzelia sect. Bartonia.

Sanderson, M., McMahon, M., & Steel, M. (2011). Terraces in Phylogenetic Tree Space. Science, 448-450.
McMahon, M., & Hufford, L. (2002). Developmental morphology and structural homology of corolla-androecium synorganization in the tribe Amorpheae (Fabaceae: Papilionoideae). American Journal of Botany, 89(12), 1884-1898.

PMID: 21665617;Abstract:

Comparative developmental morphology was used to assess structural homology of flowers in Dalea, Marina, and Psorothamnus of the tribe Amorpheae (Fabaceae: Papilionoideae). Dalea, Marina, and some species of Psorothamnus have an unusual petal-stamen synorganization (stemonozone) in which free petals are inserted on a region that is continuous with fused stamen filaments. Developmental studies of these three genera demonstrated similarity during organogenesis. Zonal growth results in several synorganized regions, including the stemonozone of Dalea, Marina, and some Psorothamnus. Psorothamnus species that lack a stemonozone have fused stamens and free petals inserted on the hypanthium, as in most other papilionoid legumes. We concluded that the stemonozone is not strictly homologous to either androecium or receptacle, but that it is the product of a modified androecial developmental program. In the prairie clover daleas, petaloid structures positioned between the stamens have been variously interpreted as petals or as staminodes; we infer that they have an extreme form of the daleoid stemonozone, on which five petals (no staminodes) and five stamens are inserted. Assessing structural homology of these flowers allows us to characterize accurately daleoid morphology for evolutionary studies in the tribe Amorpheae.

Deepak, A., Fernandez-Baca, D., Tirthapura, S., Sanderson, M. J., & McMahon, M. M. (2014). EvoMiner: frequent subtree mining in phylogenetic databases. KNOWLEDGE AND INFORMATION SYSTEMS, 41(3), 559-590.

The problem of mining collections of trees to identify common patterns, called frequent subtrees (FSTs), arises often when trying to interpret the results of phylogenetic analysis. FST mining generalizes the well-known maximum agreement subtree problem. Here we present EvoMiner, a new algorithm for mining frequent subtrees in collections of phylogenetic trees. EvoMiner is an Apriori-like levelwise method, which uses a novel phylogeny-specific constant-time candidate generation scheme, an efficient fingerprinting-based technique for downward closure, and a lowest-common-ancestor-based support counting step that requires neither costly subtree operations nor database traversal. Our algorithm achieves speedups of up to 100 times or more over Phylominer, the current state-of-the-art algorithm for mining phylogenetic trees. EvoMiner can also work in depth-first enumeration mode to use less memory at the expense of speed. We demonstrate the utility of FST mining as a way to extract meaningful phylogenetic information from collections of trees when compared to maximum agreement subtrees and majority-rule trees-two commonly used approaches in phylogenetic analysis for extracting consensus information from a collection of trees over a common leaf set.