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RESEARCH INTERESTS

The goal of my research is to characterize the mechanisms of adaptation — a driving force in evolution. A comprehensive understanding of adaptation requires the identification of selective forces in nature, the key adaptive traits that respond to selection, and elucidating the underlying genetic basis of such adaptive traits. Toward this goal, I employ an integrative evolutionary genetic approach that incorporates evolutionary ecology experiments with quantitative-, population- and molecular-genetic/genomic techniques. Below are current projects underway in my lab and information on opportunities for prospective undergraduates, graduate students, and post-docs. 

Genetics basis of adaptation in the wild relatives of rice. 

Understanding the genetic basis of adaptation has been a seminal goal in evolutionary biology for over a century. The development of quantitative trait loci (QTL) mapping has provided an empirical means for testing theories of the genetic architecture of adaptation. However, QTL regions can be quite large and may encompass hundreds of genes. To fully understand the genetic basis of adaptation we need to move beyond QTL and identify the causal genes and mutations. The wild progenitors of cultivated rice, Oryza nivara and Oryza rufipogon, present an ideal system for studying the mechanisms of adaptation. Oryza nivara and O. rufipogon are recently diverged sister species that have undergone marked adaptive differentiation to distinct habitats in the tropics and sub-tropics of Asia. Current projects in the lab are aimed at understanding the genetic basis of mating system and life history evolution in this system. Here we are conducting QTL mapping and fine mapping approaches to further dissect QTL regions to find the causal genetic elements controlling adaptive trait variation. I am also interested in studying parallel evolution of closely related species in the new world tropics (O. glumaepatula) and other patterns of evolution in the Oryza genus. 

Genetics of plant-microbe interactions

Mutualisms are ubiquitous in nature, contributing to numerous ecological processes and playing profound roles in ecosystem functioning. A striking feature of plant-microbe mutualisms is the high degree of variation maintained for both partner choice (i.e. the symbiotic partners a plant forms associations with) and partner quality (the fitness benefits a plant receives from a particular symbiont). The mutualism between plants in the legume family (Fabaceae) and rhizobia (nitrogen-fixing bacteria) is one of the most economically and ecologically important interactions on the planet. Currently, my lab is conducting genome-wide association studies (GWAS) to identify the genetic basis of mutualism variation (e.g. partner choice) in the model legume Medicago truncatula, and its symbiotic rhizobia (Ensifer spp.). We are also conducting population genomic studies in Ensifer collected from the native range in Europe. 

Beyond classic microbial mutualists (e.g. rhizobia and AMF) plants intimately associate with a remarkable diversity of bacterial and fungal species (i.e. the microbiome); and these associations can influence plant traits, distributions, and fitness. Only with modern meta-genomic sequencing approaches are we beginning to thoroughly characterize these communities and understand the factors that structure them. We are conducting various experiments to examine the genetic and environmental drivers that govern legume-associated microbiomes. 

Coevolutionary diversification in Astragalus, the most species rich plant genus.

Coevolution has been considered a primary driver of diversification since the origins of evolutionary thought. Surprisingly, limited experimental evidence exists directly testing this hypothesis and elucidating the mechanisms of coevolutionary diversification – particularly at the microevolutionary level. The central challenge in this pursuit is connecting coevolution to a form of reproductive isolation. We are testing for coevolutionary diversification in Astragalus, the single most species-rich genus of flowering plants (ca. 3,200 spp.). The genus is distributed mainly in arid to semiarid temperate regions and is particularly diverse in western North America (400+ spp.). Astragalus is renowned for specialized interactions with both mutualistic (e.g. rhizobia and fungal endophytes) and antagonistic (e.g. herbivorous insects) interactors. We are conducting a broad range of experiments to examine the role of coevolutionary interactions in contributing to the extraordinary diversity in this genus. We focus primarily on A. lentiginosus the most taxonomically diverse species in the North American flora with over 40 recognized varieties. 

Opportunities to get involved

The Grillo provides numerous opportunities for undergraduate and graduate students, as well as postdocs to become involved in research. Undergraduate students typically work in teams composed of upper and underclassman on a specific project in the lab. Undergraduate students need to be creative, dedicated, and work well independently and as part of a group. Undergraduates that are excited about the research in the lab should contact Dr. Grillo for information on getting involved. The Grillo lab trains graduate students as part of the Biology or Bioinformatics masters program. Graduate students work with Dr Grillo to design projects that will help them achieve their career goals. Graduate students also play a significant role in mentoring undergraduates. Prospective students should contact Dr. Grillo for more information. Dr. Grillo is able to support postdoctoral scholars as funds allow. Postdocs have opportunities to teach within the department and Dr. Grillo is willing to assist with applying to fellowships and other funding sources. The Grillo lab is dedicated to fostering a vibrant, diverse, safe, and inclusive research environment. https://grillolab.weebly.com/

REPRESENTATIVE PUBLICATIONS

*Brown, S.P., *Grillo, M.A., Podowski, J.C. et al. Soil origin and plant genotype structure distinct microbiome compartments in the model legume Medicago truncatula. Microbiome 8, 139 (2020). https://doi.org/10.1186/s40168-020-00915-9

*co-first authors

Grillo, M. A., De Mita, S., Burke, P. V., Solórzano-Lowell, K. L. S., & Heath, K. D. (2016). Intrapopulation genomics in a model mutualist: Population structure and candidate symbiosis genes under selection in Medicago truncatula. Evolution, 70(12), 2704-2717. https://doi.org/10.1111/evo.13095.

Grillo MA, Li C, Fowlkes AM, Briggeman TM, Zhou A, Schemske DW, Sang T. Genetic architecture for the adaptive origin of annual wild rice, Oryza nivara. Evolution. 2009 Apr; 63(4):870-83. doi: 10.1111/j.1558-5646.2008.00602.x

Berg, M.B. and R.W. Merritt. 2002. Larval Growth of Insects. Encyclopedia of Insects, V.H. Resh and R.T. Card, eds. Academic Press.

Kuhns, L.A. and M.B. Berg. 1999. Benthic invertebrate community responses to round goby (Neogobius melanostomus) and zebra mussel (Dreissena polymorpha) invasion in southern Lake Michigan. Journal of Great Lakes Research 25:910-917.  ()

Berg, M.B., L.C. Ferrington, Jr., and B.L. Hayford, eds. 1998. Part 2. Biology, ecology and natural history of Chironomidae. Journal of the Kansas Entomological Society 71(4):383-504.

Berg, M.B., L.C. Ferrington, Jr., and B.L. Hayford, eds. 1998. Part 1. Taxonomy and systematics of Chironomidae. Journal of the Kansas Entomological Society 71(3): 195-382.

Fullerton, A.H., G.A. Lamberti, D.M. Lodge, and M.B. Berg. 1998. Prey preferences of Eurasian ruffe and yellow perch: comparison of laboratory results with composition of Great Lakes benthos. Journal of Great Lakes Research 24:319-328. ()

Alexander, M.K., R.W. Merritt, and M.B. Berg. 1997. New strategies for the control of the parthenogenetic chironomid (Paratanytarsus grimmii) (Diptera: Chironomidae) infesting water systems. Journal of the American Mosquito Control Association 13:189-192. ()

Merritt, R.W., J.R. Wallace, M.J. Higgins, M.K. Alexander, M.B. Berg, W.T. Morgan, K.W. Cummins, and B. VandenEeden. 1996. Procedures for the functional analysis of invertebrate communities of the Kissimmee River-Floodplain ecosystem. Florida Scientist 59:216-275. ()

Berg, M.B., R.W. Merritt, K.W. Cummins, W.P. Coffman, and L.C. Ferrington, Jr. 1996. Ecological and distributional data for Chironomidae (Diptera). Pages 744 -754 In: R.W. Merritt and K.W. Cummins (eds.). An Introduction to the Aquatic Insects of North America. 3rd Ed. Kendall/Hunt Publishing Co., Dubuque, Iowa.

Berg, M.B. 1995. Larval food and feeding behavior. Pages 136-168 In: P.D. Armitage, P.S. Cranston and L.C.V. Pinder (eds.). The Chironomidae: The Biology and Ecology of Non-Biting Midges. Chapman and Hall, London.

Berg, M.B. 1995. Infestation of enclosed water supplies by chironomids (Diptera: Chironomidae): two case studies. In: P.S. Cranston (ed.). Chironomids - from Genes to Ecosystems. CSIRO Publications.

Lamberti, G.A. and M.B. Berg. 1995. Invertebrates and other benthic features as indicators of environmental change in Juday Creek, Indiana. Natural Areas Journal 15:249-258.