suarez lab

Phylogenetics, Systematics, and Taxonomy

Understanding the relationships among taxa is central to understanding much in evolutionary biology and I have extensively utilized phylogenies in all my research. I conducted a molecular phylogeny of tent caterpillars to better understand the evolution of trail-following and tent building behaviors, after which I collaborated on a phylogenetic and biogeographic study of the Australian goosefoots (Chenopodiaceae). During my postdoctoral fellowship at the Smithsonian Institution, I completed multi-locus species trees of two species-rich genera that include widespread invasive species: the North American Crazy Ants, genus Nylanderia, with Seán Brady and John LaPolla, and fire ants in the genus Solenopsis. The later study is currently being expanded to include the entire genus Solenopsis through a University of Illinois Research Board grant in collaboration with Andrew Suarez and Kevin Johnson.

I complement my phylogenetic research with coalescent-based population genetic analyses to better understand inter- and intraspecific evolutionary processes. Where possible, I like to include other types of data, such as morphology, ecological niche modeling, or biochemical characters, for an integrative and multi-disciplinary approach. For example, my collaborators and I used genetic, ecological, and morphological data to delimit several evolutionarily independent meta-population lineages within the nominal fire ant species Solenopsis saevissima. This integrative taxonomic study served as the blueprint for a greater project including all fire ants, for which we were awarded an NSF grant (I currently am funded by this award). We are combining multi-locus microsatellite and mitochondrial DNA sequence data with ecological niche modeling and venom alkaloid data in an integrative taxonomic approach to delimit evolutionarily independent lineages. We will then focus on the systematics and reticulate evolution of a closely related group of species in great detail using next generation sequencing data in a population genomics approach.

My molecular phylogenetic studies are an ideal starting point for further research into ecology, behavior, and evolution. However, systematic and taxonomic research remains essential to effectively combine molecular, morphological, and ecological data to fully resolve species boundaries. For example, I am starting a combined morphometric and genetic integrative taxonomic study to delimit independent evolutionary lineages in nominal Solenopsis fugax, a widespread Eurasian taxon. These large scale and in-depth evolutionary genetic projects will provide the systematic and taxonomic framework for future comparative studies on fire ants and other taxa.

• Brady S.G., et al. (in prep.) The phylogeny of Nearctic Nylanderia and implications for the evolution of social parasitism.
• Gotzek D., et al. (in prep.) Species tree of fire ants: Alternate methods to calibrating nodes.
• Ross K.G., et al. (2010) Species delimitation: A case study in a problematic ant taxon. Syst Biol 59:162-184.
• Kadereit G., et al. (2004) Origin and age of Australian Chenopodiacaea. Org Div Evol 5:59-80.

Genetic Regulation of Social Behavior

I have studied the molecular evolution and regulation of queen number in the Red Imported Fire Ant, Solenopsis invicta, as well as other fire ants using behavioral and genetic approaches. In particular, we have focused on allelic variation in the nuclear protein-coding gene, General protein-9 (Gp-9), because worker allele frequencies predict a colony’s social organization (and Gp-9 genotype). Currently, I am planning a large population genomic study of the socially polymorphic fire ants within a phylogenetic framework with my collaborators Ken Ross, DeWayne Shoemaker, and Laurent Keller in order to understand the molecular evolution and genomic architecture of the region surrounding Gp-9. This region is of interest, because it has been hypothesized to be a rare example of a “green beard” gene region that also acts as a selfish genetic element, attracting other selfish genetic elements (i.e., transposable elements) and leading to a general degradation of the region in a manner similar to the evolution of a sex chromosome.

One of my long-term goals is to develop other socially polymorphic Solenopsis species (e.g., the Tropical Fire Ant, S. geminata) as comparative model systems to S. invicta. I am advising an undergraduate student in determining the sociometry and sociogenesis of monogyne and polygyne S. geminata colonies in Costa Rica and have also begun developing genomic resources for this species, as a first step in this direction. These data will lay the groundwork for continued comparative work on the behavior, ecology and evolution of fire ants.

• Gotzek D., M. Strand, K. Ross, L. Keller, and M. Beck (in prep.) Patterns of expression and protein abundance of Gp-9, a candidate gene implicated in regulation of fire ant social behavior.
• Gotzek D., K.G. Ross (2009) Current status of a model system: The gene Gp-9 and its association with social organization in fire ants. PLoS One 4:e7713.
• Gotzek D., K.G. Ross (2008) Experimental conversion of colony social organization in fire ants (Solenopsis invicta): Worker genotype manipulation in absence of queen effects. J Insect Behav 21:337-350.
• Gotzek D., D.D. Shoemaker, K.G. Ross (2007) Molecular variation at a candidate gene implicated in the regulation of fire ant social behavior. PLoS One 2:e1088.
• Gotzek D., K.G. Ross (2007) Genetic regulation of colony social organization in fire ants: an integrative overview. Quart Rev Biol 82:201-226.
• Costa J.T., D.A. Gotzek, D.H. Janzen (2003) Late-instar shift in foraging strategy and trail pheromone use by caterpillars of the Neotropical moth Arsenura armida (Cramer) (Lepidoptera: Saturniidae: Arsenurinae). J Lep Soc 57:220-229.

Phylogenomics and Genome Evolution

In addition to my evolutionary and behavioral genetic studies, I am increasingly using genomic approaches to study the evolution of ants. Recently, I was able to describe and characterize a gene family in ants thought to be critically important for communication and odor perception, the odorant binding proteins, using EST and next-generation sequencing data. I published the complete mitochondrial genome of an ant and was part of the fire ant genome project. I am planning on following up on these projects by conducting comparative whole-genome sequencing of several ants in a collaborative effort to study the evolution social parasitism. These genomes will also contribute to a growing initiative to apply phylogenomic data to resolve the difficult rooting of the Ant Tree of Life.

• Wurm Y., et al. (2011) The genome of the fire ant Solenopsis invicta. PNAS 108:5679–5684.
• Gotzek D., H. et al. (2011) Odorant binding proteins of the Red Imported Fire Ant, Solenopsis invicta (Hymenoptera: Formicidae): An example of the problems facing the analysis of widely divergent proteins. PLoS One 6:e16289.
• Gotzek D., J. Clarke, D. Shoemaker (2010) Mitochondrial genome evolution in fire ants (Hymenoptera: Formicidae). BMC Evol Biol 10:300.

Invasion Biology

Through my work with fire ants, I have also become interested in the evolution and determinants of invasiveness, because two of the most damaging invasive insects globally are fire ants (S. invicta and S. geminata). With my collaborators at the Smithsonian, we recently identified a previously unidentified invasive ant overrunning Houston and the Gulf Coast of Texas as Nylanderia fulva (a well known invasive species from the Caribbean and Florida) using morphometric and molecular phylogenetic data. I am continuing such species identification efforts on the fire ants with a USDA grant to develop DNA barcodes to distinguish native from invasive species in the USA. This work complements the comparative phylogenetic studies I will conduct with Andy Suarez as a framework to understand ecological, morphological, and social traits promoting invasiveness in fire ants. Ultimately, our goal is to determine what information is best suited to identify, manage, and control invasive species.

• Gotzek D., et al. (in prep.) Global Invasion History of the Tropical Fire Ant, Solenopsis geminata.
• Gotzek D., S.G. Brady, R.J. Kallal, J.S. LaPolla. (2012) The importance of using multiple approaches for identifying emerging invasive species: the case of the Rasberry Crazy Ant in the United States. PLoS One 7:e54314

Biodiversity

As part of my increasing taxonomic focus, I have become increasingly interested in the study of biodiversity and I intend to make this a major research theme in the future. I regard DNA barcoding as useful tool for a rapid, heuristic approach in large, high-throughput studies of diversity, especially in taxonomically difficult groups. While I do not think barcoding should or will replace careful integrative taxonomic practice, a particular strength of this method is that it allows estimation of population structure and genetic diversity – measures that can be used for demographic and phylogeographic reconstruction.

I am currently barcoding ant collections from Cambodia and will continue to add to this collection since Cambodia has one of the most understudied ant faunas in the world (Guénard et al. 2012 PNAS). This work will also have conservation implications, since ants, as key ecosystem engineers, are useful biomonitors. Since Cambodia currently has one of the highest rates of habitat destruction in Southeast Asia, there is a particular relevance to this work and I am keen to pursue similar projects.