Phylogenetic systematics & biodiversity of malacostracan crustaceans:
Mud crabs of the superfamily Xanthoidea are geographically widespread and among the most speciose groups of brachyuran crabs with nearly 800 known species. Despite being commonly encountered in environmental studies, xanthoids remain poorly understood and are commonly misidentified. Several studies indicate that xanthoid families and subfamilies are not monophyletic (e.g. Thoma et al. 2009; Felder & Thoma 2010; Lai et al. 2011; Lasley et al. in review), which suggests present classifications are based on morphological similarity resulting from convergence (homoplasy) rather than similarity due to shared ancestry (homology).
Our present research builds upon the NSF-funded Assembling the Tree of Life Decapoda project to infer phylogenetic relationships of mud crabs using multi-gene datasets as well as adult and larval morphology. In the short-term we are completing taxonomic and systematic revisions of several commonly encountered mud crab genera (e.g. Hexapanopeus, Eurypanopeus, Panopeus) that are endemic to the Americas and have been shown to be not monophyletic (e.g. Thoma et al. 2009, 2014; Thoma & Felder 2012). Moreover, while working with students on completing these studies I will continue to pursue additional funding to further my research examining the global diversity of the mud crabs by using directed NGS approaches in combination with Sanger sequencing to infer phylogenetic relationships and 1) carry out systematic revisions of the superfamily at all levels as well as 2) characterize the impact of ecological factors such as depth, habitat heterogeneity, and hydrological patterns on the evolution of mud crabs.
In addition, there are other related crab (e.g. Pilumnoidea, Goneplacoidea) and crustacean groups (e.g. Stomatopoda, Amphipoda) that, like the mud crabs, are commonly encountered, frequently misidentified, and poorly understood in terms of their evolutionary relatedness and biodiversity. the long-term goal is to expand this research to include the examination of the phylogenetic systematics and biodiversity of these groups.
Population biology & patterns of speciation in crustaceans:
Although many marine invertebrate species have well-developed larvae with clear avenues of dispersal, other groups have no larval stage and no clear mechanism for dispersal, yet with what appear to be broad dgeographic ranges. This begs the question, what other biological and environmental factors affect the distribution and patterns of speciation in crustaceans and how do these factors interact to shape population connectivity?
To better understand the biotic and abiotic factors that have led to present day patterns of population connectivity and speciation in terrestrial and semi-terrestrial representatives of the Amphipoda (i.e. beach hoppers) we have begun to collect DNA data and voucher specimens from locations throughout the Gulf of Mexico. Although initial efforts will be focued on establishing patterns of connectivity using traditional data (ie., COI), we plan to expand this work to incude NGS data generated through restriction-site associated DNA sequencing as we are able to secure additional funding.
Spatial and Temporal variation in aquatic communities:
With nearly 40% of the United States population living within 100 km of the coast, coastal habitats are increasingly imperiled (Small & Nicholls, 2003). Coastal developments, storm water runoff, beach nourishment, and sea-level rise are among the challenges faced by coastal habitats. Despite the economic and ecological value of coastal and marine habitats, many remain un- or understudied with studies failing to account for temporal and spatial variation and measuring characteristics that do not account for genetic diversity, which has been shown to be an important indicator of long-term health and stability of coastal habitats.
At present we are focused on understanding the temporal variation in sand beach communities using traditional measures of ecosystem health. This work will form the foundation for follow-up studies examining the impacts of hurricanes, beach nourishment, storm water runoff, and other anthropogenic impacts.
Additionally, we are beginning research focused on examining the diversity of crustacean communities associated with altered marine habitats (e.g., hardened shorelines, degraded seagrass meadows). Part of this work is focused on detecting potentially invansive species associated with these altered habitats in an effort to explore the biology of human-mediated introduced species.