Gerstner Scholar Profiles

2011-2013

Dr. Mercer Brugler

RESEARCH FOCUS

Reconstructing relationships among cnidarians is complicated by extremely low rates of mitochondrial (mt) DNA sequence evolution within anthozoans (anemones, corals, zoanthids and corallimorphs). With the exception of some stony corals, anthozoans examined to date are characterized by synonymous substitution rates 50-100 times slower than most metazoans and variation is almost nonexistent at the intraspecific level. Currently applied nuclear markers are not sufficiently variable to differentiate some putative species.

Anthozoan systematists and taxonomists face a daunting challenge: in addition to slow mt sequence evolution and a lack of variable nuclear markers, simple body plans reduce the number of morphological characters available to define a species or provide phylogenetic information. Sea anemones (order Actiniaria) are among the most diverse members of the subclass Hexacorallia and are considered an emerging model system as they represent a basal eumetazoan lineage that serves as an outgroup to studies analyzing the origin and evolution of bilaterian animals. Mosaics of characters currently distinguish actiniarians, and proposed evolutionary relationships have been largely based on an absence of features. Thus, my primary focus is to search for variable, single-copy nuclear DNA markers for species-level identification. Variable markers will ultimately help determine which external / internal morphological characters are species-specific. My secondary focus is elucidating systematic relationships within, and the evolutionary history of, the order Actiniaria (1,200 species; 46 families) using 44 newly sequenced complete mitochondrial genomes (~16-18K nucleotides per individual).

To locate novel nuclear markers for reliable species-level identification and phylogenetic analysis, I am focusing on two largely Antarctic anemones: Hormathia (Hormathiidae) and Isosicyonis (Actiniidae). Markers also are being located for Aiptasia and Metridium because of their broad applicability to the scientific community. I am implementing three strategies to locate markers: building a recombinant library from whole genomic DNA; constructing a complementary DNA (cDNA) library from messenger RNA (mRNA) and screening for expressed sequence tags (ESTs); and de-novo sequencing of the transcriptome utilizing a 454 ultra-high-throughput Next Generation DNA Sequencer (the complete nuclear genome of Nematostella vectensis serves as a control). Defining species and deeper phylogenetic relationships is imperative, representing a critical step in advancing knowledge and understanding of sea anemone taxonomy and systematics. Link to CV.

BIOGRAPHY

Mercer R. Brügler is a Texas native who was born in Hurst on December 8, 1978 to Mercer L. and Donna J. Brügler. He attended the University of Miami (Florida, 1997-2001) where he earned a Bachelor of Science in Marine Biology. He then pursued a Master of Science in Marine Biology at the College of Charleston’s Grice Marine Laboratory (South Carolina, 2001-2004) and a Doctor of Philosophy in Environmental and Evolutionary Biology at the University of Louisiana at Lafayette (2004-2011).

Dr. Timothy Guiher

 RESEARCH FOCUS

I am interested in the evolutionary history of the subfamily Crotalinae, the venomous snakes commonly known as pitvipers. Despite recent efforts to reconstruct the phylogenetic history of this medically important group of snakes, using mtDNA, several key nodes remain unresolved, also leaving several unanswered biogeographic questions. For instance, estimates of time of dispersal into the New World vary from the Miocene to the Late Cretaceous. In addition, inter-generic relationships remain poorly resolved, making it difficult to identify patterns of dispersal into temperate and tropical environments.

Pitvipers are responsible for the majority of mortality and morbidity due to envenomation in many parts of the world. Antivenom effectiveness is reduced by substantial variation in composition among crotaline snakes. In contrast, venom proteins have received a great deal of interest from the medical community to develop treatments. Recent studies have identified venom proteins with properties suitable to the treatment of breast cancer, colon cancer, and tumor suppression. Describing the variability in venom composition at all taxonomic levels requires a phylogenetic framework. Providing a robust hypothesis of phylogenetic (evolutionary) relationships, which can be accomplished by combining extensive sampling with a large number of unlinked genetic loci. This study will explore applications of novel genomic techniques and next generation sequencing to greatly improve the sampling of loci and individuals that can efficiently be achieved for phylogenetic study. Recent efforts to sequence entire genomes for an increasing number of vertebrate taxa, including several squamate taxa, have identified a large number of potentially informative nuclear loci suitable for examining phylogenetic relationships. Taking advantage of this is limited by the cost and effort required to sequence a large number of markers for many individuals using standard Sanger sequencing. However, recently proposed sample barcoding techniques pool samples making it possible to simultaneously sequence hundreds of loci for hundreds of individuals. This study will be among the first to apply next generation sequencing to the field of phylogenetics. By combining extensive sampling with 48 nuclear loci I will provide new insight into the biogeographic history of Crotalinae and the evolution of venom proteins within this subfamily. Specific efforts will be made to elucidate when Crotalines invaded the New World and identify patterns of dispersal into temperate and tropical niches. Link to CV.

BIOGRAPHY

Tim Guiher received his PhD from the City University of New York in 2011. His research focuses on using molecular techniques to investigate the processes that have resulted in current species diversity and distributions of snakes. In addition, Tim uses large empirical and simulated data sets to investigate the performance of statistical methods to delineate species and infer population dynamics, including changes in historical population sizes and migration rates. He has described two new venomous snakes in the US in addition to several phylogeographic lineages of non-venomous snakes. Currently, he is using next-generation sequencing techniques to compile a massive multi-locus data set to investigate the phylogenetic relationships within Crotalinae (pitvipers) and processes influencing the radiation of this group.

2010-2012

Dr. Jonah Choiniere

RESEARCH FOCUS

I am interested in the early evolution of the Coelurosauria, a clade of theropod dinosaurs closely related to birds. Although the first bird, Archaeopteryx, is known from Jurassic deposits (~150 million years old), the fossil record of contemporaneous coelurosaurs is poor. My dissertation research focused on the anatomy and systematics of new coelurosaurs that predate Archaeopteryx from the earliest Late Jurassic (~160 million years old) of China. My Gerstner Scholar research focuses on the evolution and anatomy of the Alvarezsauroidea, an enigmatic clade of theropod dinosaurs once thought to be a flightless lineage of basal birds, and the implications for understanding the non-avian dinosaur to bird transition. Alvarezsauroids are particularly fascinating because they have short, robust forelimbs, lightly-built skulls with hundreds of teeth, and long, gracile legs. Moreover, advanced alvarezsauroids share many morphological similarities with birds, including special structures of the skull, the pelvis, and the hindlimb. Recent research on alvarezsauroids shows that the lineage had evolved by the earliest Late Jurassic and that they are not as closely related to birds as previously thought. Questions remain about the phylogenetic position of alvarezsauroids within the Theropoda and about the evolution of their bird-like morphology. I am working on a detailed anatomy of alvarezsauroids from Mongolia, incorporating data from high-resolution 3D CT scans and from new, unpublished specimens. This research will clarify alvarezsauroid relationships and illuminate morphological characteristics that alvarezsauroids share with birds. Link to CV.

BIOGRAPHY

Jonah Choiniere received his Ph.D. in Biological Sciences from the George Washington University. He studies evolution of coelurosaurian theropods, the group of meat-eating dinosaurs most closely related to birds. He has examined theropods from around the world, and his fieldwork in China, South Africa and Mongolia focuses on discovering new species of coelurosaurs and understanding dinosaur (including birds) evolution. His systematic research on theropod dinosaurs involves the use of large datasets and the application of software designed for molecular sequence alignment to questions in morphological evolution. His current research focuses on the relationships and evolution of the bizarre theropod group Alvarezsauroidea, which were previously hypothesized to be basal flightless birds.

Dr. Jose M. Padial

RESEARCH FOCUS

I’m interested in species diversity, both in how it originates and how we classify it. My current research focuses on the taxonomy and phylogenetic relationships of Pristimantis. This group of Neotropical frogs, with more than 400 species, is the largest genus of Terrestrial vertebrates. These frogs are characterized by having direct development—they lay eggs in moist areas and embryos undergo direct development without the typical tadpole phase so characteristic of other anurans— and include species inhabiting the major biomes and areas of the Neotropical realm (the Amazon, the Guiana Shield, the Cerrado, diverse habitats of Central America, some islands in the Caribbean, and multiple Andean ecosystems (paramos, interandean dry valleys, cloud forests, etc.). Such an ample distribution made this group a perfect candidate to study the historical processes that shape species diversity. The first step to study the origin and biogeography of a group of organisms is to reconstruct the phylogenetic relationships of its species, so that we can identify the split of ancient species lineages and relate them to changes in the geology, climate or ecological conditions of an area. My goal as Gerstner scholar is to reconstruct a robust phylogeny of Pristimantis using molecular and morphological data. This new phylogeny will shed light on the origin of Neotropical diversity, particularly on the diversity of the eastern slopes of the Andes and western Amazonia, for which little empirical work based on new phylogenetic hypotheses has so illuminated biogeography. Other problems that will be illuminated by an improved phylogeny and biogeography are: what is the relative role of intrinsic and extrinsic factors on the process of diversification? Has diversification occurred mainly through pulses of speciation and extinction within the same biogeographic area or through vicariance or dispersal events across different biotic zones? Do highlands promote higher diversity than lowlands? Are the Andes a diversity pump that supplies lineages to the Amazon? What’s the role of ancient areas such as the Guiana Shield in the diversification of Neotropical lineages? Has been the diversification process punctuated or constant along time? And, if punctuated, which was the period that produced a largest number of lineages and why? But also, why are so many Pristimantis out there? Ultimately, the new phylogeny will give place to an improved classification of the group. Other related projects I’m involved include, an integrative approach to Amazonian species diversity—in order to estimate how many amphibian species are still undescribed there, and how the diversity of the Amazonian forests originated; and a study on the diversity and biogeography of Andean lizards of the genus Liolaemus. Link to CV.

BIOGRAPHY

José M. Padial received his PhD from Granada University in 2007. For his PhD research he worked at Museo Nacional de Ciencias Naturales (Madrid), and Museo de Historial Natural Noel Kemppf Mercado (Santa Cruz, Bolivia). During his PhD he was awarded with the Ernst Mayr Travel Grant in Ecology and Systematics from Harvard University and with the Travel grant of the European program “Synthesys”. In 2008 he received the 9th R.J.H. Hintelmann Scientific Award for Zoological Systematics. After his PhD he moved to Sweden for a two years postdoc at the Evolutionary Biology Centre of Uppsala University, awarded with a Marie Curie Inter-European fellowship. Since January 2009 he is associated editor for amphibians of the international taxonomic journal Zootaxa. Every year since 2002 he conducts field expeditions to the Amazon Basin and tropical Andes to search for frogs, several of which have been described by him and collaborators as new species to science.

2009-2011

Dr. Christian Kammerer

RESEARCH FOCUS

My current research as a Gerstner Scholar explores the origin and evolution of mammals from early cynodonts, a diverse group of synapsids in the Permian-Triassic (approximately 200-300 million years ago). Although the evolution of mammals from “reptilian”-grade vertebrates (sometimes incorrectly termed “mammal-like reptiles”) is one of the best-understood major evolutionary transitions in the fossil record, many questions about the base of the mammalian tree of life remain. In particular, there continues to be debate about the phylogenetic relationships of several groups of cynodonts hypothesized to be close relatives of mammals. This research is working towards the resolution of these issues through broader taxon sampling and the introduction of new character data from cynodont skulls and postcranial skeletons, including endocranial data derived from high resolution, 3-D CT-scans. In addition to addressing cynodont phylogeny, this research is elucidating the biological underpinnings of the origin of mammals. Cynodonts underwent a “size squeeze” during their evolution: most Triassic cynodonts were roughly dog-sized, but along the main branch of mammal ancestry, average body size was reduced to shrew proportions, and mammals remained generally small-bodied throughout the Mesozoic. Through histological sectioning of cynodont long bones (limb bones), data on cynodont growth history and “paleo-genomics” are being obtained. Relative ages and growth rates can be extrapolated from bone growth rings, and because genome size is correlated with cell size in extant organisms, the volumes of lacunae (the spaces containing bone cells) in fossil bones can provide an estimator of genome size in long-extinct organisms. Together, these data will be used to assess how cynodont miniaturization occurred and the implications of this for later mammalian success. Link to CV.

BIOGRAPHY

Christian Kammerer received his PhD in Evolutionary Biology from the University of Chicago. He primarily studies evolution in the Synapsida, one of the two major groups of amniotes and the dominant terrestrial vertebrates of the late Paleozoic and early Mesozoic eras. He has extensively examined Permo-Triassic synapsid faunas around the world and utilizes rigorous quantitative methodologies and innovative imaging technologies to address major questions of diversification and extinction in the vertebrate fossil record. His current research focuses on the early Cynodontia, the most common synapsids of the Triassic Period, and their evolution into mammals.

Dr. Cartsen Kamenz

RESEARCH FOCUS

Carsten is interested in the phylogeny and evolution of Chelicerata (arthropods with chelicerae, including all arachnids). The phylogenetic position of scorpions is crucial for resolving chelicerate phylogeny and fossil scorpions are especially important in this regard. Some scientists believe the earliest scorpions were aquatic, suggesting either that the invasion of land occurred twice in the evolutionary history of chelicerates or else that arachnids are not monophyletic (sharing a single common ancestor). Fossil scorpions are also important for illuminating the basal lineages of Recent scorpions. Unfortunately, little detailed morphological work, let alone phylogenetic analysis, has been done on fossil scorpion. Carsten is critically reassessing and documenting the morphology of 75 fossil scorpions, based on a re-examination of almost 200 specimens in twelve European and North American collections, using traditional palaeontological methods and new techniques like variable pressure scanning electron microscopy, and CT-scanning (for 3D specimens with morphology hidden in the matrix). He is focusing on characters with implications for terrestrialization, namely the abdominal plates, legs, specialized sensory structures called pectines and book lungs. Preliminary results of Carsten’s work suggest that fossil scorpions were not aquatic (i.e. there was a single origin of terrestrialization among chelicerates) and confirm hypotheses that arachnids are the monophyletic sister-group of eurypterids (sea scorpions). These findings are independently supported by genomic data.  Link to CV.

BIOGRAPHY