Gerstner Scholar Profiles main content.

Gerstner Scholar Profiles

Current Gerstner Scholars

2018-2020:  Nathan Lujan | Ariadna Morales | David Wright

2017-2019:  Phillip Skipwith | Benjamin Titus


Dr. Nathan Lujan

Dr. Nathan Lujan

Research Focus - My research focuses on the macroevolutionary ramifications of anatomical decoupling in the vertebrate cranium. Throughout the tree of life, the decoupling or loss of anatomical linkages is thought to be one way in which evolutionary constraints on organismal morphology are reduced, thereby accelerating the rate at which organisms diversify into different forms. Technological analogies to anatomical decoupling are common, from classical watch complications that increase time-keeping functionality to the expansion cards and subroutines of computers and computer programs that handle specialized tasks. To test the hypothesis that anatomical decoupling can increase the speed at which species diversify, my project will focus on a hyperdiverse clade of Neotropical catfishes – the Loricarioidei, which comprises six families, >140 genera, and >1,600 currently recognized species (~4.5% of all fish species).

Loricarioid catfishes occupy a wide range of aquatic habitats throughout tropical Central and South America, from coastal estuaries and deep river channels to high Andean streams and lakes over 4,500 m above sea level. Across these habitats, loricarioids have diversified to fill a wide range of mostly benthic niches. For example, many members of the family Trichomycteridae (~300 spp.) are specialized to feed on slime-coats, scales or gills of larger fishes. To facilitate host attachment while feeding, parasitic trichomycterid catfishes have a modified opercular mechanism with external teeth that can be erected to lock themselves into tight crevices, such as gill chambers. In contrast, members of the Astroblepidae (~80 spp.) and Loricariidae (~980 spp.) have a suctorial oral disk that allows them to attach to substrates while feeding, and jaws and teeth that are variously specialized for eating invertebrates, detritus, algae, and even wood. Loricariids also have an independently derived mechanism for everting opercular teeth during competitive interactions.

Throughout Loricarioidei, the cranium exhibits considerable morphological diversity, particularly related to oral and opercular mechanisms. My investigation of this diversity will interweave state-of-the-art methods in phylogenomics, anatomical visualization, comparative analyses, bioinformatics and computational biology. Across the Loricarioidei, three major intracranial ligaments have been lost, which respectively link: 1) the premaxillae to the mesethmoid, 2) bilateral mandibular rami to each other, and 3) the mandible to the operculum. I will use CT technology to capture a dense taxonomic sampling of 3D cranial shape data and will build a robust phylogeny for the entire clade using a sequence capture approach targeting hundreds of exonic (protein-coding) regions of the genome. Analysis of cranial shape data using modern phylogenetic comparative methods will allow me to determine whether cranial diversification rates change in response to individual decoupling events. Examining loricarioid catfishes in this context will provide a robust test of decoupling hypotheses, establish the tempo and mode of diversification in one of Earth’s largest vertebrate radiations, and deepen our understanding of an evolutionary process that is likely widespread throughout the tree of life.

Biography - Nathan K. Lujan received his BSc in Biology from Calvin College in 2000 and his PhD from Auburn University in 2009 under the supervision of Jonathan Armbruster. His dissertation focused on the jaw morphofunctional diversity, trophic ecology, and historical biogeography of the suckermouth armored catfish family Loricariidae. Prior to this Gerstner Fellowship, he was an NSF International Research Fellow at the Royal Ontario Museum, an NSF Postdoctoral Researcher at the Academy of Natural Sciences of Drexel University, and a Canada Department of Fisheries and Oceans Postdoctoral Researcher at the University of Toronto. Top

Dr. Ariadna Morales

Dr. Ariadna Morales

Research Focus - My postdoctoral research at the AMNH focuses on the genomic mechanisms of convergent evolution. I aim to establish a model system to study the processes linked to repeated ecological and morphological adaptation in nature, using as an example the traits and foraging strategies that have evolved in parallel in the bat genus Myotis.

Parallel evolution, the independent development of the same trait in different taxa, is a common process in nature that raises questions regarding the involved genomic mechanisms and the role of natural selection as the driver of repeated adaptations. My research implements novel genomic techniques and statistical tools to explore the genetic mechanism linked to parallel evolution of phenotypic traits, using as a model the most specious genus of bats, Myotis. This genus is found worldwide and has been classified into three ecomorphs following foraging strategies that seem to be evolved repeatedly. My approach for studying parallel evolution goes from a broad genomic perspective to explore whether homologous genes are linked to the reoccurrence of phenotypes in species that have been isolated millions of years, to detailed genotype-phenotype association approaches to explore if the presence of traits linked to foraging adaptations can be predicted by certain genomic features. This study is leading to a comprehensive understanding of the genomic mechanism of parallel trait evolution in natural conditions.

Biography - Ariadna E. Morales earned a BSc in Biology in 2009 and an MSc in Evolutionary and Environmental Biology in 2012 from the Universidad Nacional Autonoma de Mexico (UNAM) under the supervision of Dr. Daniel Piñero. She earned a Ph.D. in Evolution, Ecology, and Organismal Biology and a Graduate Minor in Statistics in 2018 from The Ohio State University under the supervision of Dr. Bryan Carstens. As part of her dissertation work, Ariadna contributed to developing computational tools for phylogeographic model selection and species delimitation that handle efficiently big datasets and helped to develop the R package “PHRAPL”. She also documented striking examples of speciation with gene flow in North American bats of the genus Myotis by integrating genomic, environmental and morphometric analyses. Finally, she investigated if the convergent evolution of foraging strategies in the genus Myotis (~70-80% of 106 extant taxa) is linked to diversification shifts using phylogenetic, biogeographic and comparative methods. Top

Dr. David Wright

Dr. David Wright

Research Focus - I am an evolutionary paleontologist interested in the origin of major lineages, their adaptations, and the interplay between ecological and geological processes in large-scale evolutionary radiations throughout the history of life. I use a combination of specimen-based research (including specimens housed in the AMNH collections), phylogenetic methods, and mathematical modeling to study how physical and intrinsic biological processes shape macroevolutionary dynamics in the marine biosphere. My taxonomic specialty is the exclusively marine phylum Echinodermata.

Echinoderms are represented by more than 7,000 species in today’s oceans and include familiar animals such as starfish, sea urchins, and sand dollars. The apparent diversity of echinoderms alive today masks their more prodigious geologic history. For example, the Crinoidea (feather stars and sea lilies) comprises an evolutionary lineage of reef-dwelling to deep water echinoderms represented by ~600 species today, yet more than 8,000 fossil species have been described spanning ~480 million years of evolutionary history. My current research revolves around several facets of crinoid origins: both the early evolution of total-group Crinoidea during the Ordovician Radiation and the phylogenetic origin and radiation of the crown group during the Paleozoic—Mesozoic transition. The origin and radiation of crown-group crinoids is of particular interest because the early stages of their diversification spans the most severe extinction event in the history of life: the Permian-Triassic mass extinction. The results from my research will provide a means to test alternative theories predicting how biodiversity accumulates in “crowded” vs. “empty” (e.g., pre-vs. post-mass extinction) ecosystems more generally, such as whether diversification within lineages is driven more by ecological opportunities, the evolution of key innovation traits, or by “background” origination of novel adaptations.

I am also presently involved in a number of taxonomic projects describing new species from exceptionally well-preserved echinoderm faunas from around the world, including the Ordovician “Brechin Lagerstätte” of Ontario and the Permian of west Texas.

Biography - David F. Wright received his BSc in Geology (minor in Astrobology) from the University of Kansas in 2010, his MSc in Geological Sciences from Ohio University in 2012, and his PhD in Geological Sciences from The Ohio State University in December 2016. For his doctoral studies, Davey focused on the application of statistical phylogenetics and comparative methods to paleobiological data, with empirical work emphasizing fossil echinoderms. His doctoral research also featured a major systematics component in which he described several new crinoid species and comprehensively revised the higher taxonomic classification of Class Crinoidea (Echinodermata). Top


Dr. Phillip Skipwith

Phil Skipwith

Research Focus - My postdoctoral research focuses on the macroevolutionary dynamics of an ecologically and morphologically diverse group of snakes, the pseudoxyrhophiine lamprophiids of Madagascar. This is a diverse group of ~85 species in 20 genera representing a radiation endemic to Madagascar. Very little is known about the ecology and morphological diversity of this exceptional clade. What is known is that, since the late Paleogene, this clade has colonized a number of niches resulting in fossorial, terrestrial, and arboreal forms with accompanying variation in size and shape. Previous studies attempting account for morphological diversity have been largely descriptive in nature. Moreover, this clade represents the only insular snake radiation where there has been extensive in situ diversification. Until recently, phylogenies of the Malagasy pseudoxyrhophiines have been poorly supported and incongruous, compounding the attempts to address macroevolutionary dynamics. Using a new and fully resolved species-level phylogeny generated from hundreds of anchored tag loci, I will use morphology to investigate phenotypic diversification within this group. My project involves using 3D x-ray computed tomography (CT scanning) to generate 3D models of the skeleton and soft tissues for species within this clade. These data will be used to address: 1) morphological diversity across the entire radiation, both interspecifically and intraspecifically, 2) the dynamics of phenotypic diversification through time, 3) the relationship between net diversification and phenotypic diversification, 4) and the presence of determinism and convergent evolution. Lastly, I will examine if environmental heterogeneity, particularly climate, has influenced ecological and ecomorphogical diversification within pseudoxyrhophiines. Determining the relationships between speciation, phenotypic diversification, and extrinsic factors is critical to our understanding of how biodiversity is generated and maintained across long timescales. The Malagasy pseudoxyrhophiines represent an excellent system through which we can understand these complex patterns and processes and inform conservation initiatives.

Biography - Phillip L. Skipwith received his B.S. from the Richard Stockton College of NJ in 2008, his M.S. from Villanova University in 2011 under the supervision of Aaron Bauer, and his PhD from the University of California, Berkeley in 2017 under the supervision of Jim McGuire. His dissertation focused on the phylogenomics and macroevolutionary dynamics of the diverse diplodactyloid geckos of Australasia. Top

Dr. Benjamin Titus

Benjamin Titus

Research Focus - My research is focused on understanding how biodiversity evolves in tropical marine symbioses at the species, population, and behavioral levels. I use sea anemone symbioses that live on coral reefs as models to understand the evolutionary processes and outcomes that generate and maintain diversity in these tightly linked interactions. I have primarily focused my research program on sea anemone symbioses from the Tropical Western Atlantic and Caribbean, but for my postdoctoral work I will be focusing exclusively on the evolution of sea anemones that host clownfishes in the Indo-Pacific.

Symbiosis often confers novel abilities or characteristics in at least one partner, can lead to adaptive radiation, and contributes meaningfully to the biodiversity within ecosystems. The clownfish-sea anemone symbiosis has been a model system for understanding fundamental evolutionary and ecological processes, and is one of the most recognizable symbioses on the planet. There are 30 described species of clownfishes, which have adaptively radiated to live with sea anemones, but only 10 nominal species of host anemones. Why have the host anemones not undergone a radiation similar to the clownfishes? Given the co-dependent nature of the mutualism, their broad geographic and ecological distribution, extensive phenotypic variation, and that all 10 host species are only described morphologically, I hypothesize that there is undescribed cryptic species-level diversity within the host anemones.

Using high-throughput sequencing (i.e. RADseq, Ultra-conserved elements), molecular species delimitation, and a comparative phylogeographic framework, I will test allopatric and ecological speciation hypotheses to search for cryptic species and reconstruct the evolutionary histories of the two most common sea anemone host species from the tropical Indo-West Pacific (IWP) oceans: Entacmaea quadricolor and Heteractis crispa. A genomic perspective is likely to be critical for understanding sea anemone diversity given the inherent challenges with classic morphological studies in this group. Ultimately, the existence of undescribed cryptic anemone host species has the potential to re-write much of our understanding of this symbiosis and impact the evolutionary, ecological, and behavioral theory that has been generated from the study of these charismatic relationships. This work will also have important conservation implications as these species are among the most heavily collected species in the ornamental aquarium trade.

Biography - Benjamin Titus received his BSc in Ecology from Otterbein University in 2008, his MSc in Marine Biology from Auburn University in 2011, and his PhD from the Dept. of Evolution and Ecology from The Ohio State University. For his doctoral work he studied the comparative phylogeography of sea anemone symbioses on coral reefs in the Tropical Western Atlantic and was advised by Meg Daly. Top