Gerstner Scholar Profiles main content.

Gerstner Scholar Profiles

Current Gerstner Scholars

2019-2021:  Maxwell Bernt | Johanna Harvey | Chris Law | Carrie Mongle

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

2017-2020:  Phillip Skipwith


Dr. Maxwell Bernt

Mawell Bernt

Research Focus -My research has been primarily focused on biodiversity in large tropical river systems. I am broadly interested in the evolution of fishes and particularly the origins of phenotypic diversity. Freshwater fishes exhibit a dramatic range of morphological disparity and while our knowledge of their evolutionary relationships continues to grow, we still have little understanding of the relationship between morphological evolution and lineage diversification for most taxa.

The African clariid catfishes comprise an ideal group to study this relationship as they show a remarkable array of phenotypic extremes. These include a range of body plans from fusiform to highly elongate (anguilliform), the loss or reduction of fins and eyes, and a flattening of the head with hypertrophied jaw muscles. This body elongation is of particular interest as anguilliform species are associated with both stagnant swamp habitats as well as swift, rocky river channels. Several phylogenetic studies have suggested that these phenotypes have independently evolved several times in Clariidae, however these analyses show substantial discordance and relatively low resolution. This group poses a number of questions including, how many times did anguilliform phenotypes evolve? Is anguilliformity discrete, or is it merely an extension of the phenotypic trajectories observed in other species? Are extreme phenotypes associated with higher rates of evolution?

My postdoctoral research will combine phylogenomic and morphometric data in an integrative framework in order to reconstruct the evolutionary history of Clariidae. The first stage of this study will be generating a robust phylogeny for the family using ultraconserved elements (UCEs). The UCEs will be tested against a molecular clock model and then filtered by clocklikeness with the goal of improving phylogenetic accuracy and computational efficiency. The filtered dataset will be incorporated with all available fossil data to generate a time-calibrated phylogeny. The second stage of the project will involve gathering morphological data from clariids to analyze in a phylogenetic and temporal context. Body shape will be quantified using a series of size-corrected linear measurements, while the shape of the skull will be analyzed independently using 3D geometric morphometric data taken from micro-CT scans. In order to assess the origins of extreme morphologies, I will perform a series of tests for correlation between phenotype and rates of lineage diversification as well as habitat type. Additional tests for correlation will be performed between each of three morphological datasets to determine the degree of convergence across anguilliform phenotypes.

Biography - Maxwell Bernt received his BA in biology from Carroll College (Helena, MT) in 2013. He earned his PhD in ecology and evolutionary biology from the University of Louisiana at Lafayette in 2013 under the supervision of James Albert. His dissertation research focused on the evolutionary history of the ghost knifefishes (Apteronotidae) a poorly-known group of weakly-electric fishes from South America. The project involved extensive collection of specimens and tissues, building a multilocus phylogeny, the description of new taxa, and analysis of the clade’s biogeographic history. Top

Dr. Johanna Harvey

Johanna Harvey

Research Focus - My postdoctoral work at the AMNH focuses on the effects of climate change on the distribution and virulence of avian malaria parasites and the effects on avian host immune response along the northern extent of the North American Atlantic flyway.

Biography - Johanna A. Harvey received her BS from Texas A&M University in 2010 and her PhD from Texas A&M University in 2018 under the supervision of Gary Voelker. Her dissertation focused on the using the phylogenetic relationships of avian malaria and related haemosporidians along with their host associations and environment to determine how these factors synergistically shape the resulting diversity and distributions across Africa. Results inform the association of phylogenetic haemosporidian subgenera groups with bioclimatic variables and host associations. Results found that internal clades are restricted to various bioclimate variables and host group associations, whereas broader patterns were not found at the level of genera. Results suggest that host specificity and generalism of malaria parasites are also constrained at lower taxonomic levels. These results inform possible climate change scenarios and highlight malaria clades which may be more prone to invasion and host shifting. Prior to the Gerstner Fellowship she was a postdoctoral researcher at the University of Connecticut under the supervision of Sarah Knutie working on the effects of urbanization and an invasive parasite (Philornis downsi) on Darwin’s finches in the Galapagos. Top

Dr. Chris Law

Chris Law

Research Focus - My current research as an NSF Postdoctoral Fellow (DBI–1906248) and Gerstner Scholar at the American Museum of Natural History focuses on the evolutionary integration of the cranial, axial, and appendicular skeleton and their contributions to mammalian body shape diversity and adaptive significance. Understanding the major patterns and adaptive significance of phenotypic variation is a central goal of evolutionary biology. In vertebrates, body shape diversity is one of the most prominent features of phenotypic variation that can lead to increased diversification, niche specialization, and innovations within a clade. However, biologists still lack a full understanding of the underlying morphological components that contribute to body shape diversity, particularly in endothermic vertebrates such as mammals. Consequently, little is known about the morphology, ecology, and evolution of mammalian body shapes as well as the underlying traits that contribute to different body plans. Therefore, I am generating the first quantitative database of mammalian body shapes using skeletal specimens. This database will enable me to document the underlying skeletal components that contribute to body shape diversity and test novel hypotheses in mammals, including the relationship between body shape and limb lengths and the influences of locomotor and dietary ecologies on the evolution of body shapes.

Biography - Chris J. Law received his B.S. from the University of California Santa Diego in 2012 and his Ph.D. from the University of California Santa Cruz in 2019 with Dr. Rita Mehta. His dissertation examined the species diversity and phenotypic disparity across Musteloidea (badgers, minks, otters, raccoons, red panda, skunks, and weasels) as well as the influences of tool use variation on individual dietary specialization on sea otters in the Monterey Bay. Top

Dr. Carrie Mongle

Carrie Mongle

Research Focus - The primary focus of my postdoctoral research at the American Museum of Natural History is to address the question: What are the major phylogenetic patterns that characterize hominin diversity and evolution?

The ability to address fundamental questions about evolutionary transitions among hominins hinges on the knowledge of phylogenetic relationships among fossil species. Critically, however, no phylogenetic analysis of hominins has ever incorporated postcranial data. This represents a fundamental gap in our understanding of human evolution which could have significant implications for how we reconstruct hominin phylogenetic relationships. I am addressing this gap by undertaking an extensive character analysis of hominin postcranial fossils from both eastern and South Africa. This ongoing research builds on my previous phylogenetic work and will allow us to more directly address critical controversies in human evolution, such as the placement of Australopithecus sediba in relation to the genus Homo, and the importance of suspensory behavior as a derived or basal character in great apes. This represents a large-scale, multi-collaborator project that will form the foundation of my research program for the next 3-5 years.

In addition to the principle aims of my research outlined above, I am actively involved in the description and analysis of new hominin fossils in collaboration with Drs. Ashley Hammond, Meave Leakey, Frederick Grine, and others. In parallel with this research, I have also co-developed new software for the analysis and visualization of phylogenetic comparative data and continue to lead a collaborative project aimed at using primate teeth as a model system for linking micro and macroevolution.

Biography - Carrie S. Mongle received her BA from the University of Virginia in 2008 and her MA from Stony Brook University in 2015.  She earned her PhD from Stony Brook in 2019 under the supervision of Dr. Frederick E. Grine. For her doctoral work, Carrie developed a series of Bayesian models to understand the structure of dental variation in the fossil record in order to delimit hominin species. This work was awarded the “Anatomy in Anthropology Award for Innovative Anthropological Research” by the AAPA and the AAA professional societies, as well as the “Stony Brook President’s Award for Distinguished Doctoral Students”.  Findings from her research have been featured by international news outlets, including the BBC. Top


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