Gerstner Scholar Profiles

Current Gerstner Scholars

2020-2022: Edson Abreu Junior | Jesse Delia

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


Dr. Edson Abreu Junior

Edson Abreu
Edson Abreu

Research Focus: My postdoctoral research at the AMNH focuses on the systematics, taxonomy, and phenotypic evolution of a charismatic and diverse group of mammals, the tree squirrels (Sciuridae, Sciurini). My objectives include undertaking a comprehensive taxonomic review of Sciurini using an integrative approach to reconcile genomic and morphological data, and investigating phenotypic evolution and morphological disparification in the adaptive radiation of tree squirrels.

Sciurini represents a diverse radiation that originated around 14 Mya, most likely in North America, and successfully colonized the Holarctic and Neotropical regions. Tree squirrels exhibit strikingly high rates of diversification, especially in the Neotropics, where they experienced an explosive diversification after invading South America around 6 Mya. They are conspicuous inhabitants of forested ecosystems throughout their distribution, and they play important ecological roles as predators and dispersers of tree seeds. Tree squirrels are also often used as model organisms to address a wide range of ecological and evolutionary questions, both in their native ecosystems and as invasive species. However, unresolved taxonomic problems obscure many potentially important aspects of tree-squirrel research.

Until quite recently, the genetic diversity and molecular systematics of tree squirrels were poorly known, particularly regarding the Neotropical taxa. During my Ph.D. research, I proposed heretofore the most comprehensive phylogenetic hypotheses for tree squirrels based on mitogenomes and thousands of UCE loci recovered from almost all valid species of the tribe Sciurini. The phylogenomic results allowed the advancement of a preliminary and tentative nomenclatural designation for the taxa at the genus-group level. However, a detailed taxonomic investigation is still in very much needed to carefully evaluate the application of generic names, to provide taxon diagnoses and descriptions, as well as to evaluate the species-level taxonomy within genera.

Biography: Edson F. Abreu received his B.Sc. from the University of Santa Cruz do Sul, Brazil, in 2009 and his M.Sc. from the University of São Paulo, Brazil, in 2014. For his masters thesis, he studied the non-volant small mammal fauna of the southeastern Brazilian Atlantic Forest, and described a new rodent species. He earned his Ph.D. from the University of São Paulo, including a one-year program of doctoral research at the Smithsonian Institution’s Center for Conservation Genomics in 2020. His dissertation research focused on the phylogenomics, diversification, and biogeography of Neotropical squirrels (Sciurillinae and Sciurinae: Sciurini).

Dr. Jesse Delia

Jesse Delia
Jesse Delia

Research focus: My postdoctoral research focuses on why and how certain frogs attain transparency—a rare occurrence in terrestrial vertebrates. Glassfrogs are well known for their highly transparent skin and muscle tissue, through which their organs are visible. Under the supervision of my advisor Christopher Raxworthy, this comparative project aims to identify (i) the underlying specializations that balance the physical requirements for tissue transparency with the physiological demands of living cells, and (ii) the broader eco-evolutionary processes that explain these adaptations.

Biography: Jesse Delia received an MSc from East Carolina University (2011), where he was advised by Kyle Summers. He studied the social lives of Mexican glassfrogs in the understory cafetales of San Gabriel Mixtepec (Oaxaca). This work formed the foundation for his PhD thesis on the co-evolutionary dynamics of family life in glassfrogs, which spanned across the Americas. He received his PhD (2018) from Boston University under the supervision of Karen Warkentin. Prior to this fellowship, Jesse was a postdoctoral researcher in Lauren O’Connell’s lab at Stanford University, where he developed a protocol for in vivo cell labeling using non-model amphibians. He also began investigating the physiology of glassfrogs in collaboration with Carlos Taboada, Sönke Johnsen, and Junjie Yao at Duke University.


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