Degree

Doctor of Philosophy (PhD)

Department

Environmental and Evolutionary Biology

Document Type

Dissertation

Abstract

Neotropical electric fishes (Apteronotidae) display remarkable phenotypic and ecological diversity, offering an exceptional system for studying macroevolutionary processes in freshwater environments. Here I investigate the morphological, ecological, and historical factors shaping diversification in the clade Navajini, with a focus on craniofacial evolution, species delimitation, and biogeographic patterns. First, using high-resolution micro-CT scans, 3D geometric morphometrics, and phylogenetic comparative methods, I analyze skull shape variation across Navajini. Key traits resulting from heterocephaly exhibit strong phylogenetic signal and reflect functional differentiation among genera. Sexual dimorphism contributes significantly to cranial disparity in some lineages, while others show conserved, modular patterns likely tied to ecological specialization. These results suggest that developmental modularity and ecological opportunity jointly drive craniofacial evolution in this group. Second, I examine species boundaries and morphological diversity in Sternarchogiton, a small clade of deep-channel electric fishes. These fishes inhabit the highly diverse river channels of Greater Amazonia, a biome hosting nearly one-third of all Amazonian fish species within a compact, high-volume aquatic environment. Combining landmark-based 2D morphometrics with diaphanized and CT-imaged osteology, I rediagnose the taxonomic status of members of Sternarchogiton species. In addition to previously known skeletal characters (e.g., maxillary and dental traits), new evidence points to neurocranial shape as a valuable diagnostic feature. Lastly, I evaluate the role of habitat connectivity in driving diversification across South American rivers. By integrating data on species distributions, habitat use, phylogeny, and paleogeography, I test whether eurytopic species, those inhabiting a broad range of stream sizes, experience greater rates of dispersal and speciation due to river capture events. Clades with eurytopic species show elevated net diversification rates, supporting a model in which dynamic riverscapes repeatedly restructure species ranges and promote allopatric speciation. Together, these studies reveal how ecological versatility, morphological innovation, and geological dynamism interact to produce high species richness in Neotropical freshwater systems. They highlight the central role of rivers not only as habitats but also as evolutionary engines, shaping biodiversity at both regional and continental scales.

Date

4-6-2026

DOI

https://proquest.com/docview/3348027244

First Committee Chair

James Albert

First Committee Member

Cláudio de Oliveira

Second Committee Member

Mark Genung

Third Committee Member

Prosanta Chakrabarty

Fourth Committee Member

Suzanne Fredericq

Download

Included in

Biology Commons

Share

COinS