Degree

Doctor of Philosophy (PhD)

Department

Biology

Document Type

Dissertation

Abstract

This dissertation provides a comprehensive systematic and phylogenetic study of the electric knifefish family Sternopygidae, integrating morphological, molecular, osteological, and phylogenomic data to clarify species diversity, evolutionary relationships, and biogeographic patterns in this Neotropical group. Across six studies, the work reveals that Sternopygidae diversity has been significantly underestimated due to morphological conservatism that obscures species boundaries. Chapter 1 revises the genus Sternopygus in the Guiana Shield, identifying nine species (five new) using osteology, morphometrics, and µCT imaging. Distinct anatomical traits and distribution patterns show strong regional structuring, highlighting the Guiana Shield as a diversification center. Chapter 2 describes a new trans-Andean species of Sternopygus from northwestern Colombia. Despite morphological similarity to cis-Andean congeners, mitochondrial data place the new species in the trans-Andean S. aequilabiatus species group, suggesting processes such as introgression, incomplete lineage sorting, convergence, or paedomorphosis. Chapter 3 establishes a new monotypic genus for Distocyclus guchereauae supported by osteological and multilocus phylogenetic evidence. This expands the number of recognized sternopygid genera and refines higher-level classification. Chapter 4 uses phylogenomics (ultraconserved elements) to analyze Eigenmannia, revealing 32 species (22 previously unrecognized) and identifying four major clades. Several traditional species groups are shown to be non-monophyletic. Divergence dating suggests an origin ~10.8 million years ago, with rapid diversification linked to Andean uplift and Amazon basin reorganization. Evidence of sympatric speciation is identified in a pair of co-occurring species distinguished by electric signaling and morphology. Chapter 5 documents gymnotiform diversity in the Tres Fronteras region (Brazil-Colombia-Peru), confirming at least 33 species and providing an identification key along with ecological observations. Chapter 6 reports a developmental anomaly in captive-bred Apteronotus albifrons, interpreted as ectopic expression of fin structures, offering insight into conserved developmental mechanisms. Overall, the dissertation demonstrates that sternopygid diversity is far greater than previously recognized, shaped by geological history, biogeographic barriers, and ecological differentiation. Methodologically, it highlights the effectiveness of combining traditional taxonomy with phylogenomics and advanced imaging. The revised classification and evolutionary framework provide a foundation for future research and emphasize the importance of continued biodiversity exploration in threatened South American freshwater ecosystems.

Date

2-6-2026

DOI

https://proquest.com/docview/3347850143

First Committee Chair

James Albert

First Committee Member

Kirk Winemiller

Second Committee Member

Loren Cassin Sackett

Third Committee Member

Melanie Stiassny

Fourth Committee Member

Suzanne Fredericq

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