High-Resolution Species Delimitation of Panagrolaimus Nematodes Through Integrated Morphology and 18S/COI Sequencing

Author

• Noelle Ledoux

Date of Award

2026

Document Type

Restricted Thesis: Campus only access

Degree Name

Bachelor of Science

Department

Biology

First Advisor

Dr. Amy Treonis

Abstract

Nematodes are among the most abundant and ecologically important animals on Earth, yet their species diversity remains vastly understudied. This is due in part to the prevalence of cryptic diversity, where morphologically similar individuals represent genetically distinct lineages. The genus Panagrolaimus, a group of bacterial-feeding nematodes with limited diagnostic morphological variation, exemplifies these challenges. Despite increasing attention to nematode diversity, species-level diversity within Panagrolaimus remains poorly resolved, particularly in extreme and understudied environments such as the Namib Desert of Namibia. In this study, I assess diversity among six Panagrolaimus populations collected from the Namib Desert using an integrative approach combining morphological, morphometric, and molecular analyses. I hypothesized that detailed study of these populations would reveal previously unrecognized cryptic diversity. Scanning electron and light microscopy revealed both conserved and variable morphological traits, including differences in genital papillae arrangement, stoma shape, and excretory pore position. Morphometric analyses using principal component analysis indicated partial differentiation among populations, particularly in females. Phylogenetic analyses based on SSU (18S), LSU (28S), and mitochondrial COI sequences recovered multiple lineages, with consistent clustering of some populations and discordant placement of others across loci. Together, these results provide evidence for multiple, closely related lineages within Panagrolaimus populations in the Namib Desert, consistent with the presence of cryptic diversity. The integration of morphological and molecular data improves resolution of species boundaries and highlights the complexity of nematode diversification in extreme environments. These findings underscore the importance of integrative approaches for uncovering biodiversity in understudied systems.

Comments

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Recommended Citation

Ledoux, Noelle, "High-Resolution Species Delimitation of Panagrolaimus Nematodes Through Integrated Morphology and 18S/COI Sequencing" (2026). Honors Theses. 1966.
https://scholarship.richmond.edu/honors-theses/1966