Morphological Diversity, Natural History, and Population Genomics of Two Endemic Namibian Girdled Lizards: Herero Nama Lizard (Namazonurus pustulatus) and Jordan’s Girdled Lizard (Karusasaurus jordani)
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Authors
DeBoer, Jonathan Choe
Issue Date
2025
Type
Dissertation
Language
en_US
Keywords
Biogeography , Cordylidae , Landscape , Lizard , Morphology , Namibia
Alternative Title
Abstract
I investigate morphological diversity, natural history, and population genetic structure in Namibian endemic girdled lizards. In my first chapter, I characterize sexual dimorphism in Namazonurus pustulatus (Herero Nama lizard), by using field and museum data spanning its known range. Females are larger overall, while males exhibit larger head dimensions, patterns consistent with fecundity and sexual selection. I identify size variation across elevation gradients and a growth inflection point corresponding to sexual maturity. These results provide the first comprehensive biometric data for the species and contribute to understanding sexual dimorphism in the Namazonurus clade. In my second chapter, I integrate distribution mapping, ecological observations, and morphometric analyses in Karusasaurus jordani (Jordan’s girdled lizard), revealing sexual dimorphism and morphological patterns that follow well-known biogeographic rules. My findings extend the species’ known range and indicate wider distribution, and behavioral observations suggest niche overlap among sympatric rock-dwelling species. I identify morphological findings, which challenges prior assumptions. Morphological patterns reveal that females achieve greater body size, while males exhibit larger heads and elevated scar frequencies, indicating male-male competition. Body size also shows strong associations with climatic gradients, particularly temperature and precipitation, patterns that partially align with both Bergmann’s Rule and Inverse Bergmann’s Rule. This work highlights the combined influence of sexual selection, climate, and ecological factors on trait variation in arid-adapted lizards. Finally, in my third chapter, I use RADseq data to evaluate how geography and environmental gradients contribute to population genetic structure in K. jordani. Analyses show strong population differentiation consistent with isolation by distance, reduced connectivity in peripheral populations, and reduced gene flow across dispersal barriers. Neutral processes reveal reduced gene flow across geographic barriers, supporting patterns consistent with drift, while semi-permeable zones exhibit isolation by distance. Gene-environment associations (GEAs) identify loci linked to thermal and precipitation gradients, suggesting local adaptation, and candidate loci indicate adaptations to thermal tolerance and physiological processes. Collectively, my findings reveal how neutral and adaptive forces jointly structure genomic variation in Namibia’s complex escarpment system, offering insights into biogeographic processes in Africa’s heterogenous landscapes.