Theses and Dissertations

ORCID

https://orcid.org/0009-0006-7934-7876

Advisor

Welch, Mark

Committee Member

Gout, Jean-Francois

Committee Member

Gentile, Gabriele

Committee Member

Gratton, Paolo

Date of Degree

12-12-2025

Original embargo terms

Immediate Worldwide Access

Document Type

Dissertation - Open Access

Major

Biological Sciences

Degree Name

Doctor of Philosophy (Ph.D.)

College

College of Arts and Sciences

Department

Department of Biological Sciences

Abstract

The Galápagos archipelago is known for its unique endemic fauna shaped by isolation and geological dynamism. This thesis explores the evolutionary history of Galápagos iguanas, a monophyletic group comprising the marine iguana (Amblyrhynchus cristatus) and three land iguanas: Conolophus marthae, C. pallidus, and C. subcristatus. These species differ in distribu- tion, population size, and conservation status, with C. marthae classified as Critically Endan- gered due to its restricted range and small population. The main goal of this thesis is to fill knowledge gaps concerning the evolutionary trajectories, demographic histories, and genetic var- iability of Galápagos iguanas. The first chapter reconstructs their demographic and divergence histories using genome- wide restriction site-associated DNA sequencing (RADseq). Results support an early coloniza- tion of the Galápagos by iguanas about 10 million years ago, contemporaneous with the emer- gence of the first land masses. Contrary to previous estimates, the divergence of C. marthae from C. subcristatus was inferred at ca. 0.57 Mya, after the formation of Isabela Island, suggesting an allopatric speciation event. Demographic analyses revealed contrasting trends: C. marthae expe- rienced a long-term decline, whereas C. subcristatus remained relatively stable. The sympatric C. subcristatus population from Wolf Volcano showed demographic expansion concurrent with the decline of C. marthae, suggesting interspecific competition. Additionally, low genetic diversity and small historical size in C. pallidus support a recent divergence from C. subcristatus, with its distinct features likely shaped by genetic drift. The identification of first-generation hybrids be- tween C. subcristatus and A. cristatus on Plaza Sur Island further illustrates potential interspecies interactions. The second chapter assesses genetic load in C. marthae and C. subcristatus using low- coverage whole-genome sequencing (5×). Despite the absence of an outgroup preventing abso- lute load estimation, results revealed a lower proportion of highly deleterious variants in C. mar- thae when compared to the one of C. subcristatus, consistent with genetic purging under pro- longed small population size. While purging may have reduced the most deleterious alleles, C. marthae remains vulnerable to environmental and demographic instability. Overall, this thesis advances understanding of Galápagos iguana genomics, highlighting how demographic history and population size influence genetic diversity, load, and adaptive po- tential.

Sponsorship (Optional)

Biology Department of the University of Rome Tor Vergata, PhD Program in Evolutionary Biology and Ecology of University of Roma Tor Vergata

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