Date of Award
Doctor of Philosophy (PhD)
Sex chromosomes control sex determination in many plants and animals, playing a vital role in a species’ evolution. Current models of sex chromosome evolution have been formulated by studying clades with stable, morphologically distinct (heteromorphic) sex chromosomes, such as mammals and birds. However, many taxa have morphologically indistinguishable (homomorphic) sex chromosomes, including many fish, amphibians, and reptiles. The knowledge gained from these understudied systems may provide new insights into the overarching paradigms of sex chromosome evolution. Thus, the historical focus on stable, heteromorphic sex chromosomes and failure to consider homomorphic sex chromosomes or systems with frequent turnovers may mean the current models of sex chromosome evolution are limited or not applicable to all taxa. Here, I explore sex chromosome evolution among gecko lizards, with a particular focus on identifying novel sex chromosomes in several gecko species and examining in greater detail the ZZ/ZW sex chromosomes of the diplodactylid gecko Correlophus ciliatus. I find that sex chromosome turnover can occur among closely related species in some groups, but that species in some clades maintain stable sex chromosomes for long evolutionary periods. Additionally, I demonstrate that the sex chromosomes of Correlophus ciliatus have a high degree of genetic differentiation despite a lack of degeneration, and that genes that have been lost from sex chromosomes have not evolved dosage compensation or dosage balance. These results demonstrate that geckos are a remarkable group and highlight their importance as a model for studying sex chromosome evolution.
Available for download on Wednesday, July 19, 2023