Date of Award

Summer 2020

Document Type

Dissertation - Restricted

Degree Name

Doctor of Philosophy (PhD)


Biological Sciences

First Advisor

Gamble, Tony

Second Advisor

Petrella, Lisa N.

Third Advisor

Daza, Juan A.


Determining the mechanisms that create and maintain biodiversity is a central question in ecology and evolution. Speciation is the process that creates biodiversity. Speciation can be mediated by incompatibilities that lead to reproductive isolation between divergent populations and these incompatibilities can be observed in hybrid zones. The “two rules of speciation” (Haldane’s Rule and the Large-X effect) both involve sex chromosomes and highlight their role in maintaining reproductive incompatibility. However, sex chromosomes evolve dynamically, with inversions and transitions being extremely common in some clades—sometimes even between sister taxa. Most studies of the “two rules” haven’t generated the fine-scale information necessary to examine the dynamic aspects of sex chromosome biology leaving an expansive gap in our understanding of speciation. Gecko lizards are a speciose clade possessing an impressive diversity of behavioral and morphological traits. However, we lack a basic understanding of speciation and sex chromosome evolution in this group. To address these gaps, (1) I first review a subset of the relevant literature regarding the process of speciation as it relates to species delimitation. Then, (2) conduct explicit examinations of the patterns and processes of speciation in Gonatodes humeralis across northern South America and (3) between hybridizing species of Sphaerodactylus in southern Puerto Rico. Lastly, (4) I begin characterizing the dynamic evolution of sex chromosomes within Puerto Rican Sphaerodactylus, which sets the stage for future investigations testing the “two rules of separation” for the first time in gecko lizards. Taken together, this work provides the framework and resources to examine the genomic processes of speciation for the first time in a diverse group of amniotes, the gecko lizards.



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