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Open Access Publications from the University of California

Lava Flow Lizards and Endangered Voles: Phenotypic Adaptation and Genomic Differentiation Over Small Spatial Scales

  • Author(s): Krohn, Alexander R.
  • Advisor(s): Rosenblum, Erica B
  • et al.

Documenting phenotypic and genotypic diversity in natural populations is central to understanding evolutionary processes, and informing the conservation and management of biological diversity. My dissertation research is guided by two fundamental motivations for understanding population differentiation. First, my work is focused on the process of convergent evolution. Second, my research is oriented toward applying genetic tools to conservation of biological diversity.

In convergent evolution, divergent populations, or species, independently evolve similar phenotypes. By studying those divergent populations, we can determine whether similar phenotypes evolved in similar ways. Additionally, phenotypic differentiation may lead to genome-wide patterns of differentiation, especially if the phenotypic differences are associated with reproductive isolation. Thus, by studying differentiation at both phenotypic and genotypic levels in multiple convergent populations, we can deepen our understanding of the processes of adaptation, speciation, and the repeatability of evolution.

Knowledge about evolutionary processes can also be applied to conservation decision making. In conservation biology, studies of population differentiation can help managers prioritize among different conservation and management options. For example, when conservation involves captive insurance colonies and reintroductions, managers need to understand overall patterns of genetic differentiation in the wild and levels of differentiation between captive and wild populations. Thus, for my dissertation research, I studied phenotypic adaptation and genotypic differentiation in a variety of species to understand patterns of convergent evolution and to inform conservation decision-making.

To better understand convergent evolution, I studied the replicated evolution of melanism in three lizard species distributed on three lava flows in southern New Mexico. I found that levels of phenotypic differentiation were not equal across populations of lava flow lizards. While some populations of Crotaphytus collaris were significantly darker (i.e., melanistic) on the lava flows than in the surrounding desert, lizards from the Pedro Armendariz lava flow showed a high degree of physiological plasticity, and were not melanistic. Looking across additional species and lava flows, I found similar patterns. While Sceloporus cowlesi and C. collaris from the Carrizozo lava flow and Urosaurus ornatus from the Aden Afton lava flow were significantly darker than surrounding populations, neither C. collaris nor S. cowlesi from the Pedro Armendariz lava flow were significantly darker than surrounding populations. However, regardless of levels of phenotypic differentiation, all populations showed a similar lack of genome-wide differentiation and ongoing migration between lava flow and non-lava flow populations. Thus, possible non-mutually exclusive mechanisms of melanism in these populations include selection-migration balance, selection acting on relatively small portions of the genome, or a larger contribution of phenotypic plasticity than previously considered.

To inform conservation of an endangered species, I used genomic methods to study remnant populations of the endangered Amargosa vole. I compared patterns of genetic variation among wild Amargosa voles, captive Amargosa voles, and other related desert-dwelling California voles. I found that the Amargosa voles are most closely related to California voles in the northern clade and that Amargosa voles have approximately half the genetic diversity of other desert-dwelling California voles. However, despite low overall genetic diversity, the Amargosa voles exhibit significant population structure. Finally, captive Amargosa voles only capture a portion of the genetic diversity present in wild Amargosa voles. My work informs conservation action by demonstrating that Amargosa voles are a genetically distinct subspecies with low levels of genetic diversity and two subpopulations. To effectively conserve Amargosa voles, managers can attempt to represent both subpopulations in the captive colony or can reintroduce voles into suitable habitat regardless of genetic structure. If Amargosa voles go extinct, voles should be brought from populations in the northern clade of California voles.

In sum, by integrating studies of genetic and phenotypic differentiation across species, my work contributes to the fields of evolutionary and conservation biology. My research shows that the processes underlying convergent phenotypes may vary over small spatial scales, but that background patterns of evolution can be consistent across diverse species. Moreover, my studies demonstrate how understanding patterns of genetic differentiation in the wild can be crucial to inform conservation management

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