Date of Award

Winter 2024

Project Type

Dissertation

Program or Major

Natural Resources

Degree Name

Doctor of Philosophy

First Advisor

Adrienne Kovach

Second Advisor

Jessica Ernakovich

Third Advisor

Brian Olsen

Abstract

Salt marshes are an ecotone between terrestrial and marine environments characterized byshort, graminoid vegetation and periodic tidal inundation with saline water. Despite the generally inhospitable conditions salt marshes present for terrestrial vertebrate life—principally, exposure to heat, salinity, and flooding—several terrestrial vertebrate species have adapted to, or are capable of inhabiting salt marshes. Notably, species of passerine birds that have adapted to salt marshes have repeatedly evolved a similar suite of adaptations, which has been named the “saltmarsh syndrome,” including larger bills, darker plumage, and an increased tolerance of salt.

The myriad species of New World sparrows (Passerellidae) that breed in the expansive saltmarshes of North America provide an ideal system to explore the evolutionary basis of parallel adaptation of passerines to salt marshes. In the eastern United States, the six salt-marsh-breeding passerellid species—the seaside (Ammospiza maritima), saltmarsh (A. caudacuta), Nelson’s (A. nelsoni), song (Melospiza melodia), swamp (M. georgiana), and Savannah (Passerculus sandwichensis) sparrows—span a gradient of salt-marsh adaptation from salt-marsh-obligates to generalists. Here, I use these six species to examine the genetic basis of salt-marsh adaptation.

First, in Chapter 1, I use whole-genome data to examine the genomic landscape ofdivergence and genetic basis of adaptation between a coastal specialist and inland generalist subspecies of the song sparrow. In Chapter 2, I assess phenotype-phenotype correlations of measures of saltmarsh syndrome traits within species to explore whether pleiotropy may play a role in salt-marsh adaptation. Finally, in Chapter 3, I use low-coverage whole-genome sequencing methods to identify the genetic basis of the saltmarsh syndrome by characterizing genotype- phenotype and genotype-environment relationships across species to answer whether parallel salt- marsh adaptation has a shared or lineage-specific basis.

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