Publication Date

2017-12-19

Availability

Open access

Embargo Period

2017-12-19

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Marine Biology and Ecology (Marine)

Date of Defense

2017-10-06

First Committee Member

Douglas L. Crawford

Second Committee Member

Marjorie F. Oleksiak

Third Committee Member

Athula H. Wikramanayake

Fourth Committee Member

Kevin G. McCracken

Fifth Committee Member

James H. Marden

Abstract

Adaptive evolution on ecological timescales shapes communities. However, adaptation among environments relies on isolation or large selection coefficients that exceed migration effects. This reliance is tempered if adaptation from standing genetic variation is polygenic – does not depend on one allele completely replacing another but instead requires small allele frequency changes at many loci. Thus, whether individuals can evolve adaptation to fine-scale habitat variation is not resolved. To investigate this process, the gene expression and genetic divergence of a teleost fish, Fundulus heteroclitus, was explored. Among nearby (< 200m) microhabitats in three separate saltmarshes, and over the course of a season (spring to fall), thousands of single-nucleotide polymorphisms (SNPs) were analyzed. Among these SNPs, 1.3-2.3% have large and highly significant differences among microhabitats (mean FST = 0.15; false discovery rate (FDR) ≤ 1%), and 1.8-5.7% are significantly different between seasons (mean FST = 0.077 to 0.597; FDR ≤ 1%). The divergence among microhabitats and between seasons for these SNPs is larger than that among populations, exceeds neutral expectation, and indicates surprising population structure among microhabitats. These data suggest that polygenic selection is surprisingly effective in altering allele frequencies over very small geographic distances.

Keywords

Fundulus heteroclitus; differential variability; single nucleotide polymorphism; polygenic adaptation; GBS; gene expression

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