The population genetics of a chromosomal inversion linked to social behavior in the white-throated sparrow ( Zonotrichia albicollis) Public
Huynh, Lynn (2010)
Published
Abstract
The field of population genetics broadly addresses how genetic
diversity in natural populations is generated, shaped and
maintained. In this dissertation, I use a population genetic
approach to understand the evolution of a chromosomal inversion
that influences coloration, social behavior and mate choice in the
white-throated sparrow ( Zonotrichia albicollis).
White-striped sparrows (WS) are heterozygous for the ZAL2m
inversion and
are more territorially and sexually aggressive than tan-striped
sparrows (TS). TS do not have the inversion, invest more in
parental care and are less likely to seek extra-pair copulations.
The plumage morphs occur at approximately equal frequency and the
ZAL2m inversion is maintained in the population through an
exceptionally strong pattern of disassortative mating where almost
all breeding pairs are TS × WS. We used targeted sequencing to
survey SNPs on the standard chromosome, ZAL2, and the ZAL2m. We
found that the inversion completely suppresses recombination
between the homologous chromosomes, except in the short distal
region outside of the polymorphism. This results in exceptional
linkage disequilibrium, genetic structure and high divergence, and
suggests that the ZAL2m is a rare example of a long-term balanced
polymorphism. To understand these patterns in the context of the
rest of the genome, we sequenced loci from other autosomes, as well
as the ZW sex chromosomes. We describe a strong negative
correlation between genetic diversity and chromosome size, which is
highly varied in avian genomes. Genetic variation is greatly
reduced on the ZAL2 and ZAL2m chromosomes relative to other
similarly sized chromosomes and sex chromosome variation is also
exceedingly low. We hypothesize that the low diversity observed for
the ZAL2/ZAL2m and sex chromosomes results from the increased
sensitivity to natural selection and genetic drift associated with
regions of low recombination. Finally, we identified and
characterized polymorphisms in candidate genes that could underlie
the social behaviors associated with the inversion. In summary, our
data offer insights into the molecular evolution and maintenance of
inversions, empirical evidence supporting the relationship between
chromosome size and diversity and a set of candidate polymorphisms
that could influence social behavior the white-throated
sparrow.
Table of Contents
Table of Contents
1 Introduction
Introduction / 2
2 Chromosome-wide linkage disequilibrium caused by an inversion
polymorphism
in the white-throated sparrow ( Zonotrichia albicollis
)
2.1 Introduction / 40
2.2 Materials and methods / 45
2.3 Results / 48
2.4 Discussion / 58
3 Contrasting population genetic patterns within the
white-throated sparrow
genome ( Zonotrichia albicollis
)
3.1 Introduction / 68
3.2 Materials and methods / 73
3.3 Results / 76
3.4 Discussion / 87
4 Characterization of sequence variants in candidate genes
linked to behavior in the
white-throated sparrow ( Zonotrichia albicollis
)
4.1 Introduction / 96
4.2 Materials and methods / 104
4.3 Results / 105
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