Fitness consequences of polymorphic inversions in the zebra finch genome.
BACKGROUND
Inversion polymorphisms constitute an evolutionary puzzle: they should increase embryo mortality in heterokaryotypic individuals but still they are widespread in some taxa. Some insect species have evolved mechanisms to reduce the cost of embryo mortality but humans have not. In birds, a detailed analysis is missing although intraspecific inversion polymorphisms are regarded as common. In Australian zebra finches (Taeniopygia guttata), two polymorphic inversions are known cytogenetically and we set out to detect these two and potentially additional inversions using genomic tools and study their effects on embryo mortality and other fitness-related and morphological traits.


RESULTS
Using whole-genome SNP data, we screened 948 wild zebra finches for polymorphic inversions and describe four large (12-63 Mb) intraspecific inversion polymorphisms with allele frequencies close to 50 %. Using additional data from 5229 birds and 9764 eggs from wild and three captive zebra finch populations, we show that only the largest inversions increase embryo mortality in heterokaryotypic males, with surprisingly small effect sizes. We test for a heterozygote advantage on other fitness components but find no evidence for heterosis for any of the inversions. Yet, we find strong additive effects on several morphological traits.


CONCLUSIONS
The mechanism that has carried the derived inversion haplotypes to such high allele frequencies remains elusive. It appears that selection has effectively minimized the costs associated with inversions in zebra finches. The highly skewed distribution of recombination events towards the chromosome ends in zebra finches and other estrildid species may function to minimize crossovers in the inverted regions.
Department of Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, 82319, Seewiesen, Germany. knief@biologie.uni-muenchen.de.|Current address: Division of Evolutionary Biology, Faculty of Biology, Ludwig Maximilian University of Munich, 82152, Planegg-Martinsried, Germany. knief@biologie.uni-muenchen.de.
Ulrich
U
Knief
Institute of Clinical Molecular Biology, Christian-Albrechts-University, 24105, Kiel, Germany.
Georg
G
Hemmrich-Stanisak
Institute of Clinical Molecular Biology, Christian-Albrechts-University, 24105, Kiel, Germany.
Michael
M
Wittig
Institute of Clinical Molecular Biology, Christian-Albrechts-University, 24105, Kiel, Germany.
Andre
A
Franke
Department of Biological Sciences, Macquarie University, Sydney, NSW, 2109, Australia.|School of Biological, Earth & Environmental Sciences, University of New South Wales, Sydney, NSW, 2057, Australia.
Simon C
SC
Griffith
Department of Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, 82319, Seewiesen, Germany.
Bart
B
Kempenaers
Department of Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, 82319, Seewiesen, Germany.
Wolfgang
W
Forstmeier
Embryo mortality; Heterosis; Inversion polymorphism; Miscarriage; Overdominance; Structural variant
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