The causes and consequences of mimicry in Limenitis butterflies in western North America
Kristiansen, Evan Breaux
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Batesian mimicry is a classic example of adaptation wherein the benefit of bearing the mimetic trait is directly and positively correlated with fitness. This tangible fitness benefit makes mimicry an excellent model system for addressing one of the largest remaining questions in evolutionary biology, that of the origin and maintenance of adaptive phenotypic diversity. Here I set out to answer a small part of this larger question - namely, what maintains color pattern polymorphism between two hybridizing species of admiral butterflies (genus Limenitis) in western North America. I address this question by examining both predator-mediated selection on the phenotype, and by investigating phenotype-genotype association across the genome. In chapter one, I demonstrate the adaptive significance of the mimetic orange apical forewing patch (AFP) phenotype in Limenitis lorquini through the use of a large-scale predation experiment. In the chapter two, I localize the genomic region responsible for this color pattern variation using a mapping cross and quantitative trait locus (QTL) analysis. Finally, in chapter three I identify putative causal variants that are associated with the phenotype using linear modeling in a genome wide association study (GWAS). Collectively, my results suggest that the presence or absence of the orange AFP phenotype is associated two separate regions of the genome. The first region includes an undescribed gene, while the second contains variation near the known color patterning gene optix. Studies of the functional relationship between these gene regions and phenotype will be necessary to confirm this hypothesis and examine how selection acting on these regions of the genome impact patterns of introgression and gene flow across the species boundary between these two hybridizing admiral lineages.
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