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Title: Genetic architecture and ecological speciation in Heliconius butterflies
Author: Merrill, Richard
ISNI:       0000 0004 2733 9522
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2013
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It is now widely accepted that adaptation to different ecological niches can result in the evolution of new species. However, when gene flow persists speciation must overcome the antagonism between selection and recombination: Specifically, if gene flow persists, recombination will break down the genetic associations between alleles that characterise emerging species and cause reproductive isolation. Accordingly, genetic architectures that impede recombination can slow the breakdown of linkage disequilibrium and facilitate speciation. Mimicry in tropical butterflies has long been championed as an example of adaptation driving speciation. In the Neotropical genus Heliconius, distantly related pairs of unpalatable species often converge on the same bright warning-pattern to more efficiently advertise their distastefulness to predators. In contrast, closely related taxa often belong to different mimicry rings. The sister species, Heliconius melpomene and H. cydno are sympatric across much of Central and northern South America. Using artificial butterflies I reveal selection against non-mimetic hybrid colour patterns between these two species. These colour patterns are also used as mating cues and mimetic shifts may cause both pre-mating and post-mating isolation. However, shifts in colour pattern cannot drive reproductive isolation alone; rather, they must be accompanied by corresponding mate preferences. Associations between trait and preference loci may be broken down by mating and subsequent recombination. I demonstrate a genetic linkage between loci for both male and female mate preference and wing colour pattern in Heliconius cydno and H. melpomene. In addition, I present evidence for further associations between alleles affecting hybrid sterility and host-plant use and colour pattern loci. All this implies that linkage between traits that contribute to reproductive and ecological isolation is a general phenomenon in Heliconius with an underlying adaptive basis. Overall these results expose a genetic mechanism that, by impeding recombination, can facilitate speciation in the face of gene flow.
Supervisor: Jiggins, Chris Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Heliconius ; ecological speciation ; magic traits ; sexual selection ; mate choice