Bull, Vanessa Jane; (2003) Genealogy and Speciation in Heliconius Butterflies. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The concepts of species and of their formation are of fundamental importance to many fields of biology, such as; ecology, conservation, taxonomy and evolutionary genetics, and speciation research has recently undergone an explosion of interest. Natural hybridisation between species in the wild provides a great opportunity of studying the underlying mechanisms that lead to reproductive isolation, and eventually to the formation of new species. This thesis describes a study using Heliconius butterflies as model organisms. H. melpomene and H. cydno are recently diverged sister species, broadly sympatric throughout their range in the Andes and Central America. Both are unpalatable and warningly-coloured, and differ markedly in mimetic colour pattern. Theory predicts that F1 hybrids of aposematic insects will be preferentially taken by avian predators as they sport a novel colour pattern which will not be recognised as unpalatable. Here I provide evidence from experiments with live birds that positive frequency dependent selection against F1 hybrids may play an important role in the speciation of these butterflies. DNA sequences for a total of five genes show introgression of haplotypes between the two species at some loci, but not at others. The fact that animal species can share genetic material by occasional hybridisation has profound implications for species definition, evolutionary biology, conservation and the commercial sector.

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