Jiggins, Christopher David; (1997) The ecology and genetics of speciation in Heliconius butterflies (Lepidoptera: Nymphalidae). Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Natural hybridisation between species offers an opportunity to study the processes of speciation. This thesis describes a study of hybridisation between Heliconius himera, which is endemic to dry forest in southern Ecuador and northern Peru, and H. erato, which is ubiquitous in wet forest throughout the neotropics. In a zone of contact in southern Ecuador hybrids are found at low frequency. Collections show that the contact zone is about 5 km wide, half the width of the narrowest clines between colour pattern races of H. erato, which implies that strong selection is maintaining the parapatric distributions of the species. Polymorphic protein and mitochondrial DNA markers were used to examine patterns of genetic differentiation and gene flow across the hybrid zone. Marked genetic differences between himera and erato are maintained in sympatry. Furthermore, analysis of linkage relationships between the allozyme markers showed that species differences are distributed widely across the genome. There was no evidence for any divergence in host plant ecology, but the hybrid zone between himera and erato was closely correlated with a habitat transition from wet to dry forest. Experiments showed that the barrier to gene flow was mainly due to strong assortative mating between himera and erato. Hybrid crosses showed no reduction in viability or fertility. Analysis of these broods showed that major gene control of pattern elements is similar to that found in previous studies of H. erato races, and the loci are homologous. Another species, H. charitonia, also has a genetically distinct sister species in the dry forests of Ecuador and Peru, peruviana. In both taxa, speciation is associated with divergence in habitat and warning colour, and in the case of himera and erato at least, there is a change in mating preferences but no evidence for genomic incompatibilities.

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