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Ecological divergence and speciation in Heliconius cydno and H. melpomene

Naisbit, Russell Edward; (2002) Ecological divergence and speciation in Heliconius cydno and H. melpomene. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

We are in the midst of a renaissance in speciation research. There is a return to Darwin's belief in the role of natural selection in driving speciation, after a lengthy focus on geographic isolation and hybrid sterility. Here I describe the ecological, behavioural, and genetic bases of speciation in Heliconiiis cydno and Heliconius melpomene (Lepidoptera: Nymphalidae). The two species are sympatric in tropical rainforest across most of Central America and the foothills of the Andes. Ecological differentiation allows coexistence of these sister species despite rare hybridisation. Divergence in microhabitat and larval host plant use has reduced both the potential for gene flow and for competition. In Panama H. cydno uses most Passiflora species in closed canopy forest, whilst H. melpomene is restricted to disturbed habitats, and to Passiflora menispermifolia. This ecological differentiation probably generated selection for the key step in their speciation: divergence in warning colour pattern. Both species are unpalatable but are members of different Mullerian mimicry rings that segregate between the two habitats. In Panama H. cydno is black and white and mimics H. sapho, while H. melpomene is black, red and yellow and mimics H. erato. This shift in mimicry reduced both the survival and production of hybrids, due to selection against their non-mimetic pattern, and coevolution of mate choice with colour pattern. Major genes are involved in the control of colour pattern differences, including several homologous with inter-racial variation within each species. Two other postmating barriers affect the reproductive success of hybrids. Disruptive sexual selection acts against them, as both sexes of Fi have poor mating success with the parental species. Following Haldane's rule, female Fi hybrids are completely sterile, but males are fully fertile and backcross offspring include fertile females. In this and several recent examples, ecological adaptation has been sufficient to catalyse speciation.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Ecological divergence and speciation in Heliconius cydno and H. melpomene
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences; Lepidoptera
URI: https://discovery.ucl.ac.uk/id/eprint/10100313
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