Davies, Neil; (1995) Origins of diversity: The evolutionary genetics of Caribbean butterflies. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Darwinian evolution requires and generates biodiversity. The biodiversity of West Indian butterflies is investigated at the population and species level. The latest butterfly species numbers for West Indian islands are presented and the factors which influence community richness are determined. Area is by far the most significant physical variable. The nature of the species-area relationship is affected by community size: smaller communities seem more vagile, flattening the species-area curve. The genetic structure of four West Indian butterflies is surveyed using allozyme electrophoresis. A phenotypic tendency towards subspeciation is corroborated by the allozyme data. A long-standing controversy in West Indian biogeography is whether the fauna arose by dispersal from the continent, or is the remnants of a continental fauna isolated by ancient geological events. Whilst the action of vicariance cannot be completely ruled out, any lasting impression has certainly been masked by more recent dispersal. One of the species, Dryas iulia, has a particularly complex genetic structure in the West Indies. A survey of mtDNA variation confirms the major phylogenetic breaks identified by the allozyme data. Application of the molecular clock indicates a major separation between West Indian Dryas iulia and continental populations around 2.5 million years ago. This is too recent for the vicariance hypothesis. Classification is inevitably difficult with insular populations, some of which are on the borderline between differentiated subpopulation and separate species. Such populations, although anticipated by evolutionary biology, represent a challenge for taxonomy. The difficulties are discussed with particular reference to phylogeny reconstruction. The species-subspecies interface is also examined empirically. Pre and postzygotic isolation between two hybridising Central American butterflies are evaluated. The results are discussed in the context of speciation genetics, particularly Haldane's rule. Muller's dominance theory is assessed as an explanation for Haldane's rule.

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