The Radiating Butterflies Group studies the parallel radiations of some 300 species of mycalesine butterflies (Nymphalidae: Satyrinae) that inhabit the forests and savannah habitats of the old world tropics. Our aim is to reveal the patterns and processes of ecological speciation in this diverse group of tropical butterflies.
We are assembling several extensive datasets for these radiations, covering major traits both with respect to adaptation to ecological environments and to the acquisition of reproductive isolation.
The program is divided into several major projects of data collection and further experimental work:
Using a battery of mitochondrial and nuclear genes we are able to produce a robust phylogenetic reconstruction for the Mycalesina subtribe. Using the phylogenetic framework, we aim to establish the ultimate origin of Mycalesina and identify the important biogeography and timing of diversifications within the subtribe. There are several major radiations associated with colonization events of different geographical regions. This phylogeny then makes possible the use of more mechanistic and experimental studies to understand both evolutionary pattern and process, and the reasons behind the success of the ‘browns’ in Australasia, Africa and Madagascar.
Phenotypic Plasticity and Geometric Morphometrics
Rearing of several species across a standard series of temperatures allows us to make a comparative analysis of the reaction norm evolution that underlies the seasonal forms and phenotypic plasticity that is typical of many species. In addition, a database of images of museum and field specimens is being used to investigate the diversification in seasonal polyphenism and in patterns of wing scaling, and to examine the extent to which evolution has explored phenotypic morphospace across the radiations.
Host Plant Evolution
The early radiations of mycalesine butterflies probably occurred from forests into more open (and seasonal) grassland habitats in which their larval host plants - mainly grasses - were also evolving rapidly during the Miocene, utilizing a different means of photosynthesis – C4 based rather than C3. In adult butterflies we can test this using stable isotopes of carbon and oxygen and aim to detect differences among species, habitats and wet-dry season generations. Experiments with our lab stocks provide the basis of making sound interpretations from extensive museum surveys and field collections and integrating this with the phylogenetics will allow us to investigate the potential involvement of C4 grass evolution and expansion in the evolutionary history of mycalesine butterflies
Male Sex Pheromones and Androconia
Male sex pheromones play a crucial role in mate choice in Mycalesine butterflies. The pheromones are also to some degree linked with prominent structures on the male wings called androconia. These structures are made up of specialised wing scales and often take the form of brushes that are involved in dispersing the pheromones to female partners during courtship. By analysing the compounds found in male wings using Gas Chromatography (GC) and Mass Spectrometry (MS) we are investigating patterns linked to phylogeny and/or ecology to understand why and how these systems have evolved. By comparing the relative rate and mode of evolution in androconia and pheromones with those of other sexually linked traits such as genitalia and eyespot morphology we aim to discover the relative importance of sexually selected traits in butterflies.
Environmental Niche Modeling
We are interested in how ecological niches have evolved at the level of the geographic range of species and how this may have affected colonisation, radiation and diversity in the different biogeographic arenas we are studying. To this end we are assembling georeferenced museum and field data for all species to generate probabilistic bioclimatic and habitat models using suitable software and GIS overlays for the African and Asian tropics. The initial comparison is between Madagascar and Africa. We would like to explore the mechanistic constraints on the ranges of sister species/clades and test the role of phylogenetic niche conservatism in ecological speciation.
This extends earlier eyespot evo-devo research on the wing eyespots of Bicyclus anynana by including experimental work with three new laboratory cultures (Bicyclus safitza, Mycalesis perseoides and Heteropsis iboina) representing three of the four mycalesine radiations in Africa, Asia and Madagascar, respectively. The goal is to explore the developmental pathways that underlie the diversification of eyespot formation and patterning within the subtribe.
We are also coordinating a genome sequencing and annotation project for the model species, Bicyclus anynana, in collaboration with the Gene Pool facility at Edinburgh University and the entire Bicyclus research community. This will provide the initial framework for a deeper developmental and phylogenetic understanding of the mycalesine radiation.