Effects of changing climate on species diversification in tropical forest butterflies of the genus C ymothoe ( L epidoptera: N ymphalidae)

Extant clades may differ greatly in their species richness, suggesting differential rates of species diversification. Based on phylogenetic trees, it is possible to identify potential correlates of such differences. Here, we examine species diversification in a clade of 82 tropical A frican forest butterfly species ( C ymothoe ), together with its monotypic sister genus H arma . Our aim was to test whether the diversification of the H arma – C ymothoe clade correlates with end‐ M iocene global cooling and desiccation, or with P leistocene habitat range oscillations, both postulated to have led to habitat fragmentation. We first generated a species‐level phylogenetic tree for H arma and C ymothoe , calibrated within an absolute time scale, and then identified temporal and phylogenetic shifts in species diversification. Finally, we assessed correlations between species diversification and reconstructed global temperatures. Results show that, after the divergence of H arma and C ymothoe in the M iocene (15  M ya), net species diversification was low during the first 7  M yr. Coinciding with the onset of diversification of C ymothoe around 7.5  M ya, there was a sharp and significant increase in diversification rate, suggesting a rapid radiation, and correlating with a reconstructed period of global cooling and desiccation in the late M iocene, rather than with P leistocene oscillations. Our estimated age of 4  M yr for a clade of montane species corresponds well with the uplift of the E astern A rc M ountains where they occur. We conclude that forest fragmentation caused by changing climate in the late M iocene as well as the E astern A rc M ountain uplift are both likely to have promoted species diversification in the H arma– C ymothoe clade. Cymothoe colonized M adagascar much later than most other insect lineages and, consequently, had less time available for diversification on the island. We consider the diversification of C ymothoe to be a special case compared with other butterfly clades studied so far, both in terms of its abrupt diversification rate increase and its recent occurrence (7  M yr). It is clear that larval host plant shift(s) cannot explain the difference in diversification between C ymothoe and H arma ; however, such a shift(s) may have triggered differential diversification rates within C ymothoe . © 2013 The Linnean Society of London, Biological Journal of the Linnean Society , 2013, ●● , ●●–●●.