The influence of mutualistic and parasitic life forms on the diversification of butterflies in an increasingly arid world

Understanding the mechanisms that lead to the diversification of species over time in a changing world remains a challenge

Africa was largely covered by forests until the middle Oligocene, when geological and climatic changes led to an increasing aridification of the land mass. Today's typical savannah and grassland ecosystems only became established around 8 million years ago. The effect of this increasing aridification on diversification has not been well studied in animals and especially in insects.

More than 99% of butterflies are pure herbivores, and butterfly diversity is therefore often low in arid regions where vegetation is sparse for much of the year and fires are common. Ant parasitism, in which the caterpillars live in an ant nest and either feed directly on the ant brood or are fed by the ants for most of their development, has evolved independently several times within the families Lycaenidae and Riodinidae. This way of life has been considered an evolutionary dead end, as it occurs mainly as a single species in otherwise completely herbivorous groups.

However, it has also been hypothesised that this ant parasitism may be triggered by harsh conditions above ground, but this has never been tested.

The Afrotropical Euchrysops section comprises more than 200 species with varying degrees of association, ranging from almost none to facultative and obligate mutualists to obligate parasites and occurring from rainforest to semi-desert. The high diversity combined with different life histories and habitat requirements makes this group an excellent choice for testing hypotheses related to diversification, life history and acidification.