The impact of mutualistic and parasitic life histories on butterfly diversification in an increasingly arid world

Description

Understanding the mechanisms leading to diversification of species across 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 increasing aridification of the landmass. The current, iconic savanna and grassland ecosystems did not become well-established until around 8 million years ago. The effect of this increasing aridification on diversification has not been well-studied in animals, and especially not in insects. More than 99% of butterflies are fully herbivorous, and butterfly diversity is therefore often low in arid areas where little vegetation is available during a large part of the year and fires are frequent. Ant parasitism, where caterpillars live inside ants nest and either feed on the ant brood directly, or are being fed by the ants, for most of their development has evolved independently several times within the families Lycaenidae and Riodinidae. This life history has been considered an evolutionary dead-end since it mainly occurs as single species in otherwise fully herbivorous clades. It has, however, also been suggested that this ant parasitism can be triggered by harsh conditions above ground, but this has never been tested. The Afrotropical Euchrysops section contain over 200 species with various degrees of ant association from nearly none through facultative and obligate mutualists, to obligate parasites, and are found from rainforests to semi-deserts. The high diversity coupled with varied life histories and habitat requirements makes this group an excellent choice for testing hypotheses related to diversification, life history andaridification. A comprehensive phylogeny of the group will be generated using high-throughput sequencing. This will be coupled with morphometric data and niche modelling to test the following hypotheses: 1) Ant parasitism evolved only once in the Euchrysops section; 2) The high species diversity in the likely fully parasitic genus Lepidochrysops is real, and not a taxonomic artifact; 3) Ant parasitism is not an evolutionary dead end, but a key adaptation for survival in dry habitats; 4) Diversification of the Euchrysops section started in wetter, older habitats followed by multiple shifts to drier habitats as they became available; 5) Ant association affects niche, molecular and morphological evolution. Finally, all the collected data will together form the basis for an integrative taxonomical revision of the group.

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