Australian parasitic Ogyris butterflies: east–west divergence of highly-specialized relicts

Abstract

Not all butterflies are innocuous plant-feeders. A small number of taxa in the family Lycaenidae have graduated from mutualistic partnerships with ants to predatory or parasitic associations. These highly-specialized life histories, involving butterfly larvae living inside ant colonies, are often associated with rarity and vulnerability to extinction. In the present study, we examined the evolutionary relationships of a poorly-known group of seven taxa herein referred to as the idmo-group within the Australian lycaenid genus Ogyris. The idmo-group has a relictual distribution across southern Australia and includes taxa with highly-specialized phytophagous and myrmecophagous life histories. A phylogeny based on mitochondrial DNA (cytochrome oxidase I and cytochrome b] and the nuclear DNA locus elongation factor 1a (EF1a), generally agrees with current taxonomy and supports the recent elevation of endangered taxon Ogyris halmaturia to full species status. The transition to myrmecophagy was dated to the mid-Miocene (approximately 16 Mya), when southern Australia experienced a humid climate and extensive mesic biome. The arid Nullarbor Plain, a major biogeographical feature of central southern Australia, divides the remnants of this mesic biome into south-eastern and south-western isolates. Late-Miocene to Pliocene divergence estimates for polytypic Ogyris species across the Nullarbor were older than estimates made for similarly distributed birds, butterflies, mammals, and reptiles, which mostly date to the Pleistocene. The concept of highly-specialized life histories as evolutionary dead-end strategies is well exemplified by the idmo-group. Data compiled on the known extant subpopulations for idmo-group taxa show that all of these extraordinary butterflies are scarce and several face imminent threat of extinction.