Abstract
Complex interspecies relationships are widespread among metazoans, but the evolutionary history of these lifestyles is poorly understood. We describe a fossil beetle in 99-million-year-old Burmese amber that we infer to have been a social impostor of the earliest-known ant colonies. Promyrmister kistneri gen. et sp. nov. belongs to the haeteriine clown beetles (Coleoptera: Histeridae), a major clade of 'myrmecophiles'-specialized nest intruders with dramatic anatomical, chemical and behavioral adaptations for colony infiltration. Promyrmister reveals that myrmecophiles evolved close to the emergence of ant eusociality, in colonies of stem-group ants that predominate Burmese amber, or with cryptic crown-group ants that remain largely unknown at this time. The clown beetle-ant relationship has been maintained ever since by the beetles host-switching to numerous modern ant genera, ultimately diversifying into one of the largest radiations of symbiotic animals. We infer that obligate behavioral symbioses can evolve relatively rapidly, and be sustained over deep time.
Highlights
A pervasive feature of colony-forming insect societies is the profusion of intruder arthropods that have evolved to exploit their rich resources (Kistner, 1979; Kistner, 1982; Holldobler and Wilson, 1990; Parker, 2016)
The clown beetle family Histeridae includes multiple lineages that have independently evolved myrmecophily (Parker, 2016; Kovarik and Caterino, 2005), including Haeteriinae, a subfamily of ~335 described species comprising possibly the single largest radiation of myrmecophiles known within the Coleoptera (Parker, 2016; Kovarik and Caterino, 2005; Helava et al, 1985)
We report the discovery of a crown-group haeteriine in Upper Cretaceous Burmese amber, revealing that the clown beetle-ant interaction has an exceptionally deep evolutionary history
Summary
A pervasive feature of colony-forming insect societies is the profusion of intruder arthropods that have evolved to exploit their rich resources (Kistner, 1979; Kistner, 1982; Holldobler and Wilson, 1990; Parker, 2016). Known as myrmecophiles – after the Greek for ‘ant lovers’, many insects, spiders and mites have evolved to live alongside ants in one way or another Some of these animals display elaborate behaviors – like mouth-to-mouth feeding or grooming of worker ants – which assimilates them into the nest society; some even release chemicals that mimic the ants’ own scents to avoid being detected as an intruder. The specimen has glands near the base of its legs, implying that it released chemical signals that may have helped it to deceive or pacify the ancient ants The fact that this extinct clown beetle is as old as the earliest-known ants implies that the close relationship between these insects has been sustained for an exceptionally long time.
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