The ancient beetle encased in 99-million-year-old amber. Image credit: Zhou et al. (CC BY 4.0)
Many animals live lives that are closely intertwined with those of other species. While a clown fish sheltering within the tentacles of a sea anemone may be a textbook example, ‘symbiotic’ interactions that occur inside ant nests are among some of the most dramatic.
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 earliest examples of ancestral ants are found encapsulated in 99-million-year-old amber from a mine in northern Myanmar (Burma). Zhou et al. have now discovered an ancient beetle, perfectly preserved in the same amber deposits, that may have also lived within the colonies of those earliest-known ants. Based on its appearance, the beetle – named Promyrmister kistneri – belongs within a subfamily of clown beetles (called the Haeteriinae) that are all specialized nest intruders with dramatic behavioral and chemical adaptations that help them to infiltrate ant colonies.
The ancient clown beetle shares several of features with its modern relatives – including thick, spiked legs and well-protected head and antennae – which are believed to help the beetles withstand handling by the ants’ jaws. The specimen also has glands near the base of its legs, implying that it also 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. It is potentially the oldest known example of a symbiotic interaction in the animal kingdom that depends on social interactions between the two organisms. However, the host ants of Promyrmister are believed to be long-extinct, suggesting that symbiotic clown beetles had to switch to living inside colonies of modern ants to circumvent their own extinction. This flexibility to adapt to new partner species may be a critical feature that allows some symbiotic organisms to persist throughout evolution.
