Beetles that trick ants into raising their young have set a new benchmark for rapid evolution as they race to keep ahead of the species on which they prey.
The idea of getting another species to do the hard work of raising offspring is usually associated with cuckoos, to the point where the very name is a symbol of such behavior.
Known as brood parasitism, ant-nest beetles take this approach even further. The members of the genus Paussus interfere with the communication systems used by ants. They release pheromones similar enough to the ants to be accepted into the nest and make noises that imitate ant instructions on where to bring food. They also eat the ants and their eggs.
Just last month we reported on evidence that beetles have been doing this for 52 million years, almost as long as ants have existed.
Now scientists at the University of Arizona have found another remarkable aspect to the Paussus genus. In Current Biology, Dr. Wendy Moore and Dr. James Robertson of the University of Arizona reveal that despite this long history, it is only recently that the beetles have developed the capacity to use certain ants as hosts. "The rate at which this is happening is incredible," Moore says. "These are some of the fastest-evolving animals on Earth."
Moreover, the beetles have independently acquired this capacity in regions as widely separated as Africa and South East Asia. "These beetles are evolutionarily converging in form, and presumably in function, on completely different continents,” says Moore.
Malagasy Paussus beetles trace their ancestry to a single species 2.6 million years ago, Moore and Robertson reveal, but have now split into 86 species. According to the scientists, the diversification interval of 0.38 to 0.81 million years makes for, “a rate of radiation faster than classic textbook examples of large, recent, rapid radiations such as Anolis lizards on the Caribbean islands, cichlids of the East African Great Lakes, finches on the Galápagos Islands, and Drosophila and tetragnathid spiders on the Hawaiian Islands.”
“In order for Paussus to adapt to a new host ant species, the beetle’s ability to perceive, deceive, and communicate with the new host must evolve quickly and in synchrony in both the larval and adult life stages, resulting in unusually strong selective pressure levied by their host ants,” says Moore and Robertson.
Therefore, the beetles provide an outstanding opportunity to study evolutionary processes, particularly because comparisons can be made between separated populations. Moore notes, "Ant host species have been identified for less than a quarter of Paussus species.” She argues that identifying the missing hosts could reveal the influences that shaped the beetles, which in turn will have applications for other species.
