Symbiotic microbes are essential for the survival of many animals and plants, but the factors promoting such partnerships remain poorly understood. Now researchers find that wasps can block which bacteria their offspring receive, helping them maintain exclusive partnerships with specific microbes for at least 68 million years. The findings are detailed in the Proceedings of the National Academy of Sciences.
Scientists focused on beewolves, which are solitary wasps that engage in an alliance with microbes to protect their developing offspring against harmful germs. Female beewolves cultivate a soil bacterium known as Candidatus Streptomyces philanthi (CaSP) in specialized antennal glands — the insects pass the microbe onto their offspring, which incorporate the symbiont into their cocoons to secrete at least nine different kinds of antibiotics that defend against dangerous fungi and bacteria.
To see how long beewolves have lived with this symbiont, evolutionary biologist Martin Kaltenpoth at the Max Planck Institute for Chemical Ecology in Jena, Germany, and his colleagues looked at beewolf fossils and DNA. They discovered the symbiosis was at least 68 million years old, findings supported by the complexity of the antenna glands the beewolves use to house the bacterium.
“Understanding how an animal has used symbiont-produced antibiotics for millions of years might be relevant for the applications of antibiotics in human medicine,” Kaltenpoth says. “Due to the rapid spread of antibiotic resistance in human pathogens, we’re running out of useful drugs to cure diseases, and this happened not even 100 years after the discovery of the first antibiotic, penicillin.”
The way in which female beewolves transfer bacteria to their young potentially makes them open to transferring other kinds of bacteria as well. Despite this opportunity, just one group of CaSP strains was found in 33 species of beewolves. When the researchers experimentally infected female beewolves with another kind of bacterium, they found the insects somehow did not pass these microbes on to their offspring.
The researchers suggest a number of possible reasons why the beewolves do not transfer unfamiliar bacteria to their offspring. For instance, these other bacteria may be harmful to the developing offspring.
The scientists now want to uncover the mechanism by which the beewolves choose the bacteria they want to pass on to their offspring. “How do they manage to transmit only some bacteria and not others?” Kaltenpoth asks. “Is the insect’s immune system involved? The biggest obstacle to this will be the availability of enough beewolf females for the experiments, as it is difficult to obtain and rear them in large numbers.”