When Termites Became Monogamous, A Surprising Thing Happened to Their Sperm : ScienceAlert

Termites reveal a startling consequence of long-term monogamy – the resulting lack of competition between the reproductive sperm of rival males led to the loss of tails in their sperm.

This involved losing a suite of genes, which contributed to their complex shift from solitary cockroaches to mega-socialite termites, a new study found. So in a way, the loss of sperm mobility was the price these insects paid for their inbred mega-societies.

“This work shows that understanding social evolution isn’t just about adding new traits,” says University of Sydney evolutionary biologist Nathan Lo, one of the study authors. “Sometimes, it’s about what evolution chooses to let go.”

“Our results indicate that the ancestors of termites were strictly monogamous. Once monogamy was locked in, there was no longer any evolutionary pressure to maintain genes involved in sperm motility.”

The genes, developmental physiology, and behavior of these obligatorily social insects suggest food specialization was a major driver of their social leap.

“Termites evolved from cockroach ancestors that started living inside and eating wood,” explains Lo. “Our study shows how their DNA changed first as they specialized on this poor-quality diet and then changed again as they became social insects.”

Comparing cockroaches and termites, South China Normal University entomologist Yingying Cui and colleagues including Lo found that termites have much smaller genetic libraries than cockroaches, with fewer genes linked to metabolism, digestion, and reproduction.

“The surprising result is that termites increased their social complexity by losing genetic complexity,” says Lo. “That goes against a common assumption that more complex animal societies require more complex genomes.”

What’s more, the developmental timing of the expression of energy metabolism genes, which depended on how much food their older siblings provided them, determined whether a termite larva would develop into a worker, or a future colony king or queen.

Related: Scientists Just Found The Perfect Disguise to Sneak Into a Termite Colony

If they receive plenty of food, they develop faster and become workers; less food creates a slower-developing reproductive nymph. If these nymphs are eventually crowned, they breed with their relatives.

“These food-sharing feedback loops allow colonies to fine-tune their workforce,” explains Lo. “They help explain how termites maintain stable, highly efficient societies over long periods.”

Together, these results suggest that, at least in termites, monogamy and high relatedness were crucial for the development of their complex social system. Definitely not a model mammals would be advised to replicate, although some do seem to try.

This research was published in Science.