Before settling down with their mates for a five-year life of raising a family, some termites suddenly have second thoughts: They use their brief "honeymoon" to find a better partner.
Reporting tomorrow (Jan. 22, 1999) in Proceedings of the Royal Society of London, Series B, Cornell University biologist Janet S. Shellman-Reeve describes the not-so-blissful scene on a rotting log when the seven-year itch occurs in the insect couple's first two hours.
- Just an hour after landing on the log where she will spend most of her life with a newfound mate, a female termite might invite another male to the nest site to fight her mate for the right to father and raise her young.
- A just-paired male can wander off in search of a better female.
- Nest mates might fight each other when a potential suitor is near. Biting off the tip of a mate's antenna might squelch thoughts of separation, Shellman-Reeve hypothesizes.
Shellman-Reeve's study of the wood-dwelling, biparental termite Zootermopsis nevadensis marks the first scientific documentation of behavior called "mutual mate choice" among insect pairs that cooperatively provide long-term care for their young.
"Having second thoughts and choosing a better mate to share the heavy investment in parental care is a well-known strategy in vertebrates -- including humans -- but this is the first report of mutual mate choice in biparental insects," Shellman-Reeve says. "The process can be contentious and violent, but it makes sense. You want the best possible mate to help raise your offspring, and that's not always the first one you meet when you land on a log."
Her studies of Z. nevadensis, a species native to California woodlands, also show what is on the mind of mate-swapping termites: Females usually choose a male with a bigger head the second time around, while males go for females with bigger bodies and more lipid (fat) storage area. Big-headed males are better at ramming and biting their opponents while defending the nest, Shellman-Reeve explains. Big-bodied females are better suited, biologically speaking, for raising young.
Before her study of Z nevadensis honeymoons, Shellman-Reeve documented a pattern of termite homesteading that would make a mortgage banker proud. Within hours of flying to a likely log and making their ultimate mate choice, newly paired termites are building their future home. They erect concrete-like walls from their own fecal matter to keep interlopers away from the sections of the log they intend to mine. The nitrogen-rich cambium portion of trees is the most coveted by termites because other parts of wood are less nutritious for a growing family. The wood-mining colony, clustered around the original termite pair, can remain in place for years as offspring help with family duties, and one large log may host dozens of separate termite colonies. If the food runs out, termites sprout wings and look for another nitrogen-rich log to colonize.
Shellman-Reeve's latest study concentrated on the first 90 minutes of homesteading, when the nest site is just an unimproved, 2- or 3-centimeter spot on the log's surface. The Cornell biologist found both male and female termites willing to desert their home to search for someone better, but females are more likely to stay and invite a second male to the nest site as a way of securing a potentially better mate. Although male termites occasionally initiate what Shellman-Reeve terms the "stay-and-invite" strategy, they are more likely to follow a "leave-and-search" strategy for a better mate.
Whether at the nest or on the prowl, the dissatisfied mate rises up on its legs and begins a bouncy, stilt-walking motion while wiggling a section of its abdomen where a pheromone-producing gland is found. The airborne chemical sex-attractant in the pheromone and the characteristic posture are what advertises the termite's availability and interest in a better mate.
When termites of the same sex are battling for the affections of the opposite sex, the desired termite ceremoniously grooms each combatant in turn, as if to incite each to fight harder and prove its worth, Shellman-Reeve reports.
Almost comical is the reaction of one honeymooning termite when it detects a potential suitor for its nest mate. Instead of fighting the suitor, the termite assaults its mate. That's when intra-pair interaction gets nasty, Shellman-Reeve says.
But the Cornell biologist says she really had to laugh when she witnessed one example of off-again, on-again romance: "A male wandered off in search of a better mate but he had no luck. No one would have him. So he returned to his original mate. She assaulted him pretty severely for several minutes. Then she dragged him by the abdomen into a hole in their nest."
The study, "Courtship strategies and conflicts in a monogamous, biparental termite," was supported by Cornell, where Shellman-Reeve is a research associate in the Division of Neurobiology and Behavior. In a future study, Shellman-Reeve will use DNA fingerprinting techniques to determine whether her termites are truly mated for life -- or whether the urge to wander sometimes strikes again.