Cockroaches Show Surprising Pair Bonding Behavior
A study published in Royal Society Open Science suggests that Salganea taiwanensis, a species of wood-feeding cockroach, may exhibit pair bonding behavior. This phenomenon involves two individual organisms spending an extended period together and excluding other individuals from their bond. Nate Lo, an evolutionary biologist at the University of Sydney and study author, described this as individuals having "each other's back."
Pair bonding offers several advantages, including mutual grooming, joint defense of nests and offspring, and shared food resources. It necessitates sufficient cognitive ability for individuals to recognize and remember their partners. While common in birds, mammals, and some fish, pair bonding is rarely observed in invertebrates such as insects or crustaceans. This research indicates that these cockroaches, and potentially other insects, might possess more sophisticated cognition and social behaviors than previously understood.
The Unique Wing-Eating Ritual
The wood-feeding cockroaches, found in regions like Okinawa, Japan, form burrows in rotting wood. A unique aspect of their pairing process involves the male and female chewing off and consuming each other's wings over several hours. Haruka Osaki, a behavioral ecologist and co-author, noted that the completion of this one-time meal signifies the formation of a pair.
The wings provide a protein source, and this ritual appears to initiate their long-term association, leading to nest building, mating, and offspring care.
Experimental Evidence Confirms Exclusive Bonds
To investigate the exclusivity and strength of this bond, researchers conducted an experiment. Pairs of cockroaches, some of which had completed the wing-eating ritual and some that had not, were placed in artificial nest boxes. An intruder was then introduced to each pair.
Observations revealed that pairs that had not consumed each other's wings showed no aggression towards intruders, allowing them to remain in the nest. Conversely, pairs that had eaten each other's wings aggressively attacked intruders by ramming and wiggling their abdomens. This aggressive exclusion suggests a strong, exclusive pact resembling a pair bond, where the two cockroaches distinguish between individuals and are only tolerant of their partner.
Implications for Invertebrate Cognition and Future Questions
The findings suggest that invertebrates may possess greater complexity and cognitive abilities than previously anticipated, despite their small brains.
Jessica Ware, curator of invertebrate zoology at the American Museum of Natural History, who was not involved in the study, agreed that the research provides strong evidence for pair bonding in this cockroach species.
The study raises additional questions for future research, including the potential for pair bonding in other insect species, the evolutionary development of this behavior in Salganea taiwanensis, and the specific mechanisms by which these cockroaches recognize their partners. One hypothesis suggests that consuming wings might allow the roaches to gather chemical information for partner recognition. Researchers also plan further experiments to assess the significance of the initial 24-hour period the seemingly bonded roaches spent together prior to the experiments.