More Than a Pest: Termites as Models for Evolutionary Transitions
By Thomas Chouvenc, Ph.D.
The Formosan subterranean termite (Coptotermes formosanus) is an infamous termite pest species, but it is also an interesting model for studying the evolution of termites and complex behaviors in eusocial insects. A study published in January in Environmental Entomology investigated the social behaviors of workers in young and old termite colonies and showed that, as the termite colony matures, the task division according to the age of the workers becomes more complex.
Termites represent a diverse group which, after reaching eusociality, went through much evolutionary innovation during their radiation, with now more than 3,000 described species. Although they are related to wood roaches, many termite species display highly derived traits, with diverse morphology, physiology, behaviors, and symbiotic associations.
Historically, termites were split in two distinct categories: lower termites, which digest wood with the help of gut protozoa symbionts, and higher termites, which lost their protozoa but have evolved more complex symbiotic associations with fungi and bacteria. However, the Coptotermes clade represents an interesting group, because termite species within this group are at the interface between lower and higher termites. They still possess protozoa symbionts, but they display many higher termite-like behaviors. This group is actually paraphyletic to the rest of the lower termites, as it is rooted at the very base of the higher termite phylogeny.
During his doctoral work with Nan-Yao Su, Ph.D., at the University of Florida Institute of Food and Agricultural Sciences, He Du showed that mature C. formosanus colonies display complex age polyethism, which means that termite workers perform different tasks according to their age. This phenomenon is well known in bees and some ant species; however, in termites, it was only reported in some higher termites. Coptotermes formosanus being technically a lower termite, Du’s initial work showed that this species could be used as a model to look at evolutionary transitions, with one characteristic of the lower termites (presence of protozoa) and one characteristic of the higher termites (age polyethism).
In the study published in Environmental Entomology, Du and fellow researchers pushed their investigation further by comparing the behavioral complexity of mature colonies to the behavioral complexity of young termite colonies. They found that, as the colony grows and gets older and bigger, the colony displays more and more complex behaviors. In other words, at the very beginning of the life of the termite colony, the small group of termites displays very lower termite-like behaviors, but as the colony grows and matures, the larger group of termites progressively displays higher termite-like behaviors.
The reserachers concluded that this termite species is a good model to study evolutionary transitions, as the behavioral ontogeny of the colony recapitulates the complexity of behaviors within the termite phylogeny.
Thomas Chouvenc, Ph.D., is a research assistant in urban entomology at the Fort Lauderdale Research and Education Center at the University of Florida’s Institute of Food and Agricultural Sciences. Email: firstname.lastname@example.org