Termites, hemimetabolous diploid white ants?

Abstract

Ants and termites are the most abundant animals on earth. Their ecological success is attributed to their social life. They live in colonies consisting of few reproducing individuals, while the large majority of colony members (workers/soldiers) forego reproduction at least temporarilly. Despite their apparent resemblance in social organisation, both groups evolved social life independently. Termites are basically social cockroaches, while ants evolved from predatory wasps. In this review, I will concentrate on termites with an ancestral life type, the wood-dwelling termites, to compare them with ants. Their different ancestries provided both groups with different life history preadaptations for social evolution. Like their closest relatives, the woodroaches, wood-dwelling termites live inside their food, a piece of wood. Thus, intensive costly food provisioning of their young is not necessary, especially as young instars are rather independent due to their hemimetabolous development. In contrast, ants are progressive food provisioners which have to care intensively for their helpless brood. Corresponding to the precocial -altricial analogy, helping by workers is selected in ants, while new evidence suggests that wood-dwelling termite workers are less engaged in brood care. Rather they seem to stay in the nest because there is generally low selection for dispersal. The nest presents a safe haven with no local resource competition as long as food is abundant (which is generally the case), while founding a new colony is very risky. Despite these differences between ants and termites, their common dwelling life style resulted in convergent evolution, especially winglessness, that probably accounts for the striking similarity between both groups. In ants, all workers are wingless and winglessness in sexuals evolved in several taxa as a derived trait. In wood-dwelling termites, workers are by default wingless as they are immatures. These immatures can develop into winged sexuals that disperse and found a new nest or into neotenic replacement reproductives that inherit the natal colony. Depending on the worker instar from which the latter develop, the neotenic reproductives are either apterous or brachypterous, but never winged. I propose that this wing polyphenism might present a basis for the evolution of social life in termites.

Brood care and social evolution in termites

“…The need for external foraging introduces two differences that dramatically change the trajectory of eusocial evolution [7,17,39,43]. First, the outside foraging is associated with much larger mortality risks, increasing the level of altruism.…”

“…Rather they seem to be hopeful reproductives that become either winged sexuals or neotenic replacement reproductives [43]. The importance to gain direct fitness benefits through nest inheritance was also stressed for the occurrence of workers in another wood-dwelling species that has been studied intensively: the dampwood termite, Zootermopsis nevadensis [44,45].…”

“…The importance to gain direct fitness benefits through nest inheritance was also stressed for the occurrence of workers in another wood-dwelling species that has been studied intensively: the dampwood termite, Zootermopsis nevadensis [44,45]. Yet the high microbial load of the nest environment of dampwood termites [46] might have selected for hygienic brood care behaviour, such as allogrooming [43]. Using a standardized behavioural protocol, we set up a series of observational experiments to investigate the occurrence and degree of brood care in representative species of lower termite lineages (figure 1a).…”

Molecular traces of alternative social organization in a termite genome

“…Despite these similarities to eusocial Hymenoptera, termite societies have a phylogenetically distinct origin and divergent biological traits. They form a monophyletic clade nested within the Blattodea 4 , indicating a single origin of termite eusociality, whereas eusociality independently evolved multiple times within the Hymenoptera 3 . Termites are hemimetabolous, having several immature stages that become more adult like with each transition, while Hymenoptera have a holometabolous development in which the final larval stage develops via a pupa into adulthood.…”

“…Their complex societies have enhanced their environmental adaptability, contributing to their success. Similar to eusocial Hymenoptera (ants, some bees and wasps), termites are characterized by a caste system in which a few individuals reproduce (queens and, in termites, kings) while the large majority (workers and soldiers) perform tasks such as foraging, brood care or defence 3 . Despite these similarities to eusocial Hymenoptera, termite societies have a phylogenetically distinct origin and divergent biological traits.…”