Brood care and social evolution in termites

Abstract

Cooperative brood care is assumed to be the common driving factor leading to sociality. While this seems to be true for social Hymenoptera and many cooperatively breeding vertebrates, the importance of brood care for the evolution of eusociality in termites is unclear. A first step in elucidating this problem is an assessment of the ancestral condition in termites. We investigated this by determining the overall level of brood care behaviour across four termite species that cover the phylogenetic diversity of the lower termites. Brood care was low in the three species (all from different families) that had an ancestral wood-dwelling lifestyle of living in a single piece of wood that serves as food and shelter. In the fourth species, a lower termite that evolved outside foraging, brood care was more common. Together with data for higher termites, this suggests that brood care in termites only becomes important when switching from a wood-dwelling to a foraging lifestyle. These results imply that early social evolution in termites was driven by benefits of increased defence, while eusociality in Hymenoptera and cooperative breeding in birds and mammals are primarily based on brood care.

Figure 1.

(a) Phylogeny of termite families and (b) phylogeny of the Termitidae (both after Inward et al. [17]), with lifestyle (forager: foraging species; wood-dweller: wood-dwelling species) and studied focal species shown. The trees are cladograms so that branch lengths are arbitrary. Asterisks indicate taxa known to have brood care. M, monophyletic family; P, paraphyletic family. References for brood care in Termitidae: Nasutitermitinae [–21]; Cubitermes [22]; Macrotermitinae [–25].

Figure 2.

Results of the behavioural comparison between species. Shown are mean values (±s.e.) of the frequency/duration of different behaviours during 30 min of focal observation of (a) egg care (number of interactions with eggs), (b) stomodeal trophallaxis (in seconds). Different letters indicate significant difference between species (p < 0.05).

Figure 3.

Results of the comparison of interactive behaviours between species. Shown are mean values (±s.e.) of the duration (in seconds) during 30 min of focal observation for (a,c) donors and (b,d) recipients of (a,b) allogrooming and (c,d) proctodeal trophallaxis. Lower-case letters indicate significant differences between species (p < 0.05).

Figure 4.

Results of a principal component analysis including all behaviours. The first component (x-axis) had an eigenvalue of 3.32. The second component (y-axis) had an eigenvalue of 2.02. Shown are the mean values ±95% CI. See text for details.