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Figure 1- Termite nest cross section . |
While the eusocial
hymenoptera evolved from predatory wasps, termites instead evolved from
wood-feeding cockroaches and form a sister group with the cockroach genus
Cryptocercus (Lo et al., 2000). As discussed last week, the supersister relationship
is thought be a driving factor in the evolution of eusocality in hymenoptera,
but this genetic configuration is not present in termites. Instead nest inheritance is throught to be one of the main selective forces for the evolution of altruism and eventually the sterile worker castes (Miles, 1988).
The primitive habitat of termites was probably inside dead wood (logs, stumps, dead parts of living trees) in which the society found both food and shelter. This is a condition that seems to drive eusocial evolution, as it is also observed in vastly different species such as the marine sponge-dwelling shrimp who live and feed inside their sponge hosts (Duffy, 1996). This home and food source becomes a multi-generational asset, a source of direct fitness for these primitively eusocial insects (Leadbeater et al., 2011), one that promotes social interactions between its potentially highly related inhabitants.
Studies suggests that, in contrast to hymenoptera, brood care by termite workers is not necessary prerequisite for termite eusociality and the level of worker altruism seems to differ greatly between species (Korb et al., 2012). Brood care was shown to be low in wood-dwelling termites, suggesting that early social evolution in termites wasn’t driven by cooperative brood care but rather by the defensive benefits that a nest provides.
The degree of altruistic worker brood care seems to depend on environmental conditions, for example pathogen load appears to be a major factor in promoting altruistic allogrooming in workers (Korb et al., 2012), indicating that nest-level defence against pathogens may have been an additional driver of termite social evolution.
Although the nest is a characteristic of all eusocial insects, among them termites are distinguished by the great diversity of their nests with sprawling and complex architecture (Figure 1). This diversification is related to the evolution of social life and the changing of food sources (Noirot, 2000). As termites evolved from living inside their food source towards becoming an foraging species, new challenges had to be met. Their relatively soft bodies had to adapt to new climates and so nests modified accordingly, with the establishment of architecture that provides a microclimate suitable for termite life (Woon et al, 2019) and a structure designed for the defense of the colony against predation.
References:
The primitive habitat of termites was probably inside dead wood (logs, stumps, dead parts of living trees) in which the society found both food and shelter. This is a condition that seems to drive eusocial evolution, as it is also observed in vastly different species such as the marine sponge-dwelling shrimp who live and feed inside their sponge hosts (Duffy, 1996). This home and food source becomes a multi-generational asset, a source of direct fitness for these primitively eusocial insects (Leadbeater et al., 2011), one that promotes social interactions between its potentially highly related inhabitants.
Studies suggests that, in contrast to hymenoptera, brood care by termite workers is not necessary prerequisite for termite eusociality and the level of worker altruism seems to differ greatly between species (Korb et al., 2012). Brood care was shown to be low in wood-dwelling termites, suggesting that early social evolution in termites wasn’t driven by cooperative brood care but rather by the defensive benefits that a nest provides.
The degree of altruistic worker brood care seems to depend on environmental conditions, for example pathogen load appears to be a major factor in promoting altruistic allogrooming in workers (Korb et al., 2012), indicating that nest-level defence against pathogens may have been an additional driver of termite social evolution.
Although the nest is a characteristic of all eusocial insects, among them termites are distinguished by the great diversity of their nests with sprawling and complex architecture (Figure 1). This diversification is related to the evolution of social life and the changing of food sources (Noirot, 2000). As termites evolved from living inside their food source towards becoming an foraging species, new challenges had to be met. Their relatively soft bodies had to adapt to new climates and so nests modified accordingly, with the establishment of architecture that provides a microclimate suitable for termite life (Woon et al, 2019) and a structure designed for the defense of the colony against predation.
References:
Duffy, J.,
1996, Eusociality in a coral-reef shrimp. Nature 381, 512–514 (1996).
https://doi.org/10.1038/381512a0
Korb, J., Buschmann, M., Schafberg, S., Liebig, J., Bagnères, A., 2012, Brood care and social evolution in termites. Proceedings. Biological sciences / The Royal Society. 279. 2662-71. 10.1098/rspb.2011.2639.
Leadbeater, E., Carruthers, J., Green, J., Rosser, N., Field, J., 2011, Nest Inheritance Is the Missing Source of Direct Fitness in a Primitively Eusocial Insect. Science (New York, N.Y.). 333. 874-6. 10.1126/science.1205140.
Lo, N., Tokuda, G., Watanabe, H., Rose, H., Slaytor, M., Maekawa, K., Bandi, C., Nodam H., 2000, Evidence from multiple gene sequences indicates that termites evolved from wood-feeding cockroaches, Curr Biol., 2000 , vol. 10 (pg. 801-804)
Myles T.G., 1988, Resource inheritance in social evolution from termite to man. In: Slobodchikoff CN, editor. Ecology of Social Behavior. New York: Academic Press; 1988. pp. 379–425.
Noirot C., Darlington J.P.E.C., 2000, Termite Nests: Architecture, Regulation and Defence. In: Abe T., Bignell D.E., Higashi M. (eds) Termites: Evolution, Sociality, Symbioses, Ecology. Springer, Dordrecht
Woon, J., Boyle, Michael, Ewers, R., Chung, A., Eggleton, P., 2018, Termite environmental tolerances are more linked to desiccation than temperature in modified tropical forests. Insectes Sociaux. 10.1007/s00040-018-0664-1.
Figure:
Cross-section image of a termite mound, https://www.earthlymission.com/take-a-look-inside-a-termite-mound/, 20/05/2020
Termites are quite fascinating little beasts. If pathogen-load promotes group living, I’m curious why it wouldn’t also promote a more solitary life style, because you would be more likely to catch pathogens. Is there any indication of the value in terms of fitness gained/lost in this group?
ReplyDeleteI would guess that the relative fitness benefits between group living (with allogrooming to remove pathogens) vs solitary lifestyle tilted heavily in the favour of the former. The pathogen load was principally a problem for dampwood species that lived and fed in moist environments, so solitary species in the same environment would have the same pathogen exposure. I can't find any studies that do this particular analysis though.
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