Mutual Aid. Pablo Servigne

can change light conditions to make the latter more favourable to their neighbours, or alter air temperature, humidity, nutrients or the oxygenation of the soil. They can even serve as a substrate for other plants, attract pollinators or, on the contrary, keep herbivores at bay. In some cases, when an insect lands on a tree and begins to eat its leaves, neighbouring trees immediately start producing poisonous substances, warned by the scent emitted by the first victims.

      4 4. R. E. Kenward, ‘Hawks and doves: Factors affecting success and selection in goshawk attacks on woodpigeons’, Journal of Animal Ecology, 47, 1978, pp. 449–60.

      5 5. S. M. Cooper, ‘Optimal hunting group size: The need for lions to defend their kills against loss to spotted hyaenas’, African Journal of Ecology, 29, 1991, pp. 130–6.

      6 6. See the magnificent book by Peter Wohlleben, The Hidden Life of Trees: What They Feel, How They Communicate – Discoveries from a Secret World, trans. Jane Billinghurst (London: William Collins, 2017).

      7 7. The History of Herodotus, vol. I, trans. G. C. Macaulay, first published in 1890, available online: www.gutenberg.org/files/2707/2707-h/2707-h.htm (Book II, para. 65). The species corresponding to this ‘trochilus’ has long been considered the Egyptian plover (Pluvianus aegyptius). If the first observation was indeed recorded by Herodotus, and was then repeated for two thousand years by many authors, there have as yet been no proven modern observations (and in particular no photos). Moreover, the plover, like the crocodile, is now much rarer, and so are the opportunities for interaction. One of the few recent authors to have studied the matter has concluded that, if this partnership existed, it was not really common, and might even involve another species of bird, the spur lapwing (Hoplopterus spinosus) – but the two are not mutually exclusive. See T. R. Howell, Breeding Biology of the Egyptian Plover, Pluvianus aegyptius (vol. 113) (Berkeley: University of California Press, 1979).

      8 8. D. H. Boucher, ‘The idea of mutualism, past and future’, in D. H. Boucher (ed.), The Biology of Mutualism, Ecology and Evolution (Oxford: Oxford University Press, 1985), pp. 1–28.

      9 9. These are the Isosicyonis sea anemones, living in partnership with the gastropod Harpovoluta charcoti: E. Rodríguez and P. J. López-González, ‘The gastropod-symbiotic sea anemone genus Isosicyonis Carlgren, 1927 (Actiniaria: Actiniidae): A new species from the Weddell Sea (Antarctica) that clarifies the taxonomic position of the genus’, Scientia Marina, 72, 2008, pp. 73–86.

      10 10. B. Hölldobler and E. O. Wilson, The Ants (Cambridge, MA: Harvard University Press, 1990); C. Nielsen et al., ‘Ants defend aphids against lethal disease’, Biology Letters, 6, 2009, pp. 205–8; B. Stadler and A. F. Dixon, ‘Ecology and evolution of aphid–ant interactions’, Annual Review of Ecology, Evolution, and Systematics, 36, 2005, pp. 345–72.

      11 11. M. Heil and R. Karban, ‘Explaining evolution of plant communication by airborne signals’, Trends in Ecology and Evolution, 25, 2010, pp. 137–44.

      12 12. The six living kingdoms are: animals, plants, fungi, protists (unicellular, with nuclei), bacteria and archaea (another type of bacteria).

      13 13. B. Juniper, ‘The mysterious origin of the sweet apple’, American Scientist, 95, 2007, pp. 44–51.

      14 14. U. G. Mueller et al., ‘The evolution of agriculture in insects’, Annual Review of Ecology, Evolution, and Systematics, 36, 2005, pp. 563–95.

      15 15. D. E. Bignell and P. Eggleton, ‘Termites in ecosystems’, in T. Abe et al. (eds), Termites: Evolution, Sociality, Symbioses, Ecology (Dordrecht: Springer Netherlands, 2000), pp. 363–87.

      16 16. B. D. Farrell et al., ‘The evolution of agriculture in beetles (Curculionidae: Scolytinae and Platypodinae)’, Evolution, 55, 2001, pp. 2011–27.

      17 17. C. Darwin, The Various Contrivances by which Orchids are Fertilized by Insects (London: John Murray, 1877).

      18 18. W. Rothschild and K. Jordan, ‘Scientific books: A revision of the lepidopterous family Sphingidoe’, Science, 18, 1903, pp. 15–16.

      19 19. D.-Y. Alexandre, ‘Le rôle disséminateur des éléphants en forêt de Taï, Côte d’Ivoire’, La Terre et la Vie, 32, 1978, pp. 47–72.

      20 20. M. Greenwood et al., ‘A unique resource mutualism between the giant Bornean pitcher plant, Nepenthes rajah, and members of a small mammal community’, PLoS One, 6 (6), 2011, art. e21114.

      21 21. R. Honegger, ‘The lichen symbiosis – what is so spectacular about it?’, The Lichenologist, 30, 1998, pp. 193–212.

      22 22. J. R. Haas and O. W. Purvis, ‘Lichen biogeochemistry’, in G. M. Gadd (ed.), Fungi in Biogeochemical Cycles (Cambridge: Cambridge University Press, 2006), pp. 344–76.

      23 23. G. M. Gadd, ‘Metals, minerals and microbes: Geomicrobiology and bioremediation’, Microbiology, 156, 2010, pp. 609–43.

      24 24. R. A. Armstrong, ‘Lichens, lichenometry and global warming’, Microbiologist, 5, 2004, pp. 32–5.

      25 25. D. L. Hawksworth et al., ‘Dictionary of the fungi’, Fungal Genetics and Biology, 20, 1996, p. 173.

      26 26. G. D. Stanley and P. K. Swart, ‘Evolution of the coral–zooxanthellae symbiosis during the Triassic: A geochemical approach’, Paleobiology, 21, 1995, pp. 179–99.

      27 27. G. D. Stanley, ‘Photosymbiosis and the evolution of modern coral reefs’, Science, 312, 2006, pp. 857–8.

      28 28. L. Wegley et al., ‘Metagenomic analysis of the microbial community associated with the coral Porites astreoides’, Environmental Microbiology, 9, 2007, pp. 2707–19.

      29 29. About a hundred species of bacteria are thought to be pathogenic for humans in relation to the 10 million already described. See M. McFall-Ngai, ‘Adaptive immunity: Care for the community’, Nature, 445 (7124), 2007, art. 153. The proportion of pathogenic species still seems to be a significant overestimate, since a recent study extrapolates total microbial biodiversity, now said to number a trillion species. See K. J. Locey and J. T. Lennon, ‘Scaling laws predict global microbial diversity’, Proceedings of the National Academy of Sciences USA, 113, 2016, pp. 5970–5.

      30 30. When colonies of Escherichia coli (the most frequently studied bacteria) grow in a Petri dish, we observe that it’s the contact area (and therefore the area of exchange) between cells which is maximized, rather than the area of contact with the nutrient substrate. If the cells were in competition, the reverse would be observed. See J. A. Shapiro and C. Hsu, ‘E. coli K-12 cell–cell interactions seen by time-lapse video’, The Journal of Bacteriology, 171, 1989, pp. 5963–74.

      31 31. J. A. Shapiro, ‘Bacteria are small but not stupid: Cognition, natural genetic engineering and socio-bacteriology’, Studies in History and Philosophy of Biological and Biomedical Sciences, 38, 2007, pp. 807–19.

      32 32. And this has been the case for a very long time since, among the first traces of fossil bacteria, we find stromatolites, a veritable lasagne of biofilms of bacteria. See R. P. Reid et al., ‘The role of microbes in accretion, lamination and early lithification of modern marine stromatolites’, Nature, 406, 2000, pp. 989–92.

      33 33. R. K. Behl et al., ‘Wheat x Azotobacter x VA Mycorrhiza interactions towards plant nutrition and growth – a review’, Journal of Applied Botany and Food Quality, 81, 2007, pp. 95–109; R. Kumar et al., ‘Establishment of Azotobacter on plant roots: Chemotactic response, development and analysis of root exudates of cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.)’, Journal of Basic Microbiology, 47, 2007, pp. 436–9.

      34 34. D. G. Adams et al., ‘Cyanobacterial symbioses’, in B. A. Whitton (ed.), Ecology of Cyanobacteria II (Dordrecht: Springer Netherlands, 2012), pp. 593–647.

      35 35. R. Gordon and R. W. Drum, ‘The chemical basis of diatom morphogenesis’, International Review of Cytology, 150, 1994, pp. 243–372.

      36 36. M. D. Kane and U. G. Mueller, ‘Insights from insect–microbe symbioses’, in J. T. Staley and A.-L. Reysenbach (eds), Biodiversity of Microbial Life (New York: