Coevolution: If you had to survive, would you reap benefits, or lives?

Everyone - everything - wants to survive. But unlike Herbert Spencer’s theory that ‘survival of the fittest’ prevails in the natural world, perhaps ‘survival of the kindest’ is the essential key to the success of evolution. All living organisms evolve, adapt to the changing stimuli in their natural habitats, and through crossbreeding, develop to possess new genetic traits to survive in their environment. People often focus on the evolution within one individual species, however, whilst neglecting the idea of co-evolution: that the adaptations of one organism must also impact other living species it interacts with. Within biological relationships, coevolution can be survival of the ‘fittest’, with the prime example the predator-prey model. “Predation” describes the interaction of one species hunting, killing, and consuming a fraction of the biomass of another. Lions hunt gazelles, the Venus flytrap catches flies, and insect parasitoids may slowly consume their hosts. Not very altruistic… so how do the ‘kindest’ play their parts in coevolution? Realistically, most organisms have certainly not evolved as far as displaying humanoid altruism, and the context of ‘kindness’ shown between species takes the form of behaviours promoting mutual benefits, where both organisms adapt reciprocally and for the better of their survival. In the case of predator-prey relationships, each species coevolves to gain an advantage over the other, physically, or behaviourally. Predation has an indomitable, selective pressure on prey; as a result, prey learns from any dangerous encounters and develops anti-predator adaptations, including camouflage, alarm cries and secretion of defensive chemicals. Its next of kin, produced sexually, are then ensured to evolve to perceive the same dangers, making it easier to exercise defensive mechanisms against predators. A prime example is the monarch butterfly. Apart from displaying bright orange on its wings as an aposematic colouration, the monarch also lays eggs on milkweed. When its caterpillars consume milkweed, they ingest cardiac glycosides, causing their predators, mainly birds, to vomit them out after feeding on them. The monarch’s defensive structures make way for their learning and aversion: physical adaptations of prey in turn cause behavioural adaptations of their predators. Early studies of monarchs showed when one of its primary consumers - the blue jay - ate a monarch caterpillar, it vomited due to the cardenolides in its body. Through the bluejay’s experience of the negative effects of the monarch’s toxic defence, mutual understanding was formed through the two species: the bluejay learned to forage for food sources other than the monarch butterfly. Both these adaptations are passed on to the next generation, playing a vital part in coevolution. In contrast, instead of both species’ advantages being inversely proportional, mutualism is a symbiotic connection in which at least one of the involved species benefits. While not precisely embodying the idea of ‘kindness’, or compassion, the organisms are able to cooperate and coevolve. Have you explored the complexity behind the world’s largest coral ecosystem, the Great Barrier Reef? Reef-building corals share a mutualistic relationship with the photosynthetic algae in their tissues called zooxanthellae: algal symbiosis. The coral provides zooxanthellae with an ideal living environment: not only do they have a sturdy skeleton made of calcium carbonate - a physical shield against large predators or strong waves, but also specialised cells forming a protective tissue layer around zooxanthellae. In return, since corals do not directly photosynthesise, the zooxanthellae supply it with glucose, glycerol, and amino acids: products of photosynthesis which coral then uses to make proteins, fats, and more calcium carbonate to strengthen its skeleton. The survival of the coral and zooxanthellae are almost entirely interdependent: as much as 90% of organic material produced by the zooxanthellae is used up by the host coral to extend its growth, and the zooxanthellae will be equally unlikely to survive if it does not receive nutrients from coral mucus. Similar interactions continue to evolve to maximise the fitness benefits that organisms receive from symbiosis. While predator-prey coevolution is essential in regulating the food web and other consumer-resource relationships, ecosystems clearly suffer less stress, competition, and destruction of species through mutualistic coevolution. Still, mutualism can never really be based on ‘kindness’ between wild species: maybe us humans can take the first, wilder step to prove it wrong.