How do symbiotic relationships develop between two different animal species over time?
In: Biology
Take an example, ants keeping pets. Some ants keep pets (*myrmecophiles*); aphids eat the ants’ plants with a higher “efficiency” than ants by themselves (a quarter of the aphids in the Rocky Mountains are ant “pets”–their species is partially defined by the ants). They drop honeydew, which they ants can use. I won’t go in to what the benefits are and what the costs for both species, but assume the relationship is certainly beneficial for the ants and likely beneficial for the aphid.
The ants evolved to learn to consume honeydew (some ants had mutations which made them better at consuming honeydew, these ants had a higher chance of survival, that is evolution–I shall use anthropomorphic words here for evolution, but it boils down to a mutation and increased chances of survival). The aphids gained from this, as the honeydew is sticky and gets everywhere. Aphids evolved to “help” ants so that the ants keep doing what they do and so that the ants’ lives are easier. The ants evolve to help the aphids in return.
Another example is closer to home: prehistoric humans and dogs. Humans have brains and their actions are very intentional, making this case slightly different from other symbiosis (for example, we intentionally evolved the wolves, or “bred” them, which isn’t as common amongst other symbiotic relationships). The dogs gain from it: humans working with dogs benefit more than the dogs and the humans individually. The humans can eat more, and the dogs are fed more than they would find undomesticated. Also, humans can help dogs, by sheltering them from the rain and other animals.
The wolves ate the carcasses of the animals the humans killed and started to live near the humans. Somehow, the humans gained from this relationship. Perhaps the humans could use the carcasses of the animals the wolves killed or the wolves scared off dangerous animals for the humans. After slow evolution favouring slight symbiosis, the humans could use the wolves and started breeding them.
*Ecology and Evolution of Aphid-Ant Interactions*, Bernhard Stadler and Anthony F. G. Dixon (Annual Review of Ecology, Evolution, and Systematics (Vol. 36 (2005), pp. 345-372) for the ants and aphids
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