Category: Behaviour
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All organisms show behaviour to a certain extent. In animals, behavioural responses are often complex and diverse and, thus, evolutionary convergence in behaviour would a priori be surprising. Indeed, examples of behavioural convergence are rather limited to date (although there are probably many more awaiting recognition), but that they exist at all nicely illustrates the ubiquity of convergent evolution.
While behaviour can be innate, many animals have some capacity for learning. There are striking parallels between cephalopods (notably the octopus) and vertebrates, which extend to associative, observation, and spatial learning. But learning is very widespread, being found in many other groups such as arthropods (particularly insects) and even nematodes. Central to learning is the capacity to memorise and this is convergent as well. Interestingly, sleep, which is probably important for the processing of memories, has evolved many times, not only in mammals and birds, but also in a number of arthropods (e.g. crayfish, fruit flies and honeybees) and probably even in octopus and cubozoan jellyfish. Teaching, where a behaviour is taught by an experienced individual, is not unique to humans either, but can be observed in many animals, including meerkats, birds and ants.
Play is the hallmark of the most intelligent animal species, and there are striking similarities between birds and mammals, with a one-to-one correspondence to the four principal categories of play (chasing, fighting, invitation and object play). While highly characteristic of young mammals, only those birds with complex cognitive abilities (namely crows, hornbills and parrots, particularly kea and kakapo) engage in play. There is also some evidence for play in the octopus.
Behaviour is of particular importance when it comes to mating. In several animals, the male presents a nuptial gift (e.g. food or silk) to the female to increase his chances of fertilisation. This has evolved several times in insects and, more unusually, in spiders. Convergence is also evident in the courtship behaviour of insects (e.g. houseflies, lacewings and crickets) as well as bowerbirds, which is of particular interest as the decorated bowers are very complex. A particularly familiar example of courtship behaviour is lekking. Typically, males display within an arena to visiting females, which then choose a mate. While classical cases occur in birds, lekking is also evident in various amphibians, some mammals, fish and even a number of invertebrates, including some insects, squid and fiddler crabs.
Fiddler crabs are of further interest in the context of behavioural convergence as they demonstrate the independent evolution of surprisingly complex activities, such as defence of their patch, plugging of neighbours' burrows and erection of mud walls. The latter can be considered an example of construction behaviour, which too includes nest building (not only found in birds, but also in chimpanzees) and the construction of similar web types in different lineages of spiders. A number of animals furthermore construct and use tools, which is at its most sophisticated in primates and corvids, but simpler forms of tool use can be observed in other groups, including cephalopods and insects.
Subterranean burrowing mammals illustrate several behavioural convergences. Not only do they show a uniform preference for attacking the lower end of a carrot (!), but many of them are also solitary, show a high level of aggression and employ seismic communication. Several lineages of desert lizards have evolved similar behavioural adaptations to obtain water, such as adopting a stereotyped body posture to maximise water capture.
Societal convergences include matriarchal societies in elephants and sperm whales as well as fission-fusion societies in dolphins, chimpanzees, some New World monkeys and elephants. Perhaps the most remarkable example, however, is the repeated evolution of eusociality in mammals, crustaceans and, most importantly, insects, such as bees and ants. Ants are particularly instructive in terms of behavioural convergence, because several lineages have independently evolved slavemaking and, more benignly, agriculture or the "farming" of other insects (e.g. aphids) for their sugar secretions.
On the more curious side, behavioural convergence is evident in the process of getting drunk, which is very similar in fruit flies and mammals, the reaction to death in humans, elephants and dolphins, the independent evolution of hygiene in a number of insect groups (e.g. ants, termites, butterflies and moths) and feigning death, which may be used as a defensive strategy in many animals, such as cichlids, ants, beetles, and spiders.
