Abstract:
When a cat detects prey, it stalks the prey before attacking it. Prey detection, thus, causes the cat to
perform a series of non-random actions to conceal itself and capture the prey. These non-random
actions are repeated every time the cat encounters any sort of prey. However, these actions may not
be seen when the cat detects other non-food objects or if the prey is unfamiliar to the cat.
Sometimes, the cat may fail to show these actions even when it encounters familiar prey simply
because it may have fed recently. Such non-random actions are called behaviours and, as the above
observations illustrate, they occur in response to specific environmental stimuli in a context
dependent manner. This context specificity often depends on whether the organism stands to
receive a net benefit by performing the behaviour. Thus, behaviours serve as responses to changes
in an organism's environment that may allow the organism to adapt to these changes.
Given the importance of responding to constantly changing environments, behaviours are
ubiquitous across taxa. This ubiquity is accompanied by great diversity in form and function of
behaviours. Consequently, a variety of questions may be posed to understand how and why such
behavioural diversity exists in nature. Tinbergen (1963) broadly organized these questions into four
complementary categories - causation, ontogeny, function and phylogeny (or evolution) - and
thereby provided a framework to address different aspects of any given behaviour. These questions
may be further grouped into proximate (or how?) questions (causation and ontogeny), which
explore the biological mechanisms underlying behaviours, and ultimate (or why?) questions
(function and phylogeny) which probe the evolutionary processes that underlie behaviours.
Between them, these questions provide a comprehensive approach to studying any behaviour.
Hence, I have used this framework to organize and discuss the literature available for aggregation
behaviour in the fruit fly, Drosophila melanogaster.
