Animals beneath the cypress shade

pardal a un cementeri

Humans are not alone in their obsession with death. Pliny the Elder already left written records of elaborate animal behaviour when faced with the death of individuals of their own species. Now the subject of comparative thanatology, a sub-discipline of ethology that examines the relationship of animals with death from an evolutionary point of view, we are beginning to unravel the great diversity of ways in which animals deal with death across the tree of life.

The most common animal responses to death fall under what we call necrophoresis, and consist of avoiding or disposing of the corpses of individuals of the same species to prevent the spread of infections among the social group. For example, among honey bees, certain worker bees specialise in removing the corpses of their fallen comrades. As soon as these undertakers of the hive detect the subtle whiff of death in the chemicals of a bee’s cuticle, they drag its body to the exit and carry it in sombre flight away from the hive, up to a hundred metres or until the weight of the deathly burden overcomes them. Other species, such as some species of ants, have the more orderly custom of burying their corpses under soil or vegetation.

Several highly social bird species, primarily corvids, exhibit another type of sophisticated «funerary» behaviour that appears to serve a very different function. For example, when California scrub jays, notice a dead conspecific, they utter distressing alarm calls that attract other individuals in the social group, which join their voices in a cacophony of vocalizations around the carcass. In response, individuals in the group will restrain their foraging for a time, apparently to avoid whatever predators or gloomy destiny may await them in the dark of the woods.

Even the infamous fruit fly (Drosophila melanogaster), the same annoying visit that pays its due whenever we allow fruit to overripen, exhibits sophisticated responses to death. A recent study has shown that, when females of this species detect the presence of dead conspecifics, they dramatically increase the number of eggs they lay in a strategy known as terminal investment. Faced with a possible increase in mortality, due for example to fungal infection or the collapse of. resources (both common occurrences in the wild), females invest all available resources into reproduction. Such terminal strategies are widespread in nature, as they allow organisms to maximise their biological efficiency when survival is uncertain, but they had never been described in response to the presence of dead conspecifics.

For most animals, thus, the death of a conspecific seems to act as an alarm that triggers behaviours aimed at coping with impending threats to their survival. However, yet another group of animals exhibit much more enigmatic behaviours. Some highly social species, such as primates, display responses that seem to have no clear evolutionary function, such as carrying, caring for or grooming a body, usually that of an individual with whom they had a close social bond. While several competing hypotheses have tried to explain this mystery, some evidence suggests that such responses may be associated with emotions similar to those we experience when we bury our loved ones. Fear of death is, it seems, not unique to our species.

© Mètode 2023 - 116. Moments of science - Volume 1 (2023)
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Professor of Zoology at the University of Valencia and researcher at the Cavanilles Institute of Biodiversity and Evolutionary Biology of the University of Valencia (Spain). PhD in Ethology. He studies the evolution of ageing and animal communication, and the role of ecology in sexual selection and sexual conflict.