It’s all about smell:
An Olfactory Arms Race in the Animal Kingdom

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Animals use smell to sniff out predators, and to hide from them.

For humans, vision is the dominant sense, and we often overlook the importance of odour (although we’re reminded on those occasions we find ourselves sat next to someone who’s never discovered deodorant, or driving past a particularly pungent farm). But for most animals, it’s all about smell. Two new studies published last month highlight the importance of smell in the lives of animals as different as flies and snakes.

A study published in PLOS Biology in December last year, identified a new type of neurone in fruit flies (Drosphila melanogaster) and a dedicated neuronal network designed to detect odours produced by their main threat, Leptopilina parasitoid wasps. These wasps parasitise and kill 80% of fruit fly larvae in the wild, but the flies have evolved specialised olfactory neurons to detect a chemical called iridomyrmecin, a Leptopilina sex pheromone.

By sniffing out sex pheromones, fruit flies are eavesdropping on the chemical communication system of potential enemies, a strategy that has not previously been reported. The authors note that this chemical detection system is likely part of an evolutionary arms race, with improved detection by prey being followed by better hiding on the part of the parasite.

A second study, published in Proceedings B on the same day, provides the other side of the coin – a prey species that uses smell to hide right under the noses of their predators. In another first, scientists report that the Puff Adder (Bitis arietans) has evolved to chemically camouflage its smell and blend into the background.

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Scientists presented two potential predators, Dogs (Canis familiaris) and Meerkats (Suricatta suricata), with the odours of different species of snake, and trained them to match one scent against an array of six scents lined up in front of them. Both meerkats and dogs had no problem matching the scent of active-foraging snakes, but were unable to spot the Puff Adder odour in a lineup. This evidence suggests that the Puff Adder is using chemical crypsis to hide from predators, the first time such a tactic has been documented in vertebrates.

Together, these studies remind us of the complex olfactory world that dominantes the lives of other animals, but to which we are largely oblivious. What other elaborate evolutionary games are being played in the field of smell?

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