Category Archives: evolution

Faking it as a survival strategy

224139Cheats and Deceits: How animals and plants exploit and mislead. By Martin Stevens. Published by Oxford University Press (2016).

Last year, on a trip to Devon, I saw my first ever oil beetle (Meloe proscarabaeus). She was beautiful. Her black carapace glistened violet and blue in the sunlight. She was gravid and crawling along the footpath in search of a place to dig a nest burrow to lay her eggs. But what I did not yet appreciate was the extraordinary life cycle of these captivating beetles. The young of a related species, Meloe franciscanus, emerge from the nest and swarm up a nearby plant where they congregate in a mass mimicking the shape of a female solitary bee (Habropoda pallida) and release a chemical compound similar to the bee’s sexual pheromones.  This proves all too irresistible to male bees who are drawn to this aggregation and attempt to mate with it, presenting the larvae with the perfect opportunity to grab hold of the bee and clamber onto his back.  He then carries these passengers with him until he finds a female to mate with at which point the larvae instantly decamp onto the female. From here they then transfer to her nest where they devour the stored nectar, pollen and the bee’s eggs. The evolution of this complex mimicry is absolutely fascinating and forms part of Martin Stevens‘ interrogation of deception in Cheats and Deceits: How animals and plants exploit and mislead.

This book is an immensely informative and enjoyable exploration of the multiple roles deception plays in nature. Stevens sets out a detailed examination of a wide variety of instances of natural deception from well documented examples such as the evolution  of camouflage through industrial melanism in the Peppered Moth (Biston betularia) to current research into the resemblance to falling leaves in the movement and colouration of Draco cornutus, a gliding lizard from Borneo. It is to Stevens’ credit that this book makes for entertaining and effortless reading while clearly citing all the relevant research within context and pointing to areas where knowledge is still lacking.

The language of deception is important. Stevens takes the time to explain some of the more commonly used terms associated with deception such as camouflage (blending in to the environment), mimicry (assuming the appearance – be that visual, chemical, behavioural or acoustic – of another organism) and masquerade (taking the form of an inedible object – as with stick insects). Mimicry and masquerade therefore lead to misidentification while camouflage reduces detectability or impairs recognition. Mimicry also comes in various guises some of which can be described as: aggressive, when predators mimic harmless species to enable prey capture; Batesian, when a palatable species mimics the characters of an unpalatable species, as seen in the chicks of an Amazonian bird Laniocera hypopyrra mimicking toxic caterpillars; and imperfect mimicry, as with hoverflies roughly resembling certain species of wasps and bees (for which there are a number of competing theories).

This, of course, only scratches the surface of a vast area of research that Stevens specialises in as head of the Sensory Ecology and Evolution group at the University of Exeter where he continues to research these themes. His enthusiasm for his topic is highly infectious; you find yourself transported from an explanation of background matching in cuttlefish, to an historical aside concerning the development of military camouflage, and on again to a description of his own field experiments in testing the efficacy of disruptive colouration.

“We must trust to nothing but facts: these are presented to us by nature and cannot deceive. We ought, in every instance, to submit our reasoning to the test of experiment, and never to search for truth but by the natural road of experiment and observation.” ~ 18th-century chemist Antoine Lavoisier

The book does rely heavily on zoological examples, and although Stevens doesn’t entirely neglect plants his observations do tend to mainly focus on carnivorous plants and orchids. But to be fair, Stevens does make the point that more research into botanical forms of deception is required and suggests that this should be undertaken with a view to specifically exploring the roles of chemical signalling and sensory exploitation. One of the examples cited in the book is the orchid Epipactis veratrifolia which attracts female hoverflies to lay eggs on the plant by releasing chemicals that mimic the alarm pheromones of aphids (the food source of hoverfly larvae). This may rather be a means by which the orchid exploits an inbuilt perceptual preference for chemicals associated with hoverfly larval food sources – either way the plant is deceiving the insect in order to  ensure protection from aphid infestation.

A form of deception more commonly associated with orchids is that of exploiting male insects to pollinate plants by mimicking the female form through the shape and colouration of the flower. However, Stevens points out that this mimicry is sometimes (as in Cryptostylis orchids) not particularly convincing to human eyes, but is overwhelmingly so to the male wasp which tries to mate with the flower and thus collects the pollinium which will be deposited at the next Cryptostylis flower that he visits. With this example (as with the oil beetle, among others) the author cautions researchers of deception in nature to be aware of anthropocentric biases that may arise through our observations and study, and to (wherever possible) approach our subjects in the manner and with the senses of the deceived species.

I am utterly delighted and inspired by this book and am certain that I will return to it again and again as a point of reference. I have no hesitations in highly recommending it to researchers, field naturalists and those with a passing interest in natural history.

Postscript

At the time of writing, Phil Torres and Aaron Pomerantz have discovered and documented kleptoparasitism of ants in a species of butterfly (Adelotypa annulifera) in the Peruvian Amazon which they believe might mimic ants through their wing patterns. This seems to me an ideal opportunity for further research looking at visual and chemical mimicry given both the wing patterns and larval associations.