Wild Potatoes Trick Attackers Into Sensing Danger

Biological Strategy

Wild potato

Anika Hazra

Image: Plant Resistance Gene Wiki / PRG Wiki / CC BY SA - Creative Commons Attribution + ShareAlike

Respond to Signals

To interact with its environment, a living system must not only sense a variety of signals, but also respond to them. To be energy- and material-efficient, those responses must be appropriate to the signal. This generally requires sensing thresholds to trigger an appropriate level of response (for example, hiding under a shrub versus running away to avoid a predator). Response strategies are tied to a specific signal and often have a response threshold, which determines how strong a signal must be to warrant expending energy to respond. One example is a plant that lives in arid regions in South Africa. Its seed capsules remain closed until rainfall triggers them to open to release the seeds. But the plant only responds to a second rainfall, thus protecting against releasing its seeds before there is enough sustained water for them to grow.

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Sense Touch and Mechanical Forces in a Living System

Perceiving touch enables living systems to detect other living systems around them and environmental conditions, such as air movement, water currents, and temperature. This ability can help them sense danger as well as opportunity, as when a Venus flytrap’s hairs sense the presence of an insect to eat. Sometimes, a living system senses touch or mechanical forces at a coarse scale; other times, at a sensitive scale that detects very subtle differences. For example, a human elbow is not nearly as sensitive to textures as human fingertips. Fingertips have dermal ridges and many nerve endings that increase sensitivity, enabling them to explore the environment in detailed ways. Elbows don’t need to sense at that level of detail.

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Chemically Assemble Organic Compounds

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Protect From Animals

Animals–organisms that range from microscopic to larger than a bus–embody a wide variety of harms to living systems, including other animals. They threaten through predation, herbivory, defense, and parasitism, and they compete for resources such as water, nutrients, and space. Any given living organism commonly faces threats from a variety of animals, requiring strategies that effectively defend from each. Trout and other bony fish, for example, escape predators by having scales made of very thin, flake-like pieces of bone covered with slippery mucus. They also have behavioral strategies such as camouflage, fast swimming, and twisting and turning to achieve release from a predator’s grip.

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Flowering Plants

Clade Angiosperms (“receptacle seed”): Dandelions, oaks, grasses, cacti, apples

With 416 families containing some 300,000 known species, angiosperms are the most diverse group of plants, and they can be found around the globe in a wide variety of habitats. They are characterized by seeds that grow enclosed in ovaries, which are enclosed in flowers. The floral organs then develop into fruits of myriad kinds and dimensions, from simple seed casings on maples to elaborate fleshy growths like papayas. The oldest flower known from fossils, Montsechia vidalii, appeared during the Jurassic Period 130 million years ago. They are the primary food source for herbivorous animals, which in turn makes them the indirect food source for carnivores as well.

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The glandular hairs on wild potato plants expel a pheromone that mimics the alarm pheromone of their aphid predators

Introduction

In the never-ending give-and-take between plants and the organisms that feed on them, many have evolved sophisticated methods of deceiving their attackers. The wild potato (Solanum berthaultii), native to Bolivia, defends itself from aphids by emitting a pheromone that mimics the insects’ own alarm pheromone, thereby distracting the insects with a false danger.

The Strategy

When attacked by predators, aphids emit a chemical signal that acts as an alarm to other aphids nearby, giving them a head start to flee from the area. The wild potato has adapted to put this behavior to work as a defense of its own. Potato plants expel a pheromone similar enough to the aphid alarm pheromone to have the same effect, causing the destructive insects to disperse. The aphids keep a distance of 1-3 mm. Even entire colonies that have already settled on the plant take off when exposed to this pheromone mimic.

The wild potato’s defense pheromone is released from two types of tiny hairs on its leaves and stems: the type A hairs, which are shorter and rupture when touched to expel the pheromone, and the type B hairs, which form drops of the pheromone at their tips.

Image: Walter S. De Jong / Spud Smart /

Leaves of the wild potato (Solanum berthaultii) covered in hairs

Having both types of hairs is to the wild potato’s benefit, as the type A hairs trap aphids with their fast-shooting pheromone fluid while the type B hairs get entangled with aphids. The movement from struggling aphids caught in type B hairs leads to more type A hairs rupturing and releasing more of the pheromone.

The wild potato’s pheromone works because it contains (E)-β-farnesene—the main component of the alarm pheromone for many aphid species. It’s likely that the type B hairs on the wild potato plant are the principal source of this chemical compound.

Image: Plant Resistance Gene Wiki / CC BY SA - Creative Commons Attribution + ShareAlike

Close-up view of the fruit of the wild potato (Solanum berthaultii)

The Potential

The cultivated potato, a major food crop, is also fed on by aphids, but unlike its wild relative, it doesn’t have its own pheromone mimic to protect itself. Incorporating the wild potato’s pheromone mimic in pesticides for cultivated potato plants could protect this food staple from aphids (and the viruses they carry), and improve crop production.

It is worth conducting research on how the wild potato’s glandular hairs release (E)-β-farnesene as well, since it is an unstable and highly volatile compound that dissipates quickly. In addition to giving the cultivated potato and other crop plants the protection afforded by (E)-β-farnesene as a natural pesticide, this research could inform the development of technologies for dispersing (E)-β-farnesene so that its effects are longer-lasting.

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References

“The aphid Myzus persicae(Sulzer) is re-pelled, at a distance of 1-3 mm, from leaves of the wild potato Solanum berthaultiiHawkes. In addition, air from above the foliage Induces rapid dispersal of settled aphid colonies, behaviour similar to that of aphids exposed to the aphid alarm pheromone, (E)-β-farnesene.” (Gibson & Pickett 1983:608)

“Resistance to all these pests has been associated with the abundance of glandular hairs covering its leaves and stems. The glandular hairs are of two types: the so-called type A hairs have a short stalk and a four-lobed head which ruptures when touched to release a quick-setting fluid, andthe type B hairs which exude a sticky droplet at the tip.” (Gibson & Pickett 1983:608)

Journal article

Wild potato repels aphids by release of aphid alarm pheromone

Nature | 1983 | R. W. Gibson & J. A. Pickett

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