Choice of Plant Reduces Parasite Load

an orange and black female monarch butterfly lays a black egg on an Asclepias curassavica, or tropical milkweed, stem, which is tall and green with small orange and yellow flowers

Biological Strategy

Tropical milkweed

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Image: Derek Ramsay/ DerekRamsay.com / Wikimedia Commons / Some rights reserved

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 Disease in a Living System

Living systems that can detect diseases within themselves, or within other living systems, can direct resources toward curing those diseases or preventing their spread. This type of sensing environmental cues is not well known, probably because of the difficulty studying disease detection, including the difficulty in providing scientific proof. However, there are a few known examples, such aschimpanzees that detect illness in themselves and self-medicate through eating plants with medicinal benefits.

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Protect From Microbes

In living systems, microbes play important roles, such as breaking down organic matter and maintaining personal and system health. But they also pose threats. Bacteria can be pathogens that cause diseases. Some bacteria create colonies called biofilms that can coat surfaces, reducing their effectiveness–for example, inhibiting a leaf’s ability to photosynthesize. Living systems must have strategies for protecting from microbes that cause disease or become so numerous that they create an imbalance in the system. At the same time, living systems must continue living in harmony with other microbes. Some living systems kill microbes. Others repel without killing to reduce the chances that microbes will adapt to the lethal strategy and become resistant to it. For example, some pea seedlings exude a chemical that inhibits biofilm buildup.

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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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Monarch butterflies infected with parasites capable of infecting their offspring avoid transmission by selectively laying their eggs on plants containing therapeutic remedies.

The parasitic protozoan, Ophryocystis elektroscirrha, is known to infect monarch butterflies and produce extremely deleterious symptoms. Caterpillars ingest parasitic spores inadvertently scattered on leaves by their mothers during egg laying. After the parasite enters the body of the caterpillar, it reproduces rapidly and consumes a significant portion of the host’s nutrient intake. During pupation, the parasites produce millions of spores that cover the nascent wing scales of the developing adult butterfly. These spores are shaken off onto leaves during egg laying, thereby starting the cycle over again. Infected adults have not been observed self-medicating their own parasitic infection, but they preferentially lay their eggs on a specific species of milkweed (Asclepias curassavica) that contains compounds capable of fighting infection when consumed by their caterpillars. The anti-parasitic properties of A. curassavica are thought to be due to their special suite of cardenolides including several non-polar varieties that interfere with parasite ATPase enzymes.

Last Updated August 23, 2016

References

Journal article

Evidence for trans-generational medication in nature

Ecology Letters | 07/10/2010 | Thierry Lefèvre, Lindsay Oliver, Mark D. Hunter, Jacobus C. De Roode

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