A Mouthful of Sand: A Plant Defence Mechanism?

A study conducted by LoPresti & Karban (2016), studied an interesting defense mechanism the Abronia latifolia  and Navarretia mellita use to protect themselves against herbivory.

The plants use a mechanism called “psammophory”. Haven’t heard of that term before? Don’t worry it’s just a fancy way of saying that the plants like to cover themselves with sand. Due to both plants growing in relatively dry and dune like climates they adapted a mechanism of protection by using sand to ward off predators. The plants were able to cover themselves in sand because they were adapted to be really sticky or small and spikey so that the sand would stick to them and ward off predators?

So why sand? One would think that having toxic compounds would provide a better source of protection for a plant….

The researchers asked themselves the same question, although they hypothesized that maybe the sand acted as a camouflage for the plants to disguise them from predators.

So they did the next logical experiment, try covering the plants with green (to mimic the plants natural color) vs tan sand. The results actually showed that herbivory predation on the plants remained the same for both conditions, making it unlikely that the defense mechanism relied on disguise.

Instead the researchers found out that the mechanism that defended the sandy plants, was that the predators did not like eating sand! They concluded this because when comparing the plants that were clean and free of sand vs. the sandy plants, those that were covered in sand faired much better. In fact among sandy pincushion plants, only 1 out of 19 got beheaded (rabbit predator), compared to 8 out of 18 sand free plants.

Therefore, sand “armour” proved to be an effective defense mechanism for these plants among their predators. I guess for these plants being covered in sand is a small price to pay for protection!

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Image:  Abronia latifolia  and Navarretia mellita use sand to protect themselves against herbivory.

References:

LoPresti, E. F., & Karban, R. (2016). Chewing sandpaper: grit, plant apparency and plant defense in sand-entrapping plants. Ecology, n/a-n/a. JOUR. http://doi.org/10.1890/15-1696

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