The Fascinating World of Carnivorous Plants—How Hungry Are They?

DR Branch October 2018 Meeting

Laura Skates, a botanist and final year PhD candidate at UWA, captivated her audience at the DRB in October 2018. She started her talk by exploring popular cultures and the wonder or horror of carnivorous plants. From the Venus fly trap, known all over the world, to Victreebel (a pitcher plant Pokémon) seen eating people, to Audrey from the Little Shop of Horrors stage play and film.

She expounded that there are over 800 species worldwide, and many are under threat (Clarke et al, IUCN Red List 2017) from habitat destruction and poaching. The hierarchy of plants, herbivores and carnivores showed how predatory flowering plants are able to kill insects and animals to derive nutrition from their bodies. Most carnivorous plants are terrestrial, but there are some that are aquatic. WA has more carnivorous plant species in the Brixton wetlands, Kenwick than the whole of Europe.

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Above left: Aldrovanda vesiculosa        Above right: Utricularia menziesii (flower) (Laura Skates)

Carnivorous plants share three attributes that operate together and separate them from other plants.

  1. Capture and kill prey. Carnivorous plants pull off this trick using specialized leaves that act as traps. Many traps lure prey with bright colours, guide hairs, and/or leaf extensions.
  2. Have a mechanism to facilitate digestion of the prey. Once caught (most suffocate or drown in the enzyme juices) the prey is digested by the plant and/or partner organisms e.g. the Tree Shrew which uses Nepenthes Pitcher Plants as a toilet, feeding the plant with nitrogen rich faeces, or the resident hemipteran bugs (e.g Setocoris) that can live on sticky leaves without being caught and excrete nitrogen rich faeces.
  3. Derive a significant benefit from nutrients assimilated from the prey. Briefly her research methodology (to be published) is seeking to establish how much nitrogen the carnivorous plants obtain from prey, by comparing the natural isotope ratios of carnivorous plants to that of surrounding non-carnivorous plants and insect prey.
 
The pitcher plant Cephalotus follicularis, (Laura Skates)

Her work involved collecting from the Kimberly region plant leaves of two main carnivorous plant groups, the Sundews (e.g. Drosera banksii, burmannii and indica complex), and the Rainbow Plants (e.g. Byblis filifolia); as well as non-carnivorous plants and indigenous local insect prey. She is comparing the two methods of prey entrapment used by the plants to measure where they get their nitrogen for growth from.

Method 1: Sundews have semi-active traps where the prey lands on the leaves, sticks fast and is digested. The plant’s glandular tentacles are stimulated, adhere to the insect, and on many species the entire leaf coils around the prey. These motions are usually slow, taking minutes or hours to occur. An often-overlooked aspect of tentacle motion is the fact that a tentacle can bend in just about any direction. But when a bug is caught on a leaf, all the tentacles know the direction to bend towards.

Method 2: Byblis plants are also covered with sticky hairs. The plant does not exhibit any kind of prey-related motion. Prey that land on Byblis get snagged in the mucilage and die.

::Above left: Sundew Drosera zonaria; Above right: Two pygmy Drosera (Laura Skates)

Laura has discovered that both these plants, with different entrapment methods, morphology, habitat mutations, and symbiotic partnerships, gain over 60% of their nitrogen uptake from prey. This is looking positive for her research.

Arlene Quinn


References: All collected 13 Oct 2018

  1. https://www.iucnredlist.org/details/1141/0 Clarke et al (2017)
  2. Plants with bite (2018)
  3. Plants Are Cool Too! “The Pale Pitcher Plant” (Video 1) Martine.C and Koopman,M. (2011)
  4. Attenborough, D. The Private Life of Plants DVD Series 1.  (2003)