CARNIVOROUS PLANTS

Adapt

toEntrap

A LOOK AT IRELAND’S CARNIVOROUS PLANTS BY ANNE SUNDERMANN

Convergent evolution occurs when unrelated species independently adapt to similar circumstances in the same manner. A prime example is the emergence of carnivorous plants worldwide. Without important minerals such as nitrogen and phosphorus, a plant would not be able to survive, and several unrelated plants have adapted to a nutrient-deficient habitat by adopting methods of capturing and digesting insects, arthropods, and other invertebrates.

First and foremost, a carnivorous plant is an angiosperm (flowering plant) that can attract, capture, and digest animal prey. Carnivory in plants is estimated to have developed between 60-130 million years ago, after the advent of angiosperms and insects. Many of the carnivorous plants developed moving parts to actively catch prey. At a molecular level, carnivorous plants have evolved enzymes to support digestion and absorption of nutrients.

IRISH INSECTIVORES Ireland hosts 11 different species of carnivorous plants, belonging to four distinct groups: sundews (three species), butterworts (three species), bladderworts (four species), and a non-native pitcher plant (one species). Each use a different mechanism to catch and digest live prey. Most of Ireland’s carnivorous plants grow in moist, acidic soils of Ireland’s bogs, where the major source of nitrogen, phosphorus, and other nutrients will be derived from captured and digested invertebrates. • The sundew, genus Drosera, ensnares prey on its adhesive-covered tentacles on their leaves. The sundews are distinguished by their leaf shape, with the round leaved D. rotundifolia being most common in Ireland. • The aquatic bladderwort, genus Utricularia, uses underwater appendages, or bladders to entrap and hold live insects, not unlike a suction cup. The bladderwort lives off algae and insects found in peat bogs and can be free-floating or attached. In summer, thin stalks break the water’s surface, from which the plant sends forth yellow blooms. • Butterwort, genus Pinguicula, secretes a greasy substance through cuticular holes or gaps in the leaf. Pedunculate glands on butterwort leaves act as a glue trap and initiates digestion. At that point, the sessile glands release a large cache of enzymes. Leaves may roll up to pool the fluids, speeding digestion. Butterwort leaves die back during winter dormancy. • The pitcher plant, Sarracenia purpura, is Ireland’s lone non-native species. Unlike other Irish carnivorous species, the pitcher plant uses a passive means to capture insects, drowning them in a reservoir of digestive juices at the base of the pitcher.

"A PLANT OF DROSERA, WITH THE EDGES OF ITS LEAVES CURLED INWARDS, SO AS TO FORM A TEMPORARY STOMACH, WITH THE GLANDS OF THE CLOSELY INFLECTED TENTACLES POURING FORTH THEIR ACID SECRETION, WHICH DISSOLVES ANIMAL MATTER, AFTERWARDS TO BE ABSORBED, MAY BE SAID TO FEED LIKE AN ANIMAL".

The sticky leaves of the sundew by James O’Neill

NATURAL SELECTION In his 1875 book Insectivorous Plants, Charles Darwin applies his theory of natural selection to the ability of plants to adapt to less-than-optimal conditions. He particularly noted the adaptations of sundew (Drosera): A plant of Drosera, with the edges of its leaves curled inwards, so as to form a temporary stomach, with the glands of the closely inflected tentacles pouring forth their acid secretion, which dissolves animal matter, afterwards to be absorbed, may be said to feed like an animal.

In the natural selection game, there is usually a cost to any evolutionary benefit. In this case, the adaptations of a plant that can trap and ingest animal protein solves one problem—providing much needed nutrients to supplement photosynthesis in less than desirable habitats. But the evolutionary invoice comes due in myriad ways.

Researchers who have undertaken study of the cost and benefits of carnivory consistently cite the habitat range—restricting carnivorous plants to moist, nutrient-poor sites that receive a lot of sunlight— as the major trade-off between efficient photosynthesis and active carnivory.

Trapping mechanisms are a huge energy sink for carnivorous plants. For example, the aquatic bladderwort plant has to react in a split second to pump out water, creating negative pressure to suck its intended prey into the bladder.

 Butterwort and prey by James O’Neill

Digestion of that prey calls for another evolutionary barter. Energy created during photosynthesis needs to be further refined into food the plant can use, via respiration. It has been found that carnivorous plants trade up to one-fifth of their respiration capacity to accommodate the metabolic pathways needed for digestion.

Most plants have a suite of proteins that are commonly used to break down the common polysaccharide chitin, primarily to protect the plant from fungi and other pathogens. At a molecular level, more than a few carnivorous plants have independently altered chitin-dissolving proteins to focus on animal prey digestion. A few of those proteins are being studied for their antifungals and antibacterial properties.

It has been shown that thriving populations of carnivorous plants need water, nutrient-deficient soil, and ample sunlight. As such, most of Ireland’s carnivorous species find a home in its bogs and wetlands. Protection and preservation of these habitats are of increasing importance, not the least for the adaptive carnivorous plants found within.