By Terry Ashley
Plants and animals have developed astonishing adaptations to ensure survival in the face of changing environmental conditions. From early stages of multi-cellular animal evolutions, retention of structures for specific functions is obvious. Think eating, digesting, eliminating waste, breathing, circulating nutrients. If you are an insect, you have mouth parts. If you are a salamander and have just evolved to life on land, gills aren’t sufficient. How about lungs? Salamanders have developed them through evolution. As an organ, they have evolved, but you can still recognize them as lungs in salamanders. Sure, hearts have evolved from two to four chambers, but again they are quite recognizable. This also holds at the cellular level. It would take a highly trained comparative histologist to distinguish between two microscopic sections of kidney or muscle, one from a lizard and one from a human.
In the plant world, members of the same family have developed different adaptations to survive. There is a group of plants that live in nitrogen deficient bogs and swamps and can’t get vital elements from the soil. They solve this problem by eating animals. But these different groups of carnivorous plants have evolved different solutions to capturing and digesting them. Sundews entice with red-colored mucus droplets. Once an insect sticks a leg on one of these droplets, it is trapped. Each droplet then secretes digestive enzymes and slowly absorbs the remains. Pitcher plants have different shaped hoods lined with downward pointing hairs. An entering insect finds itself on a one way journey to oblivion. Some hairs contain enzymes so digestion starts before the insect even reaches the bottom of the plant.
The most notorious of these carnivorous plants is the Venus flytrap. The trap consists of an intricate hinged leaf. The inside is bright red and has three trigger hairs. As soon as the trap is triggered by an insect stepping on two of the hairs, the two sides snap closed. Digestive enzymes get to work and absorption follows.
My favorite group is bladderwort. They live in water with even more highly modified leaves. Each “leaf” is a bladder, which dangles from stems like fishing lines supported by a platform of modified hollow stems. These bladders have an opening. When a microorganism enters, the change in osmotic pressure springs the trap. Digestion and absorption follows.
Most animals adapt to extreme changes in temperature by changing their environment. In cold weather, bears and many other species hibernate. Prior to sleeping through the winter, they stuff themselves to fatten up. In a somewhat analogous way, some plants seem to take an opposite tactic by shedding their leaves. But before that, they store sugars in their roots in the form of starch. You could also look at bulbs as hibernating. They are metabolically very active, however, undergoing meiosis to prepare for flowering and continuation of the next generation.
Survival in extreme heat is as essential as in supreme cold. In both cases, conservation is paramount. Animals have the disadvantage here. They must expend energy to move and seek water. Plants on the other hand are constantly regulating transpiration, or water loss, by opening and closing their stomata. These are cell complexes on the epidermis that respond to the rate of photosynthesis and amount of moisture in the air. Because plants are evolutionarily adapted to their environment, their anatomy is generally suited to the area where they are naturally located. But with climate change advancing, this will no longer hold true. Adaption can include thickness of leaves, wax or hairs in the leaves and stems, number and position of stomata, and many other modifications. Think barrel cacti, think water lilies, keep thinking. Plants also have backup strategies. In a drought, trees can shed their leaves sidestepping transpiration. The seeds of some plants have been shown to survive for hundreds of years. Many plants can produce asexually which bypasses the need for sex.
Breathing is essential to all organisms. While animals have developed gills and lungs for this purpose, plants rely on their individual cells. Remember the stomata. Both plants and animals ultimately depend on subcellular organelles called mitochondria as we approach the molecular level.
While it’s true plants can’t move by themselves, they have found ways around this. In fact, seeds can move themselves in the wind — and the smaller, the farther. Seeds of aerial orchids are as small as fungal spores and can be carried around the globe in a hurricane. If you have walked through a field or meadow in late summer, you and other mammals have done your share of dispersing. (Those that that arrive home on your pant legs don’t count!) The champion of this group is burdock. The clinging of this weed seed prompted George Mestral to study its microstructure and copy it to invent Velcro. Birds help by eating and dispersing seeds through their waste. To germinate, the Galapagos tomato needs to pass through the digestion tract of a Galapagos tortoise to scar the hard shell of the seed.
Maybe you helped disperse dandelion seeds as a child — you and the wind. Scientists are now studying other ways humans have influenced plant and animal evolution through land development, pollution, and other environmental disturbances. As climate change persists, it’s a race against time to understand and triage species in distress.
Terry Ashley has always been fascinated by plants. From a young age she was asking questions like, “Why aren’t Indian Pipes green?” She earned a bachelor’s degree in botany from Duke University, where her favorite course was Plant Anatomy. There she began to learn how plant cells hold the key to how plants adapt to their environment. She earned a Ph.D. in genetics from Florida State University, and followed a career in the microscopic study of the cells that produce mammalian sperm, at Oak Ridge National Laboratory and the Department of Genetics at the Yale School of Medicine. A Gainesville, FL, native and accomplished fine arts photographer, she loves to take a picture of a plant and combine it with a microscopic image of cells of the same species. In retirement, she continues to ask questions, with a current focus on rare and endangered plants and factors that lead to their survival/extinction.