Plant-Animal Adaptations

Plants and animals often evolve by adapting to each other; for example, plants evolve defenses against herb ivory (animals feeding on plants).Spiny cacti, poisonous hemlock, thorny rosebushes, and prickly thistles are all familiar examples of defended plants. A more unusual and particularly unpleasant defense is used by plants in the milkweed family, which get their common name because their leaves and stems, when cut, ooze a white sap. However, only in appearance is the sap milky-it is sticky and thick and, in many species, it has chemical irritants that make it even more noxious to touch or taste. Nevertheless, many insects are able to feed on milkweed. Milkweed beetles overcome this defense in an innovative way by biting repeatedly into the midrib central vein) of the milkweed leaf. The sap leaks out through the bite holes before it reaches the tips of the leaves, where the beetle can then feed without its mouthparts becoming too full and sticky. This isn’t good for the plant because midrib cutting and feeding reduce the plant’s ability to photosynthesize (convert sunlight into chemical energy for food)

While roots, stems, and leaves are often defended, fruits and flowers have evolved to attract animals. Most ripe fruit is red or black, such as raspberries and blackberries. Is this because these colors have evolved to attract frugivores ( fruit eaters) that will disperse the seeds? Birds, 0ne of the main frugivores have four types of retinal cones (cells responsible for Seeing color) that give them excellent color vision. Foraging birds do prefer red and black fruits-but not because they are attracted to the color itself. Instead, red and black fruits contrast well with the typical green background of foliage, and it is this contrast that attracts birds.

Flowers have also evolved visual cues attractive to pollinators. Many plants rely on animals for sexual reproduction. A bee, hummingbird, bat, or other pollinator that visits a flower is dusted with pollen.As it moves from flower to flower, it transfers the pollen and flowers are fertilized. Many plants have evolved means of enticing pollinators to visit, such as by offering nectar rewards. Some flowers have markings called nectar guides that act like runway lights, indicating where to land and directing pollinators to the part of the flower where the nectar is stored. Even flowers that appear white may have nectar guides: bees and many other insects can see in the ultraviolet, and many flowers have markings that are visible only under ultraviolet light. Other flowers offer specialized rewards. Flowers that are pollinated by carrion flies (which feed on dead flesh) are not recommended for household decoration-their putrid odor has evolved to attract their pollinators ,not humans. An especially clear example of a coadaptation between plants and pollinators comes from a species of hummingbird that feeds on two species of Heliconia. Female birds have a long, curved bill that matches the long, curved flowers of their preferred flower species, H.bihai. The short, straight bill of the male matches their preferred flower, H. caribaea.

A different approach to herb ivory is taken by species that cultivate some or all of the food they need Agriculture has evolved independently in three insect orders:ants, termites, and ambrosia beetles. Leaf cutter ants cut fresh leaves and carry the pieces back to the nest under the ground. There they encourage the growth of a special fungus on the leaves. This fungus, whose existence is unknown outside the ant nests, is the primary food source for these ants. The ants prepare their fungus gardens by licking the leaves on both sides to remove the waxy layer covering the leaf and reduce the population of microorganisms that might compete with the desired fungus. The leaf fragments are then chewed to a pulp, placed in the fungus garden, and mixed into the fungus structure. This preparation makes the leaves a richer source of nourishment for the fungus. The ants are attentive farmers. When they tidy their gardens, they collect debris and compress it into a pocket inside their mouth. This pocket functions as a sterilization area that kills the spores of a garden parasite. Sterilization is caused by bacteria that live inside the pocket and produce antibiotics.

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1.Plants and animals often evolve by adapting to each other; for example, plants evolve defenses against herb ivory (animals feeding on plants).Spiny cacti, poisonous hemlock, thorny rosebushes, and prickly thistles are all familiar examples of defended plants. A more unusual and particularly unpleasant defense is used by plants in the milkweed family, which get their common name because their leaves and stems, when cut, ooze a white sap. However, only in appearance is the sap milky-it is sticky and thick and, in many species, it has chemical irritants that make it even more noxious to touch or taste. Nevertheless, many insects are able to feed on milkweed. Milkweed beetles overcome this defense in an innovative way by biting repeatedly into the midrib central vein) of the milkweed leaf. The sap leaks out through the bite holes before it reaches the tips of the leaves, where the beetle can then feed without its mouthparts becoming too full and sticky. This isn’t good for the plant because midrib cutting and feeding reduce the plant’s ability to photosynthesize (convert sunlight into chemical energy for food)

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