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2.7: Coevolution and Natural Selection

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  • In the pollination story above, you saw the product of a long history of coevolution. Coevolution is driven by the slow accumulation of changes in organisms (mutations) that are then acted on by a process called natural selection. For example, a purple daisy could have a mutation that caused it to produce a sugary substance. All sorts of animals would be attracted to this -- ants, bees, birds, flies, beetles, and mammals. This might help the flower get its pollen spread around, passing the sugar-production gene on to its offspring, but a lot of pollen would be wasted in the process.

    Generations down the line, its offspring could have another mutation that caused it to produce a red pigment instead of purple. Birds are drawn to the color red and might visit the flower to investigate it, discovering and drinking the sugar, and picking up pollen during their visit. However, other animals would still be drawn to the sugar. If some of this flower’s offspring were to (completely by chance) develop a deeper place within the flower to store the nectar, then maybe only birds could reach it. If only birds were visiting the flowers, it is more likely that the pollen is being transferred directly to another flower of the same species.

    If so, the deeper flowers with sugar and red pigment would be more likely to reproduce and pass on their genes, perhaps resulting in even deeper flowers in future generations. Birds would need to keep up with these changes if they were to continue to access the sugary food source. Offspring with longer beaks would be able to access the sugar more easily, spending less work finding food and perhaps more energy could be devoted to mating, resulting in the longer beak genes passing on to future generations. In this way, flowers and their pollinators can coevolve through a mutual codependence and the accumulation of random mutations. Individuals with mutations that result in more successful pollination for the flower and (usually) more reliable food for the pollinator are more likely to reproduce and pass these genes on to future generations.

    Figure \(\PageIndex{1}\)

    How does the diagram on the right illustrate the process of natural selection? Circle the moths that will survive to pass on their genes.

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