What is coevolution?

Coevolution is a reciprocal change in the genetic composition of one species in response to a genetic change in another.  Coevolution is likely to happen when different species have close ecological interactions with one another.  These relationships include predator/prey, parasite/host, competition, and mutualistic species.

There are some species of plants which evolve a complex relationship with only one specific insect where they both can benefit.  Plant pollen is valuable because it contains the genetic material which needs to be passed on to the next generation.  When plants can be pollinated by more than one type of pollinator they risk their pollen being wasted on a different species of plant.  Not just any insect can access the sweet nectar of Angraecum sesquipedale. 

The story of Angraecum sesquipedale and its pollinating insect is a unique example of coevolution.  Samples of this orchid were collected from Madagascar in 1862 and sent to Charles Darwin.  Charles Darwin was impressed not by the beautiful star-shaped flowers, but the 30 centimeter long nectary.  Based upon his knowledge of evolution, Charles Darwin predicted there had to be moth with a proboscis long enough to reach the nectar.  In 1907 a moth was discovered on Madagascar which had a proboscis more than 20 centimeters long.  But it was not until 1992 when video evidence was collected showing the Angraecum sesquipedale being pollinated by the Xanthopan morganii, Morgan’s sphinx moth.  It only took 130 years to prove Darwin’s hypothesis.

An example of an evolutionary arms race between a predator and prey is that of the wax moth and bats.  The moths have developed as a defense against echolocating bats is to use their tympanal organs to produce ultrasonic sound in response to detecting the ultrasonic cries of echolocating bats. In some moth species, this acoustic response warns bats that the moths are toxic and unfit for consumption.  Another moth, the tiger moth, will emit an ultrasonic sound which acts a jamming device interfering with the bat’s ability to use echolocation.  Currently the moths are winning this race.

When an organism uses objects in their habitat to camouflage themselves it is not an example of coevolution.  To show coevolution, we need evidence that suggests that the prey have evolved in response to the predator and that the predator has evolved in response to the prey.  The decorator crab which uses pieces of its surrounding habitat to decorate its carapace is not an example of coevolution. 

Mimicry is an example of coevolution. Mimicry is when an organism has adaptive traits which copies a specific species or behavior.   The peacock butterfly if spotted and directly threatened will flash its conspicuous eye-spots to frighten the predator away.  The bee beetle looks and sounds a lot like a bumblebee. 

Many species have close, regular relationships with other species.  If both interacting species have reciprocal effects on the fitness of the other species, the two species may co-evolve.

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