Evolution of Flightless Birds and the Shrinking Cod

How did flightless birds evolve? How did the evolution of the shrinking cod come to be? In this lesson, we learn about the evolution of the flightless birds, such as cormorants, and the evolution of the shrinking cod in our biology selection case studies. Let’s go!

The evolution of the flightless birds: From penguins to the double-crested cormorants pictured above

Evolution of the Flightless Birds

1.         Long time ago, birds like the cormorants from mainland swam or flew to the island, guided by winds or storm, etc. Since the island had no predators and there were lots of food, the cormorants had no trouble surviving and reproduced well. Over time, probably, they did not need to use their wings to fly to catch prey because there was plenty of food in the water or on the ground. Because there were lots of food in the sea, they just need to swim well.

Natural Selection on Flightless Birds

However, their wings slowed them down from catching food in the water. Even though the population was successful at a point, there was competition among the birds and at one point there was a shortage of food. The population from natural variation had birds with small and big wings, varying in sizes. It is most likely, the ones with smaller wings were able to swim faster than the ones with larger wings, due to less water resistance, and survive better with more food. The birds with smaller wings survived, and through natural selection (VIST) their favorable trait of smaller wings were passed on, inherited by the offspring, due to more reproduction from survival. Slowly, the cormorants’ wings became smaller with less use of them and natural selection. This caused a different gene pool in the population of cormorants, changing into flightless birds.

To Fly or Not To Fly?Selection Pressure in Evolution of the Flightless Birds

2.         a.  One selection pressures for short wings/ flightlessness is the fact that there were no predators in environment, so they don’t need their wings to fly away from danger. Another selection pressure is that there was plenty of food; thus, there was no point in flying around to catch food. Also, the cormorants were surrounded by the sea, with lots of water and food in it, so this environmental pressure caused them to get more food from the sea, and short wings helped them catch more food with less water resistance. Moreover, since there are no trees mostly on the island, the birds do not need their wings to fly up and build nests. This was good for short winged ones, who can easily build nest on the ground.

            b. A selection pressure against long wings/flight is harsh wind flow, like wind storms, preventing the birds to take flight and keeping them on the ground most of the time. Another selection pressure against is that most food were on ground or in water, so there was no point in having wings that slowed the birds down in the sea to catch fish.

Comorarants are flightless birds used to help with fishing. They have vestigial wings!

3.         Most flightless bird species still have vestigial wings, but since the wings are so useless and small now, they do not get in the way with catching food. Therefore, the wings are still there. It’s like how we humans have the appendix, that used to help our ancestors’ digestive system, but since it doesn’t interfere with our digestive system, it’s still there but not gone. Likewise, the cormorants’ wings are still there. Another factor is that it would take a very, very long time until the wings are totally gone.

4.         Humans and their introduced predators are threatening the cormorants’ survival. It is likely they will evolve wings in response, but they will do that very slowly. However, since their population is dwindling, it is likely that there would not be a wide range of gene pool and genetic diversity. This could potentially affect their survival before possible larger wings traits to be passed on to their future generations.

Shrinking cod as a fish filet, mmm yum 🙂 but what’s the evolution causing the cod to shrink?

Evolution of the Shrinking Cod:

1.         The Northeastern Arctic cod were originally big when they were grown to adult size. People caught them near the coastal spawning regions. Through natural variation, different cod had different sexual maturity time. The slower it reaches sexual maturity, the larger it grows. Before humans started catching cod in their feeding grounds, cod with delayed sexual maturity had an advantage of not being caught at the spawning grounds. Thus, they stayed at feeding grounds longer (later age) and grew to a large size before going to spawning grounds.

As a result, by natural selection more cod passed on their favorable traits of slow sexual maturity. However, later, people used motorized fishing boats with nets, going into feeding grounds, which consisted mostly tiny immature fish. The cod who already left the feeding grounds were the ones with fast sexual maturity. Consequently, the cod’s slow sexual maturity suddenly proved unfavorable but still favorable for the really slow maturing cod, small enough to escape through holes in net. This caused the change in the cod population in which the cod with really slow maturation survived better because they were small enough to escape through nets, and thus, cod are becoming smaller.

Natural selection on fish

2.         The shrinking cod is an example of natural selection because the humans’ catch interference is just like one of the many selection pressures of the environment. The humans are predators, and the fact that the cod is ‘shrinking’ is simply their way to adapt to their environment and escape better from their predators. Also, it is not artificial selection because the humans are not specifically choosing which ones are going to mate and pass on their traits, like actually putting all the small cods to mate and not letting big ones mate, etc. Even if it was artificial selection, the humans would not benefit this with smaller cod to eat, so this is an example of natural selection.

3.         Many people are concerned about the shrinking fish because they get less meat from these small fish and also the fishes’ commercial value is lowered, proving harm to fish industries. To solve this problem, we can make aquatic fisheries, where we breed cod fish and wait until they’re big and then eat them. We can also possibly breed larger fish and send them into ocean and make them breed small ones, bringing the population to become bigger.

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