Answer :
The less armored fish are more likely to live and reproduce when a school of fish transitions from saltwater to freshwater.
What is the difference between freshwater and marine sticklebacks?
- Stickleback, any of the eight or so species of fish in the family Gasterosteidae (order Gasterosteiformes) found in temperate fresh, brackish, and marine waters as far north as the Arctic Circle
- Additionally, they often have 12 or fewer armor plates than marine counterparts and shorter dorsal and pelvic spines. In fact, a lot of freshwater sticklebacks lack even their armour plates and pelvic spines.
- Although certain sticklebacks can be found in fresh water, they are indigenous to the temperate zone and are most frequently seen in the ocean.
- Following the Ice Age 10,000–20,000 years ago, freshwater taxa were imprisoned in Europe, Asia, and North America, where they underwent distinct evolutionary processes than marine species.
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Low-armored sticklebacks are more common in freshwater because their reduced armor allows for quicker growth and higher speed, helping them evade predators like dragonfly larvae. This is an outcome of the species evolving from saltwater to freshwater varieties over thousands of years, adapting to different freshwater environments and the unique challenges they present.
Freshwater environments contain a greater number of low-armored sticklebacks because of the evolutionary adaptations that improve their survival and reproductive success in these habitats. The three-spined stickleback (Gasterosteus aculeatus) evolved from a saltwater fish to a freshwater fish around 10,000 years ago. These sticklebacks then became isolated in different lakes, leading to genetic variations and evolutionary divergence based on micro niches used for feeding. The low-armored variety has advantages in freshwater such as rapid growth and increased speed, which reduce their vulnerability to predation by dragonfly larvae. This example of rapid evolution demonstrates how populations adapt to specific environmental pressures, resulting in traits that are beneficial for their survival in those conditions.
