Examine threespine stickleback evolution from a systems perspective
Examine threespine stickleback evolution from a systems perspective
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We have known that all sticklebacks found in the population invading Loberg Lake after 1982 were complete-plated. However, the number of complete-plated sticklebacks drastically dropped from 96% to 11%, while the number of low-plated sticklebacks significantly increased from 0% to 75% in 12 years [2]. A super simple explanation for this change could be that the population evolved. But, we can gain a deeper understanding by answering the following questions:
Where did the low-plated stickleback come from?
What led to the decrease in complete-plated sticklebacks in the population?
What led to the increase in low-plated sticklebacks in the population?
Let's examine a stickleback population from a system perspective to answer these questions.
A Threespine Stickleback Population as a Complex System
A Threespine Stickleback Population as a Complex System
It's easy to recognize that a stickleback population is a complex system.
Elements: All the sticklebacks possess similar characteristics but are not exactly the same. The characteristics relevant to our questions are the number of lateral plates. In the new population, although all sticklebacks were classified as complete-plated, some individuals still had more plates than others. These sticklebacks could behave based on their own rules. There are many predatory insects, i.e., dragonfly larvae, in Loberg Lake.
Interactions: Interactions occurred among sticklebacks and between sticklebacks and their predators. Among sticklebacks, these fish 1) compete for food, nest resources, and mates, and 2) mate to reproduce offspring. Between sticklebacks and their predators, 1) the predators always prey on sticklebacks, and 2) complete-plated sticklebacks are more likely to escape from predatory fish after being caught, while low-plated sticklebacks are more likely to outgrow and escape from predatory insects.
Decentralization: There is no central control over the stickleback population. Each stickleback reacts to its surroundings based on its own goals (e.g., seeking food and mates) and rules.
Stochasticity: The number of lateral plates is determined by the Eda gene. Complete-plated is the dominant trait, determined by genotypes (AA) or (Aa), while low-plated is the recessive, determined by (aa). There is a certain probability that allele (A) can mutate to generate allele (a) [11-12].
The decrease in complete-plated sticklebacks and the increase in low-plated sticklebacks in Loberg Lake is an emergent phenomenon, which can be explained based on the elements, interactions, decentralization, and stochasticity of the stickleback population. Consider the explanation yourself before unfolding the answer.
The decrease in complete-plated sticklebacks and the increase in low-plated sticklebacks in Loberg Lake is an emergent phenomenon, which can be explained based on the elements, interactions, decentralization, and stochasticity of the stickleback population. Consider the explanation yourself before unfolding the answer.
Emergence: The complete-plated sticklebacks invaded and settled in Loberg Lake. Some of the sticklebacks were preyed upon by dragonfly larvae, but others survived. As the sticklebacks mated and reproduced, mutations occurred, creating a new allele (a). After several generations, a small number of recessive individuals, known as low-plated sticklebacks, began to appear. Because low-plated sticklebacks could grow faster and escape dragonfly larvae predators than complete-plated sticklebacks, more low-plated sticklebacks survived and reproduced. Over time, with these interactions continuing, the population of complete-plated sticklebacks decreased while the number of low-plated sticklebacks increased.
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