99. Which one of the following statements supports the concepts of trade-off in the evolution of life history trades
    (1) Level of parental care and clutch size are positively correlated
    (2) Animals mature in early tend to live longer
    (3) An increase in the seed size is usually associated with the decrease in the seed number.
    (4) Allocation of higher energy for reproduction leads to higher population growth

Introduction

In evolutionary biology, the concept of trade-offs is central to understanding how organisms allocate limited resources to maximize their fitness. Life history trade-offs occur when an increase in one trait leads to a decrease in another due to resource constraints. One of the most widely recognized trade-offs in life history evolution involves the balance between the number and size of offspring.

What Are Life History Trade-Offs?

A trade-off in life history traits means that improving one aspect of an organism’s biology often comes at the expense of another. This is because resources such as energy, nutrients, and time are finite. The Principle of Allocation states that investing more in one function (like reproduction) leaves fewer resources for others (like growth or survival).

Classic Example: Seed Size Versus Seed Number

Among the statements given, the one that best illustrates the concept of trade-off in life history evolution is:

An increase in the seed size is usually associated with the decrease in the seed number.

This reflects the classic offspring size versus number trade-off. If a plant invests more resources into making each seed larger (to improve the survival chances of each individual offspring), it will have fewer resources left to produce a large number of seeds. Conversely, if it produces many seeds, each one will generally be smaller and may have a lower chance of survival.

Why Does This Trade-Off Occur?

• Resource Limitation: Organisms have a limited amount of energy and nutrients to allocate to reproduction.

• Fitness Optimization: Producing fewer, larger offspring may increase the survival rate of each, while producing many small offspring increases the chances that at least some will survive in unpredictable environments.

• Ecological Context: The optimal balance depends on environmental pressures, such as predation, competition, and resource availability.

Other Life History Trade-Offs

While the seed size-number relationship is a classic example, similar trade-offs exist in animals and other plants:

• Parental care vs. clutch size: More parental care often means fewer offspring can be cared for at once.

• Current vs. future reproduction: Investing heavily in current offspring may reduce the ability to reproduce in the future.

Conclusion

The statement “An increase in the seed size is usually associated with the decrease in the seed number” best supports the concept of trade-off in the evolution of life history traits. This example captures the essence of how organisms must balance competing demands to optimize their evolutionary fitness.

Correct answer:
(3) An increase in the seed size is usually associated with the decrease in the seed number.