90. What do mayflies, Pacific salmon (Oncorhynchusspp.) and annual grain crops have in common? They all are
    (1) semelparous (2) iteroparous
    (3) oviparous (4) Viviparous

Introduction

Nature is filled with a variety of reproductive strategies, each tailored to maximize survival and reproductive success in different environments. Some species reproduce multiple times throughout their lives, while others invest all their energy into a single, massive reproductive event before dying. This latter strategy, known as semelparity, is a fascinating adaptation seen in diverse organisms—including mayflies, Pacific salmon, and annual grain crops.

What Is Semelparity?

Semelparity is a life-history strategy where an organism reproduces only once in its lifetime, producing a large number of offspring in a single event, and then dies soon after. This approach contrasts with iteroparity, where organisms reproduce multiple times over the course of their lives.

Examples of Semelparous Species

• Mayflies:
  Mayflies are classic semelparous insects. After spending most of their lives as aquatic larvae, adult mayflies emerge, mate, lay eggs, and die shortly after, often within a single day.

• Pacific Salmon (Oncorhynchus spp.):
  Pacific salmon undertake a dramatic migration from the ocean to freshwater streams, where they spawn once, releasing thousands of eggs, and then die soon after reproduction.

• Annual Grain Crops:
  Plants like wheat, rice, and corn are semelparous because they complete their entire life cycle—from germination to seed production—in a single season, after which the plant dies.

Why Do These Species Use Semelparity?

Semelparity is favored in environments where:

• The likelihood of surviving to reproduce a second time is low.

• Reproductive opportunities are unpredictable or concentrated in a short period.

• Maximizing the number of offspring in one go increases the chance that at least some will survive.

For mayflies and salmon, environmental cues and life cycle constraints make a single, all-in reproductive event the most successful strategy. For annual crops, seasonal cycles and resource allocation favor a one-time, massive seed production.

How Does Semelparity Differ From Other Strategies?

• Iteroparity:
  Seen in many mammals, birds, and perennial plants, iteroparous species reproduce multiple times, spreading their reproductive effort across several seasons or years.

• Oviparity and Viviparity:
  These terms refer to how offspring are developed (egg-laying vs. live birth) and are not directly related to the number of reproductive events.

Conclusion

Mayflies, Pacific salmon, and annual grain crops are all semelparous species. They reproduce once in a spectacular, energy-intensive event, then die—ensuring their genes are passed on in environments where future opportunities are uncertain.

Correct answer:
(1) Semelparous