The hormone responsible for maintaining the diurnal rhythm and sexual behaviour in animals is

Options

A. FSH
B. aldosterone
C. androgens
D. melatonin

Answer

To solve the question regarding the hormone responsible for maintaining the diurnal rhythm and sexual behavior in animals, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Question**: The question asks for a hormone that regulates both diurnal (daily) rhythms and sexual behavior in animals.

2. **Identify the Options**: The options given are:
- A) FSH (Follicle Stimulating Hormone)
- B) Aldosterone
- C) Androgens
- D) Melatonin

3. **Analyze Each Option**:
- **FSH (Follicle Stimulating Hormone)**: This hormone is produced by the anterior pituitary gland and is primarily involved in the regulation of reproductive processes, including the maturation of eggs in females and sperm in males. However, it does not play a significant role in regulating diurnal rhythms.

- **Aldosterone**: This is a mineralocorticoid hormone produced by the adrenal cortex. Its main function is to regulate sodium and potassium levels in the body, which is crucial for blood pressure regulation. It does not have a role in diurnal rhythms or sexual behavior.

- **Androgens**: These are male sex hormones (like testosterone) that are involved in the development of male characteristics and reproductive functions. While they influence sexual behavior, they do not regulate diurnal rhythms.

- **Melatonin**: This hormone is secreted by the pineal gland and is known for its role in regulating circadian rhythms (the body's internal clock) and sleep-wake cycles. It also has been shown to influence sexual behavior in various animals.

4. **Conclusion**: Based on the analysis, the hormone that is responsible for maintaining both diurnal rhythm and sexual behavior in animals is **Melatonin** (Option D).

### Final Answer:
**D) Melatonin**