Closely related, morphologically similar reproductively isolated, sympatric populations are called as

Options

A. Clones
B. Demes
C. Sibing species
D. Biological species

Answer

To solve the question "Closely related, morphologically similar, reproductively isolated, sympatric populations are called as," we need to analyze the terms and concepts involved.

### Step-by-Step Solution:

1. **Understanding the Key Terms**:
- **Closely Related**: This indicates that the populations share a common ancestor and are genetically similar.
- **Morphologically Similar**: This means that the populations have similar physical characteristics or forms.
- **Reproductively Isolated**: This implies that even though the populations live in the same area (sympatric), they do not interbreed and produce fertile offspring.
- **Sympatric Populations**: These are populations that occupy the same geographical area.

2. **Identifying the Options**:
- **Clones**: These are exact copies of a parent organism, not applicable here.
- **Deme**: This refers to a local population of a single species that interbreeds, which does not fit the description of being reproductively isolated.
- **Sibling Species**: These are closely related species that are morphologically similar but are reproductively isolated from each other.
- **Biological Species**: This term generally refers to groups of organisms that can interbreed and produce fertile offspring, which contradicts the reproductive isolation aspect.

3. **Choosing the Correct Answer**:
- Given the definitions and characteristics, the term that best fits the description of "closely related, morphologically similar, reproductively isolated, sympatric populations" is **sibling species**.

### Final Answer:
**Sibling species**