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

Options

A. Clones
B. Clines
C. Demes
D. Sibling species

Answer

To solve the question regarding the designation of closely related, morphologically similar, reproductively isolated sympatric populations, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Key Terms**:
- **Closely related**: This implies that the populations share a recent common ancestor.
- **Morphologically similar**: This means that the populations have similar physical characteristics.
- **Reproductively isolated**: This indicates that the populations do not interbreed, even if they live in the same geographic area (sympatric).
- **Sympatric populations**: These are populations that occupy the same geographic area.

2. **Evaluate the Options**:
- **Clones**: These are genetically identical individuals from the same parent cells. This does not fit our description as it refers to asexual reproduction, not populations.
- **Clines**: This refers to a gradual change in phenotype or genotype across a geographical gradient. This does not describe isolated populations.
- **Demes**: These are local populations within a species that interbreed. While they are subsets of populations, they do not necessarily meet the criteria of being morphologically similar and reproductively isolated.
- **Sibling species**: This term refers to species that are closely related, morphologically similar, and reproductively isolated, fitting all the criteria given in the question.

3. **Select the Correct Answer**:
Based on the evaluation, the correct designation for closely related, morphologically similar, reproductively isolated sympatric populations is **sibling species**.

### Final Answer:
The answer is **sibling species**.

---