Phylogenetic Diversity (PD) is a measure of biodiversity that calculates the sum of the lengths of all phylogenetic branches that connect a given set of species to a common root. Areas with species that are more evolutionarily distinct (separated by longer branches) have a higher PD.

1. Visual Analysis of Branch Lengths

• In the provided phylogeny, the horizontal length of a branch represents the degree of evolutionary change.
• The branches leading to species P and Q are significantly longer than the branches leading to R, S, and T.
• To maximize PD, an area should contain species separated by the greatest total branch length.

2. Comparing the Area Compositions

• Area 1 (P, Q, R): This area includes the two species with the longest branches (P and Q) and one species from the other major clade (R). Because it captures two long terminal branches and the deep divergence between the two main clades, it has the highest total length. $$\text{PD}_{\text{Area 1}} \rightarrow \text{Maximum}$$
• Area 3 (Q, R, S): This area includes only one of the long branches (Q). The other two species (R and S) are very closely related and have short branches. It spans the main divergence of the tree but lacks the additional length provided by branch P. $$\text{PD}_{\text{Area 1}} > \text{PD}_{\text{Area 3}}$$
• Area 2 (R, S, T): All species in this area belong to the same sub-clade. They are closely related and share very short branch segments. This area misses the entire lineage of P and Q, resulting in the lowest evolutionary "coverage." $$\text{PD}_{\text{Area 3}} > \text{PD}_{\text{Area 2}}$$

Conclusion

Based on the sum of the evolutionary branch lengths for each species set:

Area 1 > Area 3 > Area 2

The correct statement is the first option: Area 1 > Area 3 > Area 2.