Based on the principle of parsimony, which of the following statements best represents, the evolution of male body colour in this set of species?
(1) The most recent common ancestor of all 8 species was blue; red evolved independently 5 times.
(2) The most recent common ancestor of all 8 species was blue; red evolved independently 4 times.
(3) The most recent common ancestor of all 8 species was red; blue evolved independently 3
times.
(4) The most recent common ancestor of all 8 species was red; blue evolved independently 2 times.

Parsimony and the Evolution of Male Body Color in Species: Decoding Ancestral States

Understanding how traits like male body color have evolved across related species is a fundamental question in evolutionary biology. Phylogenetic trees, which depict relationships among species, can be used to infer the evolutionary history of such traits. The principle of parsimony is a key tool in this analysis, guiding researchers to the simplest evolutionary scenario that explains the observed distribution of traits.

What Is the Principle of Parsimony?

In phylogenetics, parsimony refers to the idea that the best evolutionary hypothesis is the one that requires the fewest evolutionary changes. When reconstructing ancestral states for a trait (such as body color), the most parsimonious scenario is the one that minimizes the number of times the trait must have changed across the tree.

Applying Parsimony to Male Body Color Evolution

Given a phylogenetic tree of eight species, where males are either blue (b) or red (r), the goal is to determine:

• The most likely color of the most recent common ancestor (MRCA)

• The minimum number of independent evolutionary changes (from blue to red or vice versa) required to explain the observed pattern

Step-by-Step Reasoning

1. Map the Trait on the Tree: Assign the observed color states (blue or red) to each species at the tips of the tree.

2. Consider Ancestral State Scenarios: For each possible ancestral state (blue or red), count how many times a change from blue to red or red to blue would be required to explain the pattern.

3. Select the Most Parsimonious: Choose the scenario with the fewest total changes.

Why Blue as the Ancestral State?

If the majority of species are blue, or if blue is distributed in such a way that assuming blue as ancestral minimizes the number of required transitions to red, then blue is favored as the ancestral state under parsimony.

Counting Independent Evolutions of Red

By tracing the tree, if red appears in several branches that are not closely related, each appearance is counted as an independent evolutionary event. The scenario that requires the fewest such independent gains (or reversals) is the most parsimonious.

Conclusion: The Most Parsimonious Scenario

Applying the parsimony principle to the described phylogenetic tree, the scenario that requires the fewest evolutionary changes is:

• The most recent common ancestor of all 8 species was blue; red evolved independently 4 times.

This means blue is the likely ancestral color, and the red color trait appeared independently in four separate lineages.

Correct answer: (2) The most recent common ancestor of all 8 species was blue; red evolved independently 4 times.