Male mate choice selects for female coloration in a fish

Article by Amundsen and Forsgren (2001)

Summarized by Dr. Gier

Preview:A test of the function of female ornamentation using an experimental approach.

The Question:Male ornamentation is well-understood.

…but what about the females?Ornamentation is more rare, and more mysterious.

Three hypotheses for female ornamentation:• Genetic by-products of selection on males• Female-female competition• Male mate choice

Fish often have ornamented females, and are thus ideal model systems to test these hypotheses.

Study system:Two-spotted goby, Gobiusculus flavescens

Ideal for study: females vary in ornamentation (orange belly or not) and in shape (rounded or not). Both genders engage in displays.

Methods:Gobies caught off west coast of Sweden, maintained in captivity.

Experiment 1• Three-part tank, divided by transparent partitions.• Male in the middle.• Dull female on one side, colorful female on the other.• Authors measured the amount of time spent close to

each female, and the # of displays directed at each.Experiment 2• Same set-up as above.• This time, females were artificially colored with a

permanent marker (“Apricot” for colorful females; “Colorless” marker used as a control) .

• Same methods as above.

Results

1. Figure 1: a summary of the physical traits of the females used in experiments 1 and 2.

2. Figure 2: the results of the two choice experiments (“natural” and “colored” females).

Results, SummaryMale spent more time with, and directed more displays at, colorful females. This was true whether the coloration was natural or artificial.

DiscussionStrong evidence in favor of the “male choice” hypothesis for female ornamentation.

Discussion, continuedWhy do males prefer orange females?Hypothesis: the color is an “honest signal” of female fitness.

More studies needed to see whether these same choice patterns operate in natural habitats, and how being “choosy” benefits the male.

Discussion, continuedCritique and concerns:• The artificial coloring.• The slight “roundness” difference in

experiment 1.• Can we generalize much from this species?

QUESTIONS?