Frequency-dependent social dominance in a color polymorphic cichlid fish

Area of Science:

• Evolutionary biology
• Animal behavior
• Population genetics

Background:

• Color polymorphism in animals is often explained by negative frequency-dependent selection.
• This selection can arise from social dominance advantages for rare morphs.
• The Lake Victoria cichlid, Pundamilia, exhibits red and blue color morphs.

Purpose of the Study:

• To investigate negative frequency-dependent selection in Pundamilia cichlid males.
• To test if social dominance explains the coexistence of red and blue morphs.
• To disentangle the effects of own-morph attack bias and red morph dominance.

Main Methods:

• Experimental manipulation of red and blue male proportions in assemblages.
• Observation of social dominance in dyadic contests.
• Computer simulations to analyze frequency-dependent effects.

Main Results:

• Red males were socially dominant to blue males, but only when red males were rare.
• Blue males did not exhibit social dominance when rare.
• Simulations indicated that own-morph attack bias reduced red male dominance when abundant.

Conclusions:

• Social dominance alone does not provide symmetric negative frequency-dependent selection for Pundamilia color morphs.
• Additional fitness costs for the red morph are likely necessary to explain their coexistence.
• Findings challenge the sole reliance on social dominance for explaining color polymorphism persistence.