Male choice in the stream-anadromous stickleback complex

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Speciation

Background:

• Mating preferences and pre-mating isolation are key to speciation.
• Male preferences are increasingly recognized as important drivers of reproductive isolation.
• Threespine stickleback (Gasterosteus aculeatus) populations offer a model for studying divergence and isolation.

Purpose of the Study:

• To investigate male courtship preferences in reproductively isolated threespine stickleback ecotypes.
• To determine if male preferences are based on female body size, ecotype, or other traits.
• To assess the contribution of male preferences to reproductive isolation between anadromous and stream-resident populations.

Main Methods:

• Experimental manipulation of female body size in anadromous and stream-resident threespine stickleback.
• Observation and quantification of male courtship behaviors towards size-manipulated females.
• Principal components analysis (PCA) to analyze correlated male behaviors and identify key behavioral patterns.

Main Results:

• Stream-resident males exhibited more vigorous courtship than anadromous males.
• Anadromous males incorporated aggressive behaviors more positively into courtship than stream-resident males.
• Size-assortative male courtship was observed: smaller stream-resident males courted smaller females, and larger anadromous males courted larger females.

Conclusions:

• Size-assortative male courtship preferences may contribute to reproductive isolation between threespine stickleback ecotypes.
• Male preferences are not absolute and do not appear to be based on ecotype alone, independent of size.
• Male mate choice plays a significant role in the early stages of reproductive isolation in this system.