Sexual isolation promotes divergence between parapatric lake and stream stickleback

Area of Science:

• Evolutionary biology
• Speciation research
• Behavioral ecology

Background:

• Adaptive divergence in different habitats can drive speciation.
• The role of sexual reproductive barriers in speciation is not fully understood.
• Threespine stickleback fish provide a model system for studying speciation.

Purpose of the Study:

• To investigate sexual isolation between lake and stream ecotypes of threespine stickleback.
• To quantify the impact of sexual isolation on gene flow between ecotypes.
• To assess the relationship between sexually relevant traits and mating preferences.

Main Methods:

• Mating trials were conducted in outdoor mesocosms simulating natural conditions.
• Females were exposed to pairings of territorial lake and stream males.
• Gene flow reduction was estimated by comparing observed mating patterns to random mating.

Main Results:

• Mating preferentially occurred between partners of the same ecotype (lake-lake, stream-stream).
• Sexual isolation reduced gene flow between ecotypes by approximately 36%.
• Despite significant differences in male traits (size, color, nest size), sexual isolation was modest.

Conclusions:

• Sexually based reproductive isolation contributes to the divergence of lake-stream stickleback.
• Strong population divergence in sexually relevant traits does not necessarily imply strong sexual isolation.
• Further research is needed to understand the interplay of various reproductive barriers in speciation.