Assessing reproductive isolation using a contact zone between parapatric lake-stream stickleback ecotypes

Area of Science:

• Evolutionary biology
• Speciation research
• Ecology

Background:

• Ecological speciation drives reproductive isolation through divergent selection.
• Reproductive barriers like hybrid disadvantage, migrant disadvantage, and assortative mating are key.
• Understanding the interplay of these barriers in natural systems is crucial but limited.

Purpose of the Study:

• To investigate reproductive barriers in a contact zone of lake and stream three-spined sticklebacks (Gasterosteus aculeatus).
• To evaluate hybrid occurrence, hybrid survival, and selection against migrants.
• To understand the combined effect of multiple barriers on gene flow.

Main Methods:

• A mark-recapture experiment was conducted in a natural contact zone.
• Genetic and morphological data were used to identify hybrids and assess traits.
• Interannual survival rates of hybrids and shifts in population characteristics were analyzed.

Main Results:

• Hybrids between lake and stream sticklebacks were identified.
• No significant selection against hybrids was detected, contrary to some previous studies.
• Selection against lake-like individuals was observed, indicating a barrier to gene flow from lake to stream.

Conclusions:

• Multiple, often asymmetric, reproductive barriers contribute to restricted gene flow in this stickleback system.
• A specific barrier exists against gene flow from lake to stream populations.
• Assessing multiple reproductive barriers in natural settings is vital for understanding speciation.