Asymmetric isolating barriers between different microclimatic environments caused by low immigrant survival.

Area of Science:

• Ecology
• Evolutionary Biology
• Behavioral Ecology

Background:

• Spatially variable selection can lead to local adaptation.
• Gene flow can counteract local adaptation and hinder population divergence.
• Barriers to gene flow are crucial for maintaining distinct populations under differing selection pressures.

Purpose of the Study:

• To investigate the role of local adaptation and gene flow in population divergence.
• To examine survival differences between inland and coastal populations of Enallagma cyathigerum.
• To determine if microclimatic differences contribute to asymmetric local adaptation.

Main Methods:

• Conducted reciprocal field transplant experiments with male damselflies between inland and coastal habitats.
• Replicated experiments spatially and temporally.
• Assessed survival rates of resident and immigrant males in different environments.

Main Results:

• Coastal males exhibited lower survival rates at inland sites compared to resident inland males.
• No significant survival differences were found between immigrant and resident males at coastal sites.
• Survival differences were environment-dependent, not due to intrinsic longevity, indicating local adaptation to microclimatic factors (warmer, drier coastal vs. inland).

Conclusions:

• Asymmetric local adaptation, driven by microclimatic differences, contributes to a source-sink system.
• Low survival of immigrant males acts as a barrier, mediating reproductive isolation between adjacent populations.
• Gene flow is effectively limited by differential survival due to local adaptation, facilitating population divergence.