Variation in reproductive isolation across a species range

Area of Science:

• Evolutionary Biology
• Genetics

Background:

• Reproductive isolation is key to speciation but its variability within species is often overlooked.
• Understanding this variability can illuminate the mechanisms driving genetic incompatibilities.

Purpose of the Study:

• To investigate patterns of reproductive isolation among divergent lineages of Campanulastrum americanum.
• To characterize the geographic and genetic range of reproductive isolation in C. americanum.

Main Methods:

• Experimental greenhouse crosses were performed among three divergent genetic lineages of C. americanum.
• Patterns of reproductive isolation were assessed for survival, germination, pollen viability, and cytoplasmic male sterility.
• Results were compared with previous studies on a fourth, widespread Western lineage.

Main Results:

• Substantial, asymmetrical reproductive isolation for survival due to cytonuclear incompatibility was observed (up to 94% reduction).
• Moderate reductions in pollen viability and instances of cytoplasmic male sterility were found between some populations.
• Reproductive isolation for germination was only detected between Mountain and Western lineages, suggesting environmental influences.

Conclusions:

• Genetic incompatibilities evolve independently, leading to a mosaic of divergence across the species' range.
• Intrinsic factors primarily determine reproductive isolation for survival and pollen viability.
• Environmental or demographic factors may influence reproductive isolation for germination.