REPRODUCTIVE CHARACTER DISPLACEMENT IN PHLOX.

Area of Science:

• Plant reproductive biology
• Evolutionary botany
• Speciation mechanisms

Background:

• Interspecific hybridization can lead to genetic swamping and reduced fitness.
• Understanding reproductive isolation mechanisms is crucial for plant speciation.
• Phlox drummondii and Phlox cuspidata are sympatric species with potential for hybridization.

Purpose of the Study:

• To investigate the role of corolla color and self-compatibility in reproductive isolation between Phlox drummondii variants and Phlox cuspidata.
• To determine if sympatric populations exhibit greater reproductive isolation than allopatric populations.

Main Methods:

• Progeny testing of seeds from introduced red- and pink-flowered Phlox drummondii variants in a natural Phlox cuspidata population.
• Greenhouse studies on self- and cross-compatibility of nine sympatric and nine allopatric Phlox drummondii populations.
• Pollen germination and seed set assays to quantify hybridization and self-compatibility.

Main Results:

• Pink-flowered Phlox drummondii produced significantly more hybrid seed (38%) than red-flowered variants (13%), indicating corolla color influences hybridization.
• Sympatric Phlox drummondii populations showed higher self-compatibility (13.7% pollen germination) compared to allopatric populations (7.3%).
• Sympatric populations also exhibited a trend towards greater cross-compatibility with Phlox cuspidata, though not statistically significant.

Conclusions:

• Corolla color divergence and increased self-compatibility in Phlox drummondii reduce gametic wastage and interspecific hybridization.
• The presence of Phlox cuspidata has driven reproductive character divergence in Phlox drummondii, promoting reproductive isolation.
• These adaptive shifts enhance the reproductive success of Phlox drummondii in sympatric zones.