Recent speciation associated with the evolution of selfing in Capsella

Area of Science:

• Evolutionary Biology
• Plant Reproductive Strategies
• Population Genetics

Background:

• The transition from outcrossing to self-fertilization is a common evolutionary event in flowering plants.
• This shift, known as the "selfing syndrome," typically involves reduced flower size and loss of self-incompatibility mechanisms.
• The evolutionary timing and dynamics of the selfing syndrome are not well understood.

Purpose of the Study:

• To investigate the origin and evolutionary history of selfing in the annual plant Capsella rubella.
• To determine the timescale of the mating system transition from its outcrossing progenitor, Capsella grandiflora.
• To explore the population dynamics and evolutionary forces driving the evolution of selfing.

Main Methods:

• Characterization of multilocus patterns of DNA sequence variation at nuclear genes.
• Analysis of genetic variation in Capsella rubella and its progenitor Capsella grandiflora.
• Estimation of the timescale of the transition to selfing and geographic expansion.

Main Results:

• The transition to selfing and subsequent geographic expansion in Capsella rubella occurred within the last 20,000 years.
• This transition was associated with a severe population bottleneck, significantly reducing effective population size.
• The timing and founder event suggest selfing was favored during post-glacial colonization and agricultural expansion.

Conclusions:

• Natural selection for reproductive assurance can drive significant morphological evolution and speciation.
• These evolutionary changes can occur on relatively short evolutionary timescales.
• The study provides insights into the rapid evolution of mating systems and associated traits in plants.