Strong postmating reproductive isolation in Mimulus section Eunanus

Area of Science:

• Evolutionary Biology
• Genomics
• Plant Speciation

Background:

• Postmating reproductive isolation is key to maintaining species boundaries when premating isolation is incomplete.
• Understanding the genetic basis and evolutionary drivers of reproductive barriers is crucial but often lacks broad phylogenetic scope.
• The monkeyflower genus Mimulus provides a valuable model for studying plant speciation.

Purpose of the Study:

• To investigate patterns of genetic divergence and direct measures of postmating reproductive barriers in the Mimulus brevipes species group.
• To explore the genetic basis and evolutionary mechanisms underlying reproductive isolation in this understudied group.
• To add phylogenetic resolution to the understanding of plant speciation.

Main Methods:

• Analysis of genetic divergence patterns across sympatric Mimulus species.
• Direct measurement of postmating reproductive barriers, including prezygotic isolation, hybrid seed inviability, and hybrid male sterility.
• Investigation of potential links between seed size and hybrid inviability.

Main Results:

• Substantial genetic divergence was found among species in the Mimulus brevipes group, including a cryptic lineage.
• Rampant gene discordance and ancient introgression signals indicate a complex evolutionary history.
• Multiple strong postmating barriers were identified, with complete isolation in most species pairs, except for Mimulus brevipes and Mimulus fremontii.
• Hybrid seed inviability was linked to differences in seed size.

Conclusions:

• Strong postmating reproductive barriers play a critical role in preventing ongoing introgression in the Mimulus brevipes group.
• Despite past gene flow, current reproductive isolation mechanisms are effective in maintaining species integrity.
• This study provides foundational data on reproductive isolation and genomic divergence, enhancing our understanding of plant speciation mechanisms.