Hybridization between previously isolated species can facilitate invasion success in plants by increasing genetic diversity and altering completive or reproductive interactions. The sand dunes of the U.S. Pacific Northwest (PNW) coast are densely colonized by two non-native and congeneric dune-building beachgrasses (Ammophila arenaria and A. breviligulata). These two beachgrass species build tall, stable foredunes via a positive feedback between grass growth and sand deposition. Although superficially similar, variations in functional morphology between the two grass species mediate differential effects on coastal protection and biodiversity conservation. The purpose of this study was to verify the hybrid origin of a newly discovered beachgrass, determine whether it is a first generation (F1) hybrid or a later generation backcross, assess potential barriers to sexual reproduction and backcrossing, and compare its functional morphology with its parent species in order to predict its effects on the coastal ecosystem. Our methods include estimating the genome size of the parents and hybrid using flow cytometry, sequencing reduced representation genomic libraries for SNP genotyping, surveying flowering time of the parents and hybrid, and collecting over 500 individual plants from all known hybrid locations for morphological comparison.
Results/Conclusions
We will present morphological, cytological, and genetic evidence that Ammophila arenaria and A. breviligulata are hybridizing on the U.S. Pacific Northwest coast, the only region globally in which the two species co-occur. The A. arenaria × breviligulata hybrid has been found at 12 coastal sites in Washington and Oregon. The hybrid is intermediate between the parents in many morphological traits, including some important diagnostic characters, but exceeds either parent in height, a trait associated with its dune building potential. A survey of beachgrass phenology revealed that the flowering time of the hybrid is intermediate between both parents, with minimal overlap. The genome size of the hybrid is intermediate between both parents, indicating no allopolyploidy has occurred. Comparison of the SNP genotypes of 32 individuals confirms that the hybrids are F1 crosses between the two Ammophila beachgrasses. In a system where any change in dominant beachgrass will have profound effects on biodiversity management and coastal protection, understanding the ecological and population genetic consequences of this novel hybridization event is of the utmost importance.