A perfect storm: ploidy and preadaptation facilitate Saccharum spontaneum escape and invasion in the Republic of Panama

Kristin Saltonstall,Graham D Bonnett,Karen S Aitken

doi:10.1007/s10530-020-02421-3

Abstract

Polyploidy may contribute to invasive ability as it can lead to high survival and fitness during establishment and enhance the processes of adaptation to novel environments by increasing genetic diversity in invading propagules. Many grasses are polyploid and many are aggressive invaders, making them persistent problems in disturbed environments worldwide. Today, vast areas of central Panama are dominated by Saccharum spontaneum, a perennial grass that originates from Asia. While widely regarded as invasive, it is not known when or how it arrived in Panama. We explore hypotheses regarding the timing and origins of this invasion through literature review and comparisons of genetic diversity in Panama with accessions from available sugarcane germplasm collections, highlighting historical accessions that were likely brought to Panama in 1939 as part of a USDA sugarcane germplasm collection. Samples were haplotyped at two chloroplast loci and genotyped using eight microsatellite markers. All sequenced individuals from Panama belong to a single chloroplast lineage which is common worldwide and was common in the Historic germplasm collection. Although genotypic diversity was extremely high in all samples due to high ploidy, samples from Panama had reduced diversity and clustered with several accessions in the Historic collection which had the same haplotype and high ploidy levels. Our results suggest that accidental escape from the historical sugarcane germplasm collection is the likely origin of the S. spontaneum invasion in Panama. Intraspecific hybridization among several historical accessions and pre-adaptation to local conditions may have facilitated its rapid spread and persistence. We discuss the implications of our findings for biosecurity of germplasm collections.

Highlights

Grasses have been identified as a invasive plant group and are overly represented in ‘‘invasive alien plant’’ lists globally (D’Antonio et al 2011; Holm et al 1977)
Our results suggest that accidental escape from the historical sugarcane germplasm collection is the likely origin of the S. spontaneum invasion in Panama
As sampling at the stand level was limited, within-site measures of genetic diversity were not calculated and our analysis focuses on diversity within the S. spontaneum population in Panama compared to other locations

Summary

Introduction

Grasses have been identified as a invasive plant group and are overly represented in ‘‘invasive alien plant’’ lists globally (D’Antonio et al 2011; Holm et al 1977). Genetically depauperate invaders are known (e.g. Japanese knotweed (Fallopia japonica [Hollingsworth and Bailey 2000], fountain grass (Pennisetum setaceum [Le Roux et al 2007], giant reed (Arundo donax [Ahmad et al 2008; Hardion et al 2014]), and a multitude of traits such as broad environmental tolerance (Le Roux et al 2007), phenotypic plasticity (Richards et al 2006), escape from natural enemies (Parker and Gilbert 2007), presence of pre-adapted genotypes (Hurka et al 2003), and ability to disperse and germinate rapidly (Gioria and Pysek 2017) have been proposed to contribute to the success of species when establishing in new environments. Intraspecific hybridization of introduced lineages from geographically distinct source populations can both increase genetic diversity and facilitate adaptation to new environments by creating novel combinations of alleles and potentially stimulating hybrid vigor (Dluglosch et al 2015; Ellstrand and Schierenbeck 2000; Lavergne and Molofsky 2007; Novak and Mack 2005)

Methods

Results

Conclusion