The Overlooked Hybrid: Geographic Distribution and Niche Differentiation Between Spartina Cytotypes (Poaceae) in Wadden Sea Salt Marshes

Abstract

Whole genome duplications (WGDs) lead to polyploid specimens and are regarded as major drivers for speciation and diversification in plants. One prevalent problem when studying WGDs is that effects of polyploidization in ancient polyploids cannot be disentangled from the consequences of selective evolutionary forces. Cytotypic differences in distribution, phenotypic appearance and in response to surface elevation (determined by HOF-modeling) were identified in a relatively young taxa-group of a hexaploid F1-hybrid (Spartina× townsendii H. Groves & J. Groves, Poaceae) and its dodecaploid descendent (Spartina anglica C.E. Hubbard, Poaceae) using vegetation assessments (1029 plots; 1 × 1 m2) from the European Wadden Sea mainland salt marshes, including elevational and mean high tidal (MHT) data. While the F1-hybrid was mainly present in the eastern part of the Wadden Sea, its dodecaploid descendent occurred in the entire Wadden Sea area. The Spartina cytotypes differed in phenotypes (median of Spartina cover: hexaploid = 25% vs. dodecaploid = 12%) and in elevational niche-optimum (hexaploid = − 49.5 cm MHT vs. dodecaploid = 8.0 cm MHT). High ploidy levels correlated with establishment success in Spartina along geographic gradients but did not seem to increase the capacity to cope with abiotic severity downwards the elevational gradient in salt marshes.

Proposing a novel classification of growth periods based on biomechanical properties and seasonal changes of Spartina anglica

“…It has to be noted, that S. anglica is an invasive species in the European Wadden Sea (see for example Nehring and Hesse, 2008). Looking at the geographic distribution of Spartina cytotypes in the European Wadden Sea, the study by Granse et al (2022) showed, that along the western parts of the Wadden Sea, mainly the dodecaploid cytotype was present.…”