Cytotype displacement by intraspecific ecological niche divergence and reproductive shifts provide ecological opportunity to polyploids

KARUNARATHNE, PIYAL; SCHEDLER, MARA; MARTÍNEZ, ERIC J.; HONFI, ANA I.; NOVICHKOVA, ANASTASIIA; HOJSGAARD, DIEGO H.

ANNALS OF BOTANY

OXFORD UNIV PRESS

Lugar: Oxford; Año: 2018 vol. 121 p. 1183 - 1196

0305-7364

Background and Aims: Niche divergence between polyploids and their lower ploidyprogenitors is one of the primary mechanisms fostering polyploid establishment and adaptive divergence. However, within-species chromosomal and reproductive variability have usually been neglected in community ecology and biodiversity analyses even though it has been recognized to play a role in the adaptive diversification of lineages.Methods: We use Paspalum intermedium, a grass species with diverging genetic systems (diploidy vs. autopolyploidy, autogamy vs. allogamy, sexuality vs. apomixis), to recognize the causality of biogeographic patterns, adaptation, and ecological flexibility of cytotypes. Chromosome counts and flow cytometry were used to characterize within-species genetic systems diversity. Environmental Niche Modeling was used to evaluate intraspecific ecological attributes associated with environmental and climatic factors and to assess correlations between ploidy, reproductive modes and environmental conditions ruling speciespopulation dynamic, range expansion, adaptation, and evolutionary history.Key Results: Two dominant cytotypes non-randomly distributed along local and regional geographical scales displayed Grinnellian niche differentiation, a directional shift in niche optima and evidence of disruptive selection on ploidy-related ecological aptitudes for the exploitation of environmental resources. Ecologically specialized allogamous sexual diploids were found in northern areas associated with higher temperature, humidity, and productivity, while generalist autogamous apomictic tetraploids occurred in southern areas, along colder and less productive environments. Four localities with a documented shift in ploidy and four mixed populations in a zone of ecological transition revealed an uneven replacement of cytotypes.Conclusions: Polyploidy, phenology and contrasting reproductive traits between cytotypes have promoted shifts in niche optima, increased ecological tolerance and niche divergence. Ecologically specialized diploids maintain cytotype stability in core areas by displacing tetraploids, while broader ecological tolerance and a shift from sexuality to apomixis reinforced polyploid colonization in peripheral areas where diploids are displaced, and fostered ecological opportunity for autotetraploids supporting range expansion to opensouthern habitats.