Polyploidy and Hybridization as Main Factors of Speciation: Complex Reticulate Evolution within the Grass Genus <b><i>Helictochloa</i></b>

Abstract

To study the origin and evolution of naturally occurring polyploids, we performed phylogenetic analyses of nuclear ribosomal DNA spacers combined with molecular cytogenetics in 55 accessions of 27 taxa of the oat genus Helictochloa. A complex pattern of reticulate evolution was revealed with many diploid species and extensive polyploidy up to 20x. Altogether 11 groups of internal transcribed spacer (ITS) sequences can be distinguished. Sequences from 1-3 different ITS lineages were detected in polyploids. Cytogenetic data allow reconstruction of 8 basic monoploid chromosome sets. Six of these genomes occur in different combinations in the polyploid species. Two genomes are only found in diploids. Our sequence and karyological data highlight the occurrence of autopolyploidy and allopolyploidy, provide new information about the evolutionary history of taxa, and allow a more accurate systematic treatment of the concerned species. The geographical distribution of the 11 ITS lineages distinguished is highly structured and points to an origin of the genus in western Asia, presumably in grasslands like steppes or mountain steppes and meadows. The evolutionary basal lineages are of Asian, Minor Asian and east Mediterranean distribution and are present also in North America. The western and central parts of the Mediterranean and northern Europe harbor the modern lineages.

Are diversification rates and chromosome evolution in the temperate grasses (Pooideae) associated with major environmental changes in the Oligocene-Miocene?

“…Chromevol tracks changes along a phylogeny where relationships are expressed as dichotomies in a phylogenetic tree. It has not been designed to analyze reticulate evolution scenarios involving allopolyploidy ( Soltis et al, 2014 ; Kellogg, 2016 ), common in the Pooideae (e.g., Winterfeld et al, 2014 ; Kellogg, 2015a ). This is one of the main criticisms of the method and might affect the precision of its estimates, especially since the effect of polyploidy on topologies is not well understood ( Soltis et al, 2014 ).…”

Plastid phylogenomics of the cool-season grass subfamily: clarification of relationships among early-diverging tribes

“…A first strategy for future work should be to obtain plastomes from the currently unsampled subtribes Ammochloinae, Cynosurinae, Parapholiinae and Sesleriinae, and each of the putative lineages representing the non-monophyletic Airinae and Holcinae (at least two of these are currently unsampled). Further sampling in Helictochloa (some 30 species) and Deschampsia s.s. should aim to maximize the phylogenetic diversity in these genera as characterized in recent studies ( Chiapella 2007 ; Winterfeld et al 2014 ).…”

“…Six subtribes are recognized in Poeae clade 1 and 12 subtribes in Poeae clade 2 (Table 1 ). Evolutionary relationships within and among these lineages have been addressed in numerous studies across the tribe ( Soreng et al 2007 ; Schneider et al 2009 , 2011 , 2012 ) and within and among tribes: Airinae and Holcinae ( Chiapella 2007 ), Aveninae ( Grebenstein et al 1998 ; Röser et al 2001 ; Rodionov et al 2005 ; Winterfeld et al 2009 a , b , 2014 ; Romero-Zarco 2011 ), Brizinae ( Essi et al 2008 ), Loliinae ( Torrecilla and Catalán 2002 ; Catalán et al 2004 ; Torrecilla et al 2004 ; Inda et al 2008 ), Phalaridinae ( Voshell et al 2011 ), Poinae ( Gillespie et al 2007 , 2008 , 2009 , 2010 ; Hoffmann et al 2013 ), Poeae clade 1 ( Quintanar et al 2007 , 2010 ; Saarela et al 2010 ). However, numerous aspects of the relationships within and among the subtribes of Poeae remain unclear.…”

Mitosis and Interphase of the Highly Polyploid Palm <b><i>Voanioala</i></b><b><i>gerardii</i></b> (2n = 606 ± 3)

“…A total of 76 NORs would be arithmetically expected in Voanioala , judging from its 38-fold ploidy. Thus, there is a loss of at least 74% of potential NORs or up to 88% if considering only the active pear to be a response to the dramatic increase of chromosome number by polyploidy in Voanioala and seem to reflect some kind of 'genomic adjustment', which is characteristic of polyploids [Leitch and Leitch, 2008;Winterfeld et al, 2009Winterfeld et al, , 2011Winterfeld et al, , 2012Winterfeld et al, , 2014. The morphology of chro- 78 mosomes (arm ratio, prevalence of metacentrics and submetacentrics) obviously has not been altered considerably during polyploidization if comparing the chromosome complements of the other Cocoseae genera ( fig.…”