A Natural Homoploid Hybrid between Centaurea horrida and Centaurea filiformis (Asteraceae) as Revealed by Morphological and Genetic Traits

Abstract

Studies over the last two decades demonstrate that hybridization has played an integral role in the evolution of several sections of the genus Centaurea. Nevertheless, natural hybridization between narrow Mediterranean endemic Centaurea species has not been documented as yet. A population of fertile Centaurea individuals exhibiting intermediate morphological traits between two Sardinian narrow endemics, C. horrida and C. filiformis, was identified at the Tavolara Islet (Sardinia, Italy). Intermediate leaf length and head width characterized this population, suggesting its hybrid origin. The putative hybrid population was structured (i.e., composed of seedlings, saplings and adult individuals) and had a relatively high levels of seed production. The number of chromosomes was identical to that of the proposed progenitors (2n=18). Genotyping at five microsatellite loci showed that the putative hybrid possessed several alleles in common with the proposed parental species and intermediate values of genetic differentiation, as indicated by both F ST and R ST, between C. horrida and C. filiformis. We therefore conclude that the studied intermediate population is of hybrid origin, and discuss possible mechanisms of its reproductive isolation from the parental species, potential re-introgression, and evolutionary implications of this hybridization.

On the identity of aCentaureapopulation on Procida Island, Italy:Centaurea corensisrediscovered

“…The molecular evidence of hybridization comes as no surprise, as hybridization has been shown to play a significant role in the speciation of Centaurea, with several taxa now known to have had a hybrid origin (Garcia-Jacas 1998; Pisanu et al 2011). The fact that C. corensis shows distinct ribotypes within the same individual (Figure 1a and Table II) strongly points towards allopolyploidization for explaining the origin of the species.…”

Homoploid hybrid speciation inDoronicumL. (Asteraceae)? Morphological, karyological and molecular evidences

“…Homoploid hybrid speciation is seemingly more likely to occur between species that are less genetically divergent than those giving rise to allopolyploids (Chapman & Burke 1997). It was documented in the family Asteraceae only for the genera Argyranthemum (Gross & Rieseberg 2005;Fjellheim et al 2009), Artemisia (Garcia et al 2008), Centaurea (Pisanu et al 2011), Helianthus (Lai et al 2005;Buerkle & Rieseberg, 2007), Polymnia (Estes & Beck 2011),…”

A rare case of a natural contact zone in Morocco between an autopolyploid and an allopolyploid of Centaurea aspera with sterile tetraploid hybrids

“…Koutecký ; Blair & Hufbauer ; Pisanu et al . ). In fact, it is usually accepted that the extent of hybridisation between particular taxa depends on the ploidy level; taxa of the same ploidy level can easily cross and their hybrids are fertile and capable of backcrossing, whereas those with different ploidy levels very rarely hybridise and their hybrids are sterile (Gardou ; Hardy et al .…”