The role of parental and hybrid species in multiple introgression events: evidence of homoploid hybrid speciation inCentaurea(Cardueae, Asteraceae)

Abstract

Molecular approaches have greatly increased the number of confirmed homoploid hybrids, which suggests that the frequency of this phenomenon was underestimated in the past because it was much more difficult to detect than allopolyploidy. Centaurea is a suitable model group for studying homoploid speciation, as hybridization events have been commonly reported for this genus. Based on this, here we study Centaurea × forsythiana, a naturally occurring homoploid hybrid between two Sardinian endemics, C. horrida and C. filiformis, using a molecular approach involving nuclear and plastid markers, to understand the underlying population dynamics between homoploid hybrids and their parents. Our results confirm that C. × forsythiana is a hybrid between the abovementioned species and define the roles of the parents. Plastid markers point towards C. horrida as the maternal progenitor, and nuclear markers reveal that the other parental species, C. filiformis, is itself an old, stabilized homoploid hybrid related to the C. paniculata complex from the Italian mainland. Homoploid hybrid speciation is discussed and C. × forsythiana and C. filiformis are compared with other similar examples. The study confirms the importance of introgression between parental species mediated by hybrids and its potential implications in conservation. Furthermore, it shows how hybridization studies become even more complex when the parents are themselves of probable hybrid origin.

Is population genetic structure of vascular plants shaped more by ecological or geographic factors? A study case on the Mediterranean endemic Centaurea filiformis (Asteraceae)

“…; Mameli et al . ), and it is of interest to compare F IS values, which are −0.133 and −0.125 for C . horrida and for C .…”

“…A main finding of this work is the clear genetic substructure of C. filiformis in five clusters: the first comprises the northernmost group of populations FIG and TAVO, which have also been demonstrated to be introgressed with/by C. horrida (Mameli et al . ); the second and third clusters are relative to two populations characterised by geographic isolation, the hilly population GAL (located in an isolated limestone hill surrounded by unsuitable habitats) and the coastal population CAR (located in a peripheral ravine system). The most represented genetic cluster was found to comprise DOR, URTA, SIL, OLM and OL; this is in the central portion of the Mesozoic limestone of the Supramontes system, a priority plant conservation area (Fenu et al .…”

“…; Mameli et al . ), when the presence of hybrid plants was inferred by the presence of shared alleles and intermediate values of genetic differentiation for five SSR loci, all of which have also been used in this study.…”

“…Both factors conditioned the distribution of many plant species, which are now rare and confined to narrow ranges, often with scattered, isolated and small populations (Thompson 2005). Particular attention has recently been given to the evolution in space and time of population patches of Mediterranean plants (Garc ıa 2003(Garc ıa , 2008Garc ıa et al 2010;Budroni et al 2011Budroni et al , 2014Pisanu et al 2012), which are increasingly considered interesting subjects for evolutionary studies (Fern andez-Mazuecos et al 2014;Mameli et al 2014;Hilpold et al 2015).…”

Advances in the systematics and evolution of western Mediterranean representative species of the Pentanema conyzae clade through genetic fingerprinting

“…This hypothesis would be reinforced if the putative descendants (MO6146 and MO6147) had a level of 2 n = 8 x = 64. On the other hand, if the ploidy level of these populations corresponded to 2 n = 4 x = 32, a homoploid hybridization process could not be ruled out (Mameli et al, ; Marques et al, ; Nieto‐Feliner et al, ). However, another types of data are necessary (i.e., karyological, cross‐over studies) to understand the biology of these intermediate forms and to interpret them correctly.…”