A molecular study of hybridization and homoploid hybrid speciation inArgyranthemum(Asteraceae) on Tenerife, the Canary Islands

Abstract

Examples of recurrent homoploid hybrid speciation are few. One often-cited example is Argyranthemum sundingii. This example includes two described species, A. lemsii and A. sundingii, resulting from reciprocal hybridization between A. broussonetii and A. frutescens on Tenerife. The four species and artificial F1 and F2 hybrids have previously been investigated morphologically and cytologically. Here, we examine population differentiation based on amplified fragment length polymorphism to get a better understanding of the genetic relationships among the species and the extent of hybridization. We aim to investigate if there is molecular support for treating the hybrid species as one taxon. Seven parental and four hybrid species populations (149 individuals) were analysed and we scored 85 polymorphic markers. A few (2-5) were private to each species but variably present and mostly rare. Our principal coordinate, STRUCTURE and BAPS analyses and AMOVA resulted in a clear separation of the parental species. The hybrid species were genetically less divergent but not identical. Our data indicate that hybridization and introgression are common in all these species on Tenerife and support the hypothesis that homoploid hybrid speciation has occurred repeatedly. Intrinsic post-zygotic barriers are notoriously weak in Argyranthemum and reproductive isolation and speciation result primarily from strong ecological selection.

Molecular, Morphological, and Experimental Evidence for Hybridization between Threatened Species of the Galapagos Endemic GenusScalesia(Asteraceae)

“…Further, the variation between the different populations of a species and between different species is approximately equal (6.9% and 7.6%, respectively) and small, despite great morphological differences (as also found by Nesbitt et al [1995] for Eucalyptus globulus). This may suggest that the morphology is driven by selective forces, while the molecular markers studied are relatively selectively neutral and thus driven by other forces (Karhu et al 1996;Fjellheim et al 2009). The genetic diversity was expected to be higher within hybrid populations because they should contain alleles from both parental species.…”

“…This was, however, not the case for either the artificial hybrids or the intermediates. The explanation for the artificial hybrids may be the small sample size (10), while the intermediates might have lost diversity over generations as a result of genetic drift, inbreeding, and backcrossing (Scotti et al 2002;Chung et al 2005;Fjellheim et al 2009). Jørgensen and Mauricio (2005) found that their hybrid populations were genetically very similar to one of the parental populations and judged this to be caused by backcrossing.…”

“…Scalesia pedunculata grows in humid sites; S. crockeri, S. aspera, and 3INT grow in dry coastal sites; and 1INT and 2INT grow in the transition zone at intermediate altitude and humidity and with greater competition from other trees and shrubs than in the arid zone. Ecological differences between habitats of parent species and new habitats colonized by hybrid species have been shown to be important in homoploid hybrid speciation (Gross and Rieseberg 2005;Fjellheim et al 2009). …”

Human-induced hybridization among congeneric endemic plants on Tenerife, Canary Islands

“…Introduction of non-native species, habitat destruction through deforestation and development of human infrastructure are all well known to have a major impact on native island biodiversity (Whittaker and Fernández-Palacios 2007). Because of their often recent evolutionary origin, island endemics tend to hybridize easily despite morphological and ecological differences (Baldwin et al 1998;Francisco-Ortega et al 2000;Fjellheim et al 2009). Postzygotic barriers are typically weak (Carlquist and Cole 1974;Levin et al 1996), and hybrids are often fertile so that introgression can readily occur.…”

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),…”