Homoploid Reticulate Evolution in Helianthus (Asteraceae): Evidence From Ribosomal Genes

Abstract

Phylogenetic relationships among the 21 taxa comprising Helianthus sect. Helianthus and three outgroup species were assessed by restriction site mapping of the 18S‐25S nuclear ribosomal RNA gene family. Wagner parsimony analysis of the 41 restriction site or length mutations observed produced a single 59‐step most parsimonious tree. This tree was then compared to a cytoplasmic‐based plastid phylogeny for this group. Several major discrepancies were observed between the two phylogenies suggesting both recent and ancient introgression. Furthermore, three cases of diploid hybrid speciation are unambiguously documented and a fourth case is suggested. These data are interpreted to suggest that evolution in Heliathus is reticulate rather than exclusively dichotomous and branching.

Allozyme variation and structure of the Canarian endemic palm tree Phoenix canariensis (Arecaceae): implications for conservation

“…This occurs when a locally rare species loses its genetic integrity and becomes assimilated into a locally common species as a result of repeated events of hybridisation and introgression (Rieseberg, 1991;Ellstrand, 1992;Ellstrand et al, 1999).…”

Is homoploid hybrid speciation that rare? An empiricist’s view

“…These criteria are: (1) a strong RI mechanism between the putative parental and hybrid species; (2) genetic evidence of hybridization; and (3) isolating mechanisms derived from hybridization itself. They concluded that only four examples across the living world fulfil these three requisites and are thus considered as true homoploid hybrid species: the butterfly Heliconius heurippa (Salazar et al, 2010) and the three hybrid sunflower species, Helianthus anomalus, H. deserticola and H. paradoxus (Rieseberg, 1991).…”

Chloroplast Dna Introgression in Southern California Sunflowers

“…Furthermore, in 18 of these cases, cytoplasmic introgression appears to have occurred in the absence of significant nuclear exchange (e.g., Palmer et aI., 1983;Doebley, 1989;Brunsfeld, 1990;Rieseberget aI., 1990bRieseberget aI., . 1991Rieseberg, 1991;Smith and Sytsma, 1990;Soltis et al, 1991;Wendel et aI., 1991;Whittemore and Schaal, 1991), whereas in only two instances (Wagner et aI., 1987;Arnold et al, 1991) has nuclear gene flow been shown to occur without cpDNA gene flow. Because of the apparent frequency of differential cytoplasmic versus nuclear introgression in plants and its implications for phylogenetic reconstruction, it seems appropriate to study those factors which might lead to differential cytoplasmic introgression and to assess how easily and rapidly this process might take place.…”

“…In four ofthese cases no significant nuclear exchange was detected using isozyme or nuclear ribosomal DNA (rDNA) markers (Rieseberg et aI., 1990a. 1990b. Rieseberg, 1991Rieseberg and Seiler, 1990;Rieseberg, unpubl.…”