Molecular Tests of the Hypothesized Hybrid Origin of Two Diploid Helianthus Species (Asteraceae)

A theoretical assessment of recombinational speciation

“…of the species participating are otherwise inimical to the process. The natural recombinant species identified by Rieseberg et al (1990) and by ences, with fitness increasing with similarity to the optimal type, which would presumably facilitate that type's becoming established as a new species. Our findings, then, do not define preconditions for recombinational speciation in any absolute sense.…”

“…Grant (1971) originally postulated that the mating system would play an all-important role in the process, with homoploid derivatives emerging most rapidly and having maximal chances of surviving as a distinct population under inbreeding. The presumed requirement of a significant level of self-fertilization has been called into question, however, by recent studies indicating that two obligately outcrossing species had their origins in recombinational speciation (Gallez & Gottlieb, 1982;Rieseberg et a!., 1990 fitness of individuals in terms of the number of progeny they produce, the choice between selfing and outcrossing, the selection of mating pairs, and the positioning of offspring. Every effort has been made to make the probability distributions associated with each of these steps empirically reasonable.…”

“…Such an assumption is reasonable inasmuch as derivatives more fit than either parental species are known from nature. For example, the recombinant sunflower species Helianthus paradoxus is far more tolerant of saline conditions than either of the two species from which it is derived (Rieseberg et al, 1990;Rieseberg, 1991, and Rieseberg, pers. comm.).…”

Allozyme variation in Louisiana irises: a test for introgression and hybrid speciation

“…1988; Arnold et a!., 1990;dePamphilis and Wyatt, 1990;Rieseberg et a!., 1990). When such studies have been undertaken, a variety of evolutionary patterns have been discovered.…”

“…When such studies have been undertaken, a variety of evolutionary patterns have been discovered. Thus, data from genetic studies of plant hybridization indicate (1) hybridization with little or no apparent introgression (Doyle and Doyle, 1988), (2) hybridization with introgression occurring only in sympatric, localized associations (Rieseberg et a!., 1988), (3) hybridization with introgression apparent in parapatric and allopatric populations of the hybridizing species (Arnold et a!., 1990;dePamphilis and Wyatt, 1990) and (4) hybridization that has resulted in the origin of a new species (Rieseberg et a!., 1990). It is significant to note that genetic analyses have varied with regard to their concordance with morphological data from the same hybridization events.…”