Artificial hybridization within Saxifraga pentadactylis (Saxifragaceae)

Abstract

Saxifraga pentadactylis subsp. almanzorii, an endemic to the subalpine nucleus of Sierra de Gredos (central Spain), differs from its closest relative, subsp. willkommiana, by its less showy petals. An artificial crossing program was carried out in order to assess the degree of reproductive isolation between the subspecies. To facilitate interpretation of the results, the program was extended to 10 other interspecific hybrid combinations within sect. Saxifraga. All the data gathered are congruent with the occurrence of two evolutionary scenarios. Interspecific crossings, rendering moderate to high seed‐set (in obtaining the F1), and vigorous but relatively sterile F1 offspring, reveal reproductive barriers at the level of the F1 fertility, probably originated as a byproduct of divergent evolution. In contrast, intraspecific crossings within S. pentadactylis resulted in seed‐set values lower than expected (in obtaining the F1), in a majority of weak non‐viable F1 offspring but also in a few fertile F1 hybrid specimens which were able to originate F2 offspring. This second pattern reveals reproductive barriers at the level of the F1 vitality, probably arisen in a quite abrupt fashion. The lower P/O for subsp. almanzorii as compared to subsp. willkommiana, together with the rest of the evidence suggest that the reproductive barriers between them might be the product of active selection against hybridization achieved by incrementing the levels of autogamy in the former.

On the Evolutionary and Biogeographic History of Saxifraga sect. Trachyphyllum (Gaud.) Koch (Saxifragaceae Juss.)

“…Siplivinsky [20] postulated that S. caulescens was “undoubtedly” a hybrid of S. bronchialis and S. spinulosa , but if that were the case S. caulescens would have been nested with them in the CAS sub-clade rather than associated with the Japanese taxa in the BER sub-clade. Other Eurasian species in our analyses (e.g., S. derbekii and S. omolojensis ) are phylogenetically distinct and exhibit unique, rather than intermediate, morphologies implying that they did not arise through hybridization [91], [92]. Furthermore, there is nothing to suggest hybridization among the North American species of sect.…”

Breeding system, germination, and phenotypic differences among populations of Saxifraga aizoides (Saxifragaceae) at the periphery of its alpine distribution

“…Best seed set is usually obtained when flowers of different genets are crossed. Nevertheless, most Saxifraga species are facultative selfers (Vargas & Feliner 1996), only differing in the lower percentages of resulting viable seeds after selfing compared to the seed set after crossing. Complete self-sterility seldom occurs, e.g.…”

Molecular evidence for multiple diversification patterns of alpine plants in Mediterranean Europe

“…-This saxifrage is endemic to the northern half of the Iberian Peninsula and occurs between 1500 and 3000 m (Vargas, 1997). Neighborhood diffusion (Shigesada & al., 1995) seems to be a predominant dispersal mechanism of plants with capsules containing over 100 seeds, as are populations of the three endemic taxa of S. pentadactylis (Vargas & Nieto, 1996): subsp. pentadactylis (Pyrenees); subsp.…”