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Background and Aims A vast quantity of empirical evidence suggests that insufficient quantity or quality of pollen may lead to a reduction in fruit set, in particular for self-incompatible species. This study uses an integrative approach that combines field research with marker gene analysis to understand the factors affecting reproductive success in a widely distributed self-incompatible species, Prunus virginiana (Rosaceae). Methods Twelve patches of P. virginiana distributed within three populations that differed in degree of disturbance were examined. Two of the sites were small (7–35 km2) remnants of forest in an intensively used agricultural landscape, while the third was continuous (350 km2) and less disturbed. Field studies (natural and hand cross-pollinations) were combined with marker gene analyses (microsatellites and S-locus) in order to explore potential factors affecting pollen delivery and consequently reproductive success at landscape (between populations) and fine scales (within populations). Key Results Reductions in reproductive output were found in the two fragments compared with the continuous population, and suggest that pollen is an important factor limiting fruit production. Genetic analyses carried out in one of the fragments and in the continuous site suggest that even though S-allele diversity is high in both populations, the fragment exhibits an increase in biparental inbreeding and correlated paternity. The increase in biparental inbreeding in the fragment is potentially attributable to variation in the density of individuals and/or the spatial distribution of genotypes among populations, both of which could alter mating dynamics. Conclusions By using a novel integrative approach, this study shows that even though P. virginiana is a widespread species, fragmented populations can experience significant reductions in fruit set and pollen limitation in the field. Deatiled examination of one fragmented population suggests that these linitations may be explained by an increase in biparental inbreeding, correlated paternity and fine-scale genetic structure. The consistency of the field and fine-scale genetic analyses, and the consistency of the results within patches and across years, suggest that these are important processes driving pollen limitation in the fragment. [ABSTRACT FROM PUBLISHER]

Background Our understanding of the processes and dynamics of allopolyploid speciation, the long-term consequences of ploidal change, and the genetic and chromosomal changes in new emerged allopolyploids has substantially increased during the past few decades. Yet we remain uncertain about the time since lineage divergence when two taxa are capable of spawning such entities. Indeed, the matter has seemed intractable. Knowledge of the window of opportunity for allopolyploid production is very important because it provides temporal insight into a key evolutionary process, and a temporal reference against which other modes of speciation may be measured. Scope This Viewpoint paper reviews and integrates published information on the crossability of herbaceous species and the fertility of their hybrids in relation to species' divergence times. Despite limitations in methodology and sampling, the estimated times to hybrid sterility are somewhat congruent across disparate lineages. Whereas the waiting time for hybrid sterility is roughly 4–5 million years, the waiting time for cross-incompatibility is roughly 8–10 million years, sometimes considerably more. Strict allopolyploids may be formed in the intervening time window. The progenitors of several allopolyploids diverged between 4 and 6 million years before allopolyploid synthesis, as expected. This is the first study to propose a general temporal framework for strict allopolyploidy. This Viewpoint paper hopefully will stimulate interest in studying the tempo of speciation and the tempo of reproductive isolation in general. [ABSTRACT FROM PUBLISHER]

The genus Ipomoea (Convolvulaceae) has a sporophytic self-incompatibility system that is under the genetic control of a single multiallelic S-locus. Self-incompatibility reactions occur on the stigma surface at an early stage after pollination, and result in the complete arrest of pollen germination such that no seed is set. In a genetic analysis of 224 plants of diploid I. trifida, collected from six native populations in Central America, we identified 49 different S-alleles that showed a linear dominance-recessive hierarchy. We also obtained a spontaneous self-compatible mutant and showed that this self-compatibility trait is due to mutation at the S-locus. To investigate the molecular basis of sporophytic self-incompatibility in Ipomoea, we analysed stigma proteins and mRNAs extracted from several different S-genotypes, using two-dimensional gel electrophoresis (2D-PAGE) and AFLP-based mRNA fingerprinting (AMF), respectively. From the 2D-PAGE analyses, S-locus-linked stigma proteins (SSPs) were identified. The amino acid sequences of these proteins have a high homology to non-metallo short-chain alcohol dehydrogenases reported in several plant species. The SSP gene was mapped at a distance of 1·2 cM from the S-locus. In the AMF analysis, we obtained a clone homologous to the Brassica SRK, which showed no genetic linkage to the S-locus of Ipomoea. This suggests that the sporophytic self-incompatibility system of Ipomoea is mediated through a different molecular mechanism to that of Brassica. [ABSTRACT FROM AUTHOR]