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Selected AbstractsDarwin's cross-promotion hypothesis and the evolution of stylar polymorphismECOLOGY LETTERS, Issue 12 2004Adeline C. Cesaro Abstract There is growing appreciation that the ecological factors which impact on rates of pollen transfer can contribute significantly to reproductive trait evolution in plants. In heterostylous species, several studies support Darwin's claim that the reciprocal positions of stigmas and anthers enhance inter-morph mating in comparison to intra-morph mating and thus the maintenance of the polymorphism. In this study, we evaluate the relative importance of intra-morph and inter-morph pollen transfers in Narcissus assoanus, a species with dimorphic variation in style length but non-reciprocity of anther positions. This stigma-height dimorphism represents a transitional stage in theoretical models of the evolution of distyly. Seed set variation on recipient plants with donor plants of a single morph in experimental arrays in a natural population illustrate that inter-morph cross-pollination is more efficient that intra-morph cross-pollination as a result of high rates of pollen transfer from long-styled to short-styled plants. The observed rates of pollen transfer satisfy the theoretical conditions for the establishment of a stigma-height dimorphism in an ancestral monomorphic long-styled population in pollen-limited situations. These results provide experimental evidence for the Darwinian hypothesis that enhanced inter-morph cross-pollination facilitates not only the maintenance of heterostyly but also the establishment of transitional forms implicated in the evolution of this polymorphism. [source] Severely reduced sexual reproduction in northern populations of a clonal plant, Decodonverticillatus (Lythraceae)JOURNAL OF ECOLOGY, Issue 3 2001Marcel E. Dorken Summary 1,In flowering plants the balance between sexual and clonal, asexual reproduction can vary widely. We quantified variation in sexual reproduction in a tristylous, clonal, aquatic plant, Decodon verticillatus, and investigated the role of ecological and genetic factors in causing this variation. 2,We surveyed components of sexual fertility and vegetative growth in 28 populations distributed along a 500-km latitudinal transect in New England, USA. Northerly populations tend to be monomorphic (M) for style length, and probably therefore have reduced sexual reproduction compared with southerly, trimorphic (T) populations. 3,Compared with T populations (n = 10), M populations (n = 18) exhibited large reductions for all components of sexual reproduction, including flower production, pollen deposition, pollen tube growth, fertilization, fruit set and seeds per fruit. Seven M populations produced no seed at all, and the other 11 very little (mean = 24 vs. 1139 seeds per plant in trimorphic populations). Clonal propagation was also greatly reduced in M populations. 4,A survey of three polymorphic allozyme loci detected only single, usually heterozygous, genotypes in 15 M populations, whereas all T populations were genotypically diverse. The other three M populations contained three or fewer genotypes and one always predominated. Sexual recruitment is therefore extremely rare. 5,Comparison of the sexual fertility of M and T populations in a concurrent common glasshouse experiment with our field data revealed that reduced sexual performance in northern M populations is principally due to genetic factors, but is also caused by ecological factors that covary with latitude. 6,This abrupt shift away from sexual reproduction in populations at the northern periphery of the geographical range in D. verticillatus may greatly limit their evolutionary potential and restrict further northward expansion. [source] Direct and indirect responses to selection on pollen size in Brassica rapa L.JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 3 2001T. S. Sarkissian Pollen size varies little within angiosperm species, but differs extensively between species, suggesting the action of strong selection. Nevertheless, the potential for genetic responses of pollen size to selection, as determined by additive genetic variance and genetic correlations with other floral traits, has received little attention. To assess this potential, we subjected Brassica rapa to artificial selection for large and small pollen during three generations. This selection caused significant divergence in pollen diameter, with additive genetic effects accounting for over 30% of the observed phenotypic variation in pollen size. Such heritable genetic variation suggests that natural selection could effect evolutionary change in this trait. Selection on pollen size also elicited correlated responses in pollen number (,), flower size (+), style length (+), and ovule number (+), suggesting that pollen size cannot evolve independently. The correlated responses of pollen number, flower size and ovule number probably reflect the genetically determined and physically constrained pattern of resource allocation in B. rapa. In contrast, the positive correlation between pollen size and style length may represent a widespread gametic-phase disequilibrium in angiosperms that arises from nonrandom fertilization success of large pollen in pistils with long styles. [source] Lathyrus nivalis subsp. sahinii subsp. nov. (sect. Platystylis, Leguminosae) from TurkeyNORDIC JOURNAL OF BOTANY, Issue 5 2009Hasan Genç The new subspecies Lathyrus nivalis Hand.-Mazz. subsp. sahinii H. Genç (sect. Platystylis, Leguminosae) from Turkey is described and illustrated with diagnostic characters and taxonomic comments. The characters of the new subspecies are compared with those of the type subspecies, from which it differs mainly in the shape, length, width and venation of leaflets, length and width of the stipules, flower color, legume, and style length. In addition, the geographic distribution of the new subspecies is outlined. [source] Cybrids and tetrad sterility for developing true potato seed hybridsANNALS OF APPLIED BIOLOGY, Issue 2 2003ALI M GOLMIRZAIE Summary Potato cybrids result from the fusion between cytoplasm and nuclear gene donors. Such genetic materials are an alternative means to broaden the breeding pool by non-sexual gene transfer. Tetrad pollen sterility provides also another source of male sterility with some potential for true potato seed breeding. The objective of this research was to investigate cybrid-derived offspring for both agronomic and reproductive characteristics in two contrasting Peruvian locations, and to examine new exotic germplasm for tetrad sterility, with the aim of broadening the breeding pool available at the Centro Internacional de la Papa (CIP). The cybrids were derived from fusions between Y-245.7, a clone with tetrad sterility, and Atzimba. These cybrids were crossed with selected male parents from the CIP breeding population, and their hybrid offspring were tested in La Molina (coastal desert) and Huancayo (cool highlands). In addition, other clones with tetrad sterility were also crossed with selected testers to determine their breeding value. There were significant differences for tuber yield, style length, and berry number among the hybrid offspring, and the genotype by environment interaction was significant for tuber yield and berry number. The top 25% highest yielding cybrid-derived offspring across both locations showed the same tuber yield although they were significantly different for some of the reproductive characteristics. With the exception of one cybrid, the others did not exhibit segregation for tetrad sterility in their hybrid offspring, which were male fertile. However, the offspring derived from crosses between other sources of tetrad sterility and the same testers all showed tetrad sterility, and some of them had outstanding tuber yield at La Molina. The lack of segregation for tetrad sterility in these new crosses suggests that the non-cybrid, male sterile, female parents are triplex or quadriplex for the Tr nuclear locus, which interacts with a sensitive cytoplasm (e.g. Trs from S. verrucosum or S. stoloniferum) to produce tetrad sterility in potato. [source] | ||||||||||