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  • 1
    Electronic Resource
    Electronic Resource
    Reproductive lability in pre-dispersal biology ofRhamnus alaternus L. (Rhamnaceae) (1995)
    Springer
    Protoplasma 187 (1995), S. 49-59 
    Details
    ISSN: 1615-6102
    Keywords: Alternate-bearing ; Dioecy ; Mediterranean species ; Pollination ; Reproductive biology ; Sex expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Rhamnus alaternus L. is a dioecious, fleshy-fruited shrub, typical of Mediterranean vegetation, which has been recorded from the region since the tropical Tertiary. Reproductive biology of this species has been studied in Southern Italy over a period of 4 years with both field and laboratory experiments. In all the studied populations male plants predominate over the females, have a higher flower density and flower regularly every year while females are usually alternate-bearing. A strong negative association between fruit formation and vegetative growth has been found indicating that the presence of fruits on a branch reduces the growth of new shoots. This phenomenon, together with alternate-bearing, is evidence of a strong competition between vegetative growth and reproductive activity and indicates resource limitation. Flower morphology and quantity of pollen produced are typical of insect pollinated species, and flies of the Empididae and Muscidae were trapped bearing pollen at female plants but pollen is also dispersed by wind. Field experiments on pollination success showed that the exclusion of insects as pollen vectors produces a significant decrease in fruit development. Excess pollen provided by hand-pollination increases fruit set over open-pollination and reproductive success in the field is therefore pollen limited. The variability of sex expression, male fitness, fruit production, regrowth and pollination presented here suggests that these predispersal characteristics ofR. alaternus have been subject to evolutionary change since the tropical Tertiary climate was replaced by a Mediterranean one. This points to the possibility that reproductive, as well as morphological and physiological characteristics, may be equally selected for in extreme environments such as the Mediterranean.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01280232
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  • 2
    Electronic Resource
    Electronic Resource
    Partner limitation and restoration of sexual reproduction in the clonal dwarf shrubLinnaea borealis L. (Caprifoliaceae) (1999)
    Springer
    Protoplasma 208 (1999), S. 76-86 
    Details
    ISSN: 1615-6102
    Keywords: Clonal plants ; Breeding system ; Self-incompatibility ; Fly pollination ; Habitat fragmentation ; Plant reintroductions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Reports suggest that there is widespread reproductive failure inLinnaea borealis in Britain, Scandinavia, and North America. Our investigations of Scottish populations of this clonal dwarf shrub indicate that, although visited by a number of different insects, pollen transfer in this species is highly effective and principally occurs by small flies (Muscidae). However, natural levels of fruit set varied between populations (from 0% to 25.1%) and reproductive failure was most severe in populations which were composed of single clones. Microscopic examination of stigmas showed that there is no barrier to pollen flow since at least 85% of stigmas have sufficient germinating pollen to effect seed set. Fluorescence microscopy of germinating pollen grains indicates high levels of pollen rejection in the style and only a small proportion of the pollen tubes were able to reach the ovary. It was concluded that lack of xenogamous pollination limits fruit formation in populations ofL. borealis. Reproductive success in an isolated population with extreme reproductive failure was restored by experimental field pollination with viable pollen imported from plants from another population. In Scotland,L. borealis occurs in small, isolated populations and restoration of reproduction can be achieved by the reintroduction of compatible mating partners. This is an important consideration for the conservation management of isolated populations since their long-term recovery may only be possible by translocation of different genotypes from elsewhere into the population. Habitat fragmentation in any part of the species range may impose a potential reproductive bottleneck by causing loss of population diversity and this could explain the low levels of seed set recorded for this species in other parts of its range.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01279077
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    Paper (German National Licenses)
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