Effects of artificial frost hardening and winter stress on net photosynthesis, photosynthetic electron transport and RuBP carboxylase activity in seedlings of Pinus silvestris

Net photosynthesis of seedlings of Pinus silvestris has been measured and compared with the activities of photosynthetic electron transport and extracted RuBP carboxylase. The effects of prolonged frost hardening (photoperiod 8 h, + 3°C) followed by winter stress at subzero temperatures were analysed. There was a parallel effect of frost hardening and winter stress on the photosynthetic properties of both intact seedlings and isolated chloroplast thylakoids. The activity of extracted RuBP carboxylase was less affected by the treatments. In relation to earlier works we conclude that the decay of net photosynthesis in winter climate is determined by the electron transport properties of the chloroplast thylakoids, i.e. by the pool sizes of photosynthetically active plastoquinone. The results of this work justify the definition of two phases in the response of conifers towards autumn and winter climates: I. Frost hardening occurs at temperatures slightly above zero and it does not affect the efficiency of photosynthesis as defined by the quantum yield at rate limiting light absorption. II. Winter stress occurs at subzero temperatures and it is characterized by a suppression of the photosynthetic efficiency as a result of damage within the photosynthetic apparatus.     

Effects of SO2 on Photosynthesis and Nitrogen Fixation

Spikelets of Themeda triandra are dormant when mature and require an after-ripening period in dry storage of approximately 12 months before full germination potential is realized. Successful germination of spikelets entails the splitting of the tough upper glumes by radicles. Dormany appears to result from a combination of embryo dormancy and mechanically resistant glumes. Glume removal from dormant spikelets increases germination while glume removal plus gibberellic acid increases germination even more. During the after-ripening period, the growth potential of spikelets and caryopses increases as measured by their ability to germinate in the presence of the osmoticum polyethylene glycol 6000. The inhibition of germination by decreasing osmotic potential of the germination medium significantly interacts with the promotion caused by gibberellic acid indicating that both factors affect germination by altering the growth potential of the embryos. The increase in growth potential during after-ripening is probably related to the synthesis of gibberellin-like substances. It is hypothesized that dormancy breaking during after-ripening occurs because the growth potential of embryos increases and this consequently increases the ability of radicles to split the upper glumes during germination.     

A multidisciplinary approach to discriminating different taxa in the species complex Pachycondyla villosa (Formicidae)

A multidisciplinary approach provides new evidence that strongly supports the differentiation of three taxa previously confounded in a single species, Pachycondyla villosa . All specimens studied were collected in the same location at Ilhéus, Bahia, Brazil. Bivariate plots of petiole heights vs. petiole lengths and isozyme patterns clearly differentiate the three taxa. Chain lengths and chemical structures of cuticular hydrocarbons are characteristic of each taxon. This congruent evidence shows that there are three different valid species. Ecological hypotheses are discussed to explain the benefits of these species remaining sympatric. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 75 , 249–259.     

Genetic differentiation on multiple spatial scales in an ecotype-forming marine snail with limited dispersal: Littorina saxatilis

The population genetic structure of marine species lacking free-swimming larvae is expected to be strongly affected by random genetic drift among populations, resulting in genetic isolation by geographical distance. At the same time, ecological separation over microhabitats followed by direct selection on those parts of the genome that affect adaptation might also be strong. Here, we address the question of how the relative importance of stochastic vs. selective structuring forces varies at different geographical scales. We use microsatellite DNA and allozyme data from samples of the marine rocky shore snail Littorina saxatilis over distance scales ranging from metres to 1000 km, and we show that genetic drift is the most important structuring evolutionary force at distances > 1 km. On smaller geographical scales (< 1 km), divergent selection between contrasting habitats affects population genetic structure by impeding gene flow over microhabitat borders (microsatellite structure), or by directly favouring specific alleles of selected loci (allozyme structure). The results suggest that evolutionary drivers of population genetic structure cannot a priori be assumed to be equally important at different geographical scales. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 31–40.     

Fourteen polymorphic microsatellite loci characterized in the house sparrow Passer domesticus (Passeridae,Aves)

We characterized 14 polymorphic microsatellite loci in the house sparrow Passer domesticus. Four loci were isolated from house sparrow genomic libraries and 10 loci were identified by testing 100 loci that had been originally isolated in other passerine species. Loci were characterized in 37–54 unrelated sparrows from British and Norwegian populations. Each locus displayed between two and 31 alleles, with the observed heterozygosity ranging between 0.30 and 0.91.     

Cloning and Characterization of New Repetitive Sequences in Field Bean (Vicia fabaL.)

Five new repetitive sequences have been isolated from theViciafabagenome, by cloning bands visible on agarose gel electrophoresisafter digestion of genomic DNA with various restriction enzymes.The sequences were 109 to 584 bp long, their abundance rangingfrom 5x10⁴to 5x10⁵copies per haploid genome. Southern blot andinsituhybridization revealed that four of five newly isolatedrepeats were dispersed in theV. fabagenome. One of the repeats(TIII15) showed tandem organization with several major hybridizationspots on mitotic chromosomesin situ.These sites were distributedin euchromatic as well as in heterochromatic chromosomal regions,and in several loci they were simultaneously localized withpreviously describedFokI repeated elements. The sequence ofTIII15 comprises four 26–27 bp subrepeats, but sharesno homology toFokI elements which have similar sequence organization.All newly described sequences were highly specific forV. faba,withlittle or no hybridization to DNA of otherViciaspecies, andno hybridization to DNA of other legumes tested.Copyright 1999Annals of Botany Company Vicia faba, field bean, repeated DNA sequences, FISH, PRINS, genome organization, copy number.     

Convergent evolution of shell shape in freshwater limpets: the African genus Burnupia

Convergent evolution of shell shape is a well known phenomenon in gastropods that has caused much confusion in taxonomic and systematic studies. A paradigm is the patelliform shell shape in several taxa of the order Basommatophora. Historically, most freshwater limpets were assigned to the family Ancylidae. Based on anatomical data, some taxa were subsequently moved to different families. However, there are still doubts about the monophyly of the remaining ancylids. This is also true for the African limpets and particularly for species of the genus Burnupia Walker, 1912. In the present paper, two independent molecular markers (COI, 18S rRNA) are used to (a) infer the position of Burnupia within the Basommatophora and (b) to test whether the shell shape of Burnupia evolved independently. Bayesian and maximum likelihood analyses of 12 genera of limnic Basommatophora indicate that Burnupia not only appears to be distinct from the Ancylidae, but also from all other representatives of the superfamily Planorboidea studied here. Based on a generally well-supported phylogeny and preliminary anatomical data, it is concluded that patelliform shell shapes evolved at least three times in the taxa studied here and that the shell shape of Burnupia represents another case of convergent evolution. Previously proposed functional and evolutionary scenarios for the evolution of patelliform shell and their relevance for freshwater limpets are discussed.  © 2004 The Linnean Society of London, Zoological Journal of the Linnean Society , 2004, 140 , 577–586.