Polysome formation in Pinus resinosa at initiation of seed germination

Ribonucleic acid systems present in dormant embryos of red pine(Pinus resinosa Ait.) were studied. Sucrose gradient centrifugationwas used to isolate ribosomes of dormant embryos and embryosimbibed for various times in the light. In dormant embryos,ribosomes existed as monomers. After imbibition, a gradual decreasein the monomers was observed, with subunits and polymers ofribosomes detected within 4 hr. When poly U was added to homogenatesof dormant embryos, formation of polysomes was observed aftera 15-min incubation at 25°C. However, artificial polysomeformation required some factors from heavy particles in thehomogenates. ¹ Contribution from the Missouri Agricultural Experiment Station,Journal Series No. 7079. ² Present address: Government Forest Experiment Station, Meguro,Tokyo, Japan. (Received April 20, 1971; )     

Climate change induced hybridization in flying squirrels

There is now unequivocal evidence for global climate change; however, its potential impacts on evolutionary processes remain unclear. Many species have responded to contemporary climate change through shifts in their geographic range. This could lead to increased sympatry between recently diverged species; likely increasing the potential for hybridization. Recently, following a series of warm winters, southern flying squirrels ( Glaucomys volans ) in Ontario, Canada rapidly expanded their northern range limit resulting in increased sympatry with the closely related northern flying squirrel ( Glaucomys sabrinus ). This provided the opportunity to test the prediction that contemporary climate change can act as a catalyst creating conditions for the formation of hybrid zones. Following extensive sampling and molecular analyses (nuclear and mitochondrial DNA), we identified the occurrence of hybridization between sympatric G. sabrinus and G. volans . There was evidence of backcrossing but not of extensive introgession, consistent with the hypothesis of recent rather than historic hybridization. To our knowledge, this is the first report of hybrid zone formation following a range expansion induced by contemporary climate change. This is also the first report of hybridization between North American flying squirrel species.     

Relationships between rust resistance genes at the M locus in flax

Genes at the M locus in flax ( Linum usitatissimum ) that confer resistance to flax rust ( Melampsora lini ) occur in complex haplotypes containing up to 15 related genes or gene fragments. We have cloned two additional functional resistance genes at this locus, M1 and M3 , by transposon tagging and candidate gene approaches, and investigated the genetic relationships between four genes ( M , M1 , M3 and M4 ) by recombination analysis. M1 and M3 , like M , are members of the nucleotide binding site, leucine-rich repeat (NBS-LRR) family. Comparisons of the predicted M1 and M3 amino acid sequences with M and L6 reveal that: (i) M1 contains four additional LRRs, probably as a result of an unequal crossover event between duplicated regions; (ii) M1 shares large segments of exact identity with M and M3, indicative of intragenic recombination events; and (iii) a large number of amino acid differences are scattered throughout the M, M1 and M3 proteins. Recombination analysis (here and in previous studies) has revealed that M readily recombines with M1 , M3 and M4 , whereas these three genes fail to recombine despite large family sizes (>5800) in two test-cross families, suggesting that they may occupy allelic positions in the gene cluster. Several restriction fragment length polymorphism markers within or near the M locus were mapped with respect to seven crossover events between M and M1 . The results of this and previous studies provide evidence of structural differences between: (i) homoeologous loci in the different genomes of flax; (ii) different haplotypes at the M locus; (iii) different resistance genes in the M group; and (iv) the flanking regions downstream of M locus resistance genes.     

Changes in aboveground primary production and carbon and nitrogen pools accompanying woody plant encroachment in a temperate savanna

When woody plant abundance increases in grasslands and savannas, a phenomenon widely observed worldwide, there is considerable uncertainty as to whether aboveground net primary productivity (ANPP) and ecosystem carbon (C) and nitrogen (N) pools increase, decrease, or remain the same. We estimated ANPP and C and N pools in aboveground vegetation and surface soils on shallow clay and clay loam soils undergoing encroachment by Prosopis glandulosa in the Southern Great Plains of the United States. Aboveground Prosopis C and N mass increased linearly, and ANPP increased logarithmically, with stand age on clay loam soils; on shallow clays, Prosopis C and N mass and ANPP all increased linearly with stand age. We found no evidence of an asymptote in trajectories of C and N accumulation or ANPP on either soil type even following 68 years of stand development. Production and accumulation rates were lower on shallow clay sites relative to clay loam sites, suggesting strong edaphic control of C and N accumulation associated with woody plant encroachment. Response of herbaceous C mass to Prosopis stand development also differed between soil types. Herbaceous C declined with increasing aboveground Prosopis C on clay loams, but increased with increasing Prosopis C on shallow clays. Total ANPP (Prosopis+herbaceous) of sites with the highest Prosopis basal area were 1.2 × and 4.0 × greater than those with the lowest Prosopis basal area on clay loam and shallow clay soils, respectively. Prosopis ANPP more than offset declines in herbaceous ANPP on clay loams and added to increased herbaceous ANPP on shallow clays. Although aboveground C and N pools increased substantially with Prosopis stand development, we found no corresponding change in surface soil C and N pools (0–10 cm). Overall, our findings indicate that Prosopis stand development significantly increases ecosystem C and N storage/cycling, and the magnitude of these impacts varied with stand age, soil type and functional plant traits     

Factors affecting the vulnerability of cane toads (Bufo marinus) to predation by ants

Experimental evidence on the determinants of prey vulnerability is scarce, especially for vertebrates in the field. Invasive species offer robust opportunities to explore prey vulnerability, because the intensity of predation on or by such animals has not been eroded by coevolution. Around waterbodies in tropical Australia, native meat ants (Iridomyrmex reburrus) consume many metamorph cane toads (Bufo marinus, an invasive anuran). We document the determinants of toad vulnerability, especially the roles of toad body size and ant density. Larger metamorphs were attacked sooner (because they attracted more ants), but escaped more often. Overall, smaller toads were more likely to be killed. Ant densities influenced toad responses, as well as attack rate and success. Data on the immediate outcomes of attacks underestimate mortality: more than 73% of apparent ‘escapees’ died within 24 h. Because mortality during this period was independent of toad size, predation was less size selective than suggested by immediate outcomes. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 99 , 738–751.     

Experimental Studies of the Factors Controlling Transpiration: II. THE RELATION BETWEEN TRANSPIRATION RATE AND LEAF WATER CONTENT

Data are presented which show, when stomatal control is eliminated,that wheat leaves may lose 5–6 per cent. and Pelargoniumleaves 10–12 per cent. of their water without any reductionin the transpiration rate. Experiments in which Pelargonium and wheat leaves, with stomatalcontrol present, were submitted to cycles of changing watercontent also failed to establish any direct relation betweentranspiration rate and leaf water content. It is concluded that leaf water content over the range of 70–100per cent. of that present in the turgid state has no significanteffect in determining the rate of water loss from leaves. A repetition of Knight's experiment showed that stomata openedin still air and closed in moving air. This was not recordedby Knight, who used a porometer cup permanently attached tothe leaf. It is concluded that the higher transpiration raterecorded by Knight after a period of still air was due to widerstomatal aperture and not to the higher leaf water content assuggested by him.     

An analysis of the phenotypic effects of certain colour pattern genes in Heliconius (Lepidoptera: Nymphalidae)

The colour patterns of Heliconius butterflies are built up from an array of serially homologous pattern elements known as the nymphalid groundplan. An analysis of the phenotypic effects of ten genetic loci from H. melpomene and H. cydno reveals that each alters the expression either of a single element of the groundplan or of an entire row of serially homologous elements. Five of the ten loci affect the size (or presence/absence) of specific pattern elements, two affect the colour in which a pattern element is expressed, two affect pattern-inducing activity of the wing veins, and one appears to affect an overall threshold for pattern determination. Three of the ten loci have identical effects on homologues of the fore- and hindwing. We show that most of the apparently large and qualitative phenotypic effects of these genes can be readily explained by relatively small and quantitative changes in the dimensions or positions of specific pattern elements.     

Complex effects of habitat loss on Golden Eagles Aquila chrysaetos

The development of commercial forests presents potential threats to large raptors that rely on prey caught in open country. We examined the effect of afforestation of breeding habitat used by a population of Golden Eagles Aquila chrysaetos in Scotland where, over the last 50 years, extensive stands of exotic conifers have been planted. Using data for 31 years on territory occupancy and breeding success, together with spatiotemporally dynamic mapping of forest cover and predicted areas of territory‐use in a Geographical Information System, we examined relationships between forest cover and Eagle ecology at landscape and individual territory scales. Several territories were abandoned during the earliest phases of forest planting, but relatively few were apparently lost to later plantings. Territories with poorer breeding productivity appeared to be more vulnerable to abandonment than territories with better breeding productivity. At the landscape scale, temporal differences in breeding productivity were negatively related to the extent of forest cover, although productivity of individual territories showed no clear relationship with forest cover. Several territories with less than a 5% increase in forest cover experienced reduced productivity; however, territories least constrained by neighbouring pairs of Eagles showed an increase in productivity. Territories experiencing the greatest increases in forest cover showed a greater use of spatially separated nest‐sites by occupying pairs. Hence, pairs that were less constrained by neighbours appeared to compensate for loss of open habitat by shifting their territory‐use, whereas pairs that were more constrained could not compensate for open habitat loss and suffered reduced productivity (and, probably in some cases, abandoned the territory). We suggest that simple guidelines based on the extent and locations of habitat loss are inadequate when predicting effects on large territorial raptors such as Golden Eagles. Consideration should also be given to the ‘quality’ of a territory or occupying pair, as well as the extent to which territory‐use is constrained by neighbouring pairs or other ‘unsuitable habitat’ which may have been affected by previous episodes of open habitat loss.     

Patterns of Root Respiration Associated with the Induction of Aluminium Tolerance in Phaseolus vulgaris L.

Aluminium (Al) tolerance in an Al-tolerant cultivar of Phaseolusvulgaris L. (‘Dade’) was found to be an inducibletrait. Upon exposure to 10 µM Al, the rate of root elongationwas inhibited in comparison to controls. During the following72 h, the rate of elongation returned to levels comparable tocontrols. In contrast, root elongation of an Al-sensitive cultivar(‘Romano’) did not recover after exposure to Al.In Dade, the resumption of root elongation following exposureto Al was accompanied by increased rates of root respiration,whereas respiration rates slowly declined over the 72 h treatmentperiod in Romano. When partitioned into growth and maintenanceexpenditures, a larger proportion of root respiration of Dadeexposed to Al was allocated to maintenance processes, potentiallyreflecting diversion of energy to metabolic pathways that offsetthe adverse effects of Al toxicity. Romano did not show sucha pattern and respiration associated with both growth and maintenancewas reduced after exposure to Al. Root and shoot growth of bothcultivars were also measured to determine the effects of long-term(21 d) exposure to 10 µM Al. Dade plants exposed to Alexhibited enhanced growth in comparison to controls, whereasRomano plants were characterized by reduced shoot and root growth.Modelling the time-course of root respiration and measuringthe long-term growth responses to Al is a valuable method ofelucidating respiratory costs of stress tolerance. Key words: Aluminium, differential tolerance, maintenance respiration, Phaseolus vulgaris, root respiration     

The state of play of farmland birds: population trends and conservation status of lowland farmland birds in the United Kingdom

Many bird species of lowland farmland have declined substantially in the United Kingdom over the past 30 years. Declines among farmland specialists are steeper than for generalists and were most rapid for these specialists in the 1970s and 1980s. These changes have been linked to increased agricultural intensification and are reflected in Red or Amber conservation concern status for many common farmland species, as well as for rarer ones. We review long- and short-term population trends and the conservation status of lowland farmland birds in the UK using the latest available information from bird surveys, and examine patterns among species. Analyses of demographic parameters suggest broadly that the key factor driving population changes of seed-eating and migrant birds is overwinter survival, whereas for many non-passerine species population growth appears to be limited by productivity. Population trends for a suite of lowland farmland species were first combined in the UK Government's headline wild bird indicator published in 1998. This 'Skylark index' as it is sometimes known was intended to reflect the health of the wider countryside and struck a chord with the public and decision-makers. We look at the behaviour of the composite indicator and explore the population dynamics of the increasing and declining species separately. Simple models of population growth in these groups are then used to explore plausible scenarios for delivering the Government's Public Service Agreement target to reverse the long-term decline in the number of farmland birds by 2020.