A ratio code for vibrotactile pitch

Subjective impressions of pitch for 80 different sinusoidal vibrotactile stimuli delivered to the index finger were measured by free magnitude estimation in four subjects. In three of the subjects, pitch at a given frequency decreased as stimulus amplitude increased. The data of these subjects were well described by a model of pitch based on the relative levels of activation of the three major tactile channels. The main element in this model was a ratio of P channel activity to the sum of the activity levels of the P, NPI, and NPIII channels. Activity levels of the channels were estimated on the basis of the psychophysical literature, including a study of vibrotactile loudness using the same subjects and stimuli as those employed here. A fourth subject, whose pattern of loudness judgments had previously been shown to differ from those of the other subjects, did not conform to this pitch model: her data revealed significant increases in pitch with increases in amplitude, and appear to reflect an inability to combine signals across vibrotactile channels. Pitch changes resulting from vibrotactile adaptation were directionally consistent with our ratio model: pitch was slightly increased by adaptation to a 25 Hz stimulus, and slightly decreased by 200 Hz adaptation.     

The Diving Response Mechanism and its Surprising Evolutionary Path in Seals andSea Lions

During the last half century or more, studies of diving physiologyand biochemistry made great progress in mechanistically explainingthe basic diving response of aquatic mammals and birds. Keycomponents of the diving response (apnea, bradycardia, peripheralvasoconstriction, redistribution of cardiac output) were foundin essentially all species analyzed and were generally takento be biological adaptations. By the mid 1970s, this approachto unravelling the diving response had run 'out of steam' andwas in conceptual stasis. The breakthrough which gave renewalto the field at this time was the development of microprocessorbased monitoring of diving animals in their natural environments,which led to a flurry of studies mostly confirming the basicoutlines of the diving response based upon laboratory studiesand firmly placing it into proper biological context, underliningits plasticity and species specificities. Now towards the endof the millenium, despite ever more detailed field monitoringof physiology, behaviour and ecology, mechanistic studies areagain approaching a point of diminishing returns. To avoid anotherconceptual stasis, what seems required are new initiatives whichwe anticipate may arise from two differing approaches. The firstis purely experimental, relying on magnetic resonance imaging(MRI) and spectroscopy (MRS) to expand the framework of theoriginal "diving response" concept. The second—evolutionarystudy of the diving response—is synthetic, linked to bothfield and laboratory studies. To date the evolution of the divingresponse has only been analyzed in pinnipeds and from thesestudies two kinds of patterns have emerged. (1) Some physiologicaland biochemical characters, required and used in diving animals,are highly conserved not only in pinnipeds but in all vertebrates;these traits are necessarily similar in all pinnipeds and includediving apnea, bradycardia, tissue specific hypoperfusion, andhypometabolism of hypoperfused tissues. (2) Another group offunctionally linked characters are more malleable and include(i) spleen mass, (ii) blood volume, and (iii) hemoglobin (Hb)pool size. Increases in any of these traits improve diving capacity.Assuming that conserved physiological function means conservedsequences in specific genes and their products (and that evolvingfunction requires changes in such sequences), it is possibleto rationalize both above trait categories in pinniped phytogeny.However, it is more difficult for molecular evolution theoryto explain how complex regulatory systems like those involvedin bradycardia and peripheral vasoconstriction remain the samethrough phylogenetic time than it is to explain physiologicalchange driven by positive natural selection.     

Testing subspecies hypothesis with molecular markers and morphometrics in the Pacific white tern complex

To test the validity of subspecies designations of the white tern, genetic and morphological data were used to assess differences among four putative Pacific subspecies Gygis alba candida , Gygis alba rothschildi , Gygis alba pacifica , and Gygis alba microrhyncha . The origin(s) of a recent colonization of Oahu was also examined using molecular data. Samples were collected from 209 birds, representing island groups of the North and South Pacific. Culmen length and depth, longest and shortest rectrix lengths, and wing chord measurements from an earlier dataset were compared. Mitochondrial DNA variation suggests that there are no phylogenetically distinct species within the Pacific Ocean. The genetic and morphological similarity of G. a. candida and G. a. rothschildi warrants merging them into one subspecies ( G. a. candida ). Gygis alba microrhyncha and G. a. pacifica are distinctly smaller and larger than the other two subspecies, respectively, but are not completely diagnosable across the morphological characters examined. Although the Pacific subspecies do not exhibit reciprocal monophyly, there is significant genetic differentiation among the two South Pacific groups, G. a. microrhyncha , G. a. pacifica , and all other Pacific subspecies. This differentiation warrants treating these two South Pacific groups as separate management units, but not species or subspecies. Finally, the recently established population of white terns on Oahu shared haplotypes with all subspecies, suggesting multiple origins from populations across the Pacific and confirming contemporary gene flow.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 98 , 586–595.     

Glutamine Synthetase Isoenzymes of Striga hermonthica and other Angiosperm Root Parasites

The occurrence of multiple forms of glutamine synthetase inStriga hermonthica and other angiosperm root parasites was investigated.The facultative chlorophyllous parasite Melampyrum arvense exhibitedtwo isoenzymes in leaf tissue, the cytosolic component (GS₁)comprised less than 30% of total glutamine synthetase. In contrastGS₁ was the major component (<70%) in photosynthetic tissueof Striga hermonthica and S. gesnerioides. Only a single isoenzyme(GS₁) was detectable in the achlorophyllous root parasites Orobancheand Lathraea and in non-photosynthetic tissue of S. gesnerioides.The kinetic and physical properties of GS₁ and GS₂ of theseangiosperm parasites were similar to those of the isoenzymesin other non-parasitic angiosperms. Key words: Glutamine synthetase, Angiosperms, Root parasites     

Changes in Levels and Integrity of Ribosomal RNA During Seed Maturation and Germination in Carrot (Daucus carota L.)

Thompson, S., Bryant, J. A. and Brocklehurst, P. A. 1987. Changesin levels and integrity of ribosomal RNA during seed maturationand germination in carrot (Daucus carota L.).—J. exp.Bot. 38: 1343–1350. Amounts and integrity (percentage of complete un-nicked molecules)of ribosomal RNA (rRNA) during germination in carrot seed lotsof differing vigour and viability were examined using aqueousand formamide gel electrophoresis. In unaged seed, amounts ofrRNA per seed in dry seed are not related to maturity, vigouror viability. However, rRNA in immature seed is more vulnerableto damage by ageing than rRNA in mature seed; thus, amountsof rRNA per seed in aged seed are indicators of vigour and viability.On imbibition of aged or unaged seed, more rRNA fragmentationoccurs in immature seed than in mature seed, and the time atwhich the effects of synthesis outweigh the effects of degradationis earlier during germination in mature than in immature seed. Key words: rRNA, seed maturation, seed germination, Daucus carota L.     

Epidemiology of eyespot (Pseudocercosporella herpotrichoides) on winter wheat, with particular reference to the period of infection

The period of infection by Pseudocercosporella herpotrichoides was investigated by transplanting winter wheat from uninfested to infested sites at Cambridge. Maximum infection was found on plants moved between November and March; most conidia were trapped during winter but infection was not closely related to the numbers of conidia. Plants exposed at intervals on infested land and incubated in a standard environment became infected throughout the period from October to July; infection was not closely related to the numbers of conidia trapped or plant age, but was positively correlated with the number of wet days/wk. Thus, while enough P. herpotrichoides conidia were dispersed throughout the life of winter wheat crops to cause substantial infection, environmental factors limited the development of new infections from April onwards. Practical implications of these results for the choice of sowing date, the development of resistant varieties, and fungicide use, are discussed.     

SOME EFFECTS OF NITROGEN SUPPLY ON THE INFECTION OF TOMATO PLANTS WITH TOMATO SPOTTED WILT VIRUS

The susceptibility of tomato plants to systemic infection by tomato spotted wilt virus was increased by increasing nitrogen supply to levels above that optimal for growth. The virus content, estimated by local-lesions counts, was also raised by increasing nitrogen. The period between inoculation and the appearance of systemic symptoms was decreased by increasing nitrogen to a point slightly greater than the optimal level for growth, but increased by additional applications.
Infected plants receiving more nitrate or ammonium compounds than were needed for optimal growth showed abnormal leaf symptoms and no bronzing. N, P and Mg analyses showed that these symptoms were related primarily to nitrogen content. Such leaves contained more virus than bronzed leaves.     

Contrasting stream water NO3− and Ca2+ in two nearly adjacent catchments: the role of soil Ca and forest vegetation

Two nearly adjacent subcatchments, located in the Adirondack Mountains of New York State, US, with similar atmospheric inputs of N (0.6 kmol ha^?1 yr^?1), but markedly different stream water solute concentrations, provided a unique opportunity to evaluate the mechanisms causing this variation. Subcatchment 14 (S14) had much greater stream water Ca²⁺ and NO₃^? concentrations (851 and 73 μmol_c L^?1, respectively) than Subcatchment 15 (S15) (427 and 26 μmol_c L^?1, respectively). To elucidate factors affecting the variability in stream water concentrations, soil and forest floor samples from each subcatchment were analyzed for total elemental cations and extractable N species. Mineral soil samples were also analyzed for exchangeable cations. Tree species composition was characterized in each subcatchment and potential differences in land use history and hydrology were also assessed. Compared with S15, soils in S14 had significantly higher total elemental Ca²⁺ in the forest floor (380 vs. 84 μmol g^?1), Bs horizon (e.g. 1361 vs. 576 μmol g^?1) and C horizon (1340 vs. 717 μmol g^?1). Exchangeable Ca²⁺ was also significantly higher in the mineral soil (64 μmol g^?1 in S14 vs. 8 μmol g^?1 in S15). Extractable NO₃^? was higher in S14 compared with S15 in both the forest floor (0.1 vs. 0.01 μmol g^?1) and Bs horizon (0.2 vs. 0.07 μmol g^?1) while extractable NH₄⁺ was higher in S14 vs. S15 in the forest floor (7 vs. 5 μmol g^?1). The total basal area of ‘base‐rich indicator’ tree species (e.g. sugar maple, American basswood, eastern hophornbeam) was significantly greater in S14 compared with S15, which had species characteristic of sites with lower base concentrations (e.g. American beech and eastern white pine). The disparity in stream water Ca²⁺ and NO₃^?, concentrations and fluxes between S14 and S15 were explained by differences in tree species composition and soil properties rather than differences in land use or hydrology. The marked difference in soil Ca²⁺ concentrations in S14 vs. S15 corresponded to the higher stream water Ca²⁺ and the larger contribution of base‐rich tree species to the overstory biomass in S14. Soil under such species is associated with higher net mineralization and nitrification and likely contributed to the higher NO₃^? concentrations in the drainage waters of S14 vs. S15. Studies investigating differences in spatial and temporal patterns of the effects of chronic N deposition on surface water chemistry need to account for changes in tree species composition and how vegetation composition is influenced by soil properties, as well as climatic and biotic changes.