Neurophysiological Aspects of Song Pattern Recognition and Sound Localization in Grasshoppers

SYNOPSIS. In their intraspecific communication females of thegrasshopper Chorthippus biguttulus are able to detect minutegaps in songs. Males of this species can lateralize sound withless than 1 dB difference between the two ears. Behavioral experimentssuggested that separate pathways exist for song recognitionand sound localization. As for the neurophysiological basis,auditory receptors respond tonically and necessarily carry allinformation explaining behavioral performances in their spikingresponses. However, for pattern recognition as well as for codingof directional information, it seems necessary for the animalto evaluate a whole set of parallel receptor fibres to achievethe precision observed in behavior. The information of receptorsconverges onto thoracic neurons which drive neurons ascendingto the brain. Some of these ascending neurons exhibit dramaticresponse differences either for various temporal patterns orfor sound from different directions and therefore may representpathways specialized for song recognition or for sound localization.     

A Kinetic Theory of First Order Cyclical Processes—Phytochrome Controlled Red Light Induced Cereal Leaf Unfolding Compared with Theory

The phytochrome controlled unfolding of cereal leaves was studied as a function of irradiation time and light intensity (narrowband red light) over a wide energy range (5 decades). With different intensities, a family of similarly shaped response curves appear with distinct time-dependent maxima and minima. A theoretical kinetic model based upon a cyclical phytochrome photoconversion scheme has been calculated by us. The theoretical calculations and the experimental findings are in excellent agreement. The same model explains the early photoresponses (first maxima) as an effect of one active phytochrome form, P₂, and the delayed photoresponses as an effect of a second active form P_n. The active transitory form, P₂ (although it may not be the primary product), is formed upon light absorption from P₁. The P₂ decays by a first order dark reaction through several inactive intermediates to P_n (active). The effect of the intermediates is mainly to delay the production of the second active product. It is possible to identify the two active products, P₂ and P_n, as P_fr and P*_fr, respectively. The presented cyclical phytochrome reaction scheme is a special case of a general first order kinetic cycle which includes all possible feed back loops. The latter scheme also has been calculated and programmed since it has a more general application.     

[CO2]- and density-dependent competition between grassland species

The predicted ongoing increase of atmospheric carbon dioxide levels is considered to be one of the main threats to biodiversity due to potential changes in biotic interactions. We tested whether effects of intra‐ and interspecific planting density of the calcareous grassland perennials Bromus erectus and Carex flacca change in response to elevated [CO₂] (600 ppm) by using factorial combinations of seven densities (0, 1, 2, 4, 8, 16, 24 tillers per 8 × 8 cm² cell) of both species in plots with and without CO₂ enrichment. Although aboveground biomass of C. flacca was increased by 54% under elevated [CO₂], the combined aboveground biomass of the whole stand was not significantly increased. C. flacca tended to produce more tillers under elevated [CO₂] while B. erectus produced less tillers. The positive effect of [CO₂] on the number of tillers of C. flacca was strongest at high intraspecific densities. On the other hand, the negative effect of [CO₂] on the number of tillers of B. erectus was not present at intermediate intraspecific planting densities. Seed production of C. flacca was more than doubled under elevated [CO₂], while seed production of B. erectus was not affected. Moreover, the mass per seed of C. flacca was increased by elevated [CO₂] at intermediate interspecific planting densities while the mass per seed of B. erectus was decreased by elevated [CO₂] at high interspecific planting densities. Our results show that the responses of C. flacca and B. erectus to elevated [CO₂] depend in a complex way on initial planting densities of both species. In other words, competition between these two model species is both [CO₂]‐ and density dependent. On average, however, the effects of [CO₂] on the individual species indicate that the composition of calcareous grasslands is likely to change under elevated [CO₂] in favor of C. flacca.     

Negative changes in the scientific publication process in ecology: potential causes and consequences

1. Increasingly viewed to have societal impact and value, science is affected by complex changes such as globalisation and the increasing dominance of commercial interest. As a result, technical advancements, financial concerns, institutional prestige and journal proliferation have created challenges for ecological and other scientific journals and affected the perception of both researchers and the public about the science that they publish. 2. Journals are now used for more than dissemination of scientific research. Institutions use journal rankings for a variety of purposes and often require a pre‐established number of articles in hiring and budgetary decisions. Consequently, journal impact factors have achieved greater importance, and the splitting of articles into smaller parcels of information (‘salami‐slicing’) to increase numbers of publications has become more frequent. 3. Journals may prescribe upper limits to article length, even though the average length of articles for several ecological journals examined has increased over time. There are clear signs, however, that journals without length limits for articles will become rarer. In contrast to ecological journals, taxonomic journals are not following this trend. 4. Two case histories demonstrate how splitting longer ecological articles into a series of shorter ones results in both redundancy of information and actually increases the journal space used overall. Furthermore, with current rejection rates of ecological journals (often ～80%), many thin salami‐sliced articles jam the peer‐review system much longer (through resubmission after rejection) than unsliced articles previously did (e.g. when rejection rates were ～50%). In our experience, the increased pressure to publish many articles in ‘high‐impact’ journals also may decrease the attractiveness of a future scientific career in ecology to young people. 5. ‘Gatekeeping’ of journal quality has shifted from editors to reviewers, and several recent trends are apparent including: bias about appropriate statistical methods; reviewers being more rigid overall; non‐native English writers being criticised for poor communications skills; and favourable reviews being signed more often than unfavourable ones. In terms of production, outsourcing of copy editing has increased the final error rate of published material. 6. We supplemented our perceptions with those of older colleagues (～100 experienced ecologists) that responded to an informal survey on this topic (response rate: 81%). In the opinion of almost 90% of our respondents, the overall review process has changed and for 20% among them the professional quality of reviews has declined. 7. We, and many older colleagues, are convinced there have been some negative changes in the scientific publication process. If younger colleagues share this concern, we can collectively counter this deteriorating situation, because we are the key to the publishing and evaluation process.     

Radial growth response of four dominant boreal tree species to climate along a latitudinal gradient in the eastern Canadian boreal forest

To address the central question of how climate change influences tree growth within the context of global warming, we used dendroclimatological analysis to understand the reactions of four major boreal tree species –Populus tremuloides, Betula papyrifera, Picea mariana, and Pinus banksiana– to climatic variations along a broad latitudinal gradient from 46 to 54°N in the eastern Canadian boreal forest. Tree‐ring chronologies from 34 forested stands distributed at a 1° interval were built, transformed into principal components (PCs), and analyzed through bootstrapped correlation analysis over the period 1950–2003 to identify climate factors limiting the radial growth and the detailed radial growth–climate association along the gradient. All species taken together, previous summer temperature (negative influences), and current January and March–April temperatures (positive influences) showed the most consistent relationships with radial growth across the gradient. Combined with the identified species/site‐specific climate factors, our study suggested that moisture conditions during the year before radial growth played a dominant role in positively regulating P. tremuloides growth, whereas January temperature and growing season moisture conditions positively impacted growth of B. papyrifera. Both P. mariana and P. banksiana were positively affected by the current‐year winter and spring or whole growing season temperatures over the entire range of our corridor. Owing to the impacts of different climate factors on growth, these boreal species showed inconsistent responsiveness to recent warming at the transition zone, where B. papyrifera, P. mariana, and P. banksiana would be the most responsive species, whereas P. tremuloides might be the least. Under continued warming, B. papyrifera stands located north of 49°N, P. tremuloides at northern latitudes, and P. mariana and P. banksiana stands located north of 47°N might benefit from warming winter and spring temperatures to enhance their radial growth in the coming decades, whereas other southern stands might be decreasing in radial growth.     

Sources and sinks of nitrous oxide (N2O) in deep lakes

As reported from marine systems, we found that also in15 prealpine lakes N₂O concentrations werestrongly correlated with O₂ concentrations. Inoxic waters below the mixed surface layer, N₂Oconcentrations usually increased with decreasingO₂ concentrations. N₂O is produced in oxicepilimnia, in oxic hypolimnia and at oxic-anoxicboundaries, either in the water or at the sediment-waterinterface. It is consumed, however, incompletely anoxic layers. Anoxic water layers weretherefore N₂O undersaturated. All studied lakeswere sources for atmospheric N₂O, including thosewith anoxic, N₂O undersaturated hypolimnia.However, compared to agriculture, lakes seem not tocontribute significantly to atmospheric N₂Oemissions.