Denervated taste buds. I. General ultrastructural observations

it]Riassunto La denervazione dei calici gustativi provoca due tipi fondamentali di alterazioni cellulari: il primo è rappresentato da lisosomi e citosegregosomi che colpiscono le cellule scarsamento differenziate, il secondo è invece rappresentato da lesioni che sconvolgono l'intera organizzazione citoplasmatica delle cellule di II tipo.The author wishes to thank Mr. M. DrIorio and Mr. V.Panetta for their techeical assistance.     

The avian nature of the brain and inner ear of Archaeopteryx

Archaeopteryx, the earliest known flying bird (avialan) from the Late Jurassic period, exhibits many shared primitive characters with more basal coelurosaurian dinosaurs (the clade including all theropods more bird-like than Allosaurus), such as teeth, a long bony tail and pinnate feathers. However, Archaeopteryx possessed asymmetrical flight feathers on its wings and tail, together with a wing feather arrangement shared with modern birds. This suggests some degree of powered flight capability but, until now, little was understood about the extent to which its brain and special senses were adapted for flight. We investigated this problem by computed tomography scanning and three-dimensional reconstruction of the braincase of the London specimen of Archaeopteryx. Here we show the reconstruction of the braincase from which we derived endocasts of the brain and inner ear. These suggest that Archaeopteryx closely resembled modern birds in the dominance of the sense of vision and in the possession of expanded auditory and spatial sensory perception in the ear. We conclude that Archaeopteryx had acquired the derived neurological and structural adaptations necessary for flight. An enlarged forebrain suggests that it had also developed enhanced somatosensory integration with these special senses demanded by a lifestyle involving flying ability.     

Animal communication: ground squirrel uses ultrasonic alarms

Apart from echolocation and the pursuit of prey by bats, the function of ultrasound in animal communication is poorly understood. This is mainly because of the broad range of responses that it can evoke and the widely varied contexts in which it is used (for example, in rodents of the Muridae family it may indicate distress in infants or a sexual or predatory encounter in adults). Here we find that a purely ultrasonic signal is produced in the wild by a rodent of the Sciuridae family, Richardson's ground squirrel, and show that its function is to warn conspecifics of impending danger. To our knowledge, ultrasonic alarm calls have not previously been detected in any animal group, despite their twin advantages of being highly directional and inaudible to key predators.     

Fine-scale phylogenetic architecture of a complex bacterial community

Although molecular data have revealed the vast scope of microbial diversity, two fundamental questions remain unanswered even for well-defined natural microbial communities: how many bacterial types co-exist, and are such types naturally organized into phylogenetically discrete units of potential ecological significance? It has been argued that without such information, the environmental function, population biology and biogeography of microorganisms cannot be rigorously explored. Here we address these questions by comprehensive sampling of two large 16S ribosomal RNA clone libraries from a coastal bacterioplankton community. We show that compensation for artefacts generated by common library construction techniques reveals fine-scale patterns of community composition. At least 516 ribotypes (unique rRNA sequences) were detected in the sample and, by statistical extrapolation, at least 1,633 co-existing ribotypes in the sampled population. More than 50% of the ribotypes fall into discrete clusters containing less than 1% sequence divergence. This pattern cannot be accounted for by interoperon variation, indicating a large predominance of closely related taxa in this community. We propose that such microdiverse clusters arise by selective sweeps and persist because competitive mechanisms are too weak to purge diversity from within them.     

A confirmation of the general relativistic prediction of the Lense-Thirring effect

An important early prediction of Einstein's general relativity was the advance of the perihelion of Mercury's orbit, whose measurement provided one of the classical tests of Einstein's theory. The advance of the orbital point-of-closest-approach also applies to a binary pulsar system and to an Earth-orbiting satellite. General relativity also predicts that the rotation of a body like Earth will drag the local inertial frames of reference around it, which will affect the orbit of a satellite. This Lense-Thirring effect has hitherto not been detected with high accuracy, but its detection with an error of about 1 per cent is the main goal of Gravity Probe B--an ongoing space mission using orbiting gyroscopes. Here we report a measurement of the Lense-Thirring effect on two Earth satellites: it is 99 +/- 5 per cent of the value predicted by general relativity; the uncertainty of this measurement includes all known random and systematic errors, but we allow for a total +/- 10 per cent uncertainty to include underestimated and unknown sources of error.