L' Annee biologique最新文献

The hypothesis of a direct phylogenetic link between (non avian) dinosaurs and birds, already proposed by Huxley in the nineteenth century, and strongly supported by Ostrom since the nineteen-seventies has been definitely vindicated, to most specialist's satisfaction, by recent paleontological discoveries in China and elsewhere. Historically, those developments took place within the framework of a spectacular methodological change in comparative/evolutionary biology (systematics included), namely the shift from process-oriented explanatory functional scenarios to patterns-oriented phylogenetic analyses. For our purposes, the change in paradigm may be summarised as such: emphasis shifted from considerations of bird origin that were conflated with the origin of bird flight to the simple question of the identity of the immediate sister-group of birds. Within this changing intellectual context, the first connections between issues in comparative bone histology, on the one hand, and phylogenelic problems of bird/dinosaur relationships, on the other hand, were put forward in the late sixties and early seventies. Early ideas were based on rather indirect but independent evidences from bone histology, suggesting some kind of early dinosaurian endothermy, which could have been inherited by early birds and later built upon by more recent ones. Hence, early ideas about bird/dinosaur close phylogenetic relationships met histological evidences on the basis of a putative common endothermic regime. Reciprocally, independent morphological evidence for close bird/dinosaur phylogenetic relationships have been sometimes used to strengthen the histological case for dinosaurian endothermy itself, a clearly circular argument Later studies, including the first histological examinations of Mesozoic birds, have suggested caution about the histological arguments of an advanced (fully endothermic) physiology among early birds and (by implication) among their immediate dinosaurian forbears. Assuming an ‘Ostromian’ phylogeny, we contend here that no known bone histological characters really prevent early birds and closely related non-avian dinosaurs to have already reached an essentially endothermic level of physiological integration. We discuss the significance of bone ‘growth rings’ in that context. Peculiarities of early bird growth patterns, as currently known, may express the pervasive influences of shifts in body size and ontogenic timing (heterochronies) on skeletal histology. Those changes were probably linked to the acme of the transition and/or to later specialisation in some early bird lineages.

Development in metazoans is characterised by a morphological diversity both in the ontogenic and phylogenic fields. Unitary trends appear nevertheless. The most obvious of them are associated to the appearance of symmetries and polarities. This unity is also emphasised by a low number of cellular events as proliferation, migration, recognition, differentiation and apoptosis. The control of morphogenesis is marked itself by unitary features, as shown by analysis of the signals which initiate morphogenesis (growth factors, glycoproteins of the extracellular matrix, hormonal receptors) and genes which underlie this control.

Almost all aspects of our life are now affected by progress in the technosciences. Together with the increasing association between sciences and money and with the direct intervention of technobiology practices into living mechanisms, this substantially increases the frequency and the gravity of hazards for the Human being, hence the emergence of the precaution principle. According to this principle, it can be justified or imperative to limit or even to stop certain actions that can be potentially dangerous i.e. long before the scientific certainty of the occurrence of the danger. From examples in relation with the case of blood contamination, with the regulation of atmospheric pollution, with the GMO, with the vaccination against hepatitis B or with the mad cow alert, and the “chicken gate” it is shown that the precaution principle would has been applied in some cases, has been applied in other cases and should be applied in some other cases. However, the precaution principle that can modify the intrinsic notion of resposibility, should not lead to the inaction. In front of the three powers (sciences, media, political), this principle needs the intervention of citizens considered in their cultural choices, a situation that, beforehand, implies the organisation of an adequate information.

This paper studies the subacute toxicity of various metallic contaminants (copper, lead and platinum) already or potentially present in the environment. We used as a test organism a freshwater invertebrate, Lumbriculus variegatus (Annelid, Oligochaeta), widespread in this area. This worm reproduces only asexually (architomical scissiparity) and therefore presents a great aptitude for regeneration, especially at its cephalic part. The regeneration is achieved after 7 days (20 °C) and goes through eight characteristic stages (even if the sectionning was artificially induced). First, cephalic regeneration perturbations induced by copper, lead or platinum were tested. The subacute concentrations of he three metals induced a delay in cephalic regeneration. In addition, Pb and Pt treatments can cause atypical regenerations as compared with control (clear water regenerates) which are described in this paper. Worms arc intoxicated by water samples from well known heavy metal polluted sites. Toxic concentrations are sublethal but induce strong cephalic regeneration perturbations. Worm cephalic regeneration sensitivity to heavy metal pollution remains to be directly tested in the environment in order to qualify as an ccotoxicological test.