Are the most numerous sensilla of terrestrial isopods hygroreceptors? Ultrastructure of the dorsal tricorn sensilla of Porcellio scaber

The ultrastructure of the tricorn sensilla of the woodlouse Porcellio scaber was investigated in cryofixed and freeze-substituted, or chemically fixed specimens. The tricorn sensilla have a foramenized triangular-shaped outer hair and bear a poreless rod-like inner hair. The conical base of the inner hair is connected to the base of the outer hair by a complex cuticular structure. Each sensillum contains three sensory cells. The tip of one of the three dendrites contains a tubular body and is clamped between two bulges of the dendritic sheath. The two other dendrites protrude to the tip of the inner hair, flush against the cuticular wall. The microtubules in the ciliary segments are arranged in nine double tubuli that have neither osmiophilic cores nor arms. The ciliary rootlets are small. The inner segment of the largest dendrite wraps around the two smaller dendrites and one of seven enveloping cells in a mesaxon-like manner. Although this ultrastructure deviates considerably from most crustacean mechanosensitive sensilla, it nevertheless suggests a mechanosensitive function, at least for one of the sensory cells. In many aspects, the tricorn sensilla resemble the thermohygrosensilla of insects. However, our results suggest that the structural criteria for thermo-hygro-sensitivity used in insects cannot simply be applied to crustaceans.     

Pseudonormalisation of the T wave: old wine?

A 74-year-old woman with documented coronary artery disease presented with symptoms of angina at rest. During these episodes of angina, the initial abnormal terminal negative T waves converted to normal positive T waves. In this article the significance of pseudonormalisation as a sign of ischaemia is reviewed. The underlying electropathological basis of this phenomenon is discussed as well. (Neth Heart J 2007;15:257-9.)     

The historic biogeography of India: isolation or contact?

Geophysical maps depicting continental movement have consistently shown India, as it moved northward, to be located far out in the Tethys Sea. India split off from the African east coast about 148 m.y.a. From that time onward, according to almost all geophysical accounts, India was isolated from all of other continents until the early Miocene when it made contact with Eurasia. But the biological data, both fossil and Recent, indicate that this concept cannot be correct. If India had really existed as an isolated, oceanic continent for about 100 m.y., it should have developed a peculiar biota with many endemic genera and families in its terrestrial and shallow marine habitats. But there are virtually no remains of organisms indicating that India was isolated for any substantial time (millions of years). Instead, we find that almost all Indian taxa were possessed in common with other continents. As time went on, the northern relationships became stronger and the southern ones weaker. Most of the recent geophysical accounts show India not making contact with Eurasia until the early Miocene, but fossil materials show that this event must have taken place by the early Eocene. It has been postulated that, as India moved northward, it created a biogeographic barrier that separated marine fish populations and resulted in the east-west provinces that are now apparent in the Indian Ocean. At the same time, the barrier effect was supposed to have resulted in the formation of sister species that are now located far apart. Information currently available indicates that most living, tropical marine species are probably not over 3 m.y. old. Consequently, the northward movement of India, which took place primarily between 148 and 50 m.y.a., could have no bearing on the relationships of modern species.     

Success of ectoparasites: how important is timing of host contact?

Hosts often differ in their degree of parasitism and their expression of resistance. Yet very little is known about how the availability (and allocation) of resources to parasites at pre-infective stages influences their success in initiating parasitism, or in inducing and succumbing to resistance from hosts. We studied a damselfly-mite association to address how experimental variation in the age of first contact with hosts (timing) influenced subsequent parasite fitness. We demonstrate that timing influenced the ability of larval mites to make the transition to parasitism, but was not associated with measures of physiological resistance by hosts. Timing presumably relates to the availability of resources remaining for individuals to exploit their hosts. More research is needed on the importance of such factors, from variation in host resistance and parasite success and, ultimately, to the numbers and distributions of parasites on hosts.     

Evolving visual pigments: Hints from the opsin-based proteins in a phylogenetically old “eyeless” invertebrate

Visual pigments are photosensitive receptor proteins that trigger the transduction process producing the visual excitation once they have absorbed photons. In spite of the molecular and morpho-functional complexity that has characterized the development of animal eyes and eyeless photoreceptive systems, opsin-based protein family appears ubiquous along metazoan visual systems. Moreover, in addition to classic rhodopsin photoreceptors, all Metazoa have supplementary non-visual photosensitive structures, mainly located in the central nervous system, that sense light without forming an image and that rather regulate the organism's temporal physiology. The investigation of novel non-visual photopigments exerting extraretinal photoreception is a challenging field in vision research. Here we propose the cnidarian Hydra as a useful tool of investigation for molecular and functional differences between these pigment families. Hydra is the first metazoan owning a nervous system and it is an eyeless invertebrate showing only an extraocular photoreception, as it has no recognized visual or photosensitive structures. In this paper we provide an overview of the molecular and functional features of the opsin-based protein subfamilies and preliminary evidences in a phylogenetically old species of both image-forming and non-visual opsins. Then we give new insights on the molecular biology of Hydra photoreception and on the evolutionary pathways of visual pigments.     

The sulfide binding function of annelid hemoglobins: relic of an old biosystem?

Invertebrates living in sulfide-rich environments have developed different strategies of coping with sulfide toxicity. Some bivalves and annelids have hemoglobins that are capable of binding sulfide for detoxification and/or transporting it to internal bacterial symbionts. Annelids living in the sulfide-rich environments have giant (approximately 3.6 MDa) hemoglobin, consisting of 144 globin chains arranged in a hexagonal bilayer structure held together by 36 nonglobin linker chains. Some globin chains contain either a free cysteine residue at positions Cys+1 or at position Cys+11 relative to the E7 distal residue in the E helix and EF interhelical region, respectively, which bind sulfide. The hexagonal bilayer hemoglobins of annelids living in environments lacking sulfide, do not have the corresponding free cysteine residues and cannot bind sulphide. Given that the early stages of life occurred under anoxic conditions in the presence of sulfide, it is possible that the sulfide binding function from modern annelid globins inhabiting sulphide rich habitats is an evolutionary relic. This proposal seems supported by the recent finding of "protoglobins" which also have a corresponding cysteine residue in Archea known to exist in hyperthermophilic and sulfide-rich environments.     

Vasodilatory effects of cholecystokinin: new role for an old peptide?

Cholecystokinin (CCK) peptides are involved in the control of multiple functions both in the central nervous system (CNS) and in the gastrointestinal tract where they act as neurotransmitters and regulate digestive functions. This review deals with the role of CCK peptides as vasoactive mediators. Recent work from our group demonstrates that CCK peptides induce neurogenic vasodilatation both in cerebral and mesenteric vessels. Such an effect is mediated by nitric oxide and seems to be presynaptic. These findings suggest that endogenous CCK peptides could be relevant vasodilatory agents involved in regulating both cerebral and splanchnic blood flow. We hypothesize here how such an effect could be useful in the interpretation of, in a new conceptual frame, the eventual contribution of CCK to some physiological and physiopathological events, such as splanchnic postprandial hyperaemia, panic attack or migraine.     

Malaria: new vaccines for old?

Detailed analyses of the 5500 genes revealed by the complete Plasmodium genome sequence are yielding new candidate parasite antigens and strategies that may contribute to a successful vaccine against malaria in the coming decade.     

Power requirements of swimming: do new methods resolve old questions?

A recurring question in the study of fish biomechanics and energeticsis the mechanical power required for tail-swimming at the highspeeds seen among aquatic vertebrates. The quest for answershas been driven by conceptual advances in fluid dynamics, startingwith ideas on the boundary layer and drag initiated by Prandtl,and in measurement techniques starting with force balances focussingon drag and thrust. Drag (=thrust) from measurements on physicalmodels, carcasses, kinematics as inputs to hydromechanical models,and physiological power sources vary from less than that expectedfor an equivalent rigid reference to over an order of magnitudegreater. Estimates of drag and thrust using recent advanceslargely made possible by increased computing power have notresolved the discrepancy. Sources of drag and thrust are notseparable in axial undulatory self propulsion, are open to interpretationand Froude efficiency is zero. Wakes are not easily interpreted,especially for thrust evaluation. We suggest the best measuresof swimming performance are velocity and power consumption forwhich 2D inviscid simulations can give realistic predictions.Steady swimming power is several times that required for towingan equivalent flat plate at the same speed.     

Genetics of Alzheimer's disease: new evidences for an old hypothesis?

Alzheimer's disease (AD) is the prime cause of dementia and presents a strong genetic predisposition (60-80% of the attributable risk). In addition to APOE, a major recognized genetic determinant of AD, systematic, high-throughput genomic approaches have recently allowed the characterization of four new genetic determinants: CLU, CR1, PICALM and BIN1. Even if the complete picture of AD genetics is still not fully understood, the characterization of these new AD genetic determinants is probably going to strongly modify our perception of the pathophysiological process involved in AD. The new AD genetic landscape suggests that the common and late-onset forms of the disease are associated with a defect in peripheral Aβ peptide clearance, implying that the amyloid cascade hypothesis could be relevant not only in the AD monogenic forms.     

Dietary diversification and variations in the number of labrum sensilla in grasshoppers: Which came first?

The diversity of the diet of grasshoppers (Acrididae, Orthoptera) is related to multiple factors, including the chemoreceptors on the antennae, palps and on the epipharyngeal face of the labrum. In the present study, we sought to understand the nature of the diet of 12 Moroccan acridian species and to try to relate various aspects of their diet to the number of labrum sensilla. If the effect of the labrum size on the number of sensilla is removed, four groups of species are recorded: (i) polyphagous species with a broad diet and numerous sensilla; (ii) polyphagous species with a graminivorous diet and numerous sensilla; (iii) oligophagous species feeding exclusively on Poaceae and with a medium number of sensilla; and (iv) strictly monophagous species feeding on a single plant species and with the smallest number of sensilla. These observations show the close relationship between the diet and the number of labrum sensilla. However, Sphingonotus rubescens, a polyphagous species, is an exception to this trend as it harbours a medium number of sensilla. We propose that the modification in the number of labrum sensilla is a result of a progressive adaptation to a different diet and does not represent its cause.     

Can contact potentials reliably predict stability of proteins?

The simplest approximation of interaction potential between amino acid residues in proteins is the contact potential, which defines the effective free energy of a protein conformation by a set of amino acid contacts formed in this conformation. Finding a contact potential capable of predicting free energies of protein states across a variety of protein families will aid protein folding and engineering in silico on a computationally tractable time-scale. We test the ability of contact potentials to accurately and transferably (across various protein families) predict stability changes of proteins upon mutations. We develop a new methodology to determine the contact potentials in proteins from experimental measurements of changes in protein's thermodynamic stabilities (DeltaDeltaG) upon mutations. We apply our methodology to derive sets of contact interaction parameters for a hierarchy of interaction models including solvation and multi-body contact parameters. We test how well our models reproduce experimental measurements by statistical tests. We evaluate the maximum accuracy of predictions obtained by using contact potentials and the correlation between parameters derived from different data-sets of experimental (DeltaDeltaG) values. We argue that it is impossible to reach experimental accuracy and derive fully transferable contact parameters using the contact models of potentials. However, contact parameters may yield reliable predictions of DeltaDeltaG for datasets of mutations confined to the same amino acid positions in the sequence of a single protein.     

Convergence and parallelism: is a new life ahead of old concepts?

In comparative biology, character observations initially separate similar and dissimilar characters. Only similar characters are considered for phylogeny reconstruction; their homology is attested in a two‐step process, firstly a priori of phylogeny reconstruction by accurate similarity statements, and secondly a posteriori of phylogeny analysis by congruence with other characters. Any pattern of non‐homology is then a homoplasy, commonly, but vaguely, associated with “convergence”. In this logical scheme, there is no way to analyze characters which look similar, but cannot meet usual criteria for homology statements, i.e., false similarity detected a priori of phylogenetic analysis, even though such characters may represent evolutionarily significant patterns of character transformations. Because phylogenies are not only patterns of taxa relationships but also references for evolutionary studies, we propose to redefine the traditional concepts of parallelism and convergence to associate patterns of non‐homology with explicit theoretical contexts: homoplasy is restricted to non‐similarity detected a posteriori of phylogeny analysis and related to parallelism; non‐similarity detected a priori of phylogenetic analysis and necessarily described by different characters would then correspond to a convergence event s. str. We propose to characterize these characters as heterologous (heterology). Heterology and homoplasy correspond to different non‐similarity patterns and processes; they are also associated with different patterns of taxa relationships: homoplasy can occur only in non‐sister group taxa; no such limit exists for heterology. The usefulness of these terms and concepts is illustrated with patterns of acoustic evolution in ensiferan insects. © The Willi Hennig Society 2005.