The effect of variation in parameters of the male calling song of the katydid,Amblycorypha parvipennis (Orthoptera: Tettigoniidae), on female phonotaxis and phonoresponse

After being placed equidistant from playbacks of two computer-generated male calls, females of the katydidAmblycorypha parvipennis preferentially moved toward call phrases that were louder, longer, and leading (initiated without being overlapped by other call phrase endings). Because earlier tests with calling males had indicated that male mating success was related to these call parameters, we suggest that mating success is partly a result of female choice. Females also preferentially responded to the initial, rather than the latter, half of male phrases. Results of other tests suggested that females were responding to increased phonatome rate characteristic of the first half of the phrase. Males may compete to lead in order to prevent jamming of initial phrase information. Females also preferentially phonoresponded (ticked) in response to longer phrases. In earlier studies of male mating success and female phonotaxis using live males, male weight, sound level, and leading were intercorrelated; however, none of these parameters were correlated with phrase length. We suggest that females may respond to different call parameters under different environmental conditions.     

Regionalisation of cell fate and morphogenetic movement of the mesoderm during mouse gastrulation

The developmental fate of cells in the epiblast of early-primitive-streak-stage mouse embryos was assessed by studying the pattern of tissue colonisation displayed by lac Z-expressing cells grafted orthotopically to nontransgenic embryos. Results of these fate-mapping experiments revealed that the lateral and posterior epiblast contain cells that will give rise predominantly to mesodermal derivatives. The various mesodermal populations are distributed in overlapping domains in the lateral and posterior epiblast, with the embryonic mesoderm such as heart, lateral, and paraxial mesoderm occupying a more distal position than the extraembryonic mesoderm. Heterotopic grafting of presumptive mesodermal cells results in the grafted cells adopting the fate appropriate to the new site, reflecting a plasticity of cell fate determination before ingression. The first wave of epiblast cells that ingress through the primitive streak are those giving rise to extraembryonic mesoderm. Cells that will form the mesoderm of the yolk sac and the amnion make up a major part of the mesodermal layer of the midprimitive-streak-stage embryo. Cells that are destined for embryonic mesoderm are still found within the epiblast, but some have been recruited to the distal portion of the mesoderm. By the late-primitive-streak-stage, the mesodermal layer contains only the precursors of embryonic mesoderm. This suggests that there has been a progressive displacement of the midstreak mesoderm to extraembryonic sites, which is reminiscent of that occurring in the overlying endodermal tissue. The regionalisation of cell fate in the late-primitive-streak mesoderm bears the same spatial relationship as their ancestors in the epiblast prior to cell ingression. This implies that both the position of the cells in the proximal-distal axis and their proximity to the primitive streak are major determinants for the patterning of the embryonic mesoderm. © 1995 Wiley-Liss, Inc.     

Thermodynamic study of motor behaviour optimization

Our work is aimed at studying the optimization of a complex motor behaviour from a global perspective. First, free climbing as a sport will be briefly introduced while emphasizing in particular its psychomotor aspect called route finding. The basic question raised here is how does the optimization of a sensorimotoricity-environment system take place. The material under study is the free climber's trajectory, viewed as the signature of climbing behaviour (i.e., the spatial dimension). The concepts of learning, optimization, constraint, and degrees of freedom of a system will be discussed using the synergistic approach to the study of movement (Bernstein, 1967; Kelso, 1977). Measures of a trajectory's length and convex hull can be used to define an index whose equation resembles that of an entropy. This index is a measure of the trajectory's overall complexity. Some important concepts related to the thermodynamics of curves will also be discussed. The optimization process will be studied by examining the changes in entropy over time for a set of trajectories generated during the learning of a route (ten successive repetitions of the same climb). It will be shown that the entropy of the trajectories decreases as learning progresses, that each level of expertise has its own characteristic entropy curve, and that for the subjects tested, the mean entropy of skilled climbers is lower than that of average climbers. Basing our analysis on the concepts of degrees of freedom and constraint equations, an attempt is made to relate trajectory entropy to system entropy. Based on the postulate that trajectory entropy is equal to the difference in entropy between the unconstrained and constrained system, a model of motor optimization is proposed. This model is illustrated by an entropy graph reflecting a dynamic release process. In the light of our results, two opposing views will be examined: movement construction vs. movement emergence.     

Mismatch Repair Genes on Chromosomes 2p and 3p Account for a Major Share of Hereditary Nonpolyposis Colorectal Cancer Families Evaluable by Linkage

Two susceptibility loci for hereditary nonpolyposis colo-rectal cancer (HNPCC) have been identified, and each contains a mismatch repair gene: MSH2 on chromosome 2p and MLH1 on chromosome 3p. We studied the involvement of these loci in 13 large HNPCC kindreds originating from three different continents. Six families showed close linkage to the 2p locus, and a heritable mutation of the MSH2 gene was subsequently found in four. The 2p-linked kindreds included a family characterized by the lack of extracolonic manifestations (Lynch I syndrome), as well as two families with cutaneous manifestations typical of the Muir-Torre syndrome. Four families showed evidence for linkage to the 3p locus, and a heritable mutation of the MLH1 gene was later detected in three. One 3p-linked kindred was of Amerindian origin. Of the remaining three families studied for linkage, one showed lod scores compatible with exclusion of both MSH2 and MLH1, while lod scores obtained in the other two families suggested exclusion of one HNPCC locus (MSH2 or MLH1) but were uninformative for markers flanking the other locus. Our results suggest that mismatch repair genes on 2p and 3p account for a major share of HNPCC in kindreds that can be evaluated by linkage analysis.     

Consumption of benthic invertebrates by waterbirds in the Oosterschelde estuary,SW Netherlands

The number of waders in the Oosterschelde, S.W. Netherlands, declined after a reduction in intertidal area due to the construction of a storm surge barrier and secondary dams, suggesting that the carrying capacity had been reached (Schekkerman et al., 1993). In this paper we present data on consumption and predation pressure by birds to explore whether the reduction in their numbers is due to prey depletion or to other factors.The total annual consumption of benthic invertebrates by birds in the Oosterschelde amounted to 1573 × 10³ g ADW y^–1 in the period before the coastal engineering works (pre-barrier) and 1500 × 10³ kg ADW y^–1 in the post-barrier period. More than half of the total amount of biomass is eaten by the Oystercatcher, and only seven (pre-barrier) or even six (post-barrier) bird species together take 90% of the total.Although the consumption by individual species may vary considerably among years, the total consumption was remarkably stable, with a CV of only 3–4% of the mean, especially compared to the variability of the prey populations. In the pre-barrier period, consumption was lowest in mid summer, increased sharply from August onwards until a peak was reached in January. A sharp decrease took place in March. In the post-barrier period, consumption peaked in October.The total consumption per unit area per year does not differ much between different sectors of the Oosterschelde, apart from a distinctly lower value in the eastern part. Of the total amount of food taken by birds, only 0.1–0.4% is taken in the subtidal compartment. In several study plots on an individual tidal flat, there was a clear relation between consumption and benthic biomass.The predation pressure was 13 and 23% of the standing stock, in the post- and pre-barrier period respectively. When cockles, mussels and their main predator, the Oystercatcher, are excluded from the calculations, the predation pressure of the other species was 30 and 37% of the biomass, respectively.Predation pressure of Oystercatchers in individual study plots varied from less than 10% to more than 70% of the standing stock. On cockle beds the predation pressure was positively related to the average length of the cockles present.Based on these results and a comparison with the literature we conclude that, at least for several species that feed intertidally, carrying capacity could be limited by the stocks of food. This does not mean that birds face food shortage each season. As the variability of the benthos populations is much higher than that of the bird densities it is likely that at some times food is not limiting, at other times it is. On the other hand, consumption is very low in the subtidal compartment and species feeding here could potentially increase substantially in numbers in the Oosterschelde.     

Cloning and characterization of the platypus mitochondrial genome

The vertebrate mitochondrial genome is highly conserved in size and gene content. Among the chordates there appears to be one basic gene arrangement, but rearrangements in the mitochondrial gene order of the avian lineages have indicated that the mitochondrial genome may be more variable than once thought. Different gene orders in marsupials and eutherian mammals leave the ancestral mammalian order in some doubt. We have investigated the mitochondrial gene order in the platypus (Ornithorhynchus anatinus), a representative of the third major group of mammals, to determine which mitochondrial gene arrangement is ancestral in mammals. We have found that the platypus mtDNA conforms to the basic chordate gene arrangement, common to fish, amphibians, and eutherian mammals, indicating that this arrangement was the original mammalian arrangement, and that the unusual rearrangements observed in the avians and marsupials are probably lineage-specific. Correspondence to: N.J. Gemmell     

Neurite Outgrowth Stimulated by the Tyrosine Kinase Inhibitor Herbimycin A Requires Activation of Tyrosine Kinases and Protein Kinase C

Abstract: Activation of tyrosine kinases is established as an important mechanism for controlling growth cone motility and neurite outgrowth. We have tested the effects of a range of tyrosine kinase inhibitors on neurite outgrowth from postnatal day 4 cerebellar granule cells cultured over confluent monolayers of 3T3 fibroblasts. The only agent that had any effect was herbimycin A, which stimulated neurite outgrowth. The response is shown to be attributable to a direct effect of this tyrosine kinase inhibitor on neurones. The neurite outgrowth response to herbimycin A was inhibited by two other tyrosine kinase inhibitors, which on their own did not affect neurite outgrowth. The data suggest that the response to herbimycin A reflects either a direct or indirect activation of one or more protein tyrosine kinases. Independent signalling events downstream from tyrosine kinase activation underlying the neurite outgrowth response to herbimycin A include increased activity of protein kinase C and calcium influx into neurones through both N-and L-type calcium channels.     

Disruption of Potential α-Helix in the G Loop of the Guinea: Pig 5-Hydroxytryptamine2 Receptor Does Not Prevent Receptor Coupling to Phosphoinositide Hydrolysis

Abstract: Heterogeneity of the 5-hydroxytryptamine₂ (5-HT₂) receptor across species has been implicated in several pharmacological and physiological studies. Although 5-HT₂ receptors in the rat have been linked to increases in Phosphoinositide (PI) hydrolysis, little evidence exists to support the association of guinea pig 5-HT₂ receptors with Pl hydrolysis, the second messenger generally linked with 5-HT₂receptors. In the present study, we have taken a molecular and biochemical approach to determining whether species differences in brain 5-HT₂ receptors exist between rat and guinea pig. First, we isolated partial cortical 5-HT_a receptor cDNA clones that encompassed the third intracellular loop, a receptor area putatively important in receptor-effector coupling. The amino acid sequences deduced from the cDNA clones for rat and guinea pig brain 5-HT₂ receptor were 97% homologous. However, the guinea pig 5-HT₂ receptor had two tandem substitutions that disrupted a potential alpha helix in the region of the third cytoplasmic loop, which theoretically could alter the intracellular coupling of the guinea pig cortical 5-HT₂ receptor. Because of these molecular differences, we examined further the pharmacological activation of the brain 5-HT₂ receptor from guinea pig. 5-HT and the 5-HT₂ receptor agonist α-methyl-5-HT increased PI hydrolysis in guinea pig cortical slices whereas the 5-HT_1c receptor agonist 5-methyltryptamine was significantly less potent. In addition, the 5-HT₂ receptor antagonists LY53857, ketanserin, and spiperone blocked 5-HT-stimulated Pl hydrolysis. These pharmacological data suggested that activation of the 5-HT₂ receptor in guinea pig cortical slices was associated with PI hydrolysis. Thus, although areas of the guinea pig brain 5-HT₂ receptor that influence receptor-effector coupling were different from the rat, such differences were not critical to receptor-effector coupling because, as in the rat, guinea pig brain 5-HT₂ receptors were also coupled to PI hydrolysis.     

Turgor-dependent unloading of assimilates from coats of developing legume seed. Assessment of the significance of the phenomenon in the whole plant

The in vivo significance of turgor-dependent unloading was evaluated by examining assimilate transport to and within intact developing seeds of Phaseolus vulgaris (cv. Redland Pioneer) and Vicia faba (cv. Coles Prolific). The osmotic potentials of the seed apoplast were low. As a result, the osmotic gradients to the seed coat symplast were relatively small (i.e. 0.1 to 0.3 MPa). Sap concentrations of sucrose and potassium in the seed apoplast and coat symplast accounted for some 45 to 60% of the osmotic potentials of these compartments. Estimated turnover times of potassium and sucrose in the seed apoplast of < 1 h were some 5 to 13 times faster than the respective turnover times in the coat symplast pools. The small osmotic gradient between the seed apoplast and coat symplast combined with the relatively rapid turnover of solutes in the apoplast pool, confers the potential for a small change in assimilate uptake by the cotyledons to be rapidly translated into an amplified shift in the cell turgor of the seed coat. Observed adjustments in the osmotic potentials of solutions infused between the coat and cotyledons of intact seed were consistent with the in vivo operation of turgor-dependent unloading of solutes from the coat. Homeostatic regulation of turgor-dependent unloading was indicated by the maintenance of apoplast osmotic potentials of intact seeds when assimilate balance was manipulated by partial defoliation or elevating pod temperature. In contrast, osmotic potentials of the coat symplast adjusted upward to new steady values over a 2 to 4 h period. The resultant downward shift in coat cell turgor could serve to integrate phloem import into the seed coat with the new rates of efflux to the seed apoplast. Circumstantial evidence for this linkage was suggested by the approximate coincidence of the turgor changes with those in stem levels of ³²P used to monitor phloem transport. The results obtained provide qualified support for the in vivo operation of a turgor homeostat mechanism. It is proposed that the homeostat functions to integrate assimilate demand by the cotyledons with efflux from and phloem import into the coats of developing legume seed.     

Turgor-dependent unloading of photosynthates from coats of developing seed of Phaseolus vulgaris and Vicia faba. Turgor homeostasis and set points

Key physiological characteristics of turgor-dependent efflux of photosynthates were examined using excised coats and cotyledons of developing Phaseolus vulgaris (cv. Redland Poineer) and Vicia faba (cv. Coles Prolific) seed during the linear phase of seed fill. Exposure to solutions of high osmotic potential inhibited net uptake of [¹⁴C]sucrose by cotyledons at developmental stages less than 60% of their final dry weight. The effect could not be fully reversed by transferring cotyledons to solutions set at lower osmotic potentials. The inhibition became apparent at osmotic potentials that were higher than those that caused stimulation of efflux from seed coats. Net [¹⁴C]sucrose uptake by cotyledons at more advanced stages of development was unaffected by external osmotic potential. Specified tissue layers were removed from seed coats by pretreatment with pectinase. Efflux studies with the pectinase-modified coats of Phaseolus and Vicia seed demonstrated that the cellular site of turgordependent efflux was the ground parenchyma and thin-wall parenchyma transfer cells, respectively. Coats subjected to long-term (hours) incubations, under hypo-osmotic conditions, exhibited the capacity for turgor regulation. This was mediated by turgor-dependent efflux of solutes. The solutes exchanged were of nutritional significance to the developing embryo. The relationship between efflux and coat turgor was characterised by a turgor-independent phase at low turgors. Once turgor exceeded a minimal value (set point), efflux increased in proportion to the magnitude of the turgor deviation (error signal) from the set point. For coats of sink-limited seed of Vicia and Phaseolus, efflux exhibited apparent saturation at turgors above 0.25 and 0.5 MPa respectively. The putative turgor set point and slope of the turgor-dependent component of efflux varied with seed development, the prevailing source/sink ratio and genetic differences in seed growth rate. The nature of these kinetic variations was compatible with the competitive ability of the seed. A turgor homeostat model is proposed that incorporates the observed functional attributes of turgor-dependent efflux. Operationally, the model provides a mechanistic basis for the integration of assimilate demand by the cotyledons with assimilate import into and unloading from the seed coat.