Ontogenetic shape changes in Pomacentridae (Teleostei,Perciformes) and their relationships with feeding strategies: a geometric morphometric approach

The present study explores the shape changes of cranial structures directly involved in food capturing during growth after reef settlement in two species of Pomacentridae (Dascyllus aruanus and Pomacentrus pavo). Landmark‐based geometric morphometrics were used to study allometric patterns and related shape changes in four skeletal units: neurocranium, suspensorium and opercle, mandible and premaxilla. At settlement, the larvae of both species have a relatively similar morphology, especially with respect to the mandible. Their shapes suggest a feeding mode defined as ram/suction‐feeding. Ontogenetic shape changes show a shift to a suction feeding mode of prey capture. The main transformations involved are an increase in height of the suspensorium and the opercle, an elevation of the supraoccipital crest, a relative shortening of the mandible, and a lengthening of the ascending process of the premaxilla. Shape changes of the mandible in the two studied species also reflect an increase of biting capacities. The high disparity between adult shape results from differences in the rate and in the length of ontogenetic trajectories, from divergence of the ontogenetic trajectories (neurocranium, mandible, and premaxilla) and parallel shifts of the trajectories in the size‐shape space (suspensorium and opercle). In an evolutionary context, allometric heterochronies during ontogeny of different skeletal unit of the head may be considered as a basis for the explanation of the diversity of damselfishes. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 92–105.     

Ontogenetic changes in behavioural and histological measures of visual acuity in three species of fish

Synopsis Vision plays an important role in the early life history of fishes. We investigated the ontogenetic changes in visual acuity of early life history stages of alewife,Alosa pseudoharengus, yellow perch,Perca flavescens and bloater,Coregonus hoyi, across a range of sizes. Acuities were determined through histological examination of the retinae of larvae. Reactive distances of larvae to prey were estimated through videophotography of their response to prey and were then converted to measurements of visual angle. Both measures of visual ability improved with size (age) for all species. When behavioural and anatomical measures of ability were compared as a function of size, the data indicate that fish are anatomically more capable of seeing objects than the behavioural response suggests. In two of the three species, the relationship between histological acuity and visual angle was not constant. These results may indicate that while vision may limit initial rates of encounter and feeding, increases in visual acuity mean that in older stages limitations on encounter and feeding are more likely to be behavioural. Furthermore, these results indicate that encounter rates based upon histological estimates of visual acuity will be greater than comparable estimates based upon reactive distances. We recommend calculation of encounter rates based upon reactive distances. Present address: Department of Biology, McGill University, 1205 Ave, Dr. Penfield, Montreal, PQ H3A 1B1, Canada     

Ontogenetic pattern,morphological sexual and side dimorphism in the saccular otolith of a scaleless killifish Aphanius furcatus (Teleostei: Aphaniidae)

The relationships between ontogenetic and sexual factors with otolith morphology are poorly studied in killifish genus Aphanius Nardo, 1827. We studied the ontogeny, morphological sexual and side dimorphism in the saccular otolith of a scaleless killifish Aphanius furcatus inhabiting a high‐salinity environment in Southern Iran. The results highlighted growth‐dependent variability in the otolith of A. furcatus, which might be useful to define its certain developmental stages. We underlined those characters that were consistent during fish development, which could be valuable to identify the species. Considering the ontogenetic pattern of otolith in A. furcatus, it was found that the otoliths of young individuals have largely been influenced by sexes and that it was reduced during the fish development. Morphological side dimorphism in the otolith of A. furcatus tends to be increased during fish development. The outcomes of this study are essential since they have provided new information on ontogenetic changes and the sexual and side dimorphism of Aphanius otolith.     

Distribution of goblet and endocrine cells in the intestine: A comparative study in Amazonian freshwater Tambaqui and hybrid catfish

Goblet cells (GCs) and endocrine cells (ECs) play an important role in intestine physiology, and few studies currently exist for Amazonian fishes. This study aimed to quantify the distribution of GCs and ECs producing cholecystokinin-8 and neuropeptide Y, assessed by mucin histochemistry and peptides immunohistochemistry, in the intestine of two Amazonian species with different feeding habits Tambaqui (Colossosoma macropomum) and hybrid catfish (Pseudoplatystoma reticulatum × Leiarius marmoratus), an omnivore and carnivore, respectively. A systematic literature review correlating feeding habit and GC and EC distribution was also included to contribute to the comparative study. The results of this study provided novel information about the gut cells of Tambaqui and hybrid catfish. Both, GCs and ECs can be found sweeping the entire intestine of Tambaqui and hybrid catfish although the cells can be more concentrated in certain segments. The GCs and ECs in Tambaqui were more uniformly distributed in the midgut segments (T1, T2, and T3). Unlike, in hybrid catfish GCs were more concentrated in the hindgut (C4) and ECs mainly in the two midgut segments (C1 and C2) of hybrid catfish. Based on the comparison between Tambaqui, hybrid catfish, and other fishes in the literature review, we suggest that cell distribution can be partially explained by feeding habits, carnivorous vs. omnivorous.     

Ontogenetic patterns of frequency-power spectra elicited by flickering light in children: a comparative study of evoked and background EEGs.

Frequency-power spectra of the EEG evoked by repeptitive photic stimulation and of the background EEG were studied during childhood in 43 awake subjects aged between 2 months and 14 years. EEG activity was recorded from the middle parieto-occipital region with the aid of a 1-channel analyzer Lysograf-Alvar, analysing 16 frequencies in the range from 2 to 28 c/sec. The responsiveness of the central nervous system to flickering light improved in the course of childhood in parallel with the significant decline of delta activity and with the prominent increase of alpha intensity in the resting EEG. The 4th month of life appeared to be a marked turning point in the development of evoked and background EEGs. From that age, the bioelectric power at the flash rate corresponding to photic "driving" began to increase together with the highest and optimal driving frequencies. The flash rate, at which evoked potentials changed into the "driven" rhythm, also shifted towards higher frequencies. Subsequently, the amount of energy in the resting EEG increased significantly within the theta, alpha and beta bands and, on the contrary, a prominent decline was observed in the delta range. Marked ontogenetic changes at this age closely coincided with the rapid development of exogenous fibres in the occipital cortex, including the thalamo-cortical conncetions, and fibres of the neuropil in cortical layer I, which might play an important role in the genesis of background and "driven" in the occipital region.     

Ontogeny of routine swimming speed and startle responses in red drum, with a comparison of responses to acoustic and visual stimuli

Routine swimming speed of larval red drum Sciaenops ocellatus increased throughout development but most rapidly for larvae >10 mm L _T. Red drum of all sizes swam faster than predicted by published summary equations based on other species, possibly due to more advanced development at a given length. Frequency and magnitude of startle responses increased over the larval period for both types of stimuli with most of the improvement taking place before larvae reached 8 mm L _T. Time to response for an acoustic and visual stimulus decreased early in the larval period but levelled off after 10 mm L _T. Response distance and response speed for both stimuli generally increased throughout the larval period, but response duration remained constant. Visually stimulated responses were generally longer in duration and distance covered than acoustically stimulated responses, while mean response speeds were similar.     

Ontogeny of tracheal system structure: a light and electron-microscopy study of the metathoracic femur of the American locust, Schistocerca americana

Does oxygen delivery become more challenging for insects as they increase in size? To partially test this hypothesis, we used quantitative light and electron microscopy to estimate the oxygen delivery capacity for two steps of tracheal oxygen delivery within the metathoracic femur (jumping leg) for 2nd instar (about 47 mg) and adult (about 1.7 g) locusts, Schistocerca americana. The fractional cross‐sectional areas of the major tracheae running longitudinally along the leg were similar in adults and 2nd instars; however, since the legs of adults are longer, the mass‐specific diffusive conductances of these tracheae were 4‐fold greater in 2nd instars. Diffusive gas exchange longitudinally along the leg is easily possible for 2nd instars but not adults, who have many air sacs within the femur. Mitochondrial content fell proximally to distally within the femur in 2nd instars but not adults, supporting the hypothesis that diffusion was more important for the former. Lateral diffusing capacities of the tracheal walls were 12‐fold greater in adults than 2nd instars. This was primarily due to differences in the smallest tracheal class (tracheoles), which had thinner epidermal and cuticular layers, greater surface to volume ratios, and greater mass‐specific surface areas in adults. Adults also had greater mitochondrial contents, larger cell sizes and more intracellular tracheae. Thus, larger insects do not necessarily face greater problems with oxygen delivery; adult grasshoppers have superior oxygen delivery systems and greater mass‐specific aerobic capacities in their legs than smaller/younger insects. J. Morphol. 262:800–812, 2004. © 2004 Wiley‐Liss, Inc.     

How river structure and biological traits influence gene flow: a population genetic study of two stream invertebrates with differing dispersal abilities

1. Determined by landscape structure as well as dispersal‐related traits of species, connectivity influences various key aspects of population biology, ranging from population persistence to genetic structure and diversity. Here, we investigated differences in small‐scale connectivity in terms of gene flow between populations of two ecologically important invertebrates with contrasting dispersal‐related traits: an amphipod (Gammarus fossarum) with a purely aquatic life cycle and a mayfly (Baetis rhodani) with a terrestrial adult stage. 2. We used highly polymorphic markers to estimate genetic differentiation between populations of both species within a Swiss pre‐alpine catchment and compared these results to the broader‐scale genetic structure within the Rhine drainage. Landscape genetic approaches were used to test for correlations of genetic and geographical structures and in‐stream barrier effects. 3. We found overall very weak genetic structure in populations of B. rhodani. In contrast, G. fossarum showed strong genetic differentiation, even at spatial scales of a few kilometres, and a clear pattern of isolation by distance. Genetic diversity decreased from downstream towards upstream populations of G. fossarum, suggesting asymmetric gene flow. Correlation of genetic structure with landscape topography was more pronounced in the amphipod. Our study also indicates that G. fossarum might be capable of dispersing overland in headwater regions and of crossing small in‐stream barriers. 4. We speculate that differences in dispersal capacity but also habitat specialisation and potentially the extent of local adaptation could be responsible for the differences in genetic differentiation found between the two species. These results highlight the importance of taking into account dispersal‐related traits when planning management and conservation strategies.     

Evolution on a local scale: developmental, functional, and genetic bases of divergence in bill form and associated changes in song structure between adjacent habitats

Divergent selection on traits involved in both local adaptation and the production of mating signals can strongly facilitate population differentiation. Because of its links to foraging morphologies and cultural inheritance song of birds can contribute particularly strongly to maintenance of local adaptations. In two adjacent habitats--native Sonoran desert and urban areas--house finches (Carpodacus mexicanus) forage on seeds that are highly distinct in size and shell hardness and require different bite forces and bill morphologies. Here, we first document strong and habitat-specific natural selection on bill traits linked to bite force and find adaptive modifications of bite force and bill morphology and associated divergence in courtship song between the two habitats. Second, we investigate the developmental basis of this divergence and find that early ontogenetic tissue transformation in bill, but not skeletal traits, is accelerated in the urban population and that the mandibular primordia of the large-beaked urban finches express bone morphogenetic proteins (BMP) earlier and at higher level than those of the desert finches. Further, we show that despite being geographically adjacent, urban and desert populations are nevertheless genetically distinct corroborating findings of early developmental divergence between them. Taken together, these results suggest that divergent selection on function and development of traits involved in production of mating signals, in combination with localized learning of such signals, can be very effective at maintaining local adaptations, even at small spatial scales and in highly mobile animals.     

Acyl chain conformational ordering in liquid-crystalline bilayers: comparative FT-IR and 2H-NMR studies of phospholipids differing in headgroup structure and chain length

FT-IR spectroscopy has been used to evaluate the acyl chain conformational ordering of DMPC, DMPE, DMPA (pH 6 and 12), DMPG (pH 1 and 7), and DPPC, DPPE, DPPA (pH 6). The frequencies of the symmetric and antisymmetric methylene stretching vibrations were determined as a function of temperature. In the liquid-crystalline phase the frequencies show a qualitative dependence on the amount of chain disorder. Quantitative data for trans-gauche isomerization were obtained from the integral intensities of the conformation sensitive methylene wagging absorptions at ca. 1368 cm^–1 (gtg and gtg sequences), 1356 cm ^–1 (double gauche) and 1342 cm^–1 (end gauche). The integral band intensities were converted to the number of gauche conformers per acyl chain using the calibration factors published by Senak et al. (1991). At 69°C the highest number of gauche conformers excluding contributions from single gauche conformers and jogs (gtttg) are found for PCs (DMPC: 2.6; DPPC: 2.4), followed by DMPG^– (2.0), phosphatidylethanolamines (DMPE: 1.4; DPPE: 2.0), protonated DMPG (1.5), and phosphatidic acids (DPPA^–: 1.7; DMPA^–: 1.4, DMPA^2–: 1.7). From ²H-NMR measurements of perdeuterated samples of DMPC, DMPA, DPPC, and DPPA the quadrupolar splittings _Qi and the order parameter S _CDi of the CD₂-segments close to the chain ends could be determined whereas splittings in the plateau region of the chains could not be resolved. The quadrupolar splittings are affected by trans-gauche isomerization, long axis rotation, and restricted wobbling motions of the acyl chains. In the simplest assumption, the order parameter S_CD can be expressed as a product of a segmental order parameter S and a lhain order parameter S . For comparison of the different lipids we used average order parameters S_CD, obtained by averaging over all values, and S determined from the total number of gauche conformers per chain by FT-IR-spectroscopy, to calculate an empirical average chain order parameter S. The combination of ²H-NMR and FT-IR results allows the estimation of the relative extent of chain wobbling for the different lipid molecules. S is lowest for PCs (S 0.475) while PEs (S 0.51) and PAs (S0.52) show less chain wobbling.Abbreviations FT-IR Fourier transform infrared - ²H-NMR deuterium nuclear magnetic resonance - DMPC(–d₅₄) (perdeuterated) dimyristoyl-phosphatidylcholine - DMPE(–d₅₄) (perdeuterated) dimyristoyl-phosphatidylethanolamine - DMPA(–d₅₄) (perdeuterated) dimyristoyl-phosphatidic acid - DMPG dimyristoyl-phosphatidylglycerol - DPPC(–d₆₂) (perdeuterated) dipalmitoyl-phosphatidylcholine - DPPE(–d₆₂) (perdeuterated) dipalmitoyl-phosphatidylethanolamine - DPPA(–d₆₂) (perdeuterated) dipalmitoyl-phosphatidic acid - gtg gauche ^±-trans-gauche^± - gtg gauche^±-trans-gauche^± - dg double gauche - eg end gauche Correspondence to: A. Blume     

Dispersal ability and genetic structure in aquatic invertebrates: a comparative study in southern California streams and reservoirs

1. The natural seasonal drying and flooding of southern California streams have been altered over the past century by activities related to agriculture, flood control, and reservoir construction. The genetic structure and diversity of aquatic invertebrates inhabiting these environments is largely unexplored, and may be important for conservation. 2. We sampled two species of aquatic invertebrates with different dispersal abilities to assess genetic structure and diversity, and make inferences about the evolutionary processes that underlie these genetic patterns. The mayfly Fallceon quilleri, which has a winged terrestrial stage, was sampled from perennial and intermittent streams from three catchments across San Diego County. The amphipod Hyalella azteca was sampled from streams (perennial and intermittent) and reservoirs in a single catchment (San Dieguito). Because it is obligately aquatic throughout its life‐cycle, H. azteca was assumed to disperse less than F. quilleri. 3. Intrapopulation and overall genetic diversity was higher in F. quilleri than in H. azteca. In F. quilleri there was very little genetic divergence among populations, and most of the genetic differentiation that was observed could be attributed to a single population. In H. azteca, populations were markedly differentiated between the upper and lower segments of the San Dieguito basin, which are separated by a c. 10 km section of stream that rarely has surface flow. Within both segments, genetic divergence between sites connected by reservoirs and perennial streams was not significantly different. 4. Our results suggest that F. quilleri disperses widely and thus avoids genetic bottlenecks and marked levels of population differentiation that may be expected from frequent extinctions and recolonizations. In contrast, restricted dispersal in H. azteca is associated with relatively low genetic diversity and high genetic divergence across a portion of the catchment in which surface flow is rare.     

Ontogenetic colour change and the evolution of aposematism: a case study in panic moth caterpillars

1. Aposematism is a widely used antipredator strategy in which an organism possesses both warning coloration and unprofitable characters. Theoretical evidence suggests that aposematic colour should develop when high opportunity costs imposed by crypsis force an organism to engage in conspicuous behaviours. Hence, it is expected that ontogenetic colour change (OCC) in larval insects should include aposematism when foraging needs compel behavioural modifications that preclude a continued state of crypsis. 2. To test this idea, I first investigated whether OCC in caterpillars of the panic moth Saucrobotys futilalis was indicative of a switch from cryptic to aposematic coloration. I then examined the context of panic moth OCC as it related to foraging patterns and behavioural conspicuousness. 3. Early Saucrobotys instars are a cryptic green, but later instars become progressively more orange and develop black spots. Early instar larvae forage cryptically on the inner parenchyma of silked-together host plant leaves to avoid predation, but are rapidly forced to engage in conspicuous foraging behaviours as they outgrow the resources afforded by their shelters. Both coloration and behaviour reach maximal conspicuousness in final instar larvae. 4. As predicted, OCC encompassed a change from crypsis to aposematism in Saucrobotys. Aposematic function was demonstrated by changes in both antipredator behaviour patterns and effectiveness of predator deterrence in early and late instars. Moreover, increased opportunity costs of crypsis and behavioural conspicuousness coincided with the onset of aposematic coloration. 5. This pattern of OCC suggests that aposematic coloration in Saucrobotys develops as a response to constraints imposed by crypsis. Moreover, my study illustrates the importance of the study of ontogenetic patterns in determining how behaviour, morphology, and predator responses interact to influence the initial evolution of phenomena such as aposematism.     

Global transcriptional responses of fission and budding yeast to changes in copper and iron levels: a comparative study

Background  

Recent studies in comparative genomics demonstrate that interspecies comparison represents a powerful tool for identifying both conserved and specialized biologic processes across large evolutionary distances. All cells must adjust to environmental fluctuations in metal levels, because levels that are too low or too high can be detrimental. Here we explore the conservation of metal homoeostasis in two distantly related yeasts.     

Ontogenetic adaptation to bipedalism: age changes in femoral to humeral length and strength proportions in humans, with a comparison to baboons

The increase in lower/upper limb bone length and strength proportions in adult humans compared to most other anthropoid primates is commonly viewed as an adaptation to bipedalism. The ontogenetic development of femoral to humeral proportions is examined here using a longitudinal sample of 20 individuals measured radiographically at semiannual or annual intervals from 6 months of age to late adolescence (a subset of the Denver Growth Study sample). Anthropometric data (body weights, muscle breadths) were also available at each examination age. Results show that while femoral/humeral length proportions close to those of adults are already present in human infants, characteristically human femoral/humeral diaphyseal strength proportions only develop after the adoption of bipedalism at about 1 year of age. A rapid increase in femoral/humeral strength occurs between 1 and 3 years, followed by a slow increase until mid-late adolescence, when adult proportions are reached. When age changes in material properties are factored in, femoral strength shows an almost constant relationship to body size (body mass.bone length) after 5 years of age, while humeral strength shows a progressive decline relative to body size. Femoral/humeral length proportions increase slightly throughout growth, with no apparent change in growth trajectory at the initiation of walking, and with a small decline in late adolescence due to later growth in length of the humerus. A sex difference in femoral/humeral strength proportions (females greater) but not length proportions, develops early in childhood. Thus, growth trajectories in length and strength proportions are largely independent, with strength proportions more responsive to actual changes in mechanical loading. A cross-sectional ontogenetic sample of baboons (n=30) illustrates contrasting patterns of growth, with much smaller age changes in proportions, particularly strength proportions, although there is some indication of an adaptation to altered limb loadings early in baboon development.     

Altitudinal changes in composition and structure of mountain-temperate vegetation: a case study from the Western Carpathians

Changes in composition and structure of plant communities in relation tothe soil and snow cover variation were analyzed along an altitudinal transect(1150–1750 m) from the mountain-temperate forests to a woodyshrub community and alpine meadows on Mt Velký Gápel', Slovakia.The soils below the treeline (1510 m) had a more developedorganic layer above the mineral substratum. Generally, soil depth decreased asthe altitude increased, although the maximum values were recognized at a middlealtitude in a beech stand. Snow was redistributed by westerly winds from theridgeline down to the upper forest margin. Mean snow depth decreased withaltitude up to almost snow-free sites around the summit. In the 48 plots at 16sites we recorded 118 taxa including 6 tree, 7 shrub, 18 grass, 42 herb, 5fern,25 moss and 15 lichen species. The species diversity showed no distinctrelationship to altitude but declined with canopy consolidation. The TWINSPANfloristic classification distinguished five groups of community typescharacterised by different dominants, and a further three clusters of samplesfrom transition zones. Horizontal compositional heterogeneity increased inareaswhere trees were aggregated and tree basal area was smaller. Vegetationcomposition became more patchy at open-canopy Acerpseudoplatanus–Abies alba mixed forest at 1150 m,in Picea abies forest limit 1470 m, andin Pinus mugo krummholz at 1590 m. Speciesturnover of the entire transect was 6.1 half-changes as estimated by DCA.Despite this heterogeneity, none of the 15 elevational bands had significantaggregation of species' limits. Vegetation varied continuously, with individualspecies overlapping in transition zones delimited by dominant taxa. Thecoincident aggregation of up-slope and down-slope boundaries was found at abelt1430–1510 m. This discrete ecotone corresponds to a shiftfrom the closed coniferous forest to P. mugo krummholz.Thesecond inherent up-slope boundary aggregation indicated the P.mugo krummholz – alpine meadow vegetation transition at1700 m. Spatial analysis (K-function) of eight forest plots(0.12 ha each) showed that at lower elevation, adult trees of thebroad-leaf forest were closer to a random arrangement while at higherelevation,trees of evergreen coniferous stands became aggregated toward the forest limitwith the highest intensity from 2 to 4 m. Altitudinal gradient andrelated factors explained 35% of the variance in vegetation data.Canonical correspondence analysis also showed that main vegetation changesabovethe treeline area were associated with the topographic pattern of pine shrubsand snow cover.     

Trends in evolution of floral ontogeny in Cassia sensu stricto,Senna, and Chamaecrista (Leguminosae: Caesalpinioideae: Cassieae: Cassiinae); a study in convergence

Distinctions in floral ontogeny among three segregate genera (Cassia sensu stricto, Chamaecrista, and Senna) of Cassia L. support their separation. In all species studied, the order of floral organ initiation is: sepals, petals, antesepalous stamens plus carpel, and lastly antepetalous stamens. Sepal initiation is helical in all three genera, which however differ in whether the first sepal is initiated in median abaxial position (Senna), or abaxial and off-median (Cassia javanica), a rare character state among legumes. Order of petal initiation varies: helical in Senna vs. unidirectional in Cassia and Chamaecrista. Both stamen whorls are uniformly unidirectional. Intergeneric ontogenetic differences occur in phyllotaxy, inflorescence architecture, bracteole formation, overlap of initiation among organ whorls (calyx/corolla in Cassia; two stamen whorls in Chamaecrista), eccentric initiation on one side of a flower, anther attachment, anther pore structure, and precocious carpel initiation in Senna. The asymmetric corolla and androecium in Chamaecrista arise by precocious organ initiation on one side (left or right). The poricidal anther character can result from differing developmental pathways: lateral slits vs. sealing of lateral sutures; clasping hairs vs. sutural ridges; terminal pores (one or two) vs. none; and clamp layer formation internally that prevents lateral dehiscence. Genera differ in corolla aestivation patterns and in stigma type. Convergence is shown among the three genera, based on intergeneric dissimilarities in early floral ontogeny (floral position in the inflorescence, bracteole presence, position of the first sepal initiated, order of petal initiation, asymmetric initiation, overlap between whorls, anther morphology, and time of carpel initiation) resulting in similarities at anthesis (showy, mostly yellow salverform flowers, heteromorphic stamens, poricidal anther dehiscence, bee pollination, and chambered stigma).     

Ontogenetic study of the skull in modern humans and the common chimpanzees: neotenic hypothesis reconsidered with a tridimensional Procrustes analysis

Heterochronic studies compare ontogenetic trajectories of an organ in different species: here, the skulls of common chimpanzees and modern humans. A growth trajectory requires three parameters: size, shape, and ontogenetic age. One of the great advantages of the Procrustes method is the precise definition of size and shape for whole organs such as the skull. The estimated ontogenetic age (dental stages) is added to the plot to give a graphical representation to compare growth trajectories. We used the skulls of 41 Homo sapiens and 50 Pan troglodytes at various stages of growth. The Procrustes superimposition of all specimens was completed by statistical procedures (principal component analysis, multivariate regression, and discriminant function) to calculate separately size-related shape changes (allometry common to chimpanzees and humans), and interspecific shape differences (discriminant function). The results confirm the neotenic theory of the human skull (sensu Gould [1977] Ontogeny and Phylogeny, Cambridge: Harvard University Press; Alberch et al. [1979] Paleobiology 5:296-317), but modify it slightly. Human growth is clearly retarded in terms of both the magnitude of changes (size-shape covariation) and shape alone (size-shape dissociation) with respect to the chimpanzees. At the end of growth, the adult skull in humans reaches an allometric shape (size-related shape) which is equivalent to that of juvenile chimpanzees with no permanent teeth, and a size which is equivalent to that of adult chimpanzees. Our results show that human neoteny involves not only shape retardation (paedomorphosis), but also changes in relative growth velocity. Before the eruption of the first molar, human growth is accelerated, and then strongly decelerated, relative to the growth of the chimpanzee as a reference. This entails a complex process, which explains why these species reach the same overall (i.e., brain + face) size in adult stage. The neotenic traits seem to concern primarily the function of encephalization, but less so other parts of the skull. Our results, based on the discriminant function, reveal that additional structural traits (corresponding to the nonallometric part of the shape which is specific to humans) are rather situated in the other part of the skull. They mainly concern the equilibrium of the head related to bipedalism, and the respiratory and masticatory functions. Thus, the reduced prognathism, the flexed cranial base (forward position of the foramen magnum which is brought closer to the palate), the reduced anterior portion of the face, the reduced glabella, and the prominent nose mainly correspond to functional innovations which have nothing to do with a neotenic process in human evolution. The statistical analysis used here gives us the possibility to point out that some traits, which have been classically described as paedomorphic because they superficially resemble juvenile traits, are in reality independent of growth.     

Monitoring of potassium-stimulated catecholamine changes in striatal synaptosomal preparations and in corpus striatum of rats: a comparative voltammetric study.

Voltammetric techniques were used to compare the effects of K(+)-induced depolarization on catecholamine levels in in vitro synaptosomal preparations of the corpus striatum with those in the in vivo corpus striatum of anaesthetized animals. In vitro, the catechol-oxidation currents could be recorded only in dopamine-preloaded synaptosomes. In isolated synaptosomes prepared in the presence of elevated concentrations of Ca2+ (1 mmol.l-1) and Na+ (135 mmol.l-1), K(+)-induced depolarization had variable effects on catechol-oxidation current. The stimulatory effect of K(+)-induced depolarization (a short transient increase of catechol-oxidation current lasting for 30 s) could be observed after the addition of dopamine loaded synaptosomes in EGTA into the medium with elevated K+ concentration (90 mmol.l-1) and decreased concentrations of Na+ (75 mmol.l-1) and Ca2+ (0.75 mmol.l-1). These results suggest that experimental procedures and parameters of ionic composition of incubation media have to be carefully controlled, owing to an enhanced in vitro permeability of membranes of isolated synaptosomes for Ca2+ and Na+. In in vivo experiments, microinjection of KCl (3 microliters of 0.5 mol.l-1 KCl in 10 mmol.l-1 HEPES, pH 7.4) resulted in the appearance of several phases of catechol-oxidation current: the current increased (to severalfold of the control values) followed by a decrease or even total disappearance, with a gradual return to control values. Under conditions of depletion of extracellular calcium by EGTA (5 microliters of 0.5 mol.l-1 KCl + 0.25 mol.l-1 EGTA in 10 mmol.l-1 HEPES, pH 7.4) K(+)-induced depolarization confirmed the key role of calcium in the release of catecholamine transmitters as well as that in processes regulating the uptake and metabolism of these transmitters. The voltammetric techniques used in the present study may be a useful tool in extending of our knowledge about the cellular mechanisms of stimulus-response coupling in nerve cells.