Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Allometry”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed1999

Are there mechanical limits to size in wave-swept organisms?

Hydrodynamic forces imposed by ocean waves are thought to limit the size of nearshore plants and animals, but it has proved difficult to determine the mechanism. Explanations based on the scaling mismatch between hydrodynamic accelerational forces and the strength of organisms do not work. Mechanisms that incorporate the allometry of drag and strength accurately predict the maximal size of intertidal algae but not of animals, and internally imposed inertial forces may explain the limits to size in large kelps. The general question of size in wave-swept organisms remains open and intriguing.

Animals↗
PubMed2000

Locomotion in scombrid fishes: morphology and kinematics of the finlets of the chub mackerel Scomber japonicus.

Finlets are small non-retractable fins located on the dorsal and ventral margins of the body between the second dorsal and anal fins and the tail of scombrid fishes. The morphology of the finlets, and finlet kinematics during swimming in a flow tank at speeds of 0.8-3. 0 fork lengths s(-1), were examined in the chub mackerel Scomber japonicus. Functionally, S. japonicus has five dorsal and anal triangular finlets (the fifth finlet is a pair of finlets acting in concert). Slips of muscle that insert onto the base of each finlet indicate the potential for active movement. In animals of similar mass, finlet length and area increased posteriorly. Finlet length, height and area show positive allometry in animals from 45 to 279 g body mass. Summed finlet area was approximately 15 % of caudal fin area. During steady swimming, the finlets typically oscillated symmetrically in the horizontal and vertical planes. Finlet excursions in the x, y and z directions ranged from 1 to 5 mm, increased posteriorly and were independent of speed. The timing of the maximum amplitude of oscillation was phased posteriorly; the phase lag of the maximum amplitude of oscillation was independent of speed. During some periods of gliding, a finlet occasionally moved independently of the body and the other finlets, which indicated active control of finlet movement. The angle of attack of the finlets averaged approximately 0 degrees over a tailbeat, indicating no net contribution to thrust production via classical lift-based mechanisms. However, the timing of finlet movement relative to that of the tail suggests that more posterior finlets may direct some flow longitudinally as the tail decelerates and thereby contribute flow to the developing caudal fin vortex.

Animals↗
PubMed2001

Oxygen uptake by embryos and ovigerous females of two intertidal crabs, Heterozius rotundifrons (Belliidae) and Cyclograpsus lavauxi (Grapsidae): scaling and the metabolic costs of reproduction.

Heterozius rotundifrons and Cyclograpsus lavauxi are crabs of similar size, whose intertidal habitats overlap. They differ in the number and size of their eggs. A 2 g ovigerous H. rotundifrons incubates 675 large yolky eggs (mean single-egg mass 269 microg; egg clutch 9.15 % of mass of female crab; increasing to 435 microg and 13.4 % at hatching). The egg clutch of a 2 g C. lavauxi is larger (15.4 % of crab mass increasing to 18.9 % at hatching) and contains more numerous (28 000), smaller (10.9 microg increasing to 20.3 microg) eggs. The longer development time of the larger eggs (194 days versus 56 days at 15 degrees C) results from a delayed increase in metabolic rate (diapause) and not metabolic scaling. On the basis of the total mass of single eggs, the mass-specific metabolic rates of early embryonic stages of H. rotundifrons (0.72 micromol g(-1 )h(-1) for the blastula stage at 15 degrees C) and C. lavauxi (1.13 micromol g(-1 )h(-1)) were similar to those of the adult female crabs (0.70 micromol g(-1 )h(-1) for H. rotundifrons and 0.91 micromol g(-1 )h(-1) for C. lavauxi) and increased 13- and 10-fold, respectively, by the time of hatching. Thus, early embryonic metabolic rates were much lower than expected from their mass, but the metabolic rates of pre-hatching embryos were consistent with the allometry of juveniles and adults. Possible interpretations of this apparently anomalous scaling of embryonic metabolic rates are discussed. Mass-specific rates of oxygen consumption by ovigerous females (including the eggs) of both species were higher than for non-ovigerous crabs, in water and in air, and increased greatly during the development of the eggs. This difference was attributable mainly to the increasing metabolic rates of the attached embryos, but early ovigerous crabs (blastula stage) of both species also demonstrated a small elevation in metabolic rate by the crab itself, i.e. a metabolic cost of egg-bearing. In contrast, the elevation of the rate of oxygen consumption by late ovigerous females of C. lavauxi was less than predicted from the metabolic rate of eggs in a stirred respirometer. This suggests that, towards the end of development in C. lavauxi, the oxygen supply to the eggs in situ may be diffusion-limited by unstirred layers, an effect not observed for the larger eggs and more open egg clutch of H. rotundifrons. The cost of development, in terms of total oxygen consumption of single eggs, from extrusion to hatching, was 3.34 micromol O2 (approximately 1.5 J) for H. rotundifrons and 0.105 micromol O2 (approximately 0.05 J) for C. lavauxi. This 30-fold ratio approximates the ratios of their initial masses and yolk contents but represents only approximately one-third of the initial energy contents of the eggs.

Animals↗
PubMed2002

Scaling of rotational inertia in murine rodents and two species of lizard.

Because the force required to rotate a body about an axis is directly proportional to its rotational inertia about the axis, it is likely that animals with high rotational inertia would be constrained in their turning abilities. Given that rotational inertia scales with mass(1.67) in geometrically similar animals, whereas the ability to apply torque scales with mass(1.00), larger animals would be expected to have more difficulty turning than smaller animals of similar shape. To determine how rotational inertia scales with body mass, we used the fact that the period of a physical pendulum is proportional to its rotational inertia(0.50), and measured rotational inertia in two groups of vertebrates with greatly different body shapes: murine rodents (Mus domesticus and Rattus norvegicus) and lizards (Iguana iguana and Varanus exanthematicus). Rotational inertia did not deviate significantly from isometric scaling in the murine rodents as a group or in the varanid lizards, scaling with mass(1.63) and mass(1.59), respectively. Although rotational inertia did scale with negative allometry in iguanas and rats alone, with mass(1.56) and mass(1.42), respectively, it still increased much more quickly with increasing mass than the predicted ability to apply torque. This suggests either that these animals are not constrained by rotational inertia because of their relatively small size or that larger rodents and lizards are poorer turners than smaller ones. The murine rodents had a 3.0- to 4.9-fold lower rotational inertia than similarly sized lizards of either species. Given that the basal synapsids had body proportions and limb configurations similar to those of modern lizards, we suggest that the loss of the large muscular tail and elongated body form during the evolution of cynodonts and mammals reduced rotational inertia and probably improved turning ability.

Animals↗
PubMed2003

Paracrine overexpression of IGFBP-4 in osteoblasts of transgenic mice decreases bone turnover and causes global growth retardation.

Insulin-like growth factor binding protein 4 (IGFBP-4) is abundantly expressed in bone and is generally believed to function as an inhibitor of IGF action. To investigate the function of locally produced IGFBP-4 in bone in vivo, we targeted expression of IGFBP-4 to osteoblasts using a human osteocalcin promoter to direct transgene expression. IGFBP-4 protein levels in calvaria of transgenic (OC-BP4) mice as measured by Western ligand blot were increased 25-fold over the endogenous level. Interestingly, levels of IGFBP-5 were decreased in the OC-BP4 mice, possibly because of a compensatory alteration in IGF-1 action. Morphometric measurements showed a decrease in femoral length and total bone volume in transgenic animals compared with the controls. Quantitative histomorphometry at the distal femur disclosed a striking reduction in bone turnover in the OC-BP4 mice. Osteoblast number/bone length and bone formation rate/bone surface in OC-BP4 mice were approximately one-half that seen in control mice. At birth, OC-BP4 mice were of normal size and weight but exhibited striking postnatal growth retardation. Organ allometry (mg/g body weight) analysis revealed that, whereas most organs exhibited a proportional reduction in weight, calvarial and femoral wet weights were disproportionally small (approximately 70% and 80% of control, respectively). In conclusion, paracrine overexpression of IGFBP-4 in the bone microenvironment markedly reduced cancellous bone formation and turnover and severely impaired overall postnatal skeletal and somatic growth. We attribute these effects to the sequestration of IGF-1 by IGFBP-4 and consequent impairment of IGF-1 action in skeletal tissue.

Animals↗
PubMed2005

The temporal requirements for insulin signaling during development in Drosophila.

Recent studies have indicated that the insulin-signaling pathway controls body and organ size in Drosophila, and most metazoans, by signaling nutritional conditions to the growing organs. The temporal requirements for insulin signaling during development are, however, unknown. Using a temperature-sensitive insulin receptor (Inr) mutation in Drosophila, we show that the developmental requirements for Inr activity are organ specific and vary in time. Early in development, before larvae reach the "critical size" (the size at which they commit to metamorphosis and can complete development without further feeding), Inr activity influences total development time but not final body and organ size. After critical size, Inr activity no longer affects total development time but does influence final body and organ size. Final body size is affected by Inr activity from critical size until pupariation, whereas final organ size is sensitive to Inr activity from critical size until early pupal development. In addition, different organs show different sensitivities to changes in Inr activity for different periods of development, implicating the insulin pathway in the control of organ allometry. The reduction in Inr activity is accompanied by a two-fold increase in free-sugar levels, similar to the effect of reduced insulin signaling in mammals. Finally, we find that varying the magnitude of Inr activity has different effects on cell size and cell number in the fly wing, providing a potential linkage between the mode of action of insulin signaling and the distinct downstream controls of cell size and number. We present a model that incorporates the effects of the insulin-signaling pathway into the Drosophila life cycle. We hypothesize that the insulin-signaling pathway controls such diverse effects as total developmental time, total body size and organ size through its effects on the rate of cell growth, and proliferation in different organs.

Animals↗
PubMed1997

Prepubescents' ventilatory responses to exercise with reference to sex and body size.

STUDY OBJECTIVES: To examine the ventilatory responses of prepubescent children to submaximal and peak exercise using appropriate allometric modeling to control for differences in body size. DESIGN: Cross-sectional study of a representative sample of children. SETTING: Middle schools (8 to 11 years) in Exeter, UK. PARTICIPANTS: We studied 101 boys and 76 girls aged 11.1 (0.4) years and classified Tanner stage 1 for pubic hair (no true pubic hair). MEASUREMENTS: At rest: stature, mass, sum of skinfolds, hemoglobin concentration, FVC, and FEV1. During treadmill exercise at 7, 8, 9, and 10 km/h, and at peak exercise: oxygen uptake (VO2), minute ventilation (VE), tidal volume (VT), and respiratory frequency (Rf). RESULTS: At peak exercise, boys' VO2, VE, and VT were significantly (p<0.01) higher than girls' values and remained so even when the influence of body size was controlled using allometric principles. There were no significant (p>0.05) sex differences in Rf or the ratios VT/FVC or VE/VO2. When data were compared at the same relative exercise intensity (ie, 70 to 75% or 80 to 85% peak VO2), no significant (p>0.05) sex differences in Rf, VT/FVC, or VE/VO2 were detected. Boys' higher (p<0.001) VO2 values were reflected by their higher VE which remained higher than values for girls at both submaximal levels even when the influence of body size was covaried out. CONCLUSIONS: Prepubescent boys demonstrate higher peak VO2 than girls and this is supported by a higher VE and VT, even when the influence of body size is accounted for using allometry. Other ventilatory responses to both peak exercise and exercise at the same relative intensity are remarkably similar in both boys and girls.

Analysis of Variance↗
PubMed2002

Prediction of clearance in humans from in vitro human liver microsomes and allometric scaling. A comparative study of the two approaches.

The objective of this study was to evaluate whether the predicted clearance of a drug in humans from in vitro human liver microsomes was comparable with the predicted clearance in humans obtained by allometric scaling. Sixteen drugs were randomly selected from the literature and their hepatic clearances were predicted using human liver microsomes. For allometric scaling at least three animal species were used and three methods were utilized to generate allometric equations to predict the clearance in humans: (i) clearance vs body weight (simple allometry); (ii) product of the clearance and maximum life-span potential (MLP) vs body weight; and (iii) the product of clearance and brain weight vs body weight. The choice of one of the methods was based on the 'rule of exponents' as described by Mahmood and Balian /2,3/. The results of this study indicated that the use of human liver microsomes to predict hepatic clearance in humans may not provide reliable predictions. On the other hand, the prediction of clearance in humans using allometric scaling combined with the 'rule of exponents' can provide comparatively better prediction of clearance in humans.

Animals↗
PubMed1991

[Morphometrical study of physical growth of laboratory-bred cynomolgus monkeys aged from zero to 9 years].

The relative growth was examined in laboratory-bred cynomolgus monkeys (Macaca fascicularis) aged from zero to 9 years. The principal component analysis and multivariate allometry were applied to the biometrical data. As the result of the principal component analysis, the cumulative contribution ratio of the 1 st (PC 1) and 2 nd (PC 2) principal components accounted for 99.0 percent. According to the eigen vector values of each morphological site (14 sites), PC 1 was acceptable not only as a size factor but also as a shape factor of the morphological growth changes from birth to the 3rd year of life in both sexes. PC 2 was acceptable as a shape factor of the morphological differences between sexes after the 3rd year of life. As the result of the multivariate allometric analysis applied to the same data, proximate sites of the trunk showed relatively high growth rates compared to distal ones of the trunk. The head, limbs and arms grew slowly in contrast to the trunk. Thus, we could demonstrate the relative growth of cynomolgus monkeys morphometrically.

Animals↗
PubMed2005

Reproductive biology of Astyanax janeiroensis (Osteichthyes, Characidae) from the Ubatiba river, Maricá, RJ, Brazil.

Aspects of the reproductive biology of Astyanax janeiroensis in the Ubatiba river in Maricá, RJ, Brazil were evaluated in order to ascertain whether the strategy adopted by the species is causally related to environmental variables. Specimens were collected on a monthly basis from October 1994 to September 1995, through electrofishing. The Sex ratio was not significantly different from the expected frequency of 1:1 (G = 1.29; p > 0.50); nonetheless, considering three standard length classes, significantly larger numbers of females were recorded for the higher SL class (G = 11.07; p < 0.01). Size at first maturation showed no significant differences between sexes. Length-weight ratio analyses showed negative allometry for males and isometry, for females. Length structure was significantly different between sexes, suggesting that females are larger than males (D = 0.027, p < 0.01). Reproductive specimens were recorded during nine months of the annual cycle. Seasonal variations of reproductive specimens belonging to two different standard length classes displayed an asynchronous behavior, with larger specimens having a longer reproductive period and smaller ones reproducing for fewer months during the annual cycle. High values of fecundity (F), varying from 3169 to 18714 oocytes, were recorded for fish of 9.1 and 10.2 cm lengths, respectively. The correlation between weight and number of oocytes/unit of weight was positive, indicating that larger specimens produced more eggs.

Animals↗
PubMed2006

Nitrogen cycling during seven years of atmospheric CO2 enrichment in a scrub oak woodland.

Experimentally increasing atmospheric CO2 often stimulates plant growth and ecosystem carbon (C) uptake. Biogeochemical theory predicts that these initial responses will immobilize nitrogen (N) in plant biomass and soil organic matter, causing N availability to plants to decline, and reducing the long-term CO2-stimulation of C storage in N limited ecosystems. While many experiments have examined changes in N cycling in response to elevated CO2, empirical tests of this theoretical prediction are scarce. During seven years of postfire recovery in a scrub oak ecosystem, elevated CO2 initially increased plant N accumulation and plant uptake of tracer 15N, peaking after four years of CO2 enrichment. Between years four and seven, these responses to CO2 declined. Elevated CO2 also increased N and tracer 15N accumulation in the O horizon, and reduced 15N recovery in underlying mineral soil. These responses are consistent with progressive N limitation: the initial CO2 stimulation of plant growth immobilized N in plant biomass and in the O horizon, progressively reducing N availability to plants. Litterfall production (one measure of aboveground primary productivity) increased initially in response to elevated CO2, but the CO2 stimulation declined during years five through seven, concurrent with the accumulation of N in the O horizon and the apparent restriction of plant N availability. Yet, at the level of aboveground plant biomass (estimated by allometry), progressive N limitation was less apparent, initially because of increased N acquisition from soil and later because of reduced N concentration in biomass as N availability declined. Over this seven-year period, elevated CO2 caused a redistribution of N within the ecosystem, from mineral soils, to plants, to surface organic matter. In N limited ecosystems, such changes in N cycling are likely to reduce the response of plant production to elevated CO2.

Atmosphere↗
PubMed2006

A structural equation model to integrate changes in functional strategies during old-field succession.

From a functional perspective, changes in abundance, and ultimately species replacement, during succession are a consequence of integrated suites of traits conferring different relative ecological advantages as the environment changes over time. Here we use structural equations to model the interspecific relationships between these integrated functional traits using 34 herbaceous species from a Mediterranean old-field succession and thus quantify the notion of a plant strategy. We measured plant traits related to plant vegetative and reproductive size, leaf functioning, reproductive phenology, seed mass, and production on 15 individuals per species monitored during one growing season. The resulting structural equation model successfully accounts for the pattern of trait covariation during the first 45 years post-abandonment using just two forcing variables: time since site abandonment and seed mass; no association between time since field abandonment and seed mass was observed over these herbaceous stages of secondary succession. All other predicted traits values are determined by these two variables and the cause-effect linkage between them. Adding pre-reproductive vegetative mass as a third forcing variable noticeably increased the predictive power of the model. Increasing the time after abandonment favors species with increasing life span and pre-reproductive biomass and decreasing specific leaf area. Allometric coefficients relating vegetative and reproductive components of plant size were in accordance with allometry theory. The model confirmed the trade-off between seed mass and seed number. Maximum plant height and seed mass were major determinants of reproductive phenology. Our results show that beyond verbal conceptualization, plant ecological strategies can be quantified and modeled.

Ecology↗
PubMed2006

A novel strategy for physiologically based predictions of human pharmacokinetics.

BACKGROUND: The major aim of this study was to develop a strategy for predicting human pharmacokinetics using physiologically based pharmacokinetic (PBPK) modelling. This was compared with allometry (of plasma concentration-time profiles using the Dedrick approach), in order to determine the best approaches and strategies for the prediction of human pharmacokinetics. METHODS: PBPK and Dedrick predictions were made for 19 F. Hoffmann-La Roche compounds. A strategy for the prediction of human pharmacokinetics using PBPK modelling was proposed in this study. Predicted values (pharmacokinetic parameters, plasma concentrations) were compared with observed values obtained after intravenous and oral administration in order to assess the accuracy of the prediction methods. RESULTS: By following the proposed strategy for PBPK, a prediction would have been made prospectively for approximately 70% of the compounds. The prediction accuracy for these compounds in terms of the percentage of compounds with an average-fold error of <2-fold was 83%, 50%, 75%, 67%, 92% and 100% for apparent oral clearance (CL/F), apparent volume of distribution during terminal phase after oral administration (V(z)/F), terminal elimination half-life (t(1/2)), peak plasma concentration (C(max)), area under the plasma concentration-time curve (AUC) and time to reach C(max) (t(max)), respectively. For the other 30% compounds, unacceptable prediction accuracy was obtained in animals; therefore, a prospective prediction of human pharmacokinetics would not have been made using PBPK. For these compounds, prediction accuracy was also poor using the Dedrick approach. In the majority of cases, PBPK gave more accurate predictions of pharmacokinetic parameters and plasma concentration-time profiles than the Dedrick approach. CONCLUSIONS: Based on the dataset evaluated in this study, PBPK gave reasonable predictions of human pharmacokinetics using preclinical data and is the recommended approach in the majority of cases. In addition, PBPK modelling is a useful tool to gain insights into the properties of a compound. Thus, PBPK can guide experimental efforts to obtain the relevant information necessary to understand the compound's properties before entry into human, ultimately resulting in a higher level of prediction accuracy.

Animals↗
PubMed2006

Prediction of the clearance of eleven drugs and associated variability in neonates, infants and children.

BACKGROUND: Prediction of the exposure of neonates, infants and children to xenobiotics is likely to be more successful using physiologically based pharmacokinetic models than simplistic allometric scaling, particularly in younger children. However, such models require comprehensive information on the ontogeny of anatomical, physiological and biochemical variables; data that are not available from single sources. The Simcyp software integrates demographic, genetic, physiological and pathological information on adults with in vitro data on human drug metabolism and transport to predict population distributions of drug clearance (CL) and the extent of metabolic drug-drug interactions. The algorithms have now been extended to predict clearance and its variability in paediatric populations by incorporating information on developmental physiology and the ontogeny of specific cytochrome P450s. METHODS: Values of the clearance (median and variability) of 11 drugs (midazolam [oral and intravenous], caffeine, carbamazepine, cisapride, theophylline, diclofenac, omeprazole, S-warfarin, phenytoin, gentamicin and vancomycin) were predicted for 2,000 virtual subjects (birth to 18 years). In vitro enzyme pharmacokinetic parameters (maximum rate of metabolism [Vmax] and Michaelis-Menten constant [Km]) and in vivo clearance data were obtained from the literature. RESULTS: In neonates 70% (7/10) of predicted median clearance values were within 2-fold of the observed values. Corresponding results for infants, children and adolescents were 100% (9/9), 89% (17/19) and 94% (17/18), respectively. Predicted variability (95% confidence interval) was within 2-fold of the observed values in 70% (7/10), 67% (6/9), 63% (12/19) and 55% (10/18) of cases, respectively. The accuracy of the physiologically based model incorporated in the Simcyp software was superior to that of simple allometry, especially in children <2 years old. CONCLUSION: The in silico prediction of pharmacokinetic behaviour in paediatric patients is not intended to replace clinical studies. However, it provides a valuable aid to decision-making with regard to first-time dosing in children and study design. The clinical study then becomes 'confirmatory' rather than 'exploratory'.

Algorithms↗
PubMed2006

The role of unbound drug in pharmacokinetics/pharmacodynamics and in therapy.

The evolution of research on drug protein binding is discussed with the unbound concentration (Cu) and the unbound fraction (fu) as protagonists. Particular attention is paid to the mechanisms via which alterations in binding affect the pharmacokinetics (PK) and the effect, or independently the pharmacodynamics (PD). Apart from albumin, the important alpha-acid glycoprotein (AGP), as well as specific drug classes and applications in the clinic and development (routine monitoring, cancer and HIV therapy, allometry) are addressed. The flaws with the classical method of indirectly calculating the Cu or the unbound PK/PD parameters, based on the fu in vitro, are related to the intrinsic complexity and variability in the outcomes. Increased focus is urged on directly estimating the unbound PK/PD and also on using population statistical methods.

Animals↗
PubMed2000

Molt-related and size-dependent differences in the escape response and post-threat behavior of the American lobster, Homarus americanus.

Videotaped recordings of adult lobsters of different molt stages were analyzed. The escape response of adults was compared with that of juveniles recorded in an earlier study. Juvenile lobsters always respond to a threat with escape behavior irrespective of their molt stage, but in adults the probability of eliciting a response was a function of molt stage: more hard-shelled (intermolt stage C) and (premolt stage D) animals tailflipped than did soft-shelled (postmolt stages A and B) animals. The number, frequency, and duration of tailflips, and the average distance swum by animals in each molt stage were measured for the entire escape response, for the initial power swim, and for the subsequent swims. These measurements were used to compute several parameters: velocity, acceleration, force, and work; average distance traveled in a tailflip for each kilogram of body weight (distance/kg/tailflip); and average distance traveled for each bodylength (distance/bodylength). Among adults, intermolt (stage C) lobsters traveled significantly farther and faster than postmolt animals (stages A and B). Among juveniles, late postmolt (stage B) animals traveled farther. Among adults, although the total number of tailflips and the duration of the response were not significantly different among molt stages, the number of tailflips/second (frequency) and distance traveled/kg/tailflip were greater for intermolt animals. In juvenile intermolts, however, frequency and distance/kg/tailflip were markedly lower than in the premolt stages. Although values were lower than intermolts and premolts, postmolt adults sustained their swimming frequency, distance/kg/tailflip, and distance/bodylength for the entire escape distance (as did postmolt juveniles). These parameters then dropped off sharply for both adult and juvenile intermolt and premolt animals in the second half of the escape distance. Post-threat behaviors reveal that stage D animals have the highest aggression index and often attack the presented stimulus, whereas stage A animals are the least likely to approach the stimulus and typically back away in a non-aggressive posture. Thus, although effects of the molt cycle on adult and juvenile escape behavior are similar in some ways, other physical characteristics of adults, such as weight, allometry, and physiology, seem to become important in determining the likelihood of escape behavior and the characteristics of the escape swim in each molt stage.

Animals↗
PubMed2002

Embryonic velar structure and function of two sibling species of Crepidula with different modes of development.

The structure and function of the embryonic velum of two closely related species of Crepidula with different modes of development are examined. The velum of C. dilatata, a direct developer whose embryos feed on nurse eggs, does not differ substantially from the velum of C. fecunda, a species with planktotrophic larvae. Although velar ciliation develops earlier in embryos of C. dilatata, embryos of both species were able to feed on small particles, using the opposed-band ciliary mechanism. However, the embryos of C. dilatata lose this ability as they grow. The embryos of C. dilatata were not able to swim, whereas those of C. fecunda swam consistently in vials of seawater. This difference in swimming ability is probably due to differences in velum-body size allometry between the two species.

Animals↗
PubMed2005

Larval morphometrics and influence of adults on settlement in the gregarious ophiuroid Ophiothrix fragilis (Echinodermata).

The development of Ophiothrix fragilis was documented using light microscopy, and the allometry of larval growth was quantified. Larval development to the suspended juvenile stage took 21 days under conditions that were probably optimal compared to those in the plankton. Larval shape changed through development as the larval body and arms grew. Growth of the posterolateral larval arms was continuous throughout development, even during metamorphosis when the larva became endotrophic. During this period, these larval arms function as locomotory organs, and their continuous growth is probably essential to support the juvenile as it increases in density through development of its calcareous plates. In induction assays using adult conspecifics, initiation of metamorphosis was spontaneous. Release of the posterolateral arms was induced by the presence of adults. This response is likely to enhance a juvenile's chance of recruiting to a suitable habitat in the Ophiothrix fragilis beds of the North Sea.

Age Factors↗