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PubMed2002

Wing shape divergence between Rhodnius prolixus from Cojedes (Venezuela) and Rhodnius robustus from Mérida (Venezuela).

The existence of Rhodnius robustus as a species distinct from Rhodnius prolixus has long been the main epidemiological question about Chagas disease transmission in Venezuela and surrounding countries. These two taxa are morphologically and genetically very similar, but only R. prolixus is assumed to colonize houses and transmit Chagas disease to humans. R. robustus is assumed to be an exclusively sylvatic species, restricted to palm trees. If robustus and prolixus are actually the same species, the theoretical possibility exists of sylvatic specimens invading houses, even after insecticide application, and a control strategy similar to that of the successful Southern Cone Initiative against Triatoma infestans would be difficult to consider. Since no valid alternative control strategy exists, the answer to this biological question could be decisive about the future of vector control in this region. Although we believe genetic techniques are best suited to define species boundaries, we present here an example of the relevance of modern morphometrics in dealing with such an issue. Using both traditional and geometric morphometrics, we compared the wing size and shape in both sexes of these two taxa reared in the same laboratory for one generation. R. robustus specimens were collected from palm trees in the state of Mérida (Venezuela), and R. prolixus were collected from houses in the state of Cojedes (Venezuela). Our study provided no argument to question their specific status. Even after one generation of living in the same laboratory conditions, the two lines showed clear size differences, divergent allometric trends, and significant allometry-free differences in shape. These results suggest that R. robustus (Mérida, Venezuela) and R. prolixus (Cojedes, Venezuela) are distinct evolutionary units. Due to the epidemiological importance of this question, further studies in other geographic areas of Venezuela are required to accurately define the relationships of R. robustus and R. prolixus.

Animals↗
PubMed2006

Genetic mapping of allometric scaling laws.

Many biological processes, from cellular metabolism to population dynamics, are characterized by particular allometric scaling relationships between rate and size (power laws). A statistical model for mapping specific quantitative trait loci (QTLs) that are responsible for allometric scaling laws has been developed. We present an improved model for allometric mapping of QTLs based on a more general allometry equation. This improved model includes two steps: (1) use model II regression analysis to estimate the parameters underlying universal allometric scaling laws, and (2) substitute the estimated allometric parameters in the mixture-based mapping model to obtain the estimation of QTL position and effects. This model has been validated by a real example for a mouse F2 progeny, in which two QTLs were detected on different chromosomes that determine the allometric relationship between growth rate and body weight.

Algorithms↗
PubMed2005

Beyond the '3/4-power law': variation in the intra- and interspecific scaling of metabolic rate in animals.

In this review I show that the '3/4-power scaling law' of metabolic rate is not universal, either within or among animal species. Significant variation in the scaling of metabolic rate with body mass is described mainly for animals, but also for unicells and plants. Much of this variation, which can be related to taxonomic, physiological, and/or environmental differences, is not adequately explained by existing theoretical models, which are also reviewed. As a result, synthetic explanatory schemes based on multiple boundary constraints and on the scaling of multiple energy-using processes are advocated. It is also stressed that a complete understanding of metabolic scaling will require the identification of both proximate (functional) and ultimate (evolutionary) causes. Four major types of intraspecific metabolic scaling with body mass are recognized [based on the power function R=aMb, where R is respiration (metabolic) rate, a is a constant, M is body mass, and b is the scaling exponent]: Type I: linear, negatively allometric (b<1); Type II: linear, isometric (b=1); Type III: nonlinear, ontogenetic shift from isometric (b=1), or nearly isometric, to negatively allometric (b<1); and Type IV: nonlinear, ontogenetic shift from positively allometric (b>1) to one or two later phases of negative allometry (b<1). Ontogenetic changes in the metabolic intensity of four component processes (i.e. growth, reproduction, locomotion, and heat production) appear to be important in these different patterns of metabolic scaling. These changes may, in turn, be shaped by age (size)-specific patterns of mortality. In addition, major differences in interspecific metabolic scaling are described, especially with respect to mode of temperature regulation, body-size range, and activity level. A 'metabolic-level boundaries hypothesis' focusing on two major constraints (surface-area limits on resource/waste exchange processes and mass/volume limits on power production) can explain much, but not all of this variation. My analysis indicates that further empirical and theoretical work is needed to understand fully the physiological and ecological bases for the considerable variation in metabolic scaling that is observed both within and among species. Recommended approaches for doing this are discussed. I conclude that the scaling of metabolism is not the simple result of a physical law, but rather appears to be the more complex result of diverse adaptations evolved in the context of both physico-chemical and ecological constraints.

Adaptation, Physiological↗
PubMed2003

Allometric modeling of plant root growth and its application in rhizosphere remediation of soil contaminants.

Allometric curves relating tree trunk diameter to root biomass, depth, and breadth were compiled for mulberry (Morus sp.). The curves were based on statistical analyses of measurements made on 29 different-sized trees ranging in age from 2 to 15 yr that had grown from seed in a naturally revegetated former sludge basin containing polyaromatic hydrocarbons. Over a 15-yr period, the curves indicate that the fine root biomass (<1.5 mm diameter) increases 60-fold and, under the right circumstances, can be a part of a root system that reaches a 2-m depth. The fine roots of mulberry were shown to produce several flavonoid compounds at concentrations (ranging from 94 to 525 microg/cm3) known to support the growth of organisms capable of degrading xenobiotics. Recognizing the root system as the driver of rhizoremediation, allometry curves presented in this paper can be used to quantify the magnitude of the driver (root system) without damaging plants during the course of a multiyear field study.

Biodegradation, Environmental↗
PubMed2000

A quantitative approach to the evaluation of the morphological variability of two echinostomes, Echinostoma miyagawai Ishii, 1932 and E. revolutum (Frölich, 1802), from Europe.

A comparative morphometric analysis was conducted on two European species of Echinostoma in order to examine the degree of the variability in the metrical characteristics of the adults and to assess their value in discriminating species. Adult E. miyagawai and E. revolutum, obtained experimentally, were compared using univariate and multivariate statistical analyses of 35 and 25 metrical characters, respectively. All subsets of worms of different ages represented homogeneous samples with respect to their morphometric characteristics; however, univariate analyses revealed significant differences in 22 and 23 variables between the corresponding age subsets of the two species, and it was found that the different allometric growth patterns contribute to this. The variables, body width at the posterior border of the ventral sucker, pharynx length and width, ovary length, testes length and width and length of the pre-ovarian region, exhibited isometric or positive allometric growth in E. miyagawai and negative allometry in E. revolutum. A cluster analysis based on 61 specimens and 25 variables separated E. revolutum and E. miyagawai unambiguously, producing an exact ordering of the specimens with respect to their identity and age. A forward stepwise discriminant analysis identified five variables (body width at the posterior border of ventral sucker, head collar width, length of oesophagus, width of ventral sucker and length of the pre-ovarian region) which yielded a 100% accurate classification of the two species. We suggest, therefore, that the morphometric characteristics of the adult worms should be used in studies attempting the identification of species or isolates of Echinostoma spp. More comparative data need to be gathered in order that the species boundaries within the 'revolutum' group be defined more accurately.

Analysis of Variance↗
PubMed2002

Effects of size and temperature on developmental time.

Body size and temperature are the two most important variables affecting nearly all biological rates and times. The relationship of size and temperature to development is of particular interest, because during ontogeny size changes and temperature often varies. Here we derive a general model, based on first principles of allometry and biochemical kinetics, that predicts the time of ontogenetic development as a function of body mass and temperature. The model fits embryonic development times spanning a wide range of egg sizes and incubation temperatures for birds and aquatic ectotherms (fish, amphibians, aquatic insects and zooplankton). The model also describes nearly 75% of the variation in post-embryonic development among a diverse sample of zooplankton. The remaining variation is partially explained by stoichiometry, specifically the whole-body carbon to phosphorus ratio. Development in other animals at other life stages is also described by this model. These results suggest a general definition of biological time that is approximately invariant and common to all organisms.

Amphibians↗
PubMed2006

Insulin signaling and limb-patterning: candidate pathways for the origin and evolutionary diversification of beetle 'horns'.

Beetle 'horns' are rigid outgrowths of the insect cuticle used as weapons in contests for access to mates. Relative to their body size, beetle horns can be enormous. They protrude from any of five different regions of the head or thorax; they are curved, straight, branched or bladed; and their development is often coupled with the nutrient environment (male dimorphism) or with sex (sexual dimorphism). Here, we show that this extraordinary diversity of horns can be distilled down to four trajectories of morphological change--horn location, shape, allometry and dimorphism--and we illustrate how the developmental mechanisms regulating horn growth could generate each of these types of horn evolution. Specifically, we review two developmental pathways known to regulate growth of morphological structures in Drosophila and other insects: a limb-patterning pathway that specifies the location and shape of a structure, and the insulin pathway, which modulates trait growth in response to larval nutrition. We summarize preliminary evidence indicating that these pathways are associated with the development of beetle horns, and we show how subtle changes in the relative activities of these two pathways would be sufficient to generate most of the extant diversity of horn forms. Our objective is to intuitively connect genotype with phenotype, and to advocate an informed 'candidate gene' approach to studies of the developmental basis of evolution. We end by using this insight from development to offer a solution to the long-standing mystery of the scarabs: the observation by Darwin, Lameere, Arrow and others that this one family of beetles appeared to have a 'special tendency' towards the evolution of horns.

Animals↗
PubMed2001

Comparison of cefepime pharmacokinetics in neonatal foals and adult dogs.

The pharmacokinetics of cefepime, a new fourth generation cephalosporin with enhanced antibacterial activity, was examined in neonatal foals and adult dogs. Cefepime was administered intravenously (i.v.) at a dose of 14 mg/kg to five neonatal foals and six adult dogs. Blood samples were collected in both groups of animals and plasma cefepime concentrations measured by reverse-phase high-performance liquid chromatography (HPLC). Cefepime concentrations in both groups of animals were described by a two-compartment pharmacokinetic model with elimination half-lives of 1.65 and 1.09 h for the foal and dog, respectively. We tested whether or not pharmacokinetic parameters for cefepime could be scaled across species using principles of allometry. The parameters of elimination half-life (t(1/2)beta), apparent volume of distribution (VDarea), and systemic clearance (CL) were scaled linearly to body weight on a double logarithmic plot with allometric exponents for body weight of 0.26, 1.08 and 0.72, respectively. This study further determined doses for cefepime, a potentially useful antibiotic for neonatal foals and dogs, from the pharmacokinetic values. An i.v. dose of cefepime estimated from this study for treating sensitive bacteria was 11 mg/kg every 8 h for neonatal foals and 40 mg/kg every 6 h for dogs.

Animals↗
PubMed2004

The life history legacy of evolutionary body size change in carnivores.

We estimate the body sizes of direct ancestors of extant carnivores, and examine selected aspects of life history as a function not only of species' current size, but also of recent changes in size. Carnivore species that have undergone marked recent evolutionary size change show life history characteristics typically associated with species closer to the ancestral body size. Thus, phyletic giants tend to mature earlier and have larger litters of smaller offspring at shorter intervals than do species of the same body size that are not phyletic giants. Phyletic dwarfs, by contrast, have slower life histories than nondwarf species of the same body size. We discuss two possible mechanisms for the legacy of recent size change: lag (in which life history variables cannot evolve as quickly as body size, leading to species having the 'wrong' life history for their body size) and body size optimization (in which life history and hence body size evolve in response to changes in energy availability); at present, we cannot distinguish between these alternatives. Our finding that recent body size changes help explain residual variation around life history allometries shows that a more dynamic view of character change enables comparative studies to make more precise predictions about species traits in the context of their evolutionary background.

Age Factors↗
PubMed1999

[Growth of the cloacal bursa (bursa of Fabricius) and spleen in ducks].

The growth in weight of both the bursa of Fabricius and the spleen was investigated in different stocks of ducks between hatching and 154 days of age. The data were analysed by fitting the Janoschek growth curve and the allometric formula. Both organs showed rapid growth to their maximum dimensions and early points of inflection. The regression of the cloacal bursa started at about 12 weeks of age in Pekins and Mallards. In the Muscovy, the involution begins beyond the period of investigation. Allometrically, a biphasic relationship was found. Starting with positive allometry, the allometric exponent decreased to negative or isometric (Muscovies) values within the second week of age. If the organ weights are compared on the basis of these allometric relationships, Pekins had bursa weights that were about 30% higher than those in Mallards. For the spleen, there was no difference between wild and domesticated ducks.

Animals↗
PubMed1997

Growth pattern of the maxillary sinus in the Japanese macaque (Macaca fuscata): reflections on the structural role of the paranasal sinuses.

To investigate the claim that the primate paranasal sinuses possess not a functional but a structural role associated with the skull architecture (Blaney, 1990), the relationship between the maxillary sinus and the skull architecture was studied ontogenetically in 30 skulls of male and female Japanese macaques (Macaca fuscata). Coronal CT scan series and computerised 3-dimensional images served to evaluate the maxillary sinus. The definitive hemispherical shape of the sinus was already achieved after the completion of the primary dentition. Sinus volume increased with a trend indicating positive allometry. When compared with an ontogenetic data set of orang-utan (Koppe et al. 1995), however, the growth rate of the maxillary sinus of M. fuscata was significantly less. The maxillary sinus both of male and female macaques enlarged according to a common growth pattern. However, no sexual dimorphism could be established for the maxillary sinus size. Although the volume of the right maxillary sinus was normally bigger than that of the left side, the results suggested that asymmetry in maxillary sinus volume is related neither to skull size nor sex. Whereas a correlation analysis showed close relationships between the maxillary sinus volume and external cranial dimensions, the partial correlation coefficients revealed that these relationships were highly influenced by skull size. Although it cannot be ruled out that the paranasal sinuses are to some extent linked to the skull architecture, this study does not support a solely structural role for these air cavities.

Animals↗
PubMed2003

Pectoral fin development in the Baikalian viviparous golomyankas (Comephoridae; Cottoidei), with a remark on eggs and embryos of Comephorus baicalensis (Pallas).

Measurements of pectoral fin (PF) growth in relation to standard body length (SL) for Comephorus dybowskii (SL: 14-126 mm) and C. baicalensis (SL: 22-173 mm) were made and compared with corresponding data obtained for 13 other Baikalian cottoid species (sculpins). The allometry for the PF/SL relationships (Y = a + bX) is clearly biphasic. Expressed in percentages, these values for the larval period of C. dybowskii [Yp = -28.886 + (2.419X)] are much higher than for C. baicalensis [Yp = -11.904 + (1.233X)]. The postnatal period of development of the golomyanka up to 30-35 mm SL is considered to be the larval stage. In the postlarval period, growth of pectoral fin and the body in C. dybowskii are directly proportional [Yp' = 48.92 + (-0.009X)] whereas in C. baicalensis they rise slightly [Yp' = 30.966 + (0.0505X)]. Absence of the air bladder characterizes all Baikalian cottoid species, including the golomyankas. Various species of the golomyanka differ in the ways of obtaining neutral buoyancy. It is supposed that large pectoral fins guarantee behavioural buoyancy in small species such as C. dybowskii, whereas in C. baicalensis, obtaining much larger body size but lower PFp/SL index, the buoyancy is gained mainly due to the accumulation of large amount of lipids. This paper also documents the ovary and advanced embryos of C. baicalensis.

Animals↗
PubMed1997

Prospective and retrospective longitudinal studies of the growth, maturation, and fitness of Polish youth active in sport.

Results of three longitudinal studies of the growth, maturation and fitness of youth active in sport are summarized. Data include size attained and growth rates for height and body mass, secondary sex characteristics, skeletal age, age at peak height velocity, and two indicators of fitness, peak O2 uptake and power output at a heart rate of 170 bpm (PWC 170). The data for active youth are compared to local reference data and where appropriate to data from other European longitudinal studies. Allowing for variation in methodology and sampling, regular training in sport during puberty and the adolescent spurt does not influence size attained, growth rate, and the timing and progression of somatic, sexual and skeletal maturation in boys and girls. Active and nonactive boys and girls, respectively, do not differ significantly in the mean age at maximum growth in power output at a heart rate of 170 bpm. Boys active in sport, however, have a greater maximal gain in submaximal power output than nonactive boys. Analysis of ontogenetic allometry of peak oxygen uptake and stature and body mass indicate variation between individuals, and between boys of contrasting maturity status.

Adolescent↗
PubMed1993

The mechanosensory calcium-selective ion channel: key component of a plasmalemmal control centre?

Mechanosensory calcium-selective ion channels probably serve to detect not only mechanical stress but also electrical, thermal, and diverse chemical stimuli. Because all stimuli result in a common output, most notably a shift in second messenger calcium concentration, the channels are presumed to serve as signal integrators. Further, insofar as second messenger calcium in turn gives rise to mechanical, electrical, and diverse chemical changes, the channels are postulated to initiate regulatory feedbacks. It is proposed that the channels and the feedback loops play a wide range of roles in regulating normal plant function, as well as in mediating disturbance of normal function by environmental stressors and various pathogens. In developing evidence for the physiological performance of the channel, a model for a cluster of regulatory plasmalemmal proteins and cytoskeletal elements grouped around a set of wall-to-membrane and transmembrane linkers has proved useful. An illustration of how the model might operate is presented. It is founded on the demonstration that several xenobiotics interfere both with normal channel behaviour and with gravitropic reception. Accordingly, the first part of the illustration deals with how the channels and the control system within which they putatively operate might initiate gravitropism. Assuming that gravitropism is an asymmetric expression of growth, the activities of the channels and the plasmalemmal control system are extrapolated to account for regulation of both rate and allometry of cell expansion. Finally, it is discussed how light, hormones, redox agents and herbicides could in principle affect growth via the putative plasmalemmal control cluster or centre.

Calcium Channels↗
PubMed2002

Prediction of stage of pregnancy in prolific sheep using ultrasound measurement of fetal bones.

The use of ultrasound to estimate stage of pregnancy was assessed in 32 ewes of a prolific genotype carrying 7 singleton fetuses and 9 twin, 10 triplet and 6 quadruplet litters that were scanned on six occasions from 60 to 120 days of gestation. At least one ultrasound measurement per ewe of fetal metacarpal bone length (MCL), biparietal diameter (BPD), or of both bones was made on over 90% of attempts (n = 152). Measurement of MCL was made on 78% of attempts (n = 371), of BPD on 73% of attempts, and of both bones on 62% of attempts. The equation developed from BPD (mean absolute error (MAE) = 3.2 days) was similar to that developed from measurement of MCL (MAE = 3.3 days) in its capacity to predict stage of pregnancy. Accuracy of prediction was improved using equations that included mean values within litters for BPD (MAE = 2.5 days) and MCL (MAE = 2.6 days). Further improvement in predictive capacity was achieved using multiple regression equations developed from measurement of both bones (individual fetuses: MAE = 2.6 days; equations including mean values within litters: MAE = 2.2 days). The results demonstrate that ultrasound can be used to estimate stage of pregnancy in prolific ewes, and that the use of mean values for bone measurements from different fetuses within litters and/or measurement of bones with different growth allometry can increase the reliability of estimates. The utility of the procedure depends on the number of fetuses measured per ewe, the number of bones measured per fetus and, hence, the time required to measure bones and the degree of accuracy required.

Animals↗
PubMed2004

Adapting to an invasive species: toxic cane toads induce morphological change in Australian snakes.

The arrival of invasive species can devastate natural ecosystems, but the long-term effects of invasion are less clear. If native organisms can adapt to the presence of the invader, the severity of impact will decline with time. In Australia, invasive cane toads (Bufo marinus) are highly toxic to most snakes that attempt to eat them. Because snakes are gape-limited predators with strong negative allometry for head size, maximum relative prey mass (and thus, the probability of eating a toad large enough to be fatal) decreases with an increase in snake body size. Thus, the arrival of toads should exert selection on snake morphology, favoring an increase in mean body size and a decrease in relative head size. We tested these predictions with data from specimens of four species of Australian snakes, collected over >80 years. Geographic information system layers provided data on the duration of toad exposure for each snake population, as well as environmental variables (latitude, precipitation, and temperature). As predicted, two toad-vulnerable species (Pseudechis porphyriacus and Dendrelaphis punctulatus) showed a steady reduction in gape size and a steady increase in body length with time since exposure to toads. In contrast, two species at low risk from toads (Hemiaspis signata and Tropidonophis mairii) showed no consistent change in these morphological traits as a function of the duration of toad exposure. These results provide strong evidence of adaptive changes in native predators as a result of the invasion of toxic prey.

Adaptation, Biological↗
PubMed2003

Mammalian basal metabolic rate is proportional to body mass2/3.

The relationship between mammalian basal metabolic rate (BMR, ml of O(2) per h) and body mass (M, g) has been the subject of regular investigation for over a century. Typically, the relationship is expressed as an allometric equation of the form BMR = aM(b). The scaling exponent (b) is a point of contention throughout this body of literature, within which arguments for and against geometric (b = 2/3) and quarter-power (b = 3/4) scaling are made and rebutted. Recently, interest in the topic has been revived by published explanations for quarter-power scaling based on fractal nutrient supply networks and four-dimensional biology. Here, a new analysis of the allometry of mammalian BMR that accounts for variation associated with body temperature, digestive state, and phylogeny finds no support for a metabolic scaling exponent of 3/4. Data encompassing five orders of magnitude variation in M and featuring 619 species from 19 mammalian orders show that BMR proportional, variant M(2/3).

Analysis of Variance↗
PubMed1991

Evolution of life history variation among female mammals.

A unified approach is developed for the evolutionary structure of mammalian life histories; it blends together three basic components (individual growth or production rate as a function of body size, natural selection on age of maturity, and stable demography) to predict both the powers and the intercepts of the scaling allometry of life history variables to adult size. The theory also predicts the signs (+, -) of the correlations between life history variables when body size is held constant. Finally, the approach allows us to eliminate body size to predict the dimensionless relationships between the life history variables themselves.

Animals↗