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PubMed2001

Shape changes and growth trajectories in the early stages of three species of the genus Diplodus (Perciformes, Sparidae).

The larvae of three species of the genus Diplodus (Diplodus vulgaris, D. sargus, and D. puntazzo) colonize shallow waters along the Mediterranean coasts and, after a short period spent in the water column, they settle. For all three species this habitat transition is characterized by important shape changes mostly related to swimming capacity and feeding behavior. In this study, geometric morphometrics are used to characterize shape changes during the early juvenile life of specimens collected in a single locality in order to compare growth curves and allometric relationships. Size-related shape changes proved to be similar for all three species and are consistent with the ecological transition. A nonparametric smoothing technique (Loess) was used to fit the scatter of shape on size. The graphical representation (of most size-related shape variability) of this fitting technique shows how major shape changes are rapid for small sizes and slow down successively. The approach allows for the visualization of allometry and the fitting technique might help in defining the allometric growth pattern, thus contributing to the study of the autoecology of the species and in establishing terms for comparison with other ecologically or phylogenetically related species.

Animals↗
PubMed1998

Molar morphology and variation in two malagasy lemur families (Lemuridae and Indriidae).

The lemurs of Madagascar represent a radiation of primates exhibiting considerable ecological and morphological diversity. Dentally, all lemurs possess the characteristic strepsirhine anterior tooth comb, but exhibit variation in their postcanine teeth that may be related to dietary differences. In this study, I examine two factors that could complicate a strictly functional interpretation of tooth form variation in two families of Malagasy primates, the Lemuridae and Indriidae. (1) Allometry may be responsible for observed variation. Body size, not specific tooth features, may be the object of selection; tooth features may vary among taxa as a consequence of differences in body size. (2) Taxonomic affiliation may "explain" variation without recourse to functional explanations. Tooth morphology among closely-related taxa may be constrained developmentally or as a result of stabilizing selection. Morphological variation between families, therefore, may not be the result of current functional differences related to physical dietary properties, but may result from past events that are lineage-specific. Morphological features from the upper and lower second molars of seven lemurid and four indriid taxa are compared. The results of this study indicate that the majority of second molar features scale isometrically. Initial separation by families is warranted by the homogeneous slopes but different elevations in analyses of covariance between families. Intrafamilial variation is considerable for lemurids, but more discrete among indriids. Functional explanations for tooth form variability should take into consideration the degree of variation within taxa. For this particular dataset, the two families should be analyzed separately, and, because of the considerable overlap of subspecies with full species among lemurids, the lowest taxonomic unit recognized should be used.

Analysis of Variance↗
PubMedDate not supplied

Variations in molar enamel thickness among primates.

Because of its hardness, resistance to abrasion and its influence on crown morphology, molar enamel thickness is an important factor in adaptation of the dentition to the diet. Enamel thickness has also been discussed extensively in relation to the phylogenetic relationships among the hominoids. The aims of this study were: (1) to analyse enamel thickness/tooth size relationships among primates as a whole, and (2) to evaluate variations in enamel thickness among hominoids against the background of the other primates. We employed measures of tooth size, and of enamel thickness and quantity based on measurements of areas in longitudinal sections of 125 molars of 39 species. Among primates, there were two grades of enamel thickness, prosimians having thinner enamel for a given tooth size or body weight than anthropoids. The scaling of enamel thickness with tooth size and body weight tended to show positive allometry among anthropoids. Comparison of hominoid enamel thicknesses with that in anthropoids led to the conclusion that Hylobates has enamel of average thickness, Homo has thick enamel and Gorilla has thin enamel, while Pan and Pongo had average or thin enamel, depending on tooth type. These results may be relevant to considerations of hominoid evolution.

Analysis of Variance↗
PubMed2000

Cortical bone distribution in the femoral neck of strepsirhine primates.

The thickness of the inferior and superior cortices of the femoral neck was measured on X-rays of 181 strepsirhine primate femora representing 24 species. Neck length, neck depth and neck-shaft angle were also measured. The strength of the femoral neck in frontal bending was estimated by modeling the neck as a hollow cylinder, with neck depth as the outer diameter and cortical thickness representing the superior and inferior shell dimensions. Results indicate that the inferior cortex is always thicker than the superior cortex. The ratio of superior to inferior cortical thickness is highly variable but distinguishes two of the three locomotor groups in the sample. Vertical clingers and leapers have higher ratios (i.e., a more even distribution of cortical bone) than quadrupeds. The slow climbers tend to have the lowest ratios, although they do not differ significantly from the leapers and quadrupeds. These results do not confirm prior theoretical expectations and reported data for anthropoid primates that link greater asymmetry of the cortical shell to more stereotypical hip excursions. The ratio of superior to inferior cortical thickness is unrelated to body mass, femoral neck length, and neck-shaft angle, calling into question whether the short neck of strepsirhine primates acts as a cantilever beam in bending. On the other hand, the estimated section moduli are highly correlated with body mass and neck length, a correlation that is driven primarily by body mass. In conclusion, we believe that an alternative interpretation to the cantilever beam model is needed to explain the asymmetry in bone distribution in the femoral neck, at least in strepsirhine primates (e.g., a thicker inferior cortex is required to reinforce the strongly curved inferior surface). As in prior studies of cross-sectional geometry of long bones, we found slightly positive allometry of cortical dimensions with body mass.

Animals↗
PubMed2000

Removing allometric effects of body size in morphological analysis.

In the present paper, a normalization technique to scale data that exhibit an allometric growth is presented and the way it has to be used is described. It is shown how the method has been derived from the theoretical equations of allometric growth. Consequently, the method completely removes all the information related to size, not only scaling all individuals to the same size, but also adjusting their shape to that they would have in the new size according to allometry. In the particular case of isometry when the measures are of identical dimension, this normalization coincides with ratios (one of the most popular methods but only valid in this particular case). This procedure is a theoretical generalization of the technique used by Thorpe (1975, Biol. J. Linn. Soc.7, 27-43; 1976, Biol. Rev.51, 407-452) which was recorded as one of the most efficient methods in the empirical evaluation done by Reist (1985, Can. J. Zool.63, 1429-1439).

Animals↗
PubMed1992

Ventilatory accommodation of changing oxygen demand in sciurid rodents.

Ventilation was measured across a range of O2 consumption rates in four sciurid rodents: Tamias minimus (47 g), Spermophilus lateralis (189 g), S. beecheyi (531 g), and Marmota flaviventris juveniles (1054 g) and adults (2989 g). Maximum thermogenic oxygen consumption was measured for all but adult M. flaviventris. Aerobic scopes (maximum/minimum O2 consumption rates) were 4.6, 3.8, 5.4, and 4.8 in T. minimus, S. lateralis, S. beecheyi, and juvenile M. flaviventris, respectively. Aerobic scope was at least 4.1 in adult M. flaviventris. Ventilatory accommodation of changing O2 consumption rate was qualitatively similar in the four species, with the bulk of accommodation resulting from changes in minute volume. Nevertheless, there were significant differences in the relative importance of frequency, tidal volume, and O2 extraction in accommodation. In all species, frequency and minute volume were strongly correlated to O2 consumption rate. Tidal volume was significantly correlated to O2 consumption rate in T. minimus and S. beecheyi, but not in the other species. Oxygen extraction was not significantly correlated to O2 consumption rate in any species. Analysis of factorial ventilation changes across a standardized 3.8-fold change in O2 consumption rate revealed significant differences among species in frequency and O2 extraction, but not in tidal or minute volume. When compared to a generalized allometry for mammalian resting ventilation, the four sciurid species had consistently lower respiration frequency and higher O2 extraction than predicted, perhaps because the sciurid measurements were made on unrestrained animals. There was no indication that ventilation constrained maximum O2 consumption rate.

Animals↗
PubMed1990

Foot length growth related to crown-rump length, gestational age and weight in human staged fresh fetuses. An index for anatomical and medical use.

Several anatomical parameters are useful in the assessment of gestational age. This work studies the foot length growth analysed against age, crown-rump length (C-R) and body weight (W) in eighty human fresh fetuses (staging from 14 to 38 weeks post-conception). These data were correlated with the following statistical methods: simple regression, power formula (allometric method), exponential and reciprocal models. The foot length growth presents very high and statistically significant coefficients of correlations with fetal parameters (P less than 0.001); the allometric method was the best method for this analysis. Foot length grows with moderate (against the age and C-R) or slight (against the W) positive allometry. This study presents statistically significant curves of the foot length growth in relation to fetal parameters. These curves are useful in anatomy, forensic medicine, feto-pathology, medical imaging, obstetrics and pediatrics.

Body Height↗
PubMedDate not supplied

Allometric analysis of the atrioventricular heart-valve weights in beagle dogs.

A statistical analysis of atrioventricular heart valve weights of 218 beagle dogs was performed. Applying the allometric function, the correlation between body or heart weight and the weights of the mitral valve, tricuspid valve-angular/parietal leaflet and tricuspid valve-septal leaflet could be described statistically. In the age range between 2 and 81 weeks a significant linear, positive correlation was found for all three parts. The mitral valve and the angular and parietal leaflet of the tricuspid valve show a negative allometry or slower growth rate than body or heart, whereas the septal leaflet grows isometrically. Sex differences were not found. The relevance of such data for the evaluation of certain pathological findings is discussed.

Age Factors↗
PubMed2001

Developmental differences in the uterus of Fasciola hepatica between livestock liver fluke populations from Bolivian highlands and European lowlands.

A morphometric study of the uterus area (UA) of Fasciola hepatica adults was carried out with the aid of a computer linked to a stereomicroscopic 3CCD colour video camera using image analysis software. The UA of adult liver flukes found in naturally infected sheep, cattle and pig from the endemic human fascioliasis zone of the northern Bolivian Altiplano highlands was compared with that of flukes found infecting sheep and cattle from Valencia, Spain and cattle from Corsica, France (collectively, European lowlands). Liver fluke UA was examined using an allometric model. A comparison of the allometry of the liver fluke UA in different host species from Bolivia revealed no significant differences. Similarly, no statistically significant differences were found between UA of Valencian and Corsican populations. However, the Bolivian sheep and cattle liver fluke populations proved to have a UA smaller than that of the European populations. These results indicate differences between the liver fluke population of highlands and lowlands, regarding UA. This paper discusses the possible relationship between the characteristic of having a reduced uterine development and the liver fluke adult stage adapting to host populations living at very high altitudes.

Altitude↗
PubMed2003

Mandibular morphogenesis during soldier differentiation in the damp-wood termite Hodotermopsis sjoestedti (Isoptera: Termopsidae).

The conspicuous morphogenesis during termite soldier differentiation is one of the most remarkable examples of specialized caste development in social insects. To clarify the mechanism of morphological changes during soldier differentiation, mandibular morphogenesis prior to the presoldier moult was examined in the damp-wood termite Hodotermopsis sjoestedti. Using experimental induction of presoldier differentiation from pseudergates (7th or later instar larvae) by the application of juvenile hormone analogue (JHA), we compared mandibular morphogenesis in a presoldier moult (from pseudergate to presoldier) with that of a stationary moult (from pseudergate to pseudergate). Future presoldier mandibles were formed under the old mandibular cuticle of the pseudergates just prior to the presoldier moult. Multiple folds of both epidermis and new cuticle were observed in the developing mandible, and large concavities between teeth were formed on the mandibular surface. While in the stationary moult, the future mandibles were formed with a smooth surface. The process of the mandibular morphogenesis in soldier differentiation explains the allometry of soldier mandibles. The morphological differences in mouth parts between castes arise from a switching mechanism that triggers caste-specific mandibular epithelial growth during development.

Animals↗
PubMed2006

Winged queens replaced by reproductives smaller than workers in Mystrium ants.

In ants, winged queens that are specialized for independent colony foundation can be replaced by wingless reproductives better adapted for colony fission. We studied this shift in reproductive strategy by comparing two Mystrium species from Madagascar using morphometry, allometry and dissections. Mystrium rogeri has a single dealate queen in each colony with a larger thorax than workers and similar mandibles that allow these queens to hunt during non-claustral foundation. In contrast, Mystrium 'red' lacks winged queens and half of the female adults belong to a wingless 'intermorph' caste smaller and allometrically distinct from the workers. Intermorphs have functional ovaries and spermatheca while those of workers are degenerate. Intermorphs care for brood and a few mate and reproduce making them an all-purpose caste that takes charge of both work and reproduction. However, their mandibles are reduced and inappropriate for hunting centipedes, unlike the workers' mandibles. This together with their small thorax disallow them to perform independent colony foundation, and colonies reproduce by fission. M. rogeri workers have mandibles polymorphic in size and shape, which allow for all tasks from brood care to hunting. In M. 'red', colonial investment in reproduction has shifted from producing expensive winged queens to more numerous helpers. M. 'red' intermorphs are the first case of reproductives smaller than workers in ants and illustrate their potential to diversify their caste system for better colonial economy.

Animals↗
PubMed2006

Is BMR repeatable in deer mice? Organ mass correlates and the effects of cold acclimation and natal altitude.

Basal metabolic rate (BMR) is probably the most studied aspect of energy metabolism in vertebrate endotherms. Numerous papers have explored its mass allometry, phylogenetic and ecological relationships, and ontogeny. Implicit in many of these studies (and explicit in some) is the view that BMR responds to selection, which requires repeatability and heritability. However, BMR is highly plastic in response to numerous behavioral and environmental factors and there are surprisingly few data on its repeatability. Moreover, the mechanistic underpinnings of variation in BMR are unclear, despite considerable research. We studied BMR repeatability in deer mice (Peromyscus maniculatus) across intervals of 30-60 days, and also examined the influence of birth altitude (3,800 m versus 340 m) and temperature acclimation (to approximately 5 or approximately 20 degrees C) on BMR, and the relationship between BMR and organ size. Neither acclimation temperature nor natal altitude alone influenced BMR, but the combination of birth at high altitude and cold acclimation significantly increased BMR. Few visceral organ masses were correlated to BMR and most were inconsistent across natal altitudes and acclimation temperatures, indicating that no single organ 'controls' variation in BMR. In several treatment groups, the mass of the 'running motor' (combined musculoskeletal mass) was negatively correlated to BMR and the summed mass of visceral organs was positively correlated to BMR. We found no repeatability of BMR in any treatment group. That finding-in sharp contrast to high repeatability of BMR in several other small endotherms-suggests little potential for direct selection to drive BMR evolution in deer mice.

Acclimatization↗
PubMed1999

Maximal aerobic power and leg muscle mass and strength related to age in non-athlethic males and females.

To investigate the relationships between the age-associated decline in peak oxygen uptake (peak VO2), leg muscle mass (LMM) and leg strength (LS) under the modulating effect of gender and level of physical activity (LPA, as assessed by questionnaire), we evaluated 71 sedentary subjects [males(M):females(F), 34:37], aged 20-80 years. Peak VO2 at maximum cycle ergometry was related to LMM (dual energy X-ray absorptiometry) and LS (isokinetic dynamometry) using both standard (y x x(-1)) and power function ratios (allometry). Absolute values of all variables were higher in males and declined with age (P < 0.01). Differences between the genders disappeared after peak VO2 x LS(-1.46(M)or -1.62(F)) adjustment but remained significant between peak VO2 LMM-(-0.51 (M)or -0.45(F)) and LS LMM- (-091(M) or -1.10(F)) corrected values. Allometric correction of peak VO2 and LS by LMM slowed their age-related declines; the flattening effect however, was more evident in the females. Interestingly, while no age-related decrement in peak VO2 LS(-1) was found, power function ratio values also declined with age, and at a slower rate in females. These findings are consistent with those obtained following a multiple regression analysis using LPA as an independent covariate (P < 0.01). We conclude that using adequate scaling methods and controlling by LPA: (1) no gender differences are observed in peak VO2 adjusted for LS, (2) loss of LS and LMM are important determinants of the age-associated reduction in physical fitness in both genders but (3) age per se has an LS- and LMM-independent influence on the functional decline, although this intrinsic effect of senescence is less pronounced in females.

Adult↗
PubMed1997

There is no highly conserved embryonic stage in the vertebrates: implications for current theories of evolution and development.

Embryos of different species of vertebrate share a common organisation and often look similar. Adult differences among species become more apparent through divergence at later stages. Some authors have suggested that members of most or all vertebrate clades pass through a virtually identical, conserved stage. This idea was promoted by Haeckel, and has recently been revived in the context of claims regarding the universality of developmental mechanisms. Thus embryonic resemblance at the tailbud stage has been linked with a conserved pattern of developmental gene expression - the zootype. Haeckel's drawings of the external morphology of various vertebrates remain the most comprehensive comparative data purporting to show a conserved stage. However, their accuracy has been questioned and only a narrow range of species was illustrated. In view of the current widespread interest in evolutionary developmental biology, and especially in the conservation of developmental mechanisms, re-examination of the extent of variation in vertebrate embryos is long overdue. We present here the first review of the external morphology of tailbud embryos, illustrated with original specimens from a wide range of vertebrate groups. We find that embryos at the tailbud stage - thought to correspond to a conserved stage - show variations in form due to allometry, heterochrony, and differences in body plan and somite number. These variations foreshadow important differences in adult body form. Contrary to recent claims that all vertebrate embryos pass through a stage when they are the same size, we find a greater than 10-fold variation in greatest length at the tailbud stage. Our survey seriously undermines the credibility of Haeckel's drawings, which depict not a conserved stage for vertebrates, but a stylised amniote embryo. In fact, the taxonomic level of greatest resemblance among vertebrate embryos is below the subphylum. The wide variation in morphology among vertebrate embryos is difficult to reconcile with the idea of a phyogenetically-conserved tailbud stage, and suggests that at least some developmental mechanisms are not highly constrained by the zootype. Our study also highlights the dangers of drawing general conclusions about vertebrate development from studies of gene expression in a small number of laboratory species.

Amphibians↗
PubMed2002

Functional convergence in plant responses to the environment.

Much comparative ecophysiological research has focused on contrasting species-specific behavior or ecological strategies with regard to regulation of basic physiological processes such as transpiration, photosynthesis and growth, leading to an emphasis on divergence rather than convergence in plant functioning. This review highlights selected examples in which substantial functional convergence among taxonomically, phylogenetically and architecturally diverse species has been revealed by applying appropriate scaling factors and identifying universal constraints or trade-offs. Recent empirical and theoretical scaling models emphasize the strong role that plant size, architecture, allometry and chemistry play in constraining functional traits related to water and carbon economy and growth. Taken together, the findings summarized here strongly suggest that there are a limited number of physiological solutions to a given problem of plant adaptation to the environment. Comparative ecophysiological studies will therefore benefit from consideration of the constraints that plant anatomical, structural and chemical attributes place on physiological functioning.

Adaptation, Physiological↗
PubMed2003

The leaf size-twig size spectrum and its relationship to other important spectra of variation among species.

There is a spectrum from species with narrow, frequently branched twigs carrying small leaves and other appendages, to species with thick twigs carrying large leaves and appendages. Here we investigate the allometry of this spectrum and its relationship to two other important spectra of ecological variation between species, the seed mass-seed output spectrum and the specific leaf area-leaf lifespan spectrum. Our main dataset covered 33 woody dicotyledonous species in sclerophyll fire-prone vegetation on low nutrient soil at 1,200 mm annual rainfall near Sydney, Australia. These were phylogenetically selected to contribute 32 evolutionary divergences. Two smaller datasets, from 390 mm annual rainfall, were also examined to assess generality of cross-species patterns. There was two to three orders of magnitude variation in twig cross-sectional area, individual leaf size and total leaf area supported on a twig across the study species. As expected, species with thicker twigs had larger leaves and branched less often than species with thin twigs. Total leaf area supported on a twig was mainly driven by leaf size rather than by the number of leaves. Total leaf area was strongly correlated with twig cross-section area, both across present-day species and across evolutionary divergences. The common log-log slope of 1.45 was significantly steeper than 1. Thus on average, species with tenfold larger leaves supported about threefold more leaf area per twig cross-section, which must have considerable implications for other aspects of water relations. Species at the low rainfall site on loamy sand supported about half as much leaf area, at a given twig cross-section, as species at the low rainfall site on light clay, or at the high rainfall site. Within sites, leaf and twig size were positively correlated with seed mass, and negatively correlated with specific leaf area. Identifying and understanding leading spectra of ecological variation among species is an important challenge for plant ecology. The seed mass-seed output and specific leaf area-leaf lifespan spectra are each underpinned by a single, comprehensible trade-off and their consequences are fairly well understood. The leaf-size-twig-size spectrum has obvious consequences for the texture of canopies, but we are only just beginning to understand the costs and benefits of large versus small leaf and twig size.

Analysis of Variance↗
PubMed2004

Reassessment of the environmental mechanisms controlling developmental polyphenism in spadefoot toad tadpoles.

Identifying the environmental mechanism(s) controlling developmental polyphenism is the first step in gaining a mechanistic and evolutionary understanding of the factors responsible for its expression and evolution. Tadpoles of the spadefoot toad Spea multiplicata can display either a "typical" omnivorous or a carnivorous phenotype. Exogenous thyroxine and feeding on conspecific tadpoles have been accepted as triggers for development of the carnivorous phenotype on the basis of a series of studies in the early 1990s. I repeated the thyroxine and conspecific-feeding assays and demonstrated that neither exogenous thyroxine nor feeding on conspecifics induces the carnivorous phenotype. Previous researchers used simple ratio statistics to argue that field-collected carnivores and thyroxine-treated tadpoles are similar, and my results supported these claims if I used the same simple ratio methodology. However, investigation of trait developmental trajectories and allometries for field-collected carnivores and thyroxine-treated and conspecific-fed tadpoles show that these phenotypes are profoundly different.

Adaptation, Physiological↗
PubMed2005

Sexual dimorphism and intercohort variation in reindeer calf antler length is associated with density and weather.

We analysed intercohort variability of live weight and antler length of 5,123 reindeer calves. We further assessed the influence of climate and density on the interannual variation in antler length, and discussed sex-specific resource allocation and response to climate variability. Antler length varied significantly among years and between sexes, with interaction between year and sex. Body weight and antler length were highly positively correlated, showed similar intercohort variability, and had a strong allometrical link, suggesting that antler length could be an equally reliable measure of calf condition as live weight. We found a relative measure of antler length (i.e. antler length corrected for the allometric effect of body mass) to be positively influenced by increasing density and May-June precipitation, and also decreasing May-June temperature. We attributed the effect of early summer weather to its influence on forage availability and quality as well as the level of parasitic insect harassment. Gender difference in both the allometric exponents and the interannual variability suggest that young males and females may have different tactics for relative resource allocation towards growth of antlers as compared to body mass. Because antlers are costly to produce, they may be an honest signal of individual quality for both sexes. However, we found gender-specific allometry, as female calves more than males appear to prioritize their antler growth over body mass, especially when resources are limited. Thus, our results suggest that environmental variation may influence the extent of sexual dimorphism in antler length.

Animals↗