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PubMed1998

Cranial allometry and geographic variation in slow lorises (Nycticebus)

A series of 20 craniodental measurements was obtained for two sister taxa: Nycticebus coucang (common slow loris) and N. pygmaeus (pygmy slow loris). Multivariate analysis of variance was performed with adult data to describe patterns of subspecific and specific variation in this genus. The geometric mean of adult cranial dimensions was compared to field data on latitudinal coordinates for available specimens to investigate if size variation in Nycticebus is clinal in nature. Ontogenetic series for larger-bodied N. coucang and smaller-bodied N. pygmaeus were compared to test the hypothesis that species and subspecific variation in skull form results from the differential extension of common patterns of relative growth. A MANOVA provides independent support of Groves's [pp. 44-53 in Proceedings of the Third International Congress on Primatology, Vol. 1 (Basel: S. Karger), in 1971)] classification of Nycticebus into two species, with four subspecies in the common slow loris and one form of the pygmy slow loris. Within N. coucang, cranial proportions for all four subspecies are ontogenetically scaled, and size differentiation is mainly clinal (Bergmann's Rule). N. c. bengalensis represents the most northerly disposed and the largest form. N. c. javanicus represents the next-largest form and is located in a southerly direction the next-farthest away from the equator. N. c. coucang and N. c. menagensis are both equatorial; however, the latter subspecies is the smallest. A genetic basis for some of the taxonomic variation between N. c. coucang and N. c. menagensis is supported by such nonclinal variation in body size. Variation in the presence/absence of I2 is not size-related but rather tracks geographic proximity and isolating factors which predate the most recent inundation of the Sunda Shelf. Although they inhabit a nonequatorial environment, pygmy slow lorises are the smallest of all Nycticebus. As N. pygmaeus is sympatric with N. c. bengalensis, the largest slow loris, it appears that the evolution of its smaller body size represents a case of character displacement. Unlike N. coucang, skull size becomes significantly smaller in more northern N. pygmaeus. This may also reflect character displacement between sympatric sister taxa underlain by a cline-dependent ecological factor which is marked in more northerly latitudes. On the other hand, the negative correlation between body size and latitude in N. pygmaeus could be due to the influence of nonprimate fauna, such as predators, which themselves evince a similar clinal pattern. Analyses of relative growth indicate that skull proportions in the two species of Nycticebus are ontogenetically scaled in two-thirds of the cases. All but one of the seven comparisons (interorbital breadth) which do not indicate ontogenetic scaling represent part of the masticatory complex. This likely reflects a reorganization of N. pygmaeus maxillomandibular proportions linked to smaller size and changes in diet.

Animals↗
PubMed1988

Growth allometry of craniomandibular muscles, tendons, and bones in the laboratory rat (Rattus norvegicus): relationships to oromotor maturation and biomechanics of feeding.

This study addressed the problem of how growth of craniomandibular muscles, tendons, and bones influences the acquisition of oromotor skills and biomechanics of feeding in the laboratory rat (Rattus norvegicus). Rats representing a 6.6-fold size range were dissected, and muscles, tendons, and mandibles were weighed. Cross-sectional areas of tendons and bones providing attachment surfaces for muscles were estimated. Ontogenetic scaling of craniomandibular muscles, tendons, and bones was described by using linear regression models, and departures from size-required compensations were used to characterize changes in oromotor function. A two-dimensional model was developed which permitted calculation of mechanical advantages of four masticatory muscles; the model was used to show how mandibular growth and tooth eruption influence the biomechanics of rat feeding. Relative to mandible weight, most jaw muscles scaled either isometrically or positively, tendon cross-sectional areas scaled isometrically or negatively, and bone surfaces scaled negatively. With the exception of the superficial masseter and internal pterygoid muscles, mechanical advantages did not change significantly during mandible growth. Growth patterns of craniomandibular muscles, tendons, and bones contribute significantly to changes in morphology and oromotor function.

Animals↗
PubMed1982

Patterns of intraspecific and interspecific allometry in Old World primates.

A series of 22 variables representing many skeletal elements were measured on a sample of 255 individuals from ten species of Old World primates to discover for which variables intraspecific or intragroup allometric curves differed from interspecific curves. Skeletal weight was used to represent size. These results were then used to evaluate several hypotheses that have been advanced as possible explanations of such differences. Two explanations seem likely to apply frequently, but in different cases. First, the correlation between a variable and size is often low intraspecifically so that the reliability of the curve describing the relationship is poor. This applies equally to results from least-squares regression or reduced major axis. The low correlation may result from a situation in which a feature need not vary in close response to body size intraspecifically. The interspecific curve would be produced as a result of different optima in a series of species. Second, the results for many variables suggest that the nature of an organism's adaptive response to change in size differs between groups. The intragroup (or intraspecific) curves describe that response, while the interspecific curve is a summary of the consequences of size across all the included groups, which may be heavily influenced by the differing adaptations of those groups.

Animals↗
PubMed1984

Limb bone allometry in primates: a test of the elastic similarity model.

Morphometric data on postcranial elements of ten species of Old World primates are used to test the elastic similarity model of limb scaling. The data are divided into three groupings to exclude as much variation due to differences in locomotor adaptation as possible. The data on skeletal diameters fits the model reasonably well. The length results, however, are generally not in conformity with the model's predictions.

Animals↗
PubMed1984

Allometry between length and cross-sectional dimensions of the femur and tibia in Homo sapiens sapiens.

Allometric equations relating length and cross-sectional geometric properties of the femur and tibia are generated using skeletal remains from three recent human population samples. Approximate isometry, or geometric similarity, is found both within and between samples. Cross-sectional areas scale to approximately length2, while second moments of area scale to approximately length4. It is shown that this is consistent with the maintenance of equivalent mechanical stress in long bones of different length under dynamic loadings in vivo. Other evidence indicates that bending and torsional loadings are more critical than axial loadings in the determination of lower limb bone cross-sectional dimensions.

Adult↗
PubMed1992

Hindlimb proportions, allometry, and biomechanics in Old World monkeys (primates, Cercopithecidae).

The traditional focus on morphological rather than mechanical units has obscured some significant functional differences in the hindlimbs of primates. This paper examines the allometric and biomechanical basis for some distinctive proportional differences among pairs of morphological units in the hindlimb, and especially the foot, of cercopithecid primates. Five major conclusions are reached. First, many hindlimb dimensions scale allometrically with body mass to maintain mechanical similarity within taxonomic and locomotor groups. Therefore, the majority of traditional indices which describe the shape of the foot within cercopithecids reveal differences which are primarily a function of size. Second, the hindlimb segments in colobines, and especially in Presbytis, are relatively long, probably to enhance leaping. Third, the major distinction of terrestrial cercopithecines among the features analysed is reduction in the length of the phalanges, due to the reduced importance of grasping during locomotion and the assumption of digitigrady. Fourth, Theropithecus and male Erythrocebus have high crural indices, relative to their body masses, which can facilitate curosoriality. Female E. patas already has a high crural index as a function of its body mass. Fifth, macaques form a distinctive group among cercopithecines, characterized by relatively short hindlimbs. Relatively very short hindlimbs in Macaca fuscata and M. thibetana suggest that climatic conditions can have an added effect on the lengths of the hindlimb segments. In summary, this analysis of the lengths of the hindlimb segments relative to body size reveals taxonomic differences which are due in part to phylogeny, to differences in locomotor behavior, and to substrate use.

Analysis of Variance↗
PubMed1992

Allometry and prediction in hominoids: a solution to the problem of intervening variables.

To avoid misinterpretation of allometric exponents determined from interspecific allometric comparisons, specific conditions must be met with respect to the common reference variable. Body weight is considered to be the best general indication of overall size and is hence widely acknowledged to be the most suitable reference variable. However, because of the paucity of recorded body weights for museum specimens, various comparative studies have used other size indicators as intervening variables, although the allometric relationships to body size/weight were often unknown and possibly differed between species. Because of differences in the scaling properties of alternative intervening variables across the species investigated, conflicting conclusions may be drawn if different variables are chosen as substitutes for overall size. This is illustrated with two examples. In this study, series of skeletons with associated body weights of Gorilla, Pan, Pongo, and Homo were investigated. Both ontogenetic and static adult allometric relationships between several widely used reference variables and body weight were determined. Neither these variables nor additional estimators investigated in this study displayed allometric exponents and coefficients similar enough across species to justify direct interspecific comparison. To generate an alternative size estimator for both ontogenetic and static interspecific investigations, equations for combined sexes were derived to predict body weight from various long bone dimensions for individual hominoid species. From a total of 25 predictors, 12 prediction equations per species (six for nonadults and six for adults) were selected according to their relative suitability for reliable prediction of body weight. It is shown that the derived reference variable "predicted body weight" avoids problems of intervening variables, is valid for any interspecific ontogenetic and static allometric comparison, and displays less fluctuation in comparison to actual body weight.

Animals↗
PubMed1994

Functional allometry of the semicircular ducts in subterranean mole-rats Cryptomys (Bathyergidae, Rodentia).

BACKGROUND: Since the spatial mobility of subterranean mole-rats is restricted and their skull strongly modified, morpho-functional regression of their vestibular organ may be expected. On the other hand, vestibular sense may be indispensable for orientation in a world deprived of most external sensory cues. Since vestibular sensitivity is determined by the size of the labyrinth, morphometrical analysis may be employed to assess the sensitivity and to test whether the organ is degenerate or progressively specialized. METHODS: We analyzed the shape and size of the membranous labyrinth of vestibular organs in toto in three species of African subterranean blind mole-rats of the genus Cryptomys (Bathyergidae) differing in body size yet not in habitats, ways of life, or employed orientation and locomotory strategies. The mechanical sensitivity of the cupula was estimated according to Oman et al. (1987. Acta Otolaryngol. (Stockh.), 103:1-13) for each of the three semicircular ducts. RESULTS: The size and shape of the vestibular organ changed predictably depending on species-specific (yet not individual) body mass. In some aspects, particularly the cross-sectional area, the ducts were larger than expected for a mammal of a comparable body size. In all species examined, the anterior semicircular ducts exhibited the highest sensitivity. CONCLUSIONS: The vestibular organs of blind subterranean mole-rats are not regressed morpho-functionally.

Animals↗
PubMed2003

Cranial allometry, phylogeography, and systematics of large-bodied papionins (primates: Cercopithecinae) inferred from geometric morphometric analysis of landmark data.

The cranial morphology of the African Old World monkeys Mandrillus, Papio, and Theropithecus (i.e., baboons) has been the subject of a number of studies investigating their systematic relationships, patterns of scaling, and growth. In this study, we use landmark-based geometric morphometrics and multivariate analysis to assess the effects of size, sex, taxonomy, and geographic location on cranial shape. Forty-five landmarks were digitized in three dimensions on 452 baboon crania and subjected to generalized Procrustes analysis (GPA), which standardizes geometric size but leaves scaling-based shape differences in the data. The resulting shape coordinates were submitted to regression analysis, principal components analysis (PCA), partial least-squares (PLS) analysis, and various clustering techniques. Scaling (shape differences correlated with size) was the largest single factor explaining cranial shape variation. For instance, most (but not all) of the shape differences between the sexes were explained by size dimorphism. However, central tendencies of shape clearly varied by taxon (both specific and subspecific) even after variations in size and sex were adjusted out. Within Papio, about 60% of the size- and sex-adjusted shape variations were explained by the geographic coordinates of the specimen's provenance, revealing a stepped cline in cranial morphology, with the greatest separation between northern and southern populations. Based on evidence from genetic studies, and the presence of at least two major hybrid/interbreeding zones, we interpret the phylogeographic pattern of cranial variation as indicating that these populations are best ranked as subspecies of a single species, rather than as two or more distinct biological species. This objective approach can be applied to other vertebrate species or species groups to help determine the taxonomic rank of problematic taxa.

Africa↗
PubMed1986

On the allometry of long bones in dogs (Canis familiaris).

The allometric relations of diameter and length of humerus, ulna, femur, and tibia of 108 specimens, from 63 different breeds of dogs and 12 specimens of wolves, were calculated by means of model II of regression or major axis method. Only for the tibia were the values of wolves included in the cluster formed for dog breeds. Consequently, separate lines of regression were calculated for the other bones. Results agree in general with the exponents predicted by the theory of geometric similarity; however, the slope obtained for femur (0.865) differed significantly from this. Morphology of the long bones of the legs does not differentiate dogs and wolves; this probably reflects secondary convergence among wolves with relatively modern breeds of dogs.

Animals↗
PubMed1993

The time allometry of mammalian chewing movements: chewing frequency scales with body mass in mammals.

For a sample of 26 extant mammalian species, a significant relationship between body mass and chewing frequency was found, in which chewing frequency is proportional to body mass to the -0.128 power. This relationship is similar to previously published data relating stride frequency and body mass in quadrupedal mammals. It was also found that jaw length is proportional to body mass to the 0.312 power, which is consistent with geometric scaling of jaw length. The period of the chewing cycle was found to be proportional to jaw length to the 0.383 power. These results demonstrate that chewing frequency does not scale as metabolic rate, and support the suggestion that the natural frequency of the chewing rhythm may be derived from masses and lengths of the components of the masticatory apparatus alone.

Animals↗
PubMed1995

Developmental mechanics determine long bone allometry.

Evolutionary and developmental factors responsible for the scaling relationships observed in animal skeletons are poorly understood. We have created a mathematical model for long bone cross-sectional development which incorporates both intrinsic growth and extrinsic, adaptive bone modeling in response to changes in bone mechanical strains during ontogeny. The model successfully simulates the developing morphology in individual animals and the bone geometric allometric relationships among adults across many species (range from mouse to elephant in size). Our results suggest that long bone scaling characteristics are not a result of intrinsic genetic factors but are the results of highly conserved, extrinsic biophysical processes whereby bone tissue strains modulate skeletal morphogenesis.

Biomechanical Phenomena↗
PubMed2002

On the allometry of biomass partitioning and light harvesting for plants with leafless stems.

Prior explicit allometric models are extended to predict the scaling relationship between the ability of plants with leafless stems to harvest sunlight H and total standing plant biomass M(T) (which equals the sum of standing stem and root biomass, M(S) and M(R)). Provided that H scales in a directly proportional manner (isometrically) with respect to either stem surface area (i.e.H proportional, variant SA(S) ) or total stem biomass (i.e. H proportional, variant M(S)), the allometric model presented here predicts that SA(S) proportional, variant M(T)(3/4) or M(S) proportional, variant M(T)(3/4), respectively. These alternative predictions are tested empirically using data for standing stem and root biomass gathered for the large columnar cactus species Pachycereus pringlei. Statistical comparisons between observed and predicted scaling relationships indicate that SA(S) proportional, variant M(T)(3/4), whereas M(S) proportional, variant M(T)(3/4) is mathematically inconsistent with the observation that stem biomass scales nearly isometrically with respect to root biomass. The contention that the H of leafless stems scales isometrically with respect to stem surface area is thus reasonable both theoretically and empirically.

Biomass↗
PubMed1995

Allometry in the uptake of hydrophobic chemicals determined in vivo and in isolated perfused gills.

Uptake rate constants of different classes of hydrophobic organic chemicals have been determined in isolated perfused gills of rainbow trout (Oncorhynchus mykiss) as an alternative for studies in vivo. The uptake rate constants have been compared to those determined in guppy, Poecilia reticulata, in vivo. The organic chemicals which have been used are anthracene, hexabromobenzene, octachloronaphthalene, octachlorodibenzo-p-dioxin, phenol, polychlorinated anisoles, polychlorinated benzenes, polychlorinated biphenyls, and tetrachloroveratrole. Uptake rate constants in guppy are higher than those in rainbow trout gills, and show relatively high variation in both gills and guppy. When uptake rate constants in each study are normalized for that of pentachlorobenzene (pCBz), variation is significantly reduced both in perfused gills and in guppy. All allometric relationship is derived between weight and uptake rate constant. Uptake rate constants determined in one fish can thus be used for prediction of those in other fishes. When a reference chemical, such as pCBz, is included, the gill perfusion experiments can be highly suitable to determine uptake rate constants of organic chemicals, which can be extrapolated to fish of different sizes.

Animals↗
PubMed1985

Allometries of the durations of torpid and euthermic intervals during mammalian hibernation: a test of the theory of metabolic control of the timing of changes in body temperature.

The durations of the intervals of torpor and euthermia during mammalian hibernation were found to be dependent on body mass. These relationships support the concept that the timing of body temperature changes is controlled by some metabolic process. Data were obtained from species spanning nearly three orders of magnitude in size, that were able to hibernate for over six months without food at 5 degrees C. The timing of body temperature changes was determined from the records of copper-constantan thermocouples placed directly underneath each animal. Because all species underwent seasonal changes in their patterns of hibernation, animals were compared in mid-winter when the duration of euthermic intervals was short and relatively constant and when the duration of torpid intervals was at its longest. Large hibernators remained euthermic longer than small hibernators (Fig. 2). This was true among and within species. The duration of euthermic intervals increased with mass at the same rate (mass 0.38) that mass-specific rates of euthermic metabolism decrease, suggesting that hibernators remain at high body temperatures until a fixed amount of metabolism has been completed. These data are consistent with the theory that each interval of euthermia is necessary to restore some metabolic imbalance that developed during the previous bout of torpor. In addition, small species remained torpid for longer intervals than large species (Fig. 3). The absolute differences between different-sized species were large, but, on a proportional basis, they were comparatively slight.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗