Allometry of the postnatal cranial ontogeny and sexual dimorphism in Otaria byronia (Otariidae)

We studied the cranial postnatal ontogeny of Otaria byronia in order to detect sexual dimorphism in allometric terms, analyzing the rate of growth of functional variables linked to specific capacities as bite and head movements. We used 20 linear measurements to estimate allometric growth applying bivariate and multivariate analyses in females and males separately. Males were also analyzed in two partitioned subsets considering non-adult and adult stages, when the dimorphism is accentuated in order to reach optimal performance for intra-sexual competition. In the comparison of the employed techniques, we detected an empirical relationship between our multivariate results and the ordinary least square bivariate analysis. The quantitative analyses revealed different ontogenetic trajectories between non-adult and adult males in most variables, suggesting that the adult skull is not a scaled version of subadult skull. For instance, variables related with longitudinal dimensions decreased their allometric coefficients when the adult stage was reached, whereas those related with breadth or vertical dimensions increased their values. In adult males this could indicate that skull breadth and height are more important than longitudinal growth, relative to overall skull size. Conversely, inter-sexual comparisons showed that females and non-adult males shared similar ontogenetic growth trends, including more allometric trends than did males along their own ontogenetic trajectory. In general, adult males exhibited higher allometric coefficients than non-adult males in variables associated with bite and sexual behavior, whereas in comparison to females the latter showed higher coefficients values in these variables. Such patterns indicate a complex mode of growth in males beyond the growth extension, and are in partial agreement with changes previously reported for this and other species in the family Otariidae.     

Anointing variation across wild capuchin populations: a review of material preferences, bout frequency and anointing sociality in Cebus and Sapajus

The frequency of anointing bouts and the materials used for self- and social anointing vary across capuchin species in captivity, but there is little published data on capuchin anointing in the wild. Here we present previously unpublished data on anointing behaviors from capuchin monkey populations at ten different field sites and incorporate these data into a review of the anointing literature for captive and wild capuchins. Using a comparative phylogenetic framework, we test four hypotheses derived primarily from captive literature for variation in anointing between wild untufted capuchins (Cebus) and tufted capuchins (Sapajus), including that (1) the frequency of anointing is higher in Cebus, (2) Cebus uses a higher proportion of plant species to insect species for anointing compared with Sapajus, (3) anointing material diversity is higher in Cebus, and (4) social indices of anointing are higher in Cebus. We found that wild Cebus anoints more with plant parts, including fruits, whereas wild Sapajus anoints more with ants and other arthropods. Cebus capucinus in particular uses more plant species per site for anointing compared with other capuchins and may specialize in anointing as an activity independent from foraging, whereas most other capuchin species tend to eat the substances they use for anointing. In agreement with captive studies, we found evidence that wild Cebus anoints at a significantly higher frequency than Sapajus. However, contrary to the captive literature, we found no difference in the range of sociality for anointing between Cebus and Sapajus in the wild. We review anointing in the context of other Neotropical primate rubbing behaviors and consider the evidence for anointing as self-medication; as a mechanism for enhanced sociality; and as a behavioral response to chemical stimuli.     

Competition and Facilitation in the Capuchin–Squirrel Monkey Relationship

In Guyana, the range of the brown capuchin, Cebus apella, meets the range of its congener, the wedge‐capped capuchin, C. olivaceus, with the two species exhibiting a mutually exclusive patchy distribution. Squirrel monkeys, Saimiri sciureus, and C. apella form ubiquitous interspecific associations, but the reason remains debatable. With a large biogeographic field study, we tested the degree to which the distribution and abundance of Cebus and S. sciureus is determined by habitat type, fruit availability, and geography (i.e., determinants of the fundamental niche) relative to interspecific interactions, such as competition and facilitation (i.e., the realized niche). We used the competition between the two capuchin monkeys as a natural experiment that subjected S. sciureus to C. apella and C. olivaceus ‘treatments’. Using spatial regression models and principal components analysis, we found that S. sciureus was associated with seasonally flooded forests, and was correlated with fruit abundance and diversity (fundamental niche), but was also correlated with C. apella density even when accounting for habitat and fruit availability (realized niche). Saimiri sciureus density was unrelated to C. olivaceus density. Cebus apella was associated with a variety of forest types, but particularly included disturbed and edge habitats such as logged forests, seasonally flooded forests, and upland savanna, in addition to mature forest. Cebus apella was also positively correlated with S. sciureus density and negatively correlated with the density of C. olivaceus. In contrast, C. olivaceus avoided riparian areas and was associated with mixed‐height forests on sloped mountainous terrain. In sum, interspecific interactions such as competition between species of Cebus and facilitation between C. apella and S. sciureus were as important as habitat and fruit availability in determining the distribution and abundance of these primates.     

Morphometric analysis of the skull of Dermophis mexicanus (Amphibia: Gymnophiona)

The levels of integration, patterns of allometric growth and size-related differences in skull dimensions of the caecilian Dermophis mexicanus were investigated by means of univariate, bivariate and multivariate statistics. The analyses indicate that (1) most but not all measurements of the skull arc more variable in adults than in juveniles; (2) growth is allometric and results in changes in shape between juveniles and adults; (3) there is a high level of integration of all variables by general size; and (4) homologous paired measurements show concordant allometric trends and are integrated beyond the sole effect of general size. These analyses provide baseline data, a set of hypotheses and a methodological framework for comparative studies of patterns of variation and integration among caecilians and among other vertebrates.     

Ratios as a size adjustment in morphometrics

Simple ratios in which a measurement variable is divided by a size variable are commonly used but known to be inadequate for eliminating size correlations from morphometric data. Deficiencies in the simple ratio can be alleviated by incorporating regression coefficients describing the bivariate relationship between the measurement and size variables. Recommendations have included: 1) subtracting the regression intercept to force the bivariate relationship through the origin (intercept-adjusted ratios); 2) exponentiating either the measurement or the size variable using an allometry coefficient to achieve linearity (allometrically adjusted ratios); or 3) both subtracting the intercept and exponentiating (fully adjusted ratios). These three strategies for deriving size-adjusted ratios imply different data models for describing the bivariate relationship between the measurement and size variables (i.e., the linear, simple allometric, and full allometric models, respectively). Algebraic rearrangement of the equation associated with each data model leads to a correctly formulated adjusted ratio whose expected value is constant (i.e., size correlation is eliminated). Alternatively, simple algebra can be used to derive an expected value function for assessing whether any proposed ratio formula is effective in eliminating size correlations. Some published ratio adjustments were incorrectly formulated as indicated by expected values that remain a function of size after ratio transformation. Regression coefficients incorporated into adjusted ratios must be estimated using least-squares regression of the measurement variable on the size variable. Use of parameters estimated by any other regression technique (e.g., major axis or reduced major axis) results in residual correlations between size and the adjusted measurement variable. Correctly formulated adjusted ratios, whose parameters are estimated by least-squares methods, do control for size correlations. The size-adjusted results are similar to those based on analysis of least-squares residuals from the regression of the measurement on the size variable. However, adjusted ratios introduce size-related changes in distributional characteristics (variances) that differentially alter relationships among animals in different size classes. © 1993 Wiley-Liss, Inc.     

Frog-eating behavior of wild black-capped capuchin (Cebus apella)

We know the capuchin (Cebus apella) is an omnivorous monkey; we have a considerable amount of information given by native hunters that it feeds on small-sized species of amphibians and reptiles, young birds and birds' eggs, as well as various kinds of fruit and insects. However, how the monkey discovers, captures, and eats such food has not yet been reported. Neither has it been reported that the capuchin feeds on certain species of them purposely, not accidentally. The capuchin observed by the author fed on a kind of frog (Hylidae), which inhabits Guadua (Bambusa guadua) and each individual used the same method to discover, capture, and eat the frog. It can be suggested that the behavior in such a series are adaptive ones which guarantee the capuchin a constant supply of frogs.     

Testing the cranial evolutionary allometric ‘rule’ in Galliformes

Recent comparative studies have indicated the existence of a common cranial evolutionary allometric (CREA) pattern in mammals and birds, in which smaller species have relatively smaller faces and bigger braincases than larger species. In these studies, cranial allometry was tested using a multivariate regression between shape (described using landmarks coordinates) and size (i.e. centroid size), after accounting for phylogenetic relatedness. Alternatively, cranial allometry can be determined by comparing the sizes of two anatomical parts using a bivariate regression analysis. In this analysis, a slope higher or lower than one indicates the existence of positive or negative allometry, respectively. Thus, in those species that support the CREA ‘rule’, positive allometry is expected for the association between face size and braincase size, which would indicate that larger species have disproportionally larger faces. In this study, I applied these two approaches to explore cranial allometry in 83 Galliformes (Aves, Galloanserae), ranging in mean body weight from 30 g to 2.5 kg. The multivariate regression between shape and centroid size revealed the existence of a significant allometric pattern resembling CREA, whereas the second analysis revealed a negative allometry for beak size and braincase size (i.e. contrary to the CREA ‘rule’, larger galliform species have disproportionally shorter beaks than smaller galliform species). This study suggests that the presence of CREA may be overestimated when using cranium size as the standard measurement.     

Post-weaning cranial ontogeny in two bandicoots (Mammalia,Peramelomorphia, Peramelidae) and comparison with carnivorous marsupials

The ontogeny of the skull has been studied in several marsupial groups such as didelphids, microbiotheriids, and dasyurids. Here, we describe and compare the post-weaning ontogeny of the skull in two species of bandicoots, Echymipera kalubu (Echymiperinae) and Isoodon macrourus (Peramelinae), analyzing specific allometric trends in both groups, describing common (and specific) patterns, and discussing them on functional and phylogenetic grounds. Growth patterns were analyzed both qualitatively and quantitatively, including bivariate and multivariate analyses of allometry. We also evaluated character transformation and phylogenetic signals of the allometric patterns in several groups of marsupials and some placentals. We identified morphological changes between juvenile and adult stages in both species of peramelids, many related to the development of the trophic apparatus. Notable differences were detected in the patterns of growth, suggesting divergences in ontogenetic trajectories between both species. Both bivariate and multivariate methods indicate that positive allometries in E. kalubu apply to longitudinal dimensions, whereas in I. macrourus, positive allometries are restricted to vertical dimensions of the skull. The comparison of the allometric trends of two bandicoots with previously studied taxa reveals that although peramelids exhibit a particularly short gestation period and divergent morphology compared to other marsupials, their pattern does not show any particular trend. Some allometric trends seem to be highly conserved among the species studied, showing weak phylogenetic signal. Marsupials in general do not show particular patterns of post-weaning skull growth compared with placentals.     

The nature and basis of sexual dimorphism in the primate skeleton

This study sets out to document and analyse sexual dimorphism in the teeth and bones of five primate groups, including man. Specimens were only included in the analysis if their sexual attribution was reliable and was based on non-osteological criteria. Ninety raw measurements, both cranial and post-cranial, were used and 11 indices were computed from them.
The parameters of each sample were computed in order to compare these results with previous estimates of dimorphism which have not always been based on reliably sexed samples. Correlation matrices were computed.
The overall sex differences were subdivided into "shape" and "size" components using Penrose's size and shape distances and by computing the principal components of each data set. The visually apparent shape differences were confirmed metrically and then examined to see whether they could be explained by allometric effects or whether there was evidence for sexual differences in growth patterns.
Using femur length as the independent variable, because of its correlation with overall size, allometric coefficients were computed for the logarithmically transformed data. The coefficients were in some cases very different between sexes but the majority did not achieve statistical significance. Of those that were significantly different only in Homo did such differences narrowly exceed the number that would be expected by chance alone.
As the vast majority of allometric coefficients for the pooled male and female data differed from unity, the hypothesis that most of the considerable shape differences that exist between some male and female primates are due to underlying growth differences must be rejected. It is suggested that such differences are simply the result of disproportionate change in size.     

Size and mating success in males of the western harvester ant,Pogonomyrmex occidentalis (Hymenoptera: Formicidae)

Mating success in males of the lek mating ant species,Pogonomyrmex occidentalis, increases with increased body size. We estimated the magnitude of the selection coefficients on components of size by collecting males in copula and comparing their morphology to that of males that were collected at the lek but that were not mating. Four characters, body mass, head width, wing length, and leg length, were measured for a sample of 225 mating and 324 nonmating males and 225 females. Significant direct selection favors increased wing length and leg length. Multiple regression of transformed variables (principal components) indicated that the increased mating success of larger males is a function of all four characters. We found no evidence of positive assortative mating on the basis of any individual character or on the multivariate general size variable (the first principal component).     

The Hindlimb Elements of the Maas (Aves,Dinornithidae): A Multivariate Assessment of Size and Shape

A multivariate morphometric analysis of size and shape was performed on the hindlimb skeletal elements of the extinct New Zealand moas (Dinornithidae). Investigations were undertaken of size-shape patterns within species and among moas as a group using principal components analysis; between species investigations used canonical analysis. In addition, standard allometric curve-fitting of six femur, seven tibiotarsus, and nine tarsometatarsus variables against body size was performed. Size was the major discriminator along the first principal component for all three bones in the intraspecific and whole-group analyses. Shape was the important discriminator along the second component: in the whole-group analysis of all three bones, separation was based on relative robustness of the shaft, whereas in the intraspecific analyses shaft robustness was only expressed in the analysis of the femur, there being little correspondence in the results between the intraspeci fic and whole-group analyses of the tibiotarsus and tarsometatarsus. Size was the major discriminator along the first canonical axis for the between-group investigations of the femur and tibiotarsus, but in the analysis of the tarsometatarsus shape influences were equally as important as those of size. The second canonical axis separated groups on the basis of shape differences in all three hindlimb elements. The genus Dinornis, which contains the largest species of moas, has evolved sizeshape patterns very different from those of other moas. The species of Dinornis did not follow size-dependent allometric trends and evolved proportionately thinner legs than might be expected for their body size. All other moas exhibit allometric increase in all hindlimb variables except bone lengths. Dinornis may have evolved a cursorial mode of locomotion as an adaptation for certain intraspecific behavioral interactions.     

Cross-genus adoption of a marmoset (Callithrix jacchus) by wild capuchin monkeys (Cebus libidinosus): case report

We report a case of interspecies adoption of an infant marmoset (Callithrix jacchus) by wild capuchin monkeys (Cebus libidinosus). The marmoset was an infant when it was first observed in the capuchin group on 3 March 2004. Since it first appeared it has been observed informally and frequently. In January 2005 systematic observations were made of the marmoset and a capuchin of similar age. Throughout its period of adoption the marmoset appeared to be socially integrated into the group, benefiting from nurturant behaviors exhibited by two successive adoptive "mothers" and pronounced tolerance from all members of the group. This case highlights the flexibility of both Callithrix and Cebus in accommodating variable social behaviors and other characteristics (including size) of social partners.     

Sexual and ontogenetic morphometric variation in Xiphopenaeus kroyeri (Crustacea,Decapoda, Penaeidae): a new approach with linear and angular morphometric data

The present study evaluates the ontogenetic/sexual morphometric variation in Xiphopenaeus kroyeri. Sampling was from July 2001 to June 2003 at Ubatuba, São Paulo, Brazil. Animals were sexed and measured (cephalothorax length-CC, partial of the rostral spine-CPR, rostral spine-CR and rostral spine angulation-AR). Data analysis included linear morphometric analysis: equation ln y = ln a + ln b (sex/ontogeny fitting), k-means method (ontogenetic classification), analysis of covariance (morphological maturity), removal of the allometric effect, verification of parametricity and collinearity, principal component (PCA) and linear discriminant analysis (visualization of tendencies), permutational multivariate analysis of variance (hypothesis test). In addition, circular analysis was undertaken: circular normal distribution and concentration parameter, circular analysis of variance (hypothesis test), PCA (observe tendencies) and linear-circular regression (ontogenetic trajectory, RA-dependent variable, CL-independent variable). Morphological changes in the cephalothorax, in the adult stage, may be related to the increase in size of the gonads during sexual maturation and to the development of gills during the transition from arthrobranch (juvenile) to dendrobranch (adult). The rostral spine, in the adult stage, tends to become more elongated and more sharply angled. This feature may be related to predation pressure on larger specimens (adults), knowing that throughout its ontogeny the rostral spine of this species assumes phenotypic traits that make swallowing more difficult for predators.     

Effects of iodine deficiency on mental and psychomotor abilities

The allometric relationships between canine base area, first molar and summed molar crown area, and the glabella–opisthocranion distance, and the direct allometric relationships between canine and molar size have been established in five primate taxa. Separate sex and combined sex ‘intraspecific’, and ‘interspecific’ regression and ‘best fit’ allometry coefficients were computed. This analysis showed that for any increase in glabella–opisthocranion length, the rate of increase in canine size exceeds the rate of increase in molar area, and ‘best fit’ solutions indicate that canine base area is positively allometric when related directly to molar crown area. These results were compared with data available for the ‘gracile’ australopithecine, A. africanus, and two ‘robust’ australopithecine taxa, A. boisei and A. robustus. The differences in canine and molar size which occur between the ‘gracile’ taxon and the two ‘robust’ taxa do not correspond to any of the trends in the comparative allometric models. Data on glabella–opisthocranion length for the fossils, meagre though they are, show that while the proportional increase in molar crown area between the taxa corresponds to comparative allometry models, the reduced canine size in the ‘robust’ taxa is against comparative allometric trends. These results indicate that, at least in terms of canine/molar proportions, the differences between the ‘gracile’ and ‘robust’ australopithecines are not merely allometric and may indicate significant dietary or behavioural differences.     

Biometric variability of Hadwenius tursionis (Marchi, 1873) (Digenea,Campulidae) from the intestine of the bottlenose dolphin Tursiops truncatus (Montagu, 1821)

The species discrimination in the family Campulidae is largely based on morphometric characters (absolute measurements and ratios). To assess the variability of this characters we have studied the campulid species Hadwenius tursionis from four Mediterranean bottlenose dolphins Tursiops truncatus from the Western Mediterranean. In H. tursionis most absolute measurements differed significantly across the infrapopulations, showing high coefficients of variation. Only egg dimensions appeared to be fairly conservative. Body ratios were less variable than absolute measurements, but growth patterns did vary significantly between the infrapopulations studied. None of the ratios previously used in relation to other species of the family Campulidae indicated either isometric or allometric growth in this case. Only the ratios concerning the size of the gonads and the shape of the gonads and suckers showed isometry. It is concluded that absolute measurements and ratios should be used with caution in relation to the separation of species of the family Campulidae unless their intrinsic variability can be established beforehand.     

Canine Dimorphism and Interspecific Canine Form in Cebus

I investigated canine dimorphism and interspecific canine form in adult specimens from 4 capuchin species (Cebus albifrons, C. apella, C. capucinus, and C. olivaceus). I used various univariate and multivariate statistics, which are based on 6 variables, to test several hypotheses that are based upon the finding that canine dimorphism is strongly associated with intermale competition in platyrrhines (Kay et al., 1988), Greenfield (1992a), Plavcan and van Schaik (1992, 1994). Results from the indices of canine dimorphism and the unpaired t-tests corroborate the prediction that males of each species possess significantly larger canines than those of females. Large male canines are especially prominent in 2 variables, maxillary and mandibular canine height. Greene's t-test (1989) does not support the prediction that Cebus apella and C. olivaceus possess a larger degree of canine dimorphism relative to C. albifrons and C. capucinus. No interspecific differences in degree of canine dimorphism are indicated by this test. Results of the discriminant function analyses (DFA) do not find that Cebus apella and C. olivaceus possess different canine form relative to C. albifrons and C. capucinus as predicted. However, Cebus apella is differentiated from the untufted capuchins (C. albifrons, C. capucinus, and C. olivaceus) by the DFA. I suggest that intermale competition is the primary selective force underlying the observed morphological patterns; however, it does not explain all the variation associated with canine dimorphism in Cebus.     

Observations on the activity patterns and social interactions of a captive group of blackcapped or brown capuchin monkeys (Cebus apella)

Studies were conducted on a captive group of 16 blackcapped capuchin monkeys (Cebus apella), with observations being carried out for a total of 75 hr over a 6 month period. Records were kept of their activities and spatial distribution according to weather type and time of day. Evidence of a social hierarchy was sought and was characterized primarily by the stability of the environment in which the animals live, dominance playing little part. The behaviour of the blackcapped capuchin has been studied previously in captivity (Dobruruka, 1972;Weigel, 1979); this study is, however, unique in that the troop under observation enjoys more freedom. Weather had no effect on the rank order of behavioural activities but did affect both activity levels and distribution of individuals. TheCebus apella troop spent around 50% of its active time foraging and eating, 7–10% of this time walking and around 30% of the time inactive. These values lie between those reported for caged and wild animals. Social interactions contributed more than 10% of the time budget, which is greater than wild populations. The study here thus provides an interesting link between information collected from wildCebus apella populations and that from rather more restricted troops.     

New body mass estimates for Omomys carteri,a middle Eocene primate from North America

We report new body mass estimates for the North American Eocene primate Omomys carteri. These estimates are based on postcranial measurements and a variety of analytical methods, including bivariate regression, multiple regression, and principal components analysis (PCA). All body mass estimation equations show high coefficients of determination (R²), and some equations exhibit low prediction errors in accuracy tests involving extant species of body size similar to O. carteri. Equations derived from PCA-summarized data and multiple regression generally perform better than those based on single variables. The consensus of estimates and their statistics suggests a body mass range of 170–290 g. This range is similar to previous estimates for this species based on first molar area (Gingerich, J Hum Evol 10:345–374, 1981; Conroy, Int J Primatol 8:115–137, 1987). Am J Phys Anthropol 109:41–52, 1999. © 1999 Wiley-Liss, Inc.     

Competition,niche specialization and the evolution of brain size in the genus Peromyscus

Previous studies of relative brain size in mammals have suggested an association with complex habitats and with low reproductive rate. In order to examine the causal relationships more thoroughly, a detailed examination of relative brain size variation in the genus Peromyscus was undertaken. Endocranial volumes were used to estimate brain weight for 32 species including 161 subspecies, and relative brain size calculated as the species deviation from the allometric relationship between brain and body size. The intrageneric allometric coefficient was higher than most values previously reported from low taxonomic levels, but intraspecific coefficients were generally lower than this. Island species, and relict species isolated on mountain tops, which may be ecological ‘islands’, had consistently small relative brain sizes, but peninsular species were large brained. Among the remaining species there were significant correlations between litter size and relative brain size, and between the number of competitor species and relative brain size. Species with many competitor species have relatively large brains and small litters. It is concluded that the nature of the geographical distribution, the pattern of species formation and habitat complexity all influence relative brain size in existing forms.     

Evolutionary allometry of lumbar shape in Felidae and Bovidae

As body size increases, so do the biomechanical challenges of terrestrial locomotion. In the appendicular skeleton, increasing size is met with allometry of limb posture and structure, but much less is known about adaptations of the axial skeleton. It has been hypothesized that stabilization of the lumbar region against sagittal bending may be a response to increasing size in running mammals. However, empirical data on lumbar allometry in running mammals are scarce. This study presents quantitative data on allometry of the penultimate lumbar vertebra in two mammal families: Bovidae and Felidae. One hundred and twenty 3D landmarks were collected on the penultimate lumbar vertebra of 34 bovid (N = 123) and 23 felid (N = 93) species. Multivariate phylogenetically informed regressions were computed, and the shape variation associated with increasing size calculated. The influence of locomotor and habitat variables on size‐corrected lumbar shape was tested using phylogenetic multivariate analysis of variance (MANOVAs). Results demonstrate that the scaling patterns in both groups are consistent with the hypothesis of allometric stabilization of the lumbar region, and suggest convergent evolution of allometric responses in distantly related lineages of mammals. However, there was a relatively smaller effect of size in felids than bovids, even when size range disparities were accounted for, suggesting a trade‐off between size and running behaviour. Despite the strong influence of size and phylogeny on lumbar shape, there was no correlation with either habitat or diet within families, though certain specialized taxa (i.e., cheetah) did have divergent morphology.