Relationship between tooth and long bone size

Canonical correlations between tooth and long bone dimensions showed a greater correlation for Anglo-Saxons and apes than for Nineteenth Century Londoners, i.e., coefficients of 0.75 for gorilla, 0.72 for chimpanzee, 0.69 for orang-utans, 0.74 for Anglo-Saxons, but 0.53 for Nineteenth Century Londoners. Although based upon limited sample sizes and limited metrical profiles of teeth and long bones, the data support the thesis that modern Europeans are under reduced selection pressure to maintain tooth size compared with apes or ancient man.     

A differential environmental effect on human anterior tooth size

Factor-analytic studies of human tooth size routinely exhibit separate factors for the mesiodistal and buccolingual dimensions of anterior teeth but a single factor each for premolar and molar size. This observed independence within the anterior field is shown to be attributable to a much larger effect of environmental factors on the buccolingual vs. the mesiodistal diameters, a significant cause of which may be calculus accumulation hitherto unrecognized in the relevant literature. The heritability of dental dimensions is also discussed.     

Heritability of permanent tooth size

The aim of this investigation was to quantify the relative contributions of genetic and environmental influences to the observed variability of permanent tooth size in a group of Australian Aboriginals. Tooth size data were obtained from dental casts of Aboriginals living at Yuendumu in the Northern Territory of Australia. The custom of polygyny practised by these people enabled the analysis of associations between full-siblings and half-siblings. Phenotypic variability of tooth size was partitioned into four variance components; between sides, between fathers, between mothers and between offspring. From these components, the relative genetic and environmental contributions were quantified and heritability estimates for tooth size derived. Additional estimates of heritability were obtained by regression analysis from a small sample of parent-offspring data. Results of the analyses suggested that about 64% of the total variability of permanent tooth size could be attributed to genetic factors, while a further 6% was due to common environment. Although the findings confirm a relatively strong genetic component, they emphasise the importance of non-genetic influences in the determination of tooth size variability.     

Posterior tooth size, body size, and diet in South African gracile Australopithecines

A model relating relative size of the posterior teeth to diet is suggested for forest and savanna primates and Homo. Relative tooth size is calculated for the South African gracile australopithecine sample using posterior maxillary area sums and size estimates based on four limb bones. A number of limbs were shown to be non-hominid. Comparisons show the South African gracile sample apparently adapted to a very heavily masticated diet with relative tooth size significantly greater than any living hominoid. Periodic intensive utilization of grains and roots combined with scavenged animal protein are suggested as the most likely dietary reconstruction.     

Inheritance of tooth size in Australian aboriginals

The purpose of this study was to clarify the question of inheritance of tooth size, with particular reference to the role of the sex chromosomes. Data were obtained from the dental casts of Aboriginals living at Yuendumu in the Northern Territory of Australia, who had participated in a longitudinal growth study extending over 20 years. The compilation and verification of comprehensive genealogical records gathered over a number of years enabled the analysis of family data. Product-moment correlation coefficients between different full-sibling and half-sibling pairs were calculated for permanent tooth size. Values of individual and average correlation for both mesiodistal and buccolingual tooth diameters conformed with the theoretical correlations expected assuming polygenic inheritance. However, no evidence of sex chromosomal involvement was found.     

Interspecific and intraspecific relationships between tooth size and jaw size in primates

The association between mandibular robusticity, postcanine megadontia, and canine reduction in hominins has led to speculation that large and robust jaws might be required to spatially accommodate large canine and molar teeth in hominins and other primates. If so, then variations in mandibular form that are generally regarded as biomechanical adaptations to masticatory demands might instead be incidental effects of functional requirements of tooth support. While the association between large teeth and deep, robust jaws in hominins is well known, the relationship between tooth size and jaw size has not been systematically evaluated in a comparative sample of primates. We evaluate the relationships between molar tooth size, canine tooth size, and mandibular corpus and symphyseal dimensions in a sample of adult anthropoids in interspecific (n=84 species) and intraspecific (n=36 species) contexts. For intraspecific comparisons, tooth size and jaw size are correlated, but for a majority of species this is a function of sexual size dimorphism. Interspecific comparisons lend little direct support to the hypothesis that jaw breadth directly covaries with molar tooth breadth, but they do support the hypothesis that mandibular depth is associated with canine tooth size in males. The latter observation suggests that if there is a causal association between canine size and mandibular depth, it is subject to a threshold effect. In contrast, neither corpus nor symphyseal robusticity, measured as a shape index of breadth/height, are correlated with tooth size. Our results suggest that further studies of the relationship between tooth size and corpus morphology should focus on tooth root size and corpus bony architecture, and that species-specific factors should have a strong impact on such relationships.     

Correlation of tooth size and body size in living hominoid primates, with a note on relative brain size in Aegyptopithecus and Proconsul.

Second molar length and body weight are used to test the correlation between tooth size and body size in living Hominoidea. These variates are highly correlated (r= 0.942, p less than 0.001), indicating that tooth size can be used in dentally unspecialized fossil hominoids as one method of predicting the average body weight of species. Based on tooth size, the average body weight of Aegyptopithecus zeuxis is estimated to have been beteen 4.5 and 7.5 kg, which is corroborated by known cranial and postcranial elements. Using Radinsky's estimates of brain size, the encephalization quotient (EQ) for Aegyptopithecus was between 0.65 and 1.04. A similar analysis for Proconsul africanus yields a body weight between 16 and 34 kg, and an EQ between 1.19 and 1.96.     

Heritability of deciduous tooth size in Australian aboriginals

The contributions of genetic and evironmental influences to observed variability of deciduous tooth size were quantified in a group of Australian aboriginals. Phenotypic variability was partitioned into four components; between sides, between fathers, between mothers, and between offspring. Results suggested that about 58% of deciduous tooth-size variability was due to additive genetic variance and 15% to common environmental variance. It appears that additive genetic variance is similar in both deciduous and permanent dentitions, but that common maternal effects are more important in determining deciduous tooth-size variability.     

Patterning the size and number of tooth and its cusps

Mice and rats, two species of rodents, show some dental similarities such as tooth number and cusp number, and differences such as tooth size and cusp size. In this study, the tooth size, tooth number, cusp size and cusp number, which are four major factors of the tooth patterning, were investigated by the heterospecific recombinations of tissues from the molar tooth germs of mice and rats. Our results suggest that the dental epithelium and mesenchyme determine the cusp size and tooth size respectively and the cusp number is co-regulated by the tooth size and cusp size. It is also suggested that the mesenchymal cell number regulates not the tooth size but the tooth number. The relationships among these factors in tooth patterning including micropatterning (cusp size and cusp number) and macropatterning (tooth size and tooth number) were analyzed in a reaction diffusion mechanism. Key molecules determining the patterning of teeth remains to be elucidated for controlling the tooth size and cusp size of bioengineered tooth.     

Carabelli's trait and tooth size of human maxillary first molars

Carabelli's trait is a morphological feature that can occur on the protocone of human maxillary molars. This study tests the hypothesis that Carabelli's trait is correlated statistically with the dimensions of the crown's four principal cusps or whether, as a cingular feature, the trait truly accretes onto an otherwise unaffected crown. Computer-assisted image analysis was used to measure the 6 intercusp distances and 12 angular relationships among cusp tips on the permanent first molar of 300 young adult American whites. Carabelli's complex was scored using an 8-grade ordinal scheme. Crown size was quantified in three ways, namely as 1) maximum mesiodistal and buccolingual diameters, 2) the 6 intercusp distances, and 3) the 12 angular cusp arrangements. There was no sex difference in the morphological expression of Carabelli's trait in this sample. Overall crown size and intercusp distances were significantly and progressively larger in molars with larger Carabelli's trait expressions. There are graded size responses between crown size (mesiodistal and buccolingual diameters), sizes of the four principal cusps, and morphological stage of Carabelli's complex, though the statistical relationships are appreciably stronger in males than females. Carabelli's trait occurs preferentially in larger molars. In contrast, angular (shape) relationships among cusp tips are not discernibly affected by trait size in either sex. There is the situation, then, that Carabelli's trait is developmentally correlated with crown size, but with no apparent alteration of cusp arrangements, suggesting that the increases are isometric across the occlusal table. Why the association is much weaker in females remains speculative, but these data provide yet another line of evidence that, within a population, tooth size is associated in a positive fashion with crown complexity.     

Family studies of tooth size factors in the permanent dentition.

Correlations between dimensions of the permanent teeth in Australian Aboriginals were studied by factor analysis to disclose the main sources of shared variability. Findings indicated that in both males and females most of the common variability in the tooth dimensions could be accounted for by factors representing mesiodistal size of anterior teeth, buccolingual size of anterior teeth, generalized size of the premolars and generalized size of the molars. Factor scores derived from the analysis were used to calculate intraclass correlations among brothers and among sisters. These correlations tended to be higher for the factors contributing most to the common variability indicating that the factors might represent fields under direct genetic control. There was no trend for intraclass correlations among siblings derived from multivariate scores to be consistently higher than those based on observed tooth dimensions. The main advantage to the user of factor analysis is the ability to interpret associations between interrelated variables more objectively than is possible by conventional correlation methods.     

Secular trend in tooth size in urban Chinese assessed from two-generation family data

Environmental improvements can lead to greater size of skeletodental structures as the population comes closer to expressing its genetic growth potential. Such secular trends have been documented in many human settings, especially for increased stature and faster tempos of growth. The present study is based on 185 same-sex parent-offspring pairs of data for maximum buccolingual crown diameters of the permanent teeth from a cohort in Beijing, China, where parents experienced much of their development during and after World War II with the deprivations of the changing regime. Their offspring enjoyed the relative stability of the established Communist system, where nutrition and stability were much improved. There were significant increases in buccolingual diameters of the premolars and molars in the offspring. Increase for premolars and molars was about 1%, but larger in females than males (1.6% vs. 0.5%). Opposite changes occurred in the incisors and canines (i.e., larger parental dimensions), but we contend that these are an age-related artifact brought on by greater passive eruption of older individuals' teeth that exposes a broader portion of the crown at the gingival margin. The secular trend in crown size coincides with other research in contemporary China, disclosing increases in body size and faster tempos of growth as health and nutrition continue to improve.     

Effect of marking pheromone on clutch size in the Mediterranean fruit fly

Abstract Using acridine orange to selectively stain eggs, we showed that wild-collected female Mediterranean fruit flies (Ceratitis capitata Wiedemann) laid fewer eggs per clutch in fruit previously infested with eggs than in uninfested fruit. This effect is apparently attributable to marking pheromone deposited by females after oviposition: clutch size on fruit infested with eggs but free of marking pheromone was not statistically different from that on uninfested fruit. Clutch size on uninfested fruit on which marking pheromone was artificially transferred was significantly lower than that on uninfested and untreated fruit. Marking pheromone had a comparable though not statistically significant effect on the clutch size of females originating from a strain maintained in the laboratory for several hundred generations.     

Season length,body size,and social polymorphism: size clines but not saw tooth clines in sweat bees

1. Annual insects are predicted to grow larger where the growing season is longer. However, transitions from one to two generations per year can occur when the season becomes sufficiently long, and are predicted to result in a sharp decrease in body size because available development time is halved. The potential for resulting saw‐tooth clines has been investigated only in solitary taxa with free‐living larvae. 2. Size clines were investigated in two socially polymorphic sweat bees (Halictidae): transitions between solitary and social nesting occur along gradients of increasing season length, characterised by the absence or presence of workers and offspring that are individually mass provisioned by adults. How the body size changes with season length was examined, and whether transitions in social phenotype generate saw‐tooth size clines. We measured Lasioglossum calceatum and Halictus rubicundus nest foundresses originating from more than 1000 km of latitude, encompassing the transition between social and solitary nesting. 3. Using satellite‐collected temperature data to estimate season length, it was shown that both species were largest where the season was longest. Body size increased linearly with season length in L. calceatum and non‐linearly in H. rubicundus but the existence of saw‐tooth clines was not supported. 4. The present results suggest that because the amount of food consumed by offspring during development is determined by adults, environmental and social influences on the provisioning strategies of adult bees may be more important factors than available feeding time in determining offspring body size in socially polymorphic sweat bees.     

Body size structure in north-western Mediterranean Plio-Pleistocene mammalian faunas

Aim We investigated the patterns of body‐size changes of the north‐western Mediterranean Plio‐Pleistocene large mammal faunas (excluding rodents, bats, lagomorphs and insectivores) in order to identify the tempo and mode of the major shifts in body size distribution, and to put them in the context of Plio‐Pleistocene environmental changes and the development of the Mediterranean climate. Location We analysed fossil faunas of Spain, France and Italy. A set of recent regional faunas from several macroclimatic regions was selected to serve as elements for comparison of the size distribution of past faunas, consisting of: Spain, France and Italy together, Florida, California, Central Chile, Indochina, India, Korea‐Manchuria, Malawi, The Cape, North Africa, Turkey and Australia. Methods Mammal species were grouped into five body size categories for carnivores and four categories for noncarnivore species. The number of species in each size category was computed and the resulting matrix of body weight classes × regions and time intervals was used as an input matrix in a Correspondence Analysis. Results Recent and fossil faunas strongly differ in body size structure. The distribution of recent faunas within the CA seems to reflect both ecological and historic factors, intertwined in a complex fashion. No clear relationship has been observed between body size structure and environmental factors. During the late Pliocene to early Pleistocene there were only minor changes in the pattern of size distribution, although plant communities were in a transition process from subtropical forests to Mediterranean woodlands and steppes. The major change in body size structure of the north‐western Mediterranean fauna occurred at the Galerian, around 1 Ma ago. This marked the beginning of the modern fauna, and a general trend towards a larger body size, reduction in the number of medium sized herbivores, and an increase of large herbivores and megaherbivores. Main conclusions The Plio‐Pleistocene faunas lack modern analogues. The body size structure of mammalian regional faunas appears to be strongly dependent on historical factors. The only major shift in body size distribution occurred during the Plio‐Pleistocene, in the late Villafranchian‐Galerian transition, coincident with the onset of the Pleistocene high intensity glacial cycles.     

Sociality, ecology, and relative brain size in lemurs

The social brain hypothesis proposes that haplorhine primates have evolved relatively large brains for their body size primarily as an adaptation for living in complex social groups. Studies that support this hypothesis have shown a strong relationship between relative brain size and group size in these taxa. Recent reports suggest that this pattern is unique to haplorhine primates; many nonprimate taxa do not show a relationship between group size and relative brain size. Rather, pairbonded social monogamy appears to be a better predictor of a large relative brain size in many nonprimate taxa. It has been suggested that haplorhine primates may have expanded the pairbonded relationship beyond simple dyads towards the evolution of complex social groups. We examined the relationship between group size, pairbonding, and relative brain size in a sample of 19 lemurs; strepsirrhine primates that last share a common ancestor with monkeys and apes approximately 75 Ma. First, we evaluated the social brain hypothesis, which predicts that species with larger social groups will have relatively larger brains. Secondly, we tested the pairbonded hypothesis, which predicts that species with a pairbonded social organization will have relatively larger brains than non-pairbonded species. We found no relationship between group size or pairbonding and relative brain size in lemurs. We conducted two further analyses to test for possible relationships between two nonsocial variables, activity pattern and diet, and relative brain size. Both diet and activity pattern are significantly associated with relative brain size in our sample. Specifically, frugivorous species have relatively larger brains than folivorous species, and cathemeral species have relatively larger brains than diurnal, but not nocturnal species. These findings highlight meaningful differences between Malagasy strepsirrhines and haplorhines, and between Malagasy strepsirrhines and nonprimate taxa, regarding the social and ecological factors associated with increases in relative brain size. The results suggest that factors such as foraging complexity and flexibility of activity patterns may have driven selection for increases in brain size in lemurs.     

Prediction of the minimum effective size of a population viable in the long term

Biodiversity and Conservation - The establishment of the minimum size for a viable population (MVP) has been used as a guidance in conservation practice to determine the extinction risks of...     

Reduced tooth size in 45,X (Turner syndrome) females

Mean values and variances of deciduous and permanent tooth dimensions were compared between 121 45,X (Turner syndrome) females and 171 control subjects to clarify the role of the X chromosome on dental development. Although deciduous molars tended to be smaller than normal in 45,X females, there was no evidence of a reduction in tooth size for deciduous anterior teeth. In the permanent dentition, all mesiodistal dimensions were significantly smaller in 45,X females but only some of the buccolingual dimensions were smaller. The findings for deciduous tooth-size may reflect a sampling effect related to the extremely high frequency of spontaneous abortion in 45,X individuals. Results for permanent teeth are consistent with the concept of a decrease in enamel thickness in 45,X females.     

Relationship of incisor size to diet and anterior tooth use in sympatric sumatran anthropoids

Researchers often relate anthropoid incisor size to diet and ingestive behaviors. It is suggested that primates that frequently consume large, tough foods (i.e., fruits) require large incisors to process these items. This idea has been difficult to test because of a lack of data on anterior tooth use in wild primates, and a lack of understanding concerning the relationships between food properties and ingestive behaviors. The first field study of primate ingestive behaviors has recently been completed for four species of Sumatran anthropoids: Hylobates lar, Macaca fascicularis, Pongo pygmaeus, and Presbytis thomasi [Ungar, American Journal of Physical Anthropology 95:197–219, 1994; International Journal of Primatology 16:221–245, 1995]. This paper documents both relative and absolute incisor row width differences among these taxa, and evaluates the relationships between incisor size and feeding behaviors for specific taxa. Results indicate that differences in incisor size among these species cannot all be explained by degree of frugivory, food item size, or even degree of incisor use in ingestion alone. It is therefore suggested that inferences of dietary differences based on largely or solely on differences in incisor sizes of specific fossil anthropoid taxa should be approached with caution. © 1996 Wiley-Liss, Inc.