Genetic and environmental factors in the longitudinal growth of rats: III. Craniofacial shape change

This investigation expresses the similarity of the craniofacial shape of rats in terms of a single parameter and determines to what extent the shape variation of the craniofacial complex is genetically determined. To quantify the similarity of the craniofacial shape between any two individuals, diagrams plotted from their lateral cephalograms are so oriented that the distance from the points on the one to the corresponding points on the other is minimized. The data consist of measurements from within-strain, between-strain, maternal half-sibs and paternal half-sibs groups. The average dissimilarity is computed in each group and compared. The results indicate that this method can be used to estimate the similarity of the craniofacial shape. The dissimilarity of within-strain pairs shows the smallest Dh value, whereas between-strain pairs have the largest Dh value. Those of maternal and paternal half-sib pairs show the intermediate Dh value. The value of dissimilarity for these four pairs tends to decrease gradually with age and a considerable genetic effect acts on the change of the craniofacial shape during growth, while the maternal effect does not act significantly on the change of the craniofacial shape during growth.     

Prenatal exposure to phenytoin and its effect on postnatal growth and craniofacial proportion in the rat

Neonatal rats exposed prenatally to phenytoin (PHT) have been reported to have craniofacial abnormalities and growth retardation [Lorente et al.: Teratology 24:169-180, 1981]. This study reports on the persistence of these effects in the adult rat. Pregnant Sprague-Dawley rats were intubated on gestational days 9, 11, and 13 with 1,000 mg/kg PHT suspended in 1% carboxymethylcellulose (CMC). Six male and six female exposed offspring (PHT) and an equal number of control animals (CMC) were weighed through postnatal day 135, at which point they were killed and the skeletons were prepared for analysis. The PHT-exposed animals had reduced weights at all time points with the males more severely affected. A normal adolescent growth spurt was not observed in the exposed group. Absent or rudimentary lacrimal bones and nasolacrimal canals were note in all PHT-exposed rats. This contributed to the recessed positioning of the eyes that was grossly apparent. In addition, shorter and broader frontal bones in the PHT animals led to the appearance of hypertelorism. Ratios of craniofacial dimensions obtained by direct measurement of the skulls showed that the PHT offspring were significantly different in proportion from their control counterparts. The PHT skulls were smaller for body size with reduced facial height and broader midfacial regions. A unique craniofacial pattern was observed in the experimental offspring. Normal sexual dimorphism in craniofacial pattern was not expressed in the PHT group. These studies suggest that prenatal phenytoin exposure in the rat may interfere with the full expression of normal dimorphism based on gender and confirms the toxic effect of this drug on postnatal growth, adult body proportion, and craniofacial geometry.     

Trigeminal foraminal pattern in the face

The integration of the trigeminal nerve into the craniofacial skeleton was studied by examining cephalometrically the relationships of the openings of the branches of the trigeminal nerve to each other and to other structures. Lateral cephalograms were taken from 30 adult skulls; several linear and angular dimensions were measured from the cephalograms. The results suggest a relationship between nerve growth and bone growth in the craniofacial skeleton.     

Influences of osteoclast deficiency on craniofacial growth in osteopetrotic (op/op) mice

It is well known that the defect in bone resorption in osteopetrotic (op/op) mice brings about deformation of the cranium and failure of tooth eruption. However, the influences on longitudinal growth of the craniofacial skeleton have not been elucidated. This study was thus conducted to examine craniofacial morphology and longitudinal changes in the op/op mice by means of morphometric analysis with lateral cephalograms. Lateral cephalograms, taken every 10 days from 10- to 90-day-old mice, were analyzed on a personal computer for 11 measurement items. For the nasal bone region, the most prominent differences were found between the op/op and normal mice. The anterior cranial base and occipital bone height presented almost equivalent growth changes in both the op/op and normal mice. The size of mandible, meanwhile, was significantly smaller in the op/op mice than in the normal controls. The gonial angle was also significantly larger in the op/op mice than in the normal mice throughout the experimental period. Thus, substantial differences in craniofacial growth were demonstrated in various areas of the craniofacial complex, which are assumed essentially due to the lack of osteoclastic bone resorption during growing period. Since the difference became more prominent in the anatomic regions relevant to the masticatory functions, it would be a reasonable assumption that reduced masticatory function is also a key determinant for the less-developed craniofacial skeleton in the op/op mouse.     

The influence of incompetent lip seal on the growth and development of craniofacial complex

Abnormal orofacial functions in the period of growth and development can cause morphological anomalies of the craniofacial complex. The aim of this study was to determine the correlation between open mouth posture and morphology of craniofacial complex. The shape, size and relationships of skeletal parts of craniofacial complex were determined by analysis of lateral cephalograms in the sample of 84 children--45 girls and 39 boys (aged 8.96 +/- 0.66 years). The sample was divided into two groups--lip competence and lip incompetence group. Differences in cephalometric values between observed groups were found. The values of inclination of lower central incisors (angle ILi/NB), interbasal angle (NL/NSL), angle between occlusal and mandibular plane and anterior lower facial height were significantly higher in the group with open mouth posture. It can be concluded that lip incompetence plays an important role in growth and development of craniofacial complex.     

Genetic study of dentinal growth in mandibular first molars of mice

The dentinal growth of mandibular molars of mice could be determined by genetic and environmental factors as are other quantitative characters, such as crown size and craniofacial size. To study the relative contribution of genetic and environmental factors to dentinal growth, a partial diallel cross was carried out by the mating of one pair from each of six strains of mice. In each F1 offspring, the total amount of dentinal formation in the first molar of the right mandible was quantified as a volume by the time-marking method, using nitrilotri-acetate lead with the computerized image scanning system, and then analyzed by a quantitative genetic method. The result obtained was as follows: In either sex, both additive genetic and nonadditive genetic variance components of the accumulative volume of dentinal formation in the first molar were relatively large throughout the experimental period, while the environmental variance component was much smaller. Thus it could be concluded that the genetic factor contributed more to the whole process of dentinal growth in the first molar rather than the environmental one in this F1 population.     

Analysis and visualization of growth-related and treatment-induced craniofacial changes

An analysis and visualization of craniofacial shape changes due to growth or orthodontic treatment is presented. The suggested method is based on an adapted Karhunen-Loève decomposition of time-discrete data based on landmarks in lateral X-rays of the skull. It allows for a reduction of the high-dimensional dynamic problem to a few spatial modes representing synchronous components of growth patterns with time-dependent mode coefficients. The growth-related shape changes as well as the orthodontic treatment effects are visualized by overdrawing the underlying shape changes. The results based on this technique give insight into the still controversially discussed question to which degree the craniofacial skeletal structures can be influenced by orthodontic appliances.     

Effects of the anabolic steroid nandrolone phenylpropionate on craniofacial growth in rats

Primary testosterone and its derivatives are anabolic steroids used in the treatment of osteoporosis and Turner syndrome. They also enhance fast-twitch muscle weight in female rats. The present study examines the effect of an anabolic steroid on craniofacial growth and development in rats. Five-week-old female Sprague-Dawley rats (125) were divided into experimental and control groups. The experimental group was injected subcutaneously with 1 mg nandrolone phenylpropionate in the interscapular region on alternate days, whereas those in the control group were injected with a vehicle, arachis oil. Rats were sacrificed at 60 and 120 days of age. Cephalometric analysis of soft X-ray cephalograms showed that chronic administration of the anabolic steroid, nandrolone phenylpropionate, resulted in: (1) about a 20% increase in body weight, (2) an increase in total skull length, (3) elongation of the maxillary and mandibular incisors, (4) an increase in the depth of the antegonial notch, and (5) downward-forward growth of the viscerocranium against the neurocranium. These results suggest that nandrolone phenylpropionate may accelerate craniofacial growth and/or induce high functional activity of the masticatory muscles in female rats. © 1994 Wiley-Liss, Inc.     

Longitudinal study of craniofacial growth in Macaca fascicularis

This paper is an analysis of normal craniofacial growth in adolescent crab-eating macaques (Macaca fascicularis). Eight female adolescent monkeys were used in this study. Their individual craniofacial growth was studied for a 24-month period utilizing tantalum implants and roentgenographic cephalograms. Throughout the observation period, each monkey consistently showed a class I molar relationship with a good overjet and overbite. The amount of anterior displacement of the maxilla and the mandible was significantly dominant compared to the vertical displacements at every observation period. The midface exhibited a maxillary differential growth pattern in which the premaxilla displaced superiorly and the posterior maxilla moved inferiorly, resulting in a counterclockwise rotation of the entire maxilla. Growth of the lower anterior teeth and alveolar bone compensated for the incremental vertical spaces which were induced by superior displacement of the premaxilla and inferior repositioning of the chin. In addition, the amount of anterior displacement of the upper and lower anterior teeth were significantly larger than that of the premaxilla and the chin. The dentocraniofacial growth pattern in Macaca fascicularis was quite similar to that seen in Macaca mulatta.     

Craniofacial manifestations in the Marfan syndrome: palatal dimensions and a comparative cephalometric analysis

The purpose of this study was to determine how the craniofacial morphology, evaluated from dental casts and lateral cephalograms, in individuals affected by the Marfan syndrome diverge from healthy control groups. The high and narrow palatal vault as well as maxillary and mandibular retrognathy were strongly correlated to the syndrome. About 70% of the Marfan syndrome patients (n = 76) had been referred for orthodontic treatment, mostly because of crowded teeth or extreme maxillary overjet. In 36%, the orthodontic treatment was carried out before diagnosis or suspicion about the Marfan syndrome. In comparison to healthy orthodontic patients (n = 86), selected because of presence of high and narrow palatal vaults, crowding of teeth, extreme maxillary overjet, and open bite were much more prevalent in the Marfan syndrome patients than in the orthodontic control group.     

The MHC and non-random mating in a captive population of Chinook salmon

Detailed analysis of variation in reproductive success can provide an understanding of the selective pressures that drive the evolution of adaptations. Here, we use experimental spawning channels to assess phenotypic and genotypic correlates of reproductive success in Chinook salmon (Oncorhynchus tshawytscha). Groups of 36 fish in three different sex ratios (1:2, 1:1 and 2:1) were allowed to spawn and the offspring were collected after emergence from the gravel. Microsatellite genetic markers were used to assign parentage of each offspring, and the parents were also typed at the major histocompatibility class IIB locus (MHC). We found that large males, and males with brighter coloration and a more green/blue hue on their lateral integument sired more offspring, albeit only body size and brightness had independent effects. There was no similar relationship between these variables and female reproductive success. Furthermore, there was no effect of sex ratio on the strength or significance of any of the correlations. Females mated non-randomly at the MHC, appearing to select mates that produced offspring with greater genetic diversity as measured by amino-acid divergence. Females mated randomly with respect to male genetic relatedness and males mated randomly with respect to both MHC and genetic relatedness. These results indicate that sexual selection favours increased body size and perhaps integument coloration in males as well as increases genetic diversity at the MHC by female mate choice.     

Craniofacial alterations in adult rats prenatally exposed to ethanol

The rat was studied to determine whether gestational exposure to moderate amounts of ethanol produces permanent craniofacial malformations. Pregnant Long-Evans rats were fed a liquid diet containing 35% ethanol-derived calories or an isocaloric liquid diet between gestation days 6 and 20. Various dimensions of skulls and mandibles from adult male offspring were measured. All measurements taken in the parasagittal and coronal planes were significantly smaller in the ethanol-exposed rats than in the offspring of pair-fed controls. None of the vertical measurements was significantly altered. This report demonstrates that gestational exposure to ethanol in rats, at doses which produce lasting behavioral effects, also produces a specific constellation of craniofacial dysmorphisms without concomitant decreases in body weight.     

Ontogenic sources of variation in sexual size dimorphism in a viviparous lizard

To elucidate the developmental aspects of the evolution of sexual size dimorphism (SSD), an understanding of the sex-specific ontogeny of body size is critical. Here, we evaluate the relative importance of genetic and environmental determinants of SSD in juvenile common lizards (Lacerta vivipara). We examined the prenatal and post-natal effects of population density and habitat humidity on SSD, as well as the maternal effects of food availability, corticosterone level, humidity and heat regime during gestation. Analyses indicated strong prenatal and post-natal plasticity in body size per se and yielded three main results with respect to SSD. First, SSD in juvenile common lizards matches qualitatively the SSD observed in adults. Secondly, SSD was influenced by none of the prenatal factors investigated here, suggesting poor sex-biased maternal effects on offspring size. Thirdly, SSD was sensitive to post-natal habitat humidity, which positively affected growth rate more strongly in females than in males. Thus, natural variation in SSD in juvenile common lizards appears to be primarily determined by a combination of sex-biased genetic factors and post-natal conditions. We discuss the possibility that viviparity may constrain the evolution of sex-biased maternal effects on offspring size.     

Craniofacial growth in subjects with unilateral complete cleft lip and palate, and unilateral incomplete cleft lip, from 2 to 22 months of age

This paper reports a longitudinal quantitative cephalometric analysis of the craniofacial growth in subjects with unilateral complete cleft lip and palate (UCCLP), and unilateral incomplete cleft lip (UICL), from 2 to 22 months of age. The purpose of the study was to determine the amount and direction of growth in UCCLP compared to UICL (control group) from 2 months of age (just prior to lip repair) to 22 months of age, 20 months later. The sample comprised of 49 subjects with UCCLP (37 males and 11 females) and 45 with UICL (29 males and 16 females). The cephalometric analysis of the craniofacial morphology included lateral, frontal, and axial projections. The data were presented as mean plots of the craniofacial region including the calvaria, cranial base, orbits, nasal bone, maxilla, mandible, cervical column, pharynx, and soft-tissue profile. A valid common coordinate system (registration according to the n-s line in the lateral projection, latero-orbitale line in the frontal projection, and meatus acusticus externus line in the axial projection for the landmark positions at examination 1 and 2) was ascertained. The growth at a specific anatomical location in a patient was defined as the displacement vector from the coordinate of the corresponding landmark in the X-ray at examination 1 to its coordinate at examination 2, corrected for X-ray magnification. The growth of an anatomical region in a patient was assessed by investigating the growth pattern formed by a collection of individual growth vectors in that region. The amount of growth in the UCCLP and UICL group was very similar. The general craniofacial growth pattern, in terms of the direction of growth, was also fairly similar in the UCCLP group and the control group. However, the maxilla and mandible showed a more vertical growth pattern than that observed in the control group. This study confirms that UCCLP is a localized deviation, and not a craniofacial anomaly, due to the fact that a normal growth potential has been observed in all craniofacial regions, except where the growth had been directly influenced by surgical intervention. Furthermore, the vertical growth pattern of the maxilla and mandible supports the hypothesis of a special facial type in cleft lip and palate individuals, and the facial type as a liability factor increasing the probability of cleft lip and palate.     

Male and female effects on fertilization success and offspring viability in the Peron's tree frog,Litoria peronii

Abstract There is increasing theoretical and empirical evidence that genetic compatibility among partners is an important determinant of fertilization success and offspring viability. In amphibians, females often actively choose partners from among a variety of males and polyandry is common. Genetic compatibility among partners may therefore be an important determinant of fertilization success and offspring viability in some amphibians. Amphibians also show some of the highest levels of genetic differentiation among neighbouring populations known in vertebrates, and as such, populations may have evolved different co‐adapted gene complexes. This means that offspring from among‐population crosses may have reduced fitness. It is therefore essential to understand to what extent crossings between and within populations may interfere with successful fertilization and offspring viability. Here, we test whether crossing individuals within and between two different populations of the Australian Peron's tree frog (Litoria peronii) using artificial fertilizations affect fertilization success and offspring viability. Fertilization success per se is strongly influenced by male identity, which is likely to depend at least to some extent on the experimental procedure (e.g. resulting in variation in sperm number per ejaculate), whereas there was no fertilization effect of female identity. More importantly, male and female identity, independently of each other, explained significant variation in offspring viability, whereas no such effect could be linked to population of origin. Thus, our experiments suggest that crossing populations may not always be the most significant factor affecting fertilization success or offspring viability, but may be more influenced by the genetic quality or the genetic compatibility of partners.     

GENETIC AND MATERNAL EFFECTS ON SEEDLING CHARACTERS OF SOLIDAGO ALTISSIMA (COMPOSITAE)

The relative contributions of genetic and maternal factors to phenotypic variation were studied in seedlings of the clonal herb Solidago altissima L. Pairwise crosses were made to establish 19 full-sibships. Because crosses were reciprocal, each parent served as seed parent to half its offspring and as pollen parent to the other half. For 18 characters, genetic variation was estimated from the between sibship variance and maternal variation from the variance between maternal groups within sibships. Early in the growing season, maternal effects exerted strong influence over variation in leaf and stem dimensions, while genetic influences were weak or absent. At the end of the season genetic influences on leaf and stem dimensions, relative biomass allocation between stem and leaves, and the propensity to flower were significant but maternal effects were not. However, both genetic and maternal influences were found on the number and lengths of new rhizomes. Phenotypic, genetic, and maternal correlation matrices were examined through principal component analysis for trade-offs among vegetative growth, clonal expansion and floral reproduction which could constrain the evolution of life history patterns. At the phenotypic level, seedlings with strong vegetative growth produced more and longer rhizomes, and were more likely to flower. Genetically, correlations among these functions were weak or absent. Strong maternal contributions to seedling vegetative growth correlated positively with the number and length of rhizomes. Thus, no trade-offs acting during the seedling stage were found. However, there were indications of a genetically influenced trade-off between the number of rhizomes produced in the seedling year with the size of the ramets produced in the second year.     

Common genetic and environmental factors among craniofacial traits in Belgian nuclear families: Comparing skeletal and soft-tissue related phenotypes

The major objective of this study was to determine the possible effects of common genetic and environmental factors among 18 craniofacial anthropometric traits, with special attention to the differences between skeletal and soft-tissue related phenotypes. The studied sample consisted of 122 nuclear families living in Brussels and included 251 males and 258 females aged from 13 to 72 years. Univariate and bivariate quantitative genetic analyses were performed using a variance components procedure implemented in SOLAR software.All phenotypes were significantly influenced by additive genetic factors with heritability estimates ranging from 0.46 (nose height) to 0.72 (external biocular breadth). Sex, age and their interactions explained 7-46% of the total phenotypic variance of the traits. Bivariate analysis revealed that several traits share a common genetic and/or environmental basis while other traits show genetic and environmental independence from one another. More and greater genetic and environmental correlations were observed among skeletal phenotypes, than among soft-tissue traits and between both categories. Apart from the tissue composition, other characteristics of the craniofacial morphology such as the orientation (e.g. heights, breadths) have shown to be important factors in determining pleiotropy and common environmental effects between some pairs of traits. In conclusion, the results confirm that overall head configuration is largely determined by additive genetic effects, and that common genetic and environmental factors affecting craniofacial size and shape are stronger for the skeletal traits than for the soft-tissue traits.     

Parallel evolution by correlated response: lateral plate reduction in threespine stickleback

Recent work has revealed the molecular mechanisms governing one of the most dramatic examples of parallel evolution in nature: the repeated loss of lateral plate armor in freshwater populations of threespine stickleback. Yet, the ecological mechanisms responsible for armor loss remain unclear. Using a balanced experimental design, we examined Heuts' (1947) hypothesis that selection due to differences in salinity indirectly drive the reduction of lateral plate armor in fresh water while maintaining armor in the sea. We measured two fitness-related traits, hatching success and juvenile growth rate, in offspring of reduced (low and partial) and complete lateral plate morphs from two polymorphic populations when raised in either fresh water or salt water. In contrast to Heuts' results, there was little difference among morphs in hatching success. However, salinity strongly influenced juvenile growth: offspring of reduced lateral plate morphs grew substantially faster (up to 65%) than offspring of completely plated morphs in fresh water, but there was little difference in salt water. We suggest that the parallel loss of lateral plates in fresh water has arisen through a correlated response to selection for faster growth during lateral plate development, but the effect of salinity on hatching success and juvenile growth rate cannot explain the predominance of completely plated morphs in marine populations.     

EFFECTS OF MATERNAL AND PATERNAL ENVIRONMENT AND GENOTYPE ON OFFSPRING PHENOTYPE IN SOLIDAGO ALTISSIMA L.

To predict the possible evolutionary response of a plant species to a new environment, it is necessary to separate genetic from environmental sources of phenotypic variation. In a case study of the invader Solidago altissima, the influences of several kinds of parental effects and of direct inheritance and environment on offspring phenotype were separated. Fifteen genotypes were crossed in three 5 × 5 diallels excluding selfs. Clonal replicates of the parental genotypes were grown in two environments such that each diallel could be made with maternal/paternal plants from sand/sand, sand/soil, soil/sand, and soil/soil. In a first experiment (1989) offspring were raised in the experimental garden and in a second experiment (1990) in the glasshouse. Parent plants growing in sand invested less biomass in inflorescences but produced larger seeds than parent plants growing in soil. In the garden experiment, phenotypic variation among offspring was greatly influenced by environmental heterogeneity. Direct genetic variation (within diallels) was found only for leaf characters and total leaf mass. Germination probability and early seedling mass were significantly affected by phenotypic differences among maternal plants because of genotype ( genetic maternal effects ) and soil environment ( general environmental maternal effects ). Seeds from maternal plants in sand germinated better and produced bigger seedlings than seeds from maternal plants in soil. They also grew taller with time, probably because competition accentuated the initial differences. Height growth and stem mass at harvest (an integrated account of individual growth history) of offspring varied significantly among crosses within parental combinations ( specific environmental maternal effects ). In the glasshouse experiment, the influence of environmental heterogeneity and competition could be kept low. Except for early characters, the influence of direct genetic variation was large but again leaf characters (= basic module morphology) seemed to be under stricter genetic control than did size characters. Genetic maternal effects, general environmental maternal effects, and specific environmental maternal effects dominated in early characters. The maternal effects were exerted both via seed mass and directly on characters of young offspring. Persistent effects of the general paternal environment ( general environmental paternal effects ) were found for leaf length and stem and leaf mass at harvest. They were opposite in direction to the general environmental maternal effects, that is the same genotypes produced “better mothers” in sand but “better fathers” in soil. The general environmental paternal effects must have been due to differences in pollen quality, resulting from pollen selection within the male parent or leading to pre- or postzygotic selection within the female parent. The ranking of crosses according to mean offspring phenotypes was different in the two experiments, suggesting strong interaction of the observed effects with the environment. The correlation structure among characters changed less between experiments than did the pattern of variation of single characters, but under the competitive conditions in the garden plant height seemed to be more directly related to fitness than in the glasshouse. Reduced competition could also explain why maternal effects were less persistent in the glasshouse than in the garden experiment. Evolution via selection of maternal effects would be possible in the study population because these effects are in part due to genetic differences among parents.     

Genetic and environmental factors in the longitudinal growth of rats: I. Body weight and overall craniofacial size

By means of roentgenographic cephalometry and quantitative genetic analysis, the relative contribution of the genetic and environmental components to total variance of body weight and overall craniofacial size was shown to vary with age. The genetic component of variance significantly increased until 80 days of age. Inversely, the maternal component of variance showed a high value during the early stage of postnatal growth and gradually decreased thereafter to a very small amount by day 80. Thus it appeared that the genetic effect became larger with age of the rat and the maternal effects diminished. The environmental component of variance did not change much over the course of the experiment. We thus conclude that genetic effect contributed the change of ontogenetic variation of craniofacial complex through all experimental periods and that maternal effect contributed to it at early growth stage of the craniofacial complex.