Effects of protein-calorie malnutrition during suckling and post-weaning periods on discontinuous cranial traits in rats.код для вставкиСкачать
AMERICAN JOURNAL OF PHYSICAL AN"HR0POLOGY 60:426430(1983) Effects of Protein-Calorie Malnutrition During Suckling and Post-Weaning Periods on Discontinuous Cranial Traits in Rats SILVIA L. DAHINTEN AND HlbXOR M. PUCCIARELLI Laboratorio de Investigacwnes Morfol6gicas, C&te&a IIIa de AnatomfG Facultad de Ciencias Medicas, Universidad Nacwnul de La Plata, B u m s Aires,Argentina KEY WORDS Discontinuous traits, Protein-calorie malnutrition, Rat skull ABSTRACT The influences of proteincalorie malnutrition 0, and sex during lactation and post-lactation on the frequencies of 25 discontinuous cranial traits 0, were investigated in Holtzman rats. Significant differences were observed in about 20% of the traits. Those traits were: the interfrontal fusion, the posterior incurvation of the palatine border, the double maxillary foramen, the double posterior palatine foramen, and the double frontal foramen. Total PCM was the nutritional fador which showed the greatest influence on the variability of the DCTs. It was followed, in decreasing order, by the PCM imposed during post-lactation and lactation. Sex had more influence than early PCM but less than late PCM.It is concluded that despite their apparent stability, a substantial number of DCTs were altered by both biological (like sex) and environmental factors (like nutritional deficiencies) imposed at different stages of postnatal development. Discontinuous cranial traits (DCTs) are bone formations that may appear in man (Ossenberg, 1970; Corruccini, 1974a; Berry, 1975; Finnegan, 1978; Cheverud, Buikstra and Twichell, 1979; Perizonius, 1979a,b), nonhuman mammals Oeol, 1955; Deol and Truslove, 1957; Berry and Searle, 1963; Wickramaratne, 1974; Berry, 1977, 1978; Cheverud and Buikstra, 1978),and other vertebrates (Grewal, 1978). Those traits are frequently used for human taxonomical studies (Pucciarelli, 1971; Corruccini, 1972, 197413; Berry and Berry, 1972; Sjdvold, 1973; Berry, 1974;Finnegan and Cooprider, 1978)because their phenotypic expression is fairly independent of environmental stimuli and, in general, they possess Mendelian heritability. Many studies showed that a nutritional deficiency brings about ossification disturbances in different mammals mimes, 1978). Such disturbances would also alter the normal frequency of discontinuous skeletal traits. A recent study mahinten and Pucciarelli, 1981)revealed that a nutritional deficiency imposed on weanling rats modified the normal phenotypic expression of some DCTs. 0 1983 ALAN R.LISS, INC. The objective of the present work was to determine whether a more acute and/or prolonged nutritional deficiency, such as a proteincalorie malnutrition during lactation and post-lactation, could increase the nongenetic variation of some DCTs in the growing rat. The individual response of each sex was also evaluated. MATEXIAL AND METHODS Pregnant Holtzman rats were kept in individual cages and fed water and stock diet ad libitum until delivering. Thereafter, they were subjected to either a control (C) or a restricted (R) treatment. Control mothers were fed stock diet ad libitum until weaning. Their food intake was recorded daily. Restricted mothers were given only 50% of the stock diet eaten daily by their respective controls. At delivery, each litter was reduced to four males and four females. At weaniq-21 days of age-the offspring were allocated to one of the followingtreatments: Received October 6,1981, accepted September 27,1982. 426 S.L. DAHINTEN AND H.M.PUCCIARELLI Control (CC): pups from control mothers were fed a semisynthetic diet containing 28% protein ad libitum. Early malnutrition (RC): pups from restricted mothers were fed the same diet as the CC rats. Late malnutrition (CM): pups from control mothers were fed a low-protein semisynthetic diet (6%protein) ad libitum. pups from reTotal malnutrition 0: stricted mothers were given the same diet as CM. The semisynthetic diets were prepared weekly and according to the procedures developed by Dahinten and Pucciarelli (1981). Diets were dried to constant weight and refrigerated until use. In this way, their quality remained unaltered and similar consistencies for both control and low-protein diets were obtained. Body weights of both mothers, from delivery to weaning, and offspring, until they were 49 days of age, were recorded weekly. When the latter were 49 days old they were killed with ether; their skulls were cleaned following the technique of Luther (Searle, 1954a)and stained with alizarin-red “S”(Noback and Noback, 1944). Twenty five DCTd were observed on 128 skulls (Table 1) under a dissecting microscope (20x1. Bilateral traits were observed on both sides of the skull. All determinations were made by the same observer, who was not aware of the experimental group each skull belonged to. Another observer verified, on randomly chosen skulls, the determinations of the former. The sex and nutritional factors (Tables 2-4) were obtained from comparisons between treatments. The statistical analysis of the data consisted of z-tests between proportions; it was performed at the Centro de Estudios Superiores para el Procesamiento de la Lnformacih (CESPI). RESULTS Weight differencesbetween the control and restricted groups were observed from the fourteenth day onwards. The recuperation TABLE 1. Composition of the sample Treatment Control (CC) Earlymalnutrition(RC) LatemalnutritionCM) Totalmalnutrition(RM) Total Males Females Symbol n Symbol n Total MCC MRC MCM MRM FCC 12 FRC 18 FCM 18 FRM 62 14 15 29 10 22 22 40 19 37 66 128 TABLE 2. Comparison of the incidence of crania with traits affected by sex between different groups of control and stressed rats Comparison Proportion z Test Posterior incurvation of the left palatine border -2.08* 0.58 - 0.93 MCC - FCC -2.24* 0.60 - 1.00 MRC - FRC -2.84** 0.62 - 0.96 MCM - FCM 2.41* MRM-FRM 0.94 - 0.60 Left double frontal foramen 0.58 - 1.00 2.69** MCC - FCC 0.73 - 0.70 n.8. MRC - FRC 0.67 - 0.75 n.8. MCM - FCM MRM - FRM 0.78 - 0.75 n.s. Right double frontal foramen 0.64 - 0.67 n.s. MCC - FCC MRC- FRC 0.90 - 0.80 n.8. MCM - FCM 0.67 - 0.83 -2.24* 0.47 - 0.47 n.8. MRM - FRM Left double posterior palatine foramen 0.33 - 0.78 -2.33* MCC - FCC 0.70 - 0.70 n.8. MRC . ._- FRC MCM- FCM 0.71 - 0.67 n.8. n.8. MRM-FRM 0.71 - 0.50 ~ ~~ *P < 0.05; +*P< 0.01. after weaning was not strong enough to raise body weights to values similar to those of the controls. The late and total-malnourished groups did not increase in weight (Fig. 1). Sex affected the posterior incurvation of the left palatine border, and the double frontal and the left double posterior palatine foramina (Table 2). Nutrition affected the posterior incurvation of the palatine border, the interfrontal fusion, the double frontal foramen, the double maxillary foramen, and the double posterior palatine foramen (Table 3). Interactions between sex and nutrition were found for the posterior incurvation of the palatine border, the interfrontal fusion, the double frontal foramen, the double maxillary foramen and the right double posterior palatine foramen (Table 4). ‘The following discontinuous cranial traits were observed: double frontal foramen (Berry and Searle, 1963); double maxillary foramen (Berry and Searle, 1963);double posterior palatine foramen (Berry and Searle, 1963);mid-sphenoidal foramen (Deol and Truslove, 1957); double oval foramen (Deol, 1955); double hypoglossi foramen (Deol, 1955); double mental foramen -1, 1955); bentnose (Berry and Searle, 1963); incurvation of the palatine border (Deol, 1955); interfrontal bone (Berry and Searle, 1963); bregmatic wormian bone (Pucciarelli, 1974); lambdoid wormian bone (Pueeiarelli, 1974); third molar missing (Berry and Searle, 1963); parted frontals (Berry and Searle, 1963);bone reaorption in the eminentia incisiva of the mandible (Deol, 1955); interfrontal fusion (Deol and h l o v e , 1957); internasal fusion (Berry and Searle, 1963); squamosal-frontal fusion (Berry and Searle. 1963);squamosal-parietalfusion (Berry and Searle, 1963); occipital-periotic fusion (Berry and Searle, 1963); interparim occipital fusion (Deol and Truslove, 1957); basi-preesphenoid fusion (Berry and Searle, 1963);basioccipital-basiesphenoidfusion (Berry and Searle, 1963); basioccipital foramen present and sphenoidal fissure. EFFECTS OF F'CM ON DISCONTINUOUS TRAITS Ol 7 12 27 28 35 45 49 AGE [DAYS I Fig. 1. Increments in body weight in controls (uppertipped triangles); early malnourished (circles); late malnourished(squares); and total malnourished(down-tipped triangles)groups.White: males; black females. The traits which remained unaltered were: the double hypoglossi foramen, the double oval foramen, the bent-nose, the mid-sphenoidal foramen, the bregmatic wormian bone, the parted frontals, and the sphenoid-occipital fissure. The following traits were absent: the third molar missing, the squamosal-parietal fusion, the squamosal-frontalfusion, the occipital-periotic fusion, the double mental foramen, the bone resorption in the eminentia incisiva of the mandible, the internasal fusion, the interparieto-occipital fusion, the basi-preesphenoid fusion, the basiesphenoidbasioccipital fusion, the interfrontal bone, and the basioccipital foramen. DISCUSSION About 20% of the measured trails were influenced by either PCM or PCM and sex. PCM modified all of those traits whereas sex affected only 2% of them. Although early PCM had less influence than sex, its effect was increased when it acted together with late PCM (total PCM). In fact, the relative 427 effects of both sex and nutrition were: total PCM > late PCM > sex > early PCM. The major implications of those effects were: a) not all of the DCTs are insensitive to the influence of biological and/or environmental factors. On the contrary, there are discontinuoustraits for which their variation depends upon one or more of these fadors, acting either per se or interactively; b) traits apparently as stable as the DCTs may be altered by a nutritional stress to an extent greater than that evoked by genetically controlled fadors; and c) the DCTs seem to be more sensitive to protracted nutritional deficits Qateand total PCM)than to acute deficiencies, such as those imposed during the early period of postnatal development (early PO. The DCT which showed the greatest variation was the posterior incurvation of the left palatine border. It was followed, in decreasing order of variation, by the interfrontal fusion, the double frontal foramen, the double maxillary foramen, the posterior incurvation of the right palatine border, and the double posterior palatine foramen. In addition, some of the traits, e.g., the double maxillary foramen and the interfrontal fusion, showed specific nutritional variabilities as Pucciarelli (1980)found for traits having continuous variation. The double frontal foramen showed predominant sexual variability. The behavior of the other affected traits, i.e., the posterior incurvation of the palatine border and the double posterior palatine foramen, was not coherent because the variation of one side was independent from that of the opposite one. The concept of specific nutritional variability is in agreement with Searle (1954b) and Deol and Truslove (19571, who found nutritionally evoked changes in the discontinuous traits of the mouse. The behavior of the inter. frontal fusion concurs with both the decrease of its frequency under conditions of a PCM imposed during post-lactancy (Dahinten and Pucciarelli, 1981)and the lower frequency of the interparieto-occipital fusion, as observed in mice born from mothers malnourished during pregnancy and lactation (Deol and Truslove, 1957).The higher frequenciesfound by Deol and Truslove in oval and mid-sphenoidal foramina and the lower frequencies in the posterior incurvation of the palatine border are at variance with those observed in this experiment, presumably because of the different kind of diets and animals employed. S.L. DAHINTEN AND H.M. PUCCIARELLI 428 TABLE 3. Comparison of the incidence of crania with traits affected by nutrition between different groups of control and stressed rats Comparison Proportion Factor z Test TABLE 3. Continued Comparison Proportion Factor z Test Posterior incurvation of the left palatine border MCC - MRC 0.58 - 0.60 Early PCM n.s. 0.62 - 0.94 Early PCM -2.32* MCM - MRM 2.93* FCM - FRM 0.96 - 0.60 Early PCM n.8. 0.93 - 1.00 Early PCM FCC - FRC n.s. 0.58 - 0.62 Late PCM MCC - MCM n.s. 0.93 - 0.96 Late PCM FCC - FCM 0.60 - 0.94 Late PCM -2.20* MRC - MRM Late PCM 2.34* FRC - FRM 1.00 - 0.60 0.58 - 0.94 Total PCM -2.34* MCC - MRM 2.14* 0.93 - 0.60 Total PCM FCC .FRM Posterior incurvation of the right palatine border n.s. 0.92 - 0.70 Early PCM MCC - MRC n.6. 0.93 - 0.90 Early PCM FCC FRC n.s. 0.95 - 1.00 Early PCM MCM - MRM Early PCM n.s. FCM - FRM 0.96 - 0.95 Late PCM n.8. MCC -MCM 0.92 - 0.95 n.s. 0.93 - 0.96 Late PCM FCC - FCM 0.70 - 1.00 Late PCM -2.40* MRC - MRM Late PCM n.8. 0.90 - 0.95 FRC - FRM n.8. 0.92 - 1.00 Total PCM MCC - MRM Total PCM n.s. FCC - FRM 0.93 - 0.95 Interfrontal fusion 0.25 - 0.02 Early PCM n.8. MCC - MRC 0.21 - 0.10 Early PCM n.8. FCC - FRC 0.05 - 0.00 Earl; PCM n.s. MCM - MRM n.8. FCM - FRM 0.00 - 0.00 Early PCM n.s. Late PCM 0.25 - 0.05 MCC MCM 2.36* Late PCM FCC FCM 0.21 - 0.00 n.8. Late PCM 0.02 - 0.00 MRC - MRM n.8. 0.10 - 0.00 Late PCM FRC - FRM 2.18* 0.25 - 0.00 Total PCM MCC - MRM 2.17* Total PCM FCC - FRM 0.21 - 0.00 Left double frontal foramen MCC MRC 0.58 - 0.73 Earlv PCM n.s. -- - . -. FCC - FRC i.00 - 0.70 Earl; PCM 2.19* n.6. 0.67 - 0.78 Early PCM MCM - MRM Early PCM n.s. FCM - FRM 0.75 - 0.75 n.s. 0.58 - 0.67 Late PCM MCC - MCM 2.04* 1.00 - 0.75 Late PCM FCC - FCM n.8. 0.73 - 0.78 Late PCM MRC - MRM Late PCM n.6. 0.70 - 0.75 FRC - FRM n.8. Total PCM 0.58 - 0.78 MCC - MRM 2.03* TotalPCM 1.00 - 0.75 FCC - FRM Right double frontal foramen n.s. 0.64 - 0.90 Early PCM MCC - MRC 0.67 - 0.80 Early PCM n.s. FCC - FRC Early PCM n.8. 0.67 - 0.47 MCM MRM 0.83 - 0.47 FCM - FRM n.s. Early PCM 0.64 - 0.67 n.8. Late PCM MCC .MCM 0.67 - 0.83 Late PCM n.8. FCC - FCM 0.90 - 0.47 Late PCM 2.23 * MRC - MRM n.6. 0.80 - 0.47 Late PCM FRC - FRM 0.64 - 0.47 Total PCM n.8. MCC - MRM Total PCM n.8. FCC - FRM 0.67 - 0.47 Left double maxillary foramen 0.33 - 0.40 Early PCM n.8. MCC - MRC n.8. FCC - FRC 0.36 - 0.70 Early PCM n.8. MCM - MRM 0.24 - 0.41 Early PCM 0.08 - 0.40 Early PCM -2.50* FCM - FRM n.8. 0.33 - 0.24 MCC - MCM Late PCM 0.36 - 0.08 Late PCM 2.10* FCC - FCM 0.40 - 0.41 Late PCM n.s. MRC - MRM Late PCM n.8. FRC - FRM 0.70 - 0.40 Total PCM n.8. 0.33 - 0.41 MCC - MRM Total PCM n.s. 0.36 - 0.40 FCC - FRM Right double maxillary foramen n.8. 0.33 - 0.10 Early PCM MCC- MRC 2.39* 0.43 - 0.00 Early PCM FCC FRC n.8. MCM - MRM 0.24 - 0.35 Early PCM Earh PCM n.8. FCM - FRM 0.37 - 0.47 Late PCM n.8. 0.33 - 0.24 MCC - MCM Late PCM n.8. 0.43 - 0.37 FCC - FCM Late PCM n.8. 0.10 - 0.35 MRC - MRM Late PCM -2.92* FRC - FRM 0.00 - 0.47 n.6. 0.33 - 0.35 Total PCM MCC - MRM n.8. FCC .FRM 0.43 - 0.47 Total PCM Left double posterior palatine foramen n.8. 0.33 - 0.70 Early PCM MCC- MRC n.8. FCC - FRC 0.78 - 0.70 Early PCM n.8. 0.71 - 0.70 Early PCM MCM - MRM n.s. 0.67 - 0.50 Early PCM FCM - FRM Late PCM -2.13* 0.33 - 0.71 MCC - MCM Late PCM n.s. 0.78 - 0.67 FCC - FCM n.8. 0.70 - 0.70 Late PCM MRC - MRM n.8. 0.70 - 0.50 Late PCM FRC - FRM 0.33 - 0.70 Total PCM -2.00* MCC - MRM n.8. Total PCM FCC - FRM 0.78 - 0.50 Right double posterior palatine foramen n.8. 0.75 - 0.70 Early PCM MCC - MRC n.8. FCC - FRC 0.50 - 0.60 Early PCM Earl; PCM n.8. MCM-MRM 0.57-0.29 n.8. 0.62 - 0.60 Early PCM FCM - FRM Late PCM n.8. MCC - MCM 0.75 - 0.57 Late PCM n.8. FCC - FCM 0.50 - 0.62 2.05* 0.70 - 0.29 Late PCM MRC - MRM n.8. 0.60 - 0.60 Late PCM FRC - FRM MCC - MRM 0.75 - 0.29 Total PCM 2.42* FCC - FRM 0.50 - 0.60 Total PCM n.8. *P 6 0.05; **P4 0.01. Berry and Berry (1972) stated that discontinuous traits are independent from biological fadors. However, the present observations in the rat along with those of Howe and Parsons (1967) in the mouse and Conuccini (1974a,b) in man suggest the existence of strong influences of biological factors, such as age and sex, on discontinuous traits. Indeed, the interaction between sex and PCM was quite evident since in eight out of nine of the affected traits there was a comparison for which the combination of both fadors evoked significant differences. This interaction was made evident by the behavior of the left posterior palatine border, which suggests that a nutritional stress may affect males and females differently. While the influence of sex may be subjected to epigenetic polymorphism (Berry and Searle, 19631,the nutritional influences must ~ ~ ~ ~ ~ 429 EFFECTS OF PCM ON DISCONTINUOUS !I'RAl"s TABLE 4. Comparison of the incidence of crania with traits affected by sex-nutrition interaction between differentgroups of control and stressed rats Comparison Proportion Factors z Test TABLE 4. Continued Comparison Proportion Factors z Test Posterior incurvation of the left palatine border MCC - FRC 0.58 - 1.00 S + early PCM -2.32* FCC - MRC 0.93 - 0.60 S + early PCM n.6. MCM - FRM 0.62 - 0.60 S + early PCM n.8. FCM - MRM 0.96 - 0.94 S + early PCM n.8. MCC - FCM 0.58 - 0.96 S + late PCM -2.85* FCC - MCM 0.93 - 0.62 S + late PCM 2.05* MRC - FRM 0.60 - 0.60 S + late PCM n.8. FRC - MRM 1.00 - 0.94 S + late PCM n.8. MCC - FRM 0.58 - 0.60 S + total PCM n.8. FCC - MRM 0.93 - 0.94 S + total PCM n.8. Posterior incurvation of the right palatine border MCC - FRC 0.92 - 0.90 S + early PCM n.8. FCC - MRC 0.93 - 0.70 S + early PCM n.8. MCM - FRM 0.95 - 0.95 S + earlv PCM n.8. FCM - MRM 0.96 - 1.00 s + early PCM n.8. MCC - FCM 0.92 - 0.96 S + late PCM n.8. FCC - MCM 0.93 - 0.95 S + late PCM n.8. MRC - FRM 0.70 - 0.95 S + late PCM -1.90* FRC - MRM 0.90 - 1.00 S + late PCM n.8. MCC - FRM 0.92 - 0.95 S + total PCM n.8. FCC - MRM 0.93 - 1.00 S + total PCM n.8. Interfrontal fusion MCC - FRC 0.25 - 0.10 S + early PCM n.8. FCC MRC 0.21 - 0.02 S + early PCM n.8. MCM - FRM 0.05 - 0.00 S + early PCM n.8. FCM - MRM 0.00 - 0.00 S + early PCM n.8. MCC - FCM 0.25 - 0.00 S + late PCM 2.56* FCC - MCM 0.21 - 0.05 S + late PCM n.8. MRC - FRM 0.02 - 0.00 S + late PCM n.8. FRC - MRM 0.10 - 0.00 S + late PCM n.8. MCC - FRM 0.25 - 0.00 S + total PCM 2.35* FCC - MRM 0.21 - 0.00 S + total PCM 2.01* Left double frontal foramen MCC - FRC 0.58 - 0.70 S + early PCM n.8. FCC - MRC 1.00 - 0.73 S + early PCM n.8. MCM - FRM 0.67 - 0.75 S + early PCM n.8. FCM - MRM 0.75 - 0.78 S + early PCM n.8. MCC - FCM 0.58 - 0.75 S + late PCM n.8. FCC - MCM 1.00 - 0.67 S + late PCM 2.42* MRC - FRM 0.73 - 0.75 S + late PCM n.8. FRC - MRM 0.70 - 0.78 S + late PCM n.8. MCC - FRM 0.58 - 0.75 S + total PCM n.8. FCC - MRM 1.00 - 0.78 S + total PCM n.8. Right double frontal foramen n.8. 0.64 - 0.80 S + early PCM MCC - FRC n.8. FCC - MRC 0.67 - 0.90 S + early PCM n.8. MCM - FRM 0.67 - 0.47 S + early PCM 2.67* FCM - MRM 0.83 - 0.47 S + early PCM MCC- FCM 0.64 - 0.83 S + late PCM n.8. n.8. FCC - MCM 0.67 - 0.67 S + late PCM 2.37* MRC - FRM 0.90 - 0.47 S + late PCM n.8. FRC - MRM 0.80 - 0.47 S + late PCM n.8. MCC - FRM 0.64 - 0.47 S + total PCM n.8. FCC-MRM 0.67 - 0.47 S + total PCM Left double maxillary foramc!n n.8. MCC - FRC 0.33 - 0.70 S + early PCM n.8. FCC - MRC 0.36 - 0.40 S + early PCM n.8. MCM - FRM 0.24 - 0.40 S + early PCM S + early PCM -2.50* FCM - MRM 0.0s - 0.41 S + late PCM n.8. MCC - FCM 0.33 - 0.08 FCC 0.24 S + late PCM n.8. ~- - MCM . _ .0.36 ~- ~ n.8. MRC - FRM 0.40 - 0.40 S + late PCM n.8. FRC - MRM 0.70 - 0.41 S + late PCM n.8. MCC - FRM 0.33 - 0.40 S + total PCM n.8. FCC - MRM 0.36 - 0.41 S + total PCM Right double maxillary foramen 2.01* MCC - FRC 0.33 - 0.00 S + early PCM n.s. FCC - MRC 0.43 - 0.10 S + early PCM n.8. MCM - FRM 0.24 - 0.47 S + early PCM n.8. FCM - MRM 0.37 - 0.35 S + early PCM n.8. FCC - MCM 0.43 - 0.24 S + late PCM n.8. MCC - FCM 0.33 - 0.37 S + late PCM n.s. MRC - FRM 0.10 - 0.47 S + late PCM -2.13* FRC - MRM 0.00 - 0.35 S + late PCM n.8. MCC - FRM 0.33 - 0.47 S + total PCM n.8. FCC MRM 0.43 - 0.35 S + total PCM Right double posterior palatine foramen n.8. MCC - FRC 0.75 - 0.60 S + early PCM n.6. FCC - MRC 0.50 - 0.70 S + early PCM n.8. MCM- FRM 0.57 - 0.60 S + early PCM 2.09* FCM MRM 0.62 - 0.29 S + early PCM n.8. MCC - FCM 0.75 - 0.62 S + late PCM n.8. FCC - MCM 0.50 - 0.57 S + late PCM n.s. MRC - FRM 0.70 - 0.60 S + late PCM n.8. FRC .MRM 0.60 - 0.29 S + late PCM n.8. MCC - FRM 0.75 - 0.60 S + total PCM n.8. FCC - MRM 0.50 - 0.29 S + total PCM be explained by other factors. The behavior of the interfrontal fusion under PCM can be readily explained by other factors. The behavior of the interfrontal fusion under PCM can be readily explained because it is a hyperostotic trait, i.e., its ossification increases with age (Ossenberg, 1970). The delay in ossification brought about by PCM partly arrested the process of cranial sinostosis, and hence led to the persistence of the interfrontal suture. Because the foraminae are not hyperostotic traits, their variation might be due to their functional relation with the nerves and vessels which pass them through. The degree of branching of the blood vessels and/or nerve fibers which pass through a foramen determine its simple or multiple character. PCM might have modified that degree of branching, and given rise to the observed foraminal variation. ~ ~ - ~ *P c 0.05; **P< 0.01. S :sex. CONCLUSIONS DCTs do not show an even behavior. Although most are stable a substantial number 430 S.L. DAHINTEN AND H.M. PUCCJARELLI are not, 80 that they are prone to change with biological factors, such as sex, andlor environmental ones, such as nutrition. It is possible that there is not always reciprocity between a discontinuous trait in the rat skull and a similar trait in the human skull but the behavior shown for the DCTs of the rat represents a biological basis from which the presumptive behavior of human DCTs can be inferred. Within that conceptual framework, however, the results of the present study are relevant to physical anthropology. Despite the taxonomic distance between humans and rodents, anthropologists must be aware that the differential behavior of the DCTs cautions against the careless use of those traits as parameters for racial classification. However, the use of traits with a specific nutritional component can be fruitful for other studies, e.g., the osseous modifications in populations subjected to a nutritionally deficient environment. 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