Volume 29, Number 5 (Eight issues)



INFLUENCE OF MATERNAL REPRODUCTIVE CHARACTERISTICS ON THE BODY TRAITS OF PRESCHOOL CHILDREN

FRANCISCO BRAZA AND CRISTINA SAN JOSÉ

Estaciôn BiolOgica de Do/lana, CSIC, Spain

The authors studied the influence of maternal reproductive characteristics on their pit-school children’s body traits in a village in southern Spain, assuming that children’s size at prc-schooi age is associated with their future reproductive palterns. The variables considered were: I) mother’s age al menarche, as a more genetically informative variable, 2) as a mote environmental variable, they propose a new index of maternal time availability, and 3) birth weight to control its influence on early patterns of growth. The children’s body trails considered were weight and height, and a body mass index was also computed. According to these results, the mother’s age at menarche is related to those body parameters which probably influence the children’s future reproductive strategies.

Human reproductive charactensucs may vary from individual to individual, within the continuum between reproductive patterns which are short-term (maxiF­

rancisco Braza and Cristina San José, Estacian BiolOgica de Dodana, CSIC. Spain.

This research was supponed by the Spanish DOICYT (project No. PB94-00l0) and by the Ministry of Education and Research (research contract). Thc authors thank [he tcachers from the kindergarten of “Zahara de La Sierra” and the childrcn’s families for their collaboration. Dala were collected with the help of José A. Luna, Chari Carreras, 3. Manuel Mufloz, and Xenia Casanova, which was very much appreciated. The authors are grateful to Enrique Collado, Dr. Pedro Jordano, and Dr. Jiavier Cuervo for their help in analyzing data as well as for [heir comments. ALicia Prieto contributed to the preparation of the manuscript. Prot José RamOn Lorenzo (Fact. CC de La Educacidn, Univ. CIdiz) provided the growth curves and sables on the Andalusian children.

Appreciation is due to reviewers including: Prof. Jose Ramon Sanchez, Facullad de Psicologia, Universidad de San Sebastian, Spain, and Prof. Rosario Carreras, Faeultad Dc Formacion del Profesorado, Universidad de Cadiz, Spain.

Kcywords: Age at menarche, Mother’s availability, Reproductive strategies, Body traits, Preschool children, Spain.

Please address correspondence and reprint requests to: Francisco Braza. Estacidn BioLdgica de Doflana, CSIC, Avda. M’ bsisa s/n, Pabellón del Peru, 41013 ScvilLa, Spain. Phone: +34 5 4232340; Fax:

+34 5 4621125; Email:

417

mizing mating effort: early menarche, early sexual activity, early first reproduc­ tion, high number and low quality of offspring) and long-tenn (maximizing parenting effort: late onset of puberty, late first sexual intercourse and reproduction, and fewer but better quality — offspring).

AlL these factors could be affected by two kinds of determinants. Firstly, the

genetic influence measured by the inheritance of these factors, which would explain the characteristics shared by the individuals and their parents. There are reports suggesting the inheritance of reproductive characteristics as, for instance, the concordance of mothers and daughters in menarche timing (Campbell & Udry,

1995; Graber, Brooks-Gunn, & Warren, 1995; Wolanski, 1995). Secondly, envi­ ronmental conditions (e.g., nutrition, life quality of life, family context, etc.) could also affect the reproductive characteristics of individuals; and so Chisholm (1993) revised the consequences of early stress on the way people allocate their reproduc­ tive effort.

Genetic studies suggest that the contribution of genotypic effects to the variance

in menarcheal timing is stronger than that of environmental ones (Kaprio, et al.,

1995). However, the environmental influence on age of menarche in girls has been extensiveLy evidenced (Belsky, Steinberg & Draper, 1991; Draper & Harpending,

1982; Ellis, Mc Fadyen-Ketchum, Dodge, Petit & Bates, 1999; Graberet al., 1995;

Moffit, Caspi, Belsky & Silva 1992; Steinberg, 1988; Wierson, Long & Forehand,

1993).

On the other hand, although birth weight is correlated to growth status during childhood, Gofin, Adler, and MaddeLa (1993) pointed out that the influence of birth weight on the early pattern of growth is not maintained through adolescence, and found that, at the age of 14, most of the explained variance was attributed to the measurements at the age of six. Khan, Schroeder, Martorell, Haas, and Rivera (1996) demonstrated (hat a linear growth retardation during this period of early childhood is associated with a delay in menarche. Draper and Harpending (1982) have shown that there is a sensitive period in early childhood, approximately from birth to five years oLd, and that physical and behavioral changes during this period may have significant repercussions on the onset of puberty and future reproductive strategies of individuals.

Thus, assuming that the children’s physical development at preschool age is

important with respect to their future reproductive patterns, the aim of the present research is to study the reLationship between maternal reproductive patterns (age at menarche, number of siblings, interbirth interval) and the variation of the body traits of pre-school girls and boys.

INFLUENCE OF MATERNAL REPRODUCTIVE CHARACTERISTICS 419

METHOD

PARTICIPANTS

The study was carried out in Zahara de la Sierra, a village of around 2000 inhab­ itants in the mountain ranges of Cádiz (southern Spain) during 1997. The partici­ pants were a group of pre-school children (n= 38; 25 girls, 13 boys), who belonged to Lower-middle socio-economic class families. Both the living conditions and nu­ trition patterns in a restricted area are homogeneous. In aLl cases both mother and father were living with the children. A demographic profile of the sample is shown in Table 1.

TABLE 1

DEMOGRAPHIC CHARACTERISTICS OF ThE SAMPLE (N= 38)

| |Girls (n=25) | |Boys (n=13) | |

| |Al |SD |Al |SD |

|Age of the ehildren (years) |5.823 |0.447 |5.577 |0.435 |

|Mother’s age at the chiJd’s birth (years) |27.240 |5.659 |28.462 |4.594 |

|Father’s age at the child’s birth (years) |30.680 |6.619 |30.615 |6.158 |

|Mother’s age at menarche (years) |12.400 |1.155 |12.692 |1.251 |

Birth weight (kg) of the child studied 3.218 0.466 3.405 0.440

VAR1ABLES MEAsURED

A) Dependent variables.

1) Height: distance between the interparietal union and the floor (in meters).

2) Body weight (in kilograms).

3) A body mass index (hereafter BMI = body weight/height squared) was also computed.

The heights and weights of pre-school children were obtained during the first days of the school year. A trained staff member collected both measurements using standard anthropologic procedures, The children’s heights and weights were meas­ ured using a standard tape measure mounted to a wall, and electronic bathroom scales.

Although the range of ages of the children is small, there is still an age-related growth effect in height and weight. Height and the weight values were substituted for their z-scores ((Weight (or Height) - ii)/a) with respect to the distribution of the same sex and age of Andalusian children (Fact. CC de Ia Educación, Univ. de Cádiz).

B) independent variables.

The mothers were questioned about their reproductive histories (age at menarche, number, age and sex of their previous children, and birth weight of the children studied). The variabLes selected were:

1) Mother’s age at menarche (hereafter MAM).

2) Maternal Time Index (hereafter MTI): In order to assess the mother’s time available for the chiLd studied, the authors propose a new index which takes into account the number of siblings and birth interval up to the moment the studied child is measured; this index could provide infonnation about the proximal family environment where children grow up. The index was calculated as follows:

MTI=Z

1=0 Sp+SFj

j=o

= Birth following the birth of the study subject; Ti = Interval between one birth and the next or up to the moment when the study subject was measured (T0 is the interval between the birth of the study subject and the next birth) S= number

of siblings precedent to the birth of the subject studied; SFJ= number of siblings

born in birth j, being j=O the birth in which the subject studied was born.

3) Birth weight (hereafter BW) of the studied child: in order to control its pos­

sible influence on the early pattern of growth.

ANALYSIS

Girls and boys were analyzed separately, taking into account that sexual differ­ ences in human parental investment and sexual selection are to be expected (Kenrick & Trost, 1993). A significant difference in weight at preschool age was detected, the girls being heavier than the boys (ANOVA F = 5.773, p = 0.0216),

MultipLe least square regressions were used (Abacus Concepts, Statview 4.1,

1992) to analyze the relative contribution of maternal reproductive parameters to the children’s body characteristics at preschool age.

RESULTS

No significant correlation was detected between the three maternal reproduc­ tive characteristics (MAM, MTI, and BW) considered in the case of the preschool girls (Pearson’s Correlation ranging -0.267 r S 0.127).

Table 2 shows that, when regressing the body traits of pre-school girls to MAM

and to MTI, a significant negative contribution of the MAM to both weight and BMI at pre-schooL age was found. The MTE did not contribute significantly to the body traits of girls at pre-school age.

TABLE 2

BODY TRAiTS OF PRESCHOOL OWLS REGRESSIONS ON MuIHER’s AGE AT MENARCHE (MAM) AND

MATERNAL TIME INDEX (MTI)

Coefficient p

Lntercept 20.858 2.459 0.0223 a) Weight MAM -0.452 -2.378 0.0265

MTI -0.068 -0.360 0.7223

= 0.217, df= 22. F = 3.050, p = 0.0677

Coefficient p

Intercept -2.248 -0.289 0.7754 b) Height MAM 0.127 0,616 0.5443

MTI -0.273 -1.326 0.1986

W= 0.082, df= 22, F = 0.981, p = 0.3909

Coefficient p

Intercept 14.961 3.200 0.0041

C) BMI MAM -0.581 -3.306 0.0032

MTI 0.068 0.389 0.7009

0.332, df = 22, F 5A66, p = 0.0118

As can be seen in Table 3, when regressing the body traits of pre-school girls to MAM and to 8W, there was a tendency towards a negative contribution of the MAM to weight at pre-schooL age, and a significant negative contribution of the MAM to the BMI was found. The 8W did not contribute significantly to the body traits of girls at pre-school age.

TABLE 3

BODY TRAITS OF PRESCHOOL GiRLS RLGRESSIONS ON MOTHER’S AGE AT MENARCHE (MAM) AND BIRTH WEIGHT (BW) OF THE CHILD STUDIED

Coefficient p

Intercept 8.734 0.795 0.4354 a) Weight MAM -0.383 -2.058 0.0516

*

BW 0.291 1.563 0.1324

R2=0.291, df= 22, F = ‘4.SI9,p = 0.0227

Coefficient p

Intercept -16.537 -1.616 0.1204 b) Height MAM 0.194 0.948 0.3535

BW 0.382 1.864 00757

R20.I44,df=22F= l.847,p=O.1813

Coefficient p

Intercept 14.354 2.248 0.0349

c) BMI MAM -0.563 -3.106 0.0052 **

BW 0.034 0.188 0.8523

R2= 0.328, df= 22, F S.38O,p = 0.0125

When considering the correlation between the three maternal reproductive char­ acteristics in the case of boys, a significant positive reLationship was detected between MAM and MTI (r = 0.647, p = 0.0149, Pearson’s Correlation) only.

422 INFLUENCE OF MATERNAL REPRODUCTIVE CI-IARACTERISTICS

Table 4 shows that, when regressing the body traits of preschool boys to MAM and ?VITJ, a significant negative contribution of MAM to the weight at pre-school age was found. As can be seen in Table 5, when regressing the body traits of boys to MAM and to 8W, a significant negative contribution of the MAM to the weight and height at pm-school age was found. A significant contribution of the 8W to the height of boys at pre-school age was also found.

TABLE 4

BODY TRAITS OF PRESCHOOL Boys REGREsSIONS ON MOTHER’S AG! AT MENARCHE (NIAM) AND

MATERNAL TIME INDEX (M’I’I)

Coefficient I p

Intercept 22.021 2.509 0.0310

a) Weight MAM -0.729 -2.306 0.0438 *

Ml’! 0.139 0.441 0.6685

R2= 0.419. df= 10 F = 3.609, p = 0.0661

Coefficieni a’ p

tntercept 27.586 1.843 0.0951

b) Height MAM -0.604 -1.710 0.1181

MTI 0.140 0.398 0.6992

= 0.275, df = 10, F = 1.893, p = 0.2008

Coefficient r p

Intercept 7.721 1.545 0.1534 c)BMI MAM -0A95 -L.369 0.2011

MTI 0.009 0.025 0.9804

R2= 0.239, df= 10, F = L573, p = 0.2548

TABLE S

BODY TRAITS OF PRESCHOOL Boys REGRESSIONS ON MOTHER’S AGE AT MENARCHE (MAM) AND BIRTH WEIGHT (BW) OF THE CHILD STUDIED

Coefficieni I p

Intercept 10.336 1.301 0.2224

a) Weight MAM -0.647 -3.185 0.0097

BW 0.424 2.087 0.0635

R2= 0.588. df= 10, F = 7.l23,p = 0.0119

Coefficient a’ p

tnrercept 4.535 0.375 0.7152

b) Height MAM -0.524 -2.589 0.0270

13W 0.572 2.824 0.0180 *

= 0.590, df = 10, F = 7. t97, p = 0.01 t6

Coefficient r p

Intercept 5.805 1101 0.2969 c) BMI MAM -0.492 -1.816 0.0994

BW 0.162 0.597 0.5640

R1=0.265,df= tO,F= I.8O6,p=0.2t40

When regressing the body traits of preschool children (boys and girls) to MTI

and to 8W, no significant conthbution was detected.

DISCUSSION

A significant negative contribution of MAM to weight of girls and boys at pre­ school age has been detected independently of either MTI or BW. Furthermore, and also when controlling for MTI or BW, these results reveal a higher BMI in the we-school girls of earlier-maturing mothers, which can be considered as a good estimate of body fatness (i.e., the proportion of body mass fat, Deurenberg, Weststrate, & Seidell, 1991).

A relationship between a woman’s amount of body fat and the onset of menarche has previously been demonstrated (Ellison, 1982; Frisch, 1988; Frisch

& McArthur, 1974), young girls not entering puberty until they have reached a critical ratio of body fat to muscle. Thus, at least for girls, a greater influence of BMI at pre-school age on the future onset of menarche is to be expected.

Furthermore in these results, it is interesting to note that, when controlling for

BW, the MAM has a negative significant contribution in height at pre-school age -

but only in boys.

The pubertal onset for boys has traditionally been associated with behavioral factors and probably a bigger size (weight and height can be considered as esti­ mates of body size) at pit-school age contributes to an early reproductive behavior, (Capaldi, Crosby, & Stoolmiller, 1996).

Considering that children of earlier-maturing mothers probably also mature ear­ lier, it can be expected that these children of the same age are physically further developed than children of later-maturing mothers. Moffit, et al. (1992) have pre­ viously suggested that children of earlier-maturing mothers also matured earlier; results from Wolanski’s study (1995) of Mexican schoolgirls also suggested this possibility by reveaLing a correlation between the age at menarche of mothers and daughters; and Gofin, et al. (1993) pointed out that early menstruating girls were taller and heavier than non-menstruating girls already at six years old.

According to the results of this study, MAM is strongly related to those body

parameters that probably influence the children’s future reproductive strategies. That is, in girls, the mother’s age at menarche is more closely related not only to body weight but also to the store of fatness, whereas it is more related to body size in boys.

Following the prediction of life-history theories, in a short-term reproductive strategy low-quality offspring are more to be expected. The relationship between early menarche of mothers and more physically developed children at preschool age does not mean that these children will attain a better physical condition as adults. In the authors’ opinion, advanced development at preschool age anticipates the onset of puberty, which probably stops their growth. It has long been recog­ nized that maturation is accompanied by a decrease in — or cessation of— growth in many organisms, and recent research corroborates the results of several previ

424 INFLUENCE OF MATERNAL REPRODUCTNE CHARACTERISTICS

ous studies that describe shorter statures and higher body mass indexes during adulthood in early-maturing females (Kirchengast, Gruber, Sator, & Huber, 1998).

As regards family context, in Chisholm (1993), Pavlik pointed out that the pe­ riod from five to seven years old is important for the development of the child’s neuroendocrine phenotype, and early stress may be associated with high-mating effort reproductive patLerfls. Belsky, et al. (1991) have proposed that the first five to seven years of experience in the family enables a child to assess the availability of resources and the durability of parental bonds as a basis to develop his or her reproductive strategy. Ellis et al, (1999), suggest that the quality of fathers’ invest­ ment in the famiLy is the most important feature of the proximal family environ­ ment relative to daughters’ pubertal timing.

In spite of the importance of family experience in early childhood on future reproductive strategies, the authors have not detected a significant contribution of the context where children develop (MTI, i.e., time of maternal availability, birth interval, arid family size) to the children’s body traits at pre-school age when con­ trolling for both MAM or BW. Other authors (Kim, Smith, & Palermity, 1997; Kim & Smith, 1998), although they found developmental links between childhood stressors, onset of puberty, arid postpubertal reproductive behavior, consider that early puberty and postpubertal sexual behavior might be more influenced by intergenerational transmission of genetic characteristics.

Since birth weight might be considered as an outcome of maternal phenotype

(maternal effects) rather than of genetic constitution of the offspring, it might be thought that the positive contribution of boys’ birth weight detected to height at pre-school age when controlling for MAM, might suggest a maternal environment’s influence during the prenatal period, at least for boys, in the determination of their future reproductive strategy. Furthermore, in boys a positive correlation between MAM and MIT was found, that is —later maturing mothers of boys present long birth intervals and few offspring, suggesting a higher investment in boys than early maturing mothers. Considering that the allocation of resources before birth (BW) is related to the onset of boys’ puberty, this result could be supporting also, at least in boys, the possibility of a maternal environmental influence in Lhe reproductive strategy of their children. Thus, in boys, besides the genetic influence detected (early or later maturing mothers having early or later maturing children respec­ tively), an environmental influence has also been found.

Body traits irrespective of age are genetically and environmentally affected and

the contribution of each factor at each age is difficult to assess. Future research might explore, for girls as well as for boys, models considering simultaneously variables informative of the environment as well as those more genetically informa­ tive,

L INFLUENCE OF MATERNAL REPRODUCTIVE CHARACTERISTICS 425

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Belsky, 3., Steinberg, L. & Draper, F. (1991). Childhood experience, interpersonal development, and reproductive strategy: An evolutionary theory of socialization. Child Development, 62, 647-670. Campbell, B. C, & Udry, J. R. (1995). Stress and age at menarche of mothers and daughters. Journal

of Biosocial Science, 27, 127-134.

Capaldi, D. M., Crosby, L. & Stoolmiller, M. (1996). Predicting the timing of first sexual intercourse for at-risk adolescent males. Child Development, 67, 344-359.

Chisholm, J. 5. (1993). Death, hope and sex: Life-history and the development of reproductive strat­

egies. Current Anthropology, 34, 1-46.

Draper, P. & Harpending. H. (1982). Father absence and reproductive strategy: An evolutionary per­

spective. Journal of Anthropological Research, 35. 255-273.

Deurenberg, P., Weststrate, J. A. & Seidell, J. C, (1991). Body mass index as a measure of body fatness: Age- and sex-specilic formulas. British Journal of Nutrition, 65, 105-114.

Ellis, B. J., McFadyen-Ketchum, S., Dodge, K. A., Petit, G. S. & Bates, J. E. (1999). Quality of early

family relationships and individual differences in the timing of pubertal maturation in girls: A Longitudinal test of an evolutionary model. Journal of Personality and Social Psychology, 77,

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Ellison, P. T. (1982). Skeletal growth, fatness, and menarcheal age: A comparison of two hypotheses.

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Gofin, R., Adler, B. & Maddela, R. (1993) Birth weight and weight, stature, and body mass index at ages 6 and 14 years. American Journal of Human Biology. 5, 559-564.

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