Sexual Dimorphism In Body Weight Research Articles

Timing of puberty in F1-generation hatchery-produced greater amberjack (Seriola dumerili)

We evaluated the onset of puberty of first-generation (F1) hatchery-produced greater amberjack (Seriola dumerili) reared in sea cages for 5 years. Fish were sampled every year in June, at the expected peak of the spawning period in the Mediterranean Sea. No sexual dimorphism in body weight was observed in the study. The ovaries of 1 and 2-year-old (yo) females consisted of primary oocytes only, while at the age of 3-yo early vitellogenic (Vg) oocytes were also identified, but with extensive follicular atresia. At the age of 4-yo, late Vg oocytes were observed, but again extensive follicular atresia characterized the ovaries of 50 % of females. At the age of 5-yo, follicular atresia of Vg oocytes was very limited. In males, gametogenesis was evident already in 1- and 2-yo fish, and 100 % of sampled 3-yo males produced collectable viable sperm. Plasma testosterone (T), 17β-estradiol (E2), and 17,20β-dihydroxy-4-pregnen-3-one (17,20β-P) remained similar in 3 – 5-yo females, with T and E2 levels being highest in females in advanced vitellogenesis or with significant follicular atresia, compared to immature females. In males, plasma T declined over the years, while 11-ketotestosterone (11-KT) and 17,20β-P were highest in 4 and 5-yo males, with spermatozoa motility characteristics being improved from the 4th year onwards. The administration of GnRHa implants to 5-yo fish induced only two spawns, albeit no fertilized eggs were obtained. The results indicate that hatchery-produced greater amberjack males mature well and within the same age observed in the wild, however with smaller gonad size. On the contrary, females mature later than in the wild, also with a smaller gonad size. Spawning in response to GnRHa treatment was not effective, suggesting that Mediterranean hatchery-produced broodstocks may be dysfunctional, and further research is needed to document any improvement as the fish get older, or to determine if the results may be related to the specific stock of fish.

Sexual Dimorphism in Lipid Metabolism and Gut Microbiota in Mice Fed a High-Fat Diet.

The gut microbiome plays an essential role in regulating lipid metabolism. However, little is known about how gut microbiome modulates sex differences in lipid metabolism. The present study aims to determine whether gut microbiota modulates sexual dimorphism of lipid metabolism in mice fed a high-fat diet (HFD). Conventional and germ-free male and female mice were fed an HFD for four weeks, and lipid absorption, plasma lipid profiles, and apolipoprotein levels were then evaluated. The gut microbiota was analyzed by 16S rRNA gene sequencing. After 4-week HFD consumption, the females exhibited less body weight gain and body fat composition and significantly lower triglyceride levels in very-low-density lipoprotein (VLDL) and cholesterol levels in high-density lipoprotein (HDL) compared to male mice. The fecal microbiota analysis revealed that the male mice were associated with reduced gut microbial diversity. The female mice had considerably different microbiota composition compared to males, e.g., enriched growth of beneficial microbes (e.g., Akkermansia) and depleted growth of Adlercreutzia and Enterococcus. Correlation analyses suggested that the different compositions of the gut microbiota were associated with sexual dimorphism in body weight, fat mass, and lipid metabolism in mice fed an HFD. Our findings demonstrated significant sex differences in lipid metabolism and the microbiota composition at baseline (during LFD), along with sex-dependent responses to HFD. A comprehensive understanding of sexual dimorphism in lipid metabolism modulated by microbiota will help to develop more sex-specific effective treatment options for dyslipidemia and metabolic disorders in females.

Динамика роста молодняка норок породы альбинопастель в постнатальном онтогенезе

Coloured minks are widespread – more than 200 colour variations in hair colour are known. Currently, breeding in fur farming continues. One of the most recent breeding achievements is the albino pastel mink. An important characteristic of the new breed is the body size and growth of the organism during the postnatal period, which does not occur evenly but goes through certain phases. In different periods of growth, the organism requires appropriate conditions, in the presence of which further development occurs. As a result of studies of mink growth from birth to adulthood, data necessary for the correct organization of measures for rearing and feeding the animals are accumulated. When analysing the growth dynamics of young animals, it has been established that sexual dimorphism in body weight of males and females of the albino-pastel genotype is absent at one day of age. The most intensive increase in body weight in female and male albino-pastel minks occurs from day 50 to day 80. The increase in body weight continues after 3–4 months of life, with males more intense than females.

Mating system of Thrichomys fosteri in the Brazilian Pantanal: spatial patterns indicate promiscuity

Animal mating systems provide key insights into the relationship between evolutionary processes and ecological factors such as the spatio-temporal fluctuation of resource abundance. Characteristics of mating systems can be inferred from the spatial distribution of conspecifics and the arrangement of reproductive pairs. Here we used home-range size and overlap for Thrichomys fosteri in the Brazilian Pantanal to infer the mating system on this echimyid rodent. Our aims were to verify the existence of sexual dimorphism, to test whether home-range size varied with the sex and body weight of the individuals, to evaluate the degree of home-range overlap, to estimate mean population density, and to infer individuals’ mating system. Twenty one individuals (15 males and six females) were radio tracked from 14 to 349 days, with the number of locations by individuals ranging from 19 to 193 locations. There was a male-biased sexual dimorphism in body weight where males were 1.36 times heavier than females. Males’ home-range size increased with their body weight, while for females there was no relationship. There was extensive home-range overlap between both sexes, and no evidence of territoriality. Mean population density ranged from 0.9 to 3.03 individuals/ha. Our results indicate that multiple mates were available for both sexes, characterizing a promiscuous mating system.

Sexual dimorphism in body weight, morphometric measures and indices of African Catfish (Clarias gariepinus)

A total of 219 catfish (Clarias gariepinus) comprising 125 Male and 94 Female raised over a period of nine months from hatch were investigated for body weight, eight morphometric measures and two indices. Male fish had consistently higher values for all variables studied except for Heart Girth, growth index and Condition factor where the female fish had higher values. There was statistical difference (P < .05) across the sexes for all variables except for Body Weight and Pre Anal Length. Variables were consistently more homogenous in male than female fish resulting in more variability in the female compared to male. Multivariate correlation of all variables revealed a statistically significant (P < .001) positive relationship between majority of the variables. Sex had the biggest influence on Condition Factor, while the study revealed that morphometric measures are good indicators of fish well-being, and female outperformed male on the most important economic (growth and wellness) traits.

Sexual monomorphism in wing loading and wing aspect ratio in Black Vulture (Coragyps atratus) and Turkey Vulture (Cathartes aura)

Sexual dimorphism patterns in wing area, wing loading, and wing aspect ratio of Black Vulture (Coragyps atratus) and Turkey Vulture (Cathartes aura) are unknown but are of particular interest given the prevalence of these species in scavenging communities in the Western Hemisphere. I assessed these variables in sexed specimens from wintering populations in Nashville, Tennessee. Black Vultures exhibited higher wing loading and a lower wing aspect ratio than Turkey Vultures. Neither species exhibited significant age-related or sexual dimorphism in body weight, wing span, wing area, wing loading, or wing aspect ratio. The relatively low variance observed in the pooled sample of immatures (∼9–21 mo old) and adults suggests that definitive wing size and shape are acquired several years before individuals develop the bare rugose skin and head caruncles characteristic of adults. In a broader context, this study tentatively suggests that variance estimates for wing morphology obtained from unsexed vulture populations may not be unduly inflated by undetected sexual or age-related dimorphism.

Sex influence on genetic expressions of early growth in Afshari lambs

Abstract. Very little is known about the genetic aspects of sexual dimorphism of body weight in domestic sheep, and therefore this study was conducted to quantify the genetic basis of sexual dimorphism for early-growth-related traits in Afshari lambs. Traits evaluated included birth weight (BW), weaning weight (WW), and growth rate (GR) in male and female lambs. Male lambs were 6.6 % heavier at birth, had 14.4 % higher preweaning growth rates and were 16.0 % heavier at weaning compared to female lambs. Levels of sexual-size dimorphism (SSD), expressed as the ratio of male to female means, for BW, WW and GR were 1.07, 1.14 and 1.15, respectively, which indicated low levels of SSD in the traits studied. Fixed effects of year of birth and type of birth interacted with sex effects, with greater variability in birth and weaning weights among years and birth types in male lambs, suggesting greater environmental sensitivity in the males. Bivariate animal models and restricted maximum likelihood (REML) procedures were used to estimate phenotypic variances and their genetic and non-genetic components in male and female lambs. Estimates of the direct heritability (h2) and additive coefficient of variation (CVA) for BW were higher in males. However, for WW and GR, heritability estimates were higher in females. In contrast, whereas the contribution of maternal permanent environmental effects (c2) to variation of BW was higher in females, for WW and GR higher estimates of c2 were observed in males. Respective genetic and maternal permanent environmental correlations between records on males and females were 0.986 and 0.723 for BW, 0.995 and 0.983 for WW, and 0.995 and 0.966 for GR, indicating possible sexual dimorphism only for maternal effects on BW. Based on an approximate 95 % confidence interval, none of the observed differences in variance components between sexes differed from zero and none of the observed genetic or maternal correlations differed from 1.0, indicating no need or opportunity for sex-specific selection strategies.

Genetic analysis of sexual dimorphism of body weight in broilers

Variation in sexual dimorphism (SD) is particularly marked in meat-type chickens. This paper investigates the genetic basis of SD in an important economic trait, i.e. body weight (BW) at 35 days of age, in broilers by applying quantitative genetic analysis. A large dataset comprising 203,323 BW records of a commercial line of broiler chicken was used. First, a bivariate approach was employed treating BW as a sex-specific trait. During this approach, seven bivariate models were applied and variances due to direct additive genetic, maternal genetic and maternal environmental effects were estimated via the restricted maximum likelihood method. The best-fitting model included direct additive genetic, maternal genetic and maternal environmental effects with a direct-maternal genetic covariance. Differences between male and female direct heritabilities were non-significant (0.28 vs. 0.29 for males and females, respectively), implying no need for sex-specific selection strategies. The direct-maternal genetic correlation was more strongly negative in males than in females (-0.72 vs. -0.56), implying a more profound antagonism between direct additive and maternal genetic effects in this particular gender. The direct genetic correlation of BW between the two sexes was as high as 0.91, i.e. only slightly lower than unity. Second, variance components and genetic parameters of two measures of SD, i.e. the weight difference (Δ) and the weight ratio (R), between the genders were estimated. Direct heritabilities for both measures were significantly different to 0 but of low magnitude (0.04). Apart from the additive-maternal covariance, no other random effects were found to be of importance for Δ and R. The results of the present study suggest that only minimal selection responses due to the selection of Δ and/or R and a small capacity for amplifying or reducing the BW differences between the sexes are to be expected in this specific population. Furthermore, selection pressure on BW is expected to amplify SD.

The Number of X Chromosomes Causes Sex Differences in Adiposity in Mice

Sexual dimorphism in body weight, fat distribution, and metabolic disease has been attributed largely to differential effects of male and female gonadal hormones. Here, we report that the number of X chromosomes within cells also contributes to these sex differences. We employed a unique mouse model, known as the “four core genotypes,” to distinguish between effects of gonadal sex (testes or ovaries) and sex chromosomes (XX or XY). With this model, we produced gonadal male and female mice carrying XX or XY sex chromosome complements. Mice were gonadectomized to remove the acute effects of gonadal hormones and to uncover effects of sex chromosome complement on obesity. Mice with XX sex chromosomes (relative to XY), regardless of their type of gonad, had up to 2-fold increased adiposity and greater food intake during daylight hours, when mice are normally inactive. Mice with two X chromosomes also had accelerated weight gain on a high fat diet and developed fatty liver and elevated lipid and insulin levels. Further genetic studies with mice carrying XO and XXY chromosome complements revealed that the differences between XX and XY mice are attributable to dosage of the X chromosome, rather than effects of the Y chromosome. A subset of genes that escape X chromosome inactivation exhibited higher expression levels in adipose tissue and liver of XX compared to XY mice, and may contribute to the sex differences in obesity. Overall, our study is the first to identify sex chromosome complement, a factor distinguishing all male and female cells, as a cause of sex differences in obesity and metabolism.

SEQUENCE EVOLUTION OF THE SPERM LIGAND ZONADHESIN CORRELATES NEGATIVELY WITH BODY WEIGHT DIMORPHISM IN PRIMATES

Sexual selection has repeatedly been shown to be the probable driving force behind the positive Darwinian evolution of genes affecting male reproductive success. Here we compare the sequence evolution of the sperm ligand zonadhesin with body mass dimorphism in primates. In contrast to previous related studies, the present approach takes into account not only catarrhine primates, but also platyrrhines and lemurs. In detail, we analyze the sequence evolution of concatenated zonadhesin fragments (555 bp) of four Lemuroidea, five Platyrrhini, and seven Catarrhini, using the rate ratio of nonsynonymous to synonymous substitutions (dn/ds=omega). Unexpectedly, subsequent regression analyzes between omega estimates for the terminal branches of a primate phylogeny and residual male body mass reveal that sequence evolution of zonadhesin decreases with increasing sexual dimorphism in body weight. Mapping published mating system classifications onto these results illustrates that unimale breeding species show a tendency for rather slow sequence evolution of zonadhesin and comparably pronounced sexual dimorphism in body weight. Female choice and sperm competition can be assumed to drive the evolution of zonadhesin. We speculate that the level of sperm competition is lower in more sexually dimorphic primates because males of these species monopolize access to fertile females more successfully. Thus, variation in sperm competition may be driving the observed negative correlation of sequence evolution and sexual dimorphism in body weight.

An experimental test of hypotheses explaining social segregation in dimorphic ungulates

In many sexually dimorphic ungulates, adults spend most of their time in single-sex groups outside the mating season. We tested two hypotheses proposed to explain this social segregation. The activity budget hypothesis predicts that females spend more time grazing than males, and that activity synchrony is higher within single-sex than mixed-sex groups. The social affinity hypothesis states that higher spatial proximity and aggregation within the sexes results from sexual differences in motivation to interact socially. Fifteen merino sheep, Ovis aries , 2 or more years old, of each sex were penned together in three 1-ha paddocks in succession during 7 winter weeks. Despite the high sexual dimorphism in body weight, both sexes were found together, and did not differ substantially in activity budget. Males grazed less than females but the difference was small. The degree of activity synchrony was similar within and between the sexes. When grazing, males walked more rapidly and tended to be at the front of the group more often than females. Ewes were rarely seen interacting with other sheep, in contrast to males, which interacted twice as often with females as with males. However, same-sex pairs of nearest neighbours were found more frequently than expected, whether or not the males were at the front of the group. These results indicate a social segregation at a small spatial scale, which can be explained by differences in speed of movement between males and females and/or higher social affinity between same-sex than opposite-sex peers. The lack of single-sex groups can be explained by the strong gregariousness of merino sheep, and possibly the young age of the adult males.

Age and sex composition, biometrics, site fidelity and origin of Brambling Fringilla montifringilla wintering in Norfolk, England

We analysed data collected from approximately 2,600 Brambling Fringilla montifringilla caught while attracted to artificial food at a site in Norfolk, England over seven winters. The age and sex composition of trapped birds varied between winters in relation to the total number of birds caught, but no systematic pattern was apparent. During invasion years, when a higher number of birds were present on the study site, the proportion of males was higher. In any one winter, 38–70% of the Brambling were male and 63–86% were juvenile. Very few adult females visited the study site. Males had longer wings than females, by an average of 5–6 mm and the wings of adults averaged 1–2 mm longer than juveniles. There was sexual dimorphism in body weight, with males being on average 2 g heavier than females. Adults were on average 1 g heavier than juveniles. Within winters, mean body weights were higher in warmer months. Between winters, there was significant variation in wing length and body weight, which may have been associated with variation in the geographical origin of the birds or food availability. Approximately 70% of juveniles had undergone a partial moult of the greater coverts, with an average of between 2.7 and 3.4 old greater coverts being retained. Annual variation in the progression of moult was probably due to food availability and weather conditions on the breeding grounds or where the juveniles moulted. The mean proportion of Brambling retrapped within‐winters was 5.7% (range 0–15%) and there was no evidence to suggest that site fidelity was different in invasion years. Recoveries of ringed birds suggest that Brambling over‐wintering in Norfolk originate from Scandinavia and pass through the Low Countries on migration.

Selection against early maturity in large rainbow trout Oncorhynchus mykiss: the quantitative genetics of sexual dimorphism and genotype-by-environment interactions

In rainbow trout Oncorhynchus mykiss, females typically mature at a later age than males, and males mature either early or late. When farmed rainbow trout is produced to obtain large fillets of high quality, especially early maturation of males reduces economical benefits. To examine whether it is possible to change the degree of this sexual dimorphism using selective breeding, we estimated sex-specific heritabilities, genetic correlations between sexes, and cross-environment correlations between two production environments for age at maturity and body weight. Extensive data set including individuals in five generations measured in brackish and fresh water in a split-family design was utilised to estimate the genetic parameters. The timing of maturity ( h 2=0.12–0.56) and body weight ( h 2=0.20–0.27) exhibited significant heritabilities, allowing genetic changes in trait means in response to selection. Genetic change in sexual dimorphism of body weight is, however, strongly constrained, as shown by the high genetic correlations between sexes ( r A≥0.95). For timing of maturity, the heritabilities of males and females differed, but the genetic correlation between sexes was high and positive ( r A=0.70). Although sexual dimorphism of age at maturity is less strongly contained than that of body weights, we conclude that no rapid genetic changes can be achieved in the sexual dimorphism of age at maturity through selective breeding. However, breeders may delay the timing of maturity in both sexes to avoid the drawbacks associated with the early maturation. Cross-environment correlations for the timing of maturity and body weight were highly positive ( r A≥0.61), indicating weak genotype-by-environment interactions and allowing parallel genetic changes in two environments where rainbow trout is farmed.

Body weight and horn development im Alpine chamois, Rupicapra rupicapra (Bovidae, Caprinae).

SUMMARY With the aim of describing the trend in somatic development, especially the attainment of asymptotic body mass of Alpine chamois, Rupicapra rupicapra rupicapra, we recorded measurements (eviscerated body weight, length and height of horns) of 548 chamois harvested in 6 different valleys of the Piedmont region (Western Italian Alps), from 1984 to 1996. In male Alpine chamois, asymptotic mass was reached at 4.5 - 5.5 years of age, and after 4.5 years of age, the horns did not grow significantly between one year and the next. Females reached maximum body weight at about 3.5 years of age. Male chamois showed rapid early somatic development with consequent early development of sexual dimorphism. The mean body weights of males and females differed significantly from 3.5 years of age onwards, while horn size differed at as early as 1.5 years of age. Highest degree of sexual dimorphism in body weight (31.3 %) was found at 7.5 years of age. Male chamois reach asymptotic body mass in correspondence with first reproduction, while females mature before achieving asymptotic growth.

Genetic analysis of growth curve parameters for male and female chickens resulting from selection on shape of growth curve.

The objectives of this research were to evaluate gender differences and selection on body weight as they affect growth curves of chickens. Marginal posterior densities of growth curve parameters were studied by Gibbs sampling on 10,671 male and female chickens originating from five lines. Line X-+ was selected on low body weight at 8 wk (BW8) and high body weight at 36 wk (BW36), line X+- on high BW8 and low BW36, X++ on high BW8 and BW36, X-- on low BW8, and BW36, and X00 was an unselected control line. Growth was modeled by a Gompertz function. Heritabilities and genetic correlations among parameters of the Gompertz curve were estimated. Marginal posterior densities were drawn for parameters of the growth curve and for sexual dimorphism at ages ranging from hatching to 1 yr. Lines selected for a higher BW8 had higher initial specific growth rates (L), higher maturation rates (K), and lower ages at inflection (T(I)). Lines selected for a higher BW36 had higher asymptotic body weights (A). Estimates of A, L, and T(I) were higher in males and K was higher in females. Difference between sexes for A was greater in the line selected for a lower BW8 and a higher BW36. Dimorphism for L and K was the lowest in lines X++ and X--, respectively. The greatest difference in T(I) was observed in the line selected for lower BW8 and BW36. Sexual dimorphism of body weight was lower at most ages in the lightest line. Before 15 wk, sexual dimorphism in X++ line was lower than in the line selected for higher BW8 and lower BW36. The increase in sexual dimorphism with body weight could be reduced by selecting animals on body weight at two ages instead of one, as is usually done in commercial lines.

Heritabilities and genetic correlations of body weights and feather length in growing Muscovy selected in Taiwan

1. Heritabilities and genetic correlations in the base population of a closed strain of Muscovy duck, moderately selected for body weight at 10 weeks of age, have been estimated from the data of 9 successive generations for the following traits : male and female body weight at 10 and 18 weeks of age (BW10m, BW18m, BW10f, BW18f) and length of the 8th primary feather at 10 weeks of age (Fl10m, Fl10f). 2. Multivariate REML with an animal model was used, pooling data from the 9 generations (3283 and 3289 male and female offspring respectively). The same trait expressed in male and female was considered as 2 different traits. 3. The 8th primary feather was longer in females than in males by 6% to 22% at 10 weeks of age. Body weight was heavier in males than in females by 42% to 58% at 10 weeks of age and by 57% to 75% at 18 weeks of age. 3. The heritability estimates for body weight traits showed moderate values, being a little higher for females than for males at the same age, increasing with age from h 2=0.24 at BW10m to h 2=0.43 at BW18f. 4. The heritability estimates for feather length showed that a greater response would be obtained in selection for male feather length (h 2=0 37) than for female length (h 2=0 14). Both have high genetic correlations with body weight so they could be indirectly improved. 5. Heritabilities of the difference in body weights between males and females at 10 weeks (h 2=0.07) and 18 weeks of age (h 2=0.10) were small, as well as for feather length (h 2=0.10). It would probably be difficult to modify sexual dimorphism in body weight through selection. 6. Genetic correlations between BW10m, BW18m and BW10f, BW18f were respectively r g =0.77 and r g =0.80. They were larger for body weight at the same ages between males and females, r g =0.90 (r g =0.88 between Fl10m and Fl10f). Body weight in males and females at the same age should be better considered as 2 different traits in a selection programme. 7. The cumulated predicted genetic gains expressed per unity of the genetic standard deviation (σg) over the 8 generations of selection were 1.3 σg and 1.4 σg respectively for the BW10m and BW10f. The predicted correlated responses were 1.2 σg for body weights at 18 weeks of age, 0.9 σg and 0.7 σg for Fl10f and Fl10m respectively.

Genetic parameters of growth curve parameters in male and female chickens

1. Individual growth curves of 7143 chickens selected for the form of the growth curve were fitted using the Laird form of the Gompertz function, BWt=BWoxe(L/K)(1-e-20) where BWt is the body weight at age, BWo the estimated hatching weight, L the initial specific growth rate and K the maturation rate. 2. Line and sex effects were significant for each parameter of the growth curve. In males, L, BWo, age and body weight at inflection (TI and BWI) were higher whereas K was lower than in females. Lines selected for high adult body weight had higher BWo and BWI whereas lines selected for high juvenile body weight had larger estimates of L and lower estimates of TI. 3. Data from 38,474 animals were included in order to estimate the genetic parameters of growth curve parameters in males and females, considering them as sex-limited traits. Genetic parameters were estimated with REML (REstricted Maximum Likelihood) and an animal model. Maternal genetic effects were also included. 4. Heritabilities of the growth curve parameters were moderate to high and ranged between 0.31 and 0.54, L, BWo in both sexes and BWI in males exhibited significant maternal heritability. Heritabilities differed between males and females for BWI and TI. Genetic correlations between sexes differed significantly from one for all parameters. L , K and TI were highly correlated but correlations involving BWo and BWI were low to moderate. 5. Sexual dimorphism of body weight at 8 and 36 weeks and of L , K and TI was moderately heritable. Selection on growth curve parameters could modify the difference between sexes in precocity and thus in body weight at a given age.

Crossbreeding effect on sexual dimorphism of body weight in intergeneric hybrids obtained between Muscovy and Pekin duck

Crossbreeding effect on sexual dimorphism of body weight in intergeneric hybrids obtained between Muscovy and Pekin duck

Crossbreeding effect on sexual dimorphism of body weight in intergeneric hybrids obtained between Muscovy and Pekin duck

Effets du croisement sur le dimorphisme sexuel en poids corporel chez les hybrides intergeneriques obtenus entre les canards de Barbarie et Pekin. Dans une experience de croisement factoriel entre deux souches de canards de Barbarie et Pekin, il apparait que le dimorphisme sexuel en faveur des mâles sur les caracteres de croissance semble dependre de la mere Barbarie en pur et dans le croisement reciproque: le rapport entre les moyennes des poids corporels prennent les valeurs de 1,19; 1,47; 1,75; 1,77; 1,84; 1,64 respectivement aux âges de 4, 10, 16, 20, 30 et 40 semaines dans la descendance Barbarie. Les resultats sont comparables dans la descendance du croisement entre mâle Pekin et femelle Barbarie. Au contraire ce rapport, lorsque la difference entre poids des mâles et des femelles est significative, prend les valeurs de 1,07 et 1,11 aux âges de 10 et 16 semaines dans la descendance des Pekin. Cela est comparable dans la descendance du croisement entre le mâle Barbarie et la cane Pekin, avec des valeurs du rapport de 1,06; 1,07 et de 1,08 respectivement aux âges de 16, 20 et 30 semaines. Ces resultats mettent en evidence une contribution de la cane Barbarie, en pur et en croisement, a l'accroissement du dimorphisme sexuel en poids par un effet depressif sur la croissance corporelle sur sa descendance femelle et non sur sa descendance mâle. Si les effets genetiques maternels sont supposes etre comparables dans les descendances mâle et femelle, le classement des quatre genotypes dans le sexe femelle peut s'interpreter en additionnant aux effets de genes lies au sexe (chromosome Z) un effet de genes qui seraient situes sur le chromosome W. Dans le cadre de l'heredite Mendelienne, on peut faire l'hypothese, outre les effets habituels chez les oiseaux de genes lies au sexe, d'un effet depressif sur la croissance de genes de la region non pseudo-autosomale du chromosome W du Barbarie, comparativement au W du Pekin, si celle-ci contient des genes codants.

Seasonal field analyses of water and fat content in the long‐lived millipede Polyzonium germanicum (Diplopoda, Polyzoniidae)

Two hundred and seventy‐nine Polyzonium germanicum individuals of various stadia were collected seasonally in winter, late spring‐early summer (the breeding period) and early autumn. Fresh weight, dry weight and defatted dry weight were determined for each specimen. Seasonal changes in water content and fat content, expressed as percentages of defatted dry weight, were analysed in relation to body size and sex. Changes in water content were more pronounced in the smallest individuals (juveniles), whereas changes in fat content were more pronounced in the largest (adults). Seasonal fluctuations in water and fat content were similar in both sexes despite the sexual dimorphism of body weight. The results suggest the following relationships within the species life‐cycle: (i) water content increases during the warm months (up to 295% for juveniles in early autumn), which coincides with the moulting period, (ii) Fat content increases subsequently to moulting; overall maxima are reached in early autumn (population mean = 62–5%), as well as in early summer for the young, (iii) Both water and fat content decrease (to about 150% and 50%, respectively) in winter; however, there is no evidence of starvation–at least in ovigerous females which increase in dry weight during that season, (iv) Fat content strongly decreases (below 30% in the largest specimens) in adults of both sexes during the breeding period.