The ontogeny of sexual dimorphism in the African apes

The relationship between the growth spurt and the onset of sexual maturity is problematic in nonhuman primates. Growth data on the cranium and postcranium of dentally aged pygmy chimpanzees, common chimpanzees, and gorillas are reported here. In all three species, male means generally exceed female means throughout growth, with the exception that females exhibit a spurt during one dental-age stage when they become generally larger than the males. This female spurt occurs earlier in an absolute and relative sense in the gorillas than the chimpanzees. These growth data support field and laboratory observations suggesting that female gorillas become sexually mature earlier than do female chimpanzees. Gorillas are thus characterized by a greater degree of “sexual bimaturism” than are the chimpanzees. Implications of these differences in terms of size dimorphism, mating systems, and morphology are discussed.     

Sexual dimorphism in growth from 8 to 18 years

A mixed longitudinal study of growth and development has been conducted, centering on an analysis of differences based on sex between the ages of 8 and 18 years for a series of 12 anthropometric indicators. The sample consisted of 50 girls and 63 boys. Proceeding from the specific differences, the variables can be divided into four groups with identical structures of differences. The first group comprises measurements of body height, body mass, shoulder width and pelvic span, all of which have higher values in boys between 8 and 10 and between 14 and 18. Between the ages of 11 and 13 girls are taller, heavier, with broader shoulders and pelvises. The second group covers measurements of subcutaneous fat. which are higher for girls throughout the period under review. The third group of indicators comprises the diameters of the joints of the extremities, i.e. of elbows and knees. Throughout the period under observation, these measurements are higher in boys, with the absolute differences between the sexes being the same at the age of 8 and ten years later. The fourth group consists of circumferences measurements of the extremities. It was found that calf circumferences manifested a specific inversion of the curves between 14 and 15, with girls showing a larger calf circumference up to the age of 14, and boys from the age of 15. The effect of earlier onset of puberty in girls was found to be reflected only on the inversion of the curve flow of the variables from the first group.     

Sexual dimorphism and allometry of external morphology in Oreochromis mossambicus

Sexual dimorphism in growth of conventional morphometric characters was investigated in juveniles and young adults (size range: 31 to 91 mm) of Oreochromis mossambicus . A closely associated set of traits was identified that shows sexually dimorphic growth, which was positively allometric in the males. These traits correspond to two different morphological complexes: jaw structure and anal/dorsal fins. The best sex discriminators among this set of traits were premaxilla width, anal fin height and snout length. These findings may be explained in terms of intra– and inter–sexual selection acting together and favouring males with strong and large mouths and high dorsal and anal fins, traits that are important in agonistic displays (jaw and fins), fighting and nest digging (jaw).     

Growth patterns in the modern human skeleton

This study investigates cross sectional growth patterns in the human skeleton using a recent skeletal sample of known age and sex. Measurements were selected to reflect different functional regions of the cranium, mandible and post cranial skeleton, and growth is evaluated using a single phase Gompertz curve. Different parts of the skeleton vary in the proportion of adult size attained at birth and in their subsequent rate of attainment of adult size. The paper introduces a method for the objective and quantitative comparison of the growth of different samples, and is used in this instance to analyze sexual differences in the growth of the post cranial skeleton. The development of sexual dimorphism is evaluated in terms of differences in the rate and duration of male and female growth. Adult sexual dimorphism is generally lower in early growing variables than in later-growing variables. There is considerable diversity in the ontogenetic basis of sexual dimorphism in the human skeleton demonstrating that the development of sexual dimorphism within a species should not be regarded as a uniform phenomenon. Am J Phys Anthropol 105:57–72, 1998. © 1998 Wiley-Liss, Inc.     

奇台沙蜥生长过程中的两性异形

研究奇台沙蜥Phrynocephalus grumgrzimailoi头、尾、腋胯距大小在个体发育过程中的变化.成体体长(SVL)无显著的两性差异,两性异形主要表现为雄性个体有较大的头部(头长和头宽)和尾部,雌性具有较大的腋胯距.头、尾、腋胯距大小的两性异形在幼体就已存在,并随个体发育的进行变得更加显著.不同年龄组两性个体头部、尾部、腋胯距随SVL呈异速增长,表现为两性头部的增长速率在个体发育过程中逐渐增大,尾部的增长速率逐渐减慢,腋胯距在雌性蜥蜴中增长速率逐渐增大,在雄性中逐渐变小.     

Comparative Perspectives on Bimaturism, Ontogeny, and Dimorphism in Lemurid Primates

We address questions regarding the general absence of dimorphism in lemurid primates (Hapalemur, Eulemur, and Varecia) through comparative analyses of ontogeny. We described and analyzed body mass growth data for 9 lemurid taxa and compared them to similar data for anthropoid primates. Lemurids tend to grow rapidly over a short period of time when compared to anthropoid primates of similar body sizes. Size variation among lemurid taxa arises primarily as a consequence of differences in rates of growth. Comparative analyses of body mass growth data suggest that natural selection has produced ontogenetic adaptations in lemurids that center on relatively short periods of growth. Reduced growth periods preclude the evolution of sexual dimorphism through bimaturism—a sex difference in the length of the growth period—despite high levels of intermale competition. Selective factors related to seasonal variability of lemurid habitats play important roles in limiting the potential for the evolution of bimaturism. Other selective factors that limit bimaturism are related to female reproductive synchrony. In combination, they favor relatively early male maturation, precluding sexual selection that would otherwise promote the evolution of dimorphism through bimaturism. Natural selection on growth rates may preclude somatic responses to sexual selection that involve elevated male growth rates. In general, existing ontogenetic or life history adaptations appear to restrict responses to sexual selection in male lemurids.     

Relative growth and morphological sexual maturity of the deep-water velvet shrimp Metapenaeopsis sibogae (Crustacea,Decapoda, Penaeidae)

Metapenaeopsis sibogae inhabits the South Pacific and Southeast Asia and is an emerging fisheries resource. However, studies on the population biology of M. sibogae are scant, and their morphometric relationships have not been examined. Thus, we studied the relative growth of M. sibogae, hypothesizing that its morphological sexual maturity can be estimated based on abrupt shifts in allometry. The relationships of body length (BL) and body weight (BW) with carapace length (CL) were determined by the least squares method. Data for each sex were repeatedly partitioned into two size-delimited subsets (early and late phases), considering a CL value as a hypothesized transition point. Analysis of the sum of squared residuals indicated that two separate linear BL/CL models fit the data better than a single linear model showing clear transition points in both males (13.2 mm CL) and females (15.0 mm CL). The changes in allometry in the BL/CL relationships between early- and late-phased males and females were indicated by a 20.5 and 21.5% decrease in the slope, respectively. These transition points could be associated with sexual maturity. The growth rate of BW vs. CL slowed significantly after morphological sexual maturity was reached in both sexes, demonstrating the existence of dimorphic growth.