Understanding muscle markers: lower limbs

Musculoskeletal markers are frequently used to reconstruct past lifestyles and activity patterns. Yet the reliability of muscle marker measurements has been called into question because they may be confounded by body size. In this study, an aggregate muscle marker variable was calculated using 20 insertion sites (14 femoral, 6 tibial), and I examined their effects on lower limb size (as a proxy for body size), age, and sex. Analyses were made of a sample of 77 (57 males, 20 females) Native British Columbians (3,500-1,500 years BP) and 18th century Quebec prisoners. Muscle markers were measured using two-point observer rating scales; size was measured by standard methods; and age and sex were determined through pelvic, cranial, and dental morphology. Lower limb muscle markers correlated with: age, r=0.61; lower limb size, r=0.52; and sex, r=0.49; P <0.001. Older individuals had higher muscle marker scores, as did larger individuals and males. Based on partial correlations and regression analyses, age was the best overall predictor of lower limb muscle markers.     

Understanding muscle markers: aggregation and construct validity

Musculoskeletal markers are frequently used to reconstruct past lifestyles and activity patterns. Yet, the reliability of muscle marker measurements has been called into question because they allegedly fail to correlate with cross-sectional properties and exercise patterns, and are confounded by body size. In this study, the principle of aggregation was used to sum muscle markers over 7 insertion sites (4 humeral, 2 radial, and 1 ulnar) and examine the effects on them of body size, age, sex, and cross-sectional properties. Analyses were made of a sample of 91 (66 males, 25 females) Native British Columbians (3500-1500 years BP) and 18th century Quebec prisoners. Muscle markers were measured using three-point observer rating scales; size was measured by standard methods; age and sex were determined through pelvic, cranial, and dental morphology; and cross-sectional properties were calculated from radiographs. Whereas any single muscle marker component failed to correlate with age, size, sex, or cross-sections, aggregate muscle marker correlated with: age, r = 0.49; size, r = 0.38; sex, r = 0.40; and, cross-sections, r = 0.38; P < 0.001. Older individuals had greater muscle markers, as did larger individuals, males, and those with more robust cross-sections. Based on partial correlations and regression analyses, age was the best overall predictor of aggregate muscle marker.     

Cranial muscle markers: A preliminary examination of size, sex, and age effects

Most muscle marker research consists of post-cranial analyses, but some researchers examine crania to reconstruct activities. Regardless of bones examined, anthropologists know of some of the complexities surrounding muscle marker development. Here, posterior cranial muscle markers are analyzed to determine whether they are useful in reconstructing activities by examining effects that may hinder reconstructions. Additionally, upper limb muscle markers and humeral cross-sectional robusticity variables are correlated with cranial muscle markers to determine if robust individuals are generally robust due to the synergistic effects of muscle use.Cranial muscle markers of 65 prehistoric California Amerinds are scored using a five-point observer rating scale. Body mass is calculated from femoral head size; maximum cranial length and breadth are measured with a spreading caliper; and age and sex are determined through standard procedures. Upper limb muscle markers are scored on seven sites using two dimensions within a seven-point scale. Cross-sectional properties are calculated from biplanar humeral radiographs. Aggregates are created for cranial muscle markers, upper limb muscle markers, and cross-sectional robusticity.Cranial muscle markers correlate significantly with cranial length, r=0.25 and cross-sectional robusticity of humerus, r=0.29; P’s<0.05. All variables differed between sexes (Mann-Whitney=31.00-307.50, P’s<0.01). Results imply that some differences in cranial muscle markers are related to size; however, individuals with well-developed cranial muscle markers have greater upper limb robusticity possibly due to activity patterns. Sex differences remained after size controls and may relate to activity differences.     

Ontogenetic adaptation to bipedalism: age changes in femoral to humeral length and strength proportions in humans, with a comparison to baboons

The increase in lower/upper limb bone length and strength proportions in adult humans compared to most other anthropoid primates is commonly viewed as an adaptation to bipedalism. The ontogenetic development of femoral to humeral proportions is examined here using a longitudinal sample of 20 individuals measured radiographically at semiannual or annual intervals from 6 months of age to late adolescence (a subset of the Denver Growth Study sample). Anthropometric data (body weights, muscle breadths) were also available at each examination age. Results show that while femoral/humeral length proportions close to those of adults are already present in human infants, characteristically human femoral/humeral diaphyseal strength proportions only develop after the adoption of bipedalism at about 1 year of age. A rapid increase in femoral/humeral strength occurs between 1 and 3 years, followed by a slow increase until mid-late adolescence, when adult proportions are reached. When age changes in material properties are factored in, femoral strength shows an almost constant relationship to body size (body mass.bone length) after 5 years of age, while humeral strength shows a progressive decline relative to body size. Femoral/humeral length proportions increase slightly throughout growth, with no apparent change in growth trajectory at the initiation of walking, and with a small decline in late adolescence due to later growth in length of the humerus. A sex difference in femoral/humeral strength proportions (females greater) but not length proportions, develops early in childhood. Thus, growth trajectories in length and strength proportions are largely independent, with strength proportions more responsive to actual changes in mechanical loading. A cross-sectional ontogenetic sample of baboons (n=30) illustrates contrasting patterns of growth, with much smaller age changes in proportions, particularly strength proportions, although there is some indication of an adaptation to altered limb loadings early in baboon development.     

Blood serum concentration of lipids and lipoproteins and body composition

The purpose of this study is the analysis of the relationship of blood serum apolipoprotein E (apoE), total cholesterol (TC), triglycerides (TG) and high-density and low-density lipoproteins (HDL, LDL), with body mass index (BMI), relative body surface area (RBSA) and body muscle (BM) and body fat (BF). The subjects are males and females aged 14-16 (adolescent age group 1: n1M = 141, n1F = 151) and 18-25 (young adult group 2, n2M = 16, n2F = 46). Significant correlations of serum TG and HDL with somatometric indicators were not observed. In the female samples, TC content directly correlates (p < 0.05) with BF (r1 = 0.164; r2 = 0.418) and negatively correlates with BM (r1 = -0.165; r2 = -0.352). The blood serum concentration of apoE is significantly correlated with body composition in adolescent females (for BF r1 = -0.168; for BM r1 = 0.266; p < 0.05); in males 14-16 years old, the both correlations have a significance level p < 0.06. In young adult females TC and LDL content negatively correlates with RBSA (r2 = -0.386 and -0.377 respectively; p < 0.05) and positively correlates with BMI (r2 = 0.413 and 0.415 respectively; p < 0.05). Adolescent females and young adult females have opposite relationships between FC and apoE concentration. In females 14-15 years old apoE concentration decreases as FC increases. In females 16-17 the correlation disappears, and in older females apoE concentration and FC increase together.     

Skeletal muscle histochemical and biochemical characteristics in sedentary male and female subjects

The purpose of this study was to assess the relationship between muscle fiber type distribution and enzymatic characteristics in sedentary male and female subjects. Muscle biopsy samples from the vastus lateralis muscle of 38 females and 37 males were analyzed to determine the fiber type composition (I, IIa, and IIb), the fiber size, and maximal activities of enzyme markers of energy metabolic pathways. Significant correlations were found (p less than 0.05) between percent fiber type I area and hexokinase (r = -0.39), phosphofructokinase (r = -0.39), lactate dehydrogenase (r = -0.41), and oxoglutarate dehydrogenase (r = 0.33) activities, whereas such correlations with total phosphorylase (r = -0.02), malate dehydrogenase (r = 0.12), and 3-hydroxyacyl CoA dehydrogenase (r = 0.12) activities were not significant. The results of the present study also suggest the presence of a significant but low covariation of less than 30% between the fiber type distribution and muscle enzyme activities. They confirm the presence of an important metabolic heterogeneity independent of the muscle fiber type distribution in sedentary male and female subjects. Moreover, these results indicate that sedentary males exhibit a lower mean value of percent fiber type I and higher glycolytic enzyme activities than sedentary females.     

Divergence in Male and Female Manipulative Behaviors with the Intensification of Metallurgy in Central Europe

Humeral morphology has been shown to reflect, in part, habitual manipulative behaviors in humans. Among Central European agricultural populations, long-term social change, increasing task specialization, and technological innovation all had the potential to impact patterns of habitual activity and upper limb asymmetry. However, systematic temporal change in the skeletal morphology of agricultural populations in this region has not been well-characterized. This study investigates diachronic patterns in humeral biomechanical properties and lengths among 174 adult Central European agriculturalists through the first ∼5400 years of farming in the region. Greater asymmetry in biomechanical properties was expected to accompany the introduction of metallurgy, particularly in males, while upper limb loading patterns were expected to be more similar between the Bronze and Iron Ages. Results revealed a divergence in the lateralization of upper limb biomechanical properties by sex between the Early/Middle Neolithic and Early/Middle Bronze Age. Neolithic females had significantly more variable properties than males in both humeri, while Bronze Age female properties became homogeneous and very symmetrical relative to the right-biased lateralization of contemporaneous males. The Bronze Age to Iron Age transition was associated with morphological change among females, with a significant increase in right-biased asymmetry and a concomitant reduction in sexual dimorphism. Relative to biomechanical properties, humeral length variation and asymmetry were low though some significant sexual dimorphism and temporal change was found. It was among females that the lateralization of humeral biomechanical properties, and variation within them, changed most profoundly through time. This suggests that the introduction of the ard and plow, metallurgical innovation, task specialization, and socioeconomic change through ∼5400 years of agriculture impacted upper limb loading in Central European women to a greater extent than men.     

Sex differences in the kinematics and neuromuscular control of landing: Biological,environmental and sociocultural factors

Potential sex differences in patterns of movement of recreational and competitive athletes were investigated in a systematic review of lower limb kinematics, muscle activation and stiffness during landing and hopping tasks. Little support for sex-specific lower limb kinematic patterns was found in 17 studies retrieved on landing and hopping. Ten studies retrieved on muscle activation during landing provided no support for sex-specific patterns. Four articles retrieved on leg stiffness established that absolute stiffness was lower in females, but differences in stiffness normalized to body mass were less clear. The wider literature indicates that a combination of biological, environmental and sociocultural constraints may shape movement patterns differently in females and males. Sociocultural factors differentially affect accumulated motor experience, practice opportunities and focus of attention in females, leading to differences in motor skill that confound the comparison of female and male movements. The findings of the review support the hypothesis that such sex differences in athletic performance are likely to diminish or disappear with increasing skill. In everyday movement tasks, however, where level of skill is a less meaningful dimension than in sport, differences in movement patterns observed between females and males point instead to the influence of subtle societal expectations on movement patterns.     

Nuclear medicine studies of aging—VII. Humeral deltoid tuberosity on bone scans and radiographs

Because of the occasional finding of increased deposition of bone imaging agent in the area of the humeral deltoid tuberosity, we analyzed both bone scans and radiographs to determine if there were age related correlations. Only 29% of patients of age 35 years or younger showed any radiographie evidence of deltoid tuberosity. This increased to 48% in the 36–64 y age group (and 46% in those of age 65 y and above). Bone scans (^99mTc-MDP) of the humerus showed that 26% of individuals of ages 20–39 y had increased uptake in the deltoid tuberosity area. The figure was 21% of those in the 85–94 y age group. However, distribution between sexes in the 20–39 y age cohort was asymmetric (44% of males showed the bone scan finding, but only 15% of the females). We then reviewed cases that had shown the most prominent deltoid tuberosity on humeral radiographs. Thirteen of the 14 cases (93%) were males. Deposition of bone imaging agent in the deltoid tuberosity region was thus only slightly correlated with age (more common after age 35 y), but strongly correlated with sex (males more common) in all three major age groups (35 and under, 36–64, and 65 years and over). Possible interrelations with bone size and muscle mass were pointed out.     

A study of the anthropometric correlations between upper limb measurements for personal identification in Sudanese population

The presence of multiple isolated commingled fleshed limbs or limb parts generates a significant challenge for forensic investigators in wars, mass disasters, and criminal assaults in the process of identification. Although upper limb measurements have been used to establish individual identity in terms of sex and stature with high success, there is a scarcity of data concerning the correlations within upper limb parts. Hence, this study aims to assess the relationships within upper limb parts and develop regression formulae to reconstruct the parts from one another. The study participants were 376 Sudanese adults (187 males and 189 females). The results of this study indicated significant sexual dimorphism for all variables. The results indicated a significant correlation within the upper limb parts. Linear and multiple regression equations were developed to reconstruct the upper limb parts in the presence of a single or multiple dimension(s) from the identical limb. Multiple regression equations generated better reconstructions than simple equations. These results are significant in forensics and orthopedic reconstructive surgery.     

Robusticity and sexual dimorphism in the postcranium of modern hunter-gatherers from Australia

Throughout much of prehistory, humans practiced a hunting and gathering subsistence strategy. Elevated postcranial robusticity and sexually dimorphic mobility patterns are presumed consequences of this strategy, in which males are attributed greater robusticity and mobility than females. Much of the basis for these trends originates from populations where skeletal correlates of activity patterns are known (e.g., cross-sectional geometric properties of long bones), but in which activity patterns are inferred using evidence such as archaeological records (e.g., Pleistocene Europe). Australian hunter-gatherers provide an opportunity to critically assess these ideas since ethnographic documentation of their activity patterns is available. We address the following questions: do skeletal indicators of Australian hunter-gatherers express elevated postcranial robusticity and sexually dimorphic mobility relative to populations from similar latitudes, and do ethnographic accounts support these findings. Using computed tomography, cross-sectional images were obtained from 149 skeletal elements including humeri, radii, ulnae, femora, and tibiae. Cross-sectional geometric properties were calculated from image data and standardized for body size. Australian hunter-gatherers often have reduced robusticity at femoral and humeral midshafts relative to forager (Khoi-San), agricultural/industrialized (Zulu), and industrialized (African American) groups. Australian hunter-gatherers display more sexual dimorphism in upper limb robusticity than lower limb robusticity. Attributing specific behavioral causes to upper limb sexual dimorphism is premature, although ethnographic accounts support sex-specific differences in tool use. Virtually absent sexual dimorphism in lower limb robusticity is consistent with ethnographic accounts of equivalently high mobility among females and males. Thus, elevated postcranial robusticity and sexually dimorphic mobility do not always characterize hunter-gatherers.     

Studies on the biology of reproduction in the cichlid Tilapia nilotica (L.): gonadal maturation and fecundity

Tilapia nilotica reaches maturity in the first year of life; females mature shortly before males (11·4 and 14·3 cm in length). The distinctive morphological features of the different stages of development of the gonads are characterized. The sex ratio varied in populations of different age (size)-groups: a ratio of 2·81:1 and 0·47:1 (females:males) was obtained in populations of young and old fish. In medium-sized populations the sexes were equally abundant. There is evidence that females breed more than once a season. Fecundity varied more with body length ( r =0·860) and weight ( r =0·806) than with age ( r =0·604). These variations were of the order of 2·02; 0·83 and 0·83 exponentials of length, weight and age, respectively.     

Sex differences in humeral bilateral asymmetry in two hunter‐gatherer populations: California Amerinds and British Columbian Amerinds

This study uses two prehistoric Amerindian populations of hunter‐gatherer subsistence patterns to determine whether levels of sexual dimorphism in humeral bilateral cross‐sectional asymmetry are related to sex‐specific differences in activities among these populations. Results confirmed that males of the California Amerind population who engaged in the more unimanual activities of spear hunting and warfare were more asymmetrical than were their female counterparts who engaged in the more bimanual activities of grinding acorns. California Amerind males were also more asymmetrical than British Columbian Amerind males who rowed (using both arms) extensively. Sex differences within British Columbian Amerinds were not statistically significant, nor were female differences between populations. In general, levels of humeral asymmetry appear to be more dependent on sex and population‐specific behaviors rather than broad subsistence patterns. Am J Phys Anthropol 2009. © 2009 Wiley‐Liss, Inc.     

Age Structure of Two Species of Odorous Frogs(Odorrana margaretae and Odorrana grahami)

Variation in age structure and body size benefits are identified to understand the evolution of life history. Here, we estimated the age structure and body size of two species of odorous frogs(Odorrana margaretae and Odorrana grahami) by using skeletochronology. The ages at sexual maturity of O. grahami and O. margaretae in both sexes were 1 and 2 years, respectively. For both sexes, the maximum age observed in O. margaretae was six years. For O. grahami, the maximum age observed in males and females were 4 and 5 years, respectively. Males and females did not differ in mean age in the two species.The average body size of both species considerably differed between sexes, with females being larger than males. The body size of females was also larger than that of males when the effect of age was removed. We also found positive correlations between body size and age within each sex in O. margaretae, but only for female in O. grahami. The female-biased sexual size dimorphism of the two species suggested that fecundity selection for larger female size may increase the reproductive output.     

中国壮侗语族人群的肌肉分布及其与年龄的关系

为了解壮侗语族族群肌肉分布特点以及探讨随年龄增长壮侗语族族群各个部位肌肉量变化的基本特点,使用人体脂肪测量仪采用生物电阻抗法在海南、贵州、广西、云南、湖南五个省、自治区测量了壮侗语族13个族群的身体肌肉量。总样本量为5098例（男性为2126例,女性为2972例）。采用握力计测量了2685例男性和3793例女性的左手、右手握力。研究发现,壮侗语族族群男性、女性肌肉量总体评价接近标准,上下肢肌肉量判断属于标准水平。男性、女性均为躯干肌肉量最大,下肢肌肉量次之,上肢肌肉量最小。男性总肌肉量、四肢肌肉量、躯干肌肉量都大于女性。男性3个年龄组间总肌肉量、躯干肌肉量、上肢肌肉量、右下肢肌肉量的差异具有统计学意义,而左下肢肌肉量彼此接近;女性3个年龄组间总肌肉量、四肢肌肉量、躯干肌肉量差异均具有统计学意义。男性除左下肢肌肉量外,其余5项肌肉量指标均与年龄呈显著负相关关系;女性总肌肉量、躯干肌肉量与年龄呈显著负相关,但四肢肌肉量与年龄无显著负相关。壮侗语族族群肌肉量少于北方族群,具有中国南方族群的特点。在南方族群中,壮侗语族族群男性肌肉量中等,女性肌肉量略多一些。     

Tracing prehistoric activities: musculoskeletal stress marker analysis of a Stone-Age population on the island of Gotland in the Baltic sea

The skeletal remains from the Middle Neolithic (2750-2300 BC) burial ground at Ajvide, Gotland, are analyzed in order to explore musculoskeletal patterns and to attempt to trace general as well as three specific prehistoric activities (archery, harpooning, and kayaking) that are likely to have been performed in this marine setting of fishing, hunting, and gathering. Scoring of muscular and ligament attachments is performed using the scoring method of Hawkey and Merbs ([1995] Int. J. Osteoarchaeol. 5:324-338) for muskuloskeletal stress markers (MSM). The skeletal material consists of 24 male and 15 female adult individuals divided into three age groups: young (<24 years), middle (25-39 years), and old (>40 years). Thirty upper body MSM sites, on both the left and right sides, are scored and form the basis of the study. Results show that males most frequently have higher mean MSM scores than females. Bilateral asymmetry was noted as low in both sexes. Age proved to be a contributing factor to increased MSM scores, with a greater age-related increase in females. MSM patterns were analyzed statistically in muscle groups associated with the three investigated activities. Significant positive correlations were observed in male individuals in muscle groups associated with archery and to some extent harpooning, an indication that these activities would mainly have been performed by men. Correlations in kayaking muscles were not evidently consistent with the kayaking motion. Furthermore, the costoclavicular ligament, often referred to in connection with "kayaker's clavicle," showed no positive statistical correlation with the kayaking muscles.     

Sexual differences in locomotor performance in Tropidurus catalanensis lizards (Squamata: Tropiduridae) – body shape,size and limb musculature explain variation between males and females

Sexual dimorphism (SD) is the evolutionary outcome of selection acting differently on males and females. Several studies describe sexual differences in body size, although other morphological traits might be allometric between sexes and imply functional consequences. Here we test whether morphological differences between sexes in size and shape in the lizard Tropidurus catalanensis explain variation in performance of four locomotor traits. Our results show that males are larger than females and also exhibit longer limbs, longer muscles and larger muscle cross‐sectional areas, while females have longer trunks and more sharped anterior claws; males outperform females in all locomotor performances measured. Sexual differences in sprinting and climbing is related with body size, and climbing performance is also explained by limb lengths, by differences in lengths and cross‐sectional areas of specific muscles, and by interlimb distances. Between‐sex differences in exertion are also related to SD, despite associations with sharper posterior claws that are independent of sex. Grasping performance, however, is associated with some muscle and morphological parameters that are not sexually dimorphic. Together our results suggest that morphology might be under sexual selection in T. catalanensis, given that better locomotor performance likely favours male lizards in typical activities of this polygenic species, such as territory defence and female acquisition. Moreover, the longer trunks that characterize females may confer more space to accommodate eggs. On the other hand, territory defence by males probably increases their exposure to predators, resulting in a synergistic effect of sexual and natural selection in the evolution of SD in T. catalanensis.     

Measurement of serum leptin concentrations in university undergraduates by competitive ELISA reveals correlations with body mass index and sex

Synthesized mainly in adipocytes, leptin is a peptide hormone that plays a key role in the regulation of body weight and composition. The serum leptin concentrations of 193 Singapore university medical and bioscience undergraduates aged 19-26 yr were measured using a competitive ELISA kit, and their leptin levels were correlated with sex and body mass index (BMI). Mean leptin levels were more than twice as high in females than in males of corresponding weight status, especially among females of healthy weight who exhibited levels that were 5.7 times higher. Overweight individuals generally demonstrated higher circulating leptin concentrations than healthy-weight and underweight participants. The differences in mean leptin levels between underweight and overweight males (P = 0.006), as well as between healthy-weight and overweight males (P = 0.011) were statistically significant. Comparison tests of leptin levels between healthy-weight and underweight females were highly significant (P = 0.001). Highly significant linear correlations between BMI and the logarithm of leptin concentration were observed in the female (r = 0.44) and male (r = 0.36) groups. These results reiterate the impact of gonadal steroids as mediators of the apparent sexual dimorphism in circulating leptin. The findings also corroborate evidence that adiposity determines leptin levels. This laboratory exercise has educational value for undergraduates by determining their BMIs, by alluding to the importance of maintaining healthy body composition, and by emphasizing the molecular mechanisms of body weight regulation and obesity, with special reference to leptin. This practical study also exemplifies the principles and applications of the competitive ELISA technique and integrates certain key concepts of physiology, molecular biology, immunology, and medicine.     

Identification of a male-specific AFLP marker in a functionally dioecious fig,<Emphasis Type="Italic"> Ficus fulva</Emphasis> Reinw. ex Bl. (Moraceae)

A male-specific amplified fragment length polymorphism (AFLP) marker was identified in the functionally dioecious fig species, Ficus fulva. A total of 89 polymorphic fragments from three primer combinations were produced, of which one (246 bp) was present in all males (n=23) and absent in all females (n=24) of two populations. This strong association suggests a tight chromosomal linkage between the AFLP marker and the sex-controlling locus. Further analysis indicated that the marker segregated in open-pollinated progenies from natural populations in a 1:1 ratio (n=156), implying that males are the heterogametic sex. Chromosome preparations showed no evidence for morphologically distinct sex chromosomes. The low frequencies of associated markers argue against a morphologically cryptic non-recombining sex chromosome. The sex-locus is therefore likely to be autosomal. The male-specific AFLP marker was sequenced and converted into a sequence characterised amplified region (SCAR) marker. This SCAR marker produced a fragment of equal size in males and females, suggesting that sequence divergence between male- and female-specific chromosomal regions is low.Publication 3311 NIOO-KNAW Netherlands Institute of Ecology     

No differential consequences of reproduction according to sex in Juniperus communis var. depressa (Cupressaceae)

In dioecious plant species, males and females are thought to have dissimilar allocation patterns. Females are believed to invest more in reproduction and less in growth and maintenance than males. This differential investment between sexes could result in distinct growth patterns and contrasting survival rates, thereby affecting the sex ratio of a population and the age and size distribution of males and females, possibly leading to habitat segregation according to sex. These effects might become more apparent under particularly limiting conditions, such as in nutrient-deficient soils or in climatically stressed environments. To verify these predictions, growth patterns, microsite characteristics, and age and size distribution of male and female individuals were compared, and population sex ratio was determined in three populations of the dioecious shrub Juniperus communis var. depressa (Cupressaceae, Pinophyta) along a short latitudinal gradient on the eastern coast of Hudson Bay (Northern Québec, Canada). We found that the northernmost population had a male-biased sex ratio, but that the southernmost one had a higher proportion of females. Our results failed to reveal any significant differences in radial growth patterns, mean sensitivity, annual elongation of the main axis, and size and age frequency distribution between males and females in any population. Furthermore, there was no evidence of microhabitat segregation according to sex as indicated by the lack of differences in the physicochemical characteristics of the substrate under males and females. Clearly, the expected ecological consequences of a presumed greater investment of females in reproduction were not apparent even under the very stressful conditions prevailing on subarctic dunes. Many factors could reduce differences in the cost of reproduction between males and females, such as the number and quality of reproductive structures produced annually by individuals of each sex, the possible photosynthetic activity of the immature female cones, and the complexity of the source/sink relationship within individuals. Alternatively, there may be no differences between sexes in their reproductive investment.