Humeral cross-sectional morphology from 18th century Quebec prisoners of war: Limits to activity reconstruction

This study uses measures of cross-sectional robusticity and asymmetry (based on humeral areal and inertial cross-sectional components) to test a prediction from bone remodeling theory that a physically active 18th century Quebec prisoner of war sample (N = 25) should have more robust and asymmetrical humeri than a nonphysically active 20th century New Mexico suburbanite sample (N = 27). Narrative accounts document that prisoners of war engaged in labor-intensive activities, and these activities were confirmed by observations of osteoarthritis and other pathologies. The suburbanite sample, for the most part, did not engage in such activities. The prisoners had higher levels of pathology than the suburbanites (e.g., 80% vs. 22% osteoarthritis; F = 17.95, P < 0.01). For robusticity, the populations did not differ significantly in total area, cortical area, moment areas of inertia about the mediolateral plane, or polar moment area of inertia. The Quebec prison sample did have significantly higher values for moment areas of inertia about the anteroposterior plane. For asymmetry, the populations did not differ in any values (total area, cortical area, moment areas of inertia about the mediolateral plane, moment areas of inertia about the anteroposterior plane, or polar moment of inertia). Thus, examinations of cross-sectional robusticity and asymmetry failed to conclusively confirm the hypothesis that intensive labor leads to changes in humeral morphology. Possible explanations for the lack of differences are discussed, such as poor diet impeding bone remodeling. Nevertheless, the one significant finding suggests that cross-sectional shape is more useful in reconstructing activity patterns than amount of bone in a cross section. Results from this study join those from other recent investigations to suggest that additional controls are required before cross-sectional differences may be confidently attributed to activity patterns.     

Relationship of cranial robusticity to cranial form,geography and climate in Homo sapiens

Variation in cranial robusticity among modern human populations is widely acknowledged but not well‐understood. While the use of “robust” cranial traits in hominin systematics and phylogeny suggests that these characters are strongly heritable, this hypothesis has not been tested. Alternatively, cranial robusticity may be a response to differences in diet/mastication or it may be an adaptation to cold, harsh environments. This study quantifies the distribution of cranial robusticity in 14 geographically widespread human populations, and correlates this variation with climatic variables, neutral genetic distances, cranial size, and cranial shape. With the exception of the occipital torus region, all traits were positively correlated with each other, suggesting that they should not be treated as individual characters. While males are more robust than females within each of the populations, among the independent variables (cranial shape, size, climate, and neutral genetic distances), only shape is significantly correlated with inter‐population differences in robusticity. Two‐block partial least‐squares analysis was used to explore the relationship between cranial shape (captured by three‐dimensional landmark data) and robusticity across individuals. Weak support was found for the hypothesis that robusticity was related to mastication as the shape associated with greater robusticity was similar to that described for groups that ate harder‐to‐process diets. Specifically, crania with more prognathic faces, expanded glabellar and occipital regions, and (slightly) longer skulls were more robust than those with rounder vaults and more orthognathic faces. However, groups with more mechanically demanding diets (hunter‐gatherers) were not always more robust than groups practicing some form of agriculture. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

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.     

Skeletal biology and behavior in ancient humans

For many years, it has been known that archaic hominids had more robust long bones than do living populations, a fact that has been linked to their more physically strenuous lives. But many questions remain. How much stronger, for example, were Neanderthals than living humans? And what does this difference in strength tell us about the behavior of our ancestors? Recent research has shown that some of our earlier assumptions about robusticity and behavior in earlier humans are either simplistic or untrue. For example, it is now clear that although earlier humans were, on the average, stronger than living peoples, this is not invariably the case. Some modern human groups have even stronger humeri than those of Neanderthals. The fact that changes in robusticity do not always neatly coincide with subsistence or technological change suggests that interpretations derived in large measure from stone-tool technology and other artifactual evidence may be misleading. This new information on physical strength in earlier humans necessitates a reassessment of traditional ideas about earlier human behavior.     

Seedling performance in a trioecious cactus,Pachycereus pringlei: Effects of maternity and paternity

We studied seed germination and the growth and survivorship of seedlings of females and hermaphrodites ofPachycereus pringlei (cardon), a Mexican columnar cactus whose geographically variable breeding system includes trioecy and gynodioecy. Results of a two-year field experiment conducted near Bahia Kino, Sonora, Mexico and a ten-month laboratory experiment were similar and did not support the hypothesis that seedlings of females outperform those of hermaphrodites. In the field, percent seed germination and 2-yr seedling survivorship averaged 66% and 95%, respectively and did not differ among six treatment classes. Seedlings of hermaphrodites generally were larger than those of females at the end of both experiments. Selfed seedlings of hermaphrodites did not grow more slowly than outcrossed seedlings of hermaphrodites or females. Hermaphrodite seedlings performed best when pollinated with hermaphrodite pollen; female seedlings performed best with male pollen. We conclude that superior seedling performance cannot explain why females are able to coexist with hermaphrodites in populations of this cactus. Instead, we postulate that greater annual seed production, which averaged 1.6 times higher in females than in hermaphrodites in two years, may be sufficient to allow females to co-occur with hermaphrodites in this large, longlived plant, especially if sex determination involves cytoplasmic-nuclear inheritance.     

内蒙古和林格尔土城子农业人群与林西井沟子游牧人群股骨中部的生物力学对比

肢骨的形态结构可以反映人类进化、古代人群的生存适应性活动和生存环境等重要信息。基于“骨骼功能适应”和“杠杆原理”,有学者对不同生计方式的古代人群下肢股骨开展了大量的研究工作,但是,国内外尚未有关于农业人群和游牧人群股骨之间差异性研究的报道。本文选取两个具有代表性的古代人群,即内蒙古和林格尔土城子戍边农业人群和内蒙古林西井沟子游牧人群进行对比研究。通过对股骨骨干中部横断面生物力学分析发现,农业人群股骨粗壮度与游牧人群之间具有显著差异。前者的平均粗壮度较大,后者女性组下肢骨的活动强度明显较小,这可能与游牧人群经常从事骑马活动而下肢骨活动强度相对较少有关。农业人群股骨指数的变异范围均大于游牧人群,这可能与前者男性的士兵身份有关;同时,也提示土城子男性组股骨所反映的行为活动信息并不代表真正意义上的纯农业人群下肢骨行为模式,而是一种农业和士兵行为的混合模式。在性别分工上,井沟子组的男女性均从事骑马活动,两侧股骨受力较为一致,在两侧不对称性程度和骨干横断面形状上的男女差异不大;男性股骨的粗壮度要明显大于女性,这与井沟子组男性还从事一定的狩猎行为有关。与游牧人群女性较为纤细的股骨不同,土城子组女性作为典型的农业人群代表,其下肢骨整体的活动强度较大,几乎与同组的男性和井沟子组男性相当,组内的性别差异相对较小;骨干横断面形状的显著性差异说明,土城子组内部男性和女性的行为活动方式存在明显的性别分工。本文研究结果说明农业人群女性的下肢骨活动强度较大,在行为活动方式上,戍边农业人群具有更为明显的性别分工。     

Changes in metatarsal robusticity following experimental surgery

When a marginal metatarsal (M1 or M5) is amputated in neonatal rats, robusticity increases in all other metatarsals in both sexes. The robusticity increase is greatest in the metatarsal adjacent to the operation and declines in the direction away from it. The tripod structure of the rat's foot with its maximum robusticity of the marginal metatarsals is retained. When both marginal metatarsals are removed, this tripod arrangement is less clearly retained. When robusticity of all remaining metatarsals is averaged in a total robusticity quotient, total robusticity increase is greater in M1 than in M5 removal and greatest when both are removed. Total increase is greater in females than in males. Metatarsal robusticity increases result from retardation of longitudinal growth and increase of weight. The fact that some robusticity increases coincide with lesser length but not with increased weight suggests that in the process of robusticity increase longitudinal growth retardation precedes that of weight increase. Lesser length and greater weight of a long bone occurs also when hypofunction is produced in neonatal rats. However, in hypofunction the thickness of the compacta is increased leading to an obliteration of the medullary canal, while in the experimental metatarsals of this study, submitted to greater weight-bearing stresses, this canal is never reduced or obliterated.     

Habitual throwing and swimming correspond with upper limb diaphyseal strength and shape in modern human athletes

Variation in upper limb long bone cross‐sectional properties may reflect a phenotypically plastic response to habitual loading patterns. Structural differences between limb bones have often been used to infer past behavior from hominin remains; however, few studies have examined direct relationships between behavioral differences and bone structure in humans. To help address this, cross‐sectional images (50% length) of the humeri and ulnae of university varsity‐level swimmers, cricketers, and controls were captured using peripheral quantitative computed tomography. High levels of humeral robusticity were found in the dominant arms of cricketers, and bilaterally among swimmers, whereas the most gracile humeri were found in both arms of controls, and the nondominant arms of cricketers. In addition, the dominant humeri of cricketers were more circular than controls. The highest levels of ulnar robusticity were also found in the dominant arm of cricketers, and bilaterally amongst swimmers. Bilateral asymmetry in humeral rigidity among cricketers was greater than swimmers and controls, while asymmetry for ulnar rigidity was greater in cricketers than controls. The results suggest that more mechanically loaded upper limb elements––unilaterally or bilaterally––are strengthened relative to less mechanically loaded elements, and that differences in mechanical loading may have a more significant effect on proximal compared to distal limb segments. The more circular humerus in the dominant arm in cricketers may be an adaptation to torsional strain associated with throwing activities. The reported correspondence between habitual activity patterns and upper limb diaphyseal properties may inform future behavioral interpretations involving hominin skeletal remains. Am J Phys Anthropol 2009. © 2009 Wiley‐Liss, Inc.     

Effect of mobility on femur midshaft external shape and robusticity

This study investigates differences in femur midshaft shape, robusticity, and sexual dimorphism derived from external measurements between a broad range of prehistoric and historic North American populations with different subsistence strategies and inferred levels of mobility. The sample was divided into six groups to test whether observed femur midshaft variables follow the patterns predicted based on archaeologically and historically determined subsistence and mobility data. The results suggest significant variation in femur midshaft shape and robusticity in all populations, and that inferred mobility levels do not correspond consistently with femur midshaft structure in either males or females. Results do, however, support the prediction that sexual dimorphism is generally greater in more mobile populations.     

Metatarsal robusticity in bipedal rats

All metatarsals have a significantly greater robusticity in the male than in the female rat. The robusticity formula of the rat's foot is 1 > 5 > 2 > 3 > 4. In bipedal rats that formula remains unchanged, but the robusticity of the metatarsals is increased especially in females. The tripod arrangement of the human foot with its particular robustness of the marginal metatarsals 1 and 5 and a strong calcaneum has been related to upright posture. The similar robusticity pattern in the rat's marginal metatarsals 1 and 5 raises the question of whether that part of the formula might not represent a more general plantigrade pattern.     

Dry environments promote the establishment of females in monomorphic populations of <Emphasis Type="Italic">Wurmbea biglandulosa</Emphasis> (Colchicaceae)

In flowering plants, the evolution of dimorphic breeding systems from monomorphic ancestors can be associated with dry environments. One hypothesis to explain this pattern is that seed fertility of hermaphrodites decreases more than seed fertility of females under dry conditions, so that females have greater relative fitness. This could occur if seed production of hermaphrodites is more resource-limited than that of females, or shifts in pollination increase levels of selfing and inbreeding depression in hermaphrodites. Here we assess the role of dry environments in promoting a female fitness advantage in Wurmbea biglandulosa by focusing on monomorphic and dimorphic populations that occur along a longitudinal gradient of decreasing rainfall. Dimorphic populations occurred in sites with higher temperatures, lower rainfall and lower soil moisture. Overall, females had greater seed fertility than did hermaphrodites from monomorphic populations, which in turn had greater seed fertility than hermaphrodites from dimorphic populations. Ovuliferous flower and ovule production by the three gender morphs and seed fertility of females and hermaphrodites in monomorphic populations did not vary with soil moisture. By contrast, seed fertility of hermaphrodites in dimorphic populations was positively related to soil moisture. Accordingly, female frequency was higher in those sites where hermaphrodites produced relatively fewer seeds. Taken together our results indicate that dry environments promote the establishment of females by decreasing the relative seed fitness of hermaphrodites. Moreover, because seed fertility of hermaphrodites in monomorphic populations did not vary with soil moisture, resource limitation of female function may play only a minor role in the establishment of females. Other factors such as shifts in pollination and mating patterns of hermaphrodites could be involved. Key words:breeding system evolution, environmental stress, gender dimorphism, gynodioecy, sex ratio variationCo-ordinating editor: J.F. Stuefer     

Biomechanical approach to the reconstruction of activity patterns in Neolithic Western Liguria, Italy

This paper investigates the changes in upper and lower limb robusticity and activity patterns that accompanied the transition to a Neolithic subsistence in western Liguria (Italy). Diaphyseal robusticity measures were obtained from cross-sectional geometric properties of the humerus and femur in a sample of 16 individuals (eight males and eight females) dated to about 6,000-5,500 BP. Comparisons with European Late Upper Paleolithics (LUP) indicate increased humeral robusticity in Neolithic Ligurian (NEOL) males, but not in females, with a significant reduction in right-left differences in both sexes. Sexual dimorphism in robusticity increases in upper and lower limb bones. Regarding the femur, while all female indicators of bending strength decrease steadily through time, values for NEOL males approach those of LUP. This suggests high, and unexpected, levels of mechanical stress for NEOL males, probably reflecting the effects of the mountainous terrain on lower limb remodeling. Comparisons between NEOL males and a small sample of LUP hunter-gatherers from the same area support this interpretation. In conclusion, cross-sectional geometry data indicate that the transition to Neolithic economies in western Liguria did not reduce functional requirements in males, and suggest a marked sexual division of labor involving a more symmetrical use of the upper limb, and different male-female levels of locomotory stress. When articulated with archaeological, faunal, paleopathological, and ethnographic evidence, these results support the hypothesis of repetitive, bimanual use of axes tied to pastoral activities in males, and of more sedentary tasks linked to agriculture in females.     

Maintenance of gynodioecy in Wurmbea biglandulosa (Colchicaceae): gender differences in seed production and progeny success

 In gynodioecious species, females contribute genes to future generations only through ovules, and to persist in populations they must have a compensatory advantage compared with hermaphrodites that reproduce via ovules and pollen. This compensation can result from greater fecundity and/or superior success of progeny from females. We examined differences in seed production and progeny success between females and hermaphrodites in the geophyte Wurmbea biglandulosa to explain the maintenance of females. Females produced more ovuliferous flowers and had more ovules per flower than did hermaphrodites but this did not necessarily result in greater fecundity, in part because seed production of females was pollen-limited. Over four years in one population, open-pollinated females produced 1.32 more seeds than open-pollinated hermaphrodites (range 1.09–1.63). In two other populations examined for one year only females produced 1.07 and 0.79 as many seeds as hermaphrodites. Seed production of open-pollinated females and hermaphrodites was only 55% and 73% that of cross-pollinated plants, respectively, indicating that both genders were pollen-limited but females more so than hermaphrodites. Open-pollinated seeds from females were 1.18–1.27 times more likely to germinate than seeds from hermaphrodites. No gender differences existed in seedling growth or survival. Hermaphrodites were self-compatible, but selfed seed set was only 80% that of crossed seed set. Crossed seed set of females and hermaphrodites did not differ. Assuming nuclear control of male sterility, relative female fitness is insufficient to maintain females at their current frequencies of 17%, and substantial female fitness advantages at later life-cycle stages are required. Received May 4, 2001 Accepted February 25, 2002     

Brood desertion in Kentish Plover Charadrius alexandrinus: an experimental test of parental quality and remating opportunities

Uniparental male care combined with polyandry is rare in birds, and the best known examples are in shorebirds Charadrii. There are two current hypotheses explaining why males care for the brood, whereas females desert and remate: either males are more capable than females at providing uniparental care (“parental quality hypothesis”) or females gain a greater increase in reproductive success by deserting than do males (“remating opportunity hypothesis”). I experimentally tested both hypotheses in Kentish Plover Charadrius alexandrinus, one of the few avian species in which either parent may desert the brood. By experimentally removing one parent when the chicks hatched, I found that male-tended broods had better survival than female-tended ones, particularly up to 6 days after hatching. It is unlikely that differential brood mortality was caused by chilling of the chicks, since the brooding behaviour of males and females was not different. The results of this study are consistent with the explanation that male-tended broods survived better because males were better able to protect the brood from attacks by conspecifics and predators. The remating opportunity hypothesis was also corroborated because single females acquired new mates faster than did single males. The results of this study suggest that both the better parental capability of males and the greater remating opportunities of females predispose Kentish Plovers for uniparental male care, desertion by the female parent and sequential polyandry.     

Relationships between lower limb cross-sectional geometry and mobility: the case of a Neolithic sample from Italy

This study investigates the relationships between lower limb robusticity and mobility in a Neolithic sample (LIG) from Italy (6th millennium BP). This study tests the hypothesis that the high femoral robusticity previously observed in the LIG sample is a consequence of the subsistence strategy (i.e., high mobility on uneven terrain) practiced by LIG. Cross-sectional geometric properties of the femur and tibia at midshaft of LIG (eight males and eight females) were collected and results compared to Late Upper Paleolithic (12 males, five females), Mesolithic (24 males, 8 females), and Eneolithic (28 males, 17 females) samples from other sites throughout Europe. The results show that the LIG sample does not show the reduction of lower limb robusticity that is characteristic of the Eneolithic sample, but rather that the LIG sample is most similar to the earlier, highly mobile, populations. This high level of robusticity in the LIG sample could reflect both their pastoral subsistence strategy combined with a rugged environment, as well as their earlier temporal position within the Neolithic. The results of this study further point to significant variation in male-female mobility patterns in the region, also possibly related to pastoral behavioral patterns.     

Morphological and genetic predictors of parental care in the North American barn swallow Hirundo rustica erythrogaster

Sexually dimorphic traits often signal the fitness benefits an individual can provide to potential mates. In species with altricial young, these signals may also predict the level of parental care an individual is expected to provide to shared offspring. In this study, we tested three hypotheses that traditionally relate sexually dimorphic traits to parental care in two populations of North American barn swallows Hirundo rustica erythrogaster. The good parent hypothesis predicts a positive relationship between an individual's ornamentation and his or her care whereas the differential allocation (more care given by individuals when paired to high quality mates) and reproductive compensation (more care given by individuals when paired to low quality mates) hypotheses predict that an individual's level of parental investment is relative to the quality of their mate. Male and female North American barn swallows have colorful ventral feathers and elongated tail streamers, but there is evidence that ventral color, not tail streamer length, predicts measures of seasonal reproductive success. Accounting for the positive correlation between within‐pair feeding rates and other potentially confounding variables in all of our models, we found no support for the good parent hypothesis because in both males and females, traits shown to be under sexual selection did not predict feeding rates in either sex. However, our data reveal that male coloration, and not streamer length, predicted a female's provisioning rate to shared offspring (females fed more when paired with darker individuals) in two separate populations, supporting the differential allocation, but not the reproductive compensation hypothesis. Because genetic traits have also been shown to affect parental investment, we evaluated this variable as well and found that a male's paternity did not have significant effects on either male or female feeding rates. Overall, our results suggest that females do not pair with darker males in order to gain direct benefits in terms of his expected levels of parental care to shared offspring, but do themselves invest greater levels of care when paired to darker males. Further, our results are consistent with previous studies which suggest that ventral feather color, not streamer length, is a target of sexual selection in North American populations of barn swallow because females invested more in their offspring when paired to darker mates.     

Scent-marking behaviour by male prairie voles,Microtus ochrogaster,in response to the scent of opposite- and same-sex conspecifics

We conducted an experiment using the prairie vole (Microtus ochrogaster) to test predictions associated with the proposed functions of scent marking as a sexual attractant, in reproductive competition, and as a self-advertisement. We allowed an oestrous female, an anoestrous female, and an adult male to scent mark three portions of a clean substrate and then exposed a second male to this substrate for secondary marking. We did not support a sexual attraction hypothesis in that males did not place more scent marks in response to oestrous than anoestrous females. Similarly, we did not support a reproductive competition hypothesis in that males did not place more scent marks in response to marks of males than to those of females or bare substrate. Males did not overmark the scent of males or females and thus we did not support a scent-masking or scent-blending hypothesis. In that males deposited scent similarly in response to males, females, and on bare substrate, our results suggest that the frequency and placement of scent marks by males function primarily to advertise individual identity in an area.     

Age changes in the external dimensions of adult bone

Humeri from a large, ossuary-derived sample are used to demonstrate that considerable size variability is introduced to transverse skeletal measurements when young adults and older adults are pooled. Humeri from young adults (epiphyseal lines still visible, N ≈? 25) are smaller in transverse dimensions than those of older adults (N ≈? 300). Among left humeri, only shaft diameters demonstrate statistically significant differences. The right humeri, however, show statistically significant differences for six of the eight measurements. The increased size of the older adult humeri reflects the fact that appositional growth continues throughout adulthood. The more pronounced differences seen on the right side probably reflect developing dominance asymmetry. Recognition of this source of intrasample variability will influence the choice of skeletal measurements used for population comparisons and/or indicators of robusticity.     

Activity patterns in the Sahara Desert: an interpretation based on cross-sectional geometric properties

The Garamantian civilization flourished in modern Fezzan, Libya, between 900 BC and 500 AD, during which the aridification of the Sahara was well established. Study of the archaeological remains suggests a population successful at coping with a harsh environment of high and fluctuating temperatures and reduced water and food resources. This study explores the activity patterns of the Garamantes by means of cross-sectional geometric properties. Long bone diaphyseal shape and rigidity are compared between the Garamantes and populations from Egypt and Sudan, namely from the sites of Kerma, el-Badari, and Jebel Moya, to determine whether the Garamantian daily activities were more strenuous than those of other North African populations. Moreover, sexual dimorphism and bilateral asymmetry are assessed at an intra- and inter-population level. The inter-population comparisons showed the Garamantes not to be more robust than the comparative populations, suggesting that the daily Garamantian activities necessary for survival in the Sahara Desert did not generally impose greater loads than those of other North African populations. Sexual dimorphism and bilateral asymmetry in almost all geometric properties of the long limbs were comparatively low among the Garamantes. Only the lower limbs were significantly stronger among males than females, possibly due to higher levels of mobility associated with herding. The lack of systematic bilateral asymmetry in cross-sectional geometric properties may relate to the involvement of the population in bilaterally intensive activities or the lack of regular repetition of unilateral activities.