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.     

Intensity,repetitiveness, and directionality of habitual adolescent mobility patterns influence the tibial diaphysis morphology of athletes

Mobility patterns affect the loads placed on the lower limbs during locomotion and may influence variation in lower limb diaphyseal robusticity and shape. This relationship commonly forms the basis for inferring mobility patterns from hominin fossil and skeletal remains. This study assesses the correspondence between athletic histories, varying by loading intensity, repetition and directionality, measured using a recall questionnaire, and peripheral quantitative computed tomography‐derived measurements of tibial diaphysis rigidity and shape. Participants included male university varsity cross‐country runners (n = 15), field hockey players (n = 15), and controls (n = 20) [mean age: 22.1 (SD +/? 2.6) years]. Measurements of tibial rigidity (including J, %CA, I_max, I_min, and average cortical thickness) of both runners and field hockey players were greater than controls (P ≤ 0.05). Differences in tibial shape (I_max/I_min, P ≤ 0.05) between runners and hockey players reflect pronounced maximum plane (I_max) rigidity in runners, and more symmetrical hypertrophy (I_max, I_min) among hockey players. This corresponds with the generally unidirectional locomotor patterns of runners, and the multidirectional patterns of hockey players. These results support the relationship between mobility and tibial diaphysis morphology as it is generally interpreted in the anthropological literature, with greater levels of mobility associated with increased diaphyseal robusticity and shape variation. Although exercise intensity may be the primary influence on these properties, the repetitiveness of the activity also deserves consideration. In conclusion, bone morphological patterns can reflect habitual behaviors, with adaptation to locomotor activities likely contributing to variation in tibial rigidity and shape properties in archaeological and fossil samples. Am J Phys Anthropol 2009. © 2009 Wiley‐Liss, Inc.     

Adaptation to bipedal gait and fifth metatarsal structural properties in Australopithecus,Paranthropus, and Homo

Humans, unlike African apes, have relatively robust fifth metatarsals (Mt5) presumably reflecting substantial weight-bearing and stability function in the lateral column of the former. When this morphological difference emerged during hominin evolution is debated. Here we investigate internal diaphyseal structure of Mt5s attributed to Australopithecus (from Sterkfontein), Paranthropus (from Swartkrans), and Homo (from Olduvai, Dmanisi, and Dinaledi) placed in the context of human and African ape Mt5 internal diaphyseal structure. ‘Whole-shaft’ properties were evaluated from 17 cross sections sampling 25% to 75% diaphyseal length using computed tomography. To assess structural patterns, scaled cortical bone thicknesses (sCBT) and scaled second moments of area (sSMA) were visualized and evaluated through penalized discriminant analyses. While the majority of fossil hominin Mt5s exhibited ape-like sCBT, their sSMA were comparatively more human-like. Human-like functional loading of the lateral column existed in at least some fossil hominins, although perhaps surprisingly not in hominins from Dmanisi or Dinaledi.     

Osteoclast‐specific Dicer gene deficiency suppresses osteoclastic bone resorption

Osteoclasts are unique cells that resorb bone, and are involved in not only bone remodeling but also pathological bone loss such as osteoporosis and rheumatoid arthritis. The regulation of osteoclasts is based on a number of molecules but full details of these molecules have not yet been understood. MicroRNAs are produced by Dicer cleavage an emerging regulatory system for cell and tissue function. Here, we examine the effects of Dicer deficiency in osteoclasts on osteoclastic activity and bone mass in vivo. We specifically knocked out Dicer in osteoclasts by crossing Dicer flox mice with cathepsin K‐Cre knock‐in mice. Dicer deficiency in osteoclasts decreased the number of osteoclasts (N.Oc/BS) and osteoclast surface (Oc.S/BS) in vivo. Intrinsically, Dicer deficiency in osteoclasts suppressed the levels of TRAP positive multinucleated cell development in culture and also reduced NFATc1 and TRAP gene expression. MicroRNA analysis indicated that expression of miR‐155 was suppressed by RANKL treatment in Dicer deficient cells. Dicer deficiency in osteoclasts suppressed osteoblastic activity in vivo including mineral apposition rate (MAR) and bone formation rate (BFR) and also suppressed expression of genes encoding type I collagen, osteocalcin, Runx2, and Efnb2 in vivo. Dicer deficiency in osteoclasts increased the levels of bone mass indicating that the Dicer deficiency‐induced osteoclastic suppression was dominant over Dicer deficiency‐induced osteoblastic suppression. On the other hand, conditional Dicer deletion in osteoblasts by using 2.3 kb type I collagen‐Cre did not affect bone mass. These results indicate that Dicer in osteoclasts controls activity of bone resorption in vivo. J. Cell. Biochem. 109: 866–875, 2010. © 2009 Wiley‐Liss, Inc.     

Shared human-chimpanzee pattern of perinatal femoral shaft morphology and its implications for the evolution of hominin locomotor adaptations

Background

Acquisition of bipedality is a hallmark of human evolution. How bipedality evolved from great ape-like locomotor behaviors, however, is still highly debated. This is mainly because it is difficult to infer locomotor function, and even more so locomotor kinematics, from fossil hominin long bones. Structure-function relationships are complex, as long bone morphology reflects phyletic history, developmental programs, and loading history during an individual’s lifetime. Here we discriminate between these factors by investigating the morphology of long bones in fetal and neonate great apes and humans, before the onset of locomotion.

Methodology/Principal Findings

Comparative morphometric analysis of the femoral diaphysis indicates that its morphology reflects phyletic relationships between hominoid taxa to a greater extent than taxon-specific locomotor adaptations. Diaphyseal morphology in humans and chimpanzees exhibits several shared-derived features, despite substantial differences in locomotor adaptations. Orangutan and gorilla morphologies are largely similar, and likely represent the primitive hominoid state.

Conclusions/Significance

These findings are compatible with two possible evolutionary scenarios. Diaphyseal morphology may reflect retained adaptive traits of ancestral taxa, hence human-chimpanzee shared-derived features may be indicative of the locomotor behavior of our last common ancestor. Alternatively, diaphyseal morphology might reflect evolution by genetic drift (neutral evolution) rather than selection, and might thus be more informative about phyletic relationships between taxa than about locomotor adaptations. Both scenarios are consistent with the hypothesis that knuckle-walking in chimpanzees and gorillas resulted from convergent evolution, and that the evolution of human bipedality is unrelated to extant great ape locomotor specializations.     

Using genetic evidence to evaluate four palaeoanthropological hypotheses for the timing of Neanderthal and modern human origins

A better understanding of the evolutionary relationship between modern humans and Neanderthals is essential for improving the resolution of hominin phylogenetic hypotheses. Currently, four distinct chronologies for the timing of population divergence are available, ranging from the late Middle Pleistocene to the late Early Pleistocene, each based on different interpretations of hominin taxonomy. Genetic data can present an independent estimate of the evolutionary timescale involved, making it possible to distinguish between these competing models of hominin evolution. We analysed five dated Neanderthal mitochondrial genomes, together with those of 54 modern humans, and inferred a genetic chronology using multiple age calibrations. Our mean date estimates are consistent with a process of genetic divergence within an ancestral population, commencing approximately 410-440 ka. These results suggest that a reappraisal of key elements in the Pleistocene hominin fossil record may now be required.     

Reconstructing cranial evolution in an extinct hominin

Homo erectus is the first hominin species with a truly cosmopolitan distribution and resembles recent humans in its broad spatial distribution. The microevolutionary events associated with dispersal and local adaptation may have produced similar population structure in both species. Understanding the evolutionary population dynamics of H. erectus has larger implications for the emergence of later Homo lineages in the Middle Pleistocene. Quantitative genetics models provide a means of interrogating aspects of long-standing H. erectus population history narratives. For the current study, cranial fossils were sorted into six major palaeodemes from sites across Africa and Asia spanning 1.8–0.1 Ma. Three-dimensional shape data from the occipital and frontal bones were used to compare intraspecific variation and test evolutionary hypotheses. Results indicate that H. erectus had higher individual and group variation than Homo sapiens, probably reflecting different levels of genetic diversity and population history in these spatially disperse species. This study also revealed distinct evolutionary histories for frontal and occipital bone shape in H. erectus, with a larger role for natural selection in the former. One scenario consistent with these findings is climate-driven facial adaptation in H. erectus, which is reflected in the frontal bone through integration with the orbits.     

Increased bone mass is a part of the generalized lymphoproliferative disorder phenotype in the mouse

We investigated the bone phenotype of mice with generalized lymphoproliferative disorder (gld) due to a defect in the Fas ligand-mediated apoptotic pathway. C57BL/6-gld mice had greater whole body bone mineral density and greater trabecular bone volume than their wild-type controls. gld mice lost 5-fold less trabecular bone and had less osteoclasts on bone surfaces after ovariectomy-induced bone resorption. They also formed more bone in a model of osteogenic regeneration after bone marrow ablation, had less osteoclasts on bone surfaces and less apoptotic osteoblasts. gld and wild-type mice had similar numbers of osteoclasts in bone marrow cultures, but marrow stromal fibroblasts from gld mice formed more alkaline phosphatase-positive colonies. Bone diaphyseal shafts and bone marrow stromal fibroblasts produced more osteoprotegerin mRNA and protein than wild-type mice. These findings provide evidence that the disturbance of the bone system is a part of generalized lymphoproliferative syndrome and indicates the possible role of osteoprotegerin as a regulatory link between the bone and immune system.     

The ontogeny of Holocene and Late Pleistocene human postcranial strength

While a wide variety of studies have focused on population variation in adult cross‐sectional properties, relatively little is known about population variation in postcranial robusticity in immature individuals. Furthermore, the age at which the population differences readily detected in adults manifest during growth is also unknown. This research addresses these gaps in our current understanding through the analysis of immature humeral and femoral long bone strength. Cross‐sectional geometry was used to compare the developmental trajectories of diaphyseal strength in Late Pleistocene Neandertal and modern human subadults to a sample of immature humans from seven geographically diverse Holocene populations. Population differences in size‐standardized cross‐sectional properties appear to be systemic and develop very early in ontogeny in the Holocene sample. In many cases, these differences are present before one year of age. In general, the Late Pleistocene fossil samples fit within the range of recent human variation in long bone strength. Population differences detected here are likely related to a combination of factors including activity patterns, genetic propensities, and nutritional status. These results highlight the complex mosaic of processes that result in adult postcranial robusticity, and suggest that further exploration of the developmental interplay between intrinsic and extrinsic influences on skeletal robusticity will likely enhance our understanding of adult postcranial morphology. Am J Phys Anthropol 2010. © 2009 Wiley‐Liss, Inc.     

Emerging patterns of genetic variation in the New Zealand endemic scallop Pecten novaezelandiae

Both historical and contemporary processes influence the genetic structure of species, but the relative roles of such processes are still difficult to access. Population genetic studies of species with recent evolutionary histories such as the New Zealand endemic scallop Pecten novaezelandiae (<1 Ma) permit testing of the effects of recent processes affecting gene flow and shaping genetic structure. In addition, studies encompassing the entire distributional range of species can provide insight into colonization processes. Analyses of genetic variation in P. novaezelandiae (952 individuals from 14 locations, genotyped at 10 microsatellite loci) revealed a weak but significant regional structure across the distributional range of the species, as well as latitudinal gradients of genetic diversity and differentiation: estimates of migration rates supported these patterns. Our results suggest that the observed genetic structure and latitudinal gradients reflect a stepping‐stone model of colonization (north to south) and emerging divergence of populations as a result of ongoing limitations to gene flow and insufficient time to reach migration–drift equilibrium. The low levels of interpopulation and interregional genetic differentiation detected over hundreds of kilometres reflect the recent evolutionary history of P. novaezelandiae and stand in contrast to patterns reported for other evolutionary older species at the same spatial scale. The outcomes of this study contribute to a better understanding of evolutionary processes influencing the genetic variation of species and provide vital information on the genetic structure of P. novaezelandiae.     

Declining tibial curvature parallels ∼6150 years of decreasing mobility in central european agriculturalists

Long bones respond to mechanical loading through functional adaptation in a suite of morphological characteristics that together ensure structural competence to in vivo loading. As such, adult bone structure is often used to make inferences about past behavior from archaeological remains. However, such biomechanical approaches often investigate change in just one aspect of morphology, typically cross‐sectional morphology or trabecular structure. The relationship between longitudinal bone curvature and mobility patterns is less well understood, particularly in the tibia, and it is unknown how tibial curvature and diaphyseal cross‐sectional geometry interact to meet the structural requirements of loading. This study examines tibial curvature and its relationship with diaphyseal cross‐sectional geometry (CSG) and body size in preindustrial Central Europeans spanning ～6150 years following the introduction of agriculture in the region. Anteroposterior centroid displacement from the proximo‐distal longitudinal axis was quantified at nine diaphyseal section locations (collectively representative of diaphyseal curvature) in 216 tibial three‐dimensional laser scans. Results documented significant and corresponding temporal declines in midshaft centroid displacement and CSG properties. Significant correlations were found between mid‐diaphyseal centroid displacement and all mobility‐related CSG properties, while the relationship weakened toward the diaphyseal ends. No significant relationship was found between centroid displacement and body size variables with the exception of the most distal section location. Results support a relationship between tibial curvature and cross‐sectional geometry among prehistoric Central European agricultural populations, and suggest that changes in mechanical loading may have influenced a suite of morphological features related to bone adaptation in the lower limb. Am J Phys Anthropol 157:260–275, 2015. © 2015 Wiley Periodicals, Inc.     

Articular to diaphyseal proportions of human and great ape metatarsals

This study proposes a new way to use metatarsals to identify locomotor behavior of fossil hominins. Metatarsal head articular dimensions and diaphyseal strength in a sample of chimpanzees, gorillas, orangutans, and humans (n = 76) are used to explore the relationships of these parameters with different locomotor modes. Results show that ratios between metatarsal head articular proportions and diaphyseal strength of the hallucal and fifth metatarsal discriminate among extant great apes and humans based on their different locomotor modes. In particular, the hallucal and fifth metatarsal characteristics of humans are functionally related to the different ranges of motion and load patterns during stance phase in the forefoot of humans in bipedal locomotion. This method may be applicable to isolated fossil hominin metatarsals to provide new information relevant to debates regarding the evolution of human bipedal locomotion. The second to fourth metatarsals are not useful in distinguishing among hominoids. Further studies should concentrate on measuring other important qualitative and quantitative differences in the shape of the metatarsal head of hominoids that are not reflected in simple geometric reconstructions of the articulation, and gathering more forefoot kinematic data on great apes to better understand differences in range of motion and loading patterns of the metatarsals. Am J Phys Anthropol 143:198–207, 2010. © 2010 Wiley‐Liss, Inc.     

中更新世晚期中国古人类化石的形态多样性及其演化意义

近年对许家窑、许昌、华龙洞、澎湖、夏河、哈尔滨等人类化石开展的系统研究,引发了学界对中更新世晚期人类演化及分类的不同认识。基于对相关中国人类化石形态特征的分析,作者提出这一时期中国人类化石形态特征表现为四种类型：1）以中更新世晚期人类共有特征为主;2）以原始特征为主;3）以现代特征为主;4）独特形态组合。多数化石形态特征表现为前三种类型,而许昌和许家窑这种以硕大的头骨和巨大颅容量构成的独特形态组合在其他同时期化石还没有发现。化石形态的多样性提示,不同类型的中更新世晚期中国古人类对现代人的形成贡献不同。作者认为在该时期的人类化石形态多样性规律还未阐明的情况下,将具有混合或镶嵌特征的相关人类化石归入分类地位不确定的人群较为合适。     

Hominin Obstetrics and the Evolution of Constraints

Birth is significantly more complicated and dangerous in modern humans than in other great apes. This disparity is often hypothesized to be the result of evolutionary constraints on obstetric dimensions related to bipedalism and/or thermoregulation in later hominins. Previous attempts to test such hypotheses have used biomechanical methods and results have been mixed. But evolutionary constraints, restrictions or limitations on the course or outcome of evolution, are the result of an interaction between selective pressures and genetic constraints—the latter revealed in patterns of integration. Integration between traits can result in directional or stabilizing selection on one trait leading to correlated responses in other traits, which can bias and constrain evolutionary trajectories. Therefore, trait evolution may be constrained for reasons separate from those that can be estimated using biomechanical models, and to study evolutionary constraints it is necessary to understand the role genetic constraints play in morphological change. The results presented here show that genetic constraints can significantly reduce the evolutionary potential of the birth canal to evolve in humans, apes, and likely earlier hominins, but also point to an overall reduction in the level of constraints during hominin evolution. These findings suggest that divergent selection pressures for obstetric requirements and other pelvic functions in hominins reduced levels of genetic constraint on birth canal evolution, likely lowering the amount of time needed for evolutionary change, and permitting morphological evolution along a trajectory that might have previously been difficult or impossible to traverse.     

Bone loss induced by Runx2 Over‐expression in mice is blunted by osteoblastic over‐expression of TIMP‐1

The Runx2 gene is essential for osteoblast differentiation and function. In vivo over‐expression of Runx2 in osteoblasts increases bone resorption, and blocks terminal osteoblast differentiation. Several lines of evidence suggest that osteoblastic matrix metalloproteinases (MMPs) could contribute to the increased bone resorption observed in mice over‐expressing Runx2 (Runx2 mice). The goal of our study was to use a transgenic approach to find out whether the inhibition of osteoblastic MMPs can reduce the bone loss induced by the over‐expression of Runx2. We analyzed the effect of the in vivo over‐expression of the TIMP‐1 in osteoblasts on the severe osteopenic phenotype in Runx2 mice. Females with the different genotypes (WT, Runx2, TIMP‐1 and TIMP‐1/Runx2) were analyzed for bone density, architecture, osteoblastic and osteoclastic activity and gene expression using qPCR. TIMP‐1 over‐expression reduces the bone loss in adult Runx2 mice. The prevention of the bone loss in TIMP‐1/Runx2 mice was due to a combination of reduced bone resorption and sustained bone formation. We present evidence that the ability of osteoblastic cells to induce osteoclastic differentiation is lower in TIMP‐1/Runx2 mice than in Runx2 mice, probably due to a reduction in the expression of RANK‐L and of the Runx2 transgene. Osteoblast primary cells from TIMP‐1/Runx2 mice, but not from Runx2 mice, were able to differentiate into fully mature osteoblasts producing high osteocalcin levels. In conclusion, our findings suggest that osteoblastic MMPs can affect osteoblast differentiation. Our work also indicates that osteoblastic MMPs are partly responsible for the bone loss observed in Runx2 transgenic mice. J. Cell. Physiol. 222:219–229, 2010. © 2009 Wiley‐Liss, Inc.     

Estrogen, exercise, and the skeleton

Patterns of variation in bone size and shape provide crucial data for reconstructing hominin paleobiology, including ecogeographic adaptation, life history, and functional morphology. Measures of bone strength, including robusticity (diaphyseal thickness relative to length) and cross-sectional geometric properties such as moments of area, are particularly useful for inferring behavior because bone tissue adapts to its mechanical environment. Particularly during skeletal growth, exercise-induced strains can stimulate periosteal modeling so that, to some extent, bone thickness reflects individual behavior. Thus, patterns of skeletal robusticity have been used to identify gender-based activity differences, temporal shifts in mobility, and changing subsistence strategies. Although there is no doubt that mechanical loading leaves its mark on the skeleton, less is known about whether individuals differ in their skeletal responses to exercise. For example, the potential effects of hormones or growth factors on bone-strain interactions are largely unexplored. If the hormonal background can increase or decrease the effects of exercise on skeletal robusticity, then the same mechanical loads might cause different degrees of bone response in different individuals. Here I focus on the role of the hormone estrogen in modulating exercise-induced changes in human bone thickness.     

GPCR kinase 2 interacting protein 1 (GIT1) regulates osteoclast function and bone mass

G‐protein‐coupled receptor (GPCR) kinase 2 interacting protein‐1 (GIT1) is a scaffold protein expressed in various cell types including neurons, endothelial, and vascular smooth muscle cells. The GIT1 knockout (KO) mouse has a pulmonary phenotype due to impaired endothelial function. Because GIT1 is tyrosine phosphorylated by Src kinase, we anticipated that GIT1 KO should have a bone phenotype similar to Src KO. Microcomputed tomography of the long bones revealed that GIT1 KO mice have a 2.3‐fold increase in bone mass compared to wild‐type controls. Histomorphometry showed increased trabecular number and connectivity suggesting impaired bone remodeling. Immunoblot analysis of GIT1 expression showed that it was expressed in both osteoclasts and osteoblasts. Osteoblast activity and function assayed by alkaline phosphatase, mineral nodule formation, and in vivo calcein labeling were normal in GIT1 KO mice suggesting that the observed increase in bone mass was due to an osteoclast defect. GIT1 KO bone marrow cells differentiated into multinucleated osteoclasts, but had defective bone resorbing function on dentin slices. This defect was likely caused by loss of podosome belt based on immunofluorescence analysis and previous studies showing that GIT1 is required for podosome formation. Furthermore, we found that GIT1 was a regulator of receptor activator of NFκB (RANK) signaling since it was tyrosine phosphorylated in a Src‐dependent manner and was required for phospholipase C‐γ2 phosphorylation. These data show that GIT1 is a key regulator of bone mass in vivo by regulating osteoclast function and suggest GIT1 as a potential target for osteoporosis therapy. J. Cell. Physiol. 225: 777–785, 2010. © 2010 Wiley‐Liss, Inc.     

Epigenetic Effects on Integration of Limb Lengths in a Mouse Model: Selective Breeding for High Voluntary Locomotor Activity

Mammals exhibit a similar pattern of integration among homologous limb elements, the strength of which is believed to vary in response to selection for functional coordination or similarity. Although integration is hypothesized to primarily reflect the effect of genes intrinsic to limbs, extrinsic genetic or epigenetic factors may also affect the strength of integration through their impact on the magnitude and direction of skeletal variance or covariance. Such factors as neuromuscular coordination or bone-muscle interactions may therefore play a role in both canalization and the structure or magnitude of limb integration. If this were the case, then increased levels of locomotor activity would be predicted to increase canalization and the magnitude of covariation between limbs. To investigate whether postnatal activity levels can have a significant effect on variance within or covariance among homologous limb elements, we compared four groups of male mice from a long-term selective breeding experiment: (1) mice from lines bred for increased voluntary activity on running wheels and allowed free access to a wheel for 8 weeks beginning at weaning (“active”), (2) selected mice that did not have wheel access (“sedentary”), (3) active mice from non-selected control lines, and (4) sedentary control mice. Mice from selected lines that had wheel access ran significantly more than control-line mice. However, when controlled for activity, linetype, and body mass, results indicate few significant differences in means, variance, or covariation structure, and no significant differences in integration between limbs, suggesting that postnatal activity levels do not significantly affect canalization or integration of limb lengths. A possible explanation for this result is that whereas baseline levels of postnatal activity may help to maintain patterns of variance and integration, increased levels of activity do not further increase these measures. Investigations into disrupted epigenetic processes (e.g., via models in which neuromuscular coordination is impaired) are required to further test hypotheses about how canalization or integration of limb variation is affected by epigenetic factors.     

Evolutionary history shapes the association between developmental instability and population‐level genetic variation in three‐spined sticklebacks

Developmental instability (DI) is the sensitivity of a developing trait to random noise and can be measured by degrees of directionally random asymmetry [fluctuating asymmetry (FA)]. FA has been shown to increase with loss of genetic variation and inbreeding as measures of genetic stress, but associations vary among studies. Directional selection and evolutionary change of traits have been hypothesized to increase the average levels of FA of these traits and to increase the association strength between FA and population‐level genetic variation. We test these two hypotheses in three‐spined stickleback (Gasterosteus aculeatus L.) populations that recently colonized the freshwater habitat. Some traits, like lateral bone plates, length of the pelvic spine, frontal gill rakers and eye size, evolved in response to selection regimes during colonization. Other traits, like distal gill rakers and number of pelvic fin rays, did not show such phenotypic shifts. Contrary to a priori predictions, average FA did not systematically increase in traits that were under presumed directional selection, and the increases observed in a few traits were likely to be attributable to other factors. However, traits under directional selection did show a weak but significantly stronger negative association between FA and selectively neutral genetic variation at the population level compared with the traits that did not show an evolutionary change during colonization. These results support our second prediction, providing evidence that selection history can shape associations between DI and population‐level genetic variation at neutral markers, which potentially reflect genetic stress. We argue that this might explain at least some of the observed heterogeneities in the patterns of asymmetry.