Selection,Morphological Integration,and Strepsirrhine Locomotor Adaptations

Clades with taxa that have multiple locomotor adaptations represent a direct way to test the relationship between adaptation and integration. If integration is influenced by functional requirements, integration should be most apparent where selection is strongest and less evident where selection has been relaxed. If integration is primarily regulated by genetic constraints, integration should be present irrespective of selection pressures. Here we use patterns of integration in the strepsirrhine fore- and hind limbs as a test case. Strepsirrhine locomotion is relatively well-studied, and there are multiple clades that share different locomotor modes. We found that quadrupeds have greater limb integration than vertical leapers. These results suggest that variation can be expressed if selection for integration is relaxed. However, an unexpected pattern was revealed, in which there appears to be some broader regulatory mechanism controlling overall limb integration. Our tests identified a strong correlation between integration of the forelimb and integration of the hind limb. This broader mechanism may be evidence of the primitive genetic control of limb integration.     

Postcranial Skeleton of the Cretaceous Mammal Akidolestes cifellii and Its Locomotor Adaptations

Spalacotheroid “symmetrodontans” are a group of extinct Mesozoic mammals. They are basal taxa in the trechnotherian clade that includes modern marsupials and placentals. Therefore, fossils of spalacotheroids can provide information on the ancestral condition from which marsupials and placentals likely have evolved. Here, we describe the postcranial skeleton of Akidolestes cifellii, a spalacotheroid species from the Lower Cretaceous Yixian Formation of northeastern China. Our comparison of the skeletal features of Akidolestes and the closely related Zhangheotherium and Maotherium indicates some major morphological and functional differences in the postcranium among these spalacotheroid mammals. Akidolestes shows characters for terrestrial habitat preference. Overall it appears to be a generalized terrestrial mammal. Akidolestes differs from Zhangheotherium and Maotherium in some characteristics of the scapula, the pelvis, and the hind limb, some of which can be directly correlated with different locomotor capabilities, and possibly also habitat preferences. This suggests that a greater ecomorphological differentiation occurred in these stem therian mammals than previously thought and that ecological differentiation is a major pattern in early therian mammal evolution.     

Trabecular Bone Structure Correlates with Hand Posture and Use in Hominoids

Bone is capable of adapting during life in response to stress. Therefore, variation in locomotor and manipulative behaviours across extant hominoids may be reflected in differences in trabecular bone structure. The hand is a promising region for trabecular analysis, as it is the direct contact between the individual and the environment and joint positions at peak loading vary amongst extant hominoids. Building upon traditional volume of interest-based analyses, we apply a whole-epiphysis analytical approach using high-resolution microtomographic scans of the hominoid third metacarpal to investigate whether trabecular structure reflects differences in hand posture and loading in knuckle-walking (Gorilla, Pan), suspensory (Pongo, Hylobates and Symphalangus) and manipulative (Homo) taxa. Additionally, a comparative phylogenetic method was used to analyse rates of evolutionary changes in trabecular parameters. Results demonstrate that trabecular bone volume distribution and regions of greatest stiffness (i.e., Young''s modulus) correspond with predicted loading of the hand in each behavioural category. In suspensory and manipulative taxa, regions of high bone volume and greatest stiffness are concentrated on the palmar or distopalmar regions of the metacarpal head, whereas knuckle-walking taxa show greater bone volume and stiffness throughout the head, and particularly in the dorsal region; patterns that correspond with the highest predicted joint reaction forces. Trabecular structure in knuckle-walking taxa is characterised by high bone volume fraction and a high degree of anisotropy in contrast to the suspensory brachiators. Humans, in which the hand is used primarily for manipulation, have a low bone volume fraction and a variable degree of anisotropy. Finally, when trabecular parameters are mapped onto a molecular-based phylogeny, we show that the rates of change in trabecular structure vary across the hominoid clade. Our results support a link between inferred behaviour and trabecular structure in extant hominoids that can be informative for reconstructing behaviour in fossil primates.     

蛛网结构性能及其适应性

蛛网是蜘蛛的捕食工具,蛛网的结构性能不仅影响蜘蛛的捕食效率,也关系着蜘蛛的捕食投入。在不同的内外环境条件影响下,蜘蛛会通过蛛网结构性能上的相应变化来调整捕食策略和维持网结构的稳定性。本文主要综述了蛛网的结构性能以及蜘蛛通过蛛网结构性能表现出的对环境因子的适应性。     

Cortical Bilateral Adaptations in Rats Submitted to Focal Cerebral Ischemia: Emphasis on Glial Metabolism

This study was performed to evaluate the bilateral effects of focal permanent ischemia (FPI) on glial metabolism in the cerebral cortex. Two and 9 days after FPI induction, we analyze [¹⁸F]FDG metabolism by micro-PET, astrocyte morphology and reactivity by immunohistochemistry, cytokines and trophic factors by ELISA, glutamate transporters by RT-PCR, monocarboxylate transporters (MCTs) by western blot, and substrate uptake and oxidation by ex vivo slices model. The FPI was induced surgically by thermocoagulation of the blood in the pial vessels of the motor and sensorimotor cortices in adult (90 days old) male Wistar rats. Neurochemical analyses were performed separately on both ipsilateral and contralateral cortical hemispheres. In both cortical hemispheres, we observed an increase in tumor necrosis factor alpha (TNF-α), interleukin-1β (IL-1β), and glutamate transporter 1 (GLT-1) mRNA levels; lactate oxidation; and glutamate uptake and a decrease in brain-derived neurotrophic factor (BDNF) after 2 days of FPI. Nine days after FPI, we observed an increase in TNF-α levels and a decrease in BDNF, GLT-1, and glutamate aspartate transporter (GLAST) mRNA levels in both hemispheres. Additionally, most of the unilateral alterations were found only in the ipsilateral hemisphere and persisted until 9 days post-FPI. They include diminished in vivo glucose uptake and GLAST expression, followed by increased glial fibrillary acidic protein (GFAP) gray values, astrocyte reactivity, and glutamate oxidation. Astrocytes presented signs of long-lasting reactivity, showing a radial morphology. In the intact hemisphere, there was a decrease in MCT2 levels, which did not persist. Our study shows the bilateralism of glial modifications following FPI, highlighting the role of energy metabolism adaptations on brain recovery post-ischemia.     

What Lies Beneath: Sub-Articular Long Bone Shape Scaling in Eutherian Mammals and Saurischian Dinosaurs Suggests Different Locomotor Adaptations for Gigantism

Eutherian mammals and saurischian dinosaurs both evolved lineages of huge terrestrial herbivores. Although significantly more saurischian dinosaurs were giants than eutherians, the long bones of both taxa scale similarly and suggest that locomotion was dynamically similar. However, articular cartilage is thin in eutherian mammals but thick in saurischian dinosaurs, differences that could have contributed to, or limited, how frequently gigantism evolved. Therefore, we tested the hypothesis that sub-articular bone, which supports the articular cartilage, changes shape in different ways between terrestrial mammals and dinosaurs with increasing size. Our sample consisted of giant mammal and reptile taxa (i.e., elephants, rhinos, sauropods) plus erect and non-erect outgroups with thin and thick articular cartilage. Our results show that eutherian mammal sub-articular shape becomes narrow with well-defined surface features as size increases. In contrast, this region in saurischian dinosaurs expands and remains gently convex with increasing size. Similar trends were observed in non-erect outgroup taxa (monotremes, alligators), showing that the trends we report are posture-independent. These differences support our hypothesis that sub-articular shape scales differently between eutherian mammals and saurischian dinosaurs. Our results show that articular cartilage thickness and sub-articular shape are correlated. In mammals, joints become ever more congruent and thinner with increasing size, whereas archosaur joints remained both congruent and thick, especially in sauropods. We suggest that gigantism occurs less frequently in mammals, in part, because joints composed of thin articular cartilage can only become so congruent before stress cannot be effectively alleviated. In contrast, frequent gigantism in saurischian dinosaurs may be explained, in part, by joints with thick articular cartilage that can deform across large areas with increasing load.     

A Shared Pattern of Postnatal Endocranial Development in Extant Hominoids

By comparing species-specific developmental patterns, we can approach the question of how development shapes adult morphology and contributes to the evolution of novel forms. Studies of evolutionary changes to brain development in primates can provide important clues about the emergence of human cognition, but are hindered by the lack of preserved neural tissue in the fossil record. As a proxy, we study the shape of endocasts, virtual imprints of the endocranial cavity, using 3D geometric morphometrics. We have previously demonstrated that the pattern of endocranial shape development is shared by modern humans, chimpanzees and Neanderthals after the first year of life until adulthood. However, whether this represents a common hominoid mode of development is unknown. Here, we present the first characterization and comparison of ontogenetic endocranial shape changes in a cross-sectional sample of modern humans, chimpanzees, gorillas, orangutans and gibbons. Using developmental simulations, we demonstrate that from late infancy to adulthood ontogenetic trajectories are similar among all hominoid species, but differ in the amount of shape change. Furthermore, we show that during early ontogeny gorillas undergo more pronounced shape changes along this shared trajectory than do chimpanzees, indicative of a dissociation of size and shape change. As shape differences between species are apparent in even our youngest samples, our results indicate that the ontogenetic trajectories of extant hominoids diverged at an earlier stage of ontogeny but subsequently converge following the eruption of the deciduous dentition.     

Bone Inner Structure Suggests Increasing Aquatic Adaptations in Desmostylia (Mammalia,Afrotheria)

Background

The paleoecology of desmostylians has been discussed controversially with a general consensus that desmostylians were aquatic or semi-aquatic to some extent. Bone microanatomy can be used as a powerful tool to infer habitat preference of extinct animals. However, bone microanatomical studies of desmostylians are extremely scarce.

Methodology/Principal Findings

We analyzed the histology and microanatomy of several desmostylians using thin-sections and CT scans of ribs, humeri, femora and vertebrae. Comparisons with extant mammals allowed us to better understand the mode of life and evolutionary history of these taxa. Desmostylian ribs and long bones generally lack a medullary cavity. This trait has been interpreted as an aquatic adaptation among amniotes. Behemotops and Paleoparadoxia show osteosclerosis (i.e. increase in bone compactness), and Ashoroa pachyosteosclerosis (i.e. combined increase in bone volume and compactness). Conversely, Desmostylus differs from these desmostylians in displaying an osteoporotic-like pattern.

Conclusions/Significance

In living taxa, bone mass increase provides hydrostatic buoyancy and body trim control suitable for poorly efficient swimmers, while wholly spongy bones are associated with hydrodynamic buoyancy control in active swimmers. Our study suggests that all desmostylians had achieved an essentially, if not exclusively, aquatic lifestyle. Behemotops, Paleoparadoxia and Ashoroa are interpreted as shallow water swimmers, either hovering slowly at a preferred depth, or walking on the bottom, and Desmostylus as a more active swimmer with a peculiar habitat and feeding strategy within Desmostylia. Therefore, desmostylians are, with cetaceans, the second mammal group showing a shift from bone mass increase to a spongy inner organization of bones in their evolutionary history.     

Locomotor Ability and Wariness in Yellow-Bellied Marmots

Animals employ a variety of behaviors to reduce or manage predation risk. Often, these are studied in isolation, but selection may act on packages of behavior that are referred to as behavioral syndromes. We focused on yellow‐bellied marmots (Marmota flaviventris) and examined three commonly studied antipredator behaviors. We fitted general linear models to explain variation in maximum running speed, time allocated to vigilance and foraging during bouts of foraging, and flight initiation distance (FID). Marmot maximum running speed was influenced by the substrate run across; marmots ran fastest across dirt or low vegetation and slowest across stones or talus. Incline and several other variables shown to affect running speed in other marmot species failed to explain significant variation in yellow‐bellied marmots. From these results we expected marmots to be sensitive to substrate while foraging, but insensitive to incline. However, time allocated to foraging was affected by incline but not by substrate. In bouts of foraging observed in different habitats, and on different inclines, more time was allocated to foraging and less to vigilance on steep slopes and less on level ground. Substrate influenced FID. Marmots in tall vegetation were less tolerant of an approaching person than were those in shorter vegetation. Finally, we found significant correlations between the residuals from the maximum running speed model and the residuals from the time allocated to vigilance and foraging models. We found a tendency for marmots that ran slower than predicted to be less vigilant while foraging. We also found that relatively slow marmots engaged in more active foraging and less vigilance during foraging bouts. This finding suggests a ‘locomotor ability‐wariness while foraging’ syndrome. It also suggests that vulnerable individuals minimize their exposure while foraging.     

Locomotor strategies in obese and non-obese children

Objective: The constant strain in obese children may increase the risks of articular problems in adulthood. In the short term, obesity in children could lead to modifications of the gait pattern. The purpose of this study was to compare biomechanical parameters between obese and non‐obese children during self‐paced walking. Research Methods and Procedures: Gait analysis was performed on 10 non‐obese and 10 obese (body weight > 95th percentile) children between 8 and 13 years of age. Subjects were asked to walk at their own pace on a 10‐m walkway with two embedded AMTI force plates (Advanced Mechanical Technology, Watertown, MA) sampling at 960 Hz. Kinematics were captured with eight VICON optoelectronic cameras (Oxford Metrics Limited, Oxford, United Kingdom) recording at 60 Hz. Results: Obese children modified their hip motor pattern by shifting from extensor to flexor moment earlier in the gait cycle. This led obese children to significantly decrease the mechanical work done by the hip extensors during weight acceptance and significantly increase the mechanical work done by the hip flexors compared with non‐obese children. The ratio of power‐absorption‐by‐hip‐flexors to power‐generation‐by‐hip‐flexors was also significantly increased in the obese group compared with non‐obese children. Finally, there was a significant decrease in the single support duration in the obese group compared with non‐obese. Discussion: The kinetics analyzed showed that obese children could take advantage of a passive hip strategy to achieve forward progression during walking. However, considering that they are mechanically less efficient to transfer energy, walking at a natural cadence should be an appropriate exercise to reduce weight in obese children.     

Hominoids, hominids and the problem of the lower boundary of the Anthropogene

This paper distinguishes two phases within the Anthropogene, each being characterized by specific features of hominization: the earlier phase the Eoanthropogene, is characterized by the presence of bipedal, small-brained hominoids. These include the australopithecine and habiline fossils, all of which are classified in a separate family, the Australopithecidae. In the second phase, the Euanthropogene, the family Hominidae is present, with its two species, Homo erectus and H. sapiens. The two families, Australopithecidae and Hominidae, are united into a superfamily, the Hominoidea; whilst the pongids are placed in a separate family (Pongidae) and superfamily (Pongoidea). The bearing of the work of the Soviet palaeo-neurologist, the late V. I. Kochetkova on the status of the australopithecines, is reviewed in some detail.     

Adaptations of crop-raiding baboons in Kenya

A field study of baboon behavior as it relates to crop-raiding was conducted on the Kenya Coast. The results proved useful for quantifying the distribution, movement, and other factors of their behavior. Such variables as troop organization, crop season, and the behavior of the farmers influence raiding behavior. Apparently diversionary activities of crop-raiding baboons result from troop distribution along habitat margins between farms and forest and from baboon vigilance behavior.