Proposed mechanism for the selection of lactase persistence in childhood.

Lactase persistence/persistent (LP), the ability to express the lactase enzyme in adults, is one of the most strongly selected phenotypes in humans. It is encoded by at least five genetic variants that have rapidly become widespread in various human populations. The underlying selective mechanism is not clear however, because dairy products in general are well tolerated in adults, even by lactase non-persistence/persistent (LNP) individuals. Cultural adaptations to milk consumption, notably fermentation and transformation, which can provide most of the energy (protein, fat) to both LP and LNP individuals without any associated cost seem to have been common in ancient societies. Here, we propose that selection for LP occurred through increased glucose/galactose (energy) from fresh milk intake in early childhood, a crucial period for growth. At the age of weaning indeed, lactase activity has already begun to decline in LNP individuals so the gain in energy from fresh milk by LP children represents a major fitness increase.

Hurricane-induced selection on the morphology of an island lizard.

Hurricanes are catastrophically destructive. Beyond their toll on human life and livelihoods, hurricanes have tremendous and often long-lasting effects on ecological systems1,2. Despite many examples of mass mortality events following hurricanes3-5, hurricane-induced natural selection has not previously been demonstrated. Immediately after we finished a survey of Anolis scriptus-a common, small-bodied lizard found throughout the Turks and Caicos archipelago-our study populations were battered by Hurricanes Irma and Maria. Shortly thereafter, we revisited the populations to determine whether morphological traits related to clinging capacity had shifted in the intervening six weeks and found that populations of surviving lizards differed in body size, relative limb length and toepad size from those present before the storm. Our serendipitous study, which to our knowledge is the first to use an immediately before and after comparison6 to investigate selection caused by hurricanes, demonstrates that hurricanes can induce phenotypic change in a population and strongly implicates natural selection as the cause. In the decades ahead, as extreme climate events are predicted to become more intense and prevalent7,8, our understanding of evolutionary dynamics needs to incorporate the effects of these potentially severe selective episodes9-11.

Early euprimates already had a diverse locomotor repertoire: Evidence from ankle bone morphology.

The morphological adaptations of euprimates have been linked to their origin and early evolution in an arboreal environment. However, the ancestral and early locomotor repertoire of this group remains contentious. Although some tarsal bones like the astragalus and the calcaneus have been thoroughly studied, the navicular remains poorly studied despite its potential implications for foot mobility. Here, we evaluate early euprimate locomotion by assessing the shape of the navicular-an important component of the midtarsal region of the foot-using three-dimensional geometric morphometrics in relation to quantified locomotor repertoire in a wide data set of extant primates. We also reconstruct the locomotor repertoire of representatives of the major early primate lineages with a novel phylogenetically informed discriminant analysis and characterize the changes that occurred in the navicular during the archaic primate-euprimate transition. To do so, we included in our study an extensive sample of naviculars (36 specimens) belonging to different species of adapiforms, omomyiforms, and plesiadapiforms. Our results indicate that navicular shape embeds a strong functional signal, allowing us to infer the type of locomotion of extinct primates. We demonstrate that early euprimates displayed a diverse locomotor behavior, although they did not reach the level of specialization of some living forms. Finally, we show that the navicular bone experienced substantial reorganization throughout the archaic primate-euprimate transition, supporting the major functional role of the tarsus during early primate evolution. This study demonstrates that navicular shape can be used as a reliable proxy for primate locomotor behavior. In addition, it sheds light on the diverse locomotor behavior of early primates as well as on the archaic primate-euprimate transition, which involved profound morphological changes within the tarsus, including the navicular bone.

Hurricane effects on Neotropical lizards span geographic and phylogenetic scales.

Extreme climate events such as droughts, cold snaps, and hurricanes can be powerful agents of natural selection, producing acute selective pressures very different from the everyday pressures acting on organisms. However, it remains unknown whether these infrequent but severe disruptions are quickly erased by quotidian selective forces, or whether they have the potential to durably shape biodiversity patterns across regions and clades. Here, we show that hurricanes have enduring evolutionary impacts on the morphology of anoles, a diverse Neotropical lizard clade. We first demonstrate a transgenerational effect of extreme selection on toepad area for two populations struck by hurricanes in 2017. Given this short-term effect of hurricanes, we then asked whether populations and species that more frequently experienced hurricanes have larger toepads. Using 70 y of historical hurricane data, we demonstrate that, indeed, toepad area positively correlates with hurricane activity for both 12 island populations of Anolis sagrei and 188 Anolis species throughout the Neotropics. Extreme climate events are intensifying due to climate change and may represent overlooked drivers of biogeographic and large-scale biodiversity patterns.

Ecomorphological diversification in squamates from conserved pattern of cranial integration.

Factors intrinsic and extrinsic to organisms dictate the course of morphological evolution but are seldom considered together in comparative analyses. Among vertebrates, squamates (lizards and snakes) exhibit remarkable morphological and developmental variations that parallel their incredible ecological spectrum. However, this exceptional diversity also makes systematic quantification and analysis of their morphological evolution challenging. We present a squamate-wide, high-density morphometric analysis of the skull across 181 modern and extinct species to identify the primary drivers of their cranial evolution within a unified, quantitative framework. Diet and habitat preferences, but not reproductive mode, are major influences on skull-shape evolution across squamates, with fossorial and aquatic taxa exhibiting convergent and rapid changes in skull shape. In lizards, diet is associated with the shape of the rostrum, reflecting its use in grasping prey, whereas snakes show a correlation between diet and the shape of posterior skull bones important for gape widening. Similarly, we observe the highest rates of evolution and greatest disparity in regions associated with jaw musculature in lizards, whereas those forming the jaw articulation evolve faster in snakes. In addition, high-resolution ancestral cranial reconstructions from these data support a terrestrial, nonfossorial origin for snakes. Despite their disparate evolutionary trends, lizards and snakes unexpectedly share a common pattern of trait integration, with the highest correlations in the occiput, jaw articulation, and palate. We thus demonstrate that highly diverse phenotypes, exemplified by lizards and snakes, can and do arise from differential selection acting on conserved patterns of phenotypic integration.

Functional constraints during development limit jaw shape evolution in marsupials.

Differences in jaw function experienced through ontogeny can have striking consequences for evolutionary outcomes, as has been suggested for the major clades of mammals. By contrast to placentals, marsupial newborns have an accelerated development of the head and forelimbs, allowing them to crawl to the mother's teats to suckle within just a few weeks of conception. The different functional requirements that marsupial newborns experience in early postnatal development have been hypothesized to have constrained their morphological diversification relative to placentals. Here, we test whether marsupials have a lower ecomorphological diversity and rate of evolution in comparison with placentals, focusing specifically on their jaws. To do so, a geometric morphometric approach was used to characterize jaw shape for 151 living and extinct species of mammals spanning a wide phylogenetic, developmental and functional diversity. Our results demonstrate that jaw shape is significantly influenced by both reproductive mode and diet, with substantial ecomorphological convergence between metatherians and eutherians. However, metatherians have markedly lower disparity and rate of mandible shape evolution than observed for eutherians. Thus, despite their ecomorphological diversity and numerous convergences with eutherians, the evolution of the jaw in metatherians appears to be strongly constrained by their specialized reproductive biology.

Implantation of biologic mesh in ventral hernia repair-does it make sense?

BACKGROUND: Biological acellular porcine dermis mesh, such as Permacol™, has been used since 2009 to treat abdominal incisional hernias in a septic context. This study investigated the risk factors for incisional hernia recurrence after biological mesh augmentation. RESULTS: Over a period of 6 years from February 2009 to February 2015, 68 patients underwent surgery. The mesh was placed intraperitoneally with closure of the anterior fascia in 27 cases (39.7%). The biological mesh was placed in the retromuscular pre-fascial plane in 1 case (1.5%) and pre-aponeurotic plane in 1 case (1.5%). Closure of the anterior fascia was not achieved in 39 cases, including 20 cases in which the mesh was placed intraperitoneally (intraperitoneal bridging group, 29.4%) and 19 cases in which the mesh was placed between the edges of the fascia (inlay bridging group, 27.9%). There were 37 cases of postoperative surgical site infections (54.4%), and Clavien-Dindo morbidity staging indicated stage I-II and III-IV complications in 19.1% and 44.1% of the cases, respectively. The recurrence rate was 61.8%, and the mortality rate was 0%. The rate of recurrence was significantly lower in the «fascia approximated¼ group (37%), p = 0.001). Univariate analyses of risk factors for procedural failure indicated an increased risk of recurrence in cases of postoperative surgical site infections, complications of Clavien-Dindo grade III or higher, an absent fascial closure in front of the mesh (OR = 8.69), an operating time longer than 180 min, and a VHWG score higher than 2. After logistic regression, the risk factors for recurrence were postoperative infections (OR = 6.2), placement of bridged biological mesh (OR = 22.3), and postoperative morbidity grade III or higher (OR = 16.7). CONCLUSIONS: Patients with postoperative surgical site infections are at an increased risk for recurrence, and bridged mesh placements lack efficacy. Overall, this study challenges the purported advantage of biologics in treating incisional hernia repairs.

Femoral morphology of sciuromorph rodents in light of scaling and locomotor ecology.

Sciuromorph rodents are a monophyletic group comprising about 300 species with a body mass range spanning three orders of magnitude and various locomotor behaviors that we categorized into arboreal, fossorial and aerial. The purpose of this study was to investigate how the interplay of locomotor ecology and body mass affects the morphology of the sciuromorph locomotor apparatus. The most proximal skeletal element of the hind limb, i.e. the femur, was selected, because it was shown to reflect a functional signal in various mammalian taxa. We analyzed univariate traits (effective femoral length, various robustness variables and the in-levers of the muscles attaching to the greater, third and lesser trochanters) as well as femoral shape, representing a multivariate trait. An ordinary least-squares regression including 177 species was used to test for a significant interaction effect between body mass and locomotor ecology on the variables. Specifically, it tested whether the scaling patterns of the fossorial and aerial groups differ when compared with the arboreal, because the latter was identified as the ancestral sciuromorph condition via stochastic character mapping. We expected aerial species to display the highest trait values for a given body mass as well as the steepest slopes, followed by the arboreal and fossorial species along this order. An Ornstein-Uhlenbeck regression fitted to a phylogenetically pruned dataset of 140 species revealed the phylogenetic inertia to be very low in the univariate traits, hence justifying the utilization of standard regressions. These variables generally scaled close to isometry, suggesting that scaling adjustments might not have played a major role for most of the femoral features. Nevertheless, the low phylogenetic inertia indicates that the observed scaling patterns needed to be maintained during sciuromorph evolution. Significant interaction effects were discovered in the femoral length, the centroid size of the condyles, and the in-levers of the greater and third trochanters. Additionally, adjustments in various femoral traits reflect the acquisitions of fossorial and aerial behaviors from arboreal ancestors. Using sciuromorphs as a focal clade, our findings exemplify the importance of statistically accounting for potential interaction effects of different environmental factors in studies relating morphology to ecology.

Food mobility and the evolution of grasping behaviour: a case study in strepsirrhine primates.

Manual grasping is widespread among tetrapods but is more prominent and dexterous in primates. Whether the selective pressures that drove the evolution of dexterous hand grasping involved the collection of fruit or predation on mobile insects remains an area of debate. One way to explore this question is to examine preferences for manual versus oral grasping of a moving object. Previous studies on strepsirrhines have shown a preference for oral grasping when grasping static food items and a preference for manual grasping when grasping mobile prey such as insects, but little is known about the factors at play. Using a controlled experiment with a simple and predictable motion of a food item, we tested and compared the grasping behaviours of 53 captive individuals belonging to 17 species of strepsirrhines while grasping swinging food items and static food items. The swinging motion increased the frequency of hand-use for all individuals. Our results provide evidence that the swinging motion of the food is a sufficient parameter to increase hand grasping in a wide variety of strepsirrhine primates. From an evolutionary perspective, this result gives some support to the idea that hand-grasping abilities evolved under selective pressure associated with the predation of food items in motion. Looking at a common grasping pattern across a large set of species, this study provides important insight into comparative approaches to understanding the evolution of the hand grasping of food in primates and potentially other tetrapod taxa.

Habitat shapes the thermoregulation of Mediterranean lizards introduced to replicate experimental islets.

Both environmental temperatures and spatial heterogeneity can profoundly affect the biology of ectotherms. In lizards, thermoregulation may show high plasticity and may respond to environmental shifts. In the context of global climate change, lizards showing plastic thermoregulatory responses may be favored. In this study, we designed an experiment to evaluate the extent to which lizard thermoregulation responds to introduction to a new environment in a snapshot of time. In 2014, we captured individuals of the Aegean Wall lizard (Podarcis erhardii) from Naxos Island (429.8 km2) and released them onto two small, lizard-free islets, Galiatsos (0.0073 km2) and Kampana (0.004 km2) (Aegean Sea, Greece). In 2017, we returned to the islets and estimated the effectiveness (E), accuracy and precision of thermoregulation measuring operative, preferred (Tpref) and body temperatures. We hypothesized that the three habitats would differ in thermal quality and investigated the extent to which lizards from Naxos demonstrate plasticity when introduced to the novel, islet habitats. Thermal parameters did not differ between Galiatsos and Naxos and this was reflected in the similar E and Tpref. However, lizards from Kampana deviated in all focal traits from Naxos, resulting in higher E and a preference for higher Tpref. In sum, Naxos lizards shifted their thermoregulatory profile due to the idiosyncratic features of their new islet habitat. Our results advocate a high plasticity in lizard thermoregulation and suggest that there is room for effective responses to environmental changes, at least for Podarcis lizards in insular habitats.

Do forelimb shape and peak forces co-vary in strepsirrhines?

OBJECTIVES: In this study, we explore whether ground reaction forces recorded during horizontal walking co-vary with the shape of the long bones of the forelimb in strepsirrhines. To do so, we quantify (1) the shape of the shaft and articular surfaces of each long bone of the forelimb, (2) the peak vertical, mediolateral, and horizontal ground reaction forces applied by the forelimb during arboreal locomotion, and (3) the relationship between the shape of the forelimb and peak forces. MATERIALS AND METHODS: Geometric morphometric approaches were used to quantify the shape of the bones. Kinetic data were collected during horizontal arboreal walking in eight species of strepsirrhines that show variation in habitual substrate use and morphology of the forelimb. These data were then used to explore the links between locomotor behavior, morphology, and mechanics using co-variation analyses in a phylogenetic framework. RESULTS: Our results show significant differences between slow quadrupedal climbers (lorises), vertical clinger and leapers (sifaka), and active arboreal quadrupeds (ring-tailed lemur, ruffed lemur) in both ground reaction forces and the shape of the long bones of the forelimb, with the propulsive and medially directed peak forces having the highest impact on the shape of the humerus. Co-variation between long bone shape and ground reaction forces was detected in both the humerus and ulna even when accounting for differences in body mass. DISCUSSION: These results demonstrate the importance of considering limb-loading beyond just peak vertical force, or substrate reaction force. A re-evaluation of osseous morphology and functional interpretations is necessary in light of these findings.

Foot shape in arboreal birds: two morphological patterns for the same pincer-like tool.

The feet are the only contact between the body and the substrate in limbed animals and as such they provide a crucial interface between the animal and its environment. This is especially true for bipedal and arboreal species living in a complex three-dimensional environment that likely induces strong selection on foot morphology. In birds, foot morphology is highly variable, with different orientations of the toes, making it a good model for the study of the role of functional, developmental, and phylogenetic constraints in the evolution of phenotypic diversity. Our data on the proportions of the phalanges analyzed in a phylogenetic context show that two different morphological patterns exist that depend mainly on habitat and toe orientation. In the anisodactyl foot, the hallux is the only backward-oriented toe and is enlarged in climbing species and reduced in terrestrial ones. Moreover, a proximo-distal gradient in phalanx size is observed depending on the degree of terrestriality. In the two other cases (heterodactyl and zygodactyl) that have two toes that point backward, the hallux is rather small in contrast to the other backward-pointing toe, which is enlarged. The first pattern is convergent and common among tetrapods and follows rules of skeletal development. The second pattern is unique for the clade and under muscle-morphogenetic control. In all cases, the functional result is the same tool, a pincer-like foot.

Variation in brain anatomy in frogs and its possible bearing on their locomotor ecology.

Despite the long-standing interest in the evolution of the brain, relatively little is known about variation in brain anatomy in frogs. Yet, frogs are ecologically diverse and, as such, variation in brain anatomy linked to differences in lifestyle or locomotor behavior can be expected. Here we present a comparative morphological study focusing on the macro- and micro-anatomy of the six regions of the brain and its choroid plexus: the olfactory bulbs, the telencephalon, the diencephalon, the mesencephalon, the rhombencephalon, and the cerebellum. We also report on the comparative anatomy of the plexus brachialis responsible for the innervation of the forelimbs. It is commonly thought that amphibians have a simplified brain organization, associated with their supposedly limited behavioral complexity and reduced motor skills. We compare frogs with different ecologies that also use their limbs in different contexts and for other functions. Our results show that brain morphology is more complex and more variable than typically assumed. Moreover, variation in brain morphology among species appears related to locomotor behavior as suggested by our quantitative analyses. Thus we propose that brain morphology may be related to the locomotor mode, at least in the frogs included in our analysis.

Functional associations between support use and forelimb shape in strepsirrhines and their relevance to inferring locomotor behavior in early primates.

The evolution of primates is intimately linked to their initial invasion of an arboreal environment. However, moving and foraging in this milieu creates significant mechanical challenges related to the presence of substrates differing in their size and orientation. It is widely assumed that primates are behaviorally and anatomically adapted to movement on specific substrates, but few explicit tests of this relationship in an evolutionary context have been conducted. Without direct tests of form-function relationships in living primates it is impossible to reliably infer behavior in fossil taxa. In this study, we test a hypothesis of co-variation between forelimb morphology and the type of substrates used by strepsirrhines. If associations between anatomy and substrate use exist, these can then be applied to better understand limb anatomy of extinct primates. The co-variation between each forelimb long bone and the type of substrate used was studied in a phylogenetic context. Our results show that despite the presence of significant phylogenetic signal for each long bone of the forelimb, clear support use associations are present. A strong co-variation was found between the type of substrate used and the shape of the radius, with and without taking phylogeny into account, whereas co-variation was significant for the ulna only when taking phylogeny into account. Species that use a thin branch milieu show radii that are gracile and straight and have a distal articular shape that allows for a wide range of movements. In contrast, extant species that commonly use large supports show a relatively robust and curved radius with an increased surface area available for forearm and hand muscles in pronated posture. These results, especially for the radius, support the idea that strepsirrhine primates exhibit specific skeletal adaptations associated with the supports that they habitually move on. With these robust associations in hand it will be possible to explore the same variables in extinct early primates and primate relatives and thus improve the reliability of inferences concerning substrate use in early primates.

Does aquatic foraging impact head shape evolution in snakes?

Evolutionary trajectories are often biased by developmental and historical factors. However, environmental factors can also impose constraints on the evolutionary trajectories of organisms leading to convergence of morphology in similar ecological contexts. The physical properties of water impose strong constraints on aquatic feeding animals by generating pressure waves that can alert prey and potentially push them away from the mouth. These hydrodynamic constraints have resulted in the independent evolution of suction feeding in most groups of secondarily aquatic tetrapods. Despite the fact that snakes cannot use suction, they have invaded the aquatic milieu many times independently. Here, we test whether the aquatic environment has constrained head shape evolution in snakes and whether shape converges on that predicted by biomechanical models. To do so, we used three-dimensional geometric morphometrics and comparative, phylogenetically informed analyses on a large sample of aquatic snake species. Our results show that aquatic snakes partially conform to our predictions and have a narrower anterior part of the head and dorsally positioned eyes and nostrils. This morphology is observed, irrespective of the phylogenetic relationships among species, suggesting that the aquatic environment does indeed drive the evolution of head shape in snakes, thus biasing the evolutionary trajectory of this group of animals.

Patterns of quadrupedal locomotion in a vertical clinging and leaping primate (Propithecus coquereli) with implications for understanding the functional demands of primate quadrupedal locomotion.

OBJECTIVES: Many primates exhibit a suite of characteristics that distinguish their quadrupedal gaits from non-primate mammals including the use of a diagonal sequence gait, a relatively protracted humerus at touchdown, and relatively high peak vertical forces on the hindlimbs compared to the forelimbs. These characteristics are thought to have evolved together in early, small-bodied primates possibly in response to the mechanical demands of navigating and foraging in a complex arboreal environment. It remains unclear, however, whether primates that employ quadrupedalism only rarely demonstrate the common primate pattern of quadrupedalism or instead use the common non-primate pattern or an entirely different mechanical pattern from either group. MATERIALS AND METHODS: This study compared the kinematics and kinetics of two habitually quadrupedal primates (Lemur catta and Varecia variegata) to those of a dedicated vertical clinger and leaper (Propithecus coquereli) during bouts of quadrupedal walking. RESULTS: All three species employed diagonal sequence gaits almost exclusively, displayed similar degrees of humeral protraction, and exhibited lower vertical peak forces in the forelimbs compared to the hindlimb. DISCUSSION: From the data in this study, it is possible to reject the idea that P. coquereli uses a non-primate pattern of quadrupedal walking mechanics. Nor do they use an entirely different mechanical pattern from either most primates or most non-primates during quadrupedal locomotion. These findings provide support for the idea that this suite of characteristics is adaptive for the challenges of arboreal locomotion in primates and that these features of primate locomotion may be basal to the order or evolved independently in multiple lineages including indriids. Am J Phys Anthropol 160:644-652, 2016. © 2016 Wiley Periodicals, Inc.

Do constraints associated with the locomotor habitat drive the evolution of forelimb shape? A case study in musteloid carnivorans.

Convergence in morphology can result from evolutionary adaptations in species living in environments with similar selective pressures. Here, we investigate whether the shape of the forelimb long bones has converged in environments imposing similar functional constraints, using musteloid carnivores as a model. The limbs of quadrupeds are subjected to many factors that may influence their shape. They need to support body mass without collapsing or breaking, yet at the same time resist the stresses and strains induced by locomotion. This likely imposes strong constraints on their morphology. Our geometric morphometric analyses show that locomotion, body mass and phylogeny all influence the shape of the forelimb. Furthermore, we find a remarkable convergence between: (i) aquatic and semi-fossorial species, both displaying a robust forelimb, with a shape that improves stability and load transfer in response to the physical resistance imposed by the locomotor environment; and (ii) aquatic and arboreal/semi-arboreal species, with both groups displaying a broad capitulum. This augments the degree of pronation/supination, an important feature for climbing as well as grasping and manipulation ability, behaviors common to aquatic and arboreal species. In summary, our results highlight how musteloids with different locomotor ecologies show differences in the anatomy of their forelimb bones. Yet, functional demands for limb movement through dense media also result in convergence in forelimb long-bone shape between diverse groups, for example, otters and badgers.

Quantitative inferences on the locomotor behaviour of extinct species applied to Simocyon batalleri (Ailuridae, Late Miocene, Spain).

Inferences of function and ecology in extinct taxa have long been a subject of interest because it is fundamental to understand the evolutionary history of species. In this study, we use a quantitative approach to investigate the locomotor behaviour of Simocyon batalleri, a key taxon related to the ailurid family. To do so, we use 3D surface geometric morphometric approaches on the three long bones of the forelimb of an extant reference sample. Next, we test the locomotor strategy of S. batalleri using a leave-one-out cross-validated linear discriminant analysis. Our results show that S. batalleri is included in the morphospace of the living species of musteloids. However, each bone of the forelimb appears to show a different functional signal suggesting that inferring the lifestyle or locomotor behaviour of fossils can be difficult and dependent on the bone investigated. This highlights the importance of studying, where possible, a maximum of skeletal elements to be able to make robust inferences on the lifestyle of extinct species. Finally, our results suggest that S. batalleri may be more arboreal than previously suggested.

Morphological integration in the forelimb of musteloid carnivorans.

The forelimb forms a functional unit that allows a variety of behaviours and needs to be mobile, yet at the same time stable. Both mobility and stability are controlled, amongst others, at the level of the elbow joint. This joint is composed of the humero-ulnar articulation, mainly involved during parasagittal movements; and the radio-ulnar articulation, mainly allowing rotation. In contrast, the humero-radial articulation allows both movements of flexion-extension and rotation. Here, we study the morphological integration between each bone of the forelimb at the level of the entire arm, as well as at the elbow joint, in musteloid carnivorans. To do so, we quantitatively test shape co-variation using surface 3D geometric morphometric data. Our results show that morphological integration is stronger for bones that form functional units. Different results are obtained depending on the level of investigation: for the entire arm, results show a greater degree of shape co-variation between long bones of the lower arm than between the humerus and either bone of the lower arm. Thus, at this level the functional unit of the lower arm is comprised of the radius and ulna, permitting rotational movements of the lower arm. At the level of the elbow, results display a stronger shape co-variation between bones allowing flexion and stability (humerus and ulna) than between bones allowing mobility (ulna and radius and humerus and radius). Thus, the critical functional unit appears to be the articulation between the humerus and ulna providing the stability of the joint.

Do all frogs swim alike? The effect of ecological specialization on swimming kinematics in frogs.

Frog locomotion has attracted wide scientific interest because of the unusual and derived morphology of the frog pelvic girdle and hind limb. Previous authors have suggested that the design of the frog locomotor system evolved towards a specialized jumping morphology early in the radiation of the group. However, data on locomotion in frogs are biased towards a few groups and most of the ecological and functional diversity remains unexplored. Here, we examine the kinematics of swimming in eight species of frog with different ecologies. We use cineradiography to quantify movements of skeletal elements from the entire appendicular skeleton. Our results show that species with different ecologies do differ in the kinematics of swimming, with the speed of limb extension and especially the kinematics of the midfoot being different. Our results moreover suggest that this is not a phylogenetic effect because species from different clades with similar ecologies converge on the same swimming kinematics. We conclude that it is important to analyze frog locomotion in a broader ecological and evolutionary context if one is to understand the evolutionary origins of this behavior.