Sarah Elton

Sample size and sampling error in geometric morphometric studies of size and shape

Geometric morphometric studies are increasingly becoming common in systematics and palaeontology. The samples in such studies are often small, due to the paucity of material available for analysis. However, very few studies have tried to assess the impact of sampling error on analytical results. Here, this issue is addressed empirically using repeated randomized selection experiments to build progressively smaller samples from an original dataset of ∼400 vervet monkey (Cercopithecus aethiops) skulls. Size and shape parameters (including mean size and shape, size and shape variances, angles of allometric trajectories) that are commonly used in geometric morphometric studies, are estimated first in the original sample and then in the random subsamples. Estimates are then compared to give an indication of what is the minimum desirable sample size for each parameter. Mean size, standard deviation of size and variance of shape are found to be fairly accurate even in relatively small samples. In contrast, mean shapes and angles between static allometric trajectories are strongly affected by sampling error. If confirmed in other groups, our findings may have substantial implications for studies of morphological variation in present and fossil species. By performing rarefaction analyses like those presented in our study, morphometricians can be easily provided with important clues on how a simple but crucial factor like sample size can alter results of their studies.

What Do Medical Students Understand By Research And Research Skills? Identifying Research Opportunities Within Undergraduate Projects

Background: Undergraduate research exposure leads to increased recruitment into academic medicine, enhanced employability and improved postgraduate research productivity. Uptake of undergraduate research opportunities is reported to be disappointing, and little is known about how students perceive research. Aim: To investigate opportunities for undergraduate participation in research, recognition of such opportunities, and associated skills development. Method: A mixed method approach, incorporating student focus and study groups, and documentary analysis at five UK medical schools. Results: Undergraduates recognised the benefits of acquiring research skills, but identified practical difficulties and disadvantages of participating. Analysis of 905 projects in four main research skill areas – (1) research methods; (2) information gathering; (3) critical analysis and review; (4) data processing – indicated 52% of projects provided opportunities for students to develop one or more skills, only 13% offered development in all areas. In 17%, project descriptions provided insufficient information to determine opportunities. Supplied with information from a representative sample of projects (n = 80), there was little consensus in identifying skills among students or between students and researchers. Consensus improved dramatically following guidance on how to identify skills. Conclusions: Undergraduates recognise the benefits of research experience but need a realistic understanding of the research process. Opportunities for research skill development may not be obvious. Undergraduates require training to recognise the skills required for research and enhanced transparency in potential project outcomes.

The environmental context of human evolutionary history in Eurasia and Africa

This review has three main aims: (1) to make specific predictions about the habitat of the hypothetical last common ancestor of the chimpanzee/bonobo–human clade; (2) to outline the major trends in environments between 8–6 Ma and the late Pleistocene; and (3) to pinpoint when, and in some cases where, human ancestors evolved to cope with the wide range of habitats they presently tolerate. Several lines of evidence indicate that arboreal environments, particularly woodlands, were important habitats for late Miocene hominids and hominins, and therefore possibly for the last common ancestor of the chimpanzee/bonobo–human clade. However, as there is no clear candidate for this last common ancestor, and because the sampling of fossils and past environments is inevitably patchy, this prediction remains a working hypothesis at best. Nonetheless, as a primate, it is expected that the last common ancestor was ecologically dependent on trees in some form. Understanding past environments is important, as palaeoenvironmental reconstructions provide the context for human morphological and behavioural evolution. Indeed, the impact of climate on the evolutionary history of our species has long been debated. Since the mid‐Miocene, the Earth has been experiencing a general cooling trend accompanied by aridification, which intensified during the later Pliocene and Pleistocene. Numerous climatic fluctuations, as well as local, regional and continental geography that influenced weather patterns and vegetation, created hominin environments that were dynamic in space and time. Behavioural flexibility and cultural complexity were crucial aspects of hominin expansion into diverse environments during the Pleistocene, but the ability to exploit varied and varying habitats was established much earlier in human evolutionary history. The development of increasingly complex tool technology facilitated re‐expansion into tropical forests. These environments are difficult for obligate bipeds to negotiate, but their exploitation was accomplished by archaic and/or anatomically modern humans independently in Africa and south‐east Asia. Complex social behaviour and material culture also allowed modern humans to reach some of the most hostile regions of the globe, above the Arctic Circle, by the late Pleistocene. This, with colonization of the Americas and Australasia, established Homo sapiens as a truly cosmopolitan species.

Disrupted seasonal biology impacts health, food security and ecosystems

The rhythm of life on earth is shaped by seasonal changes in the environment. Plants and animals show profound annual cycles in physiology, health, morphology, behaviour and demography in response to environmental cues. Seasonal biology impacts ecosystems and agriculture, with consequences for humans and biodiversity. Human populations show robust annual rhythms in health and well-being, and the birth month can have lasting effects that persist throughout life. This review emphasizes the need for a better understanding of seasonal biology against the backdrop of its rapidly progressing disruption through climate change, human lifestyles and other anthropogenic impact. Climate change is modifying annual rhythms to which numerous organisms have adapted, with potential consequences for industries relating to health, ecosystems and food security. Disconcertingly, human lifestyles under artificial conditions of eternal summer provide the most extreme example for disconnect from natural seasons, making humans vulnerable to increased morbidity and mortality. In this review, we introduce scenarios of seasonal disruption, highlight key aspects of seasonal biology and summarize from biomedical, anthropological, veterinary, agricultural and environmental perspectives the recent evidence for seasonal desynchronization between environmental factors and internal rhythms. Because annual rhythms are pervasive across biological systems, they provide a common framework for trans-disciplinary research.

Variation in guenon skulls (I): species divergence, ecological and genetic differences

Guenons are the most diverse clade of African monkeys. They have varied ecologies, include arboreal and terrestrial species, and can be found in nearly every region of sub-Saharan Africa. Species boundaries are often uncertain, with a variable number of species and subspecies mostly recognised on the basis of their geographic distribution and pelage. If guenon soft tissue patterns show high variability, the same does not seem to hold for skull morphology. Guenon skulls are traditionally considered relatively undifferentiated and homogeneous. However, patterns of variation in skulls have never been examined using a large number of specimens sampled across the breadth of species diversity. Thus, in the present study, skulls of adult guenons and two outgroup species are analysed using three-dimensional geometric morphometrics. Three-dimensional coordinates of 86 anatomical landmarks were measured on 1,315 adult specimens belonging to all living guenon species except Cercopithecus dryas. Species are well-discriminated using shape but the best discrimination occurs when species have either a long evolutionary history (e.g., Allenopithecus nigroviridis) or represent extremes of size variation (Miopithecus sp. and Erythrocebus patas). Interspecific phenetic relationships reflect size differences. Four main clusters are found that mainly correspond to four size groups: the smallest species (Miopithecus sp.), the largest species (E. patas plus the study outgroups), a group of medium-small arboreal guenons, and a group of medium-large arboreal and terrestrial guenons. Correlations between interspecific shape distances and interspecific differences in size are higher than between shape distances and genetic distances. However, if only the component of interspecific shape variation which is not correlated to evolutionary allometry is used in the comparison with genetic distances, correlations are up to 1.4 times larger than those including allometric shape. The smallest correlations are those between shape and ecological distances, which is consistent with the lack of clusters clearly reflecting broad ecological specialisations (e.g., arboreality versus terrestriality). Thus, size, which is generally considered more evolutionarily labile than shape, seems to have played a major role in the evolution of the guenons. The incongruence between interspecific shape differences and phylogeny might be explained by a large proportion of shape changes having occurred along allometric trajectories that tend to be conserved within this clade.

A reappraisal of the locomotion and habitat preference of Theropithecus oswaldi

The one modern member of the genus Theropithecus, T. gelada (Primates, Cercopithecidae), inhabits grassland and is highly terrestrial. It is often supposed that Theropithecus oswaldi, one of the most common primates of the Plio-Pleistocene of East and southern Africa, was also a highly terrestrial open habitat species. Ecomorphic analysis was used to assess the locomotor strategy and habitat preference of T. oswaldi, and it was found that this species was unlikely to have had a locomotor strategy and habitat preference identical to that of T. gelada, with T. oswaldi possibly using arboreal substrates in a manner similar to some modern baboon groups. Thus, it appears that there has been considerable ecological diversity in the genus Theropithecus over the course of its evolution, mirroring the diversity evident in the hominin fossil record.

Variation in guenon skulls (II): sexual dimorphism

Patterns of size and shape sexual dimorphism in adult guenons were examined using a large sample of skulls from almost all living species. Within species, sexual dimorphism in skull shape follows the direction of size-related shape variation of adults, is proportional to differences in size, and tends to be larger in large-bodied species. Interspecific divergence among shape trajectories, which explain within species sex differences, are small (i.e., trajectories of most species are nearly parallel). Thus, changes in relative proportions of skull regions that account for the distinctive shape of females and males are relatively conserved across species, and their magnitude largely depends on differences in size between sexes. A conservative pattern of size-related sexual dimorphism and a model of interspecific divergence in shape which strongly reflects size differences suggest a major role of size and size-related shape variation in the guenon radiation. It is possible that in the guenons, as in the neotropical primates (with whom they have obvious parallels), size has helped to determine morphological change along lines of least evolutionary resistance, influencing sexual dimorphism. In Miopithecus and Erythrocebus, the smallest and largest guenon genera, it is likely that the interaction of ecology and size contributes significantly to patterns of sexual dimorphism. The results of this study thus emphasise the need to consider allometry and size alongside ecology and behaviour when examining primate sexual dimorphism.

Modern macaque dietary heterogeneity assessed using stable isotope analysis of hair and bone.

Dietary variability might have been a major factor in the dispersal and subsequent persistence of the genus Macaca in both tropical and temperate areas. Macaques are found from northern Africa to Japan, yet there have been few systematic attempts to compare diets between different modern populations. Here we have taken a direct approach and sampled museum-curated tissues (hair and bone) of Macaca mulatta (rhesus macaques) for carbon and nitrogen stable isotope dietary analyses. Samples from India, Vietnam, and Burma (Myanmar) were taken, representing both tropical and temperate populations. The delta(13)C values obtained from hair show that the temperate macaques, particularly those from Uttar Pradesh, have a delta(13)C signature that indicates at least some use of C(4) resources, while the tropical individuals have a C(3)-based diet. However, delta(13)C values from bone bioapatite indicate a C(3)-based diet for all specimens and they do not show the C(4) usage seen in the hair of some animals, possibly because bone represents a much longer turnover period than that of hair. The results of delta(15)N analyses grouped animals by geographic region of origin, which may be related to local soil nitrogen values. The greatest variation in delta(15)N values was seen in the specimens from Burma, which may be partly due to seasonality, as specimens were collected at different times of year. We also investigated the relationship between the hair, bone collagen, and bone bioapatite delta(13)C results, and found that they are highly correlated, and that one tissue can be used to extrapolate results for another. However, our results also suggest that hair may pick up discrete feeding traces (such as seasonal usage), which are lost when only bone collagen and bioapatite are examined. This has important implications for dietary reconstructions of archaeological and paleontological populations.

Cats in the forest: predicting habitat adaptations from humerus morphometry in extant and fossil Felidae (Carnivora)

Abstract Mammalian carnivores are rarely incorporated in paleoenvironmental reconstructions, largely because of their rarity within the fossil record. However, multivariate statistical modeling can be successfully used to quantify specific anatomical features as environmental predictors. Here we explore morphological variability of the humerus in a closely related group of predators (Felidae) to investigate the relationship between morphometric descriptors and habitat categories. We analyze linear measurements of the humerus in three different morphometric combinations (log-transformed, size-free, and ratio), and explore four distinct ways of categorizing habitat adaptations. Open, Mixed, and Closed categories are defined according to criteria based on traditional descriptions of species, distributions, and biome occupancy. Extensive exploratory work is presented using linear discriminant analyses and several fossils are included to provide paleoecological reconstructions. We found no significant differences in the predictive power of distinct morphometric descriptors or habitat criteria, although sample splitting into small and large cat guilds greatly improves the stability of the models. Significant insights emerge for three long-canine cats: Smilodon populator, Paramachairodus orientalis, and Dinofelis sp. from Olduvai Gorge (East Africa). S. populator and P. orientalis are both predicted to have been closed-habitat adapted taxa. The false “sabertooth” Dinofelis sp. from Olduvai Gorge is predicted to be adapted to mixed habitat. The application of felid humerus ecomorphology to the carnivoran record of Olduvai Gorge shows that the older stratigraphic levels (Bed I, 1.99–1.79 Ma) included a broader range of environments than Beds II or V, where there is an abundance of cats adapted to open environments.

Humeral epiphyseal shape in the felidae: The influence of phylogeny, allometry, and locomotion

Bone morphology of the cats (Mammalia: Felidae) is influenced by many factors, including locomotor mode, body size, hunting methods, prey size and phylogeny. Here, we investigate the shape of the proximal and distal humeral epiphyses in extant species of the felids, based on two‐dimensional landmark configurations. Geometric morphometric techniques were used to describe shape differences in the context of phylogeny, allometry and locomotion. The influence of these factors on epiphyseal shape was assessed using Principal Component Analysis, Linear Discriminant functions and multivariate regression. Phylogenetic Generalised Least Squares was used to examine the association between size or locomotion and humeral epiphyseal shape, after taking a phylogenetic error term into account. Results show marked differences in epiphyseal shape between felid lineages, with a relatively large phylogenetic influence. Additionally, the adaptive influences of size and locomotion are demonstrated, and their influence is independent of phylogeny in most, but not all, cases. Several features of epiphyseal shape are common to the largest terrestrial felids, including a relative reduction in the surface area of the humeral head and increased robusticity of structures that provide attachment for joint‐stabilising muscles, including the medial epicondyle and the greater and lesser tubercles. This increased robusticity is a functional response to the increased loading forces placed on the joints due to large body mass. J. Morphol., 2012.