Patterns of morphospace occupation and mechanical performance in extant crocodilian skulls: A combined geometric morphometric and finite element modeling approach

Extant and fossil crocodilians have long been divided into taxonomic and/or ecological groups based on broad patterns of skull shape, particularly the relative length and width of the snout. However, these patterns have not been quantitatively analyzed in detail, and their biomechanical and functional implications are similarly understudied. Here, we use geometric morphometrics and finite element analysis to explore the patterns of variation in crocodilian skull morphology and the functional implications of those patterns. Our results indicate that skull shape variation in extant crocodiles is much more complex than previously recognized. Differences in snout length and width are the main components of shape variation, but these differences are correlated with changes in other regions of the skull. Additionally, there is considerable disparity within general classes such as longirostrine and brevirostrine forms. For example, Gavialis and Tomistoma occupy different parts of morphospace implying a significant difference in skull shape, despite the fact that both are traditionally considered longirostrine. Skull length and width also strongly influence the mechanical performance of the skull; long and narrow morphotypes (e.g., Tomistoma) experience the highest amount of stress during biting, whereas short and broad morphotypes (e.g., Caiman latirostris) experience the least amount of stress. Biomechanical stress and the hydrodynamic properties of the skull show a strong relationship with the distribution of crocodilians in skull morphospace, whereas phylogeny and biogeography show weak or no correlation. Therefore, ecological specializations related to feeding and foraging likely have the greatest influence on crocodilian skull shape. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

The tooth of perfection: functional and spatial constraints on mammalian tooth shape

This paper addresses the question of how close mammalian teeth are to ideal functional forms. An 'ideal' form is a morphology predicted to be the best functional shape according to information of the relationships between shape and function. Deviations from an ideal form are likely to indicate the presence of developmental or genetic constraints on form. Model tools were constructed to conform to functional principles from engineering and dental studies. The final model shapes are very similar to several mammalian tooth forms (carnassial teeth and tribosphenic-like cusps), suggesting that these tooth forms very closely approach ideal functional forms. Further evidence that these tooth forms are close to ideal comes from the conservation over 140 million years, the independent derivation and/or the occurrence over a size range of several orders of magnitude of these basic tooth forms. One of the main functional shapes derived here is the 'protoconoid', a fundamental design for double-bladed tools that fits a large number of functional parameters. This shape occurs in tooth forms such as tribosphenic, dilambdodont and zalambdodont. This study extends our understanding of constraints on tooth shape in terms of geometry (how space influences tooth shape) and function (how teeth divide food).  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 173–191.     

A 3-D geometric morphometric study of intraspecific variation in the ontogeny of the temporal bone in modern Homo sapiens

This study addresses how the human temporal bone develops the population-specific pattern of morphology observed among adults and at what point in ontogeny those patterns arise. Three-dimensional temporal bone shape was captured using 15 landmarks on ontogenetic series of specimens from seven modern human populations. Discriminant function analysis revealed that population-specific temporal bone morphology is evident early in ontogeny, with significant shape differences among many human populations apparent prior to the eruption of the first molar. As early as five years of age, temporal bone shape reflects population history and can be used to reliably sort populations, although those in closer geographic proximity and molecular affinity are more likely to be misclassified. The deviation of cold-adapted populations from this general pattern of congruence between temporal bone morphology and genetic distances, identified in previous work, was confirmed here in adult and subadult specimens, and was revealed to occur earlier in ontogeny than previously recognized. Significant differences exist between the ontogenetic trajectories of some pairs of populations, but not among others, and the angles of these trajectories do not reflect genetic relationships or final adult temporal bone size. Significant intrapopulation differences are evident early in ontogeny, with differences becoming amplified by divergent trajectories in some groups. These findings elucidate how the congruence between adult human temporal bone morphology and population history develops, and reveal that this pattern corresponds closely to that described previously for facial ontogeny.     

Brief communication: Morphological effects of captivity: A geometric morphometric analysis of the dorsal side of the scapula in captive‐bred and wild‐caught hominoidea

Many osteological collections from museums and research institutions consist mainly of remains from captive‐bred animals. The restrictions related to the space of their enclosures and the nature of its substrate are likely to affect the locomotor and postural behaviors of captive‐bred animals, which are widely considered uninformative regarding bone morphology and anatomical adaptations of wild animals, especially so in the case of extant great apes. We made a landmark‐based geometric morphometrics analysis of the dorsal side of the scapular bone of both wild‐caught and captive‐bred great apes to clarify the effect of captivity on the morphology of a bone greatly involved in locomotion. The comparison suggested that captivity did not have a significant effect on the landmark configuration used, neither on average scapular shape nor shape variability, being impossible to distinguish the scapulae of a captive‐bred animal from that of a wild‐caught one. This indicates that the analyzed scapulae from captive Hominoidea specimens may be used in morphological or taxonomic analyses since they show no atypical morphological traits caused by living conditions in captivity. Am J Phys Anthropol 152:306–310, 2013. © 2013 Wiley Periodicals, Inc.     

A geometric morphometric approach to the study of ecogeographical and clinal variation in vervet monkeys

Aim To examine and visualize clines in size and shape of Cercopithecus aethiops Linneus, 1758 (Primate, Cercopithecidae) skulls, and to investigate environmental factors which might best explain the observed variation. Location Sub‐Saharan Africa. Methods Eighty‐six three‐dimensional anatomical landmarks were used to describe 306 skulls of adult C. aethiops sampled over its entire distribution. Geometric morphometric methods for the quantitative analysis of form variation were applied. Size and shape variables were computed and regressed onto geographical coordinates and environmental variables (elevation, temperature, rainfall, moisture and Shannon rainfall diversity index) using both linear and curvilinear models. Components (geographical, environmental, spatially structured environmental and residual) of ecogeographical variation in skull form were partitioned using partial regression. A novel approach for summarizing and visualizing nonlinear patterns of clinal variation using surface rendering of three‐dimensional shapes is presented. Results Clinal variation in size and shape was highly significant, and was best described by curvilinear models. There were strong similarities between females and males. The cline in size was especially pronounced, explaining up to about 40% of observed variation, and was mainly longitudinal rather than latitudinal. A major trend of clinal shape variation also occurred from west to east, and corresponded to an expansion of the face relative to the neurocranium in the west. In the east, skulls also tended to be deeper and with narrower zygomatic arches. Geography and the spatially structured environmental component were the major contributors to the explained variance in size in both sexes, but the proportion of variance explained by the latter was smaller in females. In contrast, geography and environment explained similar amounts of variation in shape and their contribution was about twice that of the spatially structured environmental component. About 60–80% of variation in skull form was not explained by any variable in the analysis. The main factors influencing skull size differed in females and males, with rainfall being very influential in males. Both female and male skull shapes were strongly affected by average annual rainfall. Main conclusions A strong spatial and environmental basis to variations in African vervet monkey skull form was evident. However, the observed pattern did not conform to predictions based on Bergmann's rule. Rainfall consistently emerged as an important predictor, which may contribute to intraspecific variation in the size and shape of vervet monkey skulls through its effect on habitat productivity.     

A comparison of the variation in Indian populations of pigeonpea cyst nematode, Heterodera cajani revealed by morphometric and AFLP analysis

The cyst nematode Heterodera cajani is one of the major endemic diseases of pigeonpea, an important legume for food security and protein nutrition in India. It occurs in several pulse crops grown over a range of Indian agro climatic conditions but the extent of its intraspecific variation is inadequately defined. In view of this, 11 populations of Heterodera cajani were analyzed using morphometrics and the results correlated with those obtained from an AFLP approach using 24 primer pair combinations that amplified a total of 1278 AFLP markers. The cluster solution from this binary data indicated similarities for five populations that differed from those suggested by morphometrics. The differences obtained could not be related to geographic distance between populations. The data suggests that recent and long distance dispersal has occurred whose causes need to be defined to restrict further field introductions. Four AFLP primer pairs clustered the populations similarly to that generated using all 24 primer pairs. This simplified approach may provide a rapid basis for discriminating populations for their future management and help to check further distribution in agricultural trade. It may also have potential to determine differences in populations that relate to host range or virulence to resistance genes.     

Locomotion in some small to medium-sized mammals: a geometric morphometric analysis of the penultimate lumbar vertebra,pelvis and hindlimbs

We assessed the influence of a variety of aspects of locomotion and ecology including gait and locomotor types, maximal running speed, home range, and body size on postcranial shape variation in small to medium-sized mammals, employing geometric morphometric analysis and phylogenetic comparative methods. The four views analyzed, i.e., dorsal view of the penultimate lumbar vertebra, lateral view of the pelvis, posterior view of the proximal femur and proximal view of the tibia, showed clear phylogenetic signal and interesting patterns of association with movement. Variation in home range size was related to some tibia shape changes, while speed was associated with lumbar vertebra, pelvis and tibia shape changes. Femur shape was not related to any locomotor variables. In both locomotor type and high-speed gait analyses, locomotor groups were distinguished in both pelvis and tibia shape analyses. These results suggest that adaptations to both typical and high-speed gaits could explain a considerable portion of the shape of those elements. In addition, lumbar vertebra and tibia showed non-significant relationships with body mass, which suggests that they might be used in morpho-functional analyses and locomotor inferences on fossil taxa, with little or no bias for body size. Lastly, we observed morpho-functional convergences among several mammalian taxa and detected some taxa that achieve similar locomotor features following different morphological paths.     

Leaf morphological analyses in four European oak species (Quercus) and their hybrids: A comparison of traditional and geometric morphometric methods

Abstract

In this study, leaf morphology was assessed in a mixed oak stand (western France) using two geometric morphometric (landmark and outline) datasets and one dataset of 19 leaf measures. Adult oaks (817 oaks), comprising four white oak species (Quercus petraea, Q. robur, Q. pubescens and Q. pyrenaica), were sampled for DNA extraction and genetic analysis (nuclear microsatellites). Leaf morphology was assessed on 336 oaks, comprising pure species and hybrids as determined by genetic assignment. This comparative study of oak leaf morphology, based on the use of two free size geometric morphometric methods and a set of leaf measurements, combined with the genetic assignment of individuals to pure species or hybrids, provided information about the differences among species and the intermediate leaf morphology of their hybrids.     

Variability of functional traits and their syndromes in a freshwater fish species (Phoxinus phoxinus): The role of adaptive and nonadaptive processes

Functional traits can covary to form “functional syndromes.” Describing and understanding functional syndromes is an important prerequisite for predicting the effects of organisms on ecosystem functioning. At the intraspecific level, functional syndromes have recently been described, but very little is known about their variability among populations and—if they vary—what the ecological and evolutionary drivers of this variation are. Here, we quantified and compared the variability in four functional traits (body mass, metabolic rate, excretion rate, and boldness), their covariations and the subsequent syndromes among thirteen populations of a common freshwater fish (the European minnow, Phoxinus phoxinus). We then tested whether functional traits and their covariations, as well as the subsequent syndromes, were underpinned by the phylogenetic relatedness among populations (historical effects) or the local environment (i.e., temperature and predation pressure), and whether adaptive (selection or plasticity) or nonadaptive (genetic drift) processes sustained among‐population variability. We found substantial among‐population variability in functional traits and trait covariations, and in the emerging syndromes. We further found that adaptive mechanisms (plasticity and/or selection) related to water temperature and predation pressure modulated the covariation between body mass and metabolic rate. Other trait covariations were more likely driven by genetic drift, suggesting that nonadaptive processes can also lead to substantial differences in trait covariations among populations. Overall, we concluded that functional syndromes are population‐specific, and that both adaptive and nonadaptive processes are shaping functional traits. Given the pivotal role of functional traits, differences in functional syndromes within species provide interesting perspectives regarding the role of intraspecific diversity for ecosystem functioning.     

The geographic structure of morphological variation in eight species of fiddler crabs (Ocypodidae: genus Uca) from the eastern United States and Mexico

Species with larger geographic distributions are more likely to encounter a greater variety of environmental conditions and barriers to gene flow than geographically‐restricted species. Thus, even closely‐related species with similar life‐history strategies might vary in degree and geographic structure of variation if they differ in geographic range size. In the present study, we investigated this using samples collected across the geographic ranges of eight species of fiddler crabs (Crustacea: Uca) from the Atlantic and Gulf coasts of North America. Morphological variation in the carapace was assessed using geometric morphometric analysis of 945 specimens. Although the eight Uca species exhibit different degrees of intraspecific variation, widespread species do not necessarily exhibit more intraspecific or geographic variation in carapace morphology. Instead, species with more intraspecific variation show stronger morphological divergence among populations. This morphological divergence is partly a result of allometric growth coupled with differences in maximum body size among populations. On average, 10% of total within‐species variation is attributable to allometry. Possible drivers of the remaining morphological differences among populations include gene flow mediated by ocean currents and plastic responses to various environmental stimuli, with isolation‐by‐distance playing a less important role. The results obtained indicate that morphological divergence among populations can occur over shorter distances than expected based on dispersal potential. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 248–270.     

Evolution of Hominid Femur and Tibia: A morphometric approach to the evolutionary research in anthropology

Some theoretical and methodological morphometrical approaches in evolutionary anthropology and paleoanthropology are reviewed in this study. It is shown which are the contemporary possibilities of sophisticated biometrical and biostatistical methods and the role of the morphometrical approach. A new approach, experimental morphometrics, is presented, reflecting recent trends in evolutionary morphology as well as sophisticated biostatistical methods. The approach emphasizes the complex inter-related approach to the data processing and a double nature of morphometric data, i.e. biological and biostatistical one. The practical use of experimental morphometry is given for the two examples of analyses of the evolution of the hominoid and hominid femur and tibia. The hypothesis on a two stage restructuring of morphology of the hominid femur and tibia is supported by experimental results. Two different steps during this restructuring could be recognized: 1) Structural remodelling typical for the origin of hominids and australopithecine evolution, and 2) proportional remodelling of lower limb long bones which is connected with the Australopithecus/Homo transition (i.e. mainly Homo habilis stage). The results confirm the increasing trend of bipedal adaptations on the early hominid lower limb skeleton. Analysis of microevolutionary trends on the Homo sapiens femur and tibia indicates at least three different morphological patterns, Paleolithic, Neolithic and Recent, with numerous specific features in morphology and proportions. Neanderthal morphology is very derived. Upper Paleolithic/Mesolithic/Neolithic transition has a key character for the understanding of post-Paleolithic morphology. A very high sexual dimorphism of the femur and tibia has been demonstrated for Upper Paleolithic and Neolithic populations. Presented at the Foundation of Different Approaches to the Study of Human Evolution edited by B. Sigmon & V.V. Leonovicova-Liblice, September 1–3, 1989     

Phenotypic distribution models corroborate species distribution models: A shift in the role and prevalence of a dominant prairie grass in response to climate change

Phenotypic distribution within species can vary widely across environmental gradients but forecasts of species’ responses to environmental change often assume species respond homogenously across their ranges. We compared predictions from species and phenotype distribution models under future climate scenarios for Andropogon gerardii, a widely distributed, dominant grass found throughout the central United States. Phenotype data on aboveground biomass, height, leaf width, and chlorophyll content were obtained from 33 populations spanning a ~1000 km gradient that encompassed the majority of the species’ environmental range. Species and phenotype distribution models were trained using current climate conditions and projected to future climate scenarios. We used permutation procedures to infer the most important variable for each model. The species‐level response to climate was most sensitive to maximum temperature of the hottest month, but phenotypic variables were most sensitive to mean annual precipitation. The phenotype distribution models predict that A. gerardii could be largely functionally eliminated from where this species currently dominates, with biomass and height declining by up to ~60% and leaf width by ~20%. By the 2070s, the core area of highest suitability for A. gerardii is projected to shift up to ~700 km northeastward. Further, short‐statured phenotypes found in the present‐day short grass prairies on the western periphery of the species’ range will become favored in the current core ~800 km eastward of their current location. Combined, species and phenotype models predict this currently dominant prairie grass will decline in prevalence and stature. Thus, sourcing plant material for grassland restoration and forage should consider changes in the phenotype that will be favored under future climate conditions. Phenotype distribution models account for the role of intraspecific variation in determining responses to anticipated climate change and thereby complement predictions from species distributions models in guiding climate adaptation strategies.     

The use of precision dendrometers in research on daily stem size and wood property variation: A review

Dendrometers are instruments which are used to measure the diameters of trees. This review considers the use of dendrometers with high spatial and temporal precision in past and present research, the value of which is increasingly being realised. Various insights into tree growth and physiology can be obtained using high-resolution dendrometers, including the assessment of stem daily water status and the understanding of short-term growth responses to changing environmental conditions. This kind of data is useful for irrigation scheduling, assessing site quality, and developing models of the main drivers of tree growth at sub-diurnal resolution. A third, more novel application is the potential these instruments provide as a “template” that relates temporal measurement of growth to spatial measurements of wood properties. Accordingly, this kind of “re-scaled” data is useful in linking environmental conditions which prevailed as the wood formed to varying wood properties along a pith-to-bark wood profile of the sort generated by systems like CSIRO's SilviScan™. This can provide valuable insights into how tree ring structure and radially varying wood properties represent past climates. The development of dendrometers, their use in these three main areas, and a systematic approach to growth-wood property rescaling is discussed in this review.     

A study of the diversity and geographical variation in numbers of leg‐bearing segments in centipedes (Chilopoda: Geophilomorpha) in north‐western Europe

Five species of geophilomorphs, Strigamia maritima (Leach, 1817), Geophilus flavus (De Geer, 1778), Geophilus truncorum Bergsøe and Meinert, 1866, Geophilus proximus C. L. Koch, 1847, and Pachymerium ferrugineum (C. L. Koch, 1835), from various sample sites in north‐western Europe were examined for numbers of leg‐bearing segments. Where data was adequate, mean segment numbers were correlated with latitudinal gradients for each species. Solely in S. maritima and some populations of P. ferrugineum did the results show a highly significant geographic pattern towards more leg‐bearing segments in southern populations of both sexes. As concerns G. proximus, we presented for the first time a remarkable geographic shift towards an increased number of pairs of legs in northern populations. Contrary to the conventional geographic pattern, we found that G. flavus and G. truncorum did not exhibit a north–south increase or decrease in segment number. Although there was no general/universal evidence supporting the occurrence of a significant regression slope between mean segment number and latitude/temperature, more information shows that the overall region‐to‐region segment variation was highly significant in both sexes. In S. maritima and P. ferrugineum mean segment number was correlated with the north–south temperature cline. The same was not observed in G. proximus. Parthenogenesis in G. proximus, and a series of ecological characteristics such as habitat preferences, spatial distribution, and fragmented populations could explain the presence or absence of a geographic patterning of segment number variation along a latitudinal cline. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100 , 899–909.     

A historical perspective of the genus Mytilus (Bivalvia: Mollusca) in New Zealand: multivariate morphometric analyses of fossil, midden and contemporary blue mussels

The taxonomic status of smooth shelled blue mussels of the genus Mytilus has received considerable attention in the last 25 years. Despite this, the situation in the southern hemisphere remains uncertain and is in need of clarification. Recent work suggests that contemporary New Zealand mussels from two cool/cold temperate locations are M. galloprovincialis. However, the distribution of Mytilus in New Zealand ranges from 35 ° to 52 ° south (～ 1800 km), meaning that large areas of the subtropical/warm temperate north and the subantarctic south remain unsampled, an important consideration when species of this genus exhibit pronounced macrogeographical differences in their distributions which are associated with environmental variables such as water temperature, salinity, wave action and ice cover. This study employed multivariate morphometric analyses of one fossil, 83 valves from middens, and 92 contemporary valves from sites spanning the distributional range of blue mussels to determine a historical and contemporary perspective of the taxonomic status of Mytilus in New Zealand. The findings indicated that all fossil and midden mussels are best regarded as M. galloprovincialis and confirmed that contemporary mussels, with one possible regional exception, are also best regarded as M. galloprovincialis. Contemporary mussels from the Bay of Islands (warm temperate/subtropical) exhibited much greater affinity to M. edulis than they did to M. galloprovincialis, indicating that mussels from this area require detailed genetic examination to determine their taxonomic status. The analyses revealed a significant difference between the fossil/midden mussels and the contemporary mussels, consistent with levels of present day differentiation among intraspecific populations and not thought to reflect any substantive temporal change between mussels of the two groups. The continuous distribution of M. galloprovincialis in New Zealand from the warm north to the subantarctic south indicates that the physiology of this species is adapted to a wide range of water temperature conditions. Therefore, the distribution of this species on a worldwide scale is unlikely to be restricted by its adaptation to warm water alone, as has previously been widely assumed. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82 , 329–344.     

Morphology of the vertebral centra in dolphins from the southwestern South Atlantic: A 3D morphometric approach and functional implications

In dolphins, centrum shape is one of the features that allows determination of stable and flexible regions in the vertebral column. The Commerson's (Cephalorhynchus commersonii; n = 37), Peale's (Lagenorhynchus australis; n = 24), dusky (Lagenorhynchus obscurus; n = 29), and hourglass dolphins (Lagenorhynchus cruciger; n = 10) are closely related species inhabiting the Southern Hemisphere that have diverse prey and habitat preferences. We applied 3D geometric morphometrics to describe differences in centrum shape along the vertebral columns of these species, and hypothesize how these differences may affect swimming. On each column, we chose a maximum of eight vertebrae and digitized 18 landmarks on each centrum with a Microscribe G2X. We explored shape differences amongst regions employing principal components analyses and computing Mahalanobis distances. We describe differences in centrum shape in relation to functional regions and among species; and analyze shape changes in relation to particular biomechanical requirements. The species studied here may be partially sympatric in the Southern Hemisphere, but they have important differences in foraging ecology and habitat preferences that could be related to differences in centrum shape along the vertebral column.     

Morphology of the temporal skull region in tetrapods: research history,functional explanations,and a new comprehensive classification scheme

The morphology of the temporal region in the tetrapod skull traditionally has been a widely discussed feature of vertebrate anatomy. The evolution of different temporal openings in Amniota (mammals, birds, and reptiles), Lissamphibia (frogs, salamanders, and caecilians), and several extinct tetrapod groups has sparked debates on the phylogenetic, developmental, and functional background of this region in the tetrapod skull. This led most famously to the erection of different amniote taxa based on the number and position of temporal fenestrae in their skulls. However, most of these taxa are no longer recognised to represent natural groupings and the morphology of the temporal region is not necessarily an adequate trait for use in the reconstruction of amniote phylogenies. Yet, new fossil finds, most notably of parareptiles and stem-turtles, as well as modern embryological and biomechanical studies continue to provide new insights into the morphological diversity of the temporal region. Here, we introduce a novel comprehensive classification scheme for the various temporal morphotypes in all Tetrapoda that is independent of phylogeny and previous terminology and may facilitate morphological comparisons in future studies. We then review the history of research on the temporal region in the tetrapod skull. We document how, from the early 19th century with the first recognition of differences in the temporal region to the first proposals of phylogenetic relationships and their assessment over the centuries, the phylogenetic perspective on the temporal region has developed, and we highlight the controversies that still remain. We also compare the different functional and developmental drivers proposed for the observed morphological diversity and how the effects of internal and external factors on the structure of the tetrapod skull have been interpreted.     

The eyes of a patrolling butterfly: visual field and eye structure in the Orange Sulphur, Colias eurytheme (Lepidoptera, Pieridae)

Sensory information plays a critical role in determining an animal's behavior on both proximate and evolutionary timescales. Butterflies, like many other insects, use vision extensively over their lifetimes, and yet relatively little work has been published to date on their visual capabilities. We describe the visual system of a pierid butterfly, Colias eurytheme, with the ultimate goal of better understanding its role in shaping the behavior of this animal. We made several measurements: visual field dimensions, eye surface area, interommatidial angle (Deltaphi), facet diameter (D), and eye parameter (p). C. eurytheme had a large visual field and considerable regional variation in visual acuity, as inferred by Deltaphi and D. When compared to females, males had larger eye surface areas, smaller Deltaphi, and larger D in all regions except ventrally. Both sexes had proportionally large eye surface areas compared to other butterflies. Minimum p in males was small, indicating that some regions of their eyes may operate close to the diffraction limit. Finally, we found that both eye surface area and D scaled positively, but with negative allometry to body size. We discuss the relevance of these visual characteristics to the biology and behavior of C. eurytheme.     

The importance of scale in comparative microbiome research: New insights from the gut and glands of captive and wild lemurs

Research on animal microbiomes is increasingly aimed at determining the evolutionary and ecological factors that govern host–microbiome dynamics, which are invariably intertwined and potentially synergistic. We present three empirical studies related to this topic, each of which relies on the diversity of Malagasy lemurs (representing a total of 19 species) and the comparative approach applied across scales of analysis. In Study 1, we compare gut microbial membership across 14 species in the wild to test the relative importance of host phylogeny and feeding strategy in mediating microbiome structure. Whereas host phylogeny strongly predicted community composition, the same feeding strategies shared by distant relatives did not produce convergent microbial consortia, but rather shaped microbiomes in host lineage‐specific ways, particularly in folivores. In Study 2, we compare 14 species of wild and captive folivores, frugivores, and omnivores, to highlight the importance of captive populations for advancing gut microbiome research. We show that the perturbational effect of captivity is mediated by host feeding strategy and can be mitigated, in part, by modified animal management. In Study 3, we examine various scent‐gland microbiomes across three species in the wild or captivity and show them to vary by host species, sex, body site, and a proxy of social status. These rare data provide support for the bacterial fermentation hypothesis in olfactory signal production and implicate steroid hormones as mediators of microbial community structure. We conclude by discussing the role of scale in comparative microbial studies, the links between feeding strategy and host–microbiome coadaptation, the underappreciated benefits of captive populations for advancing conservation research, and the need to consider the entirety of an animal's microbiota. Ultimately, these studies will help move the field from exploratory to hypothesis‐driven research.     

The evolutionary history of Fagus in western Eurasia: Evidence from genes, morphology and the fossil record

 Fagus (beech) is among the most abundant and economically important genera of broad-leaved trees in northern hemisphere temperate forests. The number of modern taxa present in Europe and Asia Minor has long been a matter of debate and up to five species have been recognised. To resolve taxonomic and phylogenetic relationships we conducted morphological and molecular genetic analyses in western Eurasiatic taxa and evaluated palaeontological evidence. To place our findings from western Eurasiatic populations in a broader context additional East Asiatic and North American species of the same subgenus Fagus as well as two species of the subgenus Engleriana were included in our study. The morphological features exhibited in western Eurasiatic populations of Fagus show a west-east gradient that is characterised by strongly overlapping variability between geographical races. Fagus populations from Asia Minor exhibit an even higher variability that is also reflected in their genetic variability of nuclear rDNA internal transcribed spacer (ITS) sequences. The intraspecific genetic variability recorded here is in conflict with previous ITS studies in Fagus. The high amount of ITS polymorphism within Fagus from western Eurasia along with the clinal variation observed for morphological characters suggest the presence of only a single species, Fagus sylvatica L., in Europe and Asia Minor. Previously recognised taxa such as F. orientalis Lipsky and Fagus moesiaca (Maly) Czeczott should therefore be treated as synonyms of Fagus sylvatica. Although species belonging to the subgenus Engleriana were genetically distinct from species of the subgenus Fagus, relationships within the subgenus Fagus could not be clearly resolved. A reason for this could be the low rate of diversification in Fagus during the early phase of range expansion of the genus in the Oligocene period as indicated by the uniformity of leaf and cupule/nut fossils. This may account for the low overall ITS divergence and the high degree of polymorphism encountered in the subgenus Fagus and points to a late differentiation of western Eurasiatic and eastern Asiatic species. Area disruptions during the Pleistocene and the post-glacial recolonisation of western Europe appear to have caused the west-east gradient that is apparent in modern Fagus of western Eurasia but absent in Late Tertiary ancestors of Fagus sylvatica. Received June 22, 2001 Accepted February 25, 2002