A preliminary assessment of congruence between biodiversity patterns in Afrotropical forest birds and forest mammals

Burgess, N., de Klerk, H., Fjeldsá, J., Crowe, T. & Rahbek, R. 2000. A preliminary assessment of congruence between biodiversity patterns in Afrotropical forest birds and forest mammals. Ostrich 71 (1 & 2): 286–291.

Databases compiled for forest birds and forest mammals in the Afrotropics were tested for congruence of overall patterns and hotspots of species richness and endemism. We also looked at how well a near-minimum set of priority areas for one taxon catered for the second taxon. Overall species richness and richness hotspots of forest birds were significantly correlated with those of forest mammals, as was the case for overall endemism. Endemism hotspots for forest birds and mammals were not significantly correlated. The near-minimum set for forest birds represented 136 (76.5%) forest mammal species. The near-minimum set for forest mammals represented 350 (93.62%) forest bird species. However, to represent all forest mammals three times each, 51 grids were needed in addition to the 78 chosen as a near-minimum set for forest birds, and to represent all forest birds three times each, 43 more grids were needed in addition to the 80 selected for forest mammals. There is some congruence between the patterns of richness, endemism and near-minimum sets for forest birds and mammals in the Afrotropics, but the one taxon does not provide the ideal conservation solution for the other. Further refinement of the databases used in this paper would allow for more rigorous testing of congruence between these two groups.     

Three-dimensional analysis of mandibular morphology in Otolemur

Euclidean distance matrix analysis (EDMA) of three-dimensional data is used here to examine mandibular morphology between two species of galagos. Otolemur crassicaudatus consumes primarily exudates, while O. garnettii is more frugivorous. Acquisition of exudates involves either gouging or scraping tree bark, and may involve different forces at the mandible than incising fruits. Previous studies of mandibular morphology in exudate-feeding primates produced mixed results, some suggesting that morphological specializations reflect adaptations for greater force at the anterior dentition, while others suggest specializations for producing a large gape. This study addresses these controversies by testing predictions associated with O. crassicaudatus generating greater force at the anterior dentition or producing a larger gape relative to O. garnettii. In addition, this study tests predictions associated with specializations of the anterior dentition in O. crassicaudatus as related to exudate-feeding. Crania and mandibles from 28 O. crassicaudatus and 17 O. garnettii were digitized in three dimensions, using 18 landmarks that summarize the shape of the jaw. Two-dimensional measurements were taken to assess incisor robusticity. All three-dimensional data were analyzed using EDMA, and bootstrap tests were executed to identify specific interlandmark differences that were driving any significant (P < 0.05) overall shape differences. Two-dimensional data were analyzed using Student's t-test for independent measures. Results revealed that there was a significant shape difference in mandibles between species, and that mandibles of O. crassicaudatus showed higher condyles, longer mandibles, decreased incisor procumbency, and greater incisor robusticity relative to O. garnettii. It is suggested that the results of the present study reflect adaptations for scraping in O. crassicaudatus rather than gouging.     

哺乳动物阴茎骨长度与延长性插入模式之间存在正相关的关系

阴茎骨长度增加的进化 ,部分原因与交配模式有关 ,后者涉及到延长性插入持续时间。但是 ,对于北美的食肉动物来说 ,这个假说一直有争议。为了检验这个假说 ,我们收集了来自食肉动物、蝙蝠和灵长类的 1 4 4个属 31 5种哺乳动物阴茎骨长度和体重的数据 ,除了阴茎骨长度和体重以外 ,对已知的 39个属的插入持续时间进行了线形多次回归分析。结果表明 :阴茎骨长度与插入持续时间之间存在极显著的正相关关系 (r2 =0 6 5 ,F=4 0 4 8,P <0 0 0 0 1 )。然后 ,使用了独立对比的比较分析以控制数据系统发育的偏差 ,在物种水平上对数据进行了分析 ,结果证实 :阴茎骨长度与插入持续时间之间有显著的相关关系 (r2 =0 6 9,F =34 2 3,P <0 0 0 1 )。本研究支持阴茎骨长度进化的延长性插入假说     

A preliminary study of mandibular shape

There is a growing realization that traditional osteometric data are of uncertain scientific validity, primarily due to the lack of dissociation between size and shape parameters. This study was specifically based on the metrical definition of mandibular morphologic shape, using a technique termed medial axis transformation. It was based on the digitized mandibular outlines of three age-sexed samples of microcephalics, macrocephalics, and normocephalics. Evaluation of the derived medial axis lengths and branch point distances indicated complex patterns of mandibular shape contrasts between microcephalics and macrocephalics on the one hand and normocephalics on the other. Although larger more homogeneous samples are required to evaluate the specific factors influencing mandibular shape, the present data suggest an association between mandibular shape and cranial form.     

The macroevolutionary relationship between diet and body mass across mammals

Body mass and diet are two fundamental ecological parameters that influence many other aspects of an animal's biology. Thus, the potential physiological and ecological processes linking size and diet have been the subject of extensive research, although the broad macroevolutionary relationship between the two traits remains largely unexplored phylogenetically. Using generalized Ornstein–Uhlenbeck models and data on over 1350 species of mammal, we reveal that evolutionary changes in body mass are consistently associated with dietary changes across mammals. Best‐fitting models find that herbivores are substantially heavier than other dietary groups and that omnivores are frequently intermediate in mass between herbivores and carnivores. Interestingly, although flying and swimming both place very different physical constraints on mass, bats still follow the general mammalian pattern but marine mammals do not. Such differences may be explained by reduced gravitational constraints on size in water along with ecological differences in food availability between aquatic and terrestrial realms, allowing marine carnivores to become the largest mammals on earth. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 115 , 173–184.     

Three-dimensional analysis of mandibular dental root morphology in hominoids

Although often preserved in the fossil record, mandibular dental roots are rarely used for evolutionary studies. This study qualitatively and quantitatively characterizes the three-dimensional morphology of hominoid dental roots. The sample comprises extant apes as well as two fossil species, Khoratpithecus piriyai and Ouranopithecus macedoniensis. The morphological differences between extant genera are observed, quantified and tested for their potential in systematics. Dental roots are imaged using X-ray computerized tomography, conventional microtomography and synchrotron microtomography. Resulting data attest to the high association between taxonomy and tooth root morphology, both qualitatively and quantitatively. A cladistic analysis based on the dental root characters resulted in a tree topology congruent with the consensus phylogeny of hominoids, suggesting that tooth roots might provide useful information in reconstructing hominoid phylogeny. Finally, the evolution of the dental root morphology in apes is discussed.     

Biting through constraints: cranial morphology, disparity and convergence across living and fossil carnivorous mammals

Carnivory has evolved independently several times in eutherian (including placental) and metatherian (including marsupial) mammals. We used geometric morphometrics to assess convergences associated with the evolution of carnivory across a broad suite of mammals, including the eutherian clades Carnivora and Creodonta and the metatherian clades Thylacoleonidae, Dasyuromorphia, Didelphidae and Borhyaenoidea. We further quantified cranial disparity across eutherians and metatherians to test the hypothesis that the marsupial mode of reproduction has constrained their morphological evolution. This study, to our knowledge the first to extensively sample pre-Pleistocene taxa, analysed 30 three-dimensional landmarks, focused mainly on the facial region, which were digitized on 130 specimens, including 36 fossil taxa. Data were analysed with principal components (PC) analysis, and three measures of disparity were compared between eutherians and metatherians. PC1 showed a shift from short to long faces and seemed to represent diet and ecology. PC2 was dominated by the unique features of sabre-toothed forms: dramatic expansion of the maxilla at the expense of the frontal bones. PC3, in combination with PC1, distinguished metatherians and eutherians. Metatherians, despite common comparisons with felids, were more similar to caniforms, which was unexpected for taxa such as the sabre-toothed marsupial Thylacosmilus. Contrary to previous studies, metatherian carnivores consistently exhibited disparity which exceeded that of the much more speciose eutherian carnivore radiations, refuting the hypothesis that developmental constraints have limited the morphological evolution of the marsupial cranium.     

Correlates between calcaneal morphology and locomotion in extant and extinct carnivorous mammals

Locomotor mode is an important component of an animal's ecology, relating to both habitat and substrate choice (e.g., arboreal versus terrestrial) and in the case of carnivores, to mode of predation (e.g., ambush versus pursuit). Here, we examine how the morphology of the calcaneum, the ‘heel bone’ in the tarsus, correlates with locomotion in extant carnivores. Other studies have confirmed the correlation of calcaneal morphology with locomotion behaviour and habitat. The robust nature of the calcaneum means that it is frequently preserved in the fossil record. Here, we employ linear measurements and 2D‐geometric morphometrics on a sample of calcanea from eighty‐seven extant carnivorans and demonstrate a signal of correlation between calcaneal morphology and locomotor mode that overrides phylogeny. We used this correlation to determine the locomotor mode, and hence aspects of the palaeobiology of, 47 extinct carnivorous mammal taxa, including both Carnivora and Creodonta. We found ursids (bears), clustered together, separate from the other carnivorans. Our results support greater locomotor diversity for nimravids (the extinct ‘false sabertooths’, usually considered to be more arboreal), than previously expected. However, there are limitations to interpretation of extinct taxa because their robust morphology is not fully captured in the range of modern carnivoran morphology.     

Correlations between feeding type and mandibular morphology in the sika deer

Morphological comparisons of the sika deer Cervus nippon mandible and molars were conducted between two (northern and southern) Japanese subspecific lineages and among local populations of different ('grazer' or 'intermediate feeder') feeding types. The northern lineage showed greater M₁ breadth, M₃ hypsodonty and mandibular corpus height than the southern lineage. Such differences were not observed between the 'grazer' and 'intermediate feeder' populations of the northern lineage. However, a northern population, which inhabits a particularly harsh environment (Kinkazan Island), had the largest values of relative molar size and hypsodonty, although this was not statistically significant. These results imply that, in the Japanese sika deer, the selective pressures acting on the current 'grazer' populations are not strong enough to bring out noticeable adaptive change in molar size and hypsodonty, but adaptive change in these traits may occur in an environment that promotes excessive molar wear, more than that seen in the current sika deer habitats of Japan. Combined with what is known of the Pleistocene history of the sika deer, we infer that the ancestral population of the northern Japanese lineage likely acquired their relatively larger and more hypsodont molars in an extremely harsh environment during the last or previous glacial periods.     

The ghosts of mammals past: biological and geographical patterns of global mammalian extinction across the Holocene

Although the recent historical period is usually treated as a temporal base-line for understanding patterns of mammal extinction, mammalian biodiversity loss has also taken place throughout the Late Quaternary. We explore the spatial, taxonomic and phylogenetic patterns of 241 mammal species extinctions known to have occurred during the Holocene up to the present day. To assess whether our understanding of mammalian threat processes has been affected by excluding these taxa, we incorporate extinct species data into analyses of the impact of body mass on extinction risk. We find that Holocene extinctions have been phylogenetically and spatially concentrated in specific taxa and geographical regions, which are often not congruent with those disproportionately at risk today. Large-bodied mammals have also been more extinction-prone in most geographical regions across the Holocene. Our data support the extinction filter hypothesis, whereby regional faunas from which susceptible species have already become extinct now appear less threatened; they may also suggest that different processes are responsible for driving past and present extinctions. We also find overall incompleteness and inter-regional biases in extinction data from the recent fossil record. Although direct use of fossil data in future projections of extinction risk is therefore not straightforward, insights into extinction processes from the Holocene record are still useful in understanding mammalian threat.     

Motor training induces experience-specific patterns of plasticity across motor cortex and spinal cord.

The motor cortex and spinal cord possess the remarkable ability to alter structure and function in response to differential motor training. Here we review the evidence that the corticospinal system is not only plastic but that the nature and locus of this plasticity is dictated by the specifics of the motor experience. Skill training induces synaptogenesis, synaptic potentiation, and reorganization of movement representations within motor cortex. Endurance training induces angiogenesis in motor cortex, but it does not alter motor map organization or synapse number. Strength training alters spinal motoneuron excitability and induces synaptogenesis within spinal cord, but it does not alter motor map organization. All three training experiences induce changes in spinal reflexes that are dependent on the specific behavioral demands of the task. These results demonstrate that the acquisition of skilled movement induces a reorganization of neural circuitry within motor cortex that supports the production and refinement of skilled movement sequences. We present data that suggest increases in strength may be mediated by an increased capacity for activation and/or recruitment of spinal motoneurons while the increased metabolic demands associated with endurance training induce cortical angiogenesis. Together these results show the robust pattern of anatomic and physiological plasticity that occurs within the corticospinal system in response to differential motor experience. The consequences of such distributed, experience-specific plasticity for the encoding of motor experience by the motor system are discussed.     

Wound ballistics of the pig mandibular angle: A preliminary finite element analysis and experimental study

To study wound ballistics of the mandibular angle, a combined hexahedral-tetrahedral finite element (FE) model of the pig mandible was developed to simulate ballistic impact. An experimental study was carried out by measuring impact load parameters from 14 fresh pig mandibles that were shot at the mandibular angle by a standard 7.62 mm M43 bullet. FE analysis was executed through the LS-DYNA code under impact loads similar to those obtained from the experimental study. The resulting residual velocity, the transferred energy from the bullet to the mandible, and the surface area of the entrance wound had no statistical differences between the FE simulation and the experimental study. However, the mean surface area of the exit wounds in the experimental study was significantly larger than that in the simulation. According to the FE analysis, the stress concentrated zones were mainly located at the region of impact, condylar neck, coronoid process and mandibular body. The simulation results also indicated that trabecular bone had less stress concentration and a lower speed of stress propagation compared with cortical bone. The FE model is appropriate and conforms to the basic principles of wound ballistics. This modeling system will be helpful for further investigations of the biomechanical mechanisms of wound ballistics.     

Occupancy and co-occurrence patterns of endemic mammals and introduced predators across a broad geographical gradient in eastern Australia

Biodiversity and Conservation - Invasive predators, land clearing and altered fire regimes have been implicated in species decline and extinction worldwide. Enhanced knowledge of how these factors...     

Effects of dietary inositol with sucrose stimulation on chewing and swallowing motor patterns in larvae of the silkworm Bombyx mori

The effects of dietary inositol with sucrose stimulation on chewing and swallowing motor patterns in the larvae of Bombyx mori L. are investigated. Feeding activities of the larvae are significantly enhanced by a test diet containing an inositol–sucrose mixture compared with a test diet of sucrose only. Motor patterns of the mandibular closer muscle are accelerated with shorter burst durations and shorter inter‐burst intervals with the test diet of inositol–sucrose compared with sucrose. In terms of swallowing behaviours, inositol–sucrose shortens the duration of drinking. Motor patterns of the cibarial compressor muscle are accelerated with shorter burst durations and shorter inter‐burst intervals with the inositol–sucrose mixture. Peripheral interactions between inositol‐ and sucrose‐sensitive cells in the maxilla are not detected. Thus, such interactions cannot explain the positive effects of inositol on chewing and swallowing. Responses of inositol‐sensitive cells in the epipharyngeal sensillum are not affected by sucrose. These results suggest that dietary inositol can modify chewing and swallowing motor patterns when coupled with sucrose stimuli. These modifications may occur in the central neural networks involved in chewing and swallowing motor patterns but not in peripheral sensory interactions.