Study on repairing canine mandibular defect with porous Mg-Sr alloy combined with Mg-Sr alloy membrane.

To discuss the feasibility of the application of porous Mg-Sr alloy combined with Mg-Sr alloy membrane in the repair of mandibular defects in dogs. The second and third mandibular premolars on both sides were extracted from six dogs. The model of mandible buccal fenestration bone defects were prepared after the sockets healed. Twelve bone defects were randomly divided into groups A and B, then Mg-Sr alloy was implanted in bone defects of group A and covered by Mg-Sr alloy membrane while Mg-Sr alloy was implanted in bone defects of group B and covered by mineralized collagen membrane. Bone defects observed on cone beam computed tomographic images and comparing the gray value of the two groups after 4, 8 and 12 weeks. After 12 weeks, the healing of bone defects were evaluated by gross observation, X-ray microscopes and histological observation of hard tissue. Bone defects in each group were repaired. At 8 and 12 weeks, the gray value of group A was higher than that of group B (P < 0.05). At 12 weeks, the bone volume fraction of group A was higher than that of group B (P < 0.05). The newly woven bone in group A is thick and arranged staggered, which was better than that of group B. Porous Mg-Sr alloy combined with Mg-Sr alloy membrane could further promote the repair of mandibular defects, and obtain good osteogenic effect.

Mineralized collagen/Mg-Ca alloy combined scaffolds with improved biocompatibility for enhanced bone response following tooth extraction.

Mineralized collagen has been used clinically as a bone grafting material in oral applications. We have developed a mineralized collagen/Mg-Ca alloy combined scaffold to overcome the mechanical limitations of mineralized collagen. This study discusses the cytocompatibility of the mineralized collage/Mg-Ca alloy combined scaffold in vitro and the bone regeneration following tooth extraction in vivo. Using an indirect proliferation assay adapted from ISO 10993-5, it was found that mineralized collagen/Mg-Ca alloy combined scaffold enhanced cell proliferation and migration in addition to MC3T3-E1 cells not showing a cytotoxicity response in vitro. Finally, the ability of the combined scaffold to enhance osteogenesis was assessed in a canine socket preservation model. Cone beam CT, x-ray microscopes and biomechanical analysis showed the mineralized collagen/Mg-Ca alloy combined scaffold to be more effective at reducing the absorption of alveolar ridge and preserving the socket site than mineralized collagen alone. The combined scaffolds can promote bone regeneration with good biocompatibility, providing a new concept of the combined application of mineralized collagen and magnesium alloy.

Genetic consequences of historical anthropogenic and ecological events on giant pandas.

The giant panda (Ailuropoda melanoleuca) was taken to the brink of extinction in the 1980s through a combination of deforestation, large-scale loss of bamboo in the core of its range, poaching, and zoo collection, causing over 1000 deaths from the 1950s. It was thought that the drastic population decline was likely to impose a severe impact on population viability. Here, based on temporal genotyping of individuals, we show that this rapid decline did not significantly reduce the overall effective population size and genetic variation of this species, or of the two focal populations (Minshan and Qionglai) that declined the most. These results are contrary to previously assumptions, probably because the population decline has not produced the expected negative impact due to the short time scale involved (at most 10 generations), or because previous surveys underestimated the population size at the time of decline. However, if present-day habitat fragmentation and limited migration of giant pandas remains, we predict a loss of genetic diversity across the giant pandas' range in the near future. Thus, our findings highlight the substantial resilience of this species when facing demographic and environmental stochasticity, but key conservation strategies, such as enhancing habitat connectivity and habitat restoration should be immediately implemented to retain the extant genetic variation and maintain long-term evolutionary potential of this endangered species.

Whole-genome sequencing of giant pandas provides insights into demographic history and local adaptation.

The panda lineage dates back to the late Miocene and ultimately leads to only one extant species, the giant panda (Ailuropoda melanoleuca). Although global climate change and anthropogenic disturbances are recognized to shape animal population demography their contribution to panda population dynamics remains largely unknown. We sequenced the whole genomes of 34 pandas at an average 4.7-fold coverage and used this data set together with the previously deep-sequenced panda genome to reconstruct a continuous demographic history of pandas from their origin to the present. We identify two population expansions, two bottlenecks and two divergences. Evidence indicated that, whereas global changes in climate were the primary drivers of population fluctuation for millions of years, human activities likely underlie recent population divergence and serious decline. We identified three distinct panda populations that show genetic adaptation to their environments. However, in all three populations, anthropogenic activities have negatively affected pandas for 3,000 years.

Evidence of cellulose metabolism by the giant panda gut microbiome.

The giant panda genome codes for all necessary enzymes associated with a carnivorous digestive system but lacks genes for enzymes needed to digest cellulose, the principal component of their bamboo diet. It has been posited that this iconic species must therefore possess microbial symbionts capable of metabolizing cellulose, but these symbionts have remained undetected. Here we examined 5,522 prokaryotic ribosomal RNA gene sequences in wild and captive giant panda fecal samples. We found lower species richness of the panda microbiome than of mammalian microbiomes for herbivores and nonherbivorous carnivores. We detected 13 operational taxonomic units closely related to Clostridium groups I and XIVa, both of which contain taxa known to digest cellulose. Seven of these 13 operational taxonomic units were unique to pandas compared with other mammals. Metagenomic analysis using ~37-Mbp contig sequences from gut microbes recovered putative genes coding two cellulose-digesting enzymes and one hemicellulose-digesting enzyme, cellulase, ß-glucosidase, and xylan 1,4-ß-xylosidase, in Clostridium group I. Comparing glycoside hydrolase profiles of pandas with those of herbivores and omnivores, we found a moderate abundance of oligosaccharide-degrading enzymes for pandas (36%), close to that for humans (37%), and the lowest abundance of cellulases and endohemicellulases (2%), which may reflect low digestibility of cellulose and hemicellulose in the panda's unique bamboo diet. The presence of putative cellulose-digesting microbes, in combination with adaptations related to feeding, physiology, and morphology, show that giant pandas have evolved a number of traits to overcome the anatomical and physiological challenge of digesting a diet high in fibrous matter.

Significant genetic boundaries and spatial dynamics of giant pandas occupying fragmented habitat across southwest China.

Understanding population history and genetic structure are key drivers of ecological research. Here, we studied two highly fragmented and isolated populations (Xiaoxiangling and Daxiangling) of giant pandas (Ailuropoda melanoleuca) at the extreme southwestern edge of their distribution. This area also contains the Dadu River, national road 108 and various human infrastructure and development, providing an ideal region in which we can identify the effects of different barriers on animal movements. We used partial mitochondrial control region (mtDNA) and nine microsatellite loci (nuclear DNA) data derived from 192 faecal and one blood sample collected from the wild. We found 136 genotypes corresponding to 53 unique multilocus genotypes and eight unique control region haplotypes (653 bp). Significant genetic boundaries correlated spatially with the Dadu River (K = 2). We estimate that a major divergence took place between these populations 26,000 years bp, at around the similar time the rock surface of valley bottom formed in Dadu River. The national road has resulted in further recent population differentiation (Pairwise F(S) on mtDNA and nuclear DNA) so that in effect, four smaller sub-populations now exist. Promisingly, we identified two possible first-generation migrants and their migration paths, and recommended the immediate construction of a number of corridors. Fortunately, the Chinese government has accepted our advice and is now planning corridor construction.

Old-growth forest is what giant pandas really need.

Giant pandas (Ailuropoda melanoleuca) are an iconic conservation species, but despite significant research effort, do we understand what they really need? Estimating and mapping suitable habitat play a critical role in conservation planning and policy. But if assumptions about ecological needs are wrong, maps with misidentified suitable habitat will misguide conservation action. Here, we use an information-theoretic approach to analyse the largest, landscape-level dataset on panda habitat use to date, and challenge the prevailing wisdom about panda habitat needs. We show that pandas are associated with old-growth forest more than with any ecological variable other than bamboo. Other factors traditionally used in panda habitat models, such as topographic slope, are less important. We suggest that our findings are disparate from previous research in part because our research was conducted over a larger ecological scale than previous research conducted over more circumscribed areas within individual reserves. Thus, extrapolating from habitat studies on small scales to conservation planning on large scales may entail some risk. As the Chinese government is considering the renewal of its logging ban, it should take heed of the panda's dependency on old growth.

Landscape features influence gene flow as measured by cost-distance and genetic analyses: a case study for giant pandas in the Daxiangling and Xiaoxiangling Mountains.

BACKGROUND: Gene flow maintains genetic diversity within a species and is influenced by individual behavior and the geographical features of the species' habitat. Here, we have characterized the geographical distribution of genetic patterns in giant pandas (Ailuropoda melanoleuca) living in four isolated patches of the Xiaoxiangling and Daxiangling Mountains. Three geographic distance definitions were used with the "isolation by distance theory": Euclidean distance (EUD), least-cost path distance (LCD) defined by food resources, and LCD defined by habitat suitability. RESULTS: A total of 136 genotypes were obtained from 192 fecal samples and one blood sample, corresponding to 53 unique genotypes. Geographical maps plotted at high resolution using smaller neighborhood radius definitions produced large cost distances, because smaller radii include a finer level of detail in considering each pixel. Mantel tests showed that most correlation indices, particularly bamboo resources defined for different sizes of raster cell, were slightly larger than the correlations calculated for the Euclidean distance, with the exception of Patch C. We found that natural barriers might have decreased gene flow between the Xiaoxiangling and Daxiangling regions. CONCLUSIONS: Landscape features were found to partially influence gene flow in the giant panda population. This result is closely linked to the biological character and behavior of giant pandas because, as bamboo feeders, individuals spend most of their lives eating bamboo or moving within the bamboo forest. Landscape-based genetic analysis suggests that gene flow will be enhanced if the connectivity between currently fragmented bamboo forests is increased.

Conservation implications of drastic reductions in the smallest and most isolated populations of giant pandas.

In conservation biology, understanding the causes of endangerment is a key step to devising effective conservation strategies. We used molecular evidence (coalescent simulations of population changes from microsatellite data) and historical information (habitat and human population changes) to investigate how the most-isolated populations of giant pandas (Ailuropoda melanoleuca) in the Xiaoxiangling Mountains became highly endangered. These populations experienced a strong, recent demographic reduction (60-fold), starting approximately 250 years BP. Explosion of the human population and use of non-native crop species at the peak of the Qing Empire resulted in land-use changes, deforestation, and habitat fragmentation, which are likely to have led to the drastic reduction of the most-isolated populations of giant pandas. We predict that demographic, genetic, and environmental factors will lead to extinction of giant pandas in the Xiaoxiangling Mountains in the future if the population remains isolated. Therefore, a targeted conservation action--translocation--has been proposed and is being implemented by the Chinese government.

Genetic viability and population history of the giant panda, putting an end to the "evolutionary dead end"?

The giant panda (Ailuropoda melanoleuca) is currently threatened by habitat loss, fragmentation, and human persecution. Its dietary specialization, habitat isolation, and reproductive constraints have led to a perception that this is a species at an "evolutionary dead end," destined for deterministic extinction in the modern world. Here we examine this perception by a comprehensive investigation of its genetic diversity, population structure, and demographic history across its geographic range. We present analysis of 655 base pairs of mitochondrial (mt) control region (CR) DNA and 10 microsatellite loci for samples from its 5 extant mountain populations (Qinling, Minshan, Qionglai, Liangshan, and Lesser Xiangling). Surprisingly, extant populations display average to high levels of CR and microsatellite diversity compared with other bear species. Genetic differentiation among populations was significant in most cases but was markedly higher between Qinling and the other mountain ranges, suggesting, minimally, that the Qinling population should comprise a separate management unit for conservation purposes. Recent demographic inference using microsatellite markers demonstrated a clear genetic signature for population decline starting several thousands years ago or even further back in the past, and being accelerated and enhanced by the expansion of human populations. Importantly, these data suggest that the panda is not a species at an evolutionary "dead end," but in common with other large carnivores, has suffered demographically at the hands of human pressure. Conservation strategies should therefore focus on the restoration and protection of wild habitat and the maintenance of the currently substantial regional genetic diversity, through active management of disconnected populations.