鸟类毛囊形态发生中的分子信号

鸟类羽毛形态各异、功能多样,一直是国外研究的热点。毛囊是羽毛生长的载体,近年来,国外以鸡作为模式动物,对其毛囊生长发育规律、调控因子及其调控作用进行了大量研究。研究中发现,很多调控因子参与了毛囊形态发生过程,构成了极其复杂的信号网络。     

Repeatability of Feather Mite Prevalence and Intensity in Passerine Birds

Understanding why host species differ so much in symbiont loads and how this depends on ecological host and symbiont traits is a major issue in the ecology of symbiosis. A first step in this inquiry is to know whether observed differences among host species are species-specific traits or more related with host-symbiont environmental conditions. Here we analysed the repeatability (R) of the intensity and the prevalence of feather mites to partition within- and among-host species variance components. We compiled the largest dataset so far available: 119 Paleartic passerine bird species, 75,944 individual birds, ca. 1.8 million mites, seven countries, 23 study years. Several analyses and approaches were made to estimate R and adjusted repeatability (R_adj) after controlling for potential confounding factors (breeding period, weather, habitat, spatial autocorrelation and researcher identity). The prevalence of feather mites was moderately repeatable (R = 0.26–0.53; R_adj = 0.32–0.57); smaller values were found for intensity (R = 0.19–0.30; R_adj = 0.18–0.30). These moderate repeatabilities show that prevalence and intensity of feather mites differ among species, but also that the high variation within species leads to considerable overlap among bird species. Differences in the prevalence and intensity of feather mites within bird species were small among habitats, suggesting that local factors are playing a secondary role. However, effects of local climatic conditions were partially observed for intensity.     

Allometry of the Duration of Flight Feather Molt in Birds

We used allometric scaling to explain why the regular replacement of the primary flight feathers requires disproportionately more time for large birds. Primary growth rate scales to mass (M) as M^0.171, whereas the summed length of the primaries scales almost twice as fast (M^0.316). The ratio of length (mm) to rate (mm/day), which would be the time needed to replace all the primaries one by one, increases as the 0.14 power of mass (M^0.316/M^0.171=M^0.145), illustrating why the time required to replace the primaries is so important to life history evolution in large birds. Smaller birds generally replace all their flight feathers annually, but larger birds that fly while renewing their primaries often extend the primary molt over two or more years. Most flying birds exhibit one of three fundamentally different modes of primary replacement, and the size distributions of birds associated with these replacement modes suggest that birds that replace their primaries in a single wave of molt cannot approach the size of the largest flying birds without first transitioning to a more complex mode of primary replacement. Finally, we propose two models that could account for the 1/6 power allometry between feather growth rate and body mass, both based on a length-to-surface relationship that transforms the linear, cylindrical growing region responsible for producing feather tissue into an essentially two-dimensional structure. These allometric relationships offer a general explanation for flight feather replacement requiring disproportionately more time for large birds.     

Birds of a Feather Flock Together: Experience-Driven Formation of Visual Object Categories in Human Ventral Temporal Cortex

The present functional magnetic resonance imaging study provides direct evidence on visual object-category formation in the human brain. Although brain imaging has demonstrated object-category specific representations in the occipitotemporal cortex, the crucial question of how the brain acquires this knowledge has remained unresolved. We designed a stimulus set consisting of six highly similar bird types that can hardly be distinguished without training. All bird types were morphed with one another to create different exemplars of each category. After visual training, fMRI showed that responses in the right fusiform gyrus were larger for bird types for which a discrete category-boundary was established as compared with not-trained bird types. Importantly, compared with not-trained bird types, right fusiform responses were smaller for visually similar birds to which subjects were exposed during training but for which no category-boundary was learned. These data provide evidence for experience-induced shaping of occipitotemporal responses that are involved in category learning in the human brain.     

Raptors rehabilitated in Iowa during 1986 and 1987: a retrospective study

A retrospective study was conducted on 60 raptors representing 13 species treated at the Iowa State University College of Veterinary Medicine during 1986-1987. Eight species (31 individuals) were Falconiformes and five species (29 individuals) were Strigiformes. Seventy-five percent of all injuries were due to trauma and 65% of these were injuries arising from human activity, including car collisions (28%), shooting (17%) and trapping (11%). Thirty-four percent of all raptors admitted were treated and released, 25% were permanently crippled and 41% died during treatment or were euthanized. Data from this study implicate trauma resulting from human activity as a major reason for injury in free-ranging raptors presented for treatment in Iowa.     

Evolving a Protofeather and Feather Diversity

It is likely that feathers evolved from a conical shaped tuberclerather than a plate-like structure. Although the morphologyof the presumably most primitive feather is unknown, minimalconditions for its production include the cellular capacityto synthesize feather proteins (=-keratin) which provides themolecular phenotype, and a follicular mechanism for productionand assembly of molecular and gross structure. Once the minimalstructural element, presumably recognizable as a barb, existed,a variety of phenotypes followed rapidly. A tubercular growthcenter of appropriate size could produce a simple barb-likeelement, with cortex and medulla. This might be recognized externallyas a bristle, but need never existed as a separate morphologicalunit. Rather, if individual placodes gave rise to multiple barbridges that fused proximally, a structure resembling natal downwould have resulted. Subsequent differentiation is controlledby the follicular symmetry, and the feather shape is regulatedby barb length. Barb length is directly related to growth period.As feathers appear to grow at roughly similar, size independentrates, shape is determined by individual barb growth periods.The simple fusion of individual proto-barbs would produce amorphology identifiable as natal down. Although this might bethe simplest feather structure, others could emerge quickly,perhaps simultaneously, a consequence of the same redundantprocessing. Once the machinery existed, broad phenotypic plasticitywas possible. I constructed a feather phylogram based on theseconditions, the fossil record, and ontogeny. I organized thesubsequent changes in morphology by perceived complexity. Thechanges are simply individual responses to similar processesthat might be time (when in ontogeny) and space (where on body)dependent.     

Novel Denisovan and Neanderthal Retroviruses

Following the recent availability of high-coverage genomes for Denisovan and Neanderthal hominids, we conducted a screen for endogenized retroviruses, identifying six novel, previously unreported HERV-K(HML2) elements (HERV-K is human endogenous retrovirus K). These elements are absent from the human genome (hg38) and appear to be unique to archaic hominids. These findings provide further evidence supporting the recent activity of the HERV-K(HML2) group, which has been implicated in human disease. They will also provide insights into the evolution of archaic hominids.     

Kebara 2 Neanderthal pelvis: first look at a complete inlet

The renewed excavations at the Kebara Cave revealed a Neanderthal skeleton dated at about 50-55,000 years B.P. The pelvis of this individual is the most intact Neanderthal pelvis yet discovered, presenting for the first time a complete inlet. Although the superior pubic ramus is extremely long, as typically seen in the Neanderthals, the size of the pelvic inlet is comparable to that of modern Homo sapiens. The length of the superior pubic ramus is found to stem from a more externally rotated innominate bone and not, as generally assumed, from the larger pelvic inlet. It is suggested that the uniqueness of the Neanderthal pelvis may be attributable to locomotion and posture-related biomechanics rather than to obstetric requirements.     

High and Low Intensity Hunting in Raptors

Two main hunting techniques are described. It is postulated that hunting takes place at two levels of intensity, High and Low, and that the success rate in the former is much higher than the latter. It is suggested that the function of Low Intensity hunting is to keep the Peregrine in ‘good practice’ for High Intensity hunting.