Patterns of bone microstructure have frequently been used to deduce dynamics and processes of growth in extant and fossil tetrapods. Often, the various types of primary bone tissue have been associated with different bone deposition rates and more recently such deductions have extended to patterns observed in dinosaur bone microstructure. These previous studies are challenged by the findings of the current research, which integrates an experimental neontological approach and a paleontological comparison. We use tetracycline labeling and morphometry to study the variability of bone deposition rates in Japanese quail (Coturnix japonica) growing under different experimental conditions. We compare resulting patterns in bone microstructure with those found in fossil birds and other dinosaurs. We found that a single type of primary bone varies significantly in rates of growth in response to environmental conditions. Ranging between 10-50 microm per day, rates of growth overlap with the full range of bone deposition rates that were previously associated with different patterns of bone histology. Bone formation rate was significantly affected by environmental/experimental conditions, skeletal element, and age. In the quail, the experimental conditions did not result in formation of lines of arrested growth (LAGs). Because of the observed variation of bone deposition rates in response to variation in environmental conditions, we conclude that bone deposition rates measured in extant birds cannot simply be extrapolated to their fossil relatives. Additionally, we observe the variable incidence of LAGs and annuli among several dinosaur species, including fossil birds, extant sauropsids, as well as nonmammalian synapsids, and some extant mammals. This suggests that the ancestral condition of the response of bone to environmental conditions was variable. We propose that such developmental plasticity in modern birds may be reduced in association with the shortened developmental time during the later evolution of the ornithurine birds.

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Over the past two decades, the development of methods for visualizing and analysing specimens digitally, in three and even four dimensions, has transformed the study of living and fossil organisms. However, the initial promise that the widespread application of such methods would facilitate access to the underlying digital data has not been fully achieved. The underlying datasets for many published studies are not readily or freely available, introducing a barrier to verification and reproducibility, and the reuse of data. There is no current agreement or policy on the amount and type of data that should be made available alongside studies that use, and in some cases are wholly reliant on, digital morphology. Here, we propose a set of recommendations for minimum standards and additional best practice for three-dimensional digital data publication, and review the issues around data storage, management and accessibility.

During northward migration, blackcaps that arrive to refuel at stopover sites in Israel's Negev Desert have reduced masses of organs that are important in food digestion and assimilation. We tested several predictions from the general hypothesis that smaller organs of digestion (small intestine and pancreas) and nutrient assimilation (liver) bring about a lower capacity to consume food and that the organs must be restored before blackcaps can feed and digest at a high rate. We used a fasting protocol to create a group of blackcaps with reduced intestine and liver mass (reduced by 45% and 36%, respectively) compared with controls fed ad lib. Because most of the small intestine's biochemical digestive capacity reside in enterocytes found on villi, we predicted and found that reduced intestinal mass in fasted blackcaps related mainly to changes in enterocytes rather than other cells and tissues such as nonabsorptive crypt cells or underlying muscle. Because migrating blackcaps that stop over to feed begin to increase in body mass only 2 d after arrival, we predicted and found a similar recovery period in blackcaps that were first fasted but then refed--the organ mass, structure, function, and ability to consume food was restored after 2 d of feeding. Another group of food-restricted blackcaps (fed at one-third ad lib. level) lost similar amounts of body mass as fasted blackcaps but had much greater capacity to consume food than fasted blackcaps, and so we predicted that they would exhibit little or no reduction in alimentary organs relative to controls fed ad lib. A surprising result was that, as in fasted blackcaps, in food-restricted blackcaps, the decreases in masses of small intestine, liver, and pancreas were proportionally greater than the decreases in body mass or in masses of nonalimentary organs (heart, pectoralis). Food restriction, like fasting, caused a decrease in amount of intestinal mucosa and an alteration in the phenotype of enterocytes. These results are thus not consistent with the general hypothesis, and although they can be rationalized by assuming that blackcaps fed ad lib. have excess digestive capacity, it may also be that the physiological process or processes limiting very high feeding rate lie elsewhere than in the digestive system.

SUMMARYOrganisms adjust their phenotype to fluctuating conditions of the environment and to changing internal demands. We report flexible responses of the gizzard and the small intestine of Japanese quail to a high-fibre diet. Switching from a standard diet to a high-fibre diet results in a highly significant increase in gizzard size, intestine length, mucosal surface,thickness of the intestinal muscular layer and vascularization of the mucosa. After diet switching, increased or decreased gizzard size results from changes in cell size, i.e. smooth muscle cell hypertrophy and hypotrophy,respectively. Increased cell proliferation is not the cause of increase in gizzard size. In the small intestine, however, we found elevated levels of cell proliferation after diet switching and conclude that increased capacity(upregulation) of the small intestine is based on increased rates of mitosis in the intestinal crypts. It is highly probable that elevated levels of cell proliferation in the crypts are balanced by elevated levels of cell extrusion at the tip of intestinal villi. The lipid contents of the liver were reduced,indicating that lipid stores in the liver were mobilized to fuel the flexible response of the gastrointestinal tract. During changes of organ size in response to changes in food composition, resting metabolic rate was not altered.

The vertebrate gastrointestinal tract is a flexible system that can individually be modified to account for changes in amount and quality of food as well as changes in internal demands. In this paper, I summarise some recent findings and ideas about processes on the level of tissues and cells that allow vertebrates to adjust their intestines to fluctuating conditions. In mammals and birds intestinal flexibility is based on a balance of cell proliferation and cell loss. Maintenance as well as up- and down-regulation of the mucosa involves bio-production or dystrophy of tissue. Both are assumed to be energetically expensive. In contrast, up- and down-regulation of the mucosal epithelium of ectotherm sauropsids is based on configuration changes of the pseudostratified mucosal epithelium. Up-regulation of the mucosa size does not involve cell proliferation, thus it is presumably an energetically cheap process. A comparison of mammals, birds, and ectotherm sauropsids (mainly snakes) allows the development of some new ideas about the historical path of the evolution of gastrointestinal flexibility. Snakes seem to share with other basal tetrapods a phylogenetically plesiomorphic pattern. Birds and mammals have independently evolved new mechanisms that sustain flexibility at a high metabolic level.

Based on a detailed description of hatchling skeletons of the precocial buttonquail (Turnix suscitator) and the altricial budgerigar (Melopsittacus undulatus), this report presents the hypothesis that the rate of avian posthatching growth is limited by the quantitative design (i.e., relative volumes of cartilage, bone, and marrow) of the hatchling skeletons. A Jarge portion of bone in the skeletal elements and fast growth are hypothesized to be mutually exclusive. This hypothesis is tested by morphometric techniques and by statistical comparison of morphometric and growth data. All predictions are met by the data, and the design of hatchling skeletons is described as determined by a tradeoff between tissue composition of skeletal elements and maximum rates of posthatching growth. The precocial design shows large bony areas that supposedly resist mechanical stress of locomotion; however, the relatively small cartilaginous areas exclude high growth rates. The altricial design shows the reverse relationship with small bony areas and a lack of locomotion on the one side but large cartilaginous areas and fast posthatching growth on the other side. © 1994 Wiley-Liss, Inc.