Hyaluronan is an abundant constituent of the extracellular matrix of Xenopus embryos

The spatiotemporal distribution of hyaluronan (HA), a major constituent of the vertebrate extracellular matrix, was analyzed during early embryonic development of Xenopus laevis. This polysaccharide is abundantly present in ventricular structures such as the blastocoel, the archenteron as well as later on in the hepatic cavity, the brain ventricles and the developing heart. At the blastula stage, HA was detected in the extracellular matrix of the ecto- and mesodermal primordia. Shortly before gastrulation, it becomes enriched at the basal site of the superficial cell layer of the ectoderm. During gastrulation, enhanced synthesis of HA takes place in the involuting marginal zone, shortly before invagination starts, hence, resulting in a torus-like deposition in the deep layer of the equatorial mesodermal primordium. After gastrulation, HA appears to accumulate within the extracellular matrix demarcating the primary germ layers. During tailbud stages, it is found highly enriched in many mesodermal derivatives, e.g., in mesenchyme, the heart, precordal cartilage and the lung primordia. Furthermore, extracellular matrix of the ventral mesodermal cell layer in the trunk region and the immediate proximity of blood vessels contain high amounts of HA.     

Cellular patterning of the vertebrate embryo

Recent studies show that cell dispersal is a widespread phenomenon in the development of early vertebrate embryos. These cell movements coincide with major decisions for the spatial organization of the embryo, and they parallel genetic patterning events. For example, in the central nervous system, cell dispersal is first mainly anterior–posterior and subsequently dorsal–ventral. Thus, genes expressed in signaling centers of the embryo probably control cell movements, tightly linking cellular and genetic patterning. Cell dispersal might be important for the correct positioning of cells and tissues involved in intercellular signaling. The emergence of cell dispersal at the onset of vertebrate evolution indicates a shift from early, lineage-based cellular patterning in small embryos to late, movement-based cellular patterning of polyclones in large embryos. The conservation of the same basic body plan by invertebrate and vertebrate chordates suggests that evolution of the embryonic period preceding the phylotypic stage was by intercalary co-option of basic cell activities present in the ancestral metazoan cell.     

How we are shaped: the biomechanics of gastrulation

Although it is rarely considered so in modern developmental biology, morphogenesis is fundamentally a biomechanical process, and this is especially true of one of the first major morphogenic transformations in development, gastrulation. Cells bring about changes in embryonic form by generating patterned forces and by differentiating the tissue mechanical properties that harness these forces in specific ways. Therefore, biomechanics lies at the core of connecting the genetic and molecular basis of cell activities to the macroscopic tissue deformations that shape the embryo. Here we discuss what is known of the biomechanics of gastrulation, primarily in amphibians but also comparing similar morphogenic processes in teleost fish and amniotes, and selected events in several species invertebrates. Our goal is to review what is known and identify problems for further research.     

Palm heart harvesting in the Brazilian Atlantic forest: changes in industry structure and the illegal trade

1. Until the late 1960s, Euterpe edulis was the most important edible palm species in the Brazilian markets. Since then, overharvesting of natural stands and the limited scope of plantations have caused the industry to shift to the multistemmed E. oleracea from the Amazon river estuary.
2. As a result of the relocation of the industry, the structure of the palm harvesting industry has changed and illegal trade has continued to exploit the remaining natural stands of E. edulis .
3. It is suggested that, to avoid the total harvesting of E. edulis and to achieve sustainable management of the palm heart, it will be necessary to diversify the local economy, create incentives for small land owners to improve their management practices, while keeping their competitiveness against the illegal trade, create the incentive of new sources of palm hearts and create a 'green stamping' for management palms.
4. Transformation of the illegal structure of the palm heart industry is probably the only solution to avoid the total depletion of the wild stands of E. edulis .     

TESTING HYPOTHESES OF NEURAL EVOLUTION IN GYMNOTIFORM ELECTRIC FISHES USING PHYLOGENETIC CHARACTER DATA

In this paper, we propose a method to test alternative hypotheses of phenotypic evolution. The method compares patterns observed in phylogenetic character data with patterns expected by explicit models of evolutionary process. Observed patterns of character-state diversity are assessed from four properties of character-state change derived from a phylogenetic analysis: the sequence and correlation of transformations on a cladogram and the spatial and functional localization of these transformations to parts of an organism. Patterns expressed in terms of the localization of transformations are compared with the expectations of null models that the number of transformations is proportional to measures of size or complexity. Deviations from the values expected by the null models are then compared with qualitative expectations of the models. The method is applied to characters in the nervous system of gymnotiform electric fishes. Patterns in the diversity of 63 reconstructed character-state changes are compared with the expectations of 10 published models of neural evolution. A total of 63 expectations are reviewed, of which 33 (52%) are found to be consistent with the gymnotiform neural data. In general, the models reviewed are not successful at making global predictions, in part because they have been cast in excessively general terms. The data support the conclusion that evolution in the nervous system of gymnotiforms has involved a mosaic of processes, each operating differentially on functional and developmental systems and at different spatial and temporal scales. The results also indicate that more refined models are required, each making more explicit predictions.     

Modeling the Ecological and Phenological Predictors of Fruit Consumption by Gibbons (Hylobates albibarbis)

Understanding the ecological interactions between plant reproductive strategies and frugivore feeding behavior can offer insight into the maintenance of tropical forest biodiversity. We examined the role of plant ecological and phenological characteristics in influencing fruit consumption by the White‐bearded gibbon (Hylobates albibarbis) in Gunung Palung National Park, Indonesian Borneo. Gibbons are widespread across Borneo, highly frugivorous and perform important seed dispersal services. We compare multiple models using information criteria to identify the ecological and phenological predictors that most strongly influence gibbon fruit use of 154 plant genera. The most important predictors of resource use were the overall abundance of a genus and the consistency of fruit availability. Plant genera can maintain constant fruit availability as a result of (1) individual stems fruiting often or (2) stems fruiting out of synchrony with each other (asynchrony). Our results demonstrate that gibbons prefer to feed on plant genera that provide consistent fruit availability due to fruiting asynchrony. Because gibbons feed more often on genera that fruit asynchronously, gibbons are more likely to disperse seeds of plant genera with this reproductive strategy. Research on other frugivorous species is needed to determine whether the results for gibbons are generalizable more broadly. Finally, these results suggest that asynchronously fruiting plant genera may be particularly important for habitat restoration in tropical forests designed for frugivore conservation.     

Homeostasis in the vertebrate lens: mechanisms of solute exchange

The eye lens is avascular, deriving nutrients from the aqueous and vitreous humours. It is, however, unclear which mechanisms mediate the transfer of solutes between these humours and the lens' fibre cells (FCs). In this review, we integrate the published data with the previously unpublished ultrastructural, dye loading and magnetic resonance imaging results. The picture emerging is that solute transfer between the humours and the fibre mass is determined by four processes: (i) paracellular transport of ions, water and small molecules along the intercellular spaces between epithelial and FCs, driven by Na(+)-leak conductance; (ii) membrane transport of such solutes from the intercellular spaces into the fibre cytoplasm by specific carriers and transporters; (iii) gap-junctional coupling mediating solute flux between superficial and deeper fibres, Na(+)/K(+)-ATPase-driven efflux of waste products in the equator, and electrical coupling of fibres; and (iv) transcellular transfer via caveoli and coated vesicles for the uptake of macromolecules and cholesterol. There is evidence that the Na(+)-driven influx of solutes occurs via paracellular and membrane transport and the Na(+)/K(+)-ATPase-driven efflux of waste products via gap junctions. This micro-circulation is likely restricted to the superficial cortex and nearly absent beyond the zone of organelle loss, forming a solute exchange barrier in the lens.     

The interplay between morphogens and tissue growth

Morphogens are conserved, secreted signalling molecules that regulate the size, shape and patterning of animal tissues and organs. Recent experimental evidence has emphasized the fundamental role of tissue growth in expanding the expression domains of morphogens and their target genes, in generating morphogen gradients and in modulating the response of cells to morphogens. Moreover, the classic view of how morphogens, particularly through their concentration gradient, regulate tissue size during development has been revisited recently. In this review, we discuss how morphogens and tissue growth affect each other, and we attempt to integrate genetic and molecular evidence from vertebrate and invertebrate model systems to put forward the idea that the interaction between growth and morphogens is a general feature of highly proliferative tissues.     

Seed Dispersal by Geochelone carbonaria and Geochelone denticulata in Northwestern Brazil1

The role of red‐footed tortoises (Geochelone carbonaria) and yellow‐footed tortoises (G. denticulata) as seed dispersal agents was investigated in northwestern Brazil from 5 to 26 January 2002 by analyzing fecal samples for frequency and viability of seed species and estimating daily displacement of tortoises from recaptured and thread‐trailed individuals. Fourteen of 19 fecal samples contained a total of 646 seeds represented by 11 plant species. The most abundant species was Ficus sp. (N= 400) with 100 percent of seeds viable, followed by Aechmea sp. (N = 88) with 93 percent of seeds viable, and Genipa americana (N= 59) with 91 percent of seeds viable. Mean minimum retention time of seeds was 1.6 d and mean daily displacement of tortoises based on recaptured (N= 7) and thread‐trailed tortoises (N= 2) was 57 m. Thus, the diversity and proportion of viable seeds consumed by tortoises, combined with the seed retention times and daily movements, suggest they may be effective dispersal agents. These preliminary findings warrant further investigation into the ecological role of these tortoises in Neotropical ecosystems and their contribution to the maintenance of species diversity and forest structure.