Tangential cell migration during layer formation of chick optic tectum

The laminated structure of the optic tectum is formed by radial and tangential cell migration during development. Studies of developing chick optic tectum have revealed two streams of tangential cell migration in the middle and superficial layers, which have distinctive origins, migratory paths, modes of migration, and destinations. We will review the process of the two types of tangential migrations, in order to elucidate their roles in the formation of the optic tectum layers.     

The benthic boundary layer approach and its application to Lake Päijänne,Finland

Resuspension of bottom sediments is the net result of a wide variety of different fluid mechanical processes with characteristic time and length scales that extend over six orders of magnitude. The sum of these effects is most heavily concentrated in a layer adjacent to the bottom called the benthic boundary layer (BBL). The physics of BBL must be understood before improved solutions to the resuspension problem are possible. Traditionally in lakes, sedimentation and resuspension have been modelled with the aid of equations which ignore the time and space variations of near bottom processes. This can lead to wrong estimates of material transport. With the exception of few recent studies, benthic boundary layer approach has been mainly applied to marine environments. The instrumentation has been a major problem for development of the theory and its applications, but during recent years some new instruments have been giving promising results. This paper discusses the applicability of the theory in Finnish lakes and presents results from Lake Päijänne.     

华北地区针叶林下凋落物层化学性质的研究

森林凋落物中贮积了大量的有机、无机养分物质,它是森林土壤自然肥力的重要来源之一。在森林生态系统中,养分物质的内部循环主要是通过凋落物来实现的。在分解、转化过     

Boundary layer properties of highly dissected leaves: an investigation using an electrochemical fluid tunnel

Abstract. A method for modelling heat and mass transfer by diffusion-controlled electrode reactions in a fluid tunnel is described. In this procedure, a nickelplated leaf functions as a test electrode, and the convective transfer of ions to the leaf cathode in an electrolyte-filled flow tunnel is measured as a function of flow rate. The method permits the simulation of water vapour and heat transfer, and in particular, the determination of boundary layer conductances, by analogy with observed ion transfer. The approach is applicable to many problems in modelling heat and mass transfer between leaves and their surroundings, and is especially useful in examining the properties of leaves in which surface characteristics or overall shape are complex. Using this method, the properties of the highly dissected leaves of Achillea lanulosa with regard to forced convection were investigated. The leaves showed high transfer conductances, indicating that the effective unit of heat transfer was probably the individual leaf subelements. Conductances tended to be greater and effective characteristic dimensions smaller for the larger, more open leaves of a lower altitude population in contrast with leaves from high altitude plants. While the results provide insight into the properties of these complex leaf shapes, difficulties in interpreting the findings are discussed, and a number of exploratory approaches are suggested for data analysis and interpretation.     

Tropical ant communities are in long-term equilibrium

Communities change with time. Studying long-term change in community structure permits deeper understanding of community dynamics, and allows us to forecast community responses to perturbations at local (e.g. fire, secondary succession) and global (e.g. desertification, global warming) spatial scales. Monitoring efforts exploring the temporal dynamics of indicator taxa are therefore a critical part of conservation agendas. Here, the temporal dynamics of the Otongachi leaf litter ant community, occurring in a cloud forest in coastal Ecuador, were explored. By sampling this community six times over eleven years, I assessed how the ant fauna caught by Winkler traps (more diverse and cryptic fauna) and caught by pitfall traps (larger, more mobile fauna) changed over time. The Otongachi leaf litter ant community was dynamic. Although species richness in the community remained constant, temporal turnover of species was high: on average, 51% of the ant species in Winkler traps, and 56% of those in pitfall traps, were replaced with other ant species from one year to the other. Shifts in the rank abundance of species in the community were also large across the eleven years and, on average, shifts in the rank abundance of species collected by Winkler traps doubled those occurring in pitfall traps from one census to the other. In spite of these trends, the Otongachi ant fauna showed no (Winkler) or weak (pitfall) evidence of directional change (towards a new community). Thus, this tropical ant community can be divided in two community compartments. The Winkler compartment composed by a more diverse and cryptic ant fauna appears to be resilient and stable in time. The pitfall compartment composed by larger and more mobile ants may be prone to respond to disturbance. This study suggests that 1) species appearing/disappearing from a site may be rather the rule, difficult to separate from responses to ecological stress. 2) Conclusions made in short-term studies, or studies comparing two (e.g. before and after) snapshots of a community, should thus be revisited. Finally, 3) the ant fauna caught by pitfall traps (a rather simple and cheap survey method) is the most likely community compartment to indicate ecological perturbation. This study adds to the growing evidence that using ants as ecological indicators should incorporate long-term temporal dynamics.     

Identification of 5-desmethylubiquinone-9 as an intermediate in the biosynthesis of ubiquinone-9 by rat liver mitochondria

Radioactive 5-desmethylubiquinone-9 has been isolated from mitochondria synthesizing ubiquinone-9-¹⁴C from p-hydroxybenzoate-U-¹⁴C. By mass spectrometry, the natural 5-desmethylubiquinone-9 has been shown to be identical with that chemically synthesized from fumigatol and solanesol. Synthetic 5-desmethylubiquinone-9-³H can be methylated to ubiquinone-9-³H by S-adenosyl-L-methionine in submitochondrial particles.     

Effects of forest disturbances on aquatic insect assemblages

Natural and human‐made disasters such as floods and logging occur in and around rivers. Stream‐dwelling aquatic insects respond to these disturbances in various ways. Primary consumers among them rely greatly on algae and leaf litter from riparian vegetation as food. Therefore, once a disturbance such as a flood has occurred, insects may find it difficult to find food in a stream, and the aquatic insect assemblage can be impacted greatly as a result. Disturbances in riparian areas also increase fine sediment loads into streams, damaging habitat and altering the aquatic insect assemblage. Deforestation impacts not only terrestrial but also aquatic animals. In this review paper, aquatic insect assemblages are assessed according to alterations in land use in and around streams. Following this paper, it is expected that clarification of aquatic insect fauna and their life cycles will progress and that the distribution and habitat use of aquatic insects will be afforded greater attention in forest management.     

A comparative study of breeding seasonality and litter size in eleven taxa of captive lemurs (Lemur andVarecia)

Breeding records of 11 taxa of captive lemurs housed at the Duke University Primate Center (DUPC), North Carolina, were analyzed for differences in the timing of births, for the relationship between breeding season and photoperiod, and for differences in litter size. At DUPC there are significant differences in the timing of births among certain taxa, including differences among some subspecies of Lemur fulvus.However, changes in latitude result in changes in the timing of the breeding season. Lemurs moved to higher latitudes mate at lower light-dark ratios than on Madagascar. The data presented here are consistent with the following model: a photoperiodic cue initiating reproductive activity, presumably a light-dark threshold, precedes the actual mating season by approximately 2 months, with an intervening period of physiological and social preparation. On Madagascar, selection may have favored births that coincide with the end of dry seasons and the beginning of wet seasons, which results in lactation and weaning during times of resource abundance. Taxa from the north and east have the highest mean litter sizes; those from the west have the lowest.