Quantitative immunohistochemical evidence of a functional gradient of chondroitin 4-sulphate/dermatan sulphate, developmentally regulated in the predentine of rat incisor

A quantitative examination was carried out on the early and mature stages of dentinogenesis in the rat incisor, using a post-embedding immunogold labelling with an anti-chondroitin 4 sulphate/dermatan sulphate antibody (2B6). At a very early stage of predentine formation, before polarizing odontoblasts have established junctional complexes, immunolabelling was weak. In contrast, when polarized odontoblasts established distal junctional complexes, immunolabelling in predentine was uniform and threefold denser than in initial predentine. The same gold particle density was found in the non-mineralized mantle dentine. During circumpulpal dentine formation, a gradient was seen in predentine, a larger number of gold particles being scored in the proximal zone compared with the distal region adjacent to the mineralization front. In circumpulpal dentine, some labelling was found within the lumen of the tubules and in the bordering dentine around the tubules. A few particles were also detected in intertubular matrix after demineralization. Together, these data provide evidence for a developmentally regulated gradient during the transition between mantle and circumpulpal dentine, and also in a more mature part of the tooth, a functional gradient that probably plays a role in the process of mineralization. © 1998 Chapman & Hall     

Ecophysiological aspects of bruchid reproduction. I. The influence of pod maturity and seeds of Phaseolus vulgaris and the influence of insemination on the reproductive activity ofZabrotes subfasciatus

ABSTRACT.

• 1 Economically important bruchid beetles like Zabrotes sub-fasciatus (Boh.) are able to reproduce both in the field before the legume crop harvest – whilst the seeds are still enclosed within pods – and on seeds in storage sites.
• 2 To take into account this reproductive feature, the influence of pods at different stages of maturity and seeds of Phaseolus vulgaris (Lin.) together with the influence of insemination on the reproductive activity of Zabrotes subfasciatus were examined.
• 3 Female fecundity, insemination and ovarian production were studied under laboratory conditions approximating as closely as possible to the thermal and photoperiodic regimes of the Costa Rican region from which the experimental strain originated.
• 4 The three stages of pod maturity used in experiments (fresh green, fresh yellow and dry yellow pods, all non-dehiscent) induced copulations and significantly stimulated oogenesis. Fecundities of females in the presence of pods were low and did not differ from controls.
• 5 The influence of bean seeds on female reproductive activity was more pronounced than that of pods. Contact with seeds led to a marked increase in the number of sexual meetings, ovarian production and egg-laying activity. Under these conditions, eggs are laid directly on the larvae's food.
• 6 Insemination alone stimulated oogenesis but did not induce egg-laying.
• 7 Possible additive or synergistic interactions between host plant information perceived by females, the effects of egg-laying and insemination are suggested to explain the observed results.
• 8 The adaptive value of this form of reproductive regulation by host plant seeds and pods is discussed in terms of the natural history and oviposition behaviour of Zabrotes subfasciatus.

     

Can differences in the structure of larval,juvenile and adult coral‐reef fish assemblages be detected at the family level?

Processes occurring at the end of the larval stage are of major importance in shaping spatial structure of fish assemblages in coral reefs. However, because of the difficulty in identifying larvae to species, many studies dealing with these stages are limited to the family level. It remains unknown if variation in the spatial structure of coral‐reef fish assemblages across life stages can be detected at such a coarse taxonomic level. Two different surveys conducted in a similar area of New Caledonia, Southwest Pacific, provided the opportunity to compare the structure of coral‐reef fish assemblages collected as pre‐settlement larvae, juveniles and adults along a coast to barrier reef gradient. Adult and juvenile fish were sampled using underwater visual counts (UVC) during the warm seasons of 2004 and 2005. Pre‐settlement larvae were sampled with light‐traps during the same seasons. In order to standardize data between sampling methods, analyses were conducted on the relative abundance (for larvae) and density (for juveniles and adults) of 21 families commonly collected with both methods. Relative abundances/densities of families were analysed as a function of life stage (larvae, juveniles or adults), large‐scale spatial location (coast, lagoon or barrier) and years (2004, 2005) using non‐parametric multidimensional scaling (nMDS) and permutational multivariate analysis of variance (permanova ). Kruskal–Wallis tests were then used to examine differences among life stages and locations for individual families. Different levels of spatial and temporal variability characterized fish assemblages from different life stages, and differences among life stages were detected at all locations and years. Differences among life stages were also significant at the level of individual families. Overall results indicate that studies conducted at the family level may efficiently reveal changes in coral‐reef fish spatial structure among successive life stages when large spatial scales are considered.     

Diversity patterns of stygobiotic crustaceans across multiple spatial scales in Europe

1. Using species distribution data from 111 aquifers distributed in nine European regions, we examined the pairwise relationships between local species richness (LSR), dissimilarity in species composition among localities, and regional species richness (RSR). In addition, we quantified the relative contribution of three nested spatial units – aquifers, catchments and regions – to the overall richness of groundwater crustaceans.
2. The average number of species in karst and porous aquifers (LSR) varied significantly among regions and was dependent upon the richness of the regional species pool (RSR). LSR–RSR relationships differed between habitats: species richness in karstic local communities increased linearly with richness of the surrounding region, whereas that of porous local communities levelled off beyond a certain value of RSR.
3. Dissimilarity in species composition among aquifers of a region increased significantly with increasing regional richness because of stronger habitat specialisation and a decrease in the geographic range of species among karst aquifers. Species turnover among karst aquifers was positively related to RSR, whereas this relationship was not significant for porous aquifers.
4. The contribution of a given spatial unit to total richness increased as size of the spatial unit increased, although 72% of the overall richness was attributed to among-region diversity. Differences in community composition between similar habitats in different regions were typically more pronounced than between nearby communities from different habitats.
5. We conclude by calling for biodiversity assessment methods and conservation strategies that explicitly integrate the importance of turnover in community composition and habitat dissimilarity at multiple spatial scales.     

Mating frequency of ant queens with alternative dispersal strategies, as revealed by microsatellite analysis of sperm

In social Hymenoptera (ants, bees, and wasps), the number of males that mate with the same queen affects social and genetic organization of the colony. However, the selective forces leading to single mating in certain conditions and multiple mating in others remain enigmatic. In this study, I investigated whether queens of the wood ant Formica paralugubris adopting different dispersal strategies varied in their mating frequency (the number of males with whom they mated). The frequency of multiple mating was determined by using microsatellite markers to genotype the sperm stored in the spermatheca of queens, and the validity of this method was confirmed by analysing mother–offspring combinations obtained from experimental single-queen colonies. Dispersing queens, which may found new colonies, did not mate with more males than queens that stayed within polygynous colonies, where the presence of numerous reproductive individuals ensured a high level of genetic diversity. Hence, this study provides no support to the hypotheses that multiple mating is beneficial because it increases genetic variability within colonies. Most of the F. paralugubris queens mated with a single male, whatever their dispersal strategy and life history. Moreover, multiple mating had little effect on colony genetic structure: the effective mating frequency was 1.11 when calculated from within-brood relatedness, and 1.13 when calculated from the number of mates detected in the sperm. Hence, occasional multiple mating by F. paralugubris queens may have no adaptive significance.     

Invertebrate bioturbation can reduce the clogging of sediment: an experimental study using infiltration sediment columns

1. Invertebrate bioturbation can strongly affect water‐sediment exchanges in aquatic ecosystems. The objective of this study was to quantify the influence of invertebrates on the physical characteristics of an infiltration system clogged with fine sediment. 2. Two taxa (chironomids and tubificids) with different bioturbation activities were studied in experimental slow infiltration columns filled with sand and gravel and clogged with a 2 cm layer of fine sediment at the surface. We measured the effects of each taxon separately and combined on hydraulic head, water mobility and sediment reworking. 3. The results showed that invertebrates could reduce sediment clogging and this effect was linked to the functional mode of bioturbation of each group. Tubificid worms dug networks of galleries in the fine sediment, creating pathways for water flow, which reduced the clogging of sediment. In contrast, the U‐shaped tubes of chironomids were restricted to the superficial layer of fine sediments and did not modify the hydraulic conductivity of experimental columns. The combination of invertebrates did not show any interactive effects between tubificids and chironomids. The occurrence of 80 tubificids in the combination was enough to maintain the same hydraulic conductivity that 160 worms did in monospecific treatment. 4. The invertebrates like tubificid worms can have a great benefit on functioning of clogged interfaces by maintaining high hydraulic conductivity, which contributes to increased water‐sediment exchanges and stimulates biogeochemical and microbial processes occurring in river sediments.