Structural Differentiation of the Nucellar Epidermis in the Caryopsis of Rice (Oryza sativa)

In the developing caryopsis of rice (Oryza sativa L.) the nucellarepidermis forms a uniseriate layer through which assimilatesare transported to the endosperm. An anatomical study demonstratedthat the nucellar epidermal cells are fusiform in shape andare hexagonally packed. The anticlinal walls of the nucellarepidermis are characterized by ribs of wall-thickening whichare orientated radially with respect to the caryopsis. The wall-thickeningsappear to be cellulosic primary walls, as indicated by theirstaining with Calcofluor and periodic acid-Schiff's reagent.It is proposed that the geometry of the nucellar cells and theribs of wall-thickening are structural adaptations to resistthe compressional force which is placed on the nucellar epidermisduring the latter stages of grain filling. Oryza sativa, rice, caryopsis, grain filling, nucellar epidermis, wall-thickening     

Ant mosaics in a tropical rainforest in Australia and elsewhere: A critical review

Abstract The concept of ‘ant mosaics’ has been established to describe the structure of arboreal ant communities in plantations and other relatively simple forest systems. It is essentially built upon the existence of negative and positive associations between ant species plus the concept of dominance hierarchies. Whether this concept can be applied to ant communities in more complex mature tropical rain forests has been questioned by some authors. Here we demonstrate that some previous attempts to prove or disprove the existence of such ant mosaics sampled by knockdown insecticide canopy fogging in near pristine tropical forests may have been thwarted by poor statistical power and too coarse spatial resolution, and the conclusions may be highly dependent on ant species and forest stratum selected for the study. Moreover, the presence or absence of ant mosaics may be driven by the density of suitable resources. We use an intensively studied ant community in the lowland rainforests of North‐East Queensland, Australia to outline processes that may lead to ant mosaic patterns, reasoning that competition for highly predictable resources in space and time such as honeydew and nectar is a fundamental process to maintain the mosaic structure. Honeydew and nectar sources, particularly their amino acids, are of crucial importance for nourishment of arboreal ant species. We use canopy fogging data from the same site in Australia and from two mature rainforests in South‐East Asia to compare spatial avoidance and co‐occurrence patterns implied by ant mosaics. Significant negative and positive associations were found among the three most abundant ant species in each dataset. Several problems with such spatial analyses are discussed, and we suggest that studies of ant mosaics in complex rainforest communities would benefit from a more focused approach on patterns of resource distribution and their differential utilisation by ants.     

Observed relationships between El Niño‐Southern Oscillation,rainfall variability and vegetation and fire history on Halmahera,Maluku, Indonesia

A temporally high‐resolution palynological study of the uppermost section of core MD98‐2180 from Kau Bay, Halmahera, Indonesia, provides a vegetation and fire record covering the last 250 years. The record is compared with the Maluku Rainfall Index, Southern Oscillation Index (SOI) and southern hemisphere winter sea surface temperatures (SST) for the central Pacific Ocean based on instrumental data, as well as reconstructions of the SOI and the central Pacific SST and historically recorded El Niño events. The results show that significant El Niño events are generally associated with increased representation of Dipterocarpaceae pollen, probably reflecting the mass‐flowering of this taxon during El Niño‐Southern Oscillation (ENSO) droughts, and elevated charcoal levels, reflecting a greater incidence of fires during these extremely dry periods, while humid phases show increased fern numbers. Our findings demonstrate that pollen records ‘ecological’ in scale can provide useful additional proxy records of ENSO events.     

Seaweed attachment to bedrock: biophysical evidence for a new geophycology paradigm

Seaweeds are amongst the most obvious and ecologically important components of rocky shore communities worldwide but until now little has been known about the processes involved in their attachment. This multidisciplinary study investigated for the first time the interactions between marine macroalgal holdfasts and their underlying substrata, requiring the development of specialized sample preparation techniques to maintain the structural integrity of the holdfast–bedrock interface. Transmitted plane polarized light microscopy, scanning electron microscopy with energy dispersive spectroscopy and structured light illumination microscopy were used in the examination of the interface between Ascophyllum nodosum (Fucales, Heterokontophyta) and crustose red algae Lithothamnion sp. (Corallinales, Rhodophyta) on granite and limestone substrates. The new evidence presented here represents a paradigm shift in the way we view seaweed attachment because results show that the holdfasts exploit the physical characteristics of the rock-forming minerals in order to penetrate the bedrock and thus facilitate the attachment process. Mineral cleavage planes together with intercrystalline and intracrystalline boundaries and fractures provide penetration pathways for the holdfast tissue. This process causes disaggregation of rock-forming minerals to depths <10 mm and therefore assists in the bioerosion of coastal bedrock. It is concluded that seaweeds are able to cause weathering of natural rock and the term 'geophycology' is introduced to describe seaweed–bedrock interactions, including seaweed-induced weathering.     

Body size variation among invertebrates inhabiting different canopy microhabitat: flower visitors are smaller

1. Factors such as reproductive fitness, climatic tolerance, predation pressure, energetic requirements and the quality and quantity of food sources all correlate with invertebrate body sizes. 2. This study examines body size variation between an invertebrate community inhabiting five different microhabitats (mature leaves, new leaves, flowers, fruit and suspended dead wood) that differ in quality, quantity, and availability in an Australian tropical rainforest canopy. 3. Mean body size varied significantly between invertebrate and beetle feeding guilds across microhabitats. Phylogenetically independent contrasts revealed that invertebrate taxonomic groups were significantly smaller on flowers than on mature and new leaves. Size differences between microhabitats were most pronounced among herbivorous taxa (Hemiptera, Lepidoptera). In particular, the immature stages or those groups that develop on flowers were significantly smaller on flowers and larger on leaves than expected. Taxonomic groups with many strong flying species, especially those that complete larval development on resources other than flowers, typically showed no differences in body size across microhabitats. 4. There are a number of potential hypotheses for the smaller body sizes of flower visitors, including: (i) differences in the physical sizes of the microhabitats; (ii) variation in time–dependent mortality risks that influence development times; and (iii) differences in the nutritional quality of the microhabitats, which can influence body size via metabolic pathways. 5. The findings of this study do not support hypothesis (i) (with the possible exception of one or two predatory groups). It is suggested that hypotheses (ii (time–dependent mortality factors) and particularly (iii) (nutritional variation) may be the best avenues for future study as the main drivers of body size differences between microhabitats.     

Apparatus for determining oxygen in small gas samples

A simple modification to an electronic O₂ analyser is described which enables accurate determination of O₂ in small gas samples. The response to O₂ concentration is linear over the range 0–21% by volume and as little as 0.07 μl of O₂ can be detected. Analysis of a 25 μl sample takes 25 s.