Spatial eigenfunction analyses in stream networks: do watercourse and overland distances produce different results?

1. The use of spatial variables is a common procedure in ecological studies. The technique is based on the definition of a connectivity/distance matrix that conceptually defines the dispersal of organisms. The shortest distance between two points is a straight line. Despite the fact that a straight line may not represent the easiest dispersal path for many kinds of organisms, straight‐line distances are often used to detect patterns. We argue that other types of connectivity/distance matrices will better represent dispersal paths, such as the watercourse distance for aquatic organisms (e.g. fish, shrimps). 2. We used empirical and simulated community data to evaluate the usefulness of spatial variables generated from watercourse and overland (straight‐line) distances. 3. Spatial variables based on watercourse distances captured patterns that straight‐line distances did not, and provided better representations of the spatial patterns generated by dispersal along a dendritic network.     

CAM activity and day/night changes in the ultrastructure of stem chlorenchyma of Cissus quadrangularis L. as influenced by drought

Abstract Stem chlorenchymatous cells from well-watered and water-stressed plants of Cissus quadrangularis L. were examined to evaluate the effect of drying on cell structure and metabolism. At a stem relative water content as low as 52-58%, cellular integrity was maintained, but some qualitative and quantitative alterations occurred. Chlorophyll coment was higher in stressed plants, and the intact photosynthetic apparatus exhibited an increased degree of thylakoid stacking paralleled by a lower chlorophyll a/h ratio. Overnight malate accumulation was very low. Starch was retained but its day/night fluctuation was practically suppressed. Plastosomes were smaller and fewer, and the range of their daily fluctuation was very reduced. Vacuoles underwent fragmentation and accumulated osmiophilic deposits. The maintenance of the cellular integrity accounts for the ability of C. quadrangularis to recover rapidly from water stress.     

Influence of diet on the structure and function of the bacterial hindgut community of crickets

The effect of diets varying in carbohydrate and protein content on the structure and function of the hindgut microbiota of crickets was evaluated by determining bacterial densities, fermentation activity, and guanine plus cytosine (G + C) profiles of the DNA extracted from the microbial hindgut community. DNA isolated from the gut community was fractionated and quantified according to G + C content as a comprehensive, coarse-level measure of the composition and structure of the community. The bacterial densities measured by direct counts were not significantly different among the four diets. The crickets were initially reared in the laboratory on cricket chow, which resulted in a hindgut community dominated by bacteria with a G + C content between 32% and 57%. Crickets shifted to an alfalfa diet showed a similar hindgut community G + C profile, although microbial populations with DNA between 35% and 45% G + C were more abundant in alfalfa- than chow-fed crickets. The apparent complexity of the gut community was reduced in crickets fed beet-pulp and protein-based diets compared to those fed chow and alfalfa, and was dominated by populations with a low percentage G + C content. Hindgut communities in crickets fed pulp and protein diets also showed a decrease in hydrogen and carbon dioxide production, suggesting that these diets affected the biochemical activity of the hindgut community. The protein-based diet resulted in a decrease in the rate of evolution of volatile fatty acids, while the ratio of butyrate production to acetate and propionate production was significantly higher in these crickets. Our results show the emergence of a new microbial community structure concomitant with changes in microbial biochemical activity due to shifts in the cricket's dietary regime.     

Pathways for Nutrient Transport in the Pitchers of the Carnivorous Plant Nepenthes alata

Glands of the carnivorous pitcher plant Nepenthesalata are activein transport of materials into and out of the pitcher lumen,indicating dual functions in both secretion and absorption.This study examined the potential for open transport throughthese glands using the ultrastructural tracer lanthanum, whichis restricted to the apoplast, and the fluorescent symplastictracer, 6(5)carboxyfluorescein. Glandular uptake of lanthanumfrom the pitcher fluid occurred through the outer cell wallbetween irregularly spaced cutinized deposits, but was blockedfrom entering the underlying mesophyll cell walls by thick endodermal-likeregions. Similarly, lanthanum localization showed an open apoplasticpathway from the petiole to the endodermal regions in the glandbase. Thus, transport of materials into or out of the glandmust occur through the symplast. 6(5)Carboxyfluorescein showedthat these glands transport fluids directly from the pitcherfluid into vascular endings immediately beneath them via a symplasticroute. When applied to the petiolar vascular system, the fluorescenttracer freely entered immature pitchers, but was blocked fromentering the lumen of the mature pitcher by an endodermal zone.An ultrastructural survey showed infrequent pits with plasmodesmatalconnections to adjoining subepidermal cells. These results indicatethat the function of the gland is developmentally regulated.Prior to maturity, the primary function of the gland appearsto be secretion. However, at maturity, secretion is blockedby an endodermal layer, which limits the function of the glandto absorption. These studies support the theory that the glandsof Nepenthesalata are specialized for the bi-directional transportof materials.Copyright 1999 Annals of Botany Company Apoplastic transport, 6(5)carboxyfluorescein, carnivorous plants, digestive glands, endodermal layer,Nepenthesalata Blanco, lanthanum, pitcher plants.     

Revision of the Bicyclus sciathis species group (Lepidoptera: Nymphalidae) with descriptions of four new species and corrected distributional records

In this paper we present a thorough revision of the sciathis species group of the butterfly genus Bicyclus (Kirby). Type materials are discussed and in several cases lectotypes are assigned to specimens from original type series. Four new, and morphologically distinct, species are described (B. elishiae Brattström sp.n. , B. heathi Brattström sp.n. , B. sigiussidorum Brattström sp.n. and B. subtilisurae Brattström sp.n. ), along with a comprehensive molecular phylogeny that includes exemplar taxa of all currently recognized species. We also investigate the types of all previously synonymized taxa and in the process invalidate the name B. ewondo Libert. This was done after finding the previously missing holotype of B. makomensis (Strand), which clearly belongs to the same species and thereby gives the older name priority. The phylogeny showed that some distinctly different species were surprisingly closely related, suggesting a high rate of morphological evolution in parts of the sciathis group. The distributional records for the group are updated after investigating over 1700 specimens kept in a range of museum collections. Many species previously thought to be broadly sympatric were found to have much more restricted ranges, with the previous overestimations probably based on misidentified specimens. The higher level of allopatry now established will make identification of many morphologically similar species easier. The fact that species often have smaller ranges than previously known, meaning that the level of endemism for African butterflies is likely to be higher than current estimates, has important implications for conservation management. An identification key for males of all 13 currently recognized species in the species group is included. This published work has been registered in ZooBank, http://zoobank.org/urn:lsid:zoobank.org:pub:837A9D4C‐779A‐4497‐8176‐7151D409DFA5 .     

Histochemistry, ultrastructure and possible significance of dead parenchyma cells with specialized walls in the leaf and rhizome of Sansevieria

Abstract. The internal parenchyma of the leaf and rhizome in 36 species of Sansevieria is made of dead cells and living cells arranged in a regular pattern. Intercellular spaces are lacking. The walls of dead cells consist of an inner amorphous layer positive to the fluorescence test for callose, a middle suberin-like layer and an outer fibrillar layer. In about half of the species examined, the inner layer forms distinctive thickenings. Detached leaves of Sansevieria lose water very slowly, and are able to recover it quickly. The pattern of leaf dehydration appears to be related to leaf morphology, whereas no relation is evident between the pattern of leaf rehydration and leaf morphology. Neither leaf dehydration nor leaf rehydration pattern is affected by the presence of wall thickenings in the dead parenchyma cells. The fresh weight per unit volume of both turgid and droughted leaves is nearly 1, denoting that the dead cells are filled with water and do not undergo substantial cavitation during drought. The data indicate that the dead parenchyma cells of Sansevieria are a specialized water-storing system.