A comparative study of competitive ability between two cactophilic species in their natural hosts

Abstract Competition is a major aspect of the ecology of insect communities exploiting ephemeral and fragmented resources. We analysed the effect of intraspecific (single species culture) and interspecific (mixed species culture) competition on larval viability, developmental time and wing length in the cactophilic Drosophila buzzatii and Drosophila koepferae (Diptera: Drosophilidae) reared in cultured media prepared with fermenting tissues of three common natural cactus hosts in nature at different densities. Our results show that all traits measured were affected by both intra‐ and interspecifc competition, although the effect of competition depended on the Drosophila species and the rearing cactus. In fact, flies tended to have a lower viability, shorter wing size and longer developmental time as a function of increasing density in single species culture in both D. buzzatii and D. koepferae (intraespecific competition). Besides, the performance of both species was seriously affected (shorter body size, slower developmental times, lower viability) by the presence of heterospecific competitors except in the case of D. koepferae reared in its primary host plant, Trichocereus terschekii. We also show that D. koepferae successfully utilized Opuntia quimilo, which is absent in most parts of its distribution range. We discuss the roles of intra‐ and interspecific competition as determinants of the relative abundance of these two species in the arid zones of Southern South America.     

Use of Video Probe Does Not Affect Burrowing Owl Reproductive Parameters or Return Rates

ABSTRACT We tested how repeated use of an infrared video probe influenced burrowing owl (Athene cunicularia) reproduction and recruitment. In 2001, we randomly assigned occupied burrows in Washington State, USA, to one of 2 groups: 1) inspected throughout the breeding season with an infrared video probe (n = 38), or 2) never inspected with a probe (n = 41). We did not detect differences between the 2 groups in nesting success, number of fledglings per nest, natal recruitment, or likelihood of adults returning to the same burrow the following year (2002) or to the study area in a subsequent year (2002–2005).     

Arrangement and Structure of Plastids in Dormant and Cultured Tissue from Artichoke Tubers

The plastids in the tubers of the Jerusalem artichoke are foundboth scattered in the peripheral cytoplasm of the cells andalso in compact clusters usually near the nucleus. The clustersmay be a stage in the formation of plastids. The membrane-boundstructures within the plastids themselves can be assigned toone or other of two systems: a peripheral system of irregulartubules and cisternae some of which connect with the inner membraneof the plastid envelope; and a central system of highly variablemorphology which appears not to connect with the peripheralsystem. It is, apparently, from the central system that thethylakoids of stroma lamellae and grana develop during the greeningof illuminated cultures.     

A revision of Cerdia (Caryophyllaceae)

Cerdia is a poorly understood genus of minute cushiony plants endemic to Mexico that is traditionally placed in subfamily Paronychioideae, tribe Polycarpeae (Caryophyllaceae). Morphological observations and phylogenetic analysis of ITS DNA sequences were carried out to determine the number of species, heretofore controversial, that constitute the genus as well as its position within Caryophyllaceae. Samples of Cerdia were collected through its entire range of distribution and together with previous specimens were used in morphological analyses. Nineteen terminal taxa were considered in a phylogenetic analysis with representatives of the different lineages in Caryophyllaceae. Results indicated that Cerdia is a monotypic genus, including only one variable species, C .  virescens , but its phylogenetic affinities remain doubtful.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 1–13.     

Does decomposition of standard materials differ among grassland patches maintained by livestock?

Grazing can modify vegetation structure and species composition through selective consumption, modifying plant litter quality and hence decomposability. In most grasslands, moderate stocking rates maintain a mosaic of high‐quality patches, preferentially used by herbivores (‘grazing lawns’), and low‐quality tall patches, which are avoided. In grazing lawns decomposition rates can be accelerated because of the higher litter quality of its component species and, besides, through the indirect effect of increased nutrient availability in soil. We aimed at testing this indirect effect using standard materials, comparing their decomposition in grazing lawns, open and closed tall tussock grasslands. We selected 10 patches of each type and sampled floristic composition, soil variables and cattle dung deposition. Standard materials were filter paper and Poa stuckertii litter. We prepared litterbags of 0.3 mm (thin mesh) and 1 mm mesh size (coarse mesh). Samples were incubated for 65 days in two ways: above‐ground (thin and coarse mesh) and below‐ground (only thin mesh), aiming at analysing the conditions for decomposition for surface litter and buried litter or dead roots, respectively. Physical and chemical soil variables did not differ among patch types, despite the differences in species composition. Closed tussock grasslands showed the lowest dung deposition, confirming the less intense use of these patches. Soil nitrogen availability (N‐NO₃^‐ and N‐NH₄⁺) was not significantly different among patch types. Each standard material followed a different decomposition pattern across patch types. For above‐ground incubated samples, Poa litter decomposed significantly faster in lawns, and slower in open tussock grasslands. Filter paper decomposed significantly faster in closed tussock grasslands than in the other two patch types. Decomposition of below‐ground incubated samples did not significantly differ among patch types, in line with results for soil variables. Above‐ground differences in decomposition may be associated with differences in microclimatic conditions resulting from differences in vegetation structure.     

Differential gene expression in Arabidopsis following infection by plant-parasitic nematodes Meloidogyne incognita and Heterodera schachtii

Whole genome microarrays were used to study plant gene expression in mature Meloidogyne incognita -induced galls in Arabidopsis. We found 959 genes to be significantly differentially expressed, and two-thirds of these were down-regulated. Microarray results were confirmed by qRT-PCR. The temporal and spatial responses of four differentially expressed genes were analysed using GUS reporter plants following infection with M. incognita and the cyst nematode Heterodera schachtii . The ammonium transporter gene AtAMT1;2 was consistently and locally repressed in response to both nematodes at all developmental stages. The lateral organ boundary domain gene LBD41 showed up-regulation in the feeding sites of both nematode species, although there was variation in expression in saccate H. schachtii female feeding sites. Expression of an actin depolymerizing factor ADF3 and a lipid transfer protein was induced in feeding sites of both nematodes at the fusiform stage and this persisted in feeding sites of saccate M. incognita . These results contribute to the knowledge of how plant gene expression responds to parasitism by these nematodes as well as highlighting further differences in the mechanisms of development and maintenance of these feeding site structures.     

Erwinia amylovora strains from outbreaks of fire blight in Spain: phenotypic characteristics

One hundred and thirty strains of Erwinia amylovora recovered from Spanish foci of fire blight from 1995 to 2000 were characterised and compared to reference strains from different sources and origins. Their rapid identification was performed by double antibody sandwich indirect (DASI) ELISA, using specific monoclonal antibodies against E. amylovora, and molecular confirmation by PCR using primers specific to the native plasmid pEA29. The Spanish strains of E. amylovora grew on different general and selective media producing typical colonies, except one of them that was deficient in levan production, whereas none of them grew on minimal agar medium with copper sulphate and low content of asparagine. All of them were susceptible to tetracycline, streptomycin, kasugamycin and oxolinic acid. Biochemical characterisation of selected strains by API 20E system revealed a great homogeneity, with 80% of the Spanish strains showing one of the two majority API 20E profiles described for E. amylovora, and the remaining strains showing minor differences. Pathogenicity on pear fruits and hypersensitivity reaction was confirmed, but a delayed reaction was observed for two Spanish strains. This is the first characterisation of a large collection of Spanish strains of E. amylovora.     

Changes in the Mitochondrial Complex accompanying Callus Growth

Large, vacuolated parenchyma cells from the dormant tuber ofthe Jerusalem Artichoke contain a variety of mitochondrial profiles.Cells of cultured explants contain an even wider range of mitochondrialforms including complex bell shapes, long cylindrical rods,branched structures, and plates. A theory is advanced to explainhow the complex bell-shaped mitochondria, and associated forms,may be derived from simple spheres and rods. Attention is alsodrawn to the significance of the spatial relationship that existsbetween bell-shaped mitochondria and developing vacuoles.