Sexual competition in sagebrush crickets: must males hear calling rivals?

The acoustic signals produced by male crickets and katydidsfunction in part for the maintenance of territories, broadcastareas within which males have exclusive access to sexually receptivefemales. Although it is widely assumed that a male's abilityto hear and respond appropriately to calling neighbors is vitalto his mating success, this hypothesis has never been experimentallychallenged. We tested this hypothesis by experimentally deafeningmale sagebrush crickets (Cyphoderris strepitans) and comparingtheir mating success with that of untreated and sham-treatedcontrol males. Despite the fact that deafened males had a reducedability to detect nearby rivals, we found no difference in themating success of deafened and control males in experimentsconducted over two years (1991 and 1993). We further examinedthe importance of signal detection to male spacing by establishingexperimental populations consisting exclusively of either deafenedmales or hearing controls, whose nearest-neighbor distanceshad been experimentally compressed. Assuming that calling functionsin part to repel rivals, we predicted that hearing males wouldspace themselves out more rapidly in the nights following theirrelease. However, in only two of four replicates were nearest-neighbordistances significantly different across treatments. We concludethat, in contrast to the mating systems of other acoustic Orthoptera:(1) male mating success is not contingent on auditory inputfrom calling rivals, (2) signaling in sagebrush crickets mayfunction only sporadically in territorial maintenance, and (3)calling occasionally mediates spacing of males in natural populations,but this effect may vary either over the course of the breedingseason or between populations. We attribute these results tothe unique mating system of C. strepitans. a short, highly synchronizedbreeding season coupled with a high male mating investment anda super-abundance of calling sites conspire against investmentin territorial maintenance, but instead favor a form of acousticallymediated scramble competition.     

Use of polymorphic short and clustered coding-region microsatellites to distinguish strains of Candida albicans

Abstract We describe the identification of polymorphic microsatellite loci in the pathogenic yeast, Candida albicans . A search for all coding-region microsatellites with more than four repeats that can be found in Candida sequences in GenBank was conducted. Nine such microsatellite sequences consisting of trinucleotide motifs were found. Three of these were perfect microsatellites while the remaining six sequences were found in one imperfect microsatellite and two compound microsatellites. Because of the close proximity of some of these repeats, all could be assayed with six PCR primer pairs. All of these microsatellite sequences were found in five nuclear genes, ZNF1, CCN1, CPH1, EFG1 , and MNT2 . Except for a single (CTT)₅ serine tract, all coded for polyglutamine tracts. Another locus with seven alleles, a region of the ERK1 protein kinase gene, was also examined, and may be a representative of a new class of highly polymorphic ‘clustered’ microsatellites. Such loci, in which several non-contiguous but closely linked microsatellites are clustered together, may be a useful source of DNA polymorphisms in microorganisms in which long microsatellite sequences are unavailable. All seven regions amplified were polymorphic, having between two and seven variable length alleles in the 11 strains of Candida albicans examined. The results of this and similar searches will facilitate epidemiological and evolutionary studies of Candida and other microorganisms.     

Stable acid phosphatase: II. Effects of pH and inhibitors

Summary Microdensitometry demonstrated that stable acid phosphatase (SAPhase) in rat and hamster osteoclasts, chondroclasts, and chondrocytes has very similar properties. The differences that were observed suggest that conformational alterations in the enzymes may be responsible for inhibition by some agents such as tartrate. These differences in response to inhibitors depend on the method of embedding as well as on species differences. SAPhase appears to correspond to acid nitrophenyl phosphatase, as shown by its pH dependent re-activation, resistance to fluoride inhibition at nearneutral pH, and the inverse effect of pH on inhibition by zinc versus aluminium ions. That proportion of SAPhase resistant to fluoride is an acid phosphatase with activity at near-neutral pH rather than a strict neutral phosphatase. The difference between fluoride sensitive and fluoride resistant SAPhase may relate to the varying association of a single enzyme with cell or lysosomal membrances. The close similarity of acid and neutral SAPhase suggests that both may represent a single enzyme in two forms rather than two distinct enzymes.Supported by the Medical Research Council of Great Britain     

PHLOEM OF SPHENOPHYLLUM

The phloem of most fossil plants, including that of Sphenophyllum, is very poorly known. Sphenophyllum was a relatively small type of fossil arthrophyte with jointed stems bearing whorls of leaves ranging in form from wedge or fan-shaped to bifid, to linear. The aerial stem systems of the plant exhibited determinate growth involving progressive reduction in the dimensions of the stem primary bodies, fewer leaves per whorl, and smaller and simpler leaves distally. The primary phloem occurs in three areas alternating in position with the arms of the triarch centrally placed primary xylem. Cells of the primary phloem, presumably sieve elements, are axially elongate with horizontal to slightly tapered end walls. In larger stems with abundant secondary xylem and secondary cortex or periderm, a zone of secondary phloem occurs whose structure varies in the three areas opposite the arms of the primary xylem, as opposed to the three areas lying opposite the concave sides of the primary xylem. The axial system of the secondary phloem consists of vertical series of sieve elements with horizontal end walls. In the areas opposite the protoxylem the parenchyma is present as a prominent ray system showing dilation peripherally. Sieve elements in the areas opposite the protoxylem arms have relatively small diameters. In the areas between the protoxylem poles the secondary phloem sieve elements have large diameters and are less obviously in radial files, while the parenchyma resembles that of the secondary xylem in these areas in that it consists of strands of cells extending both radially and tangentially. An actively meristematic vascular cambium has not been found, indicating that this layer changed histologically after the cessation of growth in the determinate aerial stem systems and was replaced by a post-meristematic parenchyma sheath made up of axially elongate parenchyma lacking cells indicative of being either fusiform or ray initials. A phellogen arose early in development in a tissue believed to represent pericycle and produced tissue comparable to phellem externally. Normally, derivatives of the phellogen underwent one division prior to the maturation of the cells. Concentric bands of cells with dark contents apparently represent secretory tissue in the periderm and cell arrangements indicate that a single persistent phellogen was present. Sphenophyllum is compared with other arthrophytes as to phloem structure and is at present the best documented example of a plant with a functionally bifacial vascular cambium in any exclusively non-seed group of vascular plants.     

PETRIFIED PLANTS FROM THE UPPER MISSISSIPPIAN OF NORTH AMERICA. I: THE SEED RHYNCHOSPERMA GEN. N.

Petrified seeds of Upper Mississippian age (Chester Series) are described from sediments from northwestern Arkansas. Specimens of Rhynchosperma quinnii gen. et sp. n. are radially symmetrical and range in length from 1.2 to 2.2 cm and 1.0 to 1.3 cm at the greatest diameter. The seeds are ovate with a tapered apex having 8–10 integumentary ribs and a broadly rounded chalaza. The integument is two-parted, consisting of an outer presumably soft tissue with secretory canals and an inner layer constructed of longitudinally oriented thick-walled cells. Nucellus and integument are confluent, but they diverge near the seed midlevel with the free portion of the nucellus forming a dome-shaped pollen-receiving structure. Additional features such as vasculature and the structure of well-preserved megagametophytes are described. The petrified specimens are compared with taxa instituted for casts and impressions which include Rhynchogonium and Boroviczia. The ovulate versus cupulate nature of these genera which has remained uncertain until now appears to be settled in favor of an ovular identity.     

The gingival epithelium of rodent molars with limited eruption

We have re-examined the arrangement of epithelia surrounding molar teeth with limited eruption in the rat, mouse and hamster. Our methods permitted enamel to be retained in paraffin and glycolmethacrylate sections, so providing optimal preservation of epithelial relationships. Three basic patterns of epithelial arrangement were observed on the various aspects of molars. Non-keratinized junctional epithelium covers the interdental septum and the base of all gingival crevices even in areas of gingival recession. In all areas other than the interdental septum, a fold of keratinized gingival epithelium lies beneath the lateral aspects of junctional epithelium. The buccal and lingual aspects of interdental septa show a zone of transition between these two basic types of epithelial arrangement. In intact gingiva the junctional epithelium can be seen to extend a considerable distance on to enamel surfaces, with the result that actual gingival crevice depths are even less than previously assumed. Artefacts resulting from loss of enamel during processing are discussed in the light of previous attempts to explain epithelial arrangements in rodent gingivae.     

PETRIFIED PLANTS FROM THE UPPER MISSISSIPPIAN OF NORTH AMERICA. II. LEPIDOSTROBUS FAYETTEVILLENSE SP. N.

Structurally preserved arborescent lycopsid fructifications are described from the Fayetteville Shale (Upper Mississippian) of northwestern Arkansas. Specimens of Lepidostrobus fayettevillense sp. n. range from complete cones 22.5 cm long and approximately 1.0 cm in diameter to smaller water-worn fragments. The cones consist of a central axis bearing closely spaced, spirally arranged sporophylls which extend from the cone axis at right angles. Each sporophyll consists of a pedicel which is turned up at its end to form a distal lamina. Sporangia are large and attached to the adaxial surface of each sporophyll. The vascular cylinder consists of a centrally located exarch protostele at least 1.1 mm in diameter. The new species is compared with morphologically similar lycopsid fructifications of equivalent age.     

Multiple paternity in the American dog tick, Dermacentor variabilis (Acari: Ixodidae)

The reproductive strategies and variation in reproductive success of ticks are poorly understood. We determined variation in multiple paternity in the American dog tick Dermancentor variabilis . In total, 48 blood-engorged female ticks and 22 male companion ticks were collected from 13 raccoon ( Procyon lotor ) hosts. In the laboratory, 56.3% of blood-engorged females laid eggs, of which 37.0% hatched or showed signs of development. We examined the presence of multiple paternity in the ensuing clutches by genotyping groups of eggs and larvae at 5 microsatellite loci and subtracting the known maternal alleles, thereby identifying male-contributed alleles. Seventy-five percent of the clutches presented multiple paternity, with a mode of 2 fathers siring the clutch. Males associated with the females on the host always sired some offspring. In 1 case, a male was the sire of clutches derived from 2 females, indicating both polygyny and polyandry may occur for this species. These results, combined with those of several other recent studies, suggest that multiple paternity might be frequent for ixodid ticks.     

Quantification of algal biofilms colonising building materials: chlorophyll a measured by PAM-fluorometry as a biomass parameter

The aim of this study was to quantify algal colonisation on anthropogenic surfaces (viz. building facades and roof tiles) using chlorophyll a (chl a) as a specific biomarker. Chl a was estimated as the initial fluorescence F0 of 'dark adapted' algae using a pulse-modulated fluorometer (PAM-2000). Four isolates of aeroterrestrial green algae and one aquatic isolate were included in this study. The chl a concentration and F0 showed an exponential relationship in the tested range between 0 and 400 mg chl a m(-2). The relationship was linear at chl a concentrations <20 mg m(-2). Exponential and linear models are presented for the single isolates with large coefficients of determination (exponential: r2 > 0.94, linear: r2 > 0.92). The specific power of this fluorometric method is the detection of initial algal colonisation on surfaces in thin or young biofilms down to 3.5 mg chl a m(-2), which corresponds to an abundances of the investigated isolates between 0.2 and 1.5 million cells cm(-2).