A comparative study of territory in the Reed warbler (Acrocephalus scirpaceus) and Sedge warbler (A. schoenobaenus)

Various aspects of territoriality were studied comparatively in a marked population of Reed and Sedge warblers at the Attenborough Nature Reserve, Nottinghamshire. Differences in arrival patterns, establishment of territory and particularly territory size were detected. In view of the dynamic nature of territory boundaries, a method is described for obtaining measures of mean territory size for comparative purposes. The sympatric species were largely separated by different breeding and feeding habitats, but there was also a degree of interspecific competition in some areas and interspecific territorialism was found to occur. Adults of both these migratory species were found to exhibit strong site fidelity, and there was some evidence to suggest that early post-fledging experience may influence initial selection of a particular area and territory for first breeding.
The adaptive significance of territory is discussed in relation to the findings presented and current hypotheses. There was some evidence which suggests that reduction of predation pressure and intraspecific interference through spacing out, as well as provision of a nest-site may be important functions of territory in these species, but no evidence that food supply or population regulation are involved. The significance of interspecific territorialism is considered in relation to interspecific competition. The various factors effecting territory size and the patterns of nesting dispersion are also considered in an attempt to account for the striking interspecific differences found between these closely related species. It is concluded that although a multiplicity of factors may well be interacting in complex fashion, the more important of these stem from contrasts in the physical properties of the two habitats.     

Sex biased natal dispersal in a closed, saturated population of Seychelles warblers Acrocephalus sechellensis

The distances that individuals disperse, from their natal site to the site of first breeding and between breeding sites, have important consequences for the dynamics and genetic structure of a population. Nearly all previous studies on dispersal have the problem that, because the study area encompassed only a part of the population, emigration may have been confounded with mortality. As a result long-distance dispersers may have been overlooked and dispersal data biased towards short distances. By studying a virtually closed population of Seychelles warblers Acrocephalus sechellensis we obtained almost unbiased results on several aspects of dispersal. As in the majority of other avian species, natal dispersal distance was female biased in the Seychelles warbler. Female offspring also forayed further from the natal territory in search of breeding vacancies than male offspring. The sex bias in natal dispersal distance did, however, depend on local breeding density. In males, dispersal distance decreased as the number of territories bordering the natal territory increased, while in females, dispersal distance did not vary with local density. Dispersal by breeders was rare and, unlike in most species, distances did not differ between the sexes. We argue that our results favour the idea that the sex bias in natal dispersal distance in the Seychelles warbler is due to inbreeding avoidance and not resource competition or intrasexual competition for mates.     

Genetic and phenotypic associations in morphological traits: a long term study of great reed warblers Acrocephalus arundinaceus

We present estimates of standardized selection (directional and quadratic) differentials via reproductive success on eight morphological traits in a newly founded long-term study population of great reed warblers Acrocephalus arundinaceus in Sweden. In order to predict the evolutionary response to selection in these traits we present estimates of heritabilities (h²), phenotypic (r_P) and genetic (r_A) correlations among the same traits. We also examined the extent of parental effects in the expression of the phenotypic traits. Overall, the population is subject to low levels of directional selection and higher levels of stabilizing selection. This makes us predict that the population is changing very little if anything, even though h² in many cases are considerable. Midparent-midoffspring h² ranged from 0.14 and 0.94 (mean 0.58) and were significant for seven of eight traits. We found indications of positive maternal effects in tarsus length. Phenotypic correlations between traits ranged from 0.02 to 0.43 (mean 0.15) and showed generally much lower values than the corresponding genetic correlations that ranged between 0.08 and 1.04 (mean 0.46). Overall, the correlation between r_P and r_A was significant, although moderate, but they tended to differ in magnitude, possibly due to overestimation of additive covariance between traits.     

Common cuckoo Cuculus canorus parasitism,antiparasite defence and gene flow in closely located populations of great reed warblers Acrocephalus arundinaceus

In Hungary an unusually high rate of parasitism on the great reed warbler Acrocephalus arundinaceus by the common cuckoo Cuculus canorus has been maintained for at least the last one hundred years. We evaluated parasitism rate, antiparasite defence and genetic differentiation among Hungarian great reed warblers at three sites located 40–130 km from each other, where hosts suffered from a high (41–68%), moderate (11%), and almost no (<1%) parasitism. We were especially interested in whether the level of antiparasite defence was related to the local parasitism rate, and, if not, to understand why. There was no difference among the three sites in the responses to experimental parasitism by non‐mimetic model cuckoo eggs (rejection rate 71–82%), which can be explained by strong gene flow between populations: there was low level of philopatry and no genetic differentiation in the region. Reproductive success of the host in the heavily parasitised site was about 54% of that in the unparasitised site, indicating that long‐term persistence of host populations in highly exploited areas depends on continuous immigration.     

A comparison of the song and territorial behaviour of a long-distance migrant, the Marsh Warbler Acrocephalus palustris, in summer and winter

Colour-ringed populations of Marsh Warblers Acrocephalus palustris on breeding and wintering grounds were compared with respect to song and territorial behaviour. Song and territorial defence had a short duration on the breeding grounds, peaking during the period of mate acquisition and mate-guarding. Some males later showed polyterritorial behaviour. Wintering Marsh Warblers sang and showed defensive behaviour for a longer period which included moult. This behaviour could be described in terms of defence of a short-term resource (a fertile female) in the summer and long-term defence of a reliable food resource in the winter.     

High variation reduces the value of feather stable isotope ratios in identifying new wintering areas for aquatic warblers Acrocephalus paludicola in West Africa

Stable isotope analysis of feathers can be useful in the study of seasonal interactions and migratory connectivity in birds. For the Palaearctic–African migration system, however, the lack of isotope data from feathers of known origin in Africa renders the geographic assignment of birds captured on European breeding grounds to potential wintering areas problematic. Rectrices of the threatened aquatic warbler Acrocephalus paludicola grown in Africa were sampled across six European countries to assess whether birds in different breeding populations shared similar isotopic signatures and so were likely to have wintered in the same region in Africa. Freshly grown feathers of aquatic warblers collected at the only known wintering site in Senegal showed high variation in carbon, nitrogen, and hydrogen isotope ratios. Due to similarly high variation in isotope ratios of African‐grown feathers within all breeding populations, it was not possible to determine whether different populations wintered in different regions. However, isotope signatures of 20% of birds captured on European breeding grounds fell outside the range of those captured in Senegal, suggesting a wider wintering distribution than is currently known. We therefore assessed whether the origin of these feathers could be estimated by trying to establish isotopic gradients across sub‐Saharan West Africa. Feathers of three ecologically similar surrogate species were sampled from wetlands across a 3000 km east‐west and a 2000 km north–south transect. Within‐site variation in feather isotope ratios was frequently larger than the difference predicted by gradients across West Africa. Thus, predicting the origin of individual feathers using single‐isotope gradients was not reliable. The large within‐site variability of feather isotope ratios of a habitat specialist species like the aquatic warbler indicates that using feather isotope ratios will require large sample sizes from many locations, and may thus not be an efficient tool in identifying wintering areas of Palaearctic–African migrants.     

Responses of great reed warblers Acrocephalus arundinaceus to experimental brood parasitism: the effects of a cuckoo Cuculus canorus dummy and egg mimicry

Egg rejection behaviour towards parasitic eggs was studied in a great reed warbler Acrocephalus arundinaceus population in central Hungary, which was heavily (about 65%) parasitised by the common cuckoo Cuculus canorus . Clutches were experimentally parasitised during the egg-laying period with artificial, moderately mimetic cuckoo eggs or with conspecific eggs that were good mimics of the hosts' eggs. Great reed warblers rejected 76.2% of the artificial cuckoo eggs, mainly by ejection, but accepted most of the conspecific eggs (87.5%). Cuckoo eggs in naturally parasitised clutches were rejected at a lower rate (32%). When, in addition to the egg mimicry experiments, a stuffed cuckoo was placed near the nest, accompanied by the recording of a female cuckoo call, hosts' rejection rate of the artificial cuckoo egg increased from 76% to 96%. The sight of the cuckoo, on the other hand, did not influence host's rejection behaviour when a conspecific egg was used in the experiment. A stuffed collared dove Streptopelia decaocto , accompanied by its call, was used as a control, and did not cause any increased rejection. Great reed warblers were more aggressive towards the cuckoo than to the dove dummy. When the cuckoo eggs in naturally parasitised clutches were exchanged with artificial cuckoo eggs, we observed no increase in the rejection rate. We conclude that great reed warblers in our heavily parasitised population are capable of detecting brood parasitism in their clutch by identifying the parasitic egg. The efficiency of this identification depends mainly on the mimicry of the foreign egg. The sight of the cuckoo at the nest may increase rejection rate by stimulus summation, and this conditional effect is mainly affected by the degree of mimicry of the parasitic egg.     

Spatial arrangement and genetic structure in Gentianella aspera in a regional, local, and temporal context

Gentianella aspera is a biennial plant of various nutrient-poor grasslands that has become rare in the landscapes outside the Alps of eastern Austria. Using AFLP fingerprinting we investigated: (1) effects of spatial structure on genetic structure in a large vineyard population that is confined to the embankments separating the grapevines; (2) temporal variation in genetic diversity and structure in this population; (3) relationships with other populations in a regional context. On the regional scale, moderate isolation by distance among populations was revealed by a Mantel test. Bayesian analysis of population structure indicated three spatially distinct gene pools and an additional one within the vineyard population. Within this population, spatial autocorrelation analysis revealed a positive correlation between genetic and spatial distance up to 50 m. Patterns found by PCoA were not in line with a priori defined subpopulations and indicated substantial gene flow across embankments. AMOVA revealed low differentiation among both the subpopulations that were found on the linear embankments and among two local groups of these subpopulations. We found, however, striking differences in the among-group variation between the 2 years, i.e., between two local groups within the generations and between those groups among generations. This was due to the highly variable larger group of the younger generation, in which an additional gene pool was identified by Bayesian analysis of population structure. Based on these results we discuss scenarios of local and regional dynamics within and among G. aspera populations.     

Conserved gene arrangement in the origin region of the Streptomyces coelicolor chromosome.

A 23-kb fragment of the Streptomyces coelicolor chromosome spanning the dnaA region has been isolated as a cosmid clone. Nucleotide sequence analysis of a 5-kb portion shows that the genes for the RNase P protein (rnpA), ribosomal protein L34 (rpmH), the replication initiator protein (dnaA), and the beta subunit of DNA polymerase III (dnaN) are present in the highly conserved gene arrangement found in all eubacterial genomes studied so far. The dnaA-dnaN intergenic region is approximately 1 kb and contains a cluster of at least 12 DnaA boxes with a consensus sequence of TTGTCCACA matching the consensus DnaA box in the phylogenetically related Micrococcus luteus. Two DnaA boxes precede the dnaA sequence. We propose that the chromosomal origin (oriC) of S. coelicolor lies between dnaA and dnaN. In related work, J. Zakrzewska-Czerwinska and H. Schrempf (J. Bacteriol. 174:2688-2693, 1992) have identified the homologous sequence from the closely-related Streptomyces lividans as capable of self-replication.     

A comparison of two algorithms in computerized temporal discounting procedures

Two algorithms are commonly applied in computerized temporal discounting procedures (Decreasing Adjustment and Double-Limit Algorithms); however, the degree to which the two algorithms produce similar patterns of discounting is unknown. The present experiment compared the two common algorithms across sign (gains and losses) and magnitude ($10 and $1000) conditions. Twenty participants made choices between larger later and smaller sooner alternatives that were presented by each of the algorithms in separate conditions. Strong correlations were found between the two measures; however, the Decreasing Adjustment Algorithm tended to produce lower indifference points and higher rates of discounting than the Double-Limit Algorithm. Both algorithms found significant magnitude effects. Less consistent results were found when comparing the two algorithms across sign. The present results suggest that researchers should apply caution when making comparisons between outcomes of delay discounting studies that have used the two different algorithms. However, the interpretation of findings from individual studies is probably not strongly affected by the use of different computer algorithms.     

A direct comparison of selectin-mediated transient, adhesive events using high temporal resolution

Leukocyte capture and rolling on the vascular endothelium is mediated principally by the selectin family of cell adhesion receptors. In a parallel plate flow chamber, neutrophil rolling on purified selectins or a selectin-ligand substrate was resolved by high speed videomicroscopy as a series of ratchet-like steps with a characteristic time constant (Kaplanski, G., C. Farnarier, O. Tissot, A. Pierres, A.-M. Benoliel, M. C. Alessi, S. Kaplanski, and P. Bongrand. 1993. Biophys. J. 64:1922-1933; Alon, R., D. A. Hammer, and T. A. Springer. 1995. Nature (Lond.). 374:539-542). Under shear, neutrophil arrests due to bond formation events were as brief as 4 ms. Pause time distributions for neutrophils tethering on P-, E-, L-selectin, or peripheral node addressin (PNAd) were compared at estimated single bond forces ranging from 37 to 250 pN. Distributions of selectin mediated pause times were fit to a first order exponential, resulting in a molecular dissociation constant (k(off)) for the respective selectin as a function of force. At estimated single bond forces of 125 pN and below, all three selectin dissociation constants fit the Bell and Hookean spring models of force-driven bond breakage equivalently. Unstressed k(off) values based on the Bell model were 2.4, 2.6, 2.8, 3.8 s(-1) for P-selectin, E-selectin, L-selectin, and PNAd, respectively. Bond separation distances (reactive compliance) were 0.39, 0.18, 1.11, 0.59 A for P-selectin, E-selectin, L-selectin, and PNAd, respectively. Dissociation constants for L-selectin and P-selectin at single bond forces above 125 pN were considerably lower than either Bell or Hookean spring model predictions, suggesting the existence of two regimes of reactive compliance. Additionally, interactions between L-selectin and its leukocyte ligand(s) were more labile in the presence of flow than the L-selectin endothelial ligand, PNAd, suggesting that L-selectin ligands may have different molecular and mechanical properties. Both types of L-selectin bonds had a higher reactive compliance than P-selectin or E-selectin bonds.     

A new analysis method for the comparison of 2 temporal patterns,with indices of association

A new method for evaluating the degree of association between the behavioural patterns of 2 individuals is described and illustrated. It is proposed discrimination should be made between the unit for sampling (sample interval) and the unit for analysis. The length of the sample interval affects analysis accuracy, while the length of the analysis unit affects the analysis scale. A new “moving analysis unit (MAU) method” is proposed to divide an observation period into analysis units. The MAU method, with various lengths of analysis units, allows for various aspects of interaction between 2 individuals. As a similarity coefficient between the 2 temporal patterns, Iwao's ω (Iwao 1977) is proposed. Investigation of nonparametric confidence intervals of ω is performed with the bootstrap (Efron 1979), which is also applied for obtaining the null hypothesis distribution of ω. The MAU method, ω and the bootstrap are applied to the analysis of both insect and human communication.     

A gating mechanism for sound pattern recognition is correlated with the temporal structure of echolocation sounds in the rufous horseshoe bat

Summary The rufous horseshoe bat, Rhinolophus rouxi, was trained to discriminate differences in target distance. Loud free running artificial pulses, simulating the bat's natural long-CF/FM echolocation sounds, interfered with the ability of the bat to discriminate target distance. Interference occurred when the duration of the CF component of the CF/FM artificial pulse was between 2 and 70 ms. A brief (2.0 ms) CF signal 2–68 ms before an isolated FM signal was as effective as a continuous CF component of the same duration. When coupled with the bat's own emissions, a 2 ms FM sweep alone was effective in interfering when it came 42 to 69 ms after the onset of the bat's pulse. The coupled FM artificial pulses did not interfere when they began during the bat's own emissions.It appears that the onset of the CF component activates a gating mechanism that establishes a time window during which FM component signals must occur for proper neural processing. A comparison with a similar gating mechanism in Noctillo albiventris, which emits short-CF/FM echolocation sounds, reveals that the temporal parameters of the time window of the gating mechanism are species specific and specified by the temporal structure of the echolocation sound pattern of each species.Abbreviations FM frequency modulated - CF constant frequency     

Oscillating gas bubbles as the origin of bowel sounds: a combined acoustic and imaging study

Bowel sounds have been speculated to stem from the movement of gas or a mixture in the bowel lumen, with gas as the major component. The exact role and the mechanism through which gas participates have not been elucidated. Video images of actively moving bubbles under either real-time ultrasonography (RU, n = 4) or videofluoroscopy (VF, n = 4) with synchronous sound recording were studied and a total of 24 bubbling bowel sounds (BBS's) were obtained. The physical dimensions and acoustic parameters of bubbles were analyzed. Freely oscillating bubbles were demonstrated clearly in both groups. Bubble radii ranged from 1.5 to 7.2 mm and frequencies from 258.3 to 1,078 Hz. The bubble frequency correlated inversely with the radius (P < 0.01). The relevant acoustic features and parameters of bubble dynamics further supported the identification of gas bubbles. Although the acoustic features seemed to be of minor clinical significance, increased number of clustering or fixed, repetitive pattern of occurrences might suggest a poorer prognosis. In summary, oscillating gas bubbles are capable of producing BBS's and may play a central role in this newly recognized model of bowel sound genesis. The patterns of BBS's may be of prognostic value in clinical application, underlining the need for further study.     

Habitat choice in Phylloscopus warblers: the role of morphology, phylogeny and competition

We studied ecological and evolutionary aspects of habitat choice in a group of closely related bird species to gain insight into factors influencing bird community structure. Seven species of Phylloscopus warblers breed sympatrically in the middle taiga subzone of Central Siberia. We examine how the distribution of species among habitats is related to morphology, phylogeny and competition, and we compare our results with an earlier study on the ecomorphology of Phylloscopus warblers in Kashmir. We found that in Siberia, large warbler species prefer productive habitats with mostly deciduous vegetation, whereas small species occupy poor coniferous forests. Possible explanations for this finding remain to be tested in the future. Moreover, we found a tendency for species with large feet, small bills and short wings to occupy habitats with an abundance of bush thickets near the ground. In the Kashmir study, competition was considered a major factor in structuring the Phylloscopus community, and patterns of habitat choice were not influenced by phylogenetic relationships. In strong contrast, we found that in the Siberian community, closely related species occupy similar habitats. We discuss whether this conservative evolution of habitat preferences in Siberia may be due to low intensity of interspecific competition or to other ecological factors.     

A comparison of the origin of replication of pSa with R6K

Summary The plasmid pOri3 is a derivative of the origin of replication of pSa. Replication is defective as a result of a truncated repA gene, the product of which is required for plasmid replication. The defective replication is complemented by the presence of the intact repA gene of pSa, or by the presence of the plasmid R6K. The basis of this complementation has been examined by comparing the nucleotide sequence of the origin of pSa with that of R6K. A 13 base pair sequence present twice in the origin of pSa has homology with a 13 base pair sequence that is present fourteen times in the origin of R6K. These sequences may be the binding sites for the initiator proteins of these two plasmids. The location of these binding sites relative to the genes for the initiator proteins suggests that an autoregulatory control mechanism for the synthesis of the initiator proteins may also play a role in the control of plasmid copy number.     

Winter Burning and the Reduction of Cornus sericea in Sedge Meadows in Southern Wisconsin

To control shrubs, which are increasing in dominance in wetlands worldwide, winter burning may be an important tool, especially from the perspective of minimizing urban hazards. The goal of this project was to determine if winter burning was successful in reducing the dominance (mean percentage cover and maximum height) of Cornus sericea in sedge meadows in southern Wisconsin, where shrubs proliferated after cattle were excluded. Experimental burn and control plots were set up within sedge meadows, including an ungrazed “reference” site that had been little, if ever, grazed and a “historically grazed” site, a recovery site that had not been grazed by cattle since 1973. None of the dominant species including C. sericea was significantly affected by burning for either mean percentage cover or maximum height (analysis of variance: no burning × species interaction). Both mean percentage cover and maximum height were only weakly related to burning (28.1 and 14.3% of the variability contributed to the cumulative percentage of the coefficient of determination, respectively) at both sites based on non‐metric multidimensional scaling analysis. Although species richness increased in burned plots in 1999 and 2000, no differences were apparent between pre‐burned and unburned plots in 1997 and unburned plots in 1999 and 2000 (analysis of variance: year × burning interaction). After burning in the ungrazed site, herbaceous species appeared that had not been detected for decades, including Chelone glabra and Lathyrus palustris. Exotic species were present in both the ungrazed reference and recovery site. Although winter burning treatments did not reduce the dominance of woody shrub species in the site recovering from cattle grazing, burning was useful in stimulating the maintenance of species richness in the ungrazed sedge meadow.