An empirical demonstration of the ideal free distribution: Little Grebes Tachybaptus ruficollis breeding in intensive agricultural landscapes

The ideal free distribution (IFD) model predicts that a density‐dependent mechanism operates to regulate habitat selection and reproductive performance. We studied a Little Grebe Tachybaptus ruficollis population, which breeds on irrigation ponds in the Vega Baja Valley (southeastern Spain) to test the premises of the IFD model. These ponds are highly dynamic because they are managed according to agricultural requirements, and are subject to different levels of disturbance, which can change the quality of individual ponds across the landscape. Surveys were carried out during the breeding season from 2002 to 2006, with reproduction performance estimated during two consecutive breeding seasons, 2003 and 2004. Occupation frequency differed from random, indicating preference for some ponds over others. Habitat features such as pond construction and design, the presence of submerged vegetation, vegetation along the shore and reed beds, and pond area correlated with occupation frequency and might be considered to be indicators of pond quality. Ponds were occupied sequentially from best to worst. Thus, when the population size increased, the number of low‐quality ponds occupied also increased. High‐quality ponds held more breeding pairs than low‐quality ones, resulting in the mean reproductive success per breeding pair being independent of pond quality. Little Grebes therefore occupy ponds in a manner consistent with the expectations of the IFD model.     

Vibrational communication and mating behaviour of Dichelops melacanthus (Hemiptera: Pentatomidae) recorded from loudspeaker membranes and plants

Vibrational communication is important for successful mating in various stink bugs species. The vibrational signals from males and females of Dichelops melacanthus Dallas (Hemiptera: Pentatomidae) are recorded from a nonresonant substrate (i.e. a loudspeaker membrane) to characterize the temporal and spectral properties of these vibrational signals, as well as on a resonant substrate (i.e. bean plants) to obtain information about how these signals are altered when they are transmitted through the plants. On the loudspeaker membrane, D. melacanthus males and females emit only one male or one female song, respectively. However, when the insects are placed on bean leaves, a more complex repertoire is recorded, with three different songs for each sex. The first female and male songs appear to have calling functions and the third male and female songs are emitted during courtship. The second female and male songs are emitted after the first song, although their functions in mating behaviour are not clear. The identified repertoire is similar to those of other Neotropical stink bugs, starting with songs 1 and 2 and developing into song 3. Frequency modulation is observed in the female songs recorded from the loudspeaker membrane and the plants. The signals recorded from plants present higher harmonic peaks compared with the signals recorded from the loudspeaker membrane. The presence of species and sex‐specific songs during mating confirms the important role of vibrational communication in mate location and recognition. The temporal and spectral characteristic signals are influenced by the substrate used to record the songs emitted by D. melacanthus.     

Mitochondrial DNA differentiation during the speciation process in Peromyscus

We address the problem of the possible significance of biological speciation to the magnitude and pattern of divergence of asexually transmitted characters in bisexual species. The empirical data for this report consist of restriction endonuclease site variability in maternally transmitted mitochondrial DNA (mtDNA) isolated from 82 samples of Peromyscus polionotus and P. leucopus collected from major portions of the respective species' ranges. Data are analyzed together with previously published information on P. maniculatus, a sibling species to polionotus. Maps of restriction sites indicate that all of the variation observed can be reasonably attributed to base substitutions leading to loss or gain of particular recognition sites. Magnitude of mtDNA sequence divergence within polionotus (maximum approximately equal to 2%) is roughly comparable to that observed within any of five previously identified mtDNA assemblages in maniculatus. Sequence divergence within leucopus (maximum approximately equal to 4%) is somewhat greater than that within polionotus. Consideration of probable evolutionary links among mtDNA restriction site maps allowed estimation of matriarchal phylogenies within polionotus and leucopus. Clustering algorithms and qualitative Wagner procedures were used to generate phenograms and parsimony networks, respectively, for the between-species comparisons. Three simple graphical models are presented to illustrate some conceivable relationships of mtDNA differentiation to speciation. In theoretical case I, each of two reproductively defined species (A and B) is monophyletic in matriarchal genealogy; the common female ancestor of either species can either predate or postdate the speciation. In case II, neither species is monophyletic in matriarchal genotype. In case III, species B is monophyletic but forms a subclade within A which is thus paraphyletic with respect to B. The empirical results for mtDNA in maniculatus and polionotus appear to conform closely to case III. These theoretical and empirical considerations raise a number of questions about the general relationship of the speciation process to the evolution of uniparentally transmitted traits. Some of these considerations are presented, and it is suggested that the distribution patterns of mtDNA sequence variation within and among extant species should be of considerable relevance to the particular demographies of speciation.      

Genetic and environmental factors reducing the incidence of the storage pest Sitotroga cerealella in maize

The Angoumois grain moth, Sitotroga cerealella (Olivier) (Lepidoptera: Gelechiidae), is found worldwide and infests maize grains in the field and during storage. Transgenic maize resistant to kernel attack by S. cerealella has been developed, but could pose a nutritional risk to humans and livestock. Therefore, alternative sources of resistance posing no threat to consumption should be identified. In this study, our main objectives were to assess genetic variability for kernel damage by S. cerealella under natural infestation and to determine genetic and environmental factors contributing to genotype, year, and genotype*year variability. Factorial regression was performed to obtain a biological explanation for the number of kernels damaged per ear. Seventy-seven Spanish maize landraces along with six hybrid checks were evaluated in 2004, 2005, and 2006. There was variability for kernel damage by natural infestation of S. cerealella among the landraces: popcorn landraces were among the least damaged, whereas hybrid checks were among the most susceptible genotypes. Plant characteristics associated with ear appearance could be the main stimulatory factors for oviposition and feeding of S. cerealella moths, followed by husk coverage of the ear. It was confirmed that temperature is the main environmental factor affecting S. cerealella development. Genotypes sensitive to infestation by S. cerealella were more negatively affected by higher temperatures than the least attractive genotypes, and lower temperatures reduced the number of kernels damaged on the most susceptible genotypes more than on the least susceptible.     

Hydrolysis of dolichyl esters by oviduct membranes and characterization of endogenous dolichyl esters

The chick oviduct system has been employed to study whether dolichol esters might serve as a storage form of dolichol to be converted to dolichyl phosphate (Dol-P) during periods when Dol-P levels increase. Chicken oviduct membranes catalyze the hydrolysis of dolichyl-[14C]oleate; the reaction is dependent on detergent (0.04% NP-40 is optimal), is unaffected by divalent cations and EDTA, and exhibits a pH optimum of 6.0. Oviduct membranes also hydrolyze cholesteryl-[14C]oleate, which exhibits similar properties except the pH optimum is 5.0-5.5. Neither Dol-[14C]palmitate nor Chol-[14C]palmitate is hydrolyzed by membranes. Chol-ester hydrolysis is more sensitive to heat-denaturation than is Dol-ester hydrolysis. Esterase activity was assayed in membranes prepared from immature chicks, chicks treated with diethylstilbestrol, chicks withdrawn from diethylstilbestrol, and mature hens. The highest esterase specific activity was observed in membranes obtained from chicks withdrawn from hormone. In order to characterize the fatty acid composition of Dol-esters they were purified from mature hen oviducts by chromatography on DEAE-cellulose and Fractogel ORPVA-6000, reverse-phase HPLC, and TLC. About 15-25% of oviduct dolichol is in the esterified form. Fatty acid analysis revealed that approximately 85% of the dolichol was esterified to oleic acid. The fact that the highest esterase activity is found in membranes from chicks withdrawn from hormone and that only 20% of the dolichol is esterified argues against a role for Dol-esters as a reservoir of dolichol for conversion to Dol-P.     

The replicative helicase MCM recruits cohesin acetyltransferase ESCO2 to mediate centromeric sister chromatid cohesion

Chromosome segregation depends on sister chromatid cohesion which is established by cohesin during DNA replication. Cohesive cohesin complexes become acetylated to prevent their precocious release by WAPL before cells have reached mitosis. To obtain insight into how DNA replication, cohesion establishment and cohesin acetylation are coordinated, we analysed the interaction partners of 55 human proteins implicated in these processes by mass spectrometry. This proteomic screen revealed that on chromatin the cohesin acetyltransferase ESCO2 associates with the MCM2‐7 subcomplex of the replicative Cdc45‐MCM‐GINS helicase. The analysis of ESCO2 mutants defective in MCM binding indicates that these interactions are required for proper recruitment of ESCO2 to chromatin, cohesin acetylation during DNA replication, and centromeric cohesion. We propose that MCM binding enables ESCO2 to travel with replisomes to acetylate cohesive cohesin complexes in the vicinity of replication forks so that these complexes can be protected from precocious release by WAPL. Our results also indicate that ESCO1 and ESCO2 have distinct functions in maintaining cohesion between chromosome arms and centromeres, respectively.     

The Effect of Lactobacillus salivarius SGL03 on Clinical and Microbiological Parameters in Periodontal Patients

The destruction of periodontal tissues during periodontitis is the result of the immune-inflammatory reactions to the bacteria of dental biofilm. Probiotics may reduce dysbiosis by the modification of the dental microbiome, which can influence the immune-inflammatory mechanisms. The aim of this study was to estimate the clinical and microbiological parameters, before and after 30 days of application of the dietary supplement containing Lactobacillus salivarius SGL03 or placebo. The study was conducted in 51 patients with stage I or II periodontitis during the maintenance phase of treatment. The clinical parameters and the number of colony forming units (CFU) of bacteria in supragingival plaque were assessed before and after 30 days of the oral once daily administration of the dietary supplement in the form of suspension containing L. salivarius SGL03 or placebo. There were no changes in the PI scores between and within the groups. The value of BOP decreased in both groups. In the study group the significant reduction of the mean pocket depth was revealed (from 2.5 to 2.42, p = 0,027) but without the difference between the groups. There were no significant changes in the number of bacteria within the groups. In the control, but not the study group, positive correlations were observed between the clinical parameters (variables) and the number of bacteria. The use of the dietary supplement containing L. salivarius SGL03 may reduce pocket depth despite the lack of changes in other clinical parameters and the number of bacteria in supragingival plaque.Key words: probiotics, periodontal treatment, Lactobacillus salivarius