The small-scale pattern of Cynodon dactylon in Mediterranean pastures

The abundance of Cynodon dactylon was recorded in 50 plots presenting different geomorphological conditions and along a transect of 16 500 2×2 cm contiguous quadrats within a small basin 330 m in length, in the granite pediment of the Sierra de Guadarrama (Central Spain). Soil analyses were undertaken on samples from the 50 plots and the soil information matrix obtained was analysed using Principal Components Analysis and Discriminant Analysis. Results showed that in the Mediterranean pastures Cynodon dactylon was restricted to deep, well developed soils with relatively high values of cations, conductivity and organic matter, and could be used as an indicator of such soil conditions in these grasslands. The spatial pattern of the species was analysed using New Local Variances which revealed the existence of a small-scale pattern, ranging from 8 to 18 cm, present at all levels of the analysis. The size of small-scale patterns was positively correlated with species abundance and was interpreted as a relation between plant vigour and favourable soil conditions.I would like to thank Professor González Bernáldez for his interest and encouragement.     

Resolution of complex neuronal arrangements in the blowfly visual system using triple fluorescence staining

Summary Consecutive application of the fluorescent dyes, Texas Red and Lucifer Yellow, followed by nuclear staining with Bisbenzimide, reveals spatial relationships between individual neurons and relationships between their cell bodies and the perikaryal rind. The method is particularly useful for light-microscopical studies of complex interrelationships between identified neurons. The method has specific advantages over intraneuropil staining with cobalt or with HRP. These advantages are: simplicity, speed, information content, and aesthetic considerations.     

Apparent survival of tropical birds in a wet,premontane forest in Costa Rica

Despite the importance of tropical birds in the development of life history theory, we lack information about demographic rates and drivers of population dynamics for most species. We used a 7‐year (2007–2013) capture‐mark‐recapture dataset from an exceptionally wet premontane forest at mid‐elevation in Costa Rica to estimate apparent survival for seven species of tropical passerines. For four of these species, we provide the first published demographic parameters. Recapture probabilities ranged from 0.21 to 0.53, and annual estimates of apparent survival varied from 0.23 to 1.00. We also assessed the consequences of inter‐annual variation in rainfall on demographic rates. Our results are consistent with inter‐annual rainfall increasing estimates of apparent survival for two species and decreasing estimates for three species. For the three species where we could compare our estimates of apparent survival to estimates from drier regions, our estimates were not consistently higher or lower than those published previously. The temporal and spatial variability in demographic rates we document within and among species highlights the difficulties of generalizing life history characteristics across broad biogeographic gradients. Most importantly, this work emphasizes the context‐specific role of precipitation in shaping tropical avian demographic rates and underscores the need for mechanistic studies of environmental drivers of tropical life histories.     

Convergence of visual,haltere, and prosternai inputs at neck motor neurons of Calliphora erythrocephala

Summary Neck muscles of Calliphora erythrocephala, situated in the anterior prothorax, are innervated on each side by 8 motor neurons arising in the brain (cervical nerve neurons, CN1–8) and at least 13 motor neurons arising in the prothoracic ganglion (anterior dorsal and frontal nerve neurons, ADN1,2 and FN1-11). Three prominent motor neurons (CN6 and FN1,2) are described in detail with special emphasis on their relationships with giant visual interneurons from the lobula plate, haltere interneurons, and primary afferents from the prosternal organs and halteres. These sensory organs detect head movement and body yaw, respectively. Neuronal relationships indicate that head movement is under multimodal sensory control that includes giant motion-sensitive neurons previously supposed to mediate the optomotor response in flying flies. The described pathways provide anatomical substrates for the control of optokinetic and yaw-incurred head movements that behavioural studies have shown must exist.     

Two allelic genes responsible for vegetative incompatibility in the fungus Podospora anserina are not essential for cell viability

Summary Vegetative incompatibility is a lethal reaction that destroys the heterokaryotic cells formed by the fusion of hyphae of non-isogenic strains in many fungi. That incompatibility is genetically determined is well known but the function of the genes triggering this rapid cell death is not. The two allelic incompatibility genes, s and S, of the fungus Podospora anserina were characterized. Both encode 30 kDa polypeptides, which differ by 14 amino acids between the two genes. These two proteins are responsible for the incompatibility reaction that results when cells containing s and S genes fuse. Inactivation of the s or S gene by disruption suppresses incompatibility but does not affect the growth or the sexual cycle of the mutant strains. This suggests that these incompatibility genes have no essential function in the life cycle of the fungus.     

Tropical niche conservatism as a historical narrative hypothesis for the Neotropics: a case study using the fly family Muscidae

Aim We evaluate the extent to which the tropical conservatism hypothesis can explain the evolutionary development of the Muscidae. Furthermore, we compare the geographical patterns of muscid phylogenetic structure with biogeographical regions that have been identified for Neotropical insects. Location Central and South America. Methods We modelled the geographic distributions of 658 species using Maxent and 19 environmental variables. A generic‐level supertree of the Muscidae was assembled using matrix representation with parsimony and used to map the geographic pattern of mean root distance (MRD), a metric of the relative evolutionary development of assemblages. Regression models (ordinary least squares and regression trees) were used to examine temperature and other environmental correlates of MRD to explore potential environmental drivers of muscid diversification. We used the regression tree results to recognize variable intervals that best explained MRD, and these intervals were mapped to recognize and compare with biogeographical regions of Neotropical insects. Results The geographic pattern of MRD was consistent with the tropical conservatism hypothesis: species in genera that diversified relatively early, as measured by their distance from the tree root, dominate lowland tropical South America, whereas species in genera that diversified more recently occupy extra‐tropical areas, sub‐Antarctic areas and the Andean highlands. Temperature was the strongest correlate of MRD. Three biogeographical regions were recognized and they coincided with two regions known for insects. Main conclusions Evolutionary responses of muscid flies to post‐Eocene climate change taking the form of an expansion of a tropical group into regions with colder climates may be fundamental to explaining their distribution in the Neotropics. Our biogeographical regions delimited by temperature and the phylogenetic metric, surrogates of the tropical conservatism hypothesis, were very similar to general insect patterns, supporting the ‘tropical origin and evolutionary response to climate cooling’ as a broadly based historical narrative for the Neotropics.     

5S ribosomal gene clusters in wheat: pulsed field gel electrophoresis reveals a high degree of polymorphism

Summary The long-range structure of 5S rRNA gene clusters has been investigated in wheat (Triticum aestivum L.) by means of pulsed field gel electrophoresis. Using aneuploid stocks, 5S rRNA gene clusters were assigned to sites on chromosomes 1B, 1D, 513 and 5D. Cluster sizes were evaluated and the copy number of 5S DNA repeats was estimated at 4700-5200 copies for the short repeating unit (410 bp) and about 3100 copies for the long repeat (500 bp) per haploid genome. A comparison of wheat cultivars revealed extremely high levels of polymorphism in the 5S rRNA gene clusters. With one restriction enzyme digest all varieties tested gave unique banding patterns and, on a per fragment basis, 21-fold more polymorphism was detected among cultivars for 5S DNA compared to standard restriction fragment length polymorphisms (RFLPs) detected with single copy clones. Experiments with aneuploid stocks suggest that the 5S rRNA gene clusters at several chromosomal sites contribute to this polymorphism. A number of previous reports have shown that wheat cultivars are not easily distinguished by isozymes or RFLPs. The high level of variation detected in 5S rRNA gene clusters therefore offers the possibility of a sensitive fingerprinting method for wheat. 5S DNA and other macro-satellite sequences may also serve as hypervariable Mendelian markers for genetic and breeding experiments in wheat.     

A PCR-based test for the presence of endogenous virus gene evA in chickens

An endogenous virus, denoted ev A, is present at high frequency in all brown egg layer lines. Using inverse polymerase chain reaction (PCR) based on the viral LTR regions, products were obtained containing cellular sequences 5' and 3' to the viral insertion point. PCR of chicken genomic DNA was carried out, using primers chosen from the 5' and 3' cellular sequences and a primer chosen from either the U3 or U5 portions of the viral LTR. Amplification of DNA from birds that did not carry ev A with the primer triplets always gave a single 364bp reaction product, interpreted as representing the flank-to-flank amplification product. Amplification of DNA from known homozygous or heterozygous ev A carriers, with the same primer triplets, always gave both the expected junction product and 364bp product. Therefore, these primer sequences can be used to distinguish ev A carriers from non-carriers but cannot distinguish between homozygous and heterozygous ev A carriers.