Influence of the composition of the fusion medium on the yield of electrofused yeast hybrids

Abstract Electrofusion between cells of yeast strains with different genetic markers in isotonic sorbitol solutions leads to high yields of hybrids when 0.1 mM Ca²⁺ and 0.5 mM Mg²⁺ salts are aded. On average, 1000–2000 hybrids are obtained when electrofusion is performed (in a helical chamber) compared to a yield of about 40–120 in the absence of these bivalent cations. A further increase in yield can be achieved by the addition of 1 mg/ml albumin, which results in up to 4000 hybrids per experimental run. The entire fusion process leads to very reproducible results in the presence of these substances.     

Date Palm DNA Mini-Preparation without Liquid Nitrogen

We have developed a new mini-procedure for isolation of total cellular DNA from date palm (Phoenix dactylifera L.). The procedure, which does not use liquid nitrogen, has proved useful due to temporary disruptions in supplies of liquid nitrogen that occur in countries where date palm trees are cultivated. DNA suitable for RFLP and PCR analyses is obtained.     

Plant phylogeny drives arboreal caterpillar assemblages across the Holarctic

1. Assemblages of insect herbivores are structured by plant traits such as nutrient content, secondary metabolites, physical traits, and phenology. Many of these traits are phylogenetically conserved, implying a decrease in trait similarity with increasing phylogenetic distance of the host plant taxa. Thus, a metric of phylogenetic distances and relationships can be considered a proxy for phylogenetically conserved plant traits and used to predict variation in herbivorous insect assemblages among co‐occurring plant species.
2. Using a Holarctic dataset of exposed‐feeding and shelter‐building caterpillars, we aimed at showing how phylogenetic relationships among host plants explain compositional changes and characteristics of herbivore assemblages.
3. Our plant–caterpillar network data derived from plot‐based samplings at three different continents included >28,000 individual caterpillar–plant interactions. We tested whether increasing phylogenetic distance of the host plants leads to a decrease in caterpillar assemblage overlap. We further investigated to what degree phylogenetic isolation of a host tree species within the local community explains abundance, density, richness, and mean specialization of its associated caterpillar assemblage.
4. The overlap of caterpillar assemblages decreased with increasing phylogenetic distance among the host tree species. Phylogenetic isolation of a host plant within the local plant community was correlated with lower richness and mean specialization of the associated caterpillar assemblages. Phylogenetic isolation had no effect on caterpillar abundance or density. The effects of plant phylogeny were consistent across exposed‐feeding and shelter‐building caterpillars.
5. Our study reveals that distance metrics obtained from host plant phylogeny are useful predictors to explain compositional turnover among hosts and host‐specific variations in richness and mean specialization of associated insect herbivore assemblages in temperate broadleaf forests. As phylogenetic information of plant communities is becoming increasingly available, further large‐scale studies are needed to investigate to what degree plant phylogeny structures herbivore assemblages in other biomes and ecosystems.

     

Suspending loads decreases load stability but may slightly improve body stability

Here, we seek to determine how compliantly suspended loads could affect the dynamic stability of legged locomotion. We theoretically model the dynamic stability of a human carrying a load using a coupled spring-mass-damper model and an actuated spring-loaded inverted pendulum model, as these models have demonstrated the ability to correctly predict other aspects of locomotion with a load in prior work, such as body forces and energetic cost. We report that minimizing the load suspension natural frequency and damping ratio significantly reduces the stability of the load mass but may slightly improve the body stability of locomotion when compared to a rigidly attached load. These results imply that a highly-compliant load suspension could help stabilize body motion during human, animal, or robot load carriage, but at the cost of a more awkward (less stable) load.     

Does re-creation of extensive pasture-forest mosaics provide an economically sustainable way of nature conservation in Sweden''s forest dominated regions?

There is a major risk that many of the remaining semi-natural pastures in Swedish forest dominated regions will lose their grazing in the near future with lost biodiversity as a result. The reason is the high costs of grazing small pastures with cattle from generally small herds. The approaching decoupling of the present EU income support per head of cattle will increase the risk. Calculations based on economies of scale in beef production and opportunity cost of forest and arable land suggest that re-creating extensive pasture-forest mosaics consisting of existing semi-natural pastures and adjacent arable fields and forests can secure economically sustainable grazing. The risk of local extinction of grassland species due to habitat isolation is also lower in large mosaics than in small, scattered pastures.     

Methods for rapid screening and isolation of bacteria producing acidic lipase: feasibility studies and novel activity assay protocols

Acidic lipase finds its commercial values in medical applications and bioremediation of food wastes. In this work, approaches for rapid screening of lipase-producing bacteria were developed and the feasibility assessment of the screening methods was performed. From food waste samples, the proposed screening procedures allowed isolation of sixteen pure bacterial strains expressing higher lipase activity at acidic pH (pH 6.0) than at alkaline pH (pH 9.0). To enhance the accuracy of lipase activity determination under acidic conditions, a novel assay procedure was also developed by deactivating lipase activity by microwave treatment prior to back titration. This additional step could minimize interferences arising from residual lipase activity during conventional direct back-titration methods in measuring lipase activity at acidic pH. Using the four strategies proposed in this work, the best acidic-lipase-producing isolate was obtained by strategy C (SSC) and was identified as Aeromonas sp. C14, displaying an optimal lipase activity of 0.7 U/ml at an acidic pH of 6.0.     

The debate about the biological species concept - a review

The importance of the species concept in biology has led to a continuing debate about the definition of species. This paper summarizes the recent literature in relation to the ‘biological species concept’ (MAYR 1942). Among the general attributes demanded, possible limitations of the universality and applicability of a species definition are discussed. Three different areas of criticism of the biological species concept are considered: 1. The impracticability of the criterion of reproductive isolation. The demand for more practical criteria is rejected, because reproductive isolation is seen as the factor that produces and maintains species as discrete entities in nature. 2. The inapplicability to non-bisexual organisms. A brief survey of modes of uniparental reproduction and their relative importance suggests that obligatory apomicts are of little evolutionary significance. 3. The inapplicability to multidimensional situations. Despite practical difficulties, the biological species concept is held to apply to organisms separated in space. The impossibility to delimit species in time by reproductive isolation is recognized. Out of two ways to divide continuous evolutionary lineages in time, the phylogenetic approach, which considers only speciation events (cladogenesis), is preferred as it is more objective. A list of recently published alternative definitions of species, none of which is found acceptable, is given. It is concluded that the biological species concept needs not be changed or dismissed on the basis of the discussed criticisms.     

Techniques for the detection of pathogenic Cryptococcus species in wood decay substrata and the evaluation of viability in stored samples

In this study, we evaluated several techniques for the detection of the yeast form of Cryptococcus in decaying wood and measured the viability of these fungi in environmental samples stored in the laboratory. Samples were collected from a tree known to be positive for Cryptococcus and were each inoculated on 10 Niger seed agar (NSA) plates. The conventional technique (CT) yielded a greater number of positive samples and indicated a higher fungal density [in colony forming units per gram of wood (CFU.g^-1) ] compared to the humid swab technique (ST). However, the difference in positive and false negative results between the CT-ST was not significant. The threshold of detection for the CT was 0.05.10³ CFU.g^-1, while the threshold for the ST was greater than 0.1.10³ CFU^-1. No colonies were recovered using the dry swab technique. We also determined the viability of Cryptococcus in wood samples stored for 45 days at 25ºC using the CT and ST and found that samples not only continued to yield a positive response, but also exhibited an increase in CFU.g^-1, suggesting that Cryptococcus is able to grow in stored environmental samples. The ST.1, in which samples collected with swabs were immediately plated on NSA medium, was more efficient and less laborious than either the CT or ST and required approximately 10 min to perform; however, additional studies are needed to validate this technique.     

Cryptic species in Diacyclops bicuspidatus (Copepoda:Cyclopoida): evidence from crossbreeding studies

The problem of cryptic species in Diacyclops bicuspidatus was examined using interpopulation crosses of four populations collected from a: (1) permanent flood lake in Kiev, Ukraine, (2) temporary pool in Kiev, (3) permanent pond in St. Petersburg, Russia (1200 km to north from Kiev) and (4) lake in Crimea (1100 km south of Kiev). The only interpopulation crosses to exhibit fertility were those between the St. Petersburg population and each of the two Kiev populations. The crosses between the Kiev and Crimea populations, between the St. Petersburg and Crimea populations, and between the two Kiev populations were sterile, as evidenced by either nonviable eggs, empty egg membranes or incomplete copulations. The F₁ hybrids resulting from the St. Petersburg permanent pond X Kiev flood lake cross were fertile and produced mature F₂ offspring. Some data on development times of parental and hybrid lines are presented. The St. Petersburg parental line showed development times almost twice as long as those of the Kiev flood lake population when reared at 10 °C and 20 °C in the laboratory. The F₁ offspring of the cross between St. Petersburg females and Kiev floodlake males showed similar development times to females of the St. Petersburg parental lines at both temperatures. The F₂ hybrids also showed development times that approximated those of the St. Petersburg parental line. These crossbreeding studies suggest the presence of cryptic species in the D. bicuspidatus inhabiting ecologically different populations in many parts of its large holarctic range.     

Evolutionary history of Scinax treefrogs on land‐bridge islands in south‐eastern Brazil

Aim We investigated how Pleistocene refugia and recent (c. 12,000 years ago) sea level incursions shaped genetic differentiation in mainland and island populations of the Scinax perpusillus treefrog group. Location Brazilian Atlantic Forest, São Paulo state, south‐eastern Brazil. Methods Using mitochondrial and microsatellite loci, we examined population structure and genetic diversity in three species from the S. perpusillus group, sampled from three land‐bridge islands and five mainland populations, in order to understand the roles of Pleistocene forest fragmentation and sea level incursions on genetic differentiation. We calculated metrics of relatedness and genetic diversity to assess whether island populations exhibit signatures of genetic drift and isolation. Two of the three island populations in this study have previously been described as new species based on a combination of distinct morphological and behavioural characters, thus we used the molecular datasets to determine whether phenotypic change is consistent with genetic differentiation. Results Our analyses recovered three distinct lineages or demes composed of northern mainland São Paulo populations, southern mainland São Paulo populations, and one divergent island population. The two remaining island populations clustered with samples from adjacent mainland populations. Estimates of allelic richness were significantly lower, and estimates of relatedness were significantly higher, in island populations relative to their mainland counterparts. Main conclusions Fine‐scale genetic structure across mainland populations indicates the possible existence of local refugia within São Paulo state, underscoring the small geographic scale at which populations diverge in this species‐rich region of the Atlantic Coastal Forest. Variation in genetic signatures across the three islands indicates that the populations experienced different demographic processes after marine incursions fragmented the distribution of the S. perpusillus group. Genetic signatures of inbreeding and drift in some island populations indicate that small population sizes, coupled with strong ecological selection, may be important evolutionary forces driving speciation on land‐bridge islands.