Coccidian Parasites (Apicomplexa: Eimeriidae) of Nerodia spp. (Serpentes: Colubridae), with a Description of a New Species of Eimeria

Eimeria conanli n. sp. (Apicomplexa: Eimeriidae) is described from intestinal contents and feces of Nerodia erythrogaster transversa and N harteri harteri from northcentral Texas. Oocysts of the new species are ellipsoid in shape. 17.9 × 13.0(15–21 × 12–15) μm, with a smooth, thin, single-layered wall; shape index 1.4 (1.2–1.5). One to several (usually 2) polar granule(s) and an oocyst residuum are present, but a micropyie is absent. Sporocysts are elongate, 12.9 × 5.2 (13–15 × 5–6) -m, apparently without a true Stieda body structure. Each sporoeyst contains an ellipsoid residuum, 3.9 × 3.2 (3–6 × 2–4) μm, and elongate sporozoites, 11.4 × 2.5 (10–14 × 2–3) μm in situ, each with a spherical or subspherical anterior refractile body and spherical to ellipsoid posterior refractile body. In addition to the new species, oocysts of 4 previously described eimerians from colubrid snakes were found in these hosts.     

Mechanism of Kasugamycin Resistance in <Emphasis Type="Italic">Escherichia coli</Emphasis>

Strains of Escherichia coli are resistant to the antibiotic kasugamycin due to the partial non-methylation of 16S ribosomal RNA. An RNA methylase activity, absent from resistant strains, is shown here to methylate in vitro the 16S RNA of resistant as well as sensitive strains.     

A review of the bloodsucking midges of Trinidad and Tobago,West Indies (Diptera:Ceratopogonidae)*

Data are presented recording the presence of 49 species of bloodsucking cerato-pogonids in Trinidad, West Indies. Of these, 45 are Culicoides, one is a Leptoconops, and three belong to Forcipomyia (Lasiohelea). Five species are reported from Tobago: three Culicoides, one Leptoconops, and one Lasiohelea. The males of Culicoides benarrochi and C. fluviatilis are described for the first time, and the female of C. debilipalpis is redescribed. Culicoides filariferus and C. pseudodiabolicus are resurrected from synonymy, and characters are presented distinguishing them from C. diabolicus and C. guttatus. Biological data and keys to genera and species are included.     

The Role of Farnesol as a Regulator of Stomatal Opening in Sorghum

Fine, very dilute aqueous emulsions of all-trans farnesol appliedto intact leaves of Sorghum bicolor caused appreciable inhibitionof stomatal opening which persisted for 2 d, after which timethe stomata regained their capacity to open. The inhibitoryeffect of farnesol was not overcome by flushing the leaves withCO₂-free air, indicating that it was not the result of an accumulationof CO₂. This conclusion was supported by measurements of CO₂compensation, which increased only slightly after farnesol treatment. All-trans farnesol has previously been reported to be formedin water-stressed plants of Sorghum. The data presented heresuggest that it could be acting as an endogenous antitranspirant,in a comparable role to that already established for abscisicacid in several species. It would appear, however, to have aless prolonged inhibitory effect than abscisic acid, and itcould be responsible for the rapid responses of Sorghum stomatato water stress and their quick recovery after the plant hasregained turgor, a characteristic which distinguishes Sorghumfrom many other genera so far investigated.     

Integration of hydraulic and chemical signalling in the control of stomatal conductance and water status of droughted plants

We describe here an integration of hydraulic and chemical signals which control stomatal conductance of plants in drying soil, and suggest that such a system is more likely than control based on chemical signals or water relations alone. The determination of xylem [ABA] and the stomatal response to xylem [ABA] are likely to involve the water flux through the plant. (1) If, as seems likely, the production of a chemical message depends on the root water status (Ψ_r), it will not depend solely on the soil water potential (Ψ_s) but also on the flux of water through the soil-plant-atmosphere continuum, to which are linked the difference between Ψ_r and Ψ_s. (2) The water flux will also dilute the concentration of the message in the xylem sap. (3) The stomatal sensitivity to the message is increased as leaf water potential falls. Stomatal conductance, which controls the water flux, therefore would be controlled by a water-flux-dependent message, with a water-flux-dependent sensitivity. In such a system, we have to consider a common regulation for stomatal conductance, leaf and root water potentials, water flux and concentration of ABA in the xylem. In order to test this possibility, we have combined equations which describe the generation and effects of chemical signals and classical equations of water flux. When the simulation was run for a variety of conditions, the solution suggested that such common regulation can operate. Simulations suggest that, as well as providing control of stomatal conductance, integration of chemical and hydraulic signalling may also provide a control of leaf water potential and of xylem [ABA], features which are apparent from our experimental data. We conclude that the root message would provide the plant with a means to sense the conditions of water extraction (soil water status and resisance to water flux) on a daily timescale, while the short-term plant response to this message would depend on the evaporative demand.     

A meta‐analysis of latitudinal variations in life‐history traits of roach,Rutilus rutilus,over its geographical range: linear or non‐linear relationships?

1. We collated information from the literature on life history traits of the roach (a generalist freshwater fish), and analysed variation in absolute fecundity, von Bertalanffy parameters, and reproductive lifespan in relation to latitude, using both linear and non-linear regression models. We hypothesized that because most life history traits are dependent on growth rate, and growth rate is non-linearly related with temperature, it was likely that when analysed over the whole distribution range of roach, variation in key life history traits would show non-linear patterns with latitude.
2. As fecundity depends strongly on length, and the length structure of females varied among populations, latitudinal patterns in fecundity were examined based on residuals from the length–fecundity relationship. The reproductive lifespan of roach was estimated as the difference between age at maturity and maximum age of females in each population.
3. The three life history traits of roach analysed all varied among populations and were non-linearly related to latitude. Only the relationship between reproductive lifespan and latitude was a better fit to a linear that to a quadratic model, although Loess smoothing curves revealed that this relationship was actually closer to biphasic than linear in form. A latitude of 50°N formed a break point in all three life history traits.
4. The negative relationships we have described between (i) fecundity and reproductive lifespan and (ii) fecundity and egg mass suggest that lower fecundity is compensated for by longer lifespan, while lower fecundity is compensated for by an increased egg mass, when analysed independently of location.     

Bicuculline and its Effect on γ-Amino Butyric Acid Transaminase in the Guinea-pig Brain Stem

IT has been claimed that the inhibitory effect of γ-amino butyric acid (GABA) is antagonized post-synaptically by the alkaloid bicuculline^1–3, although others⁴ have been unable to demonstrate this in feline cortical neurones. When applied through a microtap, GABA has a profound inhibitory effect on many cochlear nucleus⁵ and other brain stem neurones⁶ and the brain stem is also rich in GABA-transaminase (GABA-T) (ref. 7 and our unpublished results), the enzyme catalysing the initial step in the degradation of GABA. Although there is little doubt that GABA-T is largely a mitochondrial enzyme^8,9, there is considerable activity in purified nerve ending fractions. The data of Salganicoff and de Robertis¹⁰ indicate that two iso-enzymes of GABA-T exist, one in free mitochondria, the other in nerve ending mitochondria.