The evolution of sex‐determining mechanisms: lessons from temperature‐sensitive mutations in sex determination genes in Caenorhabditis elegans

Sexual reproduction is one of the most taxonomically conserved traits, yet sex‐determining mechanisms (SDMs) are quite diverse. For instance, there are numerous forms of environmental sex determination (ESD), in which an organism’s sex is determined not by genotype, but by environmental factors during development. Important questions remain regarding transitions between SDMs, in part because the organisms exhibiting unique mechanisms often make difficult study organisms. One potential solution is to utilize mutant strains in model organisms better suited to answering these questions. We have characterized two such strains of the model nematode Caenorhabditis elegans. These strains harbour temperature‐sensitive mutations in key sex‐determining genes. We show that they display a sex ratio reaction norm in response to rearing temperature similar to other organisms with ESD. Next, we show that these mutations also cause deleterious pleiotropic effects on overall fitness. Finally, we show that these mutations are fundamentally different at the genetic sequence level. These strains will be a useful complement to naturally occurring taxa with ESD in future research examining the molecular basis of and the selective forces driving evolutionary transitions between sex determination mechanisms.     

The small-subunit ribosomal RNA gene sequences from the hypotrichous ciliates Oxytricha nova and Stylonychia pustulata

We have determined the complete nucleotide sequence of the small- subunit ribosomal RNA genes for the ciliate protozoans Stylonychia pustulata and Oxytricha nova. The sequences are homologous and sufficiently similar that these organisms must be closely related. In a phylogeny inferred from comparisons of several eukaryotic small-subunit ribosomal RNAs, the divergence of the ciliates from the eukaryotic line of descent is seen to coincide with the radiation of the plants, the animals, and the fungi. This radiation is preceded by the divergence of the slime mold, Dictyostelium discoideum.      

Patterns of inflammation and the use of reversibility testing in smokers with airway complaints

Background

Although both smoking and respiratory complaints are very common, tools to improve diagnostic accuracy are scarce in primary care. This study aimed to reveal what inflammatory patterns prevail in clinically established diagnosis groups, and what factors are associated with eosinophilia.

Method

Induced sputum and blood plasma of 59 primary care patients with COPD (n = 17), asthma (n = 11), chronic bronchitis (CB, n = 14) and smokers with no respiratory complaints ('healthy smokers', n = 17) were collected, as well as lung function, smoking history and clinical work-up. Patterns of inflammatory markers per clinical diagnosis and factors associated with eosinophilia were analyzed by multiple regression analyses, the differences expressed in odds ratios (OR) with 95% confidence intervals.

Results

Multivariately, COPD was significantly associated with raised plasma-LBP (OR 1.2 [1.04–1.37]) and sTNF-R55 in sputum (OR 1.01 [1.001–1.01]), while HS expressed significantly lowered plasma-LBP (OR 0.8 [0.72–0.95]). Asthma was characterized by higher sputum eosinophilic counts (OR 1.3 [1.05–1.54]), while CB showed a significantly higher proportion of sputum lymphocytic counts (OR 1.5 [1.12–1.9]). Sputum eosinophilia was significantly associated with reversibility after adjusting for smoking, lung function, age, gender and allergy.

Conclusion

Patterns of inflammatory markers in a panel of blood plasma and sputum cells and mediators were discernable in clinical diagnosis groups of respiratory disease. COPD and so-called healthy smokers showed consistent opposite associations with plasma LBP, while chronic bronchitics showed relatively predominant lymphocytic inflammation compared to other diagnosis groups. Only sputum eosinophilia remained significantly associated with reversibility across the spectrum of respiratory disease in smokers with airway complaints.     

The determination of total nitrogen and total phosphorus concentrations in freshwaters from land use, stock headage and population data: testing of a model for use in conservation and water quality management

1. Nutrient concentrations (particularly N and P) determine the extent to which water bodies are or may become eutrophic. Direct determination of nutrient content on a wide scale is labour intensive but the main sources of N and P are well known. This paper describes and tests an export coefficient model for prediction of total N and total P from: (i) land use, stock headage and human population; (ii) the export rates of N and P from these sources; and (iii) the river discharge. Such a model might be used to forecast the effects of changes in land use in the future and to hindcast past water quality to establish comparative or baseline states for the monitoring of change. 2. The model has been calibrated against observed data for 1988 and validated against sets of observed data for a sequence of earlier years in ten British catchments varying from uplands through rolling, fertile lowlands to the flat topography of East Anglia. 3. The model predicted total N and total P concentrations with high precision (> 95% of the variance in observed data explained). It has been used in two forms: the first on a specific catchment basis; the second for a larger natural region which contains the catchment with the assumption that all catchments within that region will be similar. Both models gave similar results with little loss of precision in the latter case. This implies that it will be possible to describe the overall pattern of nutrient export in the UK with only a fraction of the effort needed to carry out the calculations for each individual water body. 4. Comparison between land use, stock headage, population numbers and nutrient export for the ten catchments in the pre-war year of 1931, and for 1970 and 1988 show that there has been a substantial loss of rough grazing to fertilized temporary and permanent grasslands, an increase in the hectarage devoted to arable, consistent increases in the stocking of cattle and sheep and a marked movement of humans to these rural catchments. 5. All of these trends have increased the flows of nutrients with more than a doubling of both total N and total P loads during the period. On average in these rural catchments, stock wastes have been the greatest contributors to both N and P exports, with cultivation the next most important source of N and people of P. Ratios of N to P were high in 1931 and remain little changed so that, in these catchments, phosphorus continues to be the nutrient most likely to control algal crops in standing waters supplied by the rivers studied.     

Exposure to preindustrial, current and future atmospheric CO2 and temperature differentially affects growth and photosynthesis in Eucalyptus

To investigate if Eucalyptus species have responded to industrial-age climate change, and how they may respond to a future climate, we measured growth and physiology of fast- ( E. saligna ) and slow-growing ( E. sideroxylon ) seedlings exposed to preindustrial (290), current (400) or projected (650 μL L⁻¹) CO₂ concentration ([CO₂]) and to current or projected (current +4 °C) temperature. To evaluate maximum potential treatment responses, plants were grown with nonlimiting soil moisture. We found that: (1) E. sideroxylon responded more strongly to elevated [CO₂] than to elevated temperature, while E. saligna responded similarly to elevated [CO₂] and elevated temperature; (2) the transition from preindustrial to current [CO₂] did not enhance eucalypt plant growth under ambient temperature, despite enhancing photosynthesis; (3) the transition from current to future [CO₂] stimulated both photosynthesis and growth of eucalypts, independent of temperature; and (4) warming enhanced eucalypt growth, independent of future [CO₂], despite not affecting photosynthesis. These results suggest large potential carbon sequestration by eucalypts in a future world, and highlight the need to evaluate how future water availability may affect such responses.     

Identification and functional characterization of effectors in expressed sequence tags from various life cycle stages of the potato cyst nematode Globodera pallida

In this article, we describe the analysis of over 9000 expressed sequence tags (ESTs) from cDNA libraries obtained from various life cycle stages of Globodera pallida . We have identified over 50 G. pallida effectors from this dataset using bioinformatics analysis, by screening clones in order to identify secreted proteins up-regulated after the onset of parasitism and using in situ hybridization to confirm the expression in pharyngeal gland cells. A substantial gene family encoding G. pallida SPRYSEC proteins has been identified. The expression of these genes is restricted to the dorsal pharyngeal gland cell. Different members of the SPRYSEC family of proteins from G. pallida show different subcellular localization patterns in plants, with some localized to the cytoplasm and others to the nucleus and nucleolus. Differences in subcellular localization may reflect diverse functional roles for each individual protein or, more likely, variety in the compartmentalization of plant proteins targeted by the nematode. Our data are therefore consistent with the suggestion that the SPRYSEC proteins suppress host defences, as suggested previously, and that they achieve this through interaction with a range of host targets.     

A Cotyledonary Inhibitor of Root Nodulation in Pisum sativum

Root nodule formation was studied in 11-day-old seedlings of Pisum sativum L. cv. Alaska, which were inoculated with Rhizobium leguminosarum at the time of planting. On intact plants an identical nodulation pattern was observed in the lateral roots attached to the two xylem strands connected to the cotyledons. When one cotyledon was removed before germination, however, a highly significant increase in nodultion was observed on the lateral roots attached to the xylem strand which no longer was connected to a cotyledon. Excision of one cotyledon also caused an alteration in the radial location of root nodules on the primary root. Under these conditions there was a distinct promotion of nodular proliferations in the root cortex opposite the primary phloem poles. The fact that removal of one cotyledon increased nodulation on the lateral roots but had no effect on the rhizobial infection of lateral root hairs suggested that a cotyledonary inhibitor acts at a step between the infection process and the appearance of a macroscopic nodule. The data were interpreted in terms of an inhibitor of cortical cell division which is translocated from the cotyledons to the developing root via the phloem.     

Variation in pathogenicity among isolates of Elsinoe phaseoli from Phaseolus species

Expanding primary leaves of 11 cultivars of Phaseolus vulgaris, and one each of Phaseolus coccineus, Phaseolus lunatus and Vigna unguiculata were inoculated with 23 isolates of Elsinoe phaseoli from Phaseolus spp. and one from Vigna unguiculata. On the basis of the macroscopic and microscopic appearance of the lesions, symptoms were placed into five classes. Spore yields from the lesions in each class were used to classify the types of lesions as representing resistance or susceptibility to each isolate. There was a differential response of cultivars to isolates. According to the reaction of five cultivars of P. vulgaris to infection, isolates were placed in four pathogenicity groups. In addition to the differential reaction of cultivars, there was some evidence of host specificity among the isolates. Thus, P. lunatus was susceptible to most of the P. vulgaris isolates but resistant to the ones from P. coccineus. Vigna unguiculata was susceptible only to the V. unguiculata isolate and was resistant to all the isolates from Phaseolus spp. The isolate from V. unguiculata failed to infect any of the bean cultivars or the other Phaseolus spp. The need to select suitable isolates for challenging cultivars in a breeding programme is stressed.     

The changing ecosystem of a shallow, brackish lake, Hickling Broad, Norfolk, U.K. II. Long-term trends in water chemistry and ecology and their implications for restoration of the lake

• 1 Hickling Broad underwent major changes from a clear water, charophyte-dominated state in the decades previous to 1970 to a turbid, phytoplankton-dominated state by the mid 1970s. These changes were complexly linked with increasing eutrophication by black-headed gulls and increased salinity due to agricultural changes in the catchment.
• 2 At the turn of the 1970s, the lake began to change again and during the 1980s a submerged plant community, of tall, vigorously growing species (e.g. Myriophyllum spicatum, Patamogeton pectinatus) had recovered, despite a major reduction in the roosting gull population, no change in salinity, and only small reductions in phytoplankton biomass and total phosphorus concentration.
• 3 Recovery of the plants may be linked to grazing of periphyton on them by an increased population of a mysid Neomysis integer which had been suppressed by toxicity from an alga, Prymnesium parvum formerly stimulated by the ingress of gull guano.
• 4 A cladoceran community present in the clear-water phase has not recovered and may be suppressed by continued high salinities. Further restoration of the lake requires displacement of the large phytoplankton biomass and this might best be contemplated by land use changes leading to lowered salinity and predicted recovery of grazing Cladocera.
• 5 Models are given which summarize the likely workings of the system in the early twentieth century, the mid-twentieth century, the 1970s and the late 1980s.

     

The effect of partially resistant potato clones and aldicarb on the multiplication of the potato cyst nematode Globodera pallida in field trials

Potato cultivars with different degrees of resistance to Globodera pallida (PCN) were trialled at three infested sites in 1983, 1984 and 1985. These trials were primarily intended to assess the effects of PCN damage on the yield of tubers and consequently the sites chosen had high initial population densities of G. pallida. The population density of G. pallida was determined from samples taken both pre-planting and post-harvest and results showed that there were significant differences between the clones in the nematode multiplication rates. Although actual rates of multiplication varied between sites the relative differences between clones were maintained across sites. Under the susceptible control cultivars the populations generally increased even in the presence of nematicide. The partially resistant clones gave best control, as measured by nematode multiplication, at the sites with the highest initial population densities but gave good control at all sites when treated with nematicide irrespective of initial population density. The role of partial resistance in integrated control systems and the effectiveness of nematicides against G. pallida is discussed.