Altitudinal distribution limits of aquatic macroinvertebrates: an experimental test in a tropical alpine stream

1. Temperature and oxygen are recognised as the main drivers of altitudinal limits of species distributions. However, the two factors are linked, and both decrease with altitude, why their effects are difficult to disentangle. 2. This was experimentally addressed using aquatic macroinvertebrates; larvae of Andesiops (Ephemeroptera), Claudioperla, (Plecoptera), Scirtes (Coleoptera) and Anomalocosmoecus (Trichoptera), and the amphipod Hyalella in an Ecuadorian glacier‐fed stream (4100–4500 m a.s.l.). The following were performed: (i) quantitative benthic sampling at three sites to determine altitudinal patterns in population densities, (ii) transplants of the five taxa upstream of their natural altitudinal limit to test the short‐term (14 days) effect on survival, and (iii) in situ experiments of locomotory activity as a proxy for animal response to relatively small differences in temperature (5 °C vs. 10 °C) and oxygen saturation (55% vs. 62%). 3. The transplant experiment reduced survival to a varying degree among taxa, but Claudioperla survived well at a site where it did not naturally occur. In the in situ experiment, Scirtes and Hyalella decreased their activity at lower oxygen saturation, whereas Andesiops and Anomalocosmoecus did so at a low temperature. The decrease in activity from a high to a low temperature and oxygen for the five taxa was significantly correlated with their mortality in the transplant experiment. 4. Together the present experiments indicate that even relatively small differences in temperature and oxygen may produce effects explaining ecological patterns, and depending on the taxon, either water temperature or oxygen saturation, without clear interacting effects, are important drivers of altitudinal limits.     

The effect of infra-red radiation on rectal temperature and respiration rate of unacclimated female new zealand white rabbits

1. 1.|An experiment was carried out to examine the effects of various levels of infra-red (i.r.) radiation on rectal temperature (RT) and respiration rate (RR) in New Zealand While rabbits.

2. 2.|A 4 × 3 × 6 factorial design was employed in which the factors were: four intensities of i.r. radiant heating of 0.0, 1.9, 2.1 and 2.4 MJ/m²/h, three replicates and six rabbits.

3. 3.|rectal temperature differed (P < 0.05) between treatments and were highest at the “high” level of i.r. radiation (1°C higher than for controls). At the “medium” and “low” levels of i.r. heating RTs were respectively 0.3 and 0.2°C higher than in controls.

4. 4.|At different levels of radiation RR were different (P < 0.05), with the highest (422.7 ± 218.1 breaths/min) at 2.4 MJ/m²/h i.r. radiant heating. This RR was almost 2.5 times that in controls, while at the “low” and “medium” i.r. levels RR values were respectively 1.5 and 2 times those of controls.

Seed germination traits of Ailanthus altissima,Phytolacca americana and Robinia pseudoacacia in response to different thermal and light requirements

Invasion of alien plant species (IAS) represents a serious environmental problem, particularly in Europe, where it mainly pertains to urban areas. Seed germination traits contribute to clarification of invasion dynamics. The objective of this research was to analyze how different light conditions (i.e., 12-hr light/12-hr darkness and continuous darkness) and temperature regimes (i.e., 15/6°C, 20/10°C and 30/20°C) trigger seed germination of Ailanthus altissima (AA), Phytolacca americana (PA) and Robinia pseudoacacia (RP). The relationship between seed germination and seed morphometric traits was also analyzed. Our findings highlight that temperature rather than light was the main environmental factor affecting germination. RP germinated at all tested temperatures, whereas at 15/6°C seeds of AA and PA showed physiological dormancy. RP had a higher germination capacity at a lower temperature, unlike AA and PA, which performed better at the highest temperatures. Light had a minor role in seed germination of the three species. Light promoted germination only for seeds of PA, and final germination percentage was 1.5-fold higher in light than in continuous darkness. Seed morphometric traits (thickness [T], area [A] and volume [V]) had a significant role in explaining germination trait variations. The results highlight the importance of increasing our knowledge on seed germination requirements to predict future invasiveness trends. The increase in global temperature could further advantage AA and PA in terms of germinated seeds, as well as RP by enhancing the germination velocity, therefore compensating for a lower germination percentage of this species at the highest temperatures.     

Improving efficiency of breeding for higher crop yield

Summary Exclusive selection for yield raises, the harvest index of self-pollinated crops with little or no gain in total bipmass. In addition to selection for yield, it is suggested that efficient breeding for higher yield requires simultaneous selection for yield's three major, genetically controlled physiological components. The following are needed: (1) a superior rate of biomass accumulation. (2) a superior rate of actual yield accumulation in order to acquire a high harvest index, and (3) a time to harvest maturity that is neither shorter nor longer than the duration of the growing season. That duration is provided by the environment, which is the fourth major determinant of yield. Simultaneous selection is required because genetically established interconnections among the three major physiological components cause: (a) a correlation between the harvest index and days to maturity that is usually negative; (b) a correlation between the harvest index and total biomass that is often negative, and (c) a correlation between biomass and days to maturity that is usually positive. All three physiological components and the correlations among them can be quantified by yield system analysis (YSA) of yield trials. An additive main effects and multiplicative interaction (AMMI) statistical analysis can separate and quantify the genotype × environment interaction (G × E) effect on yield and on each physiological component that is caused by each genotype and by the different environment of each yield trial. The use of yield trials to select parents which have the highest rates of accumulation of both biomass and yield, in addition to selecting for the G × E that is specifically adapted to the site can accelerate advance toward the highest potential yield at each geographical site. Higher yield for many sites will raise average regional yield. Higher yield for multiple regions and continents will raise average yield on a world-wide basis. Genetic and physiological bases for lack of indirect selection for biomass from exclusive selection for yield are explained.     

Kinetic parameters of nitrate uptake by different catch crop species: effects of low temperatures or previous nitrate starvation

The pollution of aquifers by NO^?₃ in temperate environments is aggravated by farming practices that leave the ground bare during winter. The use of catch crops during this time may decrease nitrate loss from the soil. Nitrate uptake by several catch crop species (Brassica napus L., Sinapis alba L., Brassica rapa L., Raphanus sativus L., Trifolium alexandrinum L., Trifolium incarnatum L., Phacelia tanacetifolia Benth., Lolium perenne L., Lolium multiflorum Lam. and Secale cereale L.) was here studied in relation to transpiration rate and low temperatures applied to the whole plant or to roots only. The Michaelis constant (K_m), maximum uptake rate (V_max), time of induction and contributions of inducible and constitutive mechanisms were estimated from measurements of NO^?₃ depletion in the uptake medium. There were large differences between species, with K_m (μM) values ranging between 5.12 ± 0.64 (Trifolium incarnatum) and 36.4 ± 1.97 (Lolium perenne). Maximum NO^?₃ uptake rates expressed per unit root weight were influenced by ageing, temperature and previous NO^?₃ nutrition. They were also closely correlated with water flow through the roots and with shoot/root ratio of these species. The combined results from all species and treatments showed that V_max increased with shoot/root ratio, suggesting a regulatory role for the shoots in NO^?₃ uptake. Overall, the results showed a great diversity in NO^?₃ uptake characteristics between species in terms of kinetic parameters, contribution of the constitutive system (100% of total uptake in ryegrass, nil in Fabaceae) and time of induction.     

The effect of temperature on progeny allocation and short interval timing in a parasitoid wasp

Abstract The parasitoid wasp Trichogramma dendrolimi Matsumura sets the number of progeny allocated to its insect egg hosts according to the duration of its initial transit walk across the host surface. Although cooling the wasp reduces its walking speed, reduced temperature does not affect progeny allocation. By locally heating and cooling the wasps, the initial transit can be thermally uncoupled from the subsequent oviposition. Using this technique we show that the timing of initial transit duration is temperature-dependent. These findings suggest that short interval timing by Trichogramma differs physiologically from the temperature compensated clocks that have been described for other insects.     

Effects of global environmental change on carbon partitioning in vegetative plants of Triticum aestivum and closely related Aegilops species

The use of fossil fuel is predicted to cause an increase of the atmospheric CO₂ concentration, which will affect the global pattern of temperature and precipitation. It is therefore essential to incorporate effects of temperature and water supply on carbon partitioning of plants to predict effects of elevated [CO₂] on growth and yield of Triticum aestivum. Although earlier papers have emphasized that elevated [CO₂] favours investment of biomass in roots relative to that in leaves, it has now become clear that these are indirect effects, due to the more rapid depletion of nutrients in the root environment as a consequence of enhanced growth. Broadly generalized, the effect of temperature on biomass allocation in the vegetative stage is that the relative investment of biomass in roots is lowest at a certain optimum temperature and increases at both higher and lower temperatures. This is found not only when the temperature of the entire plant is varied, but also when only root temperature is changed whilst shoot temperature is kept constant. Effects of temperature on the allocation pattern can be explained largely by the effect of root temperature on the roots' capacity to transport water. Effects of a shortage in water supply on carbon partitioning are unambiguous: roots receive relatively more carbon. The pattern of biomass allocation in the vegetative stage and variation in water-use efficiency are prime factors determining a plant's potential for early growth and yield in different environments. In a comparison of a range of T. aestivum cultivars, a high water-use efficiency at the plant level correlates positively with a large investment in both leaf and root biomass, a low stomatal conductance and a large investment in photosynthetic capacity. We also present evidence that a lower investment of biomass in roots is not only associated with lower respiratory costs for root growth, but also with lower specific costs for ion uptake. We suggest the combination of a number of traits in future wheat cultivars, i.e. a high investment of biomass in leaves, which have a low stomatal conductance and a high photosynthetic capacity, and a low investment of biomass in roots, which have low respiratory costs. Such cultivars are considered highly appropriate in a future world, especially in the dryer regions. Although variation for the desired traits already exists among wheat cultivars, it is much larger among wild Aegilops species, which can readily be crossed with T. aestivum. Such wild relatives may be exploited to develop new wheat cultivars well-adapted to changed climatic conditions.     

Marine and estuarine gradients — An overview

The Proceedings of the ECSA 21 symposium on Marine and Estuarine Gradients are reviewed. It is emphasised that this is probably the first time that a full set of papers on the tidal freshwater sections of estuaries has appeared. There is however some ambiguity in the terminology applied to such waters, and a more consistent terminology is proposed. In particular the estuary is defined as reaching upstream as far as the tidal limit, irrespective of salinity. A wide variety of gradients within estuaries and coastal waters are considered, but it is apparent that the crucial spatial gradients are based on salinity, oxygen and turbidity, and that many other gradients are co-variables with these parameters. Temperature is also important for temporal gradients.     

The effect of temperature on reproduction in three species of cyclopoid copepods

Megacyclops viridis (Jurine), Macrocyclops albidus (Jurine), and Acanthocyclops vernalis (Fischer) were raised in the laboratory at six temperatures (5, 8, 10, 12, 15 and 20°) and fed a mixture of ciliates (Paramecium caudatum and Colpidium campylum). Data were taken on clutch size, embryonic development time, interclutch period, time to first clutch, sex ratio and longevity.Clutch size, time to first clutch, embryonic development time, interclutch period and longevity are inversely related to temperature. The ratio of males to females in a cohort is independent of temperature.     

Early development and neurogenesis of Temnopleurus reevesii

Sea urchins are model non‐chordate deuterostomes, and studying the nervous system of their embryos can aid in the understanding of the universal mechanisms of neurogenesis. However, despite the long history of sea urchin embryology research, the molecular mechanisms of their neurogenesis have not been well investigated, in part because neurons appear relatively late during embryogenesis. In this study, we used the species Temnopleurus reevesii as a new sea urchin model and investigated the detail of its development and neurogenesis during early embryogenesis. We found that the embryos of T. reevesii were tolerant of high temperatures and could be cultured successfully at 15–30°C during early embryogenesis. At 30°C, the embryos developed rapidly enough that the neurons appeared at just after 24 h. This is faster than the development of other model urchins, such as Hemicentrotus pulcherrimus or Strongylocentrotus purpuratus. In addition, the body of the embryo was highly transparent, allowing the details of the neural network to be easily captured by ordinary epifluorescent and confocal microscopy without any additional treatments. Because of its rapid development and high transparency during embryogenesis, T. reevesii may be a suitable sea urchin model for studying neurogenesis. Moreover, the males and females are easily distinguishable, and the style of early cleavages is intriguingly unusual, suggesting that this sea urchin might be a good candidate for addressing not only neurology but also cell and developmental biology.