Effects of Indole-3-acetic Acid and Gibberellin on Synchronous Cultures of Chlorella fusca

The applicability of synchronous cultures of Chlorella fusca as a reproducible experimental system for the study of growth regulators has been investigated using indole-3-acetic acid (IAA) and gibberellin.

• 1 None of these compounds stimulated growth or sporulation.
• 2 IAA inhibited growth and sporulation at concentrations higher than 6 × 10^?5M, the effect increasing with increasing acidity. Gibberellin had no effect.

     

Induction of Isocitrate Lyase in Synchronous Cultures of Chlorella fusca

Isocitrate lyase (ICL) of Chlorella was induced with acetate, and induction kinetics followed in autospores and 6 h old cells of a synchronous culture. The enzyme could not be induced in illuminated cells. With both cell types 1.2 mM acetate was the optimal inducer concentration. Freeze-thawed cells and acetone powders were used for measurement of activity. With the former the time course of increase in activity was different at the two cell ages. With 6 h old cells the activity fluctuated: There was first a period of increase, then one with decrease and again one of increase. No such variation was found with freee-thawed autospores or with acetone powders of both cell stages. Darkening 6 h old cells for different periods of time before induction reduced the peak of activity, leaving the rate of the third phase unchanged. Illumination of darkened cells before induction increased the peak. Increasing the duration of both treatments increased their respective effects. Acetone extracts taken at different times after start of induction inhibited the ICL activity of a test preparation. The inhibition decreased concurrently with the variation in the ICL activity-found-when freee-thawed cells were used in the enzyme assay. The inducibility, taken as the rate of the third phase, was measured at different times during the 24 h synchronous cycle. Using three different acetate concentrations and both methods of cell preparation, we found that the inducibility was constant for 17 h whereafter it increased rapidly to a final level.     

Effect of weather on the reproductive rate of Rock Ptarmigan Lagopus muta in the eastern Pyrenees

Understanding the effects of climate on avian life history traits is essential if we wish to predict the demographic consequences of expected climatic changes. We investigated the influence of weather conditions on the reproductive success of Rock Ptarmigan Lagopus muta in the eastern French Pyrenees, one of the southernmost areas inhabited by the species. Reproductive success was estimated in early August between 1997 and 2006 by counting adults and well-grown chicks with pointing dogs. The number of young per adult varied from 0.08 to 0.72. Using Poisson regression and Akaike's information criterion, we selected the best model explaining the effect of weather (date of snowmelt and, for both laying/incubation and post-hatching periods, mean minimum and maximum temperatures, monthly rainfall and number of days with rain) on the proportion of young in August. Reproductive success was positively associated with early appearance of snow-free ground, and date of snowmelt alone was the model that best explained annual variation in reproductive success. Other models, which included a negative effect of rainfall, particularly after hatching, also had some support. Hence, both pre-laying and post-hatching weather conditions influenced reproductive success of Rock Ptarmigan in the eastern French Pyrenees. On a continental scale, reproductive success of alpine populations of Rock Ptarmigan is consistently lower than that of northern populations. This difference in productivity may be partly correlated with climatic conditions observed along an arctic–alpine gradient, the amount and variation of rainfall being greater in southern alpine areas than elsewhere in the species' range.     

Synchronous Cultures of Chlamydomonas reinhardti: Properties and Regulation of Repressible Phosphatases

De novo synthesis of phosphatase (derepression) in orthophosphate deprived synchronously growing Chlamydomonas reinhardti has been demonstrated by using a double labelling isotope technique coupled with cellulose acetate electrophoresis. Repressed and derepressed phosphatase exhibited different enzymatic properties as pH optimum, electrophoretic pattern, K_m and K_i values. Especially the acid phosphatase was located near the cell surface. Inorganic, cold TCA-extractable ³²P, decreased during the first 1–2 h after phosphate deprivation when there was little or no net synthesis of phosphatase. Results of experiments with additions of orthophosphate and cycloheximide to derepressed cells, indicated that the derepressible enzyme was relatively unstable, while its m-RNA was relatively stable.     

Interactions among intraspecific competition, emergence patterns, and host selection behaviour in Ips pini (Coleoptera: Scolytinae)

Abstract.  1. Variations in developmental conditions of bark beetles, particularly intraspecific competition, can induce morphological and physiological modifications in the offspring. It is hypothesised that intraspecific competition could also affect host selection behaviour. Such behavioural changes might be manifested in response to host (alpha-pinene) or beetle (verbenone) compounds.
2.  Ips pini were bred at different densities. The offspring were measured for size, weight, and lipid concentration, and then subjected to tunnelling bioassays in agar media amended with varying amounts of alpha-pinene or verbenone.
3. High parental colonisation densities reduced emergence time of parents and offspring. Increasing colonisation density and emergence time had a negative influence on offspring vigour, resulting in a reduction of the distance tunnelled by the beetles.
4. Both alpha-pinene and verbenone were repellent. Surprisingly, verbenone was also toxic at high concentrations, with its effect being greater on beetles arising from high densities. The repellent effect of these compounds did not vary according to colonisation density, but for both compounds, at a 1.5 mg g^–1 concentration, it increased with emergence time.
5. The consequences of varying vigour and behaviour in relation to developmental conditions and emergence patterns on population dynamics of I. pini are discussed.     

Detection of multiple β-casein (CASB) alleles by amplification created restriction sites (ACRS)

Direct sequencing of polymerase chain reaction (PCR) amplified DNA has been used to detect the DNA sequences for bovine beta-casein (CASB) A3 and B variants. Based on these sequences we have designed primers which create allele-specific restriction sites in the PCR product. Restriction analysis of PCR product generated in one reaction enable us to identify the A1, A2, A3 and B alleles of CASB rapidly without the use of radioactivity.     

Physical and physiological costs of ectoparasitic mites on host flight endurance

1. Dispersal is essential for locating mates, new resources, and to escape unfavourable conditions. Parasitism can impact a host's ability to perform energetically demanding activities such as long‐distance flight, with important consequences for gene flow and meta‐population dynamics. 2. Ectoparasites, in particular, can adversely affect host flight performance by diminishing flight aerodynamics and/or by inflicting physiological damage while feeding on host tissue. 3. Experimental flight assays were conducted using two fruit fly‐mite systems: Drosophila nigrospiracula (Patterson and Wheeler) – Macrocheles subbadius (Berlese) and D. hydei (Sturtevan) – M. muscaedomesticae (Scopoli). Flies that are burdened by mites are expected to exhibit lower flight endurance compared to uninfected flies. 4. The results show that the presence of mites (attached) significantly decreased flight endurance by 57% and 78% compared to uninfected D. nigrospiracula and D. hydei, respectively. The physiological damage caused by M. subbadius was revealed through a 53% decline in flight time among previously infected flies (mites removed just prior to flight assay). Surprisingly, the presumably phoretic M. muscaedomesticae also caused a 62% reduction in flight endurance among previously infected D. hydei. 5. These results suggest a strong deleterious effect of ectoparasitic mites on host flight performance, mediated by a reduction in flight aerodynamics and damage to host physiology. Adverse effects on host flight and/or dispersal may have broad implications for gene flow, population genetic structure, and local adaptation in both host and parasite meta‐populations.     

Effects of fertilisation on amino acid mobilisation by a plant‐manipulating insect

1. Phytophagous insects frequently manipulate their host‐plant to improve their immediate environment. This generally implies substantial modifications of host metabolism, and sometimes an alteration of nitrogen allocation within the host‐plant. However, the outcome of plant manipulation on amino acid or protein content can be modulated by environmental factors and host‐plant traits. 2. It was investigated whether the pseudogall induced by the aphid Phloeomyzus passerinii (Signoret) (Aphididae: Phloeomyzinae) in the bark of its host‐plant affects the amino acid content in bark tissues, and whether the strength of the modification is modulated by the fertilisation regime and/or the resistance level of the host‐plant. The development of aphid colonies on a resistant and a susceptible poplar genotype, under three fertilisation regimes, was studied. After the development of colonies, the free and protein‐bound amino acid content of the infested bark were quantified. 3. Fertilisation enhanced poplar growth and increased the free amino acid content of bark tissues. Infestation also triggered accumulations of both free and protein‐bound amino acids in the feeding sites, but in the susceptible genotype only. The increase in amino acid content was more pronounced when fertilisation was low, and fertilisation did not enhance aphid development. 4. In conclusion, infestation by P. passerinii triggers an accumulation of amino acids, but the effect is influenced by both the fertilisation regime and the resistance level of the host‐plant. This suggests that P. passerinii could affect the allocation of nutrients within trees during outbreaks.