Context‐dependence in an ant–aphid mutualism: direct effects of tending intensity on aphid performance

1. In ant–hemipteran mutualisms, ants receive carbohydrates in the form of honeydew, while hemipterans receive protection from natural enemies. In the absence of natural enemies, however, the direct effects of tending are generally less well known. We hypothesised that with increasing tending intensity (ant to aphid ratio), aphid performance would increase initially, then decrease at high tending levels due to the metabolic cost of producing high quality honeydew. 2. We tested our hypothesis in a greenhouse experiment by manipulating Argentine ant (Linepithema humile Mayr) colony size while holding constant the initial size of aphid (Chaitophorus populicola Thomas) aggregations. The two parameters associated with survival, aphid survivorship to maturity and longevity, declined with increasing tending intensity, whereas per capita birth rate and time to first reproduction showed no relationship to attendance. The intrinsic rate of increase declined only at relatively high tending levels, suggesting a nonlinearity in the effect of tending intensity. 3. Tending intensity measured in the experiment was similar to that observed in free‐living aggregations of C. populicola. Furthermore, the per capita recruitment rate of ants to free‐living aphid aggregations was negatively density‐dependent, indicating that small aggregations tend to experience the highest levels of tending intensity. This finding suggests that the aphid's intrinsic rate of increase may be positively density‐dependent, mediated by the aphid's mutualistic interaction with the ant. 4. In the Argentine ant–C. populicola interaction, experimental manipulation of colony size revealed a direct cost of ant attendance that was conditional upon tending intensity. Experiments that manipulate only ant presence or absence may yield an incomplete understanding of the mutualistic interaction if underlying nonlinearities exist.     

Membrane water permeability and aquaporin expression increase during growth of maize suspension cultured cells

Aquaporins (AQPs) are water channels that allow cells to rapidly alter their membrane water permeability. A convenient model for studying AQP expression and activity regulation is Black Mexican Sweet (BMS) maize cultured cells. In an attempt to correlate membrane osmotic water permeability coefficient (P_f) with AQP gene expression, we first examined the expression pattern of 33 AQP genes using macro-array hybridization. We detected the expression of 18 different isoforms representing the four AQP subfamilies, i.e. eight plasma membrane (PIP), five tonoplast (TIP), three small basic (SIP) and two NOD26-like (NIP) AQPs. While the expression of most of these genes was constant throughout all growth phases, mRNA levels of ZmPIP1;3 , ZmPIP2;1 , ZmPIP2;2, ZmPIP2;4 and ZmPIP2;6 increased significantly during the logarithmic growth phase and the beginning of the stationary phase. The use of specific anti-ZmPIP antisera showed that the protein expression pattern correlated well with mRNA levels. Cell pressure probe and protoplast swelling measurements were then performed to determine the P_f. Interestingly, we found that the P_f were significantly increased at the end of the logarithmic growth phase and during the steady-state phase compared to the lag phase, demonstrating a positive correlation between AQP abundance in the plasma membrane and the cell P_f.     

广州地区中华按蚊生理年龄的组成

中华按蚊是我国平原地区的传疟媒介,研究中华按蚊的生态学,对于疟疾的流行病学及预防均具有重要的意义。生理年龄及生殖营养环的研究,不但可以进一步认识中华按蚊在自然界的一些生态学问题,更重要的是有助于分析其传疟的作用,作为防制的依据。     

Inactivation of Bacteria in Seawater by Low-Amperage Electric Current

Seawater used in mariculture has been suspected of being a potential source of infection. In this study, the lethal effects of low-amperage electric treatment on microorganisms were examined in natural seawater and in seawater inoculated with Vibrio parahaemolyticus. In both cases, bacteria including V. parahaemolyticus in seawater were completely eliminated in 100 ms by a 0.5-A, 12-V direct current. Electron microscopic investigation of the electrically treated bacteria revealed substantial structural damage at the cellular level. In conclusion, our results indicate that low-amperage electric treatment is effective for rapid inactivation of microorganisms in seawater.     

Inactivation of Listeria monocytogenes in brine and saline by alternating high-voltage pulsed current

The inactivating efficiency of alternating high-voltage pulsed (AHVP) current was investigated in brine (20 w/v% NaCl) and saline (0.9 w/v% NaCl) inoculated with 1x 107 cells/ml of Listeria monocytogenes. AHVP current at 12 V with 1 pulse completely inactivated L. monocytogenes in brine within 3 ms, while the bacteria in saline were fully inactivated by 10-pulsed electric treatment at 12 V within the same time. Electron microscopic observation demonstrated substantial structural damage of electrically treated L. monocytogenes in brine. These results suggest that AHVP treatment would be effective for the rapid and complete inactivation of L. monocytogenes in brine or saline solution.     

Deuterium effect on ionization and fragmentation patterns of monosaccharides ionized by atmospheric pressure chemical ionization

Glucose, galactose, and mannose in H₂O and D₂O were ionized by an atmospheric pressure chemical ionization (APCI) method. Isotope effects on fragmentation patterns of the monosaccharides were examined by deuterium replacement of the -OH groups to distinguish the isomers with a single mass spectrometer. The most abundant ions were the [M+H₂O]⁺ and [M_D5+D+D₂O]⁺ for using H₂O and D₂O as solvent and eluent, respectively. Major fragment ions were the [M−OH]⁺ and [M−OH−H₂O]⁺ in H₂O, while those in D₂O were the [M_D5+D−D₂O]⁺ and [M_D5+D−2D₂O]⁺. The differences in the product ions generated in H₂O and D₂O were due to enhancement of the strength of hydrogen bonding by the deuterium replacement. Variations of the ion intensity ratios of the [M−OH]⁺/[M−OH−H₂O]⁺ and [M_D5−OD]⁺/[M_D5−OD−D₂O]⁺ with the fragmentor voltage showed different trends depending on the kind of monosaccharides. By comparing the ion intensity ratios of the [M+H₂O]⁺/M⁺, [M_D5+D+D₂O]⁺/[M_D5+D]⁺, [M−OH]⁺/[M−OH−H₂O]⁺, and [M_D5+D−D₂O]⁺/[M_D5+D−2D₂O]⁺, it was possible to distinguish the isomers of monosaccharides.     

Antimicrobial effect of medical adhesive composed of aldehyded dextran and ε-Poly(L-Lysine)

Infection of surgical wounds is a severe problem. Conventional tissue reattachment methods have limits of incomplete sealing and high susceptibility to infection. Medical adhesives have several advantages over traditional tissue reattachment techniques, but still have drawbacks, such as the probability of infection, low adhesive strength, and high cytotoxicity. Recently, a new medical adhesive (new-adhesive) with high adhesive strength and low cytotoxicity, composed of aldehyded dextran and ε-poly(L-lysine), was developed. The antimicrobial activity of the new-adhesive was assayed using agar media and porcine skin. In the agar diffusion method, inoculated microorganisms that contacted the new-adhesive were inactivated, but this was not dependent on the amount of new-adhesive. Similar to the agar media results, the topical antimicrobial effect of new-adhesive was confirmed using a porcine skin antimicrobial assay, and the effect was not due to physical blocking based on comparison with the group whose wounds were wrapped.