Optimising settlement assays of pediveligers and plantigrades of Mytilus galloprovincialis

The mussel Mytilus galloprovincialis is a common aquaculture species, and also a major fouling organism that has negative economic impacts. There are no standard assay conditions for this important species and therefore, this study quantified the effect of key factors on the settlement of pediveligers and plantigrades. Density dependent settlement did not occur for either pediveligers or plantigrades. Settlement increased in drop assays in a 12 h light:12 h dark cycle, while bottom shade had no effect of any magnitude. In addition, settlement was significantly enhanced by storing pediveligers for between 4 and 24 days at 4°C. Overall, these data provide the template to optimise and standardise static laboratory settlement assays for mussels in order to develop materials that either enhance settlement for the aquaculture industry, or deter settlement for antifouling applications. Furthermore, simple mechanisms such as storage at 4°C can enhance settlement beyond current methods used in aquaculture hatcheries.     

Where to Settle—Settlement Preferences of Mytilus galloprovincialis and Choice of Habitat at a Micro Spatial Scale

The global mussel aquaculture industry uses specialised spat catching and nursery culture ropes made of multi-filament synthetic and natural fibres to optimise settlement and retention of mussels for on-growing. However, the settlement ecology and preferences of mussels are poorly understood and only sparse information exists in a commercial context. This study quantified the settlement preferences of pediveligers and plantigrades of Mytilus galloprovincialis on increasingly complex surfaces and settlement locations at a micro spatial scale on and within ropes under commercial hatchery operating conditions using optical microscopy and X-ray micro-computed tomography (µCT). M. galloprovincialis has clear settlement preferences for more complex materials and high selectivity for settlement sites from the pediveliger through to the plantigrade stage. Pediveligers of M. galloprovincialis initially settle inside specialised culture ropes. Larger pediveligers were located close to the exterior of ropes as they increased in size over time. In contrast, smaller individuals were located deeper inside of the ropes over time. This study demonstrates that X-ray µCT is an excellent non-destructive technique for mapping settlement and attachment sites of individuals as early as one day post settlement, and quantifies the number and location of settled individuals on and within ropes as a tool to understand and optimise settlement in complex multi-dimensional materials and environments.     

Enhancing the settlement and attachment strength of pediveligers of Mytilus galloprovincialis by changing surface wettability and microtopography

Surface wettability and microtopography can either enhance or deter larval settlement of many sessile marine organisms. This study quantifies the effect of these surface properties on the settlement of pediveligers of Mytilus galloprovincialis, using polymers spanning a range of wettability and microtextured polydimethylsiloxane (PDMS). Furthermore, the adhesion strength of settled pediveligers on microtextured PDMS surfaces was quantified using a flow chamber. Settlement was enhanced at the hydrophilic end of the wettability spectrum, where mean settlement on nylon reached 33.5 ± 13.1%. In contrast, mean settlement on the most hydrophobic polymer (PDMS) was 4.2 ± 3.2%. Microtopography had a much stronger effect compared to wettability, where 400 μm textured PDMS enhanced settlement above 90%. Settlement preferences were also positively correlated to adhesion strength at flow rates of 4 knots, with all initially settled pediveligers on smooth PDMS detaching, while 79.9 ± 5.7% of pediveligers remained on the 400 μm texture.     

Enhancing the efficacy of fouling-release coatings against fouling by Mytilus galloprovincialis using nanofillers

Fouling-release (FR) coatings minimise the adhesion strength of fouling organisms. This study describes improved technologies to control the settlement and adhesion of the important fouling organism Mytilus galloprovincialis by incorporating the nanofillers titanium dioxide (TiO₂) and carbon nanotubes (CNTs) in polydimethylsiloxane (PDMS) matrices. The incorporation of TiO₂ prevented larval settlement when photoactivated with UV light, even at the lowest concentration of the nanofiller (3.75 wt%). Notably, there was 100% mortality of pediveligers exposed to photoactivated TiO₂. However, plantigrades initially settled to photoactivated TiO₂, but their adhesion strength was significantly reduced on these surfaces in comparison to blank PDMS. In addition, plantigrades had high mortality after 6 h. In contrast to the enhanced antifouling and FR properties of PDMS incorporating TiO₂, the incorporation of CNTs had no effect on the settlement and adhesion of M. galloprovincialis.     

Enhancing the settlement and attachment strength of pediveligers of Mytilus galloprovincialis bychanging surface wettability and microtopography

Surface wettability and microtopography can either enhance or deter larval settlement of many sessile marine organisms. This study quantifies the effect of these surface properties on the settlement of pediveligers of Mytilus galloprovincialis, using polymers spanning a range of wettability and microtextured polydimethylsiloxane (PDMS). Furthermore, the adhesion strength of settled pediveligers on microtextured PDMS surfaces was quantified using a flow chamber. Settlement was enhanced at the hydrophilic end of the wettability spectrum, where mean settlement on nylon reached 33.5 ± 13.1%. In contrast, mean settlement on the most hydrophobic polymer (PDMS) was 4.2 ± 3.2%. Microtopography had a much stronger effect compared to wettability, where 400 μm textured PDMS enhanced settlement above 90%. Settlement preferences were also positively correlated to adhesion strength at flow rates of 4 knots, with all initially settled pediveligers on smooth PDMS detaching, while 79.9 ± 5.7% of pediveligers remained on the 400 μm texture.     

Do Cues Matter? Highly Inductive Settlement Cues Don't Ensure High Post-Settlement Survival in Sea Urchin Aquaculture

Increasing settlement and post-settlement survival during the critical transition from planktonic larvae to benthic juveniles will increase efficiency for sea urchin aquaculture. This study investigated the effects of temperature and settlement cues on the settlement and post-settlement survival of the sea urchin Tripneustes gratilla during this phase. The current commercial methodology, which utilises natural biofilm settlement plates, was tested and resulted in low settlement (<2%) and poor post-settlement survival (<1% of settled urchins). In laboratory trials, settlement was high and unaffected by temperatures between 24 and 30°C, but significantly decreased at 33°C. Development of spines, however, was significantly affected by temperatures over 29°C. Mirroring this result, post-settlement survival was optimal between 24-28°C. In laboratory assays, the macroalgae Sargassum linearifolium and Corallina officinalis, and seawater conditioned with these algae, induced significantly higher settlement (>90%) than a natural biofilm (～25%). The addition of macroalgae-conditioned seawater to natural biofilm significantly increased settlement rates (>85%). Mixed consortia and single strains of bacteria isolated from macroalgae, biofilms and adult conspecifics all induced significant settlement, but at significantly lower rates than macroalgae. No evidence was found that higher rates of settlement to bacteria on macroalgae were generated by a cofactor from the macroalgae. Age of bacterial cultures, culturing bacteria on solid and liquid media and concentration of nutrients in cultures had little effect on settlement rates. Finally, macroalgae-conditioned seawater combined with natural biofilm settlement plates induced significantly higher settlement than to the biofilm plates alone in a commercial scale trial. However, high post-settlement mortality resulted in equivalent survival between treatments after 25 days. This study highlights that settlement studies should extend to post-settlement survival, which remains poor for T. gratilla and is a significant obstacle to increasing efficiency for aquaculture.     

Survival, growth, settlement and metamorphosis of refrigerated larvae of the mussel Mytilus galloprovincialis Lamarck and their use in settlement and antifouling bioassays

Straight-hinge veliger and pediveliger larvae of the mussel Mytilus galloprovincialis were refrigerated for varying periods for use in bioassays. Straight-hinge veliger larvae grew to the umbo-veliger stage after 2 months in the refrigerator, but no pediveligers were observed during the 3-month refrigeration period. The average survival rate of larvae in the refrigerator was 79% after 1 month, but gradually decreased with the refrigeration period, and was as low as 22% after 3 months. All refrigerated larvae grew to the pediveliger stage in the incubator at 17 degrees C at the same rate as that of the control larvae that were not refrigerated. Settlement and metamorphosis of pediveligers from both refrigerated and control groups were facilitated by microbial film and epinephrine and inhibited by phentolamine. Thus, refrigeration can be used as an effective method of storing larvae of M. galloprovincialis for use in assays to assess candidate settlement inducers and antifouling substances.     

Studies on the factors influencing larval settlement in Balanus amphitrite and Mytilus galloprovincialis

Understanding of factors influencing settlement(attachment and metamorphosis) of marine invertebratelarvae is of great importance in aquaculture andcontrol of biofouling. The influence of two factors onsettlement of larvae was assessed from two separateinvestigations: 1, the influence of age (endogenousfactor) on cyprids of the barnacle Balanusamphitrite; and 2, the influence of a microbial film(exogenous factor) on pediveligers of the mussel Mytilus galloprovincialis.The settlement response of cypris larvae of B.amphitrite was found to be age-dependent. Oldercyprids responded more readily to settlement factorsthan newly molted ones. In M.galloprovincialis, competent pediveligers settled inresponse to a microbial filmed surface but not toan unfilmed surface. Moreover, a factor with MW of lessthan 5000 dalton, derived from culture medium of abacterial strain C1.1 (Pseudomonas-Alteromonasgroup), induced the settlement of M. galloprovincialis larvae.Thus, marine invertebrate larvae may require a periodof competence acquisition, during which they arepoorly responsive to settlement inducers. Uponacquisition of competence, larvae readily respondto external cues (e.g. microbial film, bacterialextracellular products).     

Fine-scale spatial and temporal variation in settlement of the intertidal mussel Perna perna indicates differential hydrodynamic delivery of larvae to the shore

Scales of spatial and temporal variation in the settlement of early and late plantigrades of the mussel Perna perna to artificial substrata were measured on the south coast of South Africa. One study examined daily settlement over one month at three sites of similar tidal height and aspect. The sites were separated by 100′s of m with 5 replicated artificial settlement substrata approximately 1 m apart within each site. Early (< 0.5 mm) and large late plantigrades (1 - 3.5 mm) dominated samples with few individuals of 0.5-1 mm. Settler abundance showed clear peaks, synchronised among sites and apparently following spring tides, though the relationship between tide and settlement was not significant. Two-way ANOVA indicated significant spatial variation, which varied with time, at the 100 m-scale among sites. A second study investigated the local effects of substratum aspect. Seaward facing surfaces had consistently lower settlement (but higher adult cover) than horizontal and landward facing surfaces, this effect was significant for large late plantigrades. This suggests that either juveniles migrate after settlement, or that post-settlement mortality differs markedly among aspects. The high degree of temporal variation at the scale of days and weeks was expected, but the results also suggest a degree of pulsing in settlement, with maximum intensities around spring tide. A previous study of nearshore waters indicated a common pool of larvae at scales of 100 s m. Thus, consistent ranking of sites for all size classes of settlers indicates predictably differential hydrodynamic delivery of larvae to sites separated by 100 s m. The effect of aspect on settlement highlights the importance of smaller scale hydrodynamics, suggesting that the stronger turbulence experienced by seaward facing surfaces may affect larval settlement negatively.     

A comparative study of byssogenesis on zebra and quagga mussels: the effects of water temperature, salinity and light-dark cycle

The quagga mussel (Dreissena rostriformis bugensis) and zebra mussel (Dreissena polymorpha) are invasive freshwater bivalves in Europe and North America. The distribution range of both Dreissena species is still expanding and both species cause major biofouling and ecological effects, in particular when they invade new areas. In order to assess the effect of temperature, salinity and light on the initial byssogenesis of both species, 24 h re-attachment experiments in standing water were conducted. At a water temperature of 25°C and a salinity of 0.2 psu, the rate of byssogenesis of D. polymorpha was significantly higher than that of D. rostriformis bugensis. In addition, byssal thread production by the latter levelled out between 15°C and 25°C. The rate of byssogenesis at temperatures<25°C was similar for both species. Neither species produced any byssal threads at salinities of 4 psu or higher. At a salinity of 1 psu and a water temperature of 15°C, D. polymorpha produced significantly more byssal threads than D. rostriformis bugensis. There was no significant effect of the length of illumination on the byssogenesis of either species. Overall, D. polymorpha produced slightly more byssal threads than D. rostriformis bugensis at almost all experimental conditions in 24 h re-attachment experiments, but both species had essentially similar initial re-attachment abilities. The data imply that D. rostriformis bugensis causes biofouling problems identical to those of D. polymorpha.     

Photosynthetic and respiratory acclimation and growth response of Antarctic vascular plants to contrasting temperature regimes

Air temperatures have risen over the past 50 yr along the Antarctic Peninsula, and it is unclear what impact this is having on Antarctic plants. We examined the growth response of the Antarctic vascular plants Colobanthus quitensis (Caryophyllaceae) and Deschampsia antarctica (Poaceae) to temperature and also assessed their ability for thermal acclimation, in terms of whole-canopy net photosynthesis (P(n)) and dark respiration (R(d)), by growing plants for 90 d under three contrasting temperature regimes: 7°C day/7°C night, 12°C day/7°C night, and 20°C day/7°C night (18 h/6 h). These daytime temperatures represent suboptimal (7°C), near-optimal (12°C), and supraoptimal (20°C) temperatures for P(n) based on field measurements at the collection site near Palmer Station along the west coast of the Antarctic Peninsula. Plants of both species grown at a daytime temperature of 20°C had greater RGR (relative growth rate) and produced 2.2-3.3 times as much total biomass as plants grown at daytime temperatures of 12° or 7°C. Plants grown at 20°C also produced 2.0-4.1 times as many leaves, 3.4-5.5 times as much total leaf area, and had 1.5-1.6 times the LAR (leaf area ratio; leaf area:total biomass) and 1.1-1.4 times the LMR (leaf mass ratio; leaf mass:total biomass) of plants grown at 12° or 7°C. Greater RGR and biomass production at 20°C appeared primarily due to greater biomass allocation to leaf production in these plants. Rates of P(n) (leaf-area basis), when measured at their respective daytime growth temperatures, were highest in plants grown at 12°C, and rates of plants grown at 20°C were only 58 (C. quitensis) or 64% (D. antarctica) of the rates in plants grown at 12°C. Thus, lower P(n) per leaf area in plants grown at 20°C was more than offset by much greater leaf-area production. Rates of whole-canopy P(n) (per plant), when measured at their respective daytime growth temperatures, were highest in plants grown at 20°C, and appeared well correlated with differences in RGR and total biomass among treatments. Colobanthus quitensis exhibited only a slight ability for relative acclimation of P(n) (leaf-area basis) as the optimal temperature for P(n) increased from 8.4° to 10.3° to 11.5°C as daytime growth temperatures increased from 7° to 12° to 20°C. There was no evidence for relative acclimation of P(n) in D. antarctica, as plants grown at all three temperature regimes had a similar optimal temperature (10°C) for P(n). There was no evidence for absolute acclimation of P(n) in either species, as rates of P(n) in plants grown at a daytime temperature of 12°C were higher than those of plants grown at daytime temperatures of 7° or 20°C, when measured at their respective growth temperatures. The poor ability for photosynthetic acclimation in these species may be associated with the relatively stable maritime temperature regime during the growing season along the Peninsula. In contrast to P(n), both species exhibited full acclimation of R(d), and rates of R(d) on a leaf-area basis were similar among treatments when measured at their respective daytime growth temperature. Our results suggest that in the absence of interspecific competition, continued warming along the Peninsula will lead to improved vegetative growth of these species due to (1) greater biomass allocation to leaf-area production (as opposed to improved rates of P(n) per leaf area) and (2) their ability to acclimate R(d), such that respiratory losses per leaf area do not increase under higher temperature regimes.     

Pharmacological induction of larval settlement and metamorphosis in the blue mussel Mytilus edulis L

The blue mussel Mytilus edulis L. is an important aquaculture and fouling species in northern seas. Although the general role of chemical cues for settlement of larvae of the blue mussel has been proposed, few studies have focused on induction of settlement and metamorphosis by pharmacological agents. In this study, the induction of larval settlement of the blue mussel by pharmacological compounds was investigated through a series of laboratory experiments with an aim of identifying artificial cues for laboratory bioassay systems in fouling and antifouling research. Gamma-aminobutiric acid (GABA), dihydroxyphenyl L-alanine (DOPA), isobutyl methylxanthine (IBMX) and acetylcholine chloride (ACH) at 10(-7)-10(-2) M as well as KCl at 10-40 mM K+ in excess of the level in normal seawater were tested for their inductive effect on larval settlement. In filtered seawater (FSW) < 9% of the larvae settled after 48 h. Elevated K+ and GABA levels had no effect on larval settlement and metamorphosis. DOPA at 10(-5) M and IBMX at 10(-6)-10(-4) M induced 41-83% larval settlement and ACH at 10(-7)-10(-5) M induced < 40% larval settlement. While the highest settlement rates were observed after 48 h exposure to the chemical, most of the larvae settled within 24 h. Compounds at concentrations of 10(-3)-10(-2) M were either toxic to larvae or retarded the growth of the post-larvae shell. Juveniles resulting from induction by lower concentrations of chemicals had a very high survival rate, completed metamorphosis and grew as well as the juveniles that metamorphosed spontaneously. IBMX at 10(-6)-10(-4) M and L-DOPA at 10(-5) M are effective agents for induction of settlement and metamorphosis for future studies using juvenile M. edulis.     

Survival,growth, settlement and metamorphosis of refrigerated larvae of the mussel Mytilus galloprovincialis Lamarck and their use in settlement and antifouling bioassays

Abstract

Straight-hinge veliger and pediveliger larvae of the mussel Mytilus galloprovincialis were refrigerated for varying periods for use in bioassays. Straight-hinge veliger larvae grew to the umbo-veliger stage after 2 months in the refrigerator, but no pediveligers were observed during the 3-month refrigeration period. The average survival rate of larvae in the refrigerator was 79% after 1 month, but gradually decreased with the refrigeration period, and was as low as 22% after 3 months. All refrigerated larvae grew to the pediveliger stage in the incubator at 17°C at the same rate as that of the control larvae that were not refrigerated. Settlement and metamorphosis of pediveligers from both refrigerated and control groups were facilitated by microbial film and epinephrine and inhibited by phentolamine. Thus, refrigeration can be used as an effective method of storing larvae of M. galloprovincialis for use in assays to assess candidate settlement inducers and antifouling substances.     

Variability in early post-settlement mortality in intertidal mussels and the role of size at settlement

Early post-settlement mortality is difficult to measure in mobile benthic taxa such as mussels. Field studies typically employ settlement collectors that often contain empty shells of dead individuals, which are usually disregarded. Here, empty shells of pediveligers, i.e. recent settlers that died before beginning to grow as juveniles, were used to assess temporal and spatial patterns of early mortality in mussels, whether size at settlement determined mortality, and whether mortality was density-dependent. This study took place at two intertidal sites in a large harbour in central New Zealand where monthly cohorts of mussels were collected over a 2-year period. Monthly mortality varied substantially, ranging from 0% to 42.6%, but not across the two sites that were 27?km apart. Although there was no density-dependent mortality evident within cohorts, the proportion of pediveligers which were dead on collection was highly positively correlated across sites. Live settlers were on average larger than dead settlers, and the size distribution of dead settlers was shifted toward smaller sizes compared to live settlers. At the extremes, of all settlers with shell length of 260?µm or less, 72% were dead on collection. By contrast, for settlers 310?µm or greater in length, 6% were dead. Together, these results (1) suggest that in this system size at settlement may be an important determinant of very early, peri-metamorphic mortality in mussels, with smaller settlers at higher risk, and (2) demonstrate the value in evaluating dead pediveligers for assessing natural early post-settlement mortality in mussels.     

Enhancing solubilisation and methane production kinetic of switchgrass by microwave pretreatment

This study investigated the effects of microwave pretreatment of switchgrass in order to enhance its anaerobic digestibility. Response surface analysis was applied to screen the effects of temperature and time of microwave pretreatment on matter solubilisation. The composite design showed that only temperature had a significant effect on solubilisation level. Then the effects of the microwave pretreatment were correlated to the pretreatment temperature. The sCOD/tCOD ratio was equal to 9.4% at 90°C and increased until 13.8% at 180°C. The BMP assays of 42 days showed that microwave pretreatment induced no change on the ultimate volume of methane but had an interesting effect on the reaction kinetic. Indeed, the time required to reach 80% of ultimate volume CH(4) is reduced by 4.5 days at 150°C using the microwave pretreatment.     

冷层积和室温干燥贮藏对河西走廊8种荒漠植物种子萌发的影响

不同贮藏和处理条件对不同植物的种子萌发有不同的影响。该文以河西走廊干旱半干旱区8种荒漠植物为研究对象, 探讨了种子经历不同冷层积(4 ℃、-5 ℃、-26 - 10 ℃)和室温干燥贮藏后的萌发响应。研究结果表明: 1)冷层积可使种子萌发率提高、保持不变或降低, 冷层积的有效温度下界可降至-5 ℃或更低。4 ℃和-5 ℃的冷层积使多裂骆驼蓬(Peganum multisectum)和驼蹄瓣(Zygophyllum fabago)种子的萌发率升高、萌发速度加快, 冬季过低的气温以及较大的温度变幅(-26 - 10 ℃)使部分种子萌发率升高。3种冷层积和室温干燥贮藏使黑果枸杞(Lycium ruthenicum)种子萌发率达到90%-100%。唐古特白刺(Nitraria tangutorum)、甘草(Glycyrrhiza uralensis)、苦马豆(Sphaerophysa salsula)种子经过3种冷层积和室温干燥贮藏后萌发率变化较小。中亚紫菀木(Asterothamnus centrali-asiaticus)种子对各种贮藏条件的响应不明显, 部分种子活性丢失。刺沙蓬(Salsola ruthenica)种子扩散时有较高的萌发率(84%), 经-5 ℃和-26 - 10 ℃冷贮藏后, 种子仍具有较高的萌发率, 经4 ℃冷贮藏后几乎不萌发, 大部分种子活性丢失。2)不同物种的种子经过不同方式的贮藏后, 萌发对温度的响应不同。经冷层积后的多裂骆驼蓬种子萌发响应于恒温, 驼蹄瓣和刺沙蓬种子萌发更加响应于变温条件; 多数植物种子在变温培养下萌发速度慢于恒温下。     

Potential antifouling strategies for marine finfish aquaculture: the effects of physical and chemical treatments on the settlement and survival of the hydroid Ectopleura larynx

The hydroid Ectopleura larynx is a common fouling organism on aquaculture nets. To contribute to the development of novel cleaning methods, laboratory and field studies determined the effects of heat (30, 40, 50 and 60°C for immersion times of 1 and 3 s) and acetic acid (0.2 and 2.0% for immersion times of 1, 3 and 10 s, 1 and 5 min) on the settlement of actinulae and the survival of juvenile and adult E. larynx. Laboratory studies showed that, regardless of immersion time, a temperature of 50°C was effective in preventing the settlement of actinulae and the survival of juveniles, while ≤12% of adult hydroids could survive. A temperature of 60°C killed all adult hydroids. For an acetic acid concentration of 0.2%, an immersion time of 1 min substantially reduced the settlement of actinulae and the survival of juvenile and adult hydroids, and none of the juvenile and adult hydroids survived after 5 min. For an acetic acid concentration of 2.0%, all immersion times were effective and reduced the mean settlement of actinulae and the survival of juvenile and adult hydroids to ≤10%. Field studies with fouled net panels exposed to selected heat or acetic acid treatments showed small reductions in mean wet weight and net aperture occlusion of the net panels 2 and 5 days after treatment. Visual inspections of the net panels showed that hydranths of the hydroids were shed, but the dead stolons of the hydroids remained on the treated net panels. Novel cleaning methods and devices may utilise these results to effectively kill E. larynx on aquaculture nets, while further studies are needed to determine the necessity of removing the dead hydroids before further biofouling accumulates on the nets.     

Effect of temperature on the progamic phase in high-mountain plants

Progamic processes are particularly temperature-sensitive and, in lowland plants, are usually drastically reduced below 10 °C and above 30 °C. Little is known about how effectively sexual processes of mountain plants function under the large temperature fluctuations at higher altitudes. The present study examines duration and thermal thresholds for progamic processes in six common plant species (Cerastium uniflorum, Gentianella germanica, Ranunculus alpestris, R. glacialis, Saxifraga bryoides, S. caesia) from different altitudinal zones in the European Alps. Whole plants were collected from natural sites shortly before anthesis and kept in a climate chamber until further processing. Flowers with receptive stigmas were hand-pollinated with allopollen and exposed to controlled temperatures between -2 and 40 °C. Pollen performance (adhesion to the stigma, germination, tube growth, fertilisation) was quantitatively analysed, using the aniline blue fluorescence method. Pollen adhesion was possible from -2 to 40 °C. Pollen germination and tube growth occurred from around 0 to 35 °C in most species. Fertilisation was observed from 5 to 30-32 °C (0-35 °C in G. germanica). The progamic phase was shortest in G. germanica (2 h at 30 °C, 12 h at 5 °C, 24 h at 0 °C), followed by R. glacialis (first fertilisation after 2 h at 30 °C, 18 h at 5 °C). In the remaining species, first fertilisation usually occurred after 4-6 h at 30 °C and after 24-30 h at 5 °C. Thus, mountain plants show remarkably flexible pollen performance over a wide temperature range and a short progamic phase, which may be essential for successful reproduction in the stochastic high-mountain climate.     

高温对田间小菜蛾DNA损伤及4种抗药性相关酶系活性的抑制

研究了高温对福州上街菜田小菜蛾成虫4种抗药性相关酶系活性的影响。与饲养在25℃下的小菜蛾相比,33．5~C或40℃处理72h导致小菜蛾基因组DNA出现DNA凋亡特征梯度化条带。33~C饲养小菜蛾4、8、12或24h对小菜蛾成虫乙酰胆碱酯酶（AChE）和羧酸酯酶（CarE）活性无显著影响,但33℃饲养小菜蛾12或24h导致小菜蛾成虫谷胱甘肽s转移酶（GSTs）酶活性和细胞色素P450含量显著下降。36℃、24h可导致AChE活性显著下降,36℃、12h和24h可导致CarE活性显著下降,36℃、4h,8h,12h和24h可导致GST活性和细胞色素P450含量显著下降。总体上,高温对CarE、GSTs和细胞色素P450的抑制作用大于对AChE的影响,此外,3CC对AChE、CarE、GSTs酶活性和细胞色素P450含量的抑制作用大于33℃的抑制作用。     

Oxidative and nutrient stability of a standard rodent spaceflight diet during long-term storage

The National Aeronautics and Space Administration's standard spaceflight diet for rodents is the nutrient-upgraded rodent food bar (NuRFB). The shelf life of the NuRFB needs to be determined in order to avoid malnutrition of rodents and confounding of research results resulting from nutritional deficiency. The authors compared the oxidative and nutrient stability of NuRFBs stored at either ambient temperature (26 °C) or at refrigeration temperature (4 °C) for use in long-term rodent feeding experiments. After 0, 3, 6, 9 and 12 months (mo) of storage, lipid oxidation, fatty acid composition and amounts of specific vitamins and amino acids in NuRFBs were analyzed. No oxidative rancidity developed in NuRFBs stored at 4 °C for up to 12 mo, but NuRFBs stored at 26 °C for 6 mo developed oxidative rancidity and had reduced amounts of γ-linolenic acid (18:3n-6). Despite loss of vitamin E, vitamin A and thiamin after storage at 26 °C for 12 mo, vitamin levels in NuRFBs remained at or above the levels recommended for optimal rodent health. The amino acid profile of NuRFBs was unaffected by storage at 4 °C or 26 °C for 12 mo. The results suggest that NuRFBs stored at 4 °C for up to 12 mo and NuRFBs stored at 26 °C for up to 6 mo provide suitable nutrition for rodents in long-term experiments.