Effect of maturation conditions on light and temperature requirements during seed germination of Citrullus colocynthis from the Arabian Desert

• Seed germination of Citrullus colocynthis, as in many other species of Cucurbitaceae, is inhibited by light, particularly at low temperatures. Germination response to light and temperature has been attributed to day length and temperature during seed maturation. This study assessed the effects of these factors on the germination response of C. colocynthis to temperature and light quality.
• Ripe fruits were collected from natural habitats during December and February and germinated at three temperatures (15/25, 20/30 and 25/35 °C) in five light treatments (dark, white light and Red:Far Red (R:FR) ratios of 0.30, 0.87 and 1.19). Additionally, unripe fruits were also collected from natural habitats and completed their maturation in growth chambers under different day lengths (6, 16 and 24 h of darkness) at 10/20 °C, and in darkness at both 10/20 °C and 25/35 °C. Mature seeds of the different treatments were germinated in the same five light treatments at 15/25 °C.
• Germination was significantly higher in the dark than that in any light treatment. Seeds matured at higher temperatures (i.e. seeds from the December collection and those matured at 25/35 °C) had significantly higher germination than those matured at lower temperatures (i.e. seeds from the February collection and those matured at 10/20 °C). Dark germination was significantly higher for the December collection than for the February collection. Seeds of the two collections germinated in the dark only at 15/25 °C. However, seeds matured in a growth chamber at 10/20 °C in darkness germinated at 15/25 °C in all light treatments, except for the R:FR ratio 0.30. Seeds of the different treatments failed to germinate in FR‐rich light.
• This study demonstrates that both temperature and day length during seed maturation play significant roles in the germination response of C. colocynthis. Additionally, the dark requirement for germination is likely beneficial for species with the larger seeds, such as C. colocynthis, which produce bigger seedlings that are able to emerge from deep soils and are competitively superior under dense vegetation and resource‐limited conditions.

     

Effects of temperature,salinity and their interaction on growth of the benthic dinoflagellate Ostreopsis cf. ovata (Dinophyceae) from Japanese coastal waters

Benthic dinoflagellates of the genus Ostreopsis produce palytoxin (PTX)‐like compounds. The worldwide distributed Ostreopsis ovata/O. cf. ovata is potentially responsible for outbreaks of human health problems around the coasts of tropical, subtropical, and temperate regions. The present study examined growth responses of an O. cf. ovata strain s0662 collected from coastal waters of Japan with 35 different combinations of temperature (15–35°C) and salinity (20–40) and discusses the bloom dynamics of the organism in Japanese coastal environments. The O. cf. ovata strain s0662 tolerated a wide range of temperature (17.5–35°C) and salinity (25–40). Results of a two‐way ANOVA showed significant effects of temperature‐salinity interaction on growth rates and biomass yields of the O. cf. ovata strain (F(24,70) > 127, P < 0.001). The strain showed a maximal growth rate (1.03 divisions day^?1) and biomass yield (240 relative fluorescence) at temperature 25°C and salinity 30. The high growth rates of over 1.0 division day^?1 were obtained in conditions of temperature 25–30°C and salinity 30–35, which indicates that strain s0662 prefers high temperature and salinity conditions. The growth rates of O. cf. ovata under the optimal conditions were higher than those of other benthic toxic‐dinoflagellates, Coolia monotis, Gambierdiscus toxicus, and Prorocentrum lima (Dinophyceae) previously reported. Taken together, we suggest that O. cf. ovata is able to grow faster than the other benthic dinoflagellates in waters of high temperature and salinity. The physiological feature probably confers an ecological advantage on O. cf. ovata in the bloom development during warmer seasons in Japan and may be responsible for outbreaks of PTX‐like poisoning in the region especially during the warmer seasons.     

Combined effects of temperature and food concentration on growth and reproduction of Eodiaptomus japonicus (Copepoda: Calanoida) from Lake Biwa (Japan)

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THE EFFECTS OF TEMPERATURE ON THE PHOTOSYNTHETIC PARAMETERS AND RECOVERY OF TWO TEMPERATE BENTHIC MICROALGAE,AMPHORA CF. COFFEAEFORMIS AND COCCONEIS CF. SUBLITTORALIS (BACILLARIOPHYCEAE)1

Temperature and irradiance are the most important factors affecting marine benthic microalgal photosynthetic rates in temperate intertidal areas. Two temperate benthic diatoms species, Amphora cf. coffeaeformis (C. Agardh) Kütz. and Cocconeis cf. sublittoralis Hendey, were investigated to determine how their photosynthesis responded to temperatures ranging from 5°C to 50°C after short‐term exposure (1 h) to a range of irradiance levels (0, 500, and 1,100 μmol photons · m^?2 · s^?1). Significant differences were observed between the temperature responses of maximum relative electron transport rate (rETRmax), photoacclimation index (E_k), photosynthetic efficiency (α), and effective quantum yield (ΔF/F_m’) in both species. A. coffeaeformis had a greater tolerance to higher temperatures than C. sublittoralis, with nonphotochemical quenching (NPQ) activated at temperatures of 45°C and 50°C. C. sublittoralis, however, demonstrated a more rapid rate of recovery at ambient temperatures. Temperatures between 10°C and 20°C were determined to be optimal for photosynthesis for both species. High temperatures and irradiances caused a greater decrease in ΔF/F_m’ values. These results suggest that the effects of temperature are species specific and that short‐term exposure to adverse temperature slows the recovery process, which subsequently leads to photoinhibition.     

Climate change and trophic interactions in model temporary pond systems: the effects of high temperature on predation rate depend on prey size and density

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Comparative growth and metabolism of gelatinous colonies of three cyanobacteria,Nostoc commune,Nostoc pruniforme and Nostoc zetterstedtii,at different temperatures

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Effects of four constant temperatures on the development of two Bradysia (Diptera: Sciaridae) species

In this study, the effects of temperature on the growth, development, survival, fecundity and other population parameters of two local Bradysia species B. odoriphaga and B. impatiens were studied at four constant temperatures (25, 28, 31 and 34°C). The results show that 25°C is the optimum temperature for the growth and development of B. odoriphaga, while 28°C is more favourable for B. impatiens. The temperature of 31°C restricted the growth and development, while the temperature of 34°C inhibited the eggs hatching in both species, resulting in no egg survival and no subsequent development. High temperatures (>28°C) prolonged the 4th larval stage duration, mean generation time (T) and population doubling time (Dt) of both species. The high temperature of 31°C greatly shortened the female longevity, weakened the oviposition and reduced the survival of both species. Moreover, the life table parameters R₀, r_m and λ were also suppressed by this high temperature. However, the high temperature of 31°C had little impact on the egg survival, pupal weight and male longevity. In addition, at 31°C, the values of R₀, r_m and λ of B. odoriphaga were higher than those of B. impatiens, suggesting that B. odoriphaga is more tolerant to high temperature than B. impatiens. The differences between two Bradydsia species seem determined genetically. Our findings are important for better understanding their biological characteristics at a certain constant temperature and demonstrate the possibility to control and manage those two Bradysia species by increasing ambient temperature.     

Closely related freshwater macrophyte species,Ceratophyllum demersum and C. submersum,differ in temperature response

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Temperature,growth and seasonal succession of phytoplankton in Lake Baikal,Siberia

• 1 Growth rates of two dominant Lake Baikal phytoplankton, the winter diatom Aulacoseira baicalensis and the summer cyanobacterium Synechocystis limnetica, were measured in the laboratory under varied temperature and light regimes to determine the potential role of these abiotic factors in seasonal species succession in the lake.
• 2 Aulacoseira baicalensis grew best at low temperature and not at all above 8 °C. Its maximum instantaneous growth rate was 0.15 d^‐1 recorded at 2–3 °C. Cells grew faster as temperature decreased, apparently in contrast to conventional Q₁₀‐based temperature‐growth relationships.
• 3 The picoplankter Synechocystis limnetica did not grow at 2–3 or 5–6 °C, but grew at a rate of 0.24 d^‐1 at the highest incubation temperature of 17 °C. Maximum growth rate was 0.35 d^‐1 at 8 °C.
• 4 Saturation irradiances (I_k) for growth of Aulacoseira baicalensis and Synechocystis limnetica were near pre‐acclimation values of 40 µmol m^‐2 s^‐1. At temperatures conducive to growth, both phytoplankters grew at all irradiances tested, except for A. baicalensis which would not grow at values above 300 µmol m^‐2 s^‐1 at 8 °C.
• 5 We conclude that temperature is a major driving force for the seasonal succession of species in Lake Baikal. Other factors, including vertical mixing of the water column and grazing by zooplankton, may also play important roles.

     

Effects of root zone temperature and paraquat in the induction of oxidative stress in <Emphasis Type="Italic">Trichosanthes cucumerina</Emphasis> L.

We investigated the influence of root zone temperature (RZT) and the aerial application of paraquat on stress defence mechanisms of Trichosanthes cucumerina L. To achieve this objective, T. cucumerina cv Green was grown with roots at 25 and 30°C root zone temperature and maintained at 20 ± 1°C air temperature in a growth chamber. These RZT and air temperature had earlier been shown to favor growth and fruit production in T. cucumerina. Plants at each RZT were subjected to paraquat treatment (+P) and without paraquat treatment (−P). Paraquat (0.2 mmol/L) was applied as aerial spray. Results showed that the individual main effects of RZT and paraquat treatments significantly affected the chlorophyll fluorescence and gas exchange parameters, while the interaction of both treatments had no significant effect. Results showed that the total phenolics and ascorbic acid contents of T. cucumerina at 30°C were significantly higher than at 25°C. The T. cucumerina plants in +P treatment recorded significantly lower maximum photochemical efficiency (F _v/F _m), net photosynthesis (A), transpiration rate (E), intercellular CO₂ concentration (C _i) and stomatal conductance (g ₁) compared to untreated plants. Also, plants raised at 30°C recorded significantly higher F _v/F _m, A, E, C _i and g ₁ compared to plants raised at 25°C. Plants that were sampled at 48 h after paraquat treatment recorded a higher degree of oxidative damage compared to those sampled at 24 h after treatment. We showed that the degree of damage suffered by T. cucumerina, when treated with paraquat either at 25 or 30°C RZT was similar at 48 h after treatment. We concluded that either at 25 or 30°C, exposure of T. cucumerina to paraquat would impose the same degree of oxidative damage.     

Morphological and functional seed traits of the wild medicinal plant Dioscorea strydomiana,the most threatened yam in the world

• Morphological and functional seed traits have important roles in characterising the species regeneration niche and help to understand the reproductive biology of rare and threatened plants, which can thus support appropriate plant conservation measures.
• Seed morphometric and dispersal kinetics of the critically endangered Dioscorea strydomiana were measured and compared with those of four other Dioscorea species, and seed germination response under constant temperatures (5–35 °C) was compared with that of the congeneric and widespread D. sylvatica.
• Seed mass of D. strydomiana (ca. 14 mg) was twice that of D. sylvatica, but similar to or smaller than the other species examined. Seeds of D. strydomiana have the lowest speed of descent and lowest variability in most of the morphological traits considered, suggesting lower phenotypic plasticity but higher variance in the wing‐loading value. Seeds of D. strydomiana reached maximum germination at 15 °C (ca. 47%), which decreased slightly to ca. 37% at 25 °C and was completely inhibited at 35 °C. D. sylvatica seeds started to germinate at 10 °C (ca. 3%), reached 75–80% germination at 15–20 °C and maximum (ca. 90%) at 25–30 °C. Base temperatures for germination (T_b) were 9.3 and 5.7 °C, for D. strydomiana and D. sylvatica, respectively. Due to the higher germination percentages of D. sylvatica, ceiling and optimum temperatures could also be modelled for this species, suggesting higher sensitivity to high temperature for seeds of D. strydomiana.
• The detected poor seed lot quality of D. strydomiana suggests difficulties in reproduction from seed, highlighting the need for further investigation and conservation actions for this threatened yam species.

     

Effects of extended and repeated exposures to low temperature on mortality of the peach-potato aphid Myzus persicae

Abstract.

• 1 The survival of adult and first-instar Myzus persicae reared at 20°C and 10°C was investigated after brief (1 min) exposure in the absence of plant material to temperatures between −5°C and −25°C, and extended exposures on plants of 1–10 days at a constant 5°C, 3°C and −5°C and a 24 h cycling regime between 5°C (18 h) and −5°C (6 h).
• 2 Life stage, rearing temperature, period of exposure and temperature regime all had a significant effect on the ability of aphids to survive cold. The effects of life stage and rearing temperature were most noticeable following exposure to cycling temperatures and extended exposures at −5°C, and least apparent after 1 min exposures at lower sub-zero temperatures.
• 3 Mortality following exposure to temperatures cycling between −5°C and 5°C was greater than that at 3°C (the mean of the cycling temperatures) and less than at a constant −5°C, suggesting that when temperatures fluctuate by a few degrees around 0°C the minimum temperature may affect survival to a greater extent than the mean.
• 4 These results suggest that an overwintering population of acclimated M.persicae would persist without significant mortality after a period of 7–10 days with −5°C frosts each night.

     

Trans-Tasman variation in Australasian Filinia populations

Morphological comparisons of populations of Filinia from New Zealand and Australia established the presence of an undescribed species in Lake Okaro, N.Z. Filinia novaezealandiae n. sp. is described. SEM micrographs of trophi were used to distinguish closely allied Filinia species. Filinia grandis comb. nov. is redescribed from Australia on the basis of trophi differences from F. pejleri. It is suggested that Filinia species may be more restricted than global records indicate; these records reflect the distribution of authoritative taxonomic references, not necessarily the animals they depict.     

Fecundity and feeding of <Emphasis Type="Italic">Galerucella calmariensis</Emphasis> and <Emphasis Type="Italic">G. pusilla</Emphasis> on <Emphasis Type="Italic">Lythrum salicaria</Emphasis>

Fecundity and feeding of two introduced sibling biological control species, Galerucella calmariensis and G. pusilla (Coleoptera: Chrysomelidae) on purple loosestrife, Lythrum salicaria L. (Lythraceae) were compared at constant temperatures of 12.5, 15, 20, 25, and 27.5 °C. Larval feeding was also carried out at 30 °C, but at this temperature, larvae developed only to the L2 stage and none pupated. Thus, data for this temperature were not used in the analysis. There were significant species × temperature interactions in fecundity. Of the two species, Galerucella pusilla laid more eggs. Although egg production of both species was lowest at 12.5 °C and increased to 20 °C, at higher temperatures, the two species reacted differently. From 25 to 27.5 °C, egg production decreased for G. pusilla, but G. calmariensis fecundity peaked at 27.5 °C. Significant temperature × species × life-stage interactions were also observed in feeding. For each species, the amount of feeding varied with temperature and stage of development. Galerucella pusilla adults consumed more foliage at 15, 20, and 27.5 °C. However, at 12.5 °C G. calmariensis adults fed more than G. pusilla. G. pusilla larvae consumed an average of 25% less foliage than G. calmariensis. The lower larval consumption of G. pusilla suggests that when food is limited, G. pusilla larvae may have a higher survival rate because of its ability to complete larval development with less food and produce more progeny due to its greater fecundity. When food is not limited neither species would have a competitive advantage and both species could coexist temporally and spatially. However, since G. calmariensis larvae consumed more leaf material, the larval stage of this species would have a greater impact on purple loosestrife than G. pusilla.     

Modulation of physiological performance by temperature and salinity in the sugar kelp Saccharina latissima

The sugar kelp Saccharina latissima experiences a wide range of environmental conditions along its geographical and vertical distribution range. Temperature and salinity are two critical drivers influencing growth, photosynthesis and biochemical composition. Moreover, interactive effects might modify the results described for single effects. In shallow water coastal systems, exposure to rising temperatures and low salinity are expected as consequence of global warming, increased precipitation and coastal run‐off. To understand the acclimation mechanisms of S. latissima to changes in temperature and salinity and their interactions, we performed a mechanistic laboratory experiment in which juvenile sporophytes from Brittany, France were exposed to a combination of three temperatures (0, 8 and 15°C) and two salinity levels (20 and 30 psu (practical salinity units)). After a temperature acclimation of 7 days, sporophytes were exposed to low salinity (20 psu) for a period of 11 days. Growth, and maximal quantum yield of photosystem II (Fv/Fm), pigments, mannitol content and C:N ratio were measured over time. We report for the first time in S. latissima a fivefold increase in the osmolyte mannitol in response to low temperature (0°C) compared to 8 and 15°C that may have ecological and economic implications. Low temperatures significantly affected all parameters, mostly in a negative way. Chlorophyll a, the accessory pigment pool, growth and Fv/Fm were significantly lower at 0°C, while the de‐epoxidation state of the xanthophyll cycle was increased at both 0 and 8°C compared to 15°C. Mannitol content and growth decreased with decreased salinity; in contrast, pigment content and Fv/Fm were to a large extent irresponsive to salinity. In comparison to S. latissima originating from an Arctic population, despite some reported differences, this study reveals a remarkably similar impact of temperature and salinity variation, reflecting the large degree of adaptability in this species.     

Temperature‐dependent demography of Agriphila aeneociliella (Lepidoptera: Crambidae), a new insect pest of wheat in China

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Biological traits of Epitrix papa (Coleoptera: Chrysomelidae: Alticinae), a new potato pest in Europe,and implications for pest management

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Temperature dependence of UV radiation effects in Arctic and temperate isolates of three red macrophytes

The temperature dependence of UV effects was studied for Arctic and temperate isolates of the red macrophytes Palmaria palmata, Coccotylus truncatus and Phycodrys rubens. The effects of daily repeated artificial ultraviolet B and A radiation (UVBR: 280–320?nm, UVAR: 320–400?nm) treatments were examined for all isolates at 6, 12 and 18?°C by measuring growth, optimal quantum yield of PSII (F_v/F_m) and cyclobutane-pyrimidine dimer (CPD) accumulation. Furthermore, possible ecotypic differences in UV sensitivity between Arctic and temperate isolates were evaluated. Large species-specific differences in UV sensitivity were observed for all parameters: the lower subtidal species C. truncatus and P. rubens were highly sensitive to the UV treatments, whereas P. palmata, which predominantly occurs in the upper subtidal zone, was not affected by these treatments. Only minor differences were found between Arctic and temperate isolates, suggesting that no differences in UV sensitivity have evolved in these species. Relative growth rates were temperature-dependent, whereas species-specific UV effects on growth rates were relatively independent of temperature. In contrast, the species-specific decrease in F_v/F_m and its subsequent recovery were temperature-dependent in all species. UV effects on F_v/F_m were lower at 12 and 18?°C compared with 6?°C. In addition, UV effects on F_v/F_m decreased in the course of the experiment at all temperatures, indicating acclimation to the UV treatments. CPDs accumulated during the experiment in both isolates of P. rubens, whereas CPD concentrations remained low for the other two species. CPD accumulation appeared to be independent of temperature. The results suggest that summer temperatures occurring in temperate regions facilitate repair of UV-induced damage and acclimation to UV radiation in these algae compared with Arctic temperatures. Because the differences in UV effects on F_v/F_m, growth and CPD accumulation were relatively small over a broad range of temperatures, it was concluded that the influence of temperature on UV effects is small in these species.     

Influence of larval rearing temperature on the quality of cold‐stored Oomyzus sokolowskii Kurdjumov (Hymenoptera: Eulophidae)

Oomyzus sokolowskii, an important parasitoid of Plutella xylostella, has great potential for use in biological control. Storage at suboptimal temperature is valuable for increasing the shelf‐life of insect parasitoids. In this study, O. sokolowskii larvae were reared at 30/25, 25/25 and 25/20°C light/dark (65 ± 5% RH, 16 : 8 h L : D) until pupation. The pupae were then cold‐stored at 4 ± 1°C (60 ± 5% RH, full darkness). The pupae were removed out from the storage at 10, 20, 30 and 40 days after storage (DAS) and maintained at 25 ± 2°C until adults emerged or pupae died. Quality of the emerging adults and their F₁ offspring were assessed. Incidence of parasitism by O. sokolowskii was higher at 30/25°C than at 25/20°C. Cold storage of O. sokolowskii pupae greatly affected the fitness of the parasitoid: adult emergence rates were lower in the 40 DAS treatment than in other treatments; when O. sokolowskii larvae developed at 25/25°C, female proportions of the emerged adults were lower in the 40 DAS treatment than in the 0 and 10 DAS treatments. Larval rearing temperature mildly affected the adult emergence rate, post‐storage developmental time and female proportion with a few exceptions. Number of parasitoids emerged per host pupa, and incidence of parasitism by the females were neither affected by larval rearing temperature nor cold storage duration. Trans‐generational effects on F₁ offspring were evident in adult emergence rate, egg‐adult developmental time and female proportion which were negatively affected by long duration of storage (40 days), but not by larval rearing temperature with a few exceptions. In conclusion, O. sokolowskii pupae could be stored at 4°C for up to 30 days without significant fitness loss.     

Temperature elevation reduces the sensitivity of invasive cladoceran Daphnia lumholtzi to filamentous cyanobacterium Raphidiopsis raciborskii

1. Exotic cladoceran Daphnia lumholtzi is a highly invasive species in the north and south American continents and can potentially also invade European freshwaters and outcompete native Daphnia populations. However, European waterbodies are frequently dominated by less edible filamentous cyanobacteria including also invaders such as Raphidiopsis raciborskii, which might affect the fitness of D. lumholtzi. Furthermore, temperature may influence the sensitivity of D. lumholtzi to R. raciborskii filaments.
2. In this study, we determined whether the presence of R. raciborskii could obstruct the invasion of Europe by D. lumholtzi, through reducing its fitness, and whether this depends on temperature. We compared the population growth rate (r) and the somatic growth rate of D. lumholtzi maintained at two temperatures (20 or 26°C) and fed with two diets: green microalgae alone or green microalgae mixed with filaments of R. raciborskii. Three clones of D. lumholtzi were used to evaluate potential variation in response to the treatments among different clones.
3. At 20°C, the population growth rate of D. lumholtzi fed with cyanobacterial filaments declined sharply. This reduction was caused by increased egg abortion, egg degeneration, and mortality of newborn daphnids. At 26°C, R. raciborskii lost its harmful effect on the population growth of D. lumholtzi. The presence of cyanobacteria did reduce the somatic growth rate of D. lumholtzi at both temperatures and in all three clones except for one that had a similar somatic growth rate on both diets at 26°C.
4. The presence of filamentous cyanobacteria does affect growth in D. lumholtzi and may thereby substantially reduce its invasive potential, but only at lower temperatures. Therefore, the presence of filamentous cyanobacteria may not present an obstacle to the invasion of Europe by D. lumholtzi in a warmer future climate.