福寿螺的过冷却研究

福寿螺是IUCN认定的世界100种恶性外来入侵物种之一,在华南地区已对水稻生产造成严重危害。福寿螺属于热带软体动物,采用万用电表联接热敏电阻法研究了福寿螺在低温胁迫下的过冷却点,并探讨了不同个体福寿螺在过冷却发生后的死亡率和体内组织损伤。结果表明: 1)各种螺高的福寿螺冷却点均值为-6.96 ℃,范围在-6.21--7.32 ℃之间,恢复最高体温均值为-4.07 ℃,范围在-3.07--4.93 ℃之间,过冷却后维持时间均值为45.97 min,范围在18.60-75.34 min;2)福寿螺的过冷却点大小受螺高影响,螺高35 mm≤H<45 mm的福寿螺过冷却点显著高于5 mm≤H<15 mm、15 mm≤H<25 mm、25 mm≤H<35 mm体型的福寿螺,5-35 mm螺高的福寿螺过冷却点变化稳定;3)福寿螺在发生过冷却阶段的死亡率在23.33%-36.67%之间,不同体型的福寿螺之间没有显著性差异;4)过冷却后福寿螺死亡率随暴露时间的延长而提高,0到15 min内由20.9%提高到100%,过冷却后暴露时间对福寿螺死亡率影响较大;5)发生过冷却15 min后取出的福寿螺,染色后其外套膜有少量红色出现,而肾部和消化腺部未呈现明显红色,低温胁迫已经对福寿螺组织造成了显著损伤。本研究结果对于进一步探索福寿螺的生态适应性、扩散北界及福寿螺的越冬机制有一定参考价值。     

Influence of water temperature on the activity of the freshwater snail Pomacea canaliculata (Caenogastropoda: Ampullariidae) at its southernmost limit (Southern Pampas,Argentina)

1.

The effect of temperature on the activity of the freshwater snail Pomacea canaliculata was investigated through field surveys and laboratory trials.     

Structure and stability of the neurotoxin PV2 from the eggs of the apple snail Pomacea canaliculata

There is little information on the egg proteins of gastropod mollusks. Here we focus on PV2, a novel neurotoxin from snail eggs, studying its size, shape, structure, and stability, using small angle X-ray scattering (SAXS), absorption and fluorescence spectroscopy, circular dichroism, electron microscopy and partial proteolysis. Results indicate that PV2 is a compact and well folded oligomer of 130 × 44 Å. It is an octamer of four 98 kDa heterodimers composed of 67 and 31 kDa subunits. Subunits are held together by disulfide bonds. Dimers are assembled into native PV2 by non-covalent forces. The larger subunit is more susceptible to proteolysis, indicating it is less compactly folded and/or more exposed. Quenching of tryptophan fluorescence showed a single class of tryptophyl side chains occluded in hydrophobic regions. Native structure shows loss of secondary structure (α+β) at 6 M urea or 60–70 °C; the effects on the quaternary structure suggest an unfolding without disassembling of the protein. The 3D model of PV2 presented here is the first for an egg proteinaceous neurotoxin in animals.     

孵化温度对黄喉拟水龟胚胎发育和幼体特征的影响

用3个恒定温度(24、26和28℃)孵化黄喉拟水龟南方种群卵,检测孵化温度对孵化期、孵化成功率和孵出幼体特征的影响。孵化温度显著影响孵化期和孵化成功率、以及幼体的性别、大小和早期生长。黄喉拟水龟幼体的性别取决于孵化温度(属TSDⅠa型),26℃和28℃孵出幼体偏雄性,30℃孵出幼体都是雌性。随着孵化温度的升高,孵化期呈非线性缩短,而孵化成功率略微增加。较高温度下孵出的幼体较大且具有较好的功能表现,但生长较慢。低温孵出幼体较小,但胚后生长速率较快。低温孵出幼体较小可能与胚胎发育期长、总代谢消耗大有关;而生长速率快则可能是因为低温产生的雄性幼体生长快于高温产生的雌性幼体。与已报道的黄喉拟水龟北方种群卵孵化结果相比较,26℃和28℃条件下南方种群卵的孵化期和产生1∶1性比的关键温度较大。这种地理上的变异可能反映不同种群对当地热环境适应性上的差异。     

The selective advantage of avoidance of the predatory whelk Lepsiella vinosa (Lamarck) by Littorina unifasciata (Philippi)

The herbivorous snail Littorina unifasciata (Philippi) is widely distributed, and different species of predatory whelks occur in different parts of its range. At Coobowie, South Australia, L. unifasciata coexists with and avoids Lepsiella vinosa (Lamarck), while at Portobello, New Zealand, Littorina unifasciata similarly coexists with and avoids Lepsiella scobina albomarginata (Deshayes). By transporting Lepsiella vinosa from Coobowie to Portobello it was shown that Littorina unifasciata from the latter population did not avoid this foreign species but were captured, drilled and eaten by it.     

Susceptibility of neonate Lissachatina fulica (Achatinidae: Mollusca) to a US strain of the nematode Phasmarhabditis hermaphrodita (Rhabditidae: Nematoda)

ABSTRACT

The nematode Phasmarhabditis hermaphrodita is a lethal parasite of many pest slug and snail species. It is used as a commercial biological control agent (Nemaslug®) in Europe but a number of key gastropod pests (e.g. Lissachatina fulica) are thought to be unsusceptible. Our data, however, demonstrated that a recently discovered U.S. strain of P. hermaphrodita causes statistically significant mortality to neonate L. fulica and consequently this nematode could be an important IPM tool for managing this snail pest in areas where P. hermaphrodita has been discovered. Soil moisture content appears to play an important role in determining nematode efficacy.     

Control of Root Rot and Wilt caused by Pythium myriotylum in Kangaroo Paw (Anigozanthos)

Control of root rot and wilt on Kangaroo Paw (Anigozanthos) caused by Pythium myriotylum was tested, using artificial inoculations, in greenhouse experiments. Disease incidence in the inoculated but non‐treated plots was 74% in Expt A (1999) and 46% in Expt B (2000). Disease incidence was significantly reduced by treatments with fenamidon (26 and 70%) and Terraclor SuperX (65 and 41%) in Expts A and B, respectively, in comparison with the non‐treated plots. Disease incidence was reduced with Ridomil Gold by 7 and 48% in Expts A and B, respectively; with Dynone by 22 and 41% in Expts A and B, respectively; with Tachigaren by 20% in both experiments; and with Trichoderma harzianum treatment, disease incidence was reduced by 9% only in Expt B. Yields (recorded only in Expt B) obtained in plots inoculated with P. myriotylum were significantly lower than in the non‐inoculated control plots. The most efficient treatment was fenamidon, with 324% more flowers than in the non‐treated control. The number of flowers in terraclor SuperX, Ridomil Gold, Dynone and T. harzianum treatments was higher by 285, 249, 234 and 235% than in the non‐treated control. In vitro tests demonstrated that the most effective doses, causing 50% inhibition of mycelial growth (ED₅₀), were 0.09, 0.4, 0.4 and 4 μg/ml for the fungicides fenamidon, Ridomil Gold (mefenoxam), Terraclor SuperX (etridiazole + quintozene) and Dynone (prothiocarb), respectively.     

Orientation and behaviour of hatchling green turtles (Chelonia mydas) in the sea

To investigate the initial stage of the ‘lost-year puzzle’ of sea turtle ecology, both hatchlings from the natural nesting groung at Tortuguero, Costa Rica and hatchlings from Tortuguero eggs that had hatched in a beach on Bermuda were tracked individually after their departure from these beaches. Of the Bermuda beach most were tracked by swimmers equipped with face mask and flippers and followed by a boat. Tracking off Tortuguero was done by an observer in a following boat. The data showed that non-random departure courses were maintained even when swimming hatchlings and moved over the horizon from all fixed objects on the shore. Observations were made on swimming and diving behaviour and on predator relationships of travelling turtles. The procedures described are useful research techniques and will be used for more extensive tracking in future seasons.     

南方菟丝子寄生对喜旱莲子草生长及群落多样性的影响

菟丝子属植物是一种有潜力的入侵植物的生物防治剂。以南方菟丝子(Cuscuta australis)天然寄生的喜旱莲子草(Alternanthera philoxeroides)群落为研究对象,对比分析了南方菟丝子寄生对入侵植物喜旱莲子草生长的影响,同时采用群落调查的方法分析南方菟丝子寄生对入侵群落多样性的影响,以判断南方菟丝子是否具有防治喜旱莲子草的能力。结果表明南方菟丝子寄生可以降低喜旱莲子草的根生物量、茎生物量、叶生物量和总生物量,但与对照之间均不存在显著性差异;南方菟丝子寄生可以显著降低茎生物量比,显著增加根生物量比和根冠比。在无南方菟丝子寄生的喜旱莲子草群落中,除南方菟丝子和喜旱莲子草外,共有10科14属14种植物;而在南方菟丝子寄生的喜旱莲子草群落中,除南方菟丝子和喜旱莲子草外,共有16科27属28种植物,南方菟丝子能以产生吸器而寄生生长的植物共有19种,占样地植物种数的67.86%。南方菟丝子寄生可使群落物种丰富度显著性增加,也可使群落Simpson指数、Shannon-Wiener指数、McIntosh指数和均匀度指数增加,但是与对照之间不存在显著性差异。南方菟丝子寄生使喜旱莲子草的多度显著性下降,使喜旱莲子草的盖度和高度下降,但与未寄生的喜旱莲子草群落相比不存在显著性差异。但是南方菟丝子寄生可使喜旱莲子草在群落上的相对盖度、相对高度和相对多度均显著性下降,从而导致群落中喜旱莲子草的重要值显著性下降。南方菟丝子寄生可以在一定程度上抑制入侵植物喜旱莲子草的生长,促使群落多样性增加,促进本地群落的恢复。     

The feeding, growth, and energetics of two rocky intertidal predators (Pisaster ochraceus and Nucella canaliculata) under water temperatures simulating episodic upwelling

Although most upwelling regions are marked by strong fluctuations in water temperature, few studies have examined how episodic cold-water events affect the physiology and ecology of benthic marine invertebrates. I tested the hypothesis that upwelling-related variation in water temperature regulates the feeding, growth, and energetics of two rocky intertidal predators, the sea star Pisaster ochraceus (Brandt, 1835) and the whelk Nucella canaliculata (Duclos, 1832). Sea stars and whelks were maintained in laboratory tanks at a constant 9 °C, a constant 12 °C, and a treatment that simulated the Oregon coast upwelling regime by cycling between 14-day periods of 12 and 9 °C. Early in the experiments, sea stars and whelks held at 9 °C consumed about 30% fewer mussels (Mytilus trossulus) than those in warmer tanks. Despite lower consumption by whelks in colder tanks, 9 and 12 °C individuals attained the same final size. Similarly, sea stars in 9 °C tanks showed greater growth per gram of mussel tissue consumed than individuals held at 12 °C. These results suggest that reduced consumption under colder conditions was balanced by reduced metabolic costs. Moreover, there appeared to be an energetic advantage to living in the temperature regime characteristic of intermittent upwelling. Sea stars alternately exposed to 12 and 9 °C had a significantly higher growth rate, conversion efficiency, and storage of reserves in the pyloric caeca than individuals in the constant 12 °C tanks. Whelks maintained under fluctuating temperatures tended to grow faster than those held at constant 12 or 9 °C, although this trend was not statistically significant (p=0.069). These results suggest that benthic consumers experiencing cyclic temperatures may feed intensely during periods of warmer water while benefiting from reduced metabolic costs during cold-water intrusions. Because the fecundity of Pisaster and Nucella is a function of energy stored during the upwelling season, interannual variability in upwelling patterns could alter the reproductive output of these species.     

Can we predict the effects of alien species? A case-history of the invasion of South Africa by Mytilus galloprovincialis (Lamarck)

The Mediterranean mussel Mytilus galloprovincialis invaded the shores of South Africa in about the mid-1970s. It was first detected at a harbour in Saldanha on the west coast and apparently arrived accidentally. From there, it spread at a rate of about 115 km·year⁻¹ and now occupies the whole of the west coast of South Africa and at least the southern half of Namibia. It was deliberately introduced from the west coast to the south coast for mariculture. In this case study, we record its effects on intertidal rocky shores, cast in terms of predictions based on (a) the history of its invasions elsewhere, (b) its mode of dispersal, (c) its physiological performance relative to indigenous mussels, (d) the role of wave action as a moderator of competition, (e) the influence of relative body sizes, (f) the projected effects of the mussel on infauna, (g) consumption by higher trophic levels, and (h) rates of parasitism.

Several properties of M. galloprovincialis itself, and of the recipient community, conspired to favour the spread and establishment of this alien mussel, including high productivity on the west coast of South Africa, prevalently strong wave action, a sparsity of predators, an absence of parasites, the mussel's fast growth and high reproductive output, and its possession of a planktotrophic larva. It competitively displaces several species because of its physiological performance. Some of the species gain a substitute substratum on the mussels themselves, but only if they are small enough to live and reproduce on the mussels. M. galloprovincialis has had little effect on infauna, but has provided an additional source of food for higher predators, including the rare and endangered African Black Oystercatcher (Haematopus moquini).

Nearly all these effects and conditions were forecasted (or, at the least, explainable with hindsight), but despite these successes in predicting the impacts of M. galloprovincialis, its spread was not only unavoidable but was encouraged by its transfer to the south coast for mariculture. Moreover, there was one completely unpredictable effect of M. galloprovincialis—which led to mass mortalities of a swimming crab. Given the failure of even quite detailed and accurate predictions to allow control of M. galloprovincialis once it arrived, prevention rather than cure must be the prime means of avoiding future unwanted introductions of invasive species.     

Sexual reproduction of two alien invasive Ludwigia (Onagraceae) on the middle Loire River,France

Ludwigia peploides (Kunth) Raven ssp. montevidensis (Spreng.) Raven and Ludwigia grandiflora (Michaux) Greuter and Burdet ssp. hexapetala (Hooker and Arn.) Nesom and Kartesz, are expanding their geographic range due to clonal reproduction; these taxa are considered the most important nuisance aquatic plants in French river habitats. During 1970s, these two species have colonized former channels and river banks of the middle Loire River, previously scarcely covered by aquatic vegetation. Now, the exotic Ludwigia build up dense and continuous stands with potentially high impact on biodiversity and sedimentation rates.     

Survival and health improvement of Nosema infected Apis florea (Hymenoptera: Apidae) bees after treatment with propolis extract

Nosema ceranae is now considered to be an emerging infectious disease of the European honey bee Apis mellifera. Only one antibiotic, Fumagillin, is commercially available to combat Nosema infections. This antibiotic treatment is banned from use in Europe and elsewhere there is a high probability for antibiotic resistance to develop. We are therefore interested in investigating the effects of a natural propolis extract on its ability to reduce N. ceranae infection loads in the dwarf honey bee, Apis florea, a native honey bee with a range that overlaps with Apis cerana and Apis mellifera that is at risk of infection. Experimentally infected caged bees were fed a treatment consisting of 0%, 50%, or 70% propolis extract. All 50% and 70% propolis treated bees had significantly lower infection loads, and the 50% treated bees had higher survival in comparison to untreated bees. In addition, propolis treated bees had significantly higher haemolymph trehalose levels and hypopharyngeal gland protein content similar to levels of uninfected bees. Propolis ethanolic extract treatment could therefore be considered as a possible viable alternative to Fumagillin to improve bee health. This natural treatment deserves further exploration to develop it as a possible alternative to combat N. ceranae infections distributed around the world.     

Energy source utilization by embryos and larvae of the muricid snail Chorus giganteus (Lesson, 1829)

The muricacean snail Chorus giganteus presents intracapsular development and the occurrence of nurse eggs that are ingested by the early encapsulated embryos indicate both that these snails develop through a lecitotrophic type of development and that reserves would be sufficient to support settlement and metamorphosis. In order to get more information about the use of energy resources, the dynamics of biochemical components throughout development at three temperatures (9, 12 and 15 °C) and the energetic cost of free-swimming life and metamorphosis are described. The uptake of ³H-alanine, as representative of dissolved organic matter, by embryo and larval stages is also investigated. While protein levels increased at all temperature conditions after ingestion of nurse eggs, lipids only increased when embryo and larvae were reared at 15 °C, and no change in carbohydrate levels was detected at any of the temperatures. The RNA/DNA indexes showed no significant differences with temperature at any stage of development but decreased along with the development of individuals. After hatching, organic matter and energy content of juveniles steadily decreased. Individuals at any of the developmental stage showed to be able to uptake alanine from seawater; the aminoacid uptake capacity increased along with intracapsular development. Uptake of alanine showed to be an active process and to follow Michaelis-Menten kinetics. This would be the first report about dissolved organic matter uptake by encapsulated development stages of any marine invertebrate species and let conclude that these larvae have the ability to obtain exogenous food in a dissolved form and to incorporate it into metabolizable compounds.     

Distribution and population dynamics of the limpet Patella aspera (Lamarck) in Bantry Bay

The population ecology of Patella aspera (Lamarck) was studied as part of an oil pollution baseline study. Contrary to earlier reports, P. aspera appears to be a protandrous hermaphrodite. Maturation of the gonads began in May-June and spawning took place in October. Variations in density, standing crop, and mean size were related to exposure to wave action and tidal level. The low shore in extreme exposure may be designated as the centre of P. aspera's range; abundance is high but biomass and mean size are reduced. Higher on the shore, and in reduced exposure to wave action, P. aspera attains a greater mean size and biomass, but is eventually replaced by P. vulgata L. Two main factors are adduced as being critical to competition between the two species. In terms of tidal level, P. aspera is less tolerant of desiccation than P. vulgata, while in terms of the exposure-shelter gradient, P. aspera appears to have a much less variable growth rate. P. aspera may be defined, therefore, as a non-migratory, low shore, specialist species, highly adapted to a specific set of environmental conditions, but lacking the ability to adapt to others.     

Morphology and neurophysiology of tarsal vibration receptors in the water strider Aquarius paludum (Heteroptera: Gerridae)

Substrate vibratory information receptors are extensively studied in insects and spiders, however for water surface dwelling species little data is available. We studied the vibration receptive organs in tarsi of the water strider Aquarius paludum, using light, transmission and scanning electron microscopes, and recorded the neural activity of the organs in response to vibrational stimuli, which were afterwards analysed with a custom made spike sorting program.We found that the tarsal chordotonal organ has one set of three scoloparia: one in the tarsomere I and two in the tarsomere II, all of which consisted of a few scolopidia. The chordotonal organ clearly responded to vibratory stimulation. Furthermore, we found that a pair of large subapical emergent dorsal setae, which had been deemed mechanosensory by previous authors, are not so. In turn, four ventral subapical trichobothria that are in direct contact with the water surface during locomotion, proved to be mechanosensory. The anatomical and ultrastructural observations support these electro-physiological results.     

Partitioning of transpiratory water loss of the desert scorpion, Hadrurus arizonensis (Iuridae)

Terrestrial arthropods lose body water to the environment mainly through transpiration. The aim of this study was to determine the fraction of respiratory losses from total transpiratory water loss in scorpions, as relatively high respiratory losses would indicate a fitness benefit from regulation of gas-exchange rate under stressful desiccating conditions. We measured metabolic rates and water-loss rates of Hadrurus arizonensis (Iuridae) at a range of ecologically-relevant temperatures. Calculation of respiratory water losses was based on increased metabolic and water-loss rates during nocturnal activity (assuming no change in cuticular resistance at a given constant experimental temperature). Respiratory losses accounted for 9.0 ± 1.7% of total transpiratory losses at 25 °C, doubled to 17.9 ± 1.8% at 30 °C and increased to 31.0 ± 2.0% at 35 °C (n = 5, 15 and 15, respectively). Furthermore, the relative importance of respiratory transpiration is likely to be higher at temperatures above 35 °C, which have been recorded even within the burrows of H. arizonensis. Measurements of cuticular lipid melting points do not provide evidence for increased cuticular resistance to water loss at higher temperatures. However, the relatively high fraction of respiratory water losses reported here for H. arizonensis supports the notion of respiratory regulation as an evolved mechanism for conserving scorpion body water stores under stressful conditions.     

Comparisons of egg incubation and hatchling traits among captive cohorts of the Chinese three-keeled pond turtle, Chinemys reevesii

Freshly-laid eggs of the Chinese three-keeled pond turtle (Chinemys reevesii) from captive cohorts in Hunan, Shanghai and Jiangxi were incubated at four constant temperatures of 24, 26, 28 and 30 °C to assess the effects of incubation temperature and cohort origin on incubation duration and hatchling phenotypes. Eggs from the three cohorts differed in size and shape. Egg mass and width were greatest in the Hunan cohort, smallest in the Jiangxi cohort, with the Shanghai cohort in between. Incubation duration decreased with increasing temperature and differed among the cohorts, with longer incubation duration for eggs from the Jiangxi cohort than those from the Hunan or Shanghai cohorts. Incubation temperatures significantly affected hatchling size and hatchlings from 30 °C were smaller than those from the lower temperatures in terms of carapace size and body mass. When incubated at a common temperature, hatchlings from the Hunan and Shanghai cohorts were larger than those from the Jiangxi cohort. The swimming capacity of hatchlings was affected by incubation temperature, but did not differ among the cohorts. The characteristics of eggs and hatchlings were similar among the Hunan and Shanghai cohorts, but they differed significantly from the Jiangxi cohort.     

Energy and water use by invasive goats (Capra hircus) in an Australian rangeland, and a caution against using broad-scale allometry to predict species-specific requirements

Feral goats (Capra hircus) are ubiquitous across much of Australia's arid and semi-arid rangelands, where they compete with domestic stock, contribute to grazing pressure on fragile ecosystems, and have been implicated in the decline of several native marsupial herbivores. Understanding the success of feral goats in Australia may provide insights into management strategies for this and other invasive herbivores. It has been suggested that frugal use of energy and water contributes to the success of feral goats in Australia, but data on the energy and water use of free-ranging animals are lacking. We measured the field metabolic rate and water turnover rate of pregnant and non-pregnant feral goats in an Australian rangeland during late summer (dry season). Field metabolic rate of pregnant goats (601 ± 37 kJ kg^− 0.73 d^− 1) was 1.3 times that of non-pregnant goats (456 ± 24 kJ kg^− 0.73 d^− 1). The water turnover rate of pregnant goats (228 ± 18 mL kg^− 0.79 d^− 1) was also 1.3 times that of non-pregnant goats (173 ± 18 kg^− 0.79 d^− 1), but the difference was not significant (P = 0.07). There was no significant difference in estimated dry matter digestibility between pregnant and non-pregnant goats (mean ca. 58%), blood or urine osmolality, or urine electrolyte concentrations, indicating they were probably eating similar diets and were able to maintain osmohomeostasis. Overall, the metabolic and hygric physiology of non-pregnant goats conformed statistically to the predictions for non-marine, non-reproductive placental mammals according to both conventional and phylogenetically independent analyses. That was despite the field metabolic rate and estimated dry matter intake of non-pregnant goats being only 60% of the predicted level. We suggest that general allometric analyses predict the range of adaptive possibilities for mammals, but that specific adaptations, as present in goats, result in ecologically significant departures from the average allometric curve. In the case of goats in the arid Australian rangelands, predictions from the allometric regression would overestimate their grazing pressure by about 40% with implications for the predicted impact on their local ecology.     

Comparative studies on the biology of nerita atramentosa Reeve, bembicium nanum (Lamarck) and cellana tramoserica (Sowerby) (gastropoda: Prosobranchia) in S.E. Australia

Populations of three coexisting intertidal gastropods, Nerita atramentosa Reeve, Bembicium nanum (Lamarck) and Cellana tramoserica (Sowerby), were sampled from a shore in Botany Bay, New South Wales, from July 1972 to September 1973. The recruitment and growth rates of each species were analysed from size frequency distributions. Mortality of each age cohort, and longevity, were estimated from analyses of the densities of Nerita atramentosa and Bembicium nanum.Nerita atramentosa showed no significant mortality during the first two years on the shore, but high mortality (at an instantaneous rate of 0.084 deaths/individual/month) after reaching the age of reproductive maturity, which was 20 months from settlement and at a mean shell-length of 13.5 mm. No growth could be detected after reproductive maturity was reached. Longevity of N. atramentosa was estimated as 3–5.5 years. Bembicium nanum juveniles showed higher mortality (at an instantaneous rate of 0.233 deaths/individual/month) than reproductively mature animals (0.060 deaths/individual/month). Reproductive maturity was reached at a mean shell-breadth of 11.0mm, i.e., about ten months after settlement on the shore. Longevity was estimated as from 4–8 years. Cellana tramoserica showed different growth patterns depending on the time of settlement.The three species showed different patterns of growth and life history relating to variable recruitment (which was demonstrated in all three species) and different rates of mortality of age cohorts.