Larval hatching in the horseshoe crab, Limulus polyphemus: facilitation by environmental cues

Female horseshoe crabs, Limulus polyphemus (Linnaeus), lay their eggs in nests on sandy beaches near the high water line. Embryos develop within the sand, hatch into trilobite larvae, and enter the water column when the nest is inundated. Given the diversity of tidal and shoreline inundation patterns that populations of L. polyphemus experience throughout their range (semidiurnal and diurnal tides, microtidal, and nontidal), hatching may also be facilitated by environmental triggers that serve to synchronize hatching and larval emergence with periods of high water. The objective of this study was to determine if larval hatching in L. polyphemus is triggered or facilitated by environmental cues. Stage 21 embryos were subjected to one of seven different treatments that simulated conditions experienced during inundation: (1) hydration, (2) agitation, (3) hydration and agitation, (4) hydration and agitation with sand, (5) osmotic shock, (6) terrestrial hypoxia, and (7) aquatic hypoxia. Hatching rates increased significantly under all simulated tidal conditions compared to controls and were highest (96%) for eggs simultaneously exposed to both hydration and agitation with sand. Measurements of the osmolarity of the perivitelline fluid of developing eggs collected from the field indicated that it is hyperosmotic to the ambient seawater and porewater. Thus, when inundated, eggs also experience a hypoosmotic shock, which would likely facilitate hatching by causing the eggs to swell, rupturing the egg membrane and thereby increasing the likelihood that larvae would hatch and enter the water column during periods of high water.     

Effects of sodium chloride, formalin and iodine on the hatching success of common carp, Cyprinus carpio, eggs

Saprolegniales are ubiquitous in natural water supplies of fish hatcheries, and often cause serious disease problems. Sodium chloride, formalin and iodine, administered twice a day as a flush at different concentrations, were tested on infected eggs of common carp, Cyprinus carpio, to evaluate their antifungal activity and effect on hatching rates. Sodium chloride at 35 000 mg L^?1 and formalin at 400 mg L^?1 were found to be most effective in controlling Saprolegnia sp., with 85.4 and 91.8% hatching rates, respectively. Iodine increased the hatching rate by 27% at 200 mg L^?1 (P < 0.05). There were infections on eggs exposed to all levels of iodine, but not on eggs treated with sodium chloride and formalin. Sodium chloride and formalin were more effective than iodine in controlling Saprolegnia. Sodium chloride is a safe, efficacious and economical treatment of Saprolegniosis and is therefore recommended for treating common carp eggs.     

A Laboratory Investigation of the Suspension,Transport, and Settling of Silver Carp Eggs Using Synthetic Surrogates

Asian carp eggs are semi-buoyant and must remain suspended in the water to survive, supported by the turbulence of the flow, until they hatch and develop the ability to swim. Analysis of the transport and dispersal patterns of Asian carp eggs will facilitate the development and implementation of control strategies to target the early life stages. Experimenting with Asian carp eggs is complicated due to practical issues of obtaining eggs in close proximity to experimental facilities and extensive handling of eggs tends to damage them. Herein, we describe laboratory experiments using styrene beads (4.85 mm diameter) as synthetic surrogate eggs to mimic the physical properties of water-hardened silver carp eggs. The first set of experiments was completed in a rectangular vertical column filled with salt water. The salinity of the water was adjusted in an iterative fashion to obtain a close approximation of the fall velocity of the styrene beads to the mean fall velocity of silver carp water-hardened eggs. The terminal fall velocity of synthetic eggs was measured using an image processing method. The second set of experiments was performed in a temperature-controlled recirculatory flume with a sediment bed. The flume was filled with salt water, and synthetic eggs were allowed to drift under different flow conditions. Drifting behavior, suspension conditions, and settling characteristics of synthetic eggs were observed. At high velocities, eggs were suspended and distributed through the water column. Eggs that touched the sediment bed were re-entrained by the flow. Eggs saltated when they touched the bed, especially at moderate velocities and with a relatively flat bed. At lower velocities, some settling of the eggs was observed. With lower velocities and a flat bed, eggs were trapped near the walls of the flume. When bedforms were present, eggs were trapped in the lee of the bedforms in addition to being trapped near the flume walls. Results of this research study provide insights about transport, suspension, and dispersion of silver carp eggs. The knowledge gained from this study is useful to characterize the critical hydrodynamic conditions of the flow at which surrogates for silver carp water-hardened eggs settle out of suspension, and provides insight into how eggs may interact with riverbed sediments and morphology.     

海滨沙地单叶蔓荆匍匐茎对沙埋适应的生长对策

单叶蔓荆(Vitex trifolia var.simplicifoli)是一种耐盐、耐旱固沙地被植物。依据海滨沙地自然沙埋特点对单叶蔓荆匍匐茎进行了不同厚度(半埋和全埋)和不同长度交叉沙埋处理,研究探讨了单叶蔓荆沙埋适应生长对策,为其开发利用、科学管理和海滨环境修复提供指导。结果表明,正常情况下,单叶蔓荆匍匐茎基部和中部生长缓慢,顶部生长快。轻度(沙埋匍匐茎基部)和中度(沙埋匍匐茎基部和中部)半埋和全埋使匍匐茎顶部生长加速,茎长增长量较对照高出1.5到3.1倍;但重度(沙埋整个匍匐茎)半埋和全埋使匍匐茎顶部净增长量减少12%和13%。在20d沙埋中,对照整个匍匐茎各段均无不定根长出,但不同程度半埋和全埋沙埋处理下沙下匍匐茎上均长出不定根,重度半埋使不定根生长受抑;同时匍匐茎上各段茎生物量上升,枝叶生物量下降,且随着沙埋程度的增加而增减幅度提高,在重度半埋和全埋达到最大。在轻度和中度半埋和全埋下,匍匐茎上未沙埋部位枝条生长加速。研究表明,在自然环境中,单叶蔓荆匍匐茎顶端是一个对环境变化反应敏感的部位,并与沙埋后单叶蔓荆茎延伸生长和植株能否生存密切相关。当匍匐茎顶部没被沙埋时,沙埋促进沙埋部位匍匐茎和枝叶中物质转移,加速匍匐茎顶部快速生长和物质积累以弥补沙埋带来的损伤维持物质和能量的代谢平衡。沙埋后,单叶蔓荆以茎顶端快速生长、形成不定根、枝条生长维持茎水分平衡和能量和物质代谢平衡,以快速生长摆脱沙埋影响的生长方式为其对沙埋环境的重要适应对策。因此,在海岸沙地单叶蔓荆种群管理和维护中,在强风移沙引起的重度沙埋后,及时剥离匍匐茎顶部沙子对维护单叶蔓荆种群的延续生存和扩散均有重要作用。     

The reproductive success of pike, Esox lucius: aspects of fecundity, egg density and survival

Power-law relationships have been estimated between fecundity and fish length, weight and age for pike from two gravel pit lakes (Main Lake and St Peter's Lake) in Buckinghamshire, England. Relative fecundity, estimated at 17.6 eggs g⁻¹ for Main Lake pike and 19.4 g⁻¹ for St Peter's Lake pike, did not differ significantly between the lakes. Population fecundity for the Main Lake was estimated at 10.6 million eggs and 6.4 million eggs in 1986 and 1987, respectively.
Experimental work involving samples of eggs from 18 artificially fertilized Main Lake female pike showed a significant relationship between egg diameter and female length, and a significant difference between mean egg diameters for 41-cm and 101-cm females. No significant relationships were found between mean egg size and mean fry size, nor between fry length and adult length. Mean size differences between newly hatched, 18-day-old and 41-day-old fry from the 41-cm and 101-cm females were not significant.
Samples of eggs taken at 2-day intervals from 6 April to 5 May in a pike spawning area of the Main Lake revealed clumped distributions of eggs, with average egg densities ranging from 1 to 47 eggs per 0.071 m² (14–671 m ²) on sand and silt substrata. The maximum egg density of 51 per 0.071 m² (729 m⁻²) was found on flooded grass. The stages of development of the eggs were identified over the sampling period. Survival from stage 1 to fry was estimated at 3–6%. Egg losses were estimated at 9–10% day⁻¹.
Egg survival experiments gave overall hatching success rates of 11 % on sand/silt compared with 2.5% on aquatic plants (1986), and 18.9% on undisturbed sand/silt compared with 7.9% on disturbed sand/silt (1987). The effect of siltation on egg hatching is discussed.     

Patterns in the abundance,phenology, and hatching of the resting egg stage of the invasive zooplankter <Emphasis Type="Italic">Bythotrephes longimanus</Emphasis>: implications for establishment

To examine how dormancy contributes to the establishment and persistence of Bythotrephes longimanus, we investigated resting egg production and hatching in relation to the demography of the planktonic stage and environmental conditions in Island Lake Reservoir (USA). During a 3-year study, the largest contribution to the egg bank occurred in autumn and most eggs hatched in spring, but we also detected some resting egg production and hatching in summer. The difference between summer and late autumn densities of eggs in sediments averaged 47% (range 0–98%) for 18 sites throughout the reservoir, which was similar to experimental estimates of in situ hatching fraction of 67% for eggs in the spring and summer following their production. Based on emergence traps, neonates hatch in the field during May and June. We estimated mortality rates of 64% for resting eggs and embryos, and 59% for newly emerged neonates. Although hatching fraction saturated at the same level, eggs incubated offshore hatched later than those nearshore where water temperature was warmer and light was detectable at the sediment surface. Low dissolved oxygen concentration did not significantly reduce hatching fraction but resulted in some eggs that initiated development but failed to hatch. Collectively, our results demonstrate substantial annual turnover in the resting egg bank of B. longimanus and high mortality of resting eggs during recruitment from the egg to the first molt of the planktonic stage. These patterns suggest that propagule pressure in the form of resting eggs requires large numbers for establishment, and that considerable post-establishment resting egg production is necessary for inter-annual persistence.     

鲫鱼的人工和天然雌核发育

用照射处理的草鱼或华南鲤的精液授精的鲫鱼卵为单倍体雌核发育;所有单倍体胚胎都是畸形,并在孵化前死亡。如果用照射精液授精的鲫鱼卵在18—19℃的水中放置2分钟,然后在0—3℃的冰水中放置20分钟,再放回室温水中孵化,可以从每百颗受精卵中得到4.5—11.9(平均8.34)尾成活的二倍体仔鱼。根据38尾银鲫(其中33尾捕自黑龙江省方正县双凤水库)的细胞学和胚胎学检查,证实它们是雌核发育繁殖的。       

小叶锦鸡儿幼苗对沙埋的生态适应和生理响应

以中国半干旱地区固定、半固定沙地分布最广泛的灌木种之一小叶锦鸡儿(Caragana microphylla)为对象,于2010～2011年在内蒙古科尔沁沙地测定了不同深度沙埋下其幼苗的存活率、株高、渗透调节物质含量、保护酶活性和膜透性变化,探讨小叶锦鸡儿对沙埋的生理响应特征。结果显示:(1)与对照相比,当沙埋深度为小叶锦鸡儿幼苗株高的25%～75%时,存活率差异不显著;当沙埋深度为50%～75%时其存活率增加,但株高明显下降,沙埋对其生长具有抑制作用;当沙埋达到其株高100%时幼苗全部死亡。(2)不同沙埋深度对小叶锦鸡儿幼苗叶片细胞膜透性无显著影响,对沙埋深度为其株高25%时,叶片含水量增加,MDA含量下降,POD活性增强,细胞膜未受到伤害;沙埋深度为其株高50%～75%时,叶片含水量下降,MDA含量增加,但SOD和POD对细胞膜起到了协同保护作用,细胞膜也未受到损伤;沙埋深度为株高25%～75%情况下,细胞膜未受到损伤,可溶性糖和脯氨酸含量变化不明显。研究认为:小叶锦鸡儿幼苗只能耐受部分沙埋,完全沙埋则会导致其幼苗全部死亡,沙埋胁迫下可溶性糖和脯氨酸等渗透调节物质含量反应迟缓可能是其耐沙埋能力较弱的主要生理原因之一。     

Resource allocation in the submerged plant Vallisneria natans related to sediment type, rather than water-column nutrients

1. Phenotypic plasticity in resource allocation by Vallisneria natans was investigated in a greenhouse experiment, using three types of sediment [sandy loam, clay, and a 50 : 50 (by volume) mixture of the two sediments] and two levels of water‐column nutrient. The clay was collected from a highly eutrophic lake in Jiangsu Province, China, and the N and P concentrations applied in nutrient media were at the upper limits observed in most lakes of China. 2. Growth and biomass allocation were significantly affected by sediment type, rather than water‐column nutrients. Plant growth in clay and the mixture were similar, and 2.4–3.4 times higher than that in sandy loam. Compared with the plants grown in clay or the mixed sediments, the plants grown in sandy loam allocated relatively more biomass to root (11–17% versus 7–8% of total biomass), and relatively less to leaf (76–82% versus 86–87% of total biomass). Plastic variations in root area were induced by sediment type alone (P < 0.05), whereas the impacts of sediment type and water‐column nutrients on leaf area were insignificant (P > 0.05). 3. Plant N and P concentrations were significantly affected by both sediment type and water‐column nutrients. Increased nutrient availability in the water column enhanced plant N concentration by 3.5–20.2%, and plant P concentration by 19.1–25.8%. 4. Biomass accumulation and plant nutrient concentration in plants grown in different sediment types and water‐column nutrients indicate that sediment type had more significant impacts on growth and N and P concentrations of V. natans than did water‐column nutrients. Changes in phenotype are a functional response to nutrient availability in sediment, rather than to water‐column nutrients.     

Caryopsis germination and seedling emergence in an inland dune dominant grass Leymus secalinus

Leymus secalinus (Georg.) Tzvel. (Poaceae) is a dominant sand dune grass inhabiting the Mu-Us Sandland, semiarid China. Freshly harvested caryopses (seeds) are in non-deep physiological dormancy (non-deep PD) because of low percentage and slow rate of germination. Experiments were conducted to examine the effects of temperature, cold stratification, caryopsis coat scarification or partial removal of endosperm and sand burial on caryopsis dormancy, germination and seedling emergence. Caryopsis germination was significantly influenced by duration of cold stratification, temperature and their interactions. After 8 weeks of cold stratification, caryopsis germination percentage at 30 °C reached to 90%, equally in light or darkness. Rate and percentages of germination were also hastened and increased by scarifying the caryopsis coat or by artificial removal of different proportions of the endosperm. However, seedling developmental characteristics were significantly influenced by the proportion of the endosperm that remained in the caryopses. Seedling emergence, caryopsis germination and enforced dormancy in sand were significantly affected by sand burial depth. As sand burial depth increased, caryopsis germination and seedling emergence decreased whereas caryopsis enforced dormancy increased. 1–2 cm was the optimal depths for caryopses germination and seedling emergence. Although there were still 30% caryopses germinated at 8 cm, the maximal burial depth for seedling emergence was only 4 cm. The partial germination strategy regulated by non-deep PD, temperature and sand burial ensures that only a few caryopses germinated each time and may reduce risks for seedling survival.     

Bioturbation as Driver of Zooplankton Recruitment,Biodiversity and Community Composition in Aquatic Ecosystems

In an experimental study we assessed if benthic bioturbating invertebrates affect the recruitment (hatching) of zooplankton from the sediment, and if this effect persists as differences in the zooplankton community in the water column, that is, if bioturbation quantitatively stimulates benthic–pelagic coupling. We investigated the effects of four different benthic invertebrates (Asellus aquaticus, Chironomus plumosus, Tubifex tubifex in the presence or absence of the predator Sialis lutaria). In total, 45 zooplankton taxa hatched from the sediment and the hatching success of some of these was dependent on the species identity of the bioturbating invertebrate. The predator Sialis reduced the abundance of all three invertebrate species, but tended to positively influence the zooplankton recruitment rates, possibly through increasing the activity of the bioturbating invertebrates. The most striking effect of bioturbation on the hatching and pelagic zooplankton community properties was that, on average, 11% more species hatched in the Asellus treatment than in any other treatment. This was also mirrored in the zooplankton water column community where, on average, 7% more species established a viable population in treatments with Asellus as bioturbator. In a complementary field survey, Asellus was more common in littoral than in profundal sediments. Because Asellus strongly affected recruitment of zooplankton in our experiment, we argue that bioturbation may partly explain why recruitment of resting stages of both phyto- and zooplankton is generally higher in littoral than in profundal areas.     

臭氧与氯对水蚤卵的孵化效应研究

水蚤是多种人体寄生虫的中间宿主,自来水厂常用臭氧和氯灭杀水蚤.本文研究了臭氧和氯以及氯在不同pH值水体中抑制水蚤卵孵化的效应浓度.结果表明:①各臭氧处理组(1～6 mg/L)中水蚤卵的孵化率(89.52％～97.85％)明显高于对照组(76.19％),臭氧对水蚤卵无灭活作用;②氯处理组(1～5 rg/L)中水蚤卵的孵化率为66.67％ ～ 96.00％,其中80％样品高于实验组的孵化率(78％),氯对水蚤卵无灭活作用;③在偏酸或偏碱的水体环境(pH5～6,pH9),随氯浓度增加,对其孵化率有极显著的抑制作用;④臭氧与氯对水蚤成体的灭活率达90％以上.经分析认为,自来水厂水池中的水蚤来源于原水以及炭滤池、砂滤池水内死水蚤受精卵的孵化,是净水厂反复发生水蚤的主要原因.提出利用臭氧或氯有效控制水蚤发生的处理技术.本研究在净水处理工艺中控制水蚤孳生方面具有实际应用价值与指导意义.     

Effects of sand burial on survival, growth, gas exchange and biomass allocation of Ulmus pumila seedlings in the Hunshandak Sandland, China

BACKGROUND AND AIMS: In the last decade, the number of young plants of Ulmus pumila in the Hunshandak Sandland has decreased sharply because of severe sand burial, and their ecological protective function has been weakened. In order to develop an understanding of the tolerance of U. pumila to sand burial and to suggest reasonable measures to protect the sparse-elm-grassland ecosystem, the effects of burial on the survival, growth, photosynthesis and biomass allocation in U. pumila were studied. METHODS: Seedlings were buried at five different depths in pot experiments: no burial (control), partial burial (33 % and 67 % stem height), and complete burial (100 % and 133 % stem height). Growth analyses and measurements of photosynthesis were carried after the plants had been uncovered. KEY RESULTS: All the plants survived partial burial, but about 30 % and 80 % of the seedlings died as a result of the 100 % and 133 % sand burial treatments, respectively. The numbers of newly produced leaves and branches, and the height of the stems of the seedlings in the 33 % and 67 % burial treatments during the period of the experiment were significantly greater than those in the control. Furthermore, net photosynthetic rate, transpiration rate and water use efficiency were also elevated by the partial burial, but not affected by burial time. This might be attributed to the increased root length, which improved water acquisition. The biomass and biomass allocation of the seedlings were significantly changed by the burial treatments and burial times. The biomass was enhanced by partial burial but was reduced by complete burial at each burial time. However, the biomass allocation was not significantly changed by the 33 % and 67 % sand burial treatments 2 or 4 weeks following the burial. CONCLUSIONS: Ulmus pumila was shown to be tolerant to partial sand burial, but must be protected from complete burial.     

水沙条件及氮输入对黄河口滨岸潮滩湿地碱蓬和土壤15N吸收特征的影响

受自然及人为活动的影响,黄河三角洲水沙条件存在较大变化,由此带来的外源营养物质增加对潮滩湿地植被生长及元素吸收利用具有重要的影响。为此采用3因素4水平的正交试验,以黄河口滨岸潮滩湿地先锋物种碱蓬（Suaeda salsa）为研究对象,利用¹⁵N示踪技术,研究了水沙条件及氮输入对碱蓬和土壤¹⁵N吸收特征的影响。结果表明：淹水深度、泥沙沉积及氮输入对土壤全氮含量的影响不显著,但外源氮输入对土壤¹⁵N固持量（N_dff）和比例（N_dff%）的影响达到显著水平,且最大值（10.44 mg/kg和3.83%）均出现在W₄S₂N₃（30 cm淹水+3 cm泥沙沉积+6 g/m²氮输入）处理;碱蓬叶和茎中全氮含量、¹⁵N吸收量（N_dff）及比例（N_dff%）在深淹水和泥沙沉积处理时较大,而根中全氮含量、N_dff及N_dff%在高氮输入较大。且根N_dff和N_dff%最大值（1.10 mg/kg和18.21%）在W₁S₄N₄（2 cm淹水+12 cm泥沙沉积+9 g/m²氮输入）处理时取得,此时碱蓬的生长情况最好,表明适当的淹水和泥沙埋深以及高氮输入（9 g/m²）有利于根系对外源氮的吸收,从而促进植株的生长。由此可见,在黄河三角洲水沙变化大的背景下,淹水、泥沙沉积和外源氮输入的适当把控,可促进碱蓬对外源氮的吸收利用而有助于其生长,从而对维护黄河三角洲潮滩湿地的健康具有重要作用。     

一种优良淡水鱼——团头鲂(Megalobrama amblycephala)的繁殖和饲养

团头鲂原是一种野生的草食性淡水鱼类,从1960年起对它进行了一系列的观察试验,肯定它有以下六个优点:(1)在池养条件下,性腺能发育成熟;(2)以各种草类为主要食料;(3)抗病力强、成活率高;(4)容易捕捞、起水率高;(5)含肉量高,脂多、味美;(6)一年半可长至商品规格。试验结果证明团头鲂可以作为新的养殖对象,同时也提供了一套繁殖、饲养管理方法。1964年到1973年已有二十一个省市先后进行移殖饲养,有的已就地繁殖、推广。本文系历年试验和部分移殖经验的总结。       

Biology and management of grass carp (Ctenopharyngodon idella,Cyprinidae) for vegetation control: a North American perspective

Summary The grass carp is one of the largest members of the family Cyprinidae. In their native habitat, grass carp typically reach weights of 30–36 kg, but fish have been reported up to 181 kg. Successful reproduction is a function of temperature, age/size, and water conditions. Fish reach maturity when about 4 years old (4–5 kg). Spawning occurs when water temperature rises above 20°C. Because grass carp eggs are semipelagic, current during spawning is required to keep eggs in suspension while they incubate. In general, successful spawning takes place under rising water conditions in very long rivers. Fecundity is very high in normal diploid individuals; females may produce over one million eggs in a season. In triploid fish, eggs and sperm are produced, but the incidence of viable offspring (even when mated with diploids) is very low.Grass carp fry begin feeding on microscopic animals and gradually switch to plant material as they grow. Adult diploids, triploids, and hybrids ( grass carp x bighead carp (Hypophthalmichthys nobilis, Cyprinidae)) are all herbivorous. Feeding is strongly affected by temperature. Active feeding begins as temperatures rise above 7–8°C and consumption peaks at 20–26°C. Whereas triploids feed at nearly the same rate as diploids, hybrids feed at substantially lower rates. Therefore, vegetation control is most efficiently achieved with diploid or triploid fish. These fish may consume more than their own weight in plant material each day. However, feeding rate (and hence vegetation control) is affected by the forage that is available. Grass carp exhibit strong preferences for different macrophyte species depending on the aquatic system (i.e. the same plant species is not always the most preferred). Hydrilla verticillata and similar species are almost always among the most preferred species, and control or elimination is usually assured if adequate stocking densities are used. Vegetation control has been reported with stocking densities as low as six fish per vegetated ha.Grass carp currently appear to be the most effective biological control on aquatic vegetation. However, in order to avoid ecological disaster, care should be taken to limit their use to sterile forms and to prevent their invasion of ecologically sensitive areas, such as waterfowl staging areas and threatened or endangered species habitat.     

Desert locusts <Emphasis Type="Italic">Schistocerca gregaria</Emphasis> (Acrididae: Orthoptera) do not lay eggs in old sand: Why?

Schistocerca gregaria sometimes refuse to lay eggs into the “old sand” that is kept in their cages for several days. We investigated why they rejected the old sand for oviposition. Locusts exclusively laid eggs into new sand when presented together with old sand, indicating that the old sand contained an oviposition-inhibiting (OI) factor. We examined whether this factor was derived from locust feces or fed grass (Bromus catharticus). Locusts laid all eggs into the sand with grass when presented together with sand containing feces. In contrast, few eggs were laid into the sand with grass when clean sand was offered at the same time, suggesting that the OI factor originated from the grass and was concentrated in the feces. The OI factor was efficiently extracted from feces with water compared with ethanol and acetone. OI activity was detected by extraction of feces with water for 1 min, although a longer extraction time yielded higher activity. The water extract of feces retained OI activity after boiling. None of the eggs which were buried in sand containing fecal extract hatched, whereas most of the eggs buried in clean sand or sand containing grass extract hatched, showing a correlation between OI activity and a lethal effect on eggs.     

Resistance to freezing temperatures in Aedes (Ochlerotatus) albifasciatus (Macquart) eggs (Diptera: Culicidae) from two different climatic regions of Argentina

Aedes (Ochlerotatus) albifasciatus (Macquart) has the capacity to proliferate in different kinds of climates within its distribution range in South America. With the aim of studying local thermal adaptations of eggs, we exposed egg stocks from two climatically different localities: temperate humid pampa (Buenos Aires) and cold arid Patagonian (Sarmiento), to freezing conditions and then evaluated the effect on some features at this level. First, we thermally described the substrate where this species lays its eggs in the arid region. A typical thermal condition during winter was 10 h at ?12° C. Second, we evaluated the effect of freezing on primary hatching (vs total hatching) and embryo survival. We also compared the proportion of embryonated eggs from both populations. The proportions of embryonated eggs were not different between localities, with averages of 78% and 83% in Sarmiento and Buenos Aires, respectively. Survival was equally successful after freezing in the two localities with an average range between 94–99%. Whether or not the eggs from Buenos Aires and Sarmiento were under freezing conditions, hatching was more than 98% after the first flooding. The results suggest that eggs of Ae. albifasciatus from Sarmiento and Buenos Aires have the same ability to survive at extreme temperatures (<0° C), showing a regional thermal adaptation rather than a local one.     

Location and timing of Asian carp spawning in the Lower Missouri River

We sampled for eggs of Asian carps, (bighead carp Hypophthalmichthys nobilis, silver carp H. molitrix, and grass carp Ctenopharyngodon idella) in 12 sites on the Lower Missouri River and in six tributaries from the months of May through July 2005 and May through June 2006 to examine the spatial and temporal dynamics of spawning activity. We categorized eggs into thirty developmental stages, but usually they could not be identified to species. We estimated spawning times and locations based on developmental stage, temperature dependent rate of development and water velocity. Spawning rate was higher in the daytime between 05:00 and 21:00 h than at night. Spawning was not limited to a few sites, as has been reported for the Yangtze River, where these fishes are native, but more eggs were spawned in areas of high sinuosity. We employ a sediment transport model to estimate vertical egg concentration profiles and total egg fluxes during spawning periods on the Missouri River. We did not identify substantial spawning activity within tributaries or at tributary confluences examined in this study.     

海岸单叶蔓荆沙埋胁迫下碳水化合物变化与其耐沙埋的关系

选择烟台海岸沙地抗沙埋强的单叶蔓荆(Vitex trifolia var.simplicifolia)为试材,在自然环境条件下根据单叶蔓荆匍匐茎长度进行了轻度(1/3茎长)、中度(2/3茎长)和重度半埋以及全埋处理。在沙埋20d后,测定了不同沙埋处理下匍匐茎各段上匍匐茎长度、枝条高度、不定根长度,以及可溶性糖、淀粉、纤维素含量,以探讨单叶蔓荆碳水化合物变化和转化在其耐沙埋中作用。结果显示,在轻度、中度半埋和全埋下单叶蔓荆匍匐茎长度均显著大于对照,被沙埋匍匐茎处有大量不定根生成;同时,可溶性糖和淀粉含量增高和纤维素含量下降,尤其是生长最快的匍匐茎顶部(如轻度半埋),茎中可溶性糖较低、淀粉增加最多,纤维素最低。但是被重度半埋和全埋的匍匐茎生长较少,茎中纤维素含量较多、淀粉含量较少。研究表明,沙埋是一种胁迫,它损伤叶片、扰乱碳水化合物代谢平衡。但它又是胁迫信号使植物产生适应性反应,它使未遭沙埋的匍匐茎顶端通过加速碳水化合物转化、分解纤维素、提高淀粉和可溶性糖含量,为顶端生长提供能量和营养,以加速匍匐茎快速生长摆脱沙埋。同时沙埋部位枝叶通过分解其纤维素,产生更多的可溶性糖和淀粉为匍匐茎不定根生长提供能量。因此,沙埋后匍匐茎内碳水化合物的转化是其快速生长和摆脱沙埋的能量来源而在其适应沙埋生长中起重要作用。单叶蔓荆对沙埋的适应性反应表现了其具有表型可塑性特性,该特性是其沙埋后维护匍匐茎顶部快速生长、不定根形成、碳水化合物转化以及具有较高抗沙埋能力的关键。