Predator-induced life-history shifts in a freshwater snail

The snail Physella virgata virgata, a widely distributed freshwater pulmonate, was observed to change its life-history characteristics in the presence of the crayfish Orconectes virilis in spring-fed Oklahoma streams. These changes were apparently initiated by a water-borne cue released when crayfish fed on conspecific snails. In the presence of the cue, snails exhibited rapid growth rates and little reproduction until they reached a size of about 10 mm after 8 months. In the absence of the cue, snails typically grew to about 4 mm (3.5 months) and then began reproduction. The chemically inducible shift indicates that the life histories of these snails are phenotypically plastic. By increasing the variance associated with size and age of maturity, prey may increase the likelihood of coexisting with seasonal predators.     

Reduced competition and altered feeding behavior among marine snails after a mass extinction

Extinction may alter competitive interactions among surviving species, affecting their subsequent recovery and evolution, but these processes remain poorly understood. Analysis of predation traces produced by shell-drilling muricid snails on bivalve prey reveals that species interactions were substantially different before and after a Plio-Pleistocene mass extinction in the western Atlantic. Muricids edge- and wall-drilled their prey in the Pliocene, but Pleistocene and Recent snails attacked prey only through the shell wall. Experiments with living animals suggest that intense competition induces muricid snails to attack shell edges. Pliocene predators, therefore, probably competed for resources more intensely than their post-extinction counterparts.     

Calcareous septa formed in snail shells by larvae of snail-killing flies

Larvae of 13 species of Pherbellia and Colobaea that feed in exposed aquatic snails uitilize a product of the Malpighian tubules before they pupate to form a plate-like structure within the shell or to reinforce the anterior end of the puparium. The substance is partly calcium carbonate, and carbonic anhydrase may be involved in its production.     

Polymorphism and Population Density in the African Land Snail, Limicolaria martensiana

In natural populations of the African land snail, Limicolaria martensiana, the degree of polymorphism in color and pattern may vary with the density of the population. This could occur because predators eat the snails selectively and use past experience as a guide in finding further prey. Hence contrasting color forms may be at an advantage in dense populations where predators would have ample opportunity to learn to recognize prey.     

Ecological genetics and natural selection in molluscs

Polymorphic snails of the genus Cepaea have been widely used for research in ecological genetics. Natural selection by selective predation is important in controlling morph frequencies in some populations of C. nemoralis in England. The importance of environmental selection in affecting other patterns of local genetic differentiation of population structure (area effects) is a matter of controversy. Some authors emphasize divergent evolution of whole gene pools between area effects, while others feel that climatic selection acting on individual loci is important. Analysis of 500,000 C. nemoralis snails from throughout Europe shows that there is a strong positive association between gene frequencies at the shell color locus and mean summer temperature, but that no climatic correlations are obvious at other loci. Another species, C. vindobonensis, which has a much simpler system of polymorphism than does C. nemoralis, was investigated in Yugoslavia, in a region where there is known to be intense microclimatic differentiation because of the accumulation of cold air in frost hollows. There was a striking tendency for snails with lightly pigmented shell bands to be found in places with a warm microclimate. Physiological and behavioral experiments demonstrate that this is due primarily to differential energy absorption from sunshine by the different shell phenotypes. As in C. nemoralis, other C. vindobonensis phenotypes show no detectable association with the environment. It is possible that genes whose frequencies cannot be related to environmental selection may have evolved strong linkage interactions with other genes in the population's gene pool. Selection by the ecological environment and the genetic environment may therefore both be important in controlling the genetic structure of snail populations.     

高山薄壳田螺的引种试验

于2010年3月选用浙江省庆元县合湖乡高山薄壳田螺15 kg,引种放养在杭州市余杭区仁和镇,经18个月养殖,测量其基本性状。与合湖乡田螺相比,其壳质变厚明显,繁殖能力有所增强,生长速度较快,但幼螺死亡明显增多,产量不高。因此认为,高山薄壳田螺是高山地区特殊的地理位置及气候条件形成的,并不适合引种到平原地区。     

16种植物对福寿螺的趋避效果研究

于实验室内通过自制的八边形分室趋避试验装置观察研究了16种植物对福寿螺(Ampullaria gigas Spix)的趋避效果。结果表明:福寿螺具有沿壁爬行的偏好性,沿壁爬行的福寿螺数量平均为非沿壁爬行福寿螺数的3.77倍。同时发现,在所选的16种植物中,白千层(Melaleuca leucadendra L.)、扶桑(Hibiscus rosa-sinensis L.)2种植物对福寿螺有较大的吸引作用;金叶假连翘(Duranta repens cv.Dwarf Yellow)、木麻黄(Casuarina equisetifolia L.)、红龙草(Alternanthera dentata cv.Ruliginosa)、鸭脚木〔Schefflera octophylla(Lour.)Harms〕、剑麻(Agave Sisalana Perrine)5种植物对福寿螺有一定的驱赶作用。     

几种农业防控稻田福寿螺措施的效果评价

为了探寻有效防控稻田福寿螺的农业措施,对几种常用的农业防控稻田福寿螺措施进行了对比试验。结果表明,人工拾螺摘卵与设网拦截相结合和水旱轮作与设网拦截相结合两种农业防控措施对稻田福寿螺的防治效果以及经济效益均显著高于其他农业防螺措施。     

油茶枯饼抑螺的可行性分析

油茶枯饼是油茶提油后的主要副产物,加强其综合利用,是提高油茶产业整体经济效益的有效手段之一.通过分析钉螺的生活习性和危害性、当前常用灭螺药物的种类和使用剂量及灭螺机理,具有针对性的提出油茶枯饼作为植物杀螺药物的成分组成、资源现状、价格等优势.     

茶皂素对不同发育阶段福寿螺生长的影响

[目的]明确茶皂素胁迫对不同发育阶段福寿螺生长的影响,为研究茶皂素对福寿螺的作用机理奠定基础.[方法]在福寿螺的螺苗期、仔螺期和中螺期分别用茶皂素两种汰选浓度(LC25、LC50)进行处理,考查其存活率、体重增长率、体重抑制率.[结果]不同发育阶段的福寿螺在两种茶皂素汰选浓度处理后存活率较对照下降了6.2%~22.5%,最大体重抑制为11.69%~49.55%,对福寿螺体重抑制率达到最大值的时间为处理后10~40 d,其中存活率下降幅度、体重抑制率均以螺苗期处理的最大.[结论]茶皂素对福寿螺螺苗、仔螺、中螺的生长均有一定的抑制作用,其作用强度受茶皂素的汰选压力及福寿螺发育阶段的影响.     

不同控螺方式下稻田福寿螺种群的螺级结构及性比

【目的】研究福寿螺种群的结构,为了解其数量动态、发展趋势和评价福寿螺的控制效果等提供科学依据。【方法】在广东省双季稻种植区设置12个面积为100 m2的试验小区,对稻田养鸭、施杀螺剂和施茶籽饼这3种控螺方式下福寿螺种群的螺级结构及性比进行分析,并与未采取控螺措施的空白区进行对比。【结果】施杀螺剂可有效地控制稻田福寿螺幼螺的数量,但不利于对成螺的控制;施茶籽饼可有效地控制苗螺,但对中螺和成螺的控制效果较差。与稻鸭区和空白区相比,施杀螺剂和茶籽饼处理区各螺级组配的比例随时间的推移呈现出较大的不稳定性,尤其是在早稻生长期间。对稻鸭区而言,福寿螺种群在早稻生长期间以成螺为主,整体上属于下降型种群,其控螺的效果优于晚稻田。福寿螺种群内的雌雄比随时间的推移而变化,在同一时间内,不同控螺方式下种群间雌雄比的差异也比较大。施螺药区和施茶籽饼区,福寿螺的雌雄比相对较高,随时间的推移呈现出较大变幅。【结论】稻鸭共作可对稻田福寿螺种群进行持续控制,且对幼螺和中螺具有较好的控效,但不论是早稻还是晚稻,在抽穗期赶鸭上田后,需根据田间的具体情况,配合其它措施以控制福寿螺种群在后期的繁殖和生长。     

植物狼毒大戟对钉螺及血吸虫毛蚴的影响

为了探讨植物狼毒大戟对钉螺及血吸虫毛蚴的影响,分别用大戟科大戟属狼毒大戟根的提取物1与提取物2液萃取物配制成的5.0,2.5,1.25,0.625,0.3125g/L的药液浸杀钉螺及血吸虫毛蚴,并测定了被浸杀钉螺体内糖原与蛋白质的含量,同时检测了该药对水生动物鱼的毒副作用。试验结果显示,狼毒大戟根水煮液在浓度为2.5g/L时经过24h,48h,72h浸杀钉螺的死亡率分别为：36.7%,66.7%,93.3%。而以70%乙醇提取液经过相同时间浸杀钉螺的死亡率分别为：43.3%,86.7%,96.7%。同时被狼毒大戟水煮液浸杀的钉螺体内糖原含量明显下降,减少幅度从9.61%到33.60%,表明狼毒大戟通过影响钉螺的能量代谢而抑制其生长。蛋白质的含量减少不显著。     

陕西省姜片吸虫病疫源地生物生长区的研究

本文报告陕西省姜片吸虫病疫源地生物生长区的研究。首先叙述和疫源地范围有关的宿主动物、中间宿主扁卷螺和病原体姜片吸虫的分布情况。然后对疫源地范围内姜片吸虫病流行过程的特点进行了分析,追索到生物生长区的自然条件和社会条件上去。最后确定了陕西省姜片吸中病疫源地的界线。和其他疫病的疫源地一样,研究这一疫源地的范围也取决于地理屏障和疫病流行过程的特点两方面。汉中地区的地形、水文、温度和湿度决定了扁卷螺在该地区可以越冬,因而可以形成攀生地多决定了扁卷螺在该地区的季节动态和猪姜片吸虫病的季节动态,亦即流行过程的季节性特点;包括姜片吸虫虫卵从四月份开始发育,五月份起开始有毛勤,在水内感染扁卷螺,六月.份起扁卷螺内开始发现自然感染,七月至九月份水草上囊勤集结最多,八月至十月份是一猪姜片吸虫严重感染时期。安康专区由于社会因素无姜片吸虫病的存在。陕西省姜片吸虫病疫源地的范围相当于陕西省省级自然区划的陕南秦岭山地地区,落歼阔叶与常绿阔叶混交林黄褐土和棕褐土地带IA:南秦岭中山省的汉中专区部分。疫源地的界线如下: (1)北部界线,佛坪、留坝一线以秦岭高山区为地理屏障.(2)南部界线:镇巴、宁强一线,以甲山山脉为地理屏障。 (3)东部界线:相当于安康专区宁陕、石泉、紫阳各县的西部县界。 (4)西部界线:暂定以陕西东部和甘肃省接界处为界线,等待今后甘肃陇南姜片吸虫病的调查工作资料来加以证实或修正.     

陕西省姜片吸虫病疫源地媒介动物的究研(Ⅱ)扁卷螺的生态

<正> 根据家畜疫源地理论,作为疫源地要素之一的媒介动物的研究包括研究(1)媒介动物和寄生物之间的矛盾,(2)媒介动物和外界环境之间的矛盾以及(3)媒介动物体内的寄生物和外界环境之间的矛盾。陕西省姜片吸虫病疫源地媒介动物的研究已在中间宿主的确定一文中,以及部分地在病原的研究一文中作过报导。这些报导都涉及到上述媒介动物和寄生物之间的矛盾范围内。关于上述(2)(3)的矛盾研究,将在本文内提出。这些都属于媒介动物扁卷螺生态学研究的性质。1962—1963年我们在陕西     

Tracing food webs with stable hydrogen isotopes

The hydrogen isotopic content of an animal's food, not water, determines that animal's hydrogen isotopic content. Liver and muscle tissue from mice reared on a diet such that the ratio of deuterium to hydrogen (DIH) of their food and water was kept constant, have the same average D/H ratio as the food source. In a simple, natural population of snails and their possible algal diets, Littorina obtusata (northern Atlantic intertidal snails that feed almost exclusively on the brown alga Fucus vesiculosus) has the same D/H ratio as Fucus vesiculosis and not that of the other algae available to the snails.     

Larval trematodes: double infections in common mud-flat snail

Larvae of the trematode Zoogonus lasius are involved in most double infections of Nassarius obsoleta. The two most common trematode parasites of this snail do not occur together in double infections. Double infections were found in 14 of 340 infected snails in a total sample of 5025 snails.     

湖北省荆州太湖港河滩感染性钉螺及水体感染性的调查

为了解荆州太湖港河滩感染性钉螺及其水体感染性情况,在湖北省荆州太湖港河滩于5-11月用棋盘式系统抽样法逐月采集钉螺,以压碎法鉴别捕获钉螺的感染性;以哨鼠法逐月测定滩内及周围水体的感染性.调查结果表明,太湖港河滩上5-11月感染性钉螺显著,但以6-8月钉螺阳性率最高.太湖港河水6-8月感染性显著.调查结果显示.在湖北省荆州太湖港感染性钉螺滩块附近接触疫水是感染血吸虫的最危险因素,其中以6-8月危险性最大.     

文心兰设施栽培中蜗牛和蛞蝓为害规律及综合防治

介绍了海南文心兰设施栽培中蜗牛和蛞蝓的种类、发生及为害规律,并提出以物理隔离法(水碗法、矿泉水瓶法)为主,辅以毒饵诱杀、药剂防治、农业防治和生物防治等措施相结合的综合防治技术.     

基于GIS的广东地区福寿螺的潜在时空分布及对稻田的危害风险

利用GIS技术,结合福寿螺生长发育的特点和广东地区水稻的种植分布情况,预测福寿螺在广东地区的潜在时空分布及其危害风险.结果表明:广东地区存在5种福寿螺潜在生境,分别是:螺和卵都能存活且卵能孵化螺能发育;螺卵存活、螺能发育但卵不孵化;螺存活但不发育、卵不孵化;螺冬眠且不产卵;螺、卵均不能存活.5种生境从南到北依次排列,并且分布范围随着季节的变化而变化.福寿螺适宜生境夏季分布广、冬季分布窄,夏季向北扩展,冬季向南收缩.冬季粤北山区小部分地区福寿螺不能存活,5—10月全省均适宜螺及其卵的生长发育.就潜在分布区而言,全省16.68%地区处于高度发生区,中度发生区也占54.25%.以稻田的危害风险为例,结合水稻分布区的状况评价了福寿螺可能带来的危害风险等级,其中重度风险区占全省面积的21.75%,主要集中于湛江、茂名、阳江等地的稻区;中度风险区集中在广东中部的水稻区,占63.16%;轻度风险区只占14.47%.