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1.
温度对三品系角突臂尾轮虫生活史策略的影响   总被引:15,自引:5,他引:10  
应用群体累积培养法 ,以浓度为 6 .0× 10 6cells/mL蛋白核小球藻 (Chlorellapyrenoidosa)为食物 ,研究了温度(2 0℃、2 5℃和 30℃ )对青岛、广州与芜湖等品系的角突臂尾轮虫 (BrachionusangularisGosse)的种群增长、个体大小和卵大小的影响。结果表明 ,温度对各品系轮虫的种群增长率和个体大小等均有显著影响。青岛品系和广州品系轮虫种群增长的最适温度分别为 30℃和 2 5℃ ,芜湖品系轮虫则在 30℃下不能生存。青岛品系和广州品系的种群增长率均与温度呈曲线相关 ,回归方程分别为 :Y =0 .0 0 0 9X2 - 0 .0 0 6 1X 0 .4 0 90和Y =- 0 .0 14 4X2 0 .74 12X - 8.375 1。各品系轮虫个体大小和卵大小均随温度的升高而呈现出下降趋势。在本研究的温度范围内 ,广州、青岛和芜湖各品系轮虫个体变异分别达 4 2 .90 %、14 .4 3%和 6 .2 3% ;2 0℃和 2 5℃下芜湖品系分别高出青岛品系达 74 .91%和87.98%。在温度和品系两因素中 ,品系对轮虫个体体积有较大的影响  相似文献   

2.
温度和食物浓度对三品系萼花臂尾轮虫实验种群动态的影响   总被引:15,自引:5,他引:10  
应用个体培养方法,研究了温度(20、25和30℃)和藻类食物浓度(1.5×10^6、3.0×10^6、6.0×10^6和9.0×10^6cells·ml^-1)对青岛、芜湖、广州三品系萼花臂尾轮虫种群动态的影响.结果表明,温度仅对轮虫的世代时间和种群内禀增长率有显著影响,而品系对所有生命表参数均无显著影响.轮虫种群的内禀增长率随培养温度的升高而增大,世代时间则随培养温度的升高而缩短.食物浓度仅对轮虫的生命期望值和平均寿命有显著影响,品系对轮虫的净生殖率、世代时间、生命期望值和平均寿命也有显著影响.三品系间,以广州品系轮虫的净生殖率、世代时间、生命期望值和平均寿命最大,芜湖品系最短.当食物浓度为3.0×10^6cells·ml^-1时,轮虫的生命期望值和平均寿命最长,9.0×10^6cells·ml^-1时最短.各品系轮虫的净生殖率、世代时间、总生殖率、生命期望值和平均寿命均随培养温度的升高而减小,广州品系的净生殖率除外.轮虫种群的内禀增长率和广州品系轮虫的总生殖率则随培养温度的升高而增大.青岛和广州品系轮虫的各生命表参数,均与食物浓度呈曲线相关,但芜湖品系仅世代时间、平均寿命和生命期望值随食物浓度的增大而缩短.  相似文献   

3.
葛雅丽  席贻龙 《生态学报》2011,31(11):3170-3179
应用单个体培养、聚丙烯酰胺凝胶垂直板电泳技术和特异性染色方法,以具有明显生化遗传差异的3克隆萼花臂尾轮虫(Brachionus calyciflorus)为对象,对长期(世代数大于200)和短期(世代数约为12)连续孤雌生殖后的轮虫进行了生活史特征和等位酶(PGM,GPI,MDH)分析。结果表明,除3克隆轮虫的生殖后期历时和每个雌体一生中所产的后代数在长期和短期连续孤雌生殖后的个体之间均无显著的差异外(P>0.05),其它生活史特征在长期和短期连续孤雌生殖后的个体之间的差异均因轮虫克隆的不同而异。克隆对轮虫的胚胎发育时间、幼体阶段历时、生殖期历时、平均寿命、轮虫每个雌体一生中所产的后代数、幼体大小和幼体的耐饥饿时间均有显著的影响(P<0.05);连续孤雌生殖历期对轮虫幼体阶段历时、平均寿命、后代混交雌体百分率和幼体的耐饥饿时间均有显著的影响(P<0.05);而克隆和连续孤雌生殖历期间的交互作用对轮虫的胚胎发育时间、生殖期历时、平均寿命、幼体大小和幼体的耐饥饿时间均有显著的影响(P<0.05)。长期连续孤雌生殖后的轮虫幼体阶段历时和幼体的耐饥饿时间均显著短于短期连续孤雌生殖后的轮虫,平均寿命显著长于短期连续孤雌生殖后的轮虫,后代混交雌体百分率显著高于短期连续孤雌生殖后的轮虫。3克隆轮虫在长期和短期连续孤雌生殖后其3种等位酶的酶谱均未出现明显的改变。  相似文献   

4.
三个地理品系萼花臂尾轮虫生活史特征的比较   总被引:3,自引:1,他引:2  
应用单个体培养方法 ,以浓度为 4 0× 10 6 cells ml的斜生栅藻 (Scenedesmusobliquus)为食物 ,在 30℃下 ,对采自广州、芜湖和青岛等地的萼花臂尾轮虫的生活史特征进行了比较研究。结果发现 ,三个地理品系的萼花臂尾轮虫除生殖前期历时无显著差异外 ,其生殖期历时、生殖后期历时、平均寿命和产卵量等均存在显著的差异。轮虫种群的内禀增长率、周限增长率和净生殖率均以芜湖品系最大 ,广州品系最小。这表明若要在 30℃下进行萼花臂尾轮虫的规模化生产 ,芜湖品系应是首选的最适品系  相似文献   

5.
应用个体培养方法,研究了温度(20、2和30 ℃)和藻类食物浓度(1.5×106、3.0×106、6.0×106和9.0×106 cells·ml-1)对青岛、芜湖、广州三品系萼花臂尾轮虫种群动态的影响.结果表明,温度仅对轮虫的世代时间和种群内禀增长率有显著影响,而品系对所有生命表参数均无显著影响.轮虫种群的内禀增长率随培养温度的升高而增大,世代时间则随培养温度的升高而缩短.食物浓度仅对轮虫的生命期望值和平均寿命有显著影响,品系对轮虫的净生殖率、世代时间、生命期望值和平均寿命也有显著影响.三品系间,以广州品系轮虫的净生殖率、世代时间、生命期望值和平均寿命最大,芜湖品系最短.当食物浓度为3.0×106 cells·ml-1时,轮虫的生命期望值和平均寿命最长,9.0×106 cells·ml-1时最短.各品系轮虫的净生殖率、世代时间、总生殖率、生命期望值和平均寿命均随培养温度的升高而减小,广州品系的净生殖率除外.轮虫种群的内禀增长率和广州品系轮虫的总生殖率则随培养温度的升高而增大.青岛和广州品系轮虫的各生命表参数,均与食物浓度呈曲线相关,但芜湖品系仅世代时间、平均寿命和生命期望值随食物浓度的增大而缩短.  相似文献   

6.
应用单个体培养方法比较研究了藻类食物浓度(2.0、5.0、8.0和11.0×106cells/mL)和品系对采自广州、青岛和芜湖等地的萼花臂尾轮虫生殖期历时、后代数和后代中混交雌体百分率的影响。结果表明,食物浓度对轮虫的生殖期历时和轮虫全部后代中的混交雌体百分率有显著的影响,但对轮虫的总后代数无显著的影响。品系对轮虫的生殖期历时、总后代数和全部后代中的混交雌体百分率均有显著影响。3品系间,广州品系轮虫的生殖期历时最长,为(4.53±0.19)d;总后代数最多达(18.75±0.26)个;全部后代中的混交雌体百分率最低,仅为4.32%±0.51%。而青岛品系轮虫全部后代中的混交雌体百分率最高,达49.90%±2.15%;其生殖期历时和总后代数与芜湖品系间均无显著的差异。食物浓度和品系间的交互作用仅对轮虫全部后代中的混交雌体百分率有显著影响。3品系中,仅芜湖品系轮虫的生殖期历时、总后代数和全部后代中的混交雌体百分率受食物浓度的显著影响;母体年龄对轮虫每天所产后代中的混交雌体百分率的影响因轮虫品系的不同和培养时所用的食物浓度的不同而异。  相似文献   

7.
董丽丽  席贻龙  张雷 《应用生态学报》2006,17(12):2417-2420
在4个温度(15 ℃、20 ℃、25 ℃和30 ℃)下对4个不同生化遗传特征的萼花臂尾轮虫克隆(A、B、C和D)所产幼体的耐饥饿时间及其与温度、轮虫个体大小和卵大小等的关系进行研究.结果表明,15 ℃下克隆B幼体耐饥饿时间最短,为45.67 h;20 ℃和25 ℃下克隆C幼体耐饥饿时间均最长,分别为61.33 h和72.01 h;30 ℃下克隆A幼体耐饥饿时间最长,为40.11 h.4个温度间,克隆A轮虫幼体的耐饥饿时间在15 ℃下最长,克隆B和C轮虫幼体的耐饥饿时间在30 ℃下均最短,克隆D轮虫幼体的耐饥饿时间随培养温度的升高而逐步显著缩短.4个克隆轮虫的幼体耐饥饿时间均与温度呈显著负相关关系.克隆A轮虫的幼体耐饥饿时间还与卵体积呈显著负相关,克隆C相反;克隆B和克隆D轮虫幼体耐饥饿时间与个体体积呈显著正相关关系.  相似文献   

8.
红臂尾轮虫和壶状臂尾轮虫生活史特征比较   总被引:2,自引:1,他引:1  
胡存兵  席贻龙  陶李祥 《生态学报》2008,28(12):5957-5863
应用单个体培养方法,以浓度为3.0&#215;10^6 cells/ml的斜生栅藻(Scenedesmus obliquus)为食物,在18、23、28℃和33℃下,对分类存疑种类红臂尾轮虫(Brachionus rubens)和壶状臂尾轮虫(B.urceolaris)的生活史特征进行了比较研究。结果表明,随着温度的升高,两种轮虫的生殖前期和生殖期历时、平均寿命、世代时间和生命期望均逐渐显著地缩短,而种群内禀增长率却极显著地增大。红臂尾轮虫在28℃下的生殖后期历时与23℃和33℃间均无显著的差异,壶状臂尾轮虫在28℃和33℃下的生殖后期历时也无显著的差异。红臂尾轮虫的产卵量和净生殖率均在33℃下最小,在其他3个温度间都无显著的差异;壶状臂尾轮虫的产卵量和净生殖率均在33℃下最小,28℃下最大。18、23℃和28℃下红臂尾轮虫的生殖前期历时、平均寿命、生命期望和世代时间都显著短于壶状臂尾轮虫,而生殖期历时在两者间无显著差异;33℃下红臂尾轮虫的生殖期历时、平均寿命、生命期望和世代时间都显著长于壶状臂尾轮虫,而生殖前期历时在两者间无显著差异。各温度下,红臂尾轮虫的产卵量、种群内禀增长率和净生殖率均极显著地高于壶状臂尾轮虫,但两种轮虫的生殖后期历时无显著的差异。红臂尾轮虫偏向于r-对策者,体现在其较低的生命期望、较高的繁殖率和种群增长率;而壶状臂尾轮虫则显示出较高的生命期望、较低的种群增长率和繁殖率,偏向于k-对策者。  相似文献   

9.
以浓度分别为 3 0× 10 6、 6 0× 10 6、 9 0× 10 6和 12 0× 10 6cells/mL蛋白核小球藻 (Chlorellapyrenoi dosa)为食物 ,在温度为 (2 5± 1)℃下 ,应用群体累积培养法研究了食物浓度对分布于长江、珠江和淮河水系的 3个地理品系的角突臂尾轮虫 (Brachionusangularis)种群的增长、个体和卵的体积的影响。结果表明 ,食物浓度、地理品系及两者间的交互作用对轮虫种群增长率、个体和卵的体积均有显著影响。同一食物浓度下 ,广州品系的种群增长率最大 ,芜湖品系的个体和卵体积最大 ;同一品系中 ,当食物浓度为 9 0× 10 6cells/mL时轮虫有较大的种群增长率。各品系轮虫的种群增长率与食物浓度均呈曲线相关 ,但种群增长率达最大时所需的食物浓度在各品系间存在着差异。在食物浓度和品系两因素中 ,品系对轮虫个体体积有较大的影响  相似文献   

10.
对采自青岛和芜湖两地的萼花臂尾轮虫在3种温度(20 ℃、25 ℃和30 ℃)和2种藻类食物浓度(1.0×106和5.0×106 cells·ml-1)下所产休眠卵的长径、短径和体积等形态特征进行了显微测量、计算和分析.结果表明,2种食物浓度下,培养温度以及培养温度和品系间的交互作用均对轮虫休眠卵的长径、短径和体积具有显著影响.当食物浓度分别为1.0×106和5.0×106 cells·ml-1时,轮虫在20 ℃下所产休眠卵的长径、短径和体积均最大;在25 ℃和30 ℃下所产休眠卵的短径和体积均最小.品系对轮虫休眠卵长径、短径和体积的影响也取决于食物浓度.当食物浓度为1.0×106 cells·ml-1时,芜湖品系轮虫的休眠卵长径、短径和体积(156.00 μm、99.95 μm和12 269.11 μm3)均显著大于青岛品系轮虫的休眠卵(145.13 μm、91.97 μm和10 498.19 μm3);而当食物浓度为5.0×106 cells·ml-1时,芜湖品系轮虫的休眠卵长径、短径和体积(155.68 μm、100.85 μm和12 348.59 μm3)均与青岛品系轮虫的休眠卵(156.63 μm、98.04 μm和12 054.20 μm3)之间无显著差异.两品系中,仅芜湖品系轮虫休眠卵的长径、短径和体积分别与温度呈曲线相关.同一温度下,两品系轮虫的休眠卵体积均随着食物浓度升高而增大;但30 ℃下芜湖品系轮虫所产休眠卵体积却随着食物浓度的升高而减小.  相似文献   

11.
Stephen C. Weeks 《Oecologia》1993,93(3):307-314
Models of resource allocation strategies predict an array of life-history responses of individuals living in resource-stressed versus non-stressed environments. I tested a number of these predictions using three fish strains (a sexual and two clonal strains) in high and low density treatments. To examine the plasticity of life-history traits in females raised in these two environments, I measured survival, growth, egg production, egg size, and proportion mature at 10 weeks of age. Survival was not affected by density treatment. However, both growth and overall egg production were lower in females from the high density treatments, and reproductive maturity was significantly delayed at the high density for all strains. Egg production per unit size was not affected by density in any strain, signifying that differences in the numbers of eggs produced was merely a reflection of the differences in size of fish in the two density treatments. Egg size was also unaffected by density in all strains. These results are related to models of resource allocation in stressful environments. There was a consistent pattern of increased reproductive investment in the sexual strain relative to the two clonal strains. The sexual strain matured earlier, produced more eggs per unit body weight, and had larger eggs than either clone at both densities. These results are interpreted by considering the predicted adaptive responses of these three strains to the long-term environmental differences in their natural habitats.  相似文献   

12.
周金成  何玥  赵倩  董辉 《昆虫学报》2021,64(1):80-89
【目的】明确两性生殖品系和孤雌产雌品系松毛虫赤眼蜂Trichogramma dendrolimi在不同品种柞蚕Antheraea pernyi卵中的寄生及发育表现,为以柞蚕卵为替代寄主更好地规模化繁育赤眼蜂提供依据。【方法】测定两性生殖品系和孤雌产雌品系雌蜂在6个品种柞蚕卵[抗大(KD)、大四(DS)、高新(GX)、988(NEE)、青大(QD)和特大(TD)]上的寄生率、子代蜂窝蜂数(单窝羽化子代蜂数)和子代蜂雌性比等生物学指标,以及6个品种柞蚕卵的质量指标(单卵湿重、蛋白质含量、总糖含量和甘油三酯含量);利用主成分分析揭示柞蚕卵质量指标与赤眼蜂生物学指标间的相关性。【结果】NEE品种柞蚕卵育出的两性品系松毛虫赤眼蜂子代蜂个体显著大于除KD和QD品种以外的其他柞蚕品种卵育出的两性品系子代蜂。柞蚕品种对两性品系松毛虫赤眼蜂的寄生率、子代蜂窝蜂数和子代蜂雌性比均无显著影响。在孤雌产雌品系松毛虫赤眼蜂中,KD品种柞蚕卵育出的松毛虫赤眼蜂子代蜂窝蜂数最多,显著高于NEE和QD品种育出的子代蜂窝蜂数,但与DS, GX和TD品种育出的子代蜂窝蜂数相比无显著差异。柞蚕品种对孤雌产雌品系松毛虫赤眼蜂的寄生率和子代蜂个体大小均无显著影响。TD品种柞蚕卵的蛋白质含量最高,显著高于除GX品种以外的柞蚕品种。KD品种柞蚕卵的总糖含量和QD品种柞蚕卵的甘油三酯含量最高,均分别显著高于其余柞蚕品种。主成分分析表明,两性品系松毛虫赤眼蜂寄生率、柞蚕卵蛋白质含量和甘油三酯含量均与柞蚕卵总糖含量呈负相关;两性品系松毛虫赤眼蜂子代蜂个体大小和柞蚕卵甘油三酯含量与单卵湿重呈负相关;孤雌产雌品系松毛虫赤眼蜂寄生率和柞蚕卵甘油三酯含量与松毛虫赤眼蜂子代蜂窝蜂数、柞蚕卵总糖含量和单卵湿重呈负相关;孤雌产雌品系松毛虫赤眼蜂子代蜂个体大小和柞蚕卵总糖含量与蛋白质含量呈负相关。【结论】本研究通过筛选适宜两性生殖品系和孤雌产雌品系赤眼蜂繁育的柞蚕卵品种,初步明确了卵内主要营养指标与子代蜂生物学指标间的相关性。研究结果为利用柞蚕卵更好地规模化繁育松毛虫赤眼蜂提供依据与数据支撑。  相似文献   

13.
John W. Rowe 《Oecologia》1994,99(1-2):35-44
Interpopulation variation in egg size, clutch size and clutch mass was studied 3 years in four populations of painted turtles (Chrysemys picta bellii) from western Nebraska. Body size varied among all populations and was larger in two large (56–110 ha), sandhills lake populations than in two populations in smaller habitats (1.5–3.6 ha) of the Platte River floodplain. Reproductive parameters (egg mass, clutch mass, and clutch size) generally increased with maternal body size within populations. Clutch wet and dry mass varied among populations but largely as a function of maternal body size. Clutch size was largest in the sandhills lake populations, both absolutely and relative to maternal body size. Egg mass was smallest in the sandhills lakes and varied annually in one population. Over all populations, an egg sizeclutch size trade-off was detected (a negative correlation between egg mass and clutch size) after statistically removing maternal body size effects. Egg wet mass and clutch size were negatively correlated over all years within the sandhills populations and in some years in three populations. Although egg size varied within populations, egg size and clutch size covaried as expected by optimal offspring size models. Thus, patterns of egg size variation should be interpreted in the context of proximate or adaptive maternal body size and temporal effects. Comparisons among populations suggest that large egg size relative to maternal body size may occur when juvenile growth potential is poor and mean maternal body size is small.  相似文献   

14.
Geographic variation in offspring size is widespread, but the proximate causes of this variation have not yet been explicitly determined. We compared egg size and egg contents among five populations of a lizard (Takydromus septentrionalis, Günther, 1864) along a latitudinal gradient, and incubated eggs at two temperatures to determine the influence of maternal investment and incubation temperature on offspring size. The mean values for female size and egg size were both greater in the two northern populations (Chuzhou and Anji) than in the three southern populations (Lishui, Dongtou, and Ningde). The larger eggs were entirely attributable to the body size of females in the Anji population, but their increased size also stemmed from further enlargement of egg size relative to female body size in Chuzhou, the northernmost population sampled in this study. Eggs of the Chuzhou population contained more yolk and less water than those of southern populations. Despite the lower lipid content in the yolk, eggs from the Chuzhou population had higher energy contents than those from the two southern populations, owing to the larger egg size and increased volume of yolk. Hatchling size was not affected by incubation temperature, but differed significantly among populations, with hatchlings being larger in the Chuzhou population than in the other populations. Our data provide an inference that oviparous reptiles from cold climates may produce larger offspring, not only by increasing egg size but also by investing more energy into their eggs. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101 , 59–67.  相似文献   

15.
The aim of this study was to examine whether there is a relationship between cagA size of Japanese Helicobacter pylori strains and the location of these strains in the mucous layer, the degree of gastric inflammation and acid survival. Upper gastrointestinal endoscopies were done to 144 patients with dyspeptic symptom with informed consent, sera, biopsy specimens and H. pylori strains were obtained, and gastric histology and susceptibility to pH 3 of the strains were evaluated. To determine cagA size of Japanese strains using PCR, cagA of strain CPY3401 was sequenced. 74 H. pylori samples (72 cagA+) were obtained from the body and 56 samples (56 cagA +) obtained from the antrum. cagA size of 72 H. pylori strains from the body was mainly classified into 3 groups (short (48), middle (8), long (9), and others (7)) by PCR and all of that of 56 strains from the antrum except 2 was short. The size of cagA of isolated strains from the body is associated with enhanced gastritis, acid survival, and the location in the mucus. The long size cagA of which strain is acid sensitive, may be a strong selective pressure on strain that colonizes close to the host, which enhanced gastritis.  相似文献   

16.
The mechanism underlying the phase-dependent polyphenism in hatchling body coloration was studied by testing for a possible causal relationship with egg size in the desert locust, Schistocerca gregaria. Crowd-reared (gregarious) females typically produce large, black offspring, whereas females reared in isolation (solitarious) deposit small, green offspring. We first tested for possible genetic differences in the role of egg foam by washing or separating eggs from two strains of locust. No solitarizing effect was found in either of the strains tested, supporting a previous finding, using another laboratory strain, to show that the hatchling body coloration and size are pre-determined in the ovary of the mother and no egg foam factor is involved in the control of the hatchling body coloration. Topical application of fenoxycarb, a juvenile hormone analog (JHA), and implantation of extra corpora allata (CA), taken from Locusta migratoria, caused gregarious female adults of S. gregaria to produce small eggs. Some eggs laid by CA-implanted females produced green hatchlings. All large eggs chosen among those deposited by gregarious females produced black hatchlings. When eggs were either kept on dry filter paper at nearly saturated relative humidity during embryogenesis or pricked with a needle so that some egg yolk was squeezed out, some produced small, green hatchlings. These results suggested that the amount of egg yolk or the availability of yolk material may determine the body coloration of hatchlings.  相似文献   

17.
Metabolomics analysis of three Saccharopolyspora spinosa strains (wild type strain WT, ultraviolet mutant strain WH124, and metabolic engineering strain LU104) with different spinosad producing levels was performed by liquid chromatograph coupled to mass spectrometry (LC-MS). The metabolite profiles were subjected to hierarchal clustering analysis (HCA) and principal component analysis (PCA). The results of HCA on a heat map revealed that the large numbers of primary metabolism detected were more abundant in WH124 and less abundant in LU104 during the early fermentation stage as compared to the WT strain. PCA separated the three strains clearly and suggested nine metabolites that contributed predominantly to the separation. These biomarkers were associated with central carbon metabolism (succinic acid, α-ketoglutarate, acetyl-CoA, and ATP), amino acid metabolism (glutamate, glutamine, and valine), and secondary metabolism (pseudoaglycone), etc. These findings provide insight into the metabolomic characteristics of the two high-yield strains and for further regulation of spinosad production.  相似文献   

18.
Intraclutch egg size variation may non‐adaptively result from nutritional/energetic constraints acting on laying females or may reflect adaptive differential investment in offspring in relation to laying/hatching order. This variation may contribute to size hierarchies among siblings already established due to hatching asynchrony, and resultant competitive asymmetries often lead to starvation of the weakest nestling within a brood. The costs in terms of chick mortality can be high. However, the extent to which this mortality is egg size‐mediated remains unclear, especially in relation to hatching asynchrony which may operate concomitantly. I assessed effects of egg size and hatching asynchrony on nestling development and survival of Herring Gulls (Larus argentatus), where the smaller size and later hatching of c‐eggs may represent a brood‐reduction strategy. To analyze variation in egg size, I recorded the laying order and laying date of 870 eggs in 290 three‐egg clutches over a 3‐yr period (2010–2012). I measured hatchlings and monitored growth and survival of 130 chicks from enclosed nests in 2011 and 2012. The negative effect of laying date (β = ?0.18 ± SE 0.06, P = 0.002) on c‐egg size possibly reflected the fact that late breeders were either low quality or inexperienced females. The mass, size, and condition of hatchling Herring Gulls were positively related to egg size (all P < 0.0001). C‐chicks suffered from increased mortality risk during the first 12 d, identified as the brood‐reduction period in my study population. Although intraclutch variation in egg size was not directly related to patterns of chick mortality, I found that smaller relative egg size interactively increased differences in relative body condition of nestlings, primarily brought about by the degree of hatching asynchrony during this brood‐reduction period. Thus, the value of relatively small c‐eggs in Herring Gulls may lie in reinforcing brood reduction through effects on nestling body condition. A reproductive strategy Herring Gulls might have adopted to maintain a three‐egg clutch, but that also enables them to adjust the number of chicks they rear relative to the prevailing environmental conditions and to their own condition during the nestling stage.  相似文献   

19.
To obtain controlled genetic variation, colon cancer was chemically induced by use of four subcutaneous injections of azoxymethane (15 mg/kg of body weight/wk) to rats of 3 inbred strains (BDIX/OrlIco, F344/NHsd, WAG/Rij). The selection was based on the availability of established colon cancer cell lines arising from these particular strains. In the first experiment, only female rats were used; in the second experiment, both sexes were studied. The goal was to select a rat strain giving the highest tumor frequency with the shortest latency period in reproducible manner. The histologic characteristics should resemble the corresponding human tumors. The size of the tumors should be at about 1 cm in diameter, as these tumor cells were intended to be used in future transplantation studies. The two experiments yielded highly reproducible results: histologic evaluation of all colon tumors in all three rat strains revealed adenomas and adenocarcinomas closely resembling their human counterpart. The BDIX strain had the highest tumor frequency (75%) in both sexes and the shortest minimal latency period (28 weeks in experiment 1; 23 weeks in experiment 2). Tumor size of about 1 cm in diameter was found most often in the BDIX strain. On the basis of results of these two experiments, the BDIX strain has been selected for future study.  相似文献   

20.
Clutch size, egg size, larval size and duration of larval period were estimated for samples of Bombina bombina and B. variegata from several populations. Bombina variegata lays fewer eggs per batch (mean 17.4) than B. bombina (mean 32.5). The volume of B. variegata eggs is 2.4 times greater and the dry weight 2.3 times greater than that of B. bombina. As a consequence, the volume of B. variegata hatchlings and their dry weight are respectively 1.9 times and 2.5 times greater than that of B. bombina. Analysis of variance showed that variation of egg size in B. variegata is significantly greater than in B. bombina. When reared under laboratory conditions freshly metamorphosed individuals of both species showed no difference in body size or weight. Although growth rates are equal, tadpoles of B. variegata reached metamorphosis 14 days earlier than B. bombina tadpoles because of differences in size of hatchlings. Differences in reproductive parameters found for the two European Bombina species can be interpreted as adaptations to contrasting environments in which they breed.  相似文献   

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