The Comparative Biology of Closely Related Species Living in the Same Area: V. INTER- AND INTRASPECIFIC INTERFERENCE WITHIN CULTURES OF LEMNA spp. AND SALVINIA NATANS

Studies were made of the growth of populations of Lemna minor,L. polyrrhiza, L. gibba, and Salvinia natans under controlledlaboratory conditions. The intrinsic exponential growth-ratesof the clones were determined in un-crowded cultures, and thechanges in growth-rate of self-crowding cultures were measuredand interpreted in terms of an initial exponential growth-ratefollowed by a phase of arithmetic increase in weight and followedin turn by a phase in which the death of submerged and shadedfronds caused a decline from the arithmetic rate of growth.Mean frond weight declined in self-crowding cultures (exceptof L. gibba). Mixed cultures of two species were examined under self-crowdingconditions and changes in the proportions of the species werefollowed. Whereas the total weight of mixed cultures remainedvery constant between replicates, there was wide variation inthe proportions of components. The variation in the two componentswas most closely correlated (negatively) when the struggle forexistence was most evenly balanced. The mean frond weight ofthe losing component declined during the experiments. The order of decreasing vigour of species measured by variousparameters was as follows: Relative (intrinsic) growth-rate: L. minor > S. natans > L. gibba > L. polyrrhiza Arithmetic growth-rate when crowded: S. natans > L. polyrrhiza > L. gibba > L. minor Asymptotic yield per culture: L. polyrrhiza > L. minor > S. natans > L. gibba Success in mixed cultures: The success of a species in mixture could not be predicted fromthe parameters of growth in pure culture. Morphologic featuressuch as the gibbosity of L. gibba     

GROWTH AND DEVELOPMENT OF THE WATER MOLD RHIZIDIOMYCES IN PURE CULTURE

Fuller , Melvin S. (Brown U., Providence, R. I.) Growth and development of the water mold Rhizidiomyces in pure culture. Amer. Jour. Bot. 49(1): 64–71. Illus. 1962.—A method for growing pure cultures of many of the single or few-celled phycomycetous fungi such as Rhizidiomyces is described. This method facilitates both qualitative and quantitative study of such fungi during their growth and development. Zoospores of Rhizidiomyces start to grow within 3 hr after being placed in a liquid medium, and are ready to discharge new zoospores after about 40 hr growth at 25 C. The single nucleus of the zoospore goes through many synchronous mitotic divisions during the development of the mature multinucleate cell. Under carefully controlled environmental conditions, sporangium discharge occurs in a definite and predictable manner. Observations suggesting a possible mechanism of sporangium discharge are presented and discussed.     

ASYMMETRIC COMPETITION IN MIXED POPULATIONS OF TADPOLES OF THE HYBRIDOGENETIC: RANA ESCULENTA COMPLEX

Hybridogenetic Rana esculenta tadpoles display tolerance to extreme environmental conditions and fit criteria of the “general-purpose” genotype. A trade-off between generality and competitive ability is assumed to occur in asexual species, but the evidence remains unclear. The purpose of my experiment was to test the competitive ability of hemiclonal hybrid Rana esculenta tadpoles relative to the parental species Rana lessonae. Mixed and single genotype populations of R. esculenta and R. lessonae tadpoles were reared at three densities in artificial ponds. Survival of R. esculenta was higher than for R. lessonae tadpoles, but did not differ among densities. Body size at metamorphosis was the same between genotypes, but decreased with increasing density. Larval period was not affected by density, but R. esculenta tended to metamorphose earlier than R. lessonae. Percentage of individuals metamorphosing was higher for R. esculenta at both medium and high densities, but the same as R. lessonae at the low density. The difference in survival, body size, and larval period between tadpoles reared in single and mixed genotype populations was unaffected by genotype or density. The difference in the percentage of metamorphs, however, was strongly affected. The percentage of hybrids metamorphosing was 9% above the responses of single genotype populations at the highest density. Conversely, the percentage of R. lessonae metamorphosing was 12% below the responses of single genotype populations at the same density. Hybrid success in this experiment further supports the criterion of a “general-purpose” genotype without assumptions of reduced competitive ability.     

GROWTH AND DEMOGRAPHY OF POPULATIONS OF BIOMPHALARIA PFEIFFERI (GASTROPODA, PLANORBIDAE) IN THE LABORATORY

The growth and demography of the freshwater snail Biomphalariapfeifferi, an intermediate host of the parasitic worm Schistosomamansoni in Eastern Zaire, were investigated in the laboratoryunder two conditions of crowding. Both individual and populationgrowth were depressed by crowding. Crowding reduced growth rateand all the variables and parameters related to reproduction(fecundity, instantaneous birth rate, net reproduction rate),but did not affect maximum size, survivorship, instantaneousdeath rate and life expectancy. The mechanism involved in theseeffects is likely to be exploitation competition for especiallyprofitable food items such as diatoms. (Received 10 November 1986;     

池养长江蟹、辽河蟹生长性能及其遗传-环境交互作用分析

在江苏省高淳县和安徽省绩溪县两地同时进行中华绒螯蟹长江种群和辽河种群二龄成蟹生长比较试验。①在同一饲养环境里 ,4— 9月 ,两种群间差异不显著 (P >0 0 5 )。②长江蟹比辽河蟹生长期长一个月 ,长江蟹 1 0月底出池 ,故其商品蟹体重大于 9月底出池时辽河蟹体重 (P <0 0 5 )。③长江蟹成活率高于辽河蟹 (P <0 0 1 )。④两种群的雄性个体都大于雌性个体 (P <0 0 1 ) ;但雌、雄差异明显增大的时间是 ,辽河蟹始于 7、8月份 ,长江蟹始于 8、9月份。⑤在绩溪山区池塘低温和饵料贫乏的生态环境中 ,两种群的生长、成活率都比在高淳平原池塘的较好生态环境下低 (P <0 0 1 )。种群与环境、性别与环境的交互作用都极显著 (P <0 0 1 )。在优良环境中 ,长江种群的生长优势和两种群内雄性的生长优势才能得到发挥     

ESTIMATION OF THE MEAN AND VARIANCE OF CYCLE TIMES IN CINEMICROGRAPHICALLY RECORDED CELL POPULATIONS DURING BALANCED EXPONENTIAL GROWTH

The mathematical and statistical problem of estimating the mean and variance of cell cycle times from cinemicrographically observed durations until mitosis (cytokinesis at late anaphase), disintegration, collision (cells superimposing each other) or emigration (moving out of the field of vision) of randomly chosen individual cells in a population in balanced exponential growth is treated. The resulting formulae are simple and considerably reduce the average cell observation time. They are applied to two normal human foetal cell lines and their SV40-transformed counterparts. One result is that the latter seem to have longer cycle times in spite of their shorter doubling times. Another result is that the cell mobility seems somewhat increased in the transformed populations. This corroborates earlier findings, indicating that the extent of cell loss, rather than the length of cycle times, may play a decisive role for the (net) doubling time of cultivated cell populations.     

THE RATE OF GROWTH OF THE DAIRY COW : EXTRAUTERINE GROWTH IN WEIGHT.

The growth period of the Jersey and Holstein cows is made up of at least three cycles, two extrauterine cycles with maxima at about 5 and 20 months of age, and one intrauterine cycle, the maximum of which has not yet been determined. The equation of an autocatalytic monomolecular reaction was found to give very good results when applied to the cycle having its maximum at about 5 months of age. The values obtained from this equation when applied to the cycle having the maximum at about 20 months of age were higher than the observed values probably due to the retarding effect of pregnancy and lactation on growth.