Analysis of competitive ability among genotypes of perennial ryegrass

1987

Two distinct experimental designs are commonly employed for the analysis of competitive interactions in genetically heterogeneous mixtures. These are referred to as substitution and addition designs respectively, and either may be used quantitatively to separate the effects of intra-and inter-genotypic competition. The results presented in this paper relate to two characters which measure competitive success in mixed cultures of Drosophila melanogaster, namely the proportion of developing individuals which survive to emerge as adults and the mean weight of those adults. For each of these characters the estimates of intra-and inter-genotypic competitive values obtained from substitution and addition design experiments were equivalent. The implications of this result with respect to the choice of a suitable experimental design and its application to competition in various plant and animal systems are discussed. INTRODUCTIONThe importance of competition as an environmental and selective force has long been appreciated (Andrewartha and Birch, 1954;Bakker, 1961).However, detailed investigation of the nature of competitive interactions has been hampered by elusive definitions and the absence of a suitable form of analysis. Recent developments in the analysis of data from competition experiments include the introduction of nearest neighbour and spacing models (Kempton, 1982; Cannel et al., 1984;Benjamin, 1982) which are used primarily in agriculture and forestry related experiments and descriptive, density related regression models (Mather and Caligari, 1981; Spitters 1983a), where the competitive success of a genotype is related to the densities of the various competitors. This latter approach has also been found suitable for the analysis of density related forms of competition in animal systems, as exemplified by the investigation of competition between larvae of Drosophila melanogaster for a constant and limiting amount of food Caligari, 1981, 1983;Eggleston, 1985). Mather and Caligari (1981) A characteristic, therefore, of the substitution design is that the independent variable is negative.Department of Genetics, University of Liverpool, P.O. Box 147, Liverpool L69 3BX, U.K. J. RODRIGUES DE MIRANDA AND P. EGGLESTONThe slope obtained from the monoculture regression (bm) again measures intra-genotypic competition. The slope of the duoculture regression (bd) measures both intra-genotypic competition among the indicator genotype competitors and the inter-genotypic competitive effect that the associate complement has on the performance of the indicator genotype. If the associate has no effect, then bd would be the same as bm. The inter-genotypic competitive value is therefore estimated by the difference between the two slopes (bdbm). The intra-genotypic competitive value is quantified similarly as (b0_bm), b0 being the slope obtained if the indicator competitors had not been substituted. One of the useful features of this design is that with the inclusion of a monoculture density series for the secondary genotype th...

Section: Discussionmentioning

confidence: 99%

A comparison of substitution and addition designs for the analysis of competitive interactions in Drosophila melanogaster

Miranda

1987

“…The other component is exploitation and this refers to the acquisition of some necessary and limited resource, for example food or light, by the competing individuals. Exploitation has long been a subject of investigation in D. melanogaster (Bakker, 1961;Mather and Caligari, 1981;de Miranda and Eggleston, 1987) and also in other organisms, for example Lolium perenne (Mather, Hill and Caligari, 1982). Interference has also been investigated in Drosophila although usually in the context of the competition between different species.…”

Section: Introductionmentioning

confidence: 99%

Competitive interactions in Drosophila melanogaster: genetic variation for interference through media conditioning

Hemmat

1988

Interference, which is one of two aspects of the process of competition which take place in genetically heterogeneous mixtures has been studied in the Texas population of Drosophila melanogaster. Both survival and mean adult weight were investigated in the population itself (which displays high levels of aggression and little response) and in LA, a genotype derived from the population (which displays low aggression and high levels of response) in both homotypically and heterotypically conditioned media. The results presented here show that the competitive effects of conditioning depend not only on the concentration of the conditioned medium but also on the genotype of the larvae which conditioned the medium and that of the flies which respond to such media. It was also concluded that medium conditioning is one of a range of biological parameters involved in the determination of the aggression and response components of the competitive interaction among Drosophila larvae. Thus the competitive fitness of a genotype of D. melanogaster is related not only to genetic variation for aggression and response but also to genetic variation in the ability to condition media and the sensitivity to such media.

“…This distinction between aggression and response was drawn by Breese and Hill (1973) and the analytical procedure was refined by Mather and Caligari (1983). Subsequently, this model for the analysis of competitive interactions (although developed using Drosophila melanogaster as a model system) has been applied to a range of experimental and commercial material including Lolium perenne (Mather, Hill and Caligari, 1982) and Hordeum vulgare (Powell, Caligari and Thomas, 1985). In addition, the flexibility of this multiple linear regression approach has been demonstrated through a variety of experimental designs, including both substitution and addition techniques (de Miranda and Eggleston, 1987) and with a variety of competitive characters (Eggleston, 1987;Powell et a!., 1985).…”

Section: Introductionmentioning

confidence: 99%

Competitive interactions in Drosophila melanogaster: recurrent selection for aggression and response

Hemmat

1988

Recurrent selection programmes for both high response and low aggression have been employed in the Texas population of Drosophila melanogaster. Five main points have emerged from this investigation. First, the population exhibits extensive genetic variation for the aggression and response components of competitive interactions which take place in genetically heterogeneous cultures. Secondly, the two components of such interactions, namely aggression and response, can be adjusted by the selection of particular groups of genes. Thirdly, the rapid change in the selected components in the early generations suggests that a considerable amount of additive genetic variation is involved in the control of aggression and response. This is further supported by estimates of the realised heritability taken over the whole selection programme which amount to O•79 and O•74 for the low aggression and high response selections respectively. Fourthly, the rapidity with which changes in aggression and response approached plateaux suggests that such changes in the earlier generations are primarily due to the assortment of major chromosomes as units. Fifthiy, it was concluded that aggression and response do not behave entirely independently or dependently. The results suggest that a single array of genes might be responsible for the determination of both characters. The observed results would then be consistent with certain of these genes having a much larger effect on aggression than they do on response.