Effect of group, variation and heritability of the components of fitness in Eisenia foetida
Surova, G.S.; Kreslavskii, A.G.; Severtsov, A.S.
Zoologicheskii Zhurnal 74(4): 58-69
ISSN/ISBN: 0044-5134 Accession: 031085699
The high degree of phenotypic variation in Eisenia foetida was revealed under the study of such characters as the size of cocoons (mm), the number of cocoons laid throughout 30 days, the number of larvae per cocoon, the rate of maturation (days) and the weight of worms at the ages of 30, 60 and 90 days. Among all the components, moderate negative correlation was revealed between the duration of the development and the number of larvae per cocoon (r = -0.3) and between the rate of maturation and daily overweight (r = -0.46). All other growth components and reproductive efforts were not significantly correlated. The well - expressed "effect of group" was revealed. In pairs maintained under high density, one of the larvae had the rate of the development approximately equal to that observed under singular maintenance, while the growth of other one was significantly delayed. Under very high density, most of the larvae failed the rate of growth and maturation up to their complete arrest, but some individuals could grow and develop fast enough, which caused the formation of discrete groups with individuals twice as large as the rest. The heritability of main components of fitness was estimated using the method of regression "offspring - mean of parents", ANOVA analysis of interfamilial differences of full siblings, and repeated measurement in pairs of individuals. Two of the characters (the number of larvae per cocoon and the number of cocoons) are important for the overall fertility, however, we did not find additive genetic variation of these characters in a technical culture of E. foetida, while the size of cocoons and the duration of embryonal development, which are less important for the fitness, had high heritability. The heritability of growth rate was substantially affected by the conditions of maintenance of the larvae. The genetic variation of the rate of maturation was not found, which can be explained by difficulties in the precise measurement of this character. Under high density, the selection for growth rate was effective only when the parents were evaluated at later stages of ontogenesis.