A chromosomal analysis of the phenotypic plasticity of some life history traits in relation to developmental...

The capacity to delay egg deposition in D. melanogaster females in the absence of a sexual partner is genetically determined and opposite types can be artificially selected. In natural populations, the relative frequency of these genotypes varies geographically and seasonally, with temperature as a selective factor. However, the retention duration of these genotypes can be modified by developmental temperature change. To study the genetic control of this response, chromosome substitution between opposite types of line was carried out in order to produce every possible homozygous chromosomal combination of the three major chromosomes (X,2,3). Eggs of these eight constructed lines were developed at two different temperatures (25 degrees C and 14 degrees C). Low temperature development directly affected the number of ovarioles but also modified the subsequent expression of adult characteristics such as retention duration and fecundity. The comparison of the eight lines revealed that, although the 3 chromosomes were involved in the genetic determinism of each trait, only one or two of them were sensitive to temperature change, and these differed according to the trait. For retention duration and fecundity, the effect of chromosome 3 from the long retention strain was particularly affected by low temperature, showing antagonism between the selective effect detected in natural populations and the effect on phenotypic plasticity studied here.