Female Remating in Drosophila ananassae
665
Gerhart (1984) were followed to examine the effect of density on remating
frequency in D. ananassae. The results in the 2-h daily observation design with
wild-type females were similar to those of Gromko and Gerhart (1984) who
found that the frequency of female remating did not increase with a higher
density. However, ca mutant females in the 2-h daily observation and ca and
ct rb mutant females in the continuous confinement design show a significant
increase in remating frequency at higher densities in D. ananassae.
Gromko et al. (1984) have reported that under the periodic confinement
design the receptivity of females is sperm dependent. In periodic confinement
designs, Gromko and Gerhart (1984) reported that the number of sperm in
storage is not affected by density, hence female remating is also not affected
by density. Further, for continuous confinement they have postulated that
in all high-density vials, males were seldom uninterrupted while courting.
However, in low-density vials males frequently directed sustained courtship
at individual females without being displaced by other males. They also sug-
gested that the decrease in female remating frequency at higher densities
is due to increased effectiveness of female “decamping” in the continuous
confinement design. However, Eckstrand and Seiger (1975) proposed that
in a population of high density, the probability of a given fly’s being a fast
mater would be higher than in a less dense population because the inci-
dence of proper cues for the manifestation of fast mating would be higher.
Pearl (1932) has suggested that an increase in density could lead to more
mating simply by increasing the opportunity for interaction between individ-
uals in the population. Further, Harshman et al. (1988) proposed that there
is genetic variation for density dependence in remating frequency, i.e., the
effect of density on the frequency of remating depended on the fly strains
used.
The present findings in D. ananassae support the statements by Pearl
(1932), Eckstrand and Seiger (1975), and Harshman et al. (1988). If female
remating has a genetic basis (see Sgro et al., 1998), individual females may
vary in their receptivity to remate. van Viannen and Bijlsma (1993) suggested
that female remating frequency is affected by the genotype of their first male
and proposed that this could be due to differences in the amount or quality
of seminal fluid transferred during copulation.
InD. ananassae, female remating with respect to productivity and sperm
displacement has been studied by employing different mutant strains and a
wild-type strain (Singh and Singh, 2001). The comparison of productivity be-
tween once-mated and remated females reveals that the productivity of re-
mated females was significantly higher than that of once-mated females in all
crosses. Thus female productivity is increased after remating in D. ananassae
(Singh and Singh, 2001). Further, high P2 values (the proportion of second
male progeny produced after remating) were found in all the crosses, which