30 S. Singh
main categories of behaviours were observed:
(i) Mating/courtship latency (ML), which is the
time taken by the male to initiate courtship of fe-
male after its introduction into the chamber (ii)
CD, the amount of time till the female forces or
pushes out the male. Observations were recorded
for 90 min with a stopwatch.
Six-day-old virgin females and males were
introduced into cylindrical Tarsons plastic food
vials (37 × 100 mm) with cotton plug. All ob-
servations were made in morning (6.00–8.00
a.m.) in a thermo-controlled room at 21 °C. For
all the observed matings, ML and CD were re-
corded with a stop watch started at 0 s. Aspirated
mated pairs were used for estimating fecundity
in egg-laying chambers. Everyday the flies were
transferred to fresh egg-laying chambers and
fecundity was monitored under the Olympus
stereo-zoom microscope SZ-11, Japan. This was
continued for 15 successive days (7th–21st) as
this period coincided with highest egg produc-
tion and the data were shown as daily fecundity.
Total ovariole number per fly was counted from
ovaries dissected in a saturated solution of potas-
sium dichromate.
Statistical Analyses For all traits, isofemale
line and population means ± SD were used for
illustrations and tabular data. Since all the traits
showed higher repeatability values across gen-
erations, data were pooled. Mean trait values for
body melanisation and wing length in copulating
and noncopulating wild flies were compared with
ttest. Mating related traits in wild caught flies of
D. immigrans in early vs. late mating propensity
groups were also compared using t test. Further,
the trait values for overall four types of matings
(homo- and hetero-specific) on the basis of body
melanisation and size were subjected to contin-
gency χ^2 test to find whether matings are random
or not. Correlation values ( r) of mating related
traits (ML, CD and daily fecundity) with body
size and with melanisation in assorted isofemale
lines were calculated. Data on within-population
analyses were used for calculation of correlation
values of different traits as a function of body
melanisation. Statistica (Statsoft Inc., Release
5.0, Tulsa, OK, USA) was used for all calcula-
tions as well as illustrations.Results
Mean ± SD for field observations on body size
and body melanisation in copulating and non -
copulating flies of D. immigrans are shown in
Table 1. For each day observation, t test was
performed to compare wing length and body
melanisation of the copulating and noncopulat-
ing categories both for males as well as females.
No significant (ns) differences were observed
for wing length, whereas quite high significant
values (***p < 0.001) were obtained for body
melanisation (Table 1 ). The copulating flies show
higher body melanisation irrespective of wing
length compared with noncopulating flies. These
results favour the role of body melanisation and
not body size on mating success in wild flies of
D. immigrans.
No difference was found in body size (wing
length) among early and late mating groups of
flies (Table 2 ). Results showed high percentage
melanisation, mated pairs, CD and fecundity; and
lower ML in early-mating propensity flies than
late-mating propensity flies (Table 2 ; signifi-
cance level: p < 0.001).
Isofemale lines varying either in body mela-
nisation or in body size but not in both the traits
were selected. Data showed that isofemale lines
of D. immigrans similar in body size but varying
in body melanisation (dark vs. light) differ signif-
icantly in ML and CD (Fig. 1 ). By contrast, isofe-
male lines similar in body melanisation but vary-
ing in body size (large vs. small) exhibit no dif-
ference in ML and CD in D. immigrans (Fig. 2 ).
The results are illustrated in Figs. 1 and 2.
No choice matings were performed to confirm
the role of body melanisation in mating success
in D. immigrans. Data on no-choice tests based
on isofemales varying only in body melanisation
(dark—D and light—L) but not in body size; and
varying in body size (small—Sm and large—La)
but not in body melanisation are given in Table 3.
Isofemale lines differing in body melanisation