28 S. Singh
Only a few studies in Drosophila species have
shown larger males to have higher mating suc-
cess than smaller males, e.g. D. melanogaster
(Taylor and Kekic 1988 ); Drosophila simulans
and Drosophila mojavensis (Markow and Ricker
1992 ); Drosophila testacea (James and Jaenike
1992 ). By contrast, smaller males have shown
more matings than larger males in Drosophila
subobscura (Steele and Partridge 1988 ) and Dro-
sophila montana (Aspi and Hoikkala 1995 ). For
Drosophila pseudoobscura, two different stud-
ies have shown contradictory results, e.g. higher
mating success of larger males (Partridge et al.
1987) whereas no difference in the mating suc-
cess of males of different sizes (Markow and
Ricker 1992 ). Further, in Drosophila willistoni,
body size differences in males do not impact mat-
ing success (Da Silva and Valente 2001 ). Such
studies suggest that the targets of sexual selec-
tion might vary in different Drosophila species,
or body size differences within a species may not
be important to female choice. The relationships
between male mating success and body size are
inconsistent across different Drosophila species,
but these studies have not considered effects due
to changes in body melanisation.
Studies have shown that changes in body mel-
anisation affect mating behavior in diverse insect
taxa. In ladybird beetles, dark-coloured individu-
als have shown increased mating success and ear-
lier emergence times in spring (Brakefield 1984 ;
Brakefield and Larsen 1984 ). Further, changes in
body melanisation impact behavioural patterns,
e.g. mate preference in butterfly (Kronforst et al.
2006 ); alternative body colour/behaviour morphs
in grasshoppers Schistocerca gregaria (Leo et al.
2005 ); aggressive mating behaviour of body
colour morphs in the fish Gambusia holbrooki
(Horth 2003 ) and Tetrix undulata (Forsman et al.
2002 ); courtship display in two Drosophila spe-
cies (Yeh et al. 2006 ). Genetic analysis of D.
melanogaster mutants affecting body colour
also differ in mating success (de Magalhaes and
Rodrigues-Pereira 1976 ; Mizugushi and Almeida
1983 ). For wild populations of Drosophila spe-
cies, associations between body colour morphs
and copulation duration (CD) have been shown
for Drosophila elegans (Hirai et al. 1999 ). Re-
cent data on D. melanogaster has shown that
changes in body melanisation are correlated with
mating-related traits (Parkash et al. 2011 ; Dev
et al. 2013 ) and not with body size.
Mating speed and CD are fitness-related traits
in diverse insect taxa (Prakash 1967 ; Spiess
1970 ; Pitnick 1991 ; Markow 1996 ; Lefrance and
Bundgaard 2000 ). Both these traits are under
polygenic control and respond to laboratory se-
lection. Such experiments have resulted in strains
with faster and slower mating speeds (Spiess and
Langer 1964 ; Brncic and Koref-Santibanez 1964 ;
Kessler 1969 ) and longer and shorter CDs (Mac-
bean and Parsons 1966 ; Gromko et al. 1991 ).
However, laboratory selection experiments have
not considered correlated changes in body size or
body melanisation. Thus, it is not clear whether
there are direct or correlated selection responses
for mating-related traits in Drosophila species.
Drosophila immigrans is a cold-adapted cos-
mopolitan species characterised by larger body
size and lack of sexual dimorphism in body mela-
nisation; and a much longer CD of about 45 min
(Markow and O’Grady 2006 ) in comparison to
other Drosophila species. Accordingly, this spe-
cies is suitable for comparing the impact of body
size vs. abdominal melanisation on mating suc-
cess. The present study involves addressing the
following questions: (a) Whether field collected
copulating pairs and noncopulating flies dif-
fer in body size or body melanisation? (b) Do
heritable strains for body size (large vs. small)
or body melanisation (dark vs. light) differ in
mating success? (c) Do laboratory-selected dark
and light strains influence mating success in D.
immigrans? Body size and body melanisation in
both the sexes; mating latency (ML), and CD in
different strains of D. immigrans were analyzed.
Laboratory strains for mating propensity under
no choice experiments were compared in crosses
for small- and large-sized flies of both the sexes
for differences in ML, CD and body melanization
of homo- and hetero-specific matings. Finally,
mating success of laboratory selected dark and
light strains in D. immigrans was compared.