D. subobscura is
monandrous, a behavior not usually seen among
Drosophila. Visual stimuli dictate
courtship behavior.
D. subobscura do not mate in the dark and do not produce a courtship song via wing vibrations like other species of Dipterans. Instead, the lone male repeatedly “scissors” its wings, an activity augmented in the presence of other flies. This behavior indicates that the male is looking to court a female. When a female appears, the male taps her with his own front legs. The male then stands in front and directly faces the female to stick out his
proboscis. The male and female then start to “dance”, as the female rapidly sidesteps, while the male tries to keep himself directly facing the female. During the dance, the male's wings are usually raised and extended. Sometimes, mounting can occur without a dance taking place prior. At this point, the female has two options: she can either end the dance, without mating, by turning away from the male and leaving, or she can stand still, extend her own proboscis, and invite the male to mount her by parting her wings. In the latter behavior, the male stretches its wings sideways and swings behind the female to mount her. The male and female probosces may or may not touch beforehand. Although males always extend their own proboscis, this activity within the female varies greatly. Activities among three consecutive male-female courtships showed three different female behaviors: 1) no protrusion of the proboscis, 2) continued extension of the proboscis for several seconds after mounting had occurred, and 3) repeated protrusion and withdrawal of the proboscis before the male mounted.
Sexual selection D. subobscura practice
nuptial feeding, a practice where a nutritional gift is transferred from one partner to another during/directly after courtship and/or copulation. In the case of
D. subobscura, the gift is a regurgitated drop of liquid secreted from the male's crop, onto the female's proboscis. Preventing production and exchange of nutritional gifts among
D. subobscura has been shown to decrease both male mating success and egg count among females. It has been shown that males that are in good condition produce more nutritional gifts, thereby increasing their
mating success. Additionally, starved females show preference for well-fed males as a way to increase the female's
fecundity – this preference is speculated to be the case due to the greater quantity of drops that well-fed males produce. If larger males, carrying bigger nutritional gifts, are prevented from producing their gifts, then small males are more successful in female courtship, due to better tracking of the female during the courtship dance. Larger males are seen to have slower acceleration and deceleration speeds.
Inbred male behavior Reported observations of
mating behavior in
inbred males reveal that in most cases, active
courtships were seen, but mating did not normally follow. However, prolonged dances were rare. In some instances, the male directly approaches the female, in which the female steps sideways several times in front of the stationary male, before ultimately turning away. Occasionally, the male attempts to follow the sidestep movements of the female but would often lag behind and struggle to consistently face the female. In the incident that the female stands still and extends her proboscis, the male usually would attempt to mount. More often than not, the inbred male would fall on his back, or land too far forward or too far back on the female. In the case of the latter, the female normally stands still with her
wings partially extended before eventually kicking off the male. Inbred males who have continuously but unsuccessfully attempted to court a female may approach the female from the side or behind and attempt to directly mount, a behavior described as “desperation” to some scientists. These mating attempts remain unsuccessful. The observed lower mating success in inbred males has been thought to be due to lower athletic ability via physiologically-efficient
muscles,
sense organs, and neuromuscular coordination, rather than lower intensity of courtship. Upon suppressing the gut bacteria of female
D. subobscura with
antibiotics, researchers observed that these females mated faster with males that had intact
microbiota. Females with intact gut bacteria were less willing to mate with males that had intact microbiota. Additionally,
fecundity was seen to increase when the gut bacteria of male and female
D. subobscura were suppressed through antibiotics, compared to no suppression. == Genetics ==