The environment and social dynamics influence the brain and sensory mechanisms underlying courtship: this is the case in fruit flies, but not only.
Not a simple one step by stepbut a biological dynamic strongly influenced by the surrounding environment and sociality: according to a study published in Naturethis second definition better describes courtship. Ecology and social context influence sexual attraction between animals much more than previously believed, acting down to the level of the neural circuits that govern flirting.
The authors of the research, a group of evolutionary neuroscientists from the Max Planck Institute for Brain Research in Frankfurt (Germany) demonstrated this not on humans but on a species of fruit fly which, like us, needs the right atmosphere to trigger courtship.
The dance floor effect
If for us the spark that makes us move towards the potential partner is – sometimes – a crowded dance floor, with the right music and the desire to dance, for the Drosophila erecta it is the smell of ripe fruit that ignites passion and awakens courtship. An environment full of other moving midges and pervaded by the aroma of food is a powerful aphrodisiac for these insects, who are not a social species.
Knowing this “weak point” of theirs, scientists have for once studied courtship between fruit flies by broadening their gaze beyond the individual couples forced to court each other in the aseptic environment of the laboratory and looking at a broader context, populated by fruit flies and more similar to what occurs in nature.
No fruit, no party
Scientists recreated different environments that reproduced as many possible situations in which a male D. erecta he could find himself: alone or with others of his kind, in an environment pervaded by the smell of fermenting fruit (reproduced in the study with apple cider vinegar) or without odors.
While other drosophila commonly used in biology studies, such as D. melanogasterthey mated with the females both in the presence of the smell of apple cider vinegar and without, distributing themselves uniformly in the space available, the males of D. erectain the absence of the scent, they remained motionless and uninterested in the other midges.
Turned on by food and the presence of others
But the smell of vinegar woke them up, triggering an intense courtship towards any fly, male or female, nearby, until they found a partner: 9 out of 10 matings took place in the area where the vinegar had been sprayed. Not only that: the movement of nearby midges increased the excitement of the males, who in more populous contexts courted more vigorously than when only their partner was present.
Time pressure
The visual neurons of D. erecta they were activated only in the presence of the smell of food, and the greater visual acuity attracted the males towards their peers, pushing them towards the most crowded area (the one with apple cider vinegar).
This dynamic increased the stimuli in the flies’ visual field, increasing sexual arousal, in a sort of vicious circle.
“This feedback mechanism gives rise to collective behaviors of the type observed in schools of fish, flocks of birds or swarms of locusts,” explains Vanessa Ruta, head of the laboratory. «These creatures, typically non-social, are actually strongly influenced by their social environment and the ecological context in which they live. And olfactory information acts like a very rigid filter that modifies the weight that visual cues have on courtship behavior.”
From an evolutionary perspective, this makes perfect sense for Drosophila. The D. erecta they feed on the fruit of a plant – the Pandanus candelabrum, a species of palm typical of Senegal and Cameroon – which is only available for two to four months of the year: when this is ripe, the environment becomes very competitive and you cannot lag behind in courtship.
