What will satisfy
these cravings? I should ask my
tiny passengers.
Choosing what and how much to eat is crucial as even those nutrients that are normally beneficial can be harmful if consumed excessively. But the mechanism for how animals regulate the amount they eat isn’t always clear.
The common fruit fly develops a strong appetite for amino acid-rich food if fed a diet lacking in certain essential amino acids, and the fly’s reproductive effort will also decrease. However, this change in appetite and reproduction is suppressed if the fly has certain species of gut bacteria. Interestingly, when given the choice fruit flies will eat more food that contains these bacteria than food that doesn’t suggesting an ability of the flies to direct their own gut bacterial microbiome.
How the bacteria influence fruit fly behaviour and physiology is uncertain but results suggest that it is not down to the bacteria producing the missing amino acids for the flies or that the flies are consuming the bacteria themselves. Possible explanations are that the bacteria secrete metabolites that help the flies use their remaining amino acids more effectively or that the bacteria directly modulate the flies own nutrient sensing pathways so that the flies don’t recognise a decrease in amino acids. Leitão-Gonçalves et al, 2017.