Reproductive Biology

Even Flies Have Cravings

Science Signaling  15 Jun 2010:
Vol. 3, Issue 126, pp. ec178
DOI: 10.1126/scisignal.3126ec178

Mated female flies exhibit several behavioral changes, including enhanced food intake after mating. Many of these responses are lost if female flies are mated with males lacking sex peptide (SP), a hormone present in seminal fluid (see Kubli). Two groups (Ribeiro and Dickson and Vargas et al.) investigated the mechanism underlying food preferences in fruit flies. Ribeiro and Dickson found that mated female flies, but not virgin females, ate more yeast-containing food after a period of protein deprivation. (Yeast are a major source of protein for flies.) Males also exhibited a switch from sugar-rich food to yeast-rich food but required a longer period of deprivation. Vargas et al. reported that even without nutrient deprivation, the mated females ate more yeast-rich food than did either males or virgin females. Ribeiro and Dickson found that mated female flies lacking the receptor for SP (SPR) failed to show the switch in food preference after deprivation, and restoration of SPR function in reproductive tract sensory neurons rescued the food preference defect. Furthermore, females mated to SP-deficient males showed a reduced switch in food preference, which suggests that SP and other SPR ligands likely contribute to this phenomenon. Egg production (and thus altered nutrient status due to increased demand) was not required for the switch in food preference because females rendered genetically deficient in egg production continued to show the increase in yeast consumption after mating and deprivation.

However, both groups provide evidence that the nutrient-sensing pathway mediated by TOR (target of rapamycin) and S6K (ribosomal S6 kinase) in the brain plays a complex role in food preferences in flies. Ribeiro and Dickson reported that overexpression of inhibitors of the TOR pathway (Tsc1 and Tsc2) triggered a switch to yeast-containing food in males. Vargas et al. found that overexpression of constitutively active dS6K triggered an increase in yeast consumption in virgin females compared with virgins expressing either wild-type dS6K or a dominant-negative mutant. In contrast, mated female flies showed a similar preference for yeast-rich foods regardless of the type of overexpressed dS6K. Virgin flies with the active dS6K also exhibited increased production of neuronal serotonin, and addition of a serotonin precursor to the food stimulated an increase in yeast-rich food consumption in the virgin females. This effect was lost if the virgins expressed the constitutively active dS6K, and increasing serotonin did not alter feeding of mated females. Together these two reports suggest that virgin fly food preference appears to be regulated by neuronal TOR and serotonin signaling but that process is overridden upon mating by other signals, especially those mediated by SPR.

C. Ribeiro, B. J. Dickson, Sex peptide receptor and neuronal TOR/S6K signaling modulate nutrient balancing in Drosophila. Curr. Biol. 20, 1000–1005 (2010). [PubMed]

M. A. Vargas, N. Luo, A. Yamaguchi, P. Kapahi, A role for S6 kinase and serotonin in postmating dietary switch and balance of nutrients in D. melanogaster. Curr. Biol. 20, 1006–1011 (2010). [PubMed]

E. Kubli, Sexual behavior: Dietary food switch induced by sex. Curr. Biol. 20, R474–R476 (2010). [PubMed]