Humans wax the surfaces of beautiful objects to show them off at their best, but for most creatures, wax is much more than a cosmetic. Jean-Francois Ferveur explains that each strain of Drosophila secretes a distinct waxy mixture that protects them from dehydration in the climate they are adapted to. The mixtures have even been used to identify some rare species in museum collections. The males and females from each strain also subtly modify the wax mixture, so that it uniquely identifies each gender's identity, so reading a male's hydrocarbon signature is critical for female flies to find their perfect mate. Knowing the importance of the hydrocarbon gender differences in communication, Ferveur wants to understand how the flies synthesise their distinct wax message within the first 24 hours of life. Knowing that the environmental temperature affects the size distribution of the hydrocarbon chains, Ferveur used temperature shock to modify the male and female hydrocarbon signatures, and found that the unique mixture of hydrocarbons that define male flies are synthesised within the first twelve hours of adult life(p. 3241).
Out of the complex hydrocarbon mixtures produced by most fruit flies, only a few major components are necessary to define the fly's sex and species. Females tend to express longer chained hydrocarbons, while males secrete shorter hydrocarbons, but how the flies control the ratios of hydrocarbons that identify them, wasn't clear.
Ferveur looked at the way two groups of flies from different climatic regions altered their hydrocarbon pattern in response to different environmental temperatures. The flies that had originated from a temperate region, responded in the way he'd expected, producing shorter chained hydrocarbons when reared at cooler temperatures, and longer more waterproof hydrocarbons at higher temperatures, while flies that originated from a hot climate didn't modify the mix when transferred to a colder climate, they stuck to the longer chains.
But Ferveur needed a way of interfering with the flies' hydrocarbon synthesising machinery to understand how they establish their wax identity. The idea of using the fly's heat shock response came by chance. Ferveur had generated a transgenic male Drosophila that carried an active sex specific gene usually expressed in females. The transgenic males secreted a mixture of males and female signature hydrocarbons, unless they experienced a heat shock within 24 hours of hatching. The heat shock completely stopped all production of the waxy hydrocarbon layer.
Heat shocking the transgenic males at three-hour intervals, Ferveur found that the male defining hydrocarbon chains vanished when the flies were heat shocked within six hours of hatching. A heat shock delivered between six and twelve hours knocked out synthesis of both sexes' defining hydrocarbons. Male and female signatures are synthesised at different times, giving Ferveur the chance to identify the key enzymes that set the sexes apart.
Temperature is clearly a significant factor involved in establishing the flies' sexual identity, which could explain why Drosophila cocoons hatch before the dew has evaporated. He wonders if this is more than just happenstance, or is it a strategy to stop male flies sending out mixed messages?