LEPCO, Faculté des Sciences, Parc de Grandmont, 37200, Tours, France.
Many insects living in the deserts escape to the climate's rigors by sheltering or by diapausing during the most unfavorable periods. On the contrary, Cataglyphis ants leave their nest in the full heat. In this study, we investigated if their adaptation is due to a reinforcement of the impermeability of their cuticle, limiting their body water losses by transpiration. The surface cuticular lipids, mainly composed of hydrocarbons (HC), are the principle responsible of the tegument impermeability. We hypothesized that there is a correlation between quantity and/or composition of cuticular HC and the impermeability of the cuticle. We compared the rate of transpiration, the lethal temperature and the cuticular HC composition of various species of Cataglyphis and of Myrmica rubra (living in temperate environments). Cataglyphis workers lose less water than Myrmica, but this greater cuticular impermeability is not due to an increase in HC quantity, Myrmica containing nearly 4 times more than Cataglyphis. On the other hand, the latter has a relative quantity of saturated and long chain HC higher than that of Myrmica. The cuticular permeability is the same both in small and big ants, which thus loose the same quantity of water per unit of surface. Consequently, small ants handicapped by their surface /volume/ratio, will be less resistant.We discuss the implications of these results in relation to the adaptation to the arid environments.