Relationships between water balance properties and habitat characteristics in the sibling Hawaiian Drosophilids,D. mimica and D. kambysellisi

Summary Four populations of Drosophila mimica and 1 population of D. kambysellisi collected at sites which differed in wetness were examined for several water balance characteristics. Net water loss per hour increased as a_v (relative humidity/100) decreased in all populations, but the rate of increase was lower in populations from dry sites. When exposed to 0.70 a_v, D. kambysellisi, which were from a rain forest, lost water faster and died sooner than did D. mimica. Two D. mimica collecting sites were divided into smaller units based on substrate type at one site and on litter wettness at the other site. The D. mimica at the first site were homogeneous with respect to the water balance properties studied here, but in the second site, there was evidence of population differentiation associated with litter wettness.Supported by research grant NSF DEB77-23370, training grants NIH 5 TO1 GM 00337-16 and NIH 5 T32 GM 07126-02 and a Grant-in-Aid from the Sigma Xi Society     

Physiological aspects of water balance in the Hawaiian drosophilid, Drosophila mimica

The ability to resist desiccation is an important component of biological fitness for terrestrial organisms. Several water balance characteristics have been studied for a strain of laboratory-reared Drosophila mimica and for four populations of D. mimica collected at sites differing in altitude and wetness. In the absence of drinking water, D. mimica are unable to maintain a water balance, even in nearly saturated environments. However, as a_v ($\text{a}{}_{\mathrm{v}}\text{=}\text{r.h.}\text{100}$) decreases, transpiration does not increase as rapidly as expected and absorption remains nearly constant. The size of the fly is not correlated with its water loss characteristics, but some differences in regulation between the sexes are suggested.