ALBERS, MA; BRADLEY, TJ; Univ. of California, Irvine; Univ. of California, Irvine: The Evolution of Saline-Tolerance in Mosquito Larvae

Of the mosquito species belonging to the genus, Ochlerotatus, several have been shown to be saline-tolerant as aquatic larvae while others are restricted to freshwater. This saline-tolerance is associated with a morphological difference in the rectum, an organ that serves an osmoregulatory function in these insects. The saline-tolerant forms have a two-part rectum while the freshwater obligates have a one-part rectum. Of the many species among this genus whose saline-tolerance has not been described, we have collected several in their larval stages. Upon collections we have performed a salinity assay and a morphological analysis of the rectum. To determine saline-tolerance, mosquito larvae were gradually taken from dilute waters to 1000 mOsm. Those with high survival to pupation in solutions up to 1000 mOsm were determined to be saline-tolerant. We then looked at the evolutionary patterns of saline-tolerance in this genus by mapping this character onto a phylogenetic tree. We constructed this tree by direct sequencing the 18s rRNA gene and the D2 region of the 28s rRNA gene for each species and used MEGA3 software to assemble the tree. This robust tree does not indicate a single point when the saline-tolerant and intolerant forms split. Instead, it is evidence that saline-tolerance evolved once and was subsequently lost or arose multiple times.