For her M.S. thesis, Valerie is studying the physiological basis for range limits of sea slugs in the genus Alderia. These estuarine slugs are specialist herbivores that settle and feed solely on the alga Vaucheria longicaulis. Val found the range boundary between sister species of Alderia shifts seasonally between San Francisco and Tomales bays, and has moved 180 km north in the last 50 years, likely due to global warming. The southern species A. willowi tolerates higher temperatures (up to 36°C), allowing it to colonize northern bays in summer, but is eliminated by winter rain. Conversely, the northern species is adapted to high rainfall, surviving salinities down to 2‰, but cannot tolerate summer temperatures south of Tomales. Physiological tolerance of larvae mirrored that of adults, but the buffered environment of the water column protects larvae from the extremes of the intertidal.
Val found that A. willowi has been selected for low salinity tolerance at its northern range limit, but as a result shows trade-offs in reproduction and growth. Such constraints are predicted by evolutionary theory but have rarely been documented in marine invertebrates, and will be studied by future students.
Valerie gave oral presentations at two international conferences, and has presented at numerous area middle and high schools.