2. Alderia willowi. Identifying why populations switch from dispersing to non-dispersing larvae should yield insight into how natural selection drives the evolution of alternative larval strategies, an outstanding question in life-history evolution.  We described A. willowi after molecular and morphological data revealed populations south of Bodega Harbor, CA were distinct from A. modesta, its northern (and exclusively planktotrophic) congener (Ellingson & Krug 2006; Krug et al. 2007). Alderia willowi is the only known animal in which an individual can produce both planktotrophic and lecithotrophic larvae during its lifetime (Krug 2007). Although all opisthobranch sea slugs are hermaphrodites, A. willowi is the only species confirmed to self-fertilize in the recent literature (Smolensky et al. 2009). This species was named in joint tribute to willow trees, beloved by my grandmother and which the cerata of Alderia resemble, and the character Willow from TV's Buffy the Vampire Slayer who displayed a similarly flexible sexual behavior.

Field populations of A. willowi seasonally switch to non-dispersive lecithotrophic larvae in the summer, a potential adaptation to the historical closure of estuaries during the dry season, when water levels are low in Californian lagoons. Rearing experiments showed that slugs raised at high temperature and salinity produced primarily lecithotrophic larvae, while those raised at low temperature and salinity produced mostly planktotrophic larvae (Krug et al. 2012). Thus, slugs use environmental cues to produce dispersive larvae during the rainy season when the input of runoff opens estuaries to the coastal ocean, suggesting selection favors lecithotrophy when dispersal is rendered unlikely by physical transport regimes.