Abiotic factors
Organisms may remember more accurate and reliable cues in order to predict and know the presence of predators, although reliable cue selection mechanisms are unknown. If the emergence of predators is seasonal/temporal, daphniids may be able to detect and respond to abiotic seasonal factors. Abiotic factors, including water temperature (Bernot et al. 2006; Hanazato 1991; Lass and Spaak 2003; Sakwinska 1998; Yurista 2000; Weetman and Atkinson 2004), turbulence (Havel and Dodson 1985; Laforsch and Tollrian 2004), light (Boeing et al. 2002; Rhode et al. 2001; Rose et al. 2012), and copper and other minerals (Hunter and Pyle 2004; Mirza and Pyle 2009), can affect the degree of predator-induced plasticity, but there is no fixed trend. These factors may work together with the primary factors, or they may work on their own. These abiotic factors may change the chemical composition of the predatory kairomone and thus reduce their effect on the organism. Temperature manipulation have shown that the degree of plasticity varies with differences in temperature alone, regardless of kairomone concentration (Sakwinska 1998), and that other crustaceans have spines that elongate in the absence of kairomone but only at high temperatures (Miehles et al. 2013). Since these abiotic factors strongly influence the survival and life history traits of daphniids in the first place, abiotic factors may often limit expression plasticity even when the primary factors are detected.
The degree of expressed plasticity is thought to be both enhanced and suppressed in such environments, and may be enhanced when Daphnialinks periodic changes (i.e., seasons) in predator presence to physical stimuli and may be suppressed in the absence of relationships with cycles (Riessen and Gilbert 2018). Miehles and her colleagues, studying the plasticity of Bythotrephes , have called this type of factor a ”proxy cue” (Miehles et al. 2013). These factors are associated with local predator regimes and thereby cause intraspecific variation between populations. If primary factors are not reliable cues of predation risk, the abiotic factors would be accurate and useful factors. Moreover, abiotic factors that correlate with selective agents work similarly to primary factors and alone can cause an inducible defense on their own (Miehles et al. 2013). The phenomenon of inducible defense without primary factors is well known, although there is a lack of experimental support for identifying these factors. This factor may be the most reliable cue of the emergence, presence, and predation cycle of predators that is closest to Daphnia itself.