HIREC-driven superiority of plastic individuals
Natural selection will favor well-adapted heritable phenotypes in a new
environment and lead to genotypic change over time. However, most
environmental changes associated with HIRECs seem to occur rapidly and
plasticity plays an essential role in determining the phenotype that
will survive (Diamond & Martin 2016). Phenotypic changes for
individuals exposed to HIREC are largely documented in response to
exposition to contaminants, temperature, acidification, environmental
noise, etc. Individuals with the best capacities to respond rapidly via
changes in behavior (van Baaren & Candolin 2018) or physiology (Taff &
Vitousek 2016) are therefore the most likely to survive HIREC, as seen
with climate change (Beever et al. 2017). In a number of taxa,
proactive and reactive phenotypes diverge in their capacities to respond
to environmental changes (Table 1). Case studies highlighted the ability
of reactive individuals to be more behaviorally plastic in a wide range
of circumstances. In rats selected for their aggressive behavior,
proactive individuals developed routines, a superior strategy when in
predictable environments (or situations) but not when the environment
frequently changes (Benus et al. 1991).
Plasticity has nevertheless an energetic cost (Moran 1992; Murrenet al. 2015). Consequently, in a stable environment, proactive
individuals, which are less plastic than reactive individuals, are
expected to better perform because less energy is invested in coping
abilities, memory and learning capacities (Table 1). The costs of
plasticity have been demonstrated in great tits (Parus major ),
where fast exploring/proactive individuals performed better in stable
environments, while the slow exploring/reactive individuals performed
better in a variable and fluctuating environment (Dingemanse & de Goede
2004). And, after transport from UK to Norway, reactive rainbow trout
(Oncorhynchus mykiss ), had greater feeding motivation and started
to win dyadic fights against proactive opponents which was not the case
prior transportation (Ruiz-Gomez et al. 2008). Moreover, reactive
rainbow trout are also more efficient at finding food than proactive
ones in response to environmental changes (Ruiz-Gomez et al.2011). In addition, reactive fish performed better in cognitively
complex foraging tasks, even after modifications to their environment
(White et al. 2017). Similar conclusions were drawn in birds
(Verbeek et al. 1994) and pigs (Bolhuis et al. 2004) where
proactive individuals were less successful in reversal learning than
reactive pigs, suggesting that proactive individuals display a less
plastic behavior. In a monogamous species, the red point cichlid
(Amatitlania siquia ), reactive individuals were better at varying
their behavioral profile within pair (Laubu et al. 2016) which is
important to enhance their reproductive success (Gabriel & Black 2012;
Harris & Siefferman 2014). Finally, fish with different coping styles
also diverge in their sensitivity to environmental cues. Indeed,
reactive individuals have been shown to be more responsive to negative,
aversive, stimuli while proactive individuals are more sensitive to
positive stimuli (Millot et al. 2014).
Altogether, reactive individuals have increased behavioral capacities to
cope with rapid environmental changes. This is also seen at the
physiological level, with reactive individuals showing higher capacities
to mount physiological responses required to cope with environmental
challenges (Fig. 1.2) due to greater HPI/A axis activation when facing a
stress.