Evolutionary shifts observed in response to HIREC
Artificial selection pressures, such as those created by humans, are capable of driving both behavioral and physiological changes in response to selection. For example, fish with bold phenotypes can be preferentially (and unintentionally) harvested, resulting in the selective depletion of bold individuals (Biro & Post 2008). Differences in personality can also result in sampling biases during scientific sampling, with bolder individuals being caught more often (Biro & Dingemanse 2009). Intensive fishing selects on life history traits (growth, maturation, reproduction), but demonstrations of fishing’s effects on behavior remained scarce until the last decade (Uusi-Heikkiläet al. 2008). Fishing methods are diverse, apparently leading to distinct selection pressures on behavior (Diaz Pauli et al. 2015; Arlinghaus et al. 2017). Passive fishing (e.g., using long-lining, angling, trapping or gill nets) preferentially catch proactive individuals (Biro & Post 2008; Arlinghaus et al.2017), while active gear (e.g., trawls or purse seines) unintentionally targets reactive individuals (Heino & Godø 2002; Diaz Pauli et al. 2015).
Although hunting has less pressure on wild populations in many places compared to fisheries, it too selects for specific behavioral traits. Madden and Whiteside (Madden & Whiteside 2014) showed for example that shyer pheasant (Phasianus colchicus) are more likely to survive to the hunting season than bolder ones. In wild reindeer (Rangifer tarandus ), a long-term study also showed that hunting pressure is correlated with an increase in flight distance over years, suggesting that populations become shyer because of hunting pressure (Reimers et al. 2009). Ciuti et al (Ciuti et al. 2012) drew similar conclusions with elk (Cervus elaphus ), where harvested individuals were bolder. In this context, hunting leads to the same result than passive fishing, selecting for bold individuals and therefore favoring reactive phenotypes. Inversely, the less active animals die from active hunting techniques, such as when dogs are used to chase animals, as seen in bear-hunting (Leclerc et al. 2019). As a consequence, the HIRECs linked to fishing and hunting seem to favor one coping style over the other depending on whether the harvesting technique is active or passive.
Rapid environmental changes also may lead to evolutionary changes in the physiology and behavior of wild populations. For instance, climate change has been demonstrated to favor selection for highly plastic individuals over multiple generations (Nussey et al. 2005). In addition, multigenerational exposure to high temperatures reduces standard metabolic rate (Pilakouta et al. 2019). Global climate change may lead to the reduction of migratory distances in birds (Visseret al. 2009), and this phenomenon is an evolutionary response to selection (Pulido & Berthold 2010). High plasticity, reduced metabolic rate, and low standard metabolic rate all favor reactive phenotypes, and we may infer that climate change is driving the evolution of reactive phenotypes (Fig. 1.3.2). It is nevertheless worth noting that tropical cyclones seemingly select for aggressive phenotypes (Little et al. 2019), and in this case we would infer that proactive individuals are better adapted to survive.
We have long known that populations evolve in response to exposure to pollutants and with the toxification of Earth; this has become a common driver of HIREC. Empirical studies in the lab monitoring the evolution of behavioral and physiological traits following exposure to pollutants are rare, despite abundant evidence of rapid evolutionary responses (Whitehead et al. 2017; Saaristo et al. 2018). If the exposure to only one pollutant selected one behavioral response (e.g., boldness or activity), it could be attenuated by a plastic behavioral response (Saaristo et al. 2018). However, the large number and diversity of pollutants, each with different properties, and the possible interactions between them (Peterson et al. 2017; Saaristo et al. 2018), as well as the method of exposure, act as multiple environmental stressors for organisms which have to continuously adapt to new threats and stressors. We suggest that plasticity, a characteristic of reactive phenotypes, will be the key to cope with the diversity of stressors created by pollution.
Urbanization, ecotourism and domestication, have all been found to increase boldness of affected populations (Geffroy et al. 2015b). Effects of urbanization on bird behavior have been extensively studied and show that living in urban areas leads to reduced flight initiation distance (Samia et al. 2015), and higher risk-taking behavior (Miranda et al. 2013). However, adaptation to an urbanized environment also requires substantial individual plasticity. For instance, in response to urban noise, great tits increase their pitch during mating calls to increase the likelihood that potential mates receive the signal (Slabbekoorn & Peet 2003). Similar results have been seen in killer whale (Orcinus orca ) which increased the amplitude of their calls as a function of background noise levels related to ships or tourism boats (Holt et al. 2009). In terms of physiology, reduced stress reactivity was also observed for urban individuals (Partecke et al. 2006; Atwell et al. 2012). Taken together, these studies show that urban areas select for more proactive individuals. In the context of domestication, individuals are often selected for either their docility or their reproductive potential. Both types of selection types lead to bolder individuals in response to both human and potentially other predators (Geffroy et al. 2015b), and reduced HPI/A reactivity (Rauw et al. 2017), which favors proactive individuals. In the context of both, urbanization and domestication, humans create a “human shield” (Berger 2007), where selection pressure is relaxed and bold individuals are favored. Disappear