Abstract
Behavioural lateralization, the asymmetric expression of cognitive functions, is reported to enhance key fitness-relevant traits such as group coordination, multitasking and predator escape. Therefore, studies reporting negative effects on lateralization in fish due to environmental stressors such as ocean acidification, hypoxia and pollutants are worrisome. However, such studies tend to use a detour test and focus on population level measures, without validating whether lateralization is consistent within individuals across time. We conducted a multispecies, international assessment of the repeatability (R) of lateralization in four previously studied fish species using a detour test (T-maze), a common method for testing lateralization. We also reanalysed a published data set on a fifth species using new statistical methods. We expected the three shoaling species to exhibit greater within-individual consistency in lateralization than their nonshoaling counterparts given previous reports of stronger lateralization in group-living fishes. Absolute and relative lateralization scores were highly nonrepeatable in all five species (0.01
Highlights
Behavioural lateralization in a detour test is not repeatable in fishes Dominique G
Population level lateralization was statistically apparent in five of the 22 trial series; two species exhibited a population side bias, but this bias changed with test day for D. rerio and with stimulus type for P. reticulata (Supplemetnary Table S2, Figs S4eS8)
lateralization index (LR) was highly variable within individuals, and individual identity explained less than 6% of the variance in relative lateralization across the four species tested, with repeatability estimates ranging from R 1⁄4 0.006 to R 1⁄4 0.028 (Table 1, Fig. 3, Supplementary Fig. S1)
Summary
Behavioural lateralization in a detour test is not repeatable in fishes Dominique G. Lateralization score in a detour test is reported to be heritable (Bisazza, Facchin, & Vallortigara, 2000b; Brown, Western, & Braithwaite, 2007), lateralization strength decreases rapidly across generations in artificial selection lines (Bisazza, Dadda, Facchin, & Vigo, 2007; Facchin, Argenton, & Bisazza, 2009) These results have led researchers to assert that the detour test does, assess inherent asymmetry in an individual's brain function that influences fitness-relevant behavioural strategies. Ocean acidification is reported to decrease lateralization across a range of marine fishes, including tropical (Domenici, Allan, McCormick, & Munday, 2012; Nilsson et al, 2012; Welch, Watson, Welsh, McCormick, & Munday, 2014) and temperate species (Jutfelt, Bresolin de Souza, Vuylsteke, & Sturve, 2013; Lopes et al, 2016; Maulvault et al, 2018) Such effects are concerning given, for example, the important benefits of lateralization reported for fishes under high predation risk Establishing the consistency of lateralization within individuals is essential for determining the relevance of this trait for evaluating fitness as well as the responses of animals to exogenous stressors (see Roche, Bennett et al, 2019)
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