Abstract
Vertebrates exhibit extensive variation in brain size. The long‐standing assumption is that this variation is driven by ecologically mediated selection. Recent work has shown that an increase in predator‐induced mortality is associated with evolved increases and decreases in brain size. Thus, the manner in which predators induce shifts in brain size remains unclear. Increased predation early in life is a key driver of many adult traits, including life‐history and behavioral traits. Such results foreshadow a connection between age‐specific mortality and selection on adult brain size. Trinidadian killifish, Rivulus hartii, are found in sites with and without guppies, Poecilia reticulata. The densities of Rivulus drop dramatically in sites with guppies because guppies prey upon juvenile Rivulus. Previous work has shown that guppy predation is associated with the evolution of adult life‐history traits in Rivulus. In this study, we compared second‐generation laboratory‐born Rivulus from sites with and without guppies for differences in brain size and associated trade‐offs between brain size and other components of fitness. Despite the large amount of existing research on the importance of early‐life events on the evolution of adult traits, and the role of predation on both behavior and brain size, we did not find an association between the presence of guppies and evolutionary shifts in Rivulus brain size. Such results argue that increased rates of juvenile mortality may not alter selection on adult brain size.
Highlights
It has long been known that vertebrates exhibit extensive variation in brain size (Bauchot, Bauchot, Platel, & Ridet, 1977; Crile & Quiring, 1940; Jarvis et al, 2005; Mink, Blumenschine, & Adams, 1981; Striedter, 2005; Taylor & van Schaik, 2007)
Research has shown that increased allocation to brain tissue leads to declines in other components of fitness (Kaufman, Hladik, & Pasquet, 2003; Kotrschal et al, 2013a; Mink et al, 1981; Navarrete et al, 2011; Raichle & Gusnard, 2002; Tsuboi et al, 2015)
Our results show that increased rates of juvenile predation and correlated increases in resources in fish communities with guppies are not associated with consistent divergence in adult brain size of Rivulus (Table 1; Figures 1 and 3)
Summary
It has long been known that vertebrates exhibit extensive variation in brain size (Bauchot, Bauchot, Platel, & Ridet, 1977; Crile & Quiring, 1940; Jarvis et al, 2005; Mink, Blumenschine, & Adams, 1981; Striedter, 2005; Taylor & van Schaik, 2007). 2013b; MacLean et al, 2014; Kotrschal et al, 2015a; Kotrschal, Corral-Lopez, Amcoff, & Kolm, 2015b; Benson-Amram, Dantzer, Stricker, Swanson, & Holekamp, 2016; and see Drake, 2007). Key hypotheses, such as the expensive tissue hypothesis (i.e., expensive metabolic cost of brain tissue) (Aiello & Wheeler, 1995; Isler & van Schaik, 2009) and energy trade-off hypothesis (increased encephalization leads to trade-offs with other functions) (Isler & van Schaik, 2006a,b, 2009; Navarrete, van Schaik, & Isler, 2011; Tsuboi et al, 2015), recognize that brain tissue is costly and that fitness trade-offs likely underlie increased encephalization (Aiello & Wheeler, 1995). The specific ecological drivers of brain size variation have largely remained elusive
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