Increased juvenile predation is not associated with evolved differences in adult brain size in Trinidadian killifish (Rivulus hartii)

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.

The evolution of vertebrate eye size across an environmental gradient: phenotype does not predict genotype in a Trinidadian killifish

“…Similar to the current study, Rivulus from low predation and Rivulus ‐only sites did not differ in brain size (Beston et al. ). Rivulus from high predation sites also exhibited significantly smaller brains than fish from Rivulus ‐only sites (Walsh et al.…”

“…; Beston et al. ). The question that naturally arises is: Did we observe parallel trajectories of evolution for brain and eye size?…”

“…; see also Beston et al. ). These known connections between predation and the evolution of other components of fitness provide a means to test the role of predation, and the ecological correlates of predation, on eye size evolution.…”

“…Research has shown that there is a strong covariation between eye size and brain size across taxa (Garamszegi et al 2002). We previously evaluated Rivulus for evolved differences in brain size among high predation, low predation, and Rivulus-only sites (Walsh et al 2016;Beston et al 2017). The question that naturally arises is: Did we observe parallel trajectories of evolution for brain and eye size?…”

“…Increased light availability is commonly associated with declines in eye size (Hiller-Adams and Case 1985;Garamszegi et al 2002;Thomas et al 2006;Lisney and Collin 2007;Ross and Kirk 2007;Hall 2008;Veilleux and Lewis 2011;Pearce and Dunbar 2012), while higher resource availability is correlated with the production of a larger relative eye size (Brandon and Dudycha 2014). The "direct" (i.e., increased mortality) and "indirect" (i.e., increased food availability) consequences of predation intensity in the Trinidad system have been linked to shifts in life history traits, behavior, and even complex traits such as brain size (Gilliam and Fraser 2001;Walsh and Reznick 2008Walsh et al 2016; see also Beston et al 2017). These known connections between predation and the evolution of other components of fitness provide a means to test the role of predation, and the ecological correlates of predation, on eye size evolution.…”