Dietary quality and encephalization in platyrrhine primates

Abstract

The high energetic costs of building and maintaining large brains are thought to constrain encephalization. The 'expensive-tissue hypothesis' (ETH) proposes that primates (especially humans) overcame this constraint through reduction of another metabolically expensive tissue, the gastrointestinal tract. Small guts characterize animals specializing on easily digestible diets. Thus, the hypothesis may be tested via the relationship between brain size and diet quality. Platyrrhine primates present an interesting test case, as they are more variably encephalized than other extant primate clades (excluding Hominoidea). We find a high degree of phylogenetic signal in the data for diet quality, endocranial volume and body size. Controlling for phylogenetic effects, we find no significant correlation between relative diet quality and relative endocranial volume. Thus, diet quality fails to account for differences in platyrrhine encephalization. One taxon, in particular, Brachyteles, violates predictions made by ETH in having a large brain and low-quality diet. Dietary reconstructions of stem platyrrhines further indicate that a relatively high-quality diet was probably in place prior to increases in encephalization. Therefore, it is unlikely that a shift in diet quality was a primary constraint release for encephalization in platyrrhines and, by extrapolation, humans.

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

“…Research has shown that ecological variables, such as social environment (Connor, 2007; Kotrschal, Rogell, Maklakov, & Kolm, 2012a; Shultz & Dunbar, 2006b), diet (Allen & Kay, 2012; Shultz & Dunbar, 2006a), habitat (Crispo & Chapman, 2010; Gonda et al., 2009b; Kotrschal, Sundstrom, Brelin, Devlin, & Kolm, 2012b), and predators (Gonda et al., 2009a,b, 2011; Walsh et al., 2016), play an important role in brain size plasticity and brain size evolution (see also Gonda, Herczeg, & Merila, 2013). These latter studies exploring the connection between predators and selection on brain size have largely compared populations where adults are susceptible to predators (Gonda et al., 2009a,b, 2011; Walsh et al., 2016).…”

The evolution of self-control

“…If these behaviors conferred fitness benefits, selection for these traits in particular lineages may have been an important factor in the evolution of species differences in self-control. A second possibility is that dietary breadth represents an ecological constraint on brain evolution, rather than a selective pressure per se (116,155,184,185). Accordingly, species with broad diets may be most capable of meeting the metabolic demands of growing and maintaining larger brains, with brain enlargement favored through a range of ecological selective pressures (86).…”

On folivory, competition, and intelligence: generalisms, overgeneralizations, and models of primate evolution

“…The common wisdom is that fruits are of higher quality than leaves (Aiello and Wheeler 1995; Fish and Lockwood 2003; Allen and Kay 2012), which implicitly suggests, in the context of the socioecological model, that fruits are more likely to be targets of competition (Wrangham 1980). There are several serious objections to such assertions.…”