Brain size predicts problem-solving ability in mammalian carnivores

Abstract

Despite considerable interest in the forces shaping the relationship between brain size and cognitive abilities, it remains controversial whether larger-brained animals are, indeed, better problem-solvers. Recently, several comparative studies have revealed correlations between brain size and traits thought to require advanced cognitive abilities, such as innovation, behavioral flexibility, invasion success, and self-control. However, the general assumption that animals with larger brains have superior cognitive abilities has been heavily criticized, primarily because of the lack of experimental support for it. Here, we designed an experiment to inquire whether specific neuroanatomical or socioecological measures predict success at solving a novel technical problem among species in the mammalian order Carnivora. We presented puzzle boxes, baited with food and scaled to accommodate body size, to members of 39 carnivore species from nine families housed in multiple North American zoos. We found that species with larger brains relative to their body mass were more successful at opening the boxes. In a subset of species, we also used virtual brain endocasts to measure volumes of four gross brain regions and show that some of these regions improve model prediction of success at opening the boxes when included with total brain size and body mass. Socioecological variables, including measures of social complexity and manual dexterity, failed to predict success at opening the boxes. Our results, thus, fail to support the social brain hypothesis but provide important empirical support for the relationship between relative brain size and the ability to solve this novel technical problem.brain size | problem-solving | carnivore | social complexity | intelligence

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

“…One potential explanation for the differences in relative brain size between food treatments is that they are adaptive. For instance, increased brain size is broadly associated with higher levels of intelligence, problem‐solving abilities, and cognition across species (Benson‐Amram et al., 2016). It is thus plausible that larger brains are favored when resources are scarce because larger brains may improve foraging capabilities and ultimately fitness.…”

“…There are clear fitness benefits associated with a larger brain as brain size is positively correlated with increased intelligence, cognition, learning capability, population persistence, and decreased susceptibility to predation (Sol & Lefebvre, 2000; Tebbich & Bshary, 2004; Shultz & Dunbar, 2006a; Sol, Szekely, Liker, & Lefebvre, 2007; Sol, Bacher, Reader, & Lefebvre, 2008; Overington, Morand‐Ferron, Boogert, & Lefebvre, 2009; Barrickman, Bastian, Isler, & van Schaik, 2008; Amiel, Tingley, & Shine, 2011; Reader, Hager, & Laland, 2011; Kotrschal et al., 2013b; MacLean et al., 2014; Kotrschal et al., 2015a; Kotrschal, Corral‐Lopez, Amcoff, & Kolm, 2015b; Benson‐Amram, Dantzer, Stricker, Swanson, & Holekamp, 2016; but also 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).…”

Bigger brains may make better problem-solving carnivores

“…Because the numbers of individuals tested varied substantially for different species in Benson-Amram et al (2016; from one to nine), it is difficult to draw firm conclusions regarding species differences, given the lack of attention to individual differences within a species, particularly in light of the vast differences in rearing history and environmental enrichment that captive animals experience. Furthermore, the number of individuals that eventually succeeded (a dichotomous measure of success) fails to capture the full range of cognitive traits involved in problem solving.…”

“…Furthermore, the latter study was limited to three species of felines and hyenasspecies that do not vary considerably with regard to diet and brain size, perhaps leaving sociality as the only differentiating factor to explain differences in problem-solving ability. Neither study tested social problem solving, so both are mute with regard to the advantages of predictive factors for specific cognitive domains.Because the numbers of individuals tested varied substantially for different species in Benson-Amram et al (2016; from one to nine), it is difficult to draw firm conclusions regarding species differences, given the lack of attention to individual differences within a species, particularly in light of the vast differences in rearing history and environmental enrichment that captive animals experience. Furthermore, the number of individuals that eventually succeeded (a dichotomous measure of success) fails to capture the full range of cognitive traits involved in problem solving.…”

“…Benson-Amram and colleagues (Benson-Amram, Dantzer, Stricker, Swanson, & Holekamp, 2016) recently published the results of an ambitious study designed to investigate whether problem-solving abilities in a large number of carnivore species (140 members of 39 species from nine families) could be predicted by neuroanatomical and socio-ecological measures. This undertaking is all the more impressive when one considers how grossly understudied carnivores have been with regard to their cognitive abilities, relative to other orders (e.g., primates, cetaceans, Passeriformes).…”