The influence of domestication, insularity and sociality on the tempo and mode of brain size evolution in mammals

Abstract

The ability to develop complex social bonds and an increased capacity for behavioural flexibility in novel environments have both been forwarded as selective forces favouring the evolution of a large brain in mammals. However, large brains are energetically expensive, and in circumstances in which selective pressures are relaxed, e.g. on islands, smaller brains are selected for. Similar reasoning has been offered to explain the reduction of brain size in domestic species relative to their wild relatives. Herein, we assess the effect of domestication, insularity and sociality on brain size evolution at the macroevolutionary scale. Our results are based on analyses of a 426-taxon tree, including both wild species and domestic breeds. We further develop the phylogenetic ridge regression comparative method (RRphylo) to work with discrete variables and compare the rates (tempo) and direction (mode) of brain size evolution among categories within each of three factors (sociality, insularity and domestication). The common assertion that domestication increases the rate of brain size evolution holds true. The same does not apply to insularity. We also find support for the suggested but previously untested hypothesis that species living in medium-sized groups exhibit faster rates of brain size evolution than either solitary or herding taxa.

Modularity patterns in mammalian domestication: Assessing developmental hypotheses for diversification

“…Notably, evolutionary rates in domesticates have been shown to be both faster than (Castaglione et al. 2021), and the same as (Geiger et al. 2018), wild mammals.…”

The Effects of Domestication on the Brain and Behavior of the Chicken in the Light of Evolution

“…Indeed, recent studies show that the role of allometry in determining brain variables should be revised, but its significant influence on brain studies is obvious. Repeated analyses with different methods have even confirmed the original conclusions made from allometric approaches [Finlay et al, 2011;Castiglione et al, 2021]. Taxon-specific brain/body allometry is still widely acknowledged and gives insights into the development of brain (parts) size [Willemet, 2013].…”

“…Therefore, the reduction in brain size is not a regrettable degeneration, but rather an optimal adaptation to the actual conditions. Large brains are energetically expensive, and in circumstances in which selective pressure is relaxed, e.g., in a man-made environment, selection is for smaller brains [Castiglione et al, 2021]. Given the worldwide distribution and numbers of domestic animals, there is no doubt that they are very successful in their ecological niche (man-made).…”

How to behave when marooned: the behavioural component of the island syndrome remains underexplored

“…of extant dog spp. (Canidae) insular dwarf canid has normal relative brain size Sardinia, Italy comparative analysis of brain size [ 96 ] Minorcan giant rabbit ( Nuralagus rex ), compared to extant rabbit species (Leporidae) Late Neogene insular giant had relatively small brain; especially sense-dependent areas are small Minorca, Balearic Islands, Spain absence of predators; limited energy availability comparative analysis of brain size [ 97 ] 426 mammalian species no effect of insularity on relative brain size islands worldwide mainland sites throughout the world poor dietary resources on islands natural selection for smaller brains comparative analysis of brain size [ 98 ] dodo ( Raphus cucullatus ) compared to nine spp. of pigeons (Columbiformes) endocranial volume not smaller than expected from pigeon allometry Mauritius allometric analysis [ 99 ] Rodrigues Island giant owl (Otus murivorus ), compared to 10 extant spp.…”

“…[ 95 ], the Sardinian dhole ( Cynotherium sardous ) [ 96 ], or even the long-thought-dim dodo ( Raphus cucullatus ) [ 99 ]. Third, recent comparative studies on extant mammals [ 98 ] and crows and ravens [ 102 ] found no effect of insularity on relative brain size. A meta-analysis of over 1900 species of birds even suggests a tendency towards larger brains in insular species.…”