Variation in the strength of allometry drives rates of evolution in primate brain shape

Abstract

<jats:p>Large brains are a defining feature of primates, as is a clear allometric trend between body mass and brain size. However, important questions on the macroevolution of brain shape in primates remain unanswered. Here we address two: (i), does the relationship between the brain size and its shape follow allometric trends and (ii), is this relationship consistent over evolutionary time? We employ three-dimensional geometric morphometrics and phylogenetic comparative methods to answer these questions, based on a large sample representing 151 species and most primate families. We found two distinct trends regarding the relationship between brain shape and brain size. Hominoidea and Cercopithecinae showed significant evolutionary allometry, whereas no allometric trends were discernible for Strepsirrhini, Colobinae or Platyrrhini. Furthermore, we found that in the taxa characterized by significant allometry, brain shape evolution accelerated, whereas for taxa in which such allometry was absent, the evolution of brain shape decelerated. We conclude that although primates in general are typically described as large-brained, strong allometric effects on brain shape are largely confined to the order's representatives that display more complex behavioural repertoires.</jats:p>

Global elongation and high shape flexibility as an evolutionary hypothesis of accommodating mammalian brains into skulls

“…"Spatial packing" is thought to explain the co-evolution of mammalian brain and cranial base shape in primates (Gould 1977;Ross and Ravosa 1993;Ross and Henneberg 1995;Bastir et al 2011) and mouse strains (Lieberman et al 2008). There is also evidence that absolute brain size (rather than relative brain size) correlates with primate endocast shape, probably differentially in different clades (Aristide et al 2016;Sansalone et al 2020). However, beyond primates, there are multiple hypotheses of how the mammalian brain is shaped, involving different levels of organization.…”

A three-dimensional approach to visualize pairwise morphological variation and its application to fragmentary palaeontological specimens

“…One alternate use of the ICP-based pairwise approach presented here could be the graphical representation of morphological continua across canonical axes of variation ( Claude, 2008 ; Márquez et al, 2012 ; Sansalone et al, 2020 ). Given a three-dimensional reference landmark configuration (e.g.…”

“…the mean configuration following principal component ordination), target configurations at theoretical values along the canonical axes, whether at the extreme of the axes or at given intervals ( Olsen, 2017 ), could be visualised using ICP. The outcome of this approach would be a 3D depiction of variation along the axes of variance, akin to that generated by Sansalone et al (2020) , which similarly depicted variation in 3D as a heat map through a processes of interpolation. The ICP algorithm for landmarks was implemented as part of the R package Morpho , via the function icpmat ( Schlager, 2017 ) but, to our knowledge, no such implementation yet exists for meshes in R.…”

Global elongation and high shape flexibility as an evolutionary hypothesis of accommodating mammalian brains into skulls

“…“Spatial packing” is thought to explain the co-evolution of mammalian brain and cranial base shape in primates (Gould 1977; Ross and Ravosa 1993; Ross and Henneberg 1995; Bastir et al 2011) and mouse strains (Lieberman et al 2008). There is also general support that absolute brain size (rather than relative brain size) correlates with primate endocast shape, probably differentially in different clades (Aristide et al 2016; Sansalone et al 2020). However, beyond primates, there are multiple hypotheses of how the mammalian brain is shaped, involving different levels of organisation.…”