Predictable evolution towards larger brains in birds colonizing oceanic islands

Abstract

Theory and evidence suggest that some selective pressures are more common on islands than in adjacent mainland habitats, leading evolution to follow predictable trends. The existence of predictable evolutionary trends has nonetheless been difficult to demonstrate, mainly because of the challenge of separating in situ evolution from sorting processes derived from colonization events. Here we use brain size measurements of >1900 avian species to reveal the existence of one such trend: increased brain size in island dwellers. Based on sister-taxa comparisons and phylogenetic ancestral trait estimations, we show that species living on islands have relatively larger brains than their mainland relatives and that these differences mainly reflect in situ evolution rather than varying colonization success. Our findings reinforce the view that in some instances evolution may be predictable, and yield insight into why some animals evolve larger brains despite substantial energetic and developmental costs.

Larger brains spur species diversification in birds

“…One possible explanation is that a large brain enhances evolutionary diversification by facilitating range expansions (Sol et al 2005b), thereby increasing opportunities for allopatric speciation (Rosenzweig 1995;Kisel and Barraclough 2010). However, successful colonization of a new area not only involves establishment but also departure from the natal area and dispersal across a barrier , and there is no evidence that larger brains favor the colonization of distant regions such as oceanic islands (Sayol et al 2018). However, successful colonization of a new area not only involves establishment but also departure from the natal area and dispersal across a barrier , and there is no evidence that larger brains favor the colonization of distant regions such as oceanic islands (Sayol et al 2018).…”

“…This possibility is supported by evidence showing that large-brained species are more likely to establish themselves after being introduced to novel areas (Sol et al 2005aAmiel et al 2011). However, successful colonization of a new area not only involves establishment but also departure from the natal area and dispersal across a barrier , and there is no evidence that larger brains favor the colonization of distant regions such as oceanic islands (Sayol et al 2018).…”

China’s online parrot trade: Generation length and body mass determine sales volume via price

“…Lengths of wing, tail, bill and tarsus were 119obtained from Parrots(Juniper and Parr,1998) applying residuals from observed minus 120 predicted lengths based on log-log regression controlling for body mass effect. Relative 121 (allometrically scaled) brain size was taken fromSayol et al (2018), as a proxy of 122 ability to exhibit novel behavior(Lefebvre et al, 1997;Overington et al, 2009).…”

Ecology, phylogeny, and the evolution of developmental duration in birds

“…These variables have been used extensively in the comparative avian life history literature and represent standardised measurements of avian developmental periods that are broadly comparable across all bird species (51). Furthermore, the sum of incubation plus fledging time represents a commonly-used metric for species’ ‘total development period’ that integrates variation in both pre- and postnatal development times (11-14). While we acknowledge that in some bird lineages individuals continue to grow after fledging, we argue that in most cases post-fledging growth accounts for a relatively minor proportion of offspring development and as such the combined duration of incubation plus fledging periods represents an informative metric of the total development time.…”

“…refs. (11-14)] and use the sum of incubation and fledging periods, thereby capturing variation in both pre-natal and post-natal development rates. Furthermore, by combining data on incubation and fledging duration, we are able to define a second variable, which we refer to as the incubation fraction .…”