Experimental translocations to low predation lead to non-parallel increases in relative brain size

Abstract

Cite this article: Mitchell DJ, Vega-Trejo R, Kotrschal A. 2020 Experimental translocations to low predation lead to non-parallel increases in relative brain size. Biol. Lett. 16: 20190654. http://dx.Predation is a near ubiquitous factor of nature and a powerful selective force on prey. Moreover, it has recently emerged as an important driver in the evolution of brain anatomy, though population comparisons show ambiguous results with considerable unexplained variation. Here, we test the reproducibility of reduced predation on evolutionary trajectories of brain evolution. We make use of an introduction experiment, whereby guppies (Poecilia reticulata) from a single high predation stream were introduced to four low predation streams. After 8-9 years of natural selection in the wild and two generations of common garden conditions in the laboratory, we quantified brain anatomy. Relative brain region sizes did not differ between populations. However, we found a general increase and striking variation in relative brain size of introduced populations, which varied from no change to a 12.5% increase in relative brain weight, relative to the ancestral high predation population. We interpret this as evidence for nonparallel evolution, which implies a weak or inconsistent association of relative brain size with fitness in low predation sites. The evolution of brain anatomy appears sensitive to unknown environmental factors, or contingent on either chance events or historical legacies of environmental change.

Intraspecific variation in inhibitory motor control in guppies, Poecilia reticulata

“…Trinidadian guppies vary drastically in morphology, life history and behavioural traits due to variation in selection pressures such as predation levels (Devigili et al ., 2019; Endler, 1980; Handelsman et al ., 2013; Hasenjager & Dugatkin, 2017; Herbert‐Read et al ., 2017; Reznick, 1982), water turbidity (Borner et al ., 2015) or ambient light (Endler, 1991, 1993; Gamble et al ., 2003). Recently predation has also been linked to brain evolution in guppies (Kotrschal et al ., 2017; Mitchell et al ., 2020; Reddon et al ., 2018) and killifish ( Rivulus hartii ) (Walsh et al ., 2016) albeit showing contrasting effects for brain size or brain anatomy. Reddon et al .…”

Brain size variation along altitudinal gradients in the Asiatic Toad (Bufo gargarizans)

“…All individuals were euthanized with 0.25% MS‐222 solution (Dodd, 2010; Mitchell et al., 2020). Specimens were fixated and stored in neutralized 10% formalin (Carson et al., 1973).…”

Testing hypotheses of marsupial brain size variation using phylogenetic multiple imputations and a Bayesian comparative framework

“…We confirm previous reports that marsupials from New Guinea have the largest brains among marsupials, but this relationship only exists for small body masses and is mainly due to an increased intercept. This might be due to several reasons - the relationship between vulnerability and brain size (see below), or the effects of seasonality, where the more uniform, stable tropical climate in NG can facilitate the evolution of larger brains [6, 77], or the effects of predation pressure in NG, both of human and non-human animals [78–80] (but see [81]).…”