Plastic changes in brain morphology in relation to learning and environmental enrichment in the guppy (Poecilia reticulata)

Abstract

Despite the common assumption that the brain is malleable to surrounding conditions mainly during ontogeny, plastic neural changes can occur also in adulthood. One of the driving forces responsible for alterations in brain morphology is increasing environmental complexity that may demand enhanced cognitive abilities (e.g. attention, memory and learning). However, studies looking at the relationship between brain morphology and learning are scarce. Here, we tested the effects of both learning and environmental enrichment on neural plasticity in guppies (Poecilia reticulata), by means of either a reversal-learning test or a spatial-learning test. Given considerable evidence supporting environmentally induced plastic alterations, two separate control groups that were not subjected to any cognitive test were included to account for potential changes induced by the experimental setup alone. We did not find any effect of learning on any of our brain measurements. However, we found strong evidence for an environmental effect, where fish given access to the spatial-learning environment had larger relative brain size and optic tectum size in relation to those exposed to the reversal-learning environment. Our results demonstrate the plasticity of the adult brain to respond adaptively mainly to environmental conditions, providing support for the environmental enhancement theory.

Brain morphology predicts social intelligence in wild cleaner fish

“…We then caught and tested a total of 40 female cleaners from these sites to evaluate their performance in the ephemeral reward task. It is important to note that we did not expect the exposure of individuals to the cognitive test to impact brain plasticity per se 53 .…”

“…As this experiment captures key aspects of cleaners' interspecific social interactions, an avenue for future research is to explore the links between brain features and social competence at the intraspecific level. In addition, other factors like environmental enrichment 15,25,53 should be considered for further studies to understand better brain morphology in cleaner fish.…”

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

“…Environmental variability often requires high cognitive capacity and therefore favors larger brains (Sayol et al., 2016). Nevertheless, whether environmental challenges lead to a large brain depends on both the cognitive benefits and physical environment (Fong et al., 2019); only when the brain or a given region acquires the performance or fitness that offsets the increased energy demand, the brain or brain region may increase its size (Axelrod et al., 2018; De Meester et al., 2019; Safi et al., 2005). In turn, extra investment for a specific brain region could reflect the increased demands in response to biotic or abiotic challenges (Puga et al., 2018).…”

Artificial selection on brain size leads to matching changes in overall number of neurons

“…; Fong et al. ) and potentially also region‐specific changes in neuronal numbers and densities. Local control and variation in cell proliferation or survival may facilitate mosaic brain evolution in wild populations, when favored by selection (Montgomery et al.…”

“…Thus, individual variation in neuronal density in wild populations inhabiting the same selective environment might be decreased due to directional selection and therefore lower than that observed in captive populations. On the other hand, changes in the environment can trigger substantial changes in brain region size (for review, see Kotrschal et al 2017b;Kotrschal et al 2012;Gonda et al 2013;Fong et al 2019) and potentially also regionspecific changes in neuronal numbers and densities. Local control and variation in cell proliferation or survival may facilitate mosaic brain evolution in wild populations, when favored by selection (Montgomery et al 2016).…”