Microhabitat Use Affects Brain Size and Structure in Intertidal Gobies

Abstract

The ecological cognition hypothesis poses that the brains and behaviours of individuals are largely shaped by the environments in which they live and the associated challenges they must overcome during their lives. Here we examine the effect of environmental complexity on relative brain size in 4 species of intertidal gobies from differing habitats. Two species were rock pool specialists that lived on spatially complex rocky shores, while the remainder lived on dynamic, but structurally simple, sandy shores. We found that rock pool-dwelling species had relatively larger brains and telencephalons in particular, while sand-dwelling species had a larger optic tectum and hypothalamus. In general, it appears that various fish species trade off neural investment in specific brain lobes depending on the environment in which they live. Our previous research suggests that rock pool species have greater spatial learning abilities, enabling them to navigate their spatially complex environment, which may account for their enlarged telencephalon, while sand-dwelling species likely have a reduced need for spatial learning, due to their spatially simple habitat, and a greater need for visual acuity. The dorsal medulla and cerebellum size was unaffected by the habitat in which the fish lived, but there were differences between species indicative of species-specific trade-offs in neural investment.

The Central Nervous System of Jawless Vertebrates: Encephalization in Lampreys and Hagfishes

“…This is similar to patterns documented in other vertebrates where variation in brain size is closely correlated with ecology [Yopak et al, 2007;Yopak and Montgomery, 2008;Eifert et al, 2015;White and Brown, 2015]. For example, the brains of fresh water genera (e.g., Ichthyomyzon and Eudontomyzon ) were rel-atively smaller than those of their closest anadromous relatives ( Fig.…”

Variation in Brain Morphology of Intertidal Gobies: A Comparison of Methodologies Used to Quantitatively Assess Brain Volumes in Fish

“…Thus, all methods provide support for the theory that various fish species trade off neural investment in specific brain lobes depending on the environment in which they live. These data suggest that rock pool species require greater spatial learning abilities to navigate in their spatially complex environment, while sand-dwelling species, on the other hand, likely have reduced need for spatial learning due to their spatially simple habitat and a greater need for visual acuity (for further detail on brain lobe differences between species, see [White, 2015]). Therefore, it seems that for the species studied here -regardless of the method used -there is a guarantee to obtain fairly precise estimates of volume differences between the species for comparative purposes even if the volume estimates are not entirely accurate.…”

“…A study by Ullmann et al [2010] looking at barramundi brain volumes found that the olfactory bulbs closely mimic the shape of idealised ellipsoids, while the shape of the telencephalon and optic tectum deviated from the elliptical shape and thus was overestimated by the ellipsoid method. Histology is a long-established method for calculating brain volumes and a considerable number of studies have utilised varying stereological techniques [Haug, 1986;Rosen and Harry, 1990;White, 2015]. However, histology is labour-intensive, time-consuming and provides only 2D views of brain areas ( table 3 ).…”

“…Many comparative studies across species have linked these variations in brain size to differences in a spe-cies' ecology, which suggests that variation in cognitive demands has resulted in the adaptive evolution of different brain sizes among species. For example, variables such as habitat complexity [Safi and Dechmann, 2005;White, 2015], social behaviour [Dunbar, 1995;Pollen et al, 2007;Gonzalez-Voyer et al, 2009a], diet [Hutcheon et al, 2002;Gonzalez-Voyer et al, 2009a], parental care strategies [Young et al, 1998], life-history traits [Iwaniuk and Nelson, 2001], mating strategy [Kolm et al, 2009] and sexual selection [Garamszegi et al, 2005;Pitnick et al, 2006] have all been shown to correlate with variation in brain size and structure in a range of vertebrate taxa.…”

“…telencephalon, optic tectum, cerebellum, hypothalamus and dorsal medulla) were measured in the following sequence using the ellipsoid model and then micro-CT or sectioning in order to determine if any volumetric differences arise between the three methods. To explore how well these techniques are able to highlight species differences in brain lobes, we used four species of intertidal gobies with already known differences in brain volumes [White, 2015] found on temperate rocky shores and sandy beaches in the Sydney region of Australia. These species were comprised of a mixture of rock pool resident species, Cocos frillgoby (Bathygobius cocosensis) and Krefft's frillgoby (Bathygobius krefftii) , and sandy shore species, eastern longfin goby (Favonigobius lentiginosus) and Hoese's sandgoby (Istigobius hoesei) .…”