Brain differences in ecologically differentiated sticklebacks

Abstract

Populations that have recently diverged offer a powerful model for studying evolution. Ecological differences are expected to generate divergent selection on multiple traits, including neurobiological ones. Animals must detect, process, and act on information from their surroundings and the form of this information can be highly dependent on the environment. We might expect different environments to generate divergent selection not only on the sensory organs, but also on the brain regions responsible for processing sensory information. Here, we test this hypothesis using recently evolved reproductively isolated species pairs of threespine stickleback fish Gasterosteus aculeatus that have well-described differences in many morphological and behavioral traits correlating with ecological differences. We use a state-of-the-art method, magnetic resonance imaging, to get accurate volumetric data for 2 sensory processing regions, the olfactory bulbs and optic tecta. We found a tight correlation between ecology and the size of these brain regions relative to total brain size in 2 lakes with intact species pairs. Limnetic fish, which rely heavily on vision, had relatively larger optic tecta and smaller olfactory bulbs compared with benthic fish, which utilize olfaction to a greater extent. Benthic fish also had larger total brain volumes relative to their body size compared with limnetic fish. These differences were erased in a collapsed species pair in Enos Lake where anthropogenic disturbance has led to intense hybridization. Together these data indicate that evolution of sensory processing regions can occur rapidly and independently.

Ecology and evolution along environmental gradients

“…Their finding of increased feeding selectivity under elevated thermal conditions may provide important new insights into the effects of climate change on various aspects of energy flow and general ecosystem functioning. Keagy et al. (2018) examine an aspect of evolutionary divergence that received little attention in studies on the ecology and evolution along ecological gradients: they examined brain divergence in a fish species, G. aculeatus , that serves as a model organism for various questions in evolutionary ecology, such as the mechanisms of sympatric diversification and speciation.…”

Coordinated evolution of brain size, structure, and eye size in Trinidadian killifish

“…A growing body of literature has provided links between ecologically divergent conditions and evolutionary shifts in brain size. Ecological conditions such as habitat (Axelrod et al., 2018; Gonda, Herczeg, & Merilä, 2009a, 2011; Keagy et al., 2018; Park & Bell, 2010) and predation (Samuk et al., 2018; Walsh et al., 2016) have been linked to phenotypic shifts in brain size and brain structure. For example, Keagy et al.…”

“…For example, Keagy et al. (2018) found that stickleback that are adapted to forage on benthic invertebrates ('benthic sticklebacks') exhibited larger relative brain volumes than stickleback that forage in open water environments (i.e., ‘limnetic sticklebacks'). This same study showed that benthic stickleback had larger relative optic tecta and smaller olfactory bulbs than limnetic fish (see also Park & Bell, 2010).…”

“…Ecological conditions such as habitat (Axelrod et al, 2018;Gonda, Herczeg, & Merilä, 2009aKeagy et al, 2018;Park & Bell, 2010) and predation (Samuk et al, 2018;Walsh et al, 2016) have been linked to phenotypic shifts in brain size and brain structure. For example, Keagy et al (2018) found that stickleback that are adapted to forage on benthic invertebrates ('benthic sticklebacks') exhibited larger relative brain volumes than stickleback that forage in open water environments (i.e., 'limnetic sticklebacks'). This same study showed that benthic stickleback had larger relative optic tecta and smaller olfactory bulbs than limnetic fish (see also Park & Bell, 2010).…”

Causes and consequences of social phenotypic variation in the Caribbean facultative cleaning goby "Elacatinus"

“…The Nucleus glomerulosus receives tectal input from the Tectum opticum and projects to the Inferior lobe. The Tectum opticum is the primary visual center in fishes (Butler and Hodos, 2005) and some fish species that do rely more on vision do have larger Tectum opticum (Keagy et al, 2018). On the other hand, the lateral line axis would be composed by the Torus semicircularis, Crista cerebellaris and the Torus longitudinalis.…”