Stickleback brain size and behaviour in relation to the physicochemical properties of water
Creators: name: Ramsey, Mike
Publisher: name: University of Lincoln
Year: 2023
Subjects: C180 - Ecology
D300 - Animal science

description: It is becoming ever more recognised that global climate change is intensifying the symptoms of eutrophication in freshwaters causing changes in the visual and chemical properties of marine habitats. It is expected that human-induced environmental change will act to degrade the sensory environment by masking signals and their reception. However, this environmental change could have the potential result in adaptation towards novel communication traits or change the traits that are under selection. It was suggested that brains are plastic structures that are manipulated by experience and this neurological change will act to alter the behaviour of the individual. Brain plasticity has since been demonstrated in a number of studies but so far the links between the two have merely been suggestive and needs to be studied unequivocally. Additionally, sensory preference in numerical cognition has never been explored. This study aimed to bridge this gap. The first experiment is one that examines how brain size varies between populations of the same species. Three-spined stickleback specimens were taken from 10 lochs of North Uist, selected for their differing characteristics. Their whole brains and various individual brain regions were then dissected and measured. It was shown that overall brain size was affected by social complexity and the olfactory region was affected by the pH of the water, with more alkaline lochs producing fish with larger olfactory bulbs. In the next experiment, 9-spined sticklebacks were house in two treatments, dark and clear water. The fish were given sensory preference trials through the use of a series of numerosity trials that gave them a choice between two shoals, where the ratio of individuals ranged from 0.4 to 0.8. The olfactory and visual stimuli were presented diametrically and simultaneously. The fish were then dissected and their brains measured. Fish housed in dark water had brains that were that were the same size as fish in clear water but had smaller optic tectum and larger olfactory bulbs than those in clear water. Neither dark nor clear water reared fish showed any deviation from chance and thus showed no preference for either vision or olfaction for shoaling at any ratio. However, when the data was examined further in terms of 1st choice, it was seen that the dark water fish showed an affinity towards the olfactory stimulus and the clear water group showed an affinity for the visual stimulus.4 | P a g eThis indicates that the behaviour had in fact started to deviate in relation to the associated sensory brain region. On a broad spectrum, what we have shown here is that individuals possess the ability to adapt their behaviour and morphology to that what is most appropriate to the environment in which they find themselves. Climate change is affecting the planet as a whole but places are changing differently to others in terms of temperature, acidity and so on and this may give rise to speciation through the different ways that populations of the same species adapt their modalities of such behaviours as communication, shoaling and mate choice.