ADAPTATIVE FUNCTIONS OF SENSORY AND BEHAVIOR LATERALITY IN ASTYANAX MEXICANUS

Abstract

Laterality consists of the asymmetrical use of the left or the right side in terms of morphology (the asymmetrical disposition of visceral organs), behavior (left or right-handedness), and neural processing. For example, regarding neural processing in humans, the left side of the brain is more often associated with analytical reasoning, while the right-side hemisphere is associated with emotion-processing tasks. Laterality is widely reported across vertebrates and several studies demonstrate that it confers a variety of advantages, such as performing intricate motor activities, spatial learning, cognitive and multitasking abilities, and escaping from predators. However, there is a major gap regarding how laterality arose through the course of evolution. Astyanax mexicanus, commonly known as the blind cavefish, has been presented as an excellent vertebrate model to study evolutionary processes. This teleost species is composed of two morphs: an eyed, river-dwelling surface morph (surface fish) and a blind cave-dwelling morph (cavefish). Sensory-behavior laterality has been described for cavefish regarding the detection of novel immotile objects. Cave-dwelling morphs have evolved different foraging strategies, such as attraction to a source of water disturbance/vibration, which is associated with the enhancement of non-visual sensory systems. This behavior is advantageous for capturing prey in the dark. Vibration Attraction Behavior (VAB) is a foraging behavior differently expressed in cave and surface morphs. Cavefish approaches the vibrating rod significantly more than surface fish, showing that cave individuals have a higher VAB level in comparison with the surface counterpart. Prey-capture assays have shown that cavefish (VAB positive) outcompeted surface fish (VAB negative) in the dark, which indicates that this foraging behavior may be crucial for survival in a cave environment. Further studies have demonstrated that VAB is mediated by the Lateral Line system, more precisely by the mechanosensory units present at the third infraorbital bone (IO3) region. The IO3 bone shows a higher degree of asymmetrical patterning and fragmentation across different cavefish populations. Furthermore, studies in zebrafish have reported an association between bone formation and neuromasts disposition during embryonic development. We will first investigate if the bone formation and consequently mechanosensory development at the IO3 region influence VAB output, and we will address if this sensory-behavior system exhibits laterality (Chapter 2). Additionally, we will discriminate both sensory and behavior laterality across different populations of Astyanax mexicanus, and we will functionally assess the asymmetric contribution of the mechanosensory system towards VAB (Chapter 3). Finally, we will address this foraging behavior lateral/asymmetrical modality in response to starvation (Chapter 3). Our results indicate that mechanosensory asymmetrical usage and behavior laterality vary according to food availability and across different cave populations over time. The most diversified cave population showed a combination of sensory and behavioral laterality, suggesting a novel advantage as a strategy to save energy in food-limited environments.