Differences in behavior between surface and cave Astyanax mexicanus may be mediated by changes in catecholamine signaling

Abstract

Astyanax mexicanus is a teleost fish that is in the process of allopatric speciation. Ancestral Astyanax are found in surface rivers and derived blind forms are found in cave systems. Adaptation to life in nutrient poor caves without predation includes the evolution of enhanced food seeking behaviors and loss of defensive responses. These behavioral adaptations may be mediated by changes in catecholaminergic control systems in the brain. We examined the distribution of tyrosine hydroxylase, a conserved precursor for the synthesis of the catecholamines dopamine and noradrenaline, in the brains of surface and cave Astyanax using immunohistochemistry. We found differences in tyrosine hydroxylase staining in regions that are associated with nonvisual sensory perception, motor control, endocrine release, and attention. These differences included significant increases in the diameters of tyrosine hydroxylase immunoreactive soma in cave Astyanax in the olfactory bulb, basal telencephalon, preoptic nuclei, ventral thalamus, posterior tuberculum, and locus coeruleus. These increases in modulation by dopamine and noradrenaline likely indicate changes in behavioral control that underlie adaptations to the cave environment.

Genetic bias in repeated evolution of pigment loss in cave populations of the Asellus aquaticus species complex

“…In A. mexicanus, evidence supporting this has been found for several traits and genes behind them. For example, due to the shared pool of the Ltyrosine precursor loss-of-function mutations in oca2 gene responsible for complete pigment loss (i.e., albino phenotype) also affect catecholamine synthesis which in turn affects several physiological and behavioral traits (Bilandžija et al, 2013(Bilandžija et al, , 2018Gallman et al, 2020;O'Gorman et al, 2021). Recently, a genome wide analysis of A. mexicanus found that losses of traits like pigment and eyes show signatures of positive selection which again speaks for the pleiotropic function of associated genes (Moran et al, 2023).…”