Behavioural changes controlled by catecholaminergic systems explain recurrent loss of pigmentation in cavefish

Abstract

Multiple cave populations of the teleost have repeatedly reduced or lost eye and body pigmentation during adaptation to dark caves. Albinism, the complete absence of melanin pigmentation, is controlled by loss-of-function mutations in the gene. The mutation is accompanied by an increase in the melanin synthesis precursor l-tyrosine, which is also a precursor for catecholamine synthesis. In this study, we show a relationship between pigmentation loss, enhanced catecholamine synthesis and responsiveness to anaesthesia, determined as a proxy for catecholamine-related behaviours. We demonstrate that anaesthesia resistance (AR) is enhanced in multiple depigmented and albino cavefish (CF), inversely proportional to the degree of pigmentation loss, controlled by the gene, and can be modulated by experimental manipulations of l-tyrosine or the catecholamine norepinephrine (NE). Moreover, NE is increased in the brains of multiple albino and depigmented CF relative to surface fish. The results provide new insights into the evolution of pigment modification because NE controls a suite of adaptive behaviours similar to AR that may represent a target of natural selection. Thus, understanding the relationship between loss of pigmentation and AR may provide insight into the role of natural selection in the evolution of albinism via a melanin-catecholamine trade-off.

Astyanax surface and cave fish morphs

“…4 c) can be used to identify maternal effects [ 32 ]. Hybridization followed by artificial selection can generate strains with combined surface fish and cavefish traits [ 47 ], which are useful to investigate antagonistic tradeoffs [ 48 ].…”

Application of PEG-Covered Non-Biodegradable Polyelectrolyte Microcapsules in the Crustacean Circulatory System on the Example of the Amphipod Eulimnogammarus verrucosus

“…The process of exoskeleton healing after the injection was monitored for four weeks. We defined three stages of repair based on the observed wound melanization [30]: no healing (no black coloration); healing is ongoing (indicated by the black coloration of the wound border); the exoskeleton is repaired. The external examination of the chitin state was followed by an internal checkup after the dissection of four–five individuals (euthanized with clove oil suspension) at each time point.…”

Dual Roles of the Retinal Pigment Epithelium and Lens in Cavefish Eye Degeneration

“…If such traits can be combined into a single line then their complete antagonistic nature would be faulted, whereas if they are not capable of coexisting then a mutually exclusive relationship would be supported. As a proof of principle, the AE stain was recently used to provide evidence supporting a pleiotropic trade-off between melanin pigmentation and catecholamine synthesis in Astyanax (Bilandžija et al, 2018).…”