Circadian rhythms and photic entrainment of swimming activity in cave-dwelling fishAstyanax mexicanus(Actinopterygii: Characidae), from El Sotano La Tinaja, San Luis Potosi, Mexico

Abstract

Running title: Circadian rhythms in cave-dwelling fish Astyanax Abstract:Circadian regulation has a profound adaptive meaning in timing the best performance of biological functions in a cyclic niche. However, in cave-dwelling animals (troglobiotic) a lack of photic cyclic environment may represent a disadvantage for persistence of circadian rhythms. There are different populations of cave-dwelling fish Astyanax mexicanus in caves of the Sierra El Abra, Mexico, with different evolutive history. In the present work we report that fish collected from El Sótano la Tinaja show circadian rhythms of swimming activity in laboratory conditions. Rhythms observed in some of the organisms entrain to either continuous light-dark cycles or discrete skeleton photoperiods tested. Our results indicate that circadian rhythm of swimming activity and their ability to entrain in discrete and continuous photoperiods persist in some organisms that might represent one of the oldest populations of cave-dwelling Astyanax mexicanus in the Sierra

Characterization and comparison of activity profiles exhibited by the cave and surface morphotypes of the blind Mexican tetra, Astyanax mexicanus

“…Previous studies in Astyanax have suggested that locomotor activity is controlled by a passive system that can be entrained by exposure to cyclic photic cues (Thines and Wolff-Van Ermengem 1965; Thines and Weyers 1978; Erckens and Martin 1982a; Erckens and Martin 1982b; Duboué et al 2011; Beale et al 2013; Caballero-Hernández et al 2015). This conclusion is further supported by the fact that the results of the present study demonstrate significant rhythms in mean velocity and usage of both the bottom and the top portion of the trial tank in both surface and cavefish under l2:12hr light/dark conditions (LD R –LD T ).…”

“…Recently, a growing community of researchers, aided by advances in genetic resources, laboratory techniques and assay methods, has shown renewed interest in studying these questions in Astyanax (Romero et al 2003; Espinasa and Jeffery 2006; Yoshizawa and Jeffery 2008), with a dramatic increase in the number of publications on related topics in the last several years (Duboué et al 2011; Duboué et al 2012; Beale et al 2013; Moran et al 2014; Caballero-Hernández et al 2015; Yoshizawa et al 2015; Jaggard et al 2017a; Jaggard et al 2017b). However, before we can fully explore the potential use of this species as a natural model for clinically relevant phenomena, we must refine our understanding of exactly how cave-adapted specimens deviate from normal circadian rhythmicity and how these differences can best be observed and characterized.…”

Expression of extraocular opsin genes and light-dependent basal activity of blind cavefish

“…Second, in adult Mexican cavefish (e.g., Pachón cavefish) there is no circadian locomotor activity during 24 h dark conditions following a 12:12 h light-dark training period (Beale et al, 2013; Moran, Softley & Warrant, 2014). In other independently arisen cave populations (e.g., Tinaja cave population), a weakly trainable circadian clock appears to have been retained, i.e., light-dark cycles make expression levels of circadian clock genes oscillate and these oscillations continue briefly after the removal of the light-dark cycle (∼1 day) (Caballero-Hernández et al, 2015; Carlson & Gross, 2018; Carlson et al, 2018). However, the majority of light-dependent basal locomotor activity seems to be regulated by “masking”, where the ambient light overwrites 24 h-rhythmic circadian behaviors (Rietveld, Minors & Waterhouse, 1993; Caballero-Hernández et al, 2015).…”

“…In other independently arisen cave populations (e.g., Tinaja cave population), a weakly trainable circadian clock appears to have been retained, i.e., light-dark cycles make expression levels of circadian clock genes oscillate and these oscillations continue briefly after the removal of the light-dark cycle (∼1 day) (Caballero-Hernández et al, 2015; Carlson & Gross, 2018; Carlson et al, 2018). However, the majority of light-dependent basal locomotor activity seems to be regulated by “masking”, where the ambient light overwrites 24 h-rhythmic circadian behaviors (Rietveld, Minors & Waterhouse, 1993; Caballero-Hernández et al, 2015). The molecular mechanism for masking in fish is largely unknown (but see mouse studies in Panda et al, 2003; Van Gelder, 2003).…”