The rise of <i>Astyanax</i> cavefish

Gross, Joshua B.; Meyer, Bradley J; Perkins, Molly

doi:10.1002/dvdy.24253

Cited by 29 publications

(9 citation statements)

References 111 publications

(179 reference statements)

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“…This could reflect differences in their evolutionary timescales. Cavefish evolved over the past one to five million years 11 , while naked mole rats evolved seventy-three million years ago 13 , allowing sufficient time to fix and select acquired mutations in genes essential for eye 12 24…”

Section: Ikmoq)mentioning

confidence: 99%

“…Loss of eyes is one of the most common morphological features of cave-adapted animals, including many fish species. Blind cave fish (CF) morphs of Astyanax mexicanus evolved from surface fish (SF) during a few million years of isolation in dark Mexican caves 11 , with recent studies suggesting that regression of eyes evolved as part of a strategy to conserve energy in fish adapted to dark and nutrient deficient caves 12 .…”

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An epigenetic mechanism for cavefish eye degeneration

Gore

Tomins

Iben

et al. 2017

Preprint

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DNA methylation in cavefishGore et al 2 Coding and non-coding mutations in DNA contribute significantly to phenotypic variability during evolution. However, less is known about the role of epigenetics in this process. Although previous studies have identified eye development genes associated with the loss of eyes phenotype in the Pachón blind cave morph of the Mexican tetra Astyanax mexicanus 1-6 , no inactivating mutations have been found in any of these genes 2,3,7-10 . Here we show that excess DNA methylation-based epigenetic silencing promotes eye degeneration in blind cave Astyanax mexicanus.By performing parallel analyses in Astyanax mexicanus cave and surface morphs and in the zebrafish Danio rerio, we have discovered that DNA methylation mediates eye-specific gene repression and globally regulates early eye development.The most significantly hypermethylated and down-regulated genes in the cave morph are also linked to human eye disorders, suggesting the function of these genes is conserved across the vertebrates. Our results show that changes in DNA methylation-based gene repression can serve as an important molecular mechanism generating phenotypic diversity during development and evolution.Subterranean animals offer an excellent opportunity to study morphological, molecular and physiological changes that allow organisms to adapt to unique environments. Loss of eyes is one of the most common morphological features of cave-adapted animals, including many fish species. Blind cave fish (CF) morphs of Astyanax mexicanus evolved from surface fish (SF) during a few million years of isolation in dark Mexican caves 11 , with recent studies suggesting that regression of eyes evolved as part of a strategy to conserve energy in fish adapted to dark and nutrient deficient caves 12 .Although a number of studies have examined molecular mechanisms underlying eye loss DNA methylation in cavefish Gore et al 3 in Pachón cave-derived Astyanax mexicanus CF, recent sequencing of the Pachón CF genome and other studies revealed no inactivating null mutations in essential eye development genes 2,3,7-9 . In contrast, genome sequencing of another subterranean animal, the naked mole rat Heterocephalus glaber, showed combined functional loss of more than a dozen key eye genes due to inactivating mutations 13 . These findings suggest the possibility that epigenetic rather than genetic changes may mediate eye loss in Pachón cave fish. To test this possibility, we used CF and SF morphs of Astyanax mexicanus as well as wild type and DNA methylation and demethylation-deficient zebrafish Danio rerio to examine whether DNA methylation regulates eye formation, and whether eye loss in Pachón cave fish evolved at least in part through hypermethylation of key eye genes.At 36 hpf Astyanax mexicanus CF and SF embryos are superficially indistinguishable with properly formed lenses and optic cups in both morphs (Fig. 1a,b). By five days of development, however, degeneration of eye tissue is clearly evident (Fig. 1c,d), and by adulthood CF eyes ar...

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Section: Ikmoq)mentioning

confidence: 99%

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confidence: 99%

An epigenetic mechanism for cavefish eye degeneration

Gore

Tomins

Iben

et al. 2017

Preprint

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“…Astyanax mexicanus has found favor as a study system for regressive traits and cave evolution owing to the fact that this species is tractable in a lab setting, includes 29 different cave populations and consists of both a derived, cave morphotype and an extant surface morphotype that can be readily hybridized (Mitchell et al 1977; Jeffery 2009; Gross et al 2015). In the decades following its initial scientific characterization by Hubbs and Innes in 1936, Astyanax was the subject of a number of studies aimed at 1) examining sensitivity and behavioral responses to light (Breder and Gresser 1941a; Breder and Gresser 1941b; Breder 1944; Breder and Rasquin 1947; Kuhn and Kähling 1954; Lüling 1954; Kähling 1961; Gertychowa 1970; Romero 1984; Romero 1985; Langecker 1989) and 2) determining whether Astyanax cavefish displayed circadian rhythmicity (Thines and Wolff-Van Ermengem 1965; Erckens and Weber 1976; Thines and Weyers 1978; Erckens and Martin 1982a; Erckens and Martin 1982b).…”

Section: Introductionmentioning

confidence: 99%

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

Carlson

Gross

2018

Comparative Biochemistry and Physiology Part C: Toxicology &

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Departure from normal circadian rhythmicity and exposure to atypical lighting cues has been shown to adversely affect human health and wellness in a variety of ways. In contrast, adaptation to extreme environments has led many species to alter or even entirely abandon their reliance upon cyclic environmental inputs, principally daily cycles of light and darkness. The extreme darkness, stability and isolation of cave ecosystems has made cave-adapted species particularly attractive systems in which to study the consequences of life without light and the strategies that allow species to survive and even thrive in such environments. In order to further explore these questions, we have assessed the rhythmicity of locomotion in the blind Mexican tetra, Astyanax mexicanus, under controlled laboratory conditions. Using high-resolution video tracking assays, we characterized patterns in locomotor activity and spatial tank usage for members of the surface and Pachón cave populations. Here we demonstrate that cavefish have a higher overall level of activity and use the space within the trial tank differently than surface fish. Further, Pachón cavefish show circadian rhythmicity in both activity and spatial tank usage under a 12:12 light/dark cycle. We provide further evidence that these cavefish retain a weakly light-entrainable, endogenous circadian oscillator with limited capability to sustain rhythms in activity, but not spatial tank usage, in the absence of photic cues. Finally, we demonstrate a putative behavioral "masking effect" contributing to behavioral rhythms and provide evidence that exposure to constant darkness during development may alter behavioral patterns later in life.

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“…Astyanax are helping to understand how it has adapted to subterranean life. There are excellent reviews about the cave-related morphological adaptations ( Figure 1) in Astyanax CF (Atukorala, Bhatia, & Ratnayake, 2019;Borowsky, 2018;Gross, Meyer, & Perkins, 2015;Jeffery, 2001Jeffery, , 2009Jeffery, , 2016Krishnan & Rohner, 2017;Ojha & Watve, 2018;Torres-Paz, Hyacinthe, Pierre, & Retaux, 2018). In this review, we first describe what is known about the origins of A. mexicanus CF (when and how invaded the caves).…”

Section: Studies Inmentioning

confidence: 99%

Subterranean life: Behavior, metabolic, and some other adaptations of Astyanax cavefish

et al. 2020

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The ability of fishes to adapt to any aquatic environment seems limitless. It is enthralling how new species keep appearing at the deep sea or in subterranean environments. There are close to 230 known species of cavefishes, still today the best-known cavefish is Astyanax mexicanus, a Characid that has become a model organism, and has been studied and scrutinized since 1936. There are two morphotypes for A. mexicanus, a surface fish and a cavefish. The surface fish lives in central and northeastern Mexico and south of the United States, while the cavefish is endemic to the "Sierra del Abra-Tanchipa region" in northeast Mexico. The extensive genetic and genomic analysis depicts a complex origin for Astyanax cavefish, with multiple cave invasions and persistent gene flow among cave populations. The surface founder population prevails in the same region where the caves are. In this review, we focus on both morphotype's main morphological and physiological differences, but mainly in recent discoveries about behavioral and metabolic adaptations for subterranean life. These traits may not be as obvious as the troglomorphic characteristics, but are key to understand how Astyanax cavefish thrives in this environment of perpetual darkness.

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The rise of Astyanax cavefish

Cited by 29 publications

References 111 publications

An epigenetic mechanism for cavefish eye degeneration

An epigenetic mechanism for cavefish eye degeneration

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

Subterranean life: Behavior, metabolic, and some other adaptations of Astyanax cavefish

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