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Astyanax

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Sylvie Retaux – 1st expert on this subject based on the ideXlab platform

  • Evolution of acoustic communication in blind cavefish
    Nature Communications, 2019
    Co-Authors: Carole Hyacinthe, Joël Attia, Sylvie Retaux

    Abstract:

    Acoustic communication allows the exchange of information within specific contexts and during specific behaviors. The blind, cave-adapted and the sighted, river-dwelling morphs of the species Astyanax mexicanus have evolved in markedly different environments. During their evolution in darkness, cavefish underwent a series of morphological, physiological and behavioral changes, allowing the study of adaptation to drastic environmental change. Here we discover that Astyanax is a sonic species, in the laboratory and in the wild, with sound production depending on the social contexts and the type of morph. We characterize one sound, the “Sharp Click”, as a visually-triggered sound produced by dominant surface fish during agonistic behaviors and as a chemosensory-, food odor-triggered sound produced by cavefish during foraging. Sharp Clicks also elicit different reactions in the two morphs in play-back experiments. Our results demonstrate that acoustic communication does exist and has evolved in cavefish, accompanying the evolution of its behaviors. The fish Astyanax mexicanus has divergent cave and river-dwelling eco-morphotypes. Here, Hyacinthe et al. show that cave and river fish communicate sonically, but that the sounds produced and the responses elicited in the two morphs depend differently on the social and behavioral context.

  • lens apoptosis in the Astyanax blind cavefish is not triggered by its small size or defects in morphogenesis
    PLOS ONE, 2017
    Co-Authors: Helene Hinaux, Alexandre Alie, Maryline Blin, Laurent Legendre, Gaelle Recher, Sylvie Retaux

    Abstract:

    Blindness is a convergent trait in many cave animals of various phyla. Astyanax mexicanus cavefish is one of the best studied cave animals; however the mechanisms underlying eye degeneration in this species are not yet completely understood. The lens seems to play a central role, but only relatively late differentiation defects have been implicated in the cavefish lens apoptosis phenotype so far. Here, we used genetic crosses between Astyanax cavefish and surface fish to confirm that during development, lens size is independent of retina size. We then investigated whether the small size of the cavefish lens could directly cause cell death. Laser ablation experiments of lens placode cells in surface fish embryos showed that a small lens size is not sufficient to trigger lens apoptosis. We further examined potential lens morphogenesis defects through classical histology and live-imaging microscopy. From lens placode to lens ball, we found that lens invagination and formation of the lens epithelium and fiber cells occur normally in cavefish. We conclude that the main and deleterious defect in the Astyanax cavefish lens must concern the molecular control of lens cell function.

  • evolutionary genetics of the cavefish Astyanax mexicanus
    Advances in Genetics, 2016
    Co-Authors: Didier Casane, Sylvie Retaux

    Abstract:

    Abstract Blind and depigmented fish belonging to the species Astyanax mexicanus are outstanding models for evolutionary genetics. During their evolution in the darkness of caves, they have undergone a number of changes at the morphological, physiological, and behavioral levels, but they can still breed with their river-dwelling conspecifics. The fertile hybrids between these two morphotypes allow forward genetic approaches, from the search of quantitative trait loci to the identification of the mutations underlying the evolution of troglomorphism. We review here the past 30 years of evolutionary genetics on Astyanax : from the first crosses and the discovery of convergent evolution of different Astyanax cavefish populations to the most recent evolutionary transcriptomics and genomics studies that have provided researchers with potential candidate genes to be tested using functional genetic approaches. Although significant progress has been made and some genes have been identified, cavefish have not yet fully revealed the secret of their adaptation to the absence of light. In particular, the genetic determinism of their loss of eyes seems complex and still puzzles researchers. We also discuss future research directions, including searches for the origin of cave alleles and searches for selection genome-wide, as well as the necessary but missing information on the timing of cave colonization by surface fish.

William R. Jeffery – 2nd expert on this subject based on the ideXlab platform

  • Astyanax surface and cave fish morphs.
    Evodevo, 2020
    Co-Authors: William R. Jeffery

    Abstract:

    The small teleost fish Astyanax mexicanus has emerged as an outstanding model for studying many biological topics in the context of evolution. A major attribute is conspecific surface dwelling (surface fish) and blind cave dwelling (cavefish) morphs that can be raised in the laboratory and spawn large numbers of transparent and synchronously developing embryos. More than 30 cavefish populations have been discovered, mostly in northeastern Mexico, and some are thought to have evolved independently from surface fish ancestors, providing excellent models of parallel and convergent evolution. Cavefish have evolved eye and pigmentation regression, as well as modifications in brain morphology, behaviors, heart regenerative capacity, metabolic processes, and craniofacial organization. Thus, the Astyanax model provides researchers with natural “mutants” to study life in the challenging cave environment. The application of powerful genetic approaches based on hybridization between the two morphs and between the different cavefish populations are key advantages for deciphering the developmental and genetic mechanisms regulating trait evolution. QTL analysis has revealed the genetic architectures of gained and lost traits. In addition, some cavefish traits resemble human diseases, offering novel models for biomedical research. Astyanax research is supported by genome assemblies, transcriptomes, tissue and organ transplantation, gene manipulation and editing, and stable transgenesis, and benefits from a welcoming and interactive research community that conducts integrated community projects and sponsors the International Astyanax Meeting (AIM).

  • complex evolutionary and genetic patterns characterize the loss of scleral ossification in the blind cavefish Astyanax mexicanus
    PLOS ONE, 2015
    Co-Authors: Kelly E Oquin, Pooja Doshi, Anastasia Lyon, Emma Hoenemeyer, Masato Yoshizawa, William R. Jeffery

    Abstract:

    The sclera is the tough outer covering of the eye that provides structural support and helps maintain intraocular pressure. In some fishes, reptiles, and birds, the sclera is reinforced with an additional ring of hyaline cartilage or bone that forms from scleral ossicles. Currently, the evolutionary and genetic basis of scleral ossification is poorly understood, especially in teleost fishes. We assessed scleral ossification among several groups of the Mexican tetra (Astyanax mexicanus), which exhibit both an eyed and eyeless morph. Although eyed Astyanax surface fish have bony sclera similar to other teleosts, the ossicles of blind Astyanax cavefish generally do not form. We first sampled cavefish from multiple independent populations and used ancestral character state reconstructions to determine how many times scleral ossification has been lost. We then confirmed these results by assessing complementation of scleral ossification among the F1 hybrid progeny of two cavefish populations. Finally, we quantified the number of scleral ossicles present among the F2 hybrid progeny of a cross between surface fish and cavefish, and used this information to identify quantitative trait loci (QTL) responsible for this trait. Our results indicate that the loss of scleral ossification is common–but not ubiquitous–among Astyanax cavefish, and that this trait has been convergently lost at least three times. The presence of wild-type, ossified sclera among the F1 hybrid progeny of a cross between different cavefish populations confirms the convergent evolution of this trait. However, a strongly skewed distribution of scleral ossicles found among surface fish x cavefish F2 hybrids suggests that scleral ossification is a threshold trait with a complex genetic basis. Quantitative genetic mapping identified a single QTL for scleral ossification on Astyanax linkage group 1. We estimate that the threshold for this trait is likely determined by at least three genetic factors which may control the severity and onset of lens degeneration in cavefishes. We conclude that complex evolutionary and genetic patterns underlie the loss of scleral ossification in Astyanax cavefish.

  • quantitative genetic analysis of retinal degeneration in the blind cavefish Astyanax mexicanus
    PLOS ONE, 2013
    Co-Authors: Kelly E Oquin, Pooja Doshi, Masato Yoshizawa, William R. Jeffery

    Abstract:

    The retina is the light-sensitive tissue of the eye that facilitates vision. Mutations within genes affecting eye development and retinal function cause a host of degenerative visual diseases, including retinitis pigmentosa and anophthalmia/microphthalmia. The characin fish Astyanax mexicanus includes both eyed (surface fish) and eyeless (cavefish) morphs that initially develop eyes with normal retina; however, early in development, the eyes of cavefish degenerate. Since both surface and cave morphs are members of the same species, they serve as excellent evolutionary mutant models with which to identify genes causing retinal degeneration. In this study, we crossed the eyed and eyeless forms of A. mexicanus and quantified the thickness of individual retinal layers among 115 F2 hybrid progeny. We used next generation sequencing (RAD-seq) and microsatellite mapping to construct a dense genetic map of the Astyanax genome, scan for quantitative trait loci (QTL) affecting retinal thickness, and identify candidate genes within these QTL regions. The map we constructed for Astyanax includes nearly 700 markers assembled into 25 linkage groups. Based on our scans with this map, we identified four QTL, one each associated with the thickness of the ganglion, inner nuclear, outer plexiform, and outer nuclear layers of the retina. For all but one QTL, cavefish alleles resulted in a clear reduction in the thickness of the affected layer. Comparative mapping of genetic markers within each QTL revealed that each QTL corresponds to an approximately 35 Mb region of the zebrafish genome. Within each region, we identified several candidate genes associated with the function of each affected retinal layer. Our study is the first to examine Astyanax retinal degeneration in the context of QTL mapping. The regions we identify serve as a starting point for future studies on the genetics of retinal degeneration and eye disease using the evolutionary mutant model Astyanax.

Klaus Reutter – 3rd expert on this subject based on the ideXlab platform

  • ultrastructure of the taste buds in the blind cave fish Astyanax jordani anoptichthys and the sighted river fish Astyanax mexicanus teleostei characidae
    The Journal of Comparative Neurology, 2001
    Co-Authors: Friederike Boudriot, Klaus Reutter

    Abstract:

    This study describes the ultrastructure of the taste buds of the sighted river fish Astyanax mexicanus and of the blind cave fish Astyanax jordani (=Anoptichthys) (Teleostei, Characiformes, Characidae). In Astyanax and Anoptichthys, taste buds occur in the epithelia of the lips, oral cavity, and, in Anoptichthys, lower jaw. Both possess three types of taste buds: type I (elevated), type II (slightly elevated), and type III taste buds (not elevated or sunken). The taste buds are up to 60 μm high and up to 35 μm wide. The taste bud’s sensory epithelium consists of 100–130 elongated cells: light cells, dense-cored-vesicles (dcv) -cells, dark cells, and degenerating cells. The dcv-cells are rich in dense-cored vesicles and are described for the first time in a teleostean taste bud. At the taste bud’s base, there lie two to three basal cells. The basal cells of type I and type II taste buds have microvillus (spine)-like processes, in contrast to those of type III taste buds. The taste bud’s nerve fiber plexus is situated between the bases of the elongated taste bud cells and the basal cells. Afferent synapses occur between dcv-cells and basal cells (presynaptic sides) and axons (postsynaptic side). Indistinct synapses occur between light cells and dark cells (presynaptic sides) and axons (postsynaptic side). The nerve fiber plexes of Anoptichthys type II and type III taste buds contain significantly more axon profiles than those of Astyanax. This may be associated with a compensatory improvement of the sense of taste in the blind, cave-dwelling fish. J. Comp. Neurol. 434:428–444, 2001. © 2001 Wiley-Liss, Inc.