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      Troglomorphic features of Astroblepus pholeter, a cavefish from Ecuador, and possible introgressive hybridization

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      Subterranean Biology

      Pensoft Publishers

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          Abstract

          Cave organisms are often characterized by reduced pigmentation, eyesight, and enhanced mechanosensory functions. The stygobitic catfish Astroblepuspholeter is found within some subterranean drainages in Ecuador. The species was first described in 1962 with specimens that were all highly depigmented and troglomorphic. The next observations in the field occurred until 2011, 2015 and 2018. At such dates, specimens examined progressively displayed more surface-like appearance. Appendages in these individuals were progressively shorter and pigmentation levels are now as high as some surface Astroblepus. Based on sampled specimens, it would appear that since 1962, the population has been progressively composed of less troglomorphic individuals. One possibility is that the population has undergone introgressive hybridization in recent years as surface Astroblepus are known to enter the caves and cohabitate with the troglomorphic Astroblepus. Lastly, we report that Individuals are able to detect and respond to light. Histological analyses show that A.pholeter’s eyes have all of the major ocular structures (lens, optic nerve, and all retinal layers).

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          Most cited references 11

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          Cavefish as a model system in evolutionary developmental biology.

          The Mexican tetra Astyanax mexicanus has many of the favorable attributes that have made the zebrafish a model system in developmental biology. The existence of eyed surface (surface fish) and blind cave (cavefish) dwelling forms in Astyanax also provides an attractive system for studying the evolution of developmental mechanisms. The polarity of evolutionary changes and the environmental conditions leading to the cavefish phenotype are known with certainty, and several different cavefish populations have evolved constructive and regressive changes independently. The constructive changes include enhancement of the feeding apparatus (jaws, taste buds, and teeth) and the mechanosensory system of cranial neuromasts. The homeobox gene Prox 1, which is expressed in the expanded taste buds and cranial neuromasts, is one of the genes involved in the constructive changes in sensory organ development. The regressive changes include loss of pigmentation and eye degeneration. Although adult cavefish lack functional eyes, small eye primordia are formed during embryogenesis, which later arrest in development, degenerate, and sink into the orbit. Apoptosis and lens signaling to other eye parts, such as the cornea, iris, and retina, result in the arrest of eye development and ultimate optic degeneration. Accordingly, an eye with restored cornea, iris, and retinal photoreceptor cells is formed when a surface fish lens is transplanted into a cavefish optic cup, indicating that cavefish optic tissues have conserved the ability to respond to lens signaling. Genetic analysis indicates that multiple genes regulate eye degeneration, and molecular studies suggest that Pax6 may be one of the genes controlling cavefish eye degeneration. Further studies of the Astyanax system will contribute to our understanding of the evolution of developmental mechanisms in vertebrates.
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            Limbs in whales and limblessness in other vertebrates: mechanisms of evolutionary and developmental transformation and loss

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              Sensory Adaptations of Fishes to Subterranean Environments

              (2013)
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                Author and article information

                Journal
                Subterranean Biology
                SB
                Pensoft Publishers
                1314-2615
                1768-1448
                August 15 2018
                August 15 2018
                : 27
                : 17-29
                Article
                10.3897/subtbiol.27.27098
                © 2018

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