Mechanisms of pigmentation loss in subterranean fishes
Mechanisms of pigmentation loss in subterranean fishes
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DOI：
10.1590/s1679-62252008000400015
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发表时间：
2008-12-01
影响因子：
1.7
通讯作者：
Trajano, Eleonora
中科院分区：
文献类型：
--
作者：
Felice, Vanessa;Visconti, Maria Aparecida;Trajano, Eleonora
穴居生物（只在地下）通常存在，在其与地下生活有关的无形态（troglomorphies）中，眼睛退化和黑色素沉着。退化的程度因物种而异，从轻微减少到完全失去眼睛和深色色素沉着，没有分类相关性。虽然眼睛缩小的机制已经在一些穴居动物中进行了深入的研究，如墨西哥盲四特征，Astyanax属和欧洲蝾螈，Proteus anguinus，很少有研究集中在色素沉着上。巴西地下鱼类区系的区别不仅在于物种丰富度（23 troglobitic鱼类迄今已知），但也通过眼睛和色素沉着的减少程度的变化。这项研究的重点是巴西鱼类完全没有黑色素沉着：characiform Stygichthys typhlops（科）和siluriforms Ancistrus formoso（Loricariidae），Rhamdiopsis sp. 1（Heptapteridae;来自Chapada迪亚曼蒂纳，巴伊亚的洞穴）和Rhamdiopsis sp. 2（Campo Formoso，巴伊亚的洞穴）。为了研究这种色素脱失是否是黑素生成中某些步骤的阻断的结果，使用从活鱼中提取的尾鳍片段进行了施用L-DOPA的体外试验。除Rhamdiopsis sp. 2外，其它所有种均为DOPA（+）。例如，施用L-DOPA后合成黑色素。这表明这些鱼确实有黑色素细胞，但它们不能将L-酪氨酸转化为L-多巴。另一方面，Rhamdiopsis sp. 2，像以前研究过的Trichomycterus itacarambiensis的白化病标本（相当于种群的三分之一）一样，是多巴（-），或者是因为黑素合成的阻断发生在黑素生成的下游，这可能是T. itacarambiensis（单基因系统，鉴于表型不连续性），或者因为所谓的白化病人不具有黑色素细胞。DOPA（+）和DOPA（-）鱼类合成黑色素能力的生理丧失，显然是由不同的遗传过程引起的，可能与黑色素细胞密度的降低共存于地下种群中，如在三分之二的黑色素T. itacarambiensis人口，一个形态减少明显控制的多基因系统产生连续的表型变异。
Troglobitic (exclusively subterranean) organisms usually present, among their apomorphies related to the subterranean life (troglomorphisms), the regression of eyes and melanic pigmentation. The degree of regression varies among species, from a slight reduction to the complete loss of eyes and dark pigmentation, without a taxonomic correlation. While mechanisms of eye reduction have been intensively investigated in some troglobites such as the Mexican blind tetra characins, genus Astyanax, and the European salamander, Proteus anguinus, few studies have focused on pigmentation. The Brazilian subterranean ichthyofauna distinguishes not only by the species richness (23 troglobitic fishes so far known) but also by the variation in the degree of reduction of eyes and pigmentation. This study focused on Brazilian fishes completely devoid of melanic pigmentation: the characiform Stygichthys typhlops (Characidae) and the siluriforms Ancistrus formoso (Loricariidae), Rhamdiopsis sp. 1 (Heptapteridae; from caves in the Chapada Diamantina, Bahia) and Rhamdiopsis sp. 2 (cave in Campo Formoso, Bahia). In order to investigate if such depigmentation is the result of blockage in some step in the melanogenesis, in vitro tests of administration of L-DOPA were done, using caudal-fin fragments extracted from living fish. Except for Rhamdiopsis sp. 2, all the studied species were DOPA(+), i. e., melanin was synthesized after L-DOPA administration. This indicates these fish do have melanophores but they are unable to convert L-tyrosine to L-DOPA. On the other hand, Rhamdiopsis sp. 2, like the albino specimens of Trichomycterus itacarambiensis previously studied (which correspond to one third of the population), are DOPA(-), either because the block of melanin synthesis occurs downstream in melanogenesis, which is probably the case with T. itacarambiensis (monogenic system in view of the phenotypic discontinuity), or because the so-called albinos do no possess melanophores. The physiological loss in the ability to synthesize melanin, apparently caused by different genetic processes in DOPA(+) and in DOPA(-) fishes, may co-exist in subterranean populations with a decrease in the density of melanophores, as observed in the pigmented two thirds of T. itacarambiensis population, a morphological reduction apparently controlled by polygenic systems producing a continuous phenotypic variation.