Morfologia comparativa de Astyanax fasciatus e Astyanax scabripinnis (Characiformes: Characidae) através de análises de morfometria geométrica
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Data
2016-08-24
Autores
Lima, Paloma Aparecida de [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
O gênero Astyanax é taxonomicamente complexo e possui grande diversidade de espécies. O número de espécies válidas ultrapassa 140 e, provavelmente, um número maior está por ser descrito. Diversos autores indicam a existência de complexos de espécies, como por exemplo, para Astyanax fasciatus e A. scabripinnis. Análises do gene Citocromo C Oxidase subunidade 1 (COI) mostraram que essas espécies apresentam distância intra-específica menor que 2%, o que indicaria, em teoria, não só a inexistência de tais complexos, como que estas representam uma única espécie. Apesar da elevada proximidade genética, as espécies em questão apresentam diferenciação morfológica bem descrita e demonstrada na literatura e suas identidades nunca foram questionadas. No entanto, dado o alto grau de similaridade genética, um estudo morfológico mais detalhado pode trazer informações inéditas sobre a evolução e transformação de caracteres e/ou apontar para um grau de semelhança, em algum nível, não detectado pelos métodos tradicionais. O presente estudo tem o intuito de quantificar a diferenciação entre essas espécies e avaliar se existem diferentes graus de diferenciação morfológica em indivíduos jovens e adultos e inferir se a elevada similaridade genética se reflete em algum estágio do desenvolvimento dessas espécies. Para isso, espécimes de diferentes classes de tamanho foram radiografados e analisados através do método de morfometria geométrica. Os marcos anatômicos apresentaram diferenças significativas entre as espécies e uma maior diferença entre os grupos ontogenéticos. Tanto os jovens e adultos dentro da mesma espécie, como os jovens e os adultos de A. fasciatus quando comparados com os de A. scabripinnis possuem o mesmo grau de diferenciação morfológica. O formato do corpo de A. scabripinnis parece estar relacionado com o ambiente em que normalmente são encontrados, como rios de correntezas moderadas e em riachos localizados nas cabeceiras em locais com forte correnteza. Normalmente, nesses ambientes são encontrados peixes com um formato do corpo fusiforme e mais alongados, para a redução do gasto de energia e produzir natação prolongada, o que confirma os resultados aqui encontrados. O formato generalizado do corpo de A. fasciatus está relacionado a nadadores ativos em ambientes mais lênticos, também confirmado pelas análises aqui apresentadas. Assim, embora extremamente similares geneticamente, ambas as espécies acumularam, num provável curto espaço de tempo (dada à similaridade genética), um alto grau de diferenciação morfológica que, provavelmente, as impedem de se reconhecerem como uma única espécie. Reforça-se, assim, a afirmação de que a proposta de um DNA Barcode, através da análise do gene mitocondrial Citocromo Oxidase I, deve ser empregada apenas como evidência adicional na identificação e proposição de novas espécies em peixes caracídeos.
The genus Astyanax is taxonomically complex and has great diversity of species. The number of valid species exceeds 140 and probably a greater number is to be described. Several authors indicate that there are species of complexes, as for example, A. fasciatus and A. scabripinnis. Analysis of cytochrome c oxidase subunit 1 gene (IOC) have shown that these species exhibit intraspecific distance lower than 2%, which indicates, in theory, not only the absence of such complexes, but they also represent a single species. Despite the high genetic closeness, the species in question show an already well described morphological differentiation demonstrated in the literature and their identities were never questioned. However, given the high degree of genetic similarity, a more detailed morphological study can bring new information on the evolution and transformation of characters and/or point to a degree of morphological similarity, at some level, not detected by traditional methods. This study aims to quantify the differentiation between these species and to assess whether there are different degrees of morphological differentiation in young and adults and to infer if the high genetic similarity is reflected in some stage of development of these species. For this, specimens of different size classes were radiographed and analyzed by geometric morphometric method. The anatomical landmarks showed significant differences between species and a greater difference between the ontogenetic groups. Both young and adults within the same species, such as young people and adults of A. fasciatus compared to the A. scabripinnis have the same degree of morphological differentiation. The body shape of A. scabripinnis seems to be related to the environment in which they are usually found, as rivers of moderate currents and streams located in the headwaters in places with strong current. Typically, in these environments are found fish with fusiform and elongate body to reduce energy used and to produce prolonged swimming, confirming the results found herein. The general format of the body of A. fasciatus is related to active swimmers in more lentic environments, also confirmed by our analysis. Thus, although extremely similar genetically, both species accumulated in a likely short time (given the genetic similarity), a high degree of morphological differentiation that probably prevents them to recognize as a single species. There exists, therefore, the claim that the proposal of a DNA Barcode, through the mitochondrial gene Cytochrome Oxidase I analysis, should be used only as additional evidence in the identification and proposal of new species in characins fish.
The genus Astyanax is taxonomically complex and has great diversity of species. The number of valid species exceeds 140 and probably a greater number is to be described. Several authors indicate that there are species of complexes, as for example, A. fasciatus and A. scabripinnis. Analysis of cytochrome c oxidase subunit 1 gene (IOC) have shown that these species exhibit intraspecific distance lower than 2%, which indicates, in theory, not only the absence of such complexes, but they also represent a single species. Despite the high genetic closeness, the species in question show an already well described morphological differentiation demonstrated in the literature and their identities were never questioned. However, given the high degree of genetic similarity, a more detailed morphological study can bring new information on the evolution and transformation of characters and/or point to a degree of morphological similarity, at some level, not detected by traditional methods. This study aims to quantify the differentiation between these species and to assess whether there are different degrees of morphological differentiation in young and adults and to infer if the high genetic similarity is reflected in some stage of development of these species. For this, specimens of different size classes were radiographed and analyzed by geometric morphometric method. The anatomical landmarks showed significant differences between species and a greater difference between the ontogenetic groups. Both young and adults within the same species, such as young people and adults of A. fasciatus compared to the A. scabripinnis have the same degree of morphological differentiation. The body shape of A. scabripinnis seems to be related to the environment in which they are usually found, as rivers of moderate currents and streams located in the headwaters in places with strong current. Typically, in these environments are found fish with fusiform and elongate body to reduce energy used and to produce prolonged swimming, confirming the results found herein. The general format of the body of A. fasciatus is related to active swimmers in more lentic environments, also confirmed by our analysis. Thus, although extremely similar genetically, both species accumulated in a likely short time (given the genetic similarity), a high degree of morphological differentiation that probably prevents them to recognize as a single species. There exists, therefore, the claim that the proposal of a DNA Barcode, through the mitochondrial gene Cytochrome Oxidase I analysis, should be used only as additional evidence in the identification and proposal of new species in characins fish.
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Palavras-chave
Astyanax, COI, DNA barcode, Diferenciação morfológica, Morfometria