Morfologia e distribuição dos dentículos e papilas orais em tubarões Galeomorphii (Chondrichthyes: Elasmobranchii): implicações ecológicas e filogenéticas
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Data
2022-08-25
Autores
Poscai, Aline Nayara [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
Os dentículos dérmicos são uma sinapomorfia em Chondrichthyes, e revestem além do tegumento, a membrana nictitante e a cavidade orofaríngea, desempenhando diferentes funções dependendo de sua morfologia e localização no corpo. Na cavidade orofaríngea, associadas aos dentículos, as papilas gustativas constituem o sistema quimiossensorial, desempenhando papel crucial na gustação. Apesar disso, ambas estruturas foram pouco exploradas na literatura. Pensando nisso, foram examinados os dentículos e papilas orais de 39 espécies de tubarões Galeomorphii, buscando compreender a morfologia e suas implicações funcionais diante de pressões seletivas ambientais (e.g. hábitos alimentares e habitat) e implicações filogenéticas. Por meio de microscopia eletrônica de varredura (MEV) e microtomografia computadorizada (MC), os dentículos e papilas foram analisados, medidos e suas densidades foram estimadas. Através da MEV, foram observadas as papilas e somente a coroa dos dentículos, limitando a visualização de outras estruturas. Enquanto a MC possibilitou a visualização do pedúnculo, placa basal, cavidade pulpar e a distinção entre dentículos em formação e dos completamente desenvolvidos, mostrando-se uma técnica que, unida à MEV se tornam uma combinação eficaz para o estudo dessas estruturas. Por meio da análise morfológica, foram identificados três morfotipos de dentículos orais nas espécies examinadas, sendo eles, resistência à abrasão (50%), funções generalizadas (46,8%) e defesa (3,2%). A alta ocorrência de resistência à abrasão indica que os dentículos desempenham primariamente a função de proteger a cavidade orofaríngea, seguido pelo modo contínuo do morfotipo de funções generalizadas indicando que os dentículos orais não estão relacionados necessariamente à ecologia, como estabelecido para os dentículos dérmicos do tegumento. Eles desempenham diversas funções como proteção contra abrasão e injúrias, canalização do fluxo de água para as papilas, entre outros. Em Atelomycterus marmoratus e Sphyrna tudes foi observado indícios de dimorfismo sexual nos dentículos orais, no qual as fêmeas apresentaram maiores densidades do que os machos. A ausência de dentículos orais indica uma possível sinapomorfia em Scyliorhinidae e Pentanchidae, assim como em Orectolobidae e Hemigaleidae. As papilas orais foram observadas em todas as espécies, sendo identificadas morfologicamente como circulares e ovais. Em Hemigaleus microstoma foi identificado o Tipo I, e nas demais espécies o Tipo II. No estudo ontogenético de Carcharias taurus, a densidade de papilas foi a mais alta nos embriões menores, indicando potencial relação com a adelfofagia e ovofagia. Adicionalmente, não é possível inferir se a morfologia das papilas está diretamente associada ao habitat e alimentação. Por fim, vale ressaltar que mesmo que os dentículos orais não sejam usualmente utilizados como ferramenta taxonômica, a identificação de alguns táxons como Heterodontidae, Mitsukurinidae e alguns Carcharhinidae, principalmente Carcharhinus spp. é viável, mesmo levando em consideração as possíveis variações intra e interespecíficas.
Dermal denticles are a synapomorphy for Chondrichthyes and cover the integument, nictitating membrane and oropharyngeal cavity, performing different functions depending on their morphology and body location. In the oropharyngeal cavity, associated with denticles, taste buds or oral papillae constitute the chemosensory system, playing a crucial role in taste. However, in the literature these structures have been little explored. Herein, we examined denticles and papillae of 39 species of Galeomorphii sharks, evaluating the morphology considering environmental pressures such as feeding and habitat, as well as phylogenetic implications. Under scanning electron microscopy (SEM) and CT scan, denticles and papillae were analyzed, measured and the density was estimated. Noteworthily, under SEM, only the papillae and denticles crown were observed; this method limited the visualization of other structures. The CT scan allowed to observe the peduncle, basal plate, pulp cavity, and the differences between under development to fully developed denticles. This method is complementary and allied with SEM, can be more effective for the study of these structures. The morphology of denticles revealed three morphotypes in the species examined: abrasion strength (50%), generalized functions (46.8%), and defense (3.2%). The high occurrence of abrasion strength indicates that the denticles primarily play the role of protecting the oropharyngeal cavity, followed by the continuous type of the generalized functions indicating that the oral denticles are not necessarily related to ecology, as established for the dermal denticles of the integument. They perform different functions such as protection against abrasion and injuries, channeling the water flow into the papillae, etc. In Atelomycterus marmoratus and Sphyrna tudes, evidence of sexual dimorphism was observed in the oral denticles, in which females have higher densities than males. The absence of oral denticles indicates a putative synapomorphy in Scyliorhinidae and Pentanchidae, and possibly in Orectolobidae and Hemigaleidae. Oral papillae were observed in all species, however, Type I was identified only in Hemigaleus microstoma, and Type II in the other species. In the ontogenetic study of Carcharias taurus, papillae density was highest in the smallest embryos, indicating a potential relationship with adelphophagy and oophagy. Additionally, it is not possible to infer whether the morphology of the papillae is directly associated with habitat and feeding. Finally, it is worth mentioning that even though oral denticles are not usually used as 9 a taxonomic tool, the identification of some taxa such as Heterodontidae, Mitsukurinidae and some Carcharhinidae, especially Carcharhinus spp. is possible, even if considered the potential intra and interspecific variations.
Dermal denticles are a synapomorphy for Chondrichthyes and cover the integument, nictitating membrane and oropharyngeal cavity, performing different functions depending on their morphology and body location. In the oropharyngeal cavity, associated with denticles, taste buds or oral papillae constitute the chemosensory system, playing a crucial role in taste. However, in the literature these structures have been little explored. Herein, we examined denticles and papillae of 39 species of Galeomorphii sharks, evaluating the morphology considering environmental pressures such as feeding and habitat, as well as phylogenetic implications. Under scanning electron microscopy (SEM) and CT scan, denticles and papillae were analyzed, measured and the density was estimated. Noteworthily, under SEM, only the papillae and denticles crown were observed; this method limited the visualization of other structures. The CT scan allowed to observe the peduncle, basal plate, pulp cavity, and the differences between under development to fully developed denticles. This method is complementary and allied with SEM, can be more effective for the study of these structures. The morphology of denticles revealed three morphotypes in the species examined: abrasion strength (50%), generalized functions (46.8%), and defense (3.2%). The high occurrence of abrasion strength indicates that the denticles primarily play the role of protecting the oropharyngeal cavity, followed by the continuous type of the generalized functions indicating that the oral denticles are not necessarily related to ecology, as established for the dermal denticles of the integument. They perform different functions such as protection against abrasion and injuries, channeling the water flow into the papillae, etc. In Atelomycterus marmoratus and Sphyrna tudes, evidence of sexual dimorphism was observed in the oral denticles, in which females have higher densities than males. The absence of oral denticles indicates a putative synapomorphy in Scyliorhinidae and Pentanchidae, and possibly in Orectolobidae and Hemigaleidae. Oral papillae were observed in all species, however, Type I was identified only in Hemigaleus microstoma, and Type II in the other species. In the ontogenetic study of Carcharias taurus, papillae density was highest in the smallest embryos, indicating a potential relationship with adelphophagy and oophagy. Additionally, it is not possible to infer whether the morphology of the papillae is directly associated with habitat and feeding. Finally, it is worth mentioning that even though oral denticles are not usually used as 9 a taxonomic tool, the identification of some taxa such as Heterodontidae, Mitsukurinidae and some Carcharhinidae, especially Carcharhinus spp. is possible, even if considered the potential intra and interspecific variations.
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Palavras-chave
Chondrichthyes, Morfologia, Dentículos dérmicos, Microscopia, Elasmobranch, Body integument, Gustation, Microscopy, Ecomorphology