Reprodução dos Anfíbios
Autor: Reprodução Animal | Publicado: 2010-12-03T15:07:00-08:00

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 <![endif]-->  &nbsp;&nbsp;&nbsp;&nbsp; Os anfíbios, que em latim tem significado vida dupla, são seres vivos que durante a sua vida passam por duas fases: uma terrestre e outra aquática, por isso, na época da reprodução , eles retornam ao ambiente aquático onde machos e fêmeas se unem.&nbsp;&nbsp;&nbsp;&nbsp; São animais de sexos separados (dióicos) e geralmente possuem&nbsp;dimorfismo sexual&nbsp;claramente visível. A reprodução dos anfíbios é uma característica que os sujeita a dependência da água, e é uma reprodução sexuada por fecundação externa, podendo haver fecundação interna. Os ovos, sem casca (e por este motivo necessitam da água para proteger os ovos de radiação solar e choques mecânicos), que apenas possui uma envoltória cápsula gelatinosa, só se mantém vivos em meio aquático. Geralmente os machos em cópula despejam o liquido seminal sobre um longo cordão ou fileira gelatinosa que envolve os&nbsp;óvulos na medida em que saem da cloaca da fêmea e se depositam no fundo da água parada. A fecundação dos anfíbios ocorre em água doce e pelo fato de estarem protegidos pela água os ovos dos anfíbios não necessitam de&nbsp;anexos embrionários&nbsp;como, por exemplo, bolsa amniótica ou alantóide e essas são algumas das características que diferem os anfíbios de outros vertebrados terrestres. Uma vez fecundado o óvulo os cuidados variam de acordo com a espécie. Em alguns casos os óvulos são desenvolvidos em sacos vocais, em cavidades da pele dorsal, enrolados nas pernas, algumas vezes podendo ser enovelados em milhares em plantas aquáticas. Após a desova o macho e a fêmea se separam. A fêmea sai normalmente e o macho continua na área vocalizando em busca de uma nova fêmea. Os anfíbios podem apresentar 39 tipos de reprodução distintas, sendo superado apenas pelos peixes.    &nbsp;&nbsp;&nbsp; Aos poucos as larvas dos anfíbios vão desenvolvendo suas extremidades, primeiro as anteriores depois as posteriores, fazendo assim reduzir a cauda progressivamente até que desapareça. Neste processo de&nbsp;metamorfose os anfíbios adquirem pulmões, ao mesmo tempo em que as&nbsp;brânquias desaparecem.&nbsp; Este processo é regulado pela tireóide, que por sua vez é a glândula que promove o desenvolvimento, para atuar a tireóide dos anfíbios depende da presença de iodo no organismo.
  Fonte: http://www.infoescola.com/animais/reproducao-dos-anfibios/