title: Environmental factors related to the production of a complex set of spicules in a tropical freshwater sponge.
abstract: Adverse natural conditions will, generally, induce gemmulation in freshwater sponges. Because of this environmental dependence, gemmoscleres are given exceptional value in taxonomic, ecological and paleoenvironmental studies. Other spicules categories such as microscleres and beta megascleres have received little attention with regard to their occurrence and function during the sponge biological cycle. Metania spinata, a South American species common to bog waters in the Cerrado biome, produces alpha and beta megascleres, microscleres and gemmoscleres. To detect the environmental factors triggering the production of all these kinds of spicules, the species annual seasonal cycle was studied. Artificial substrates were devised, supplied with gemmules and placed in Lagoa Verde pond which contained a natural population of M. spinata. Field monitoring was conducted for eight months in order to observe the growth of sponges and spicules formation. Samples of water were taken monthly for physical and chemical parameters determination. The appearance of the alpha megascleres was sequentially followed by that of microscleres, gemmoscleres and beta megascleres. The first ones built the new sponge skeleton, the last three were involved in keeping inner moisture in the sponge body or its gemmules. The water level, temperature and the silicon (Si) concentration in the pond were the most important factors related to this sequential production of spicules, confirming environmental reconstructions based on the presence or absence of alpha megascleres and gemmoscleres in past sediments.
authors.affiliation: Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil.
authors.forename: Marcela C
authors.initials: MC
authors.lastname: Matteuzzo
authors.affiliation: Museu de Ciências Naturais, Fundação Zoobotânica do Rio Grande do Sul, Porto Alegre, RS, Brasil.
authors.forename: Cecília
authors.initials: C
authors.lastname: Volkmer-Ribeiro
authors.affiliation: Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil.
authors.forename: Angélica F D C
authors.initials: AF
authors.lastname: Varajão
authors.affiliation: Departamento de Geologia, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil.
authors.forename: César A C
authors.initials: CA
authors.lastname: Varajão
authors.affiliation: Université Aix-Marseille, Aix en Provence, France.
authors.forename: Anne
authors.initials: A
authors.lastname: Alexandre
authors.affiliation: Departamento de Ecologia, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil.
authors.forename: Demetrio L
authors.initials: DL
authors.lastname: Guadagnin
authors.affiliation: Instituto Federal de Minas Gerais, Ouro Preto, MG, Brasil.
authors.forename: Ariana C S
authors.initials: AC
authors.lastname: Almeida
mesh_terms: D000818:Animals; D001938:Brazil; D004777:Environment; D060106:Lakes / Q000737:chemistry*; D011161:Porifera / Q000196:embryology / Q000254:growth & development*; D012621:Seasons