Selection of siliceous structures for test building in Testaceans from South American peatbog

LUCIANA BURDMAN; VALERIA CASA; ENRIQUE LARA; GABRIELA MATALONI

Simposio; 8th International Society for Testate Amoebae Research (ISTAR).; 2016

Sociedade Brasileira de Protozoologia

Testate amoebae are key members of the microbial communities in peatbogsworldwide. They are frequent inhabitants of the interstitial water amongSphagnum mosses and of the periphyton and benthos of peat bog ponds. Theyalso contribute to the silica cycle by accumulating siliceous structures (SS) builtby other organisms in their tests. Some species from genera Difflugia andPhryganella (Arcellinida) and Amphitrema (Labyrinthulomycetes) reinforce theirtests with SS, presumably taken from their preys and consisting of diatomvalves and chrysophycean cysts.In this work, we investigated whether these species actively selected the SSforming their tests in two ponds from a peat bog located in Tierra del Fuego.Phryganella sp1 and Phryganella sp2 from Pond 1 (P1); Phryganella sp1,Difflugia oblonga and Amphitrema sp1 from Pond 2 (P2). The taxonomiccomposition and size structure of the SS composing five tests from eachspecies as well as those in the fitobenthic communities, were analysed bymeans of a new technique of test digestion. Occurrence of length-basedselection of SS was evaluated through a nested Variance Analysis. Also, asPhryganella sp. 1 was the only species present in both ponds, we testedwhether selective behavior, if any, was a constant character. For this purposePearre Index (IP) of selectivity was calculated. Relative abundances of SS inthe tests and the benthos were analyzed through a Principal ComponentsAnalysis and tested by a variance general linear model through a varidentfunction.For P1, the first two axes of the PCA explained 75.9% of total variability. Firstaxis clearly separated the phytobenthic community from both Phryganellaspecies. While P. sp1 and the phytobenthos had higher Pinnularia frequencies,P. sp2 presented the highest Chrysophyta frequencies.For P2, the first two axis of the PCA explained 73.1% of total variability.Nevertheless, no selectivity pattern was observed, as no significant differenceswere found among the three testaceans studied or with benthic SS.In the case of Phryganella sp1, the first two axis of the PCA explained 75,8% ofthe variance. Composition of benthic SS in both ponds was significantlydifferent (p