SELECTION OF SILICEOUS STRUCTURES FOR TEST BUILDING IN TESTACEANS FROM A SOUTH AMERICAN PEATBOG

BURDMAN, L.; CASA, V.; LARA, E.; MATALONI, G.

Ilha Belha

Simposio; 8th International Symposium on Testate Amoebae; 2016

Universidae de Sao Paulo

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<0,001**), with the presence of Pinnularia spp. accounting for thehigher diversity in P2. Notably, the tests of both populations differed even morefrom each other than to their respective benthic samples. In P1, wherePinnularia was present, the testacean population differed significantly(p<0,001**) from the benthic SS due to the absence of Frustulia in all tests anda negative selection of Chamaepinnularia (IP: -0,113±0,069). On the otherhand, in P2 where Pinnularia was absent, Phryganella sp1 incorporated ahigher proportion of Frustulia and Chamaepinnularia valves.Our results show a distinct and common selective behavior for both Phryganellaspecies in P1 on one hand, and no selectivity in any of the three species in P2on the other. Moreover, the different behavior shown by Phryganella sp1 in thetwo ponds strongly suggests that neither is this a species-specific treat, butrather environmentally driven. While causes for SS selection are not clear atthis point, particle size is definitely not a key one, since no size selection of thematerial was recorded for any of the testacean species in this study. While thepresence of Pinnularia seems to relate to selective behavior, such relationshipis not due to a positive selection for this species. Whether Pinnularia could beindicative of other environmental conditions driving the selective behavior ofPhryganella sp1 remains open to future research. We thus contribute to thescarce knowledge about testaceans ecology by posing new questions on theinteraction of these organisms with their environment. New advances can beexpected by using the new digestion technique in analyzing trophicrelationships between testaceans and diatoms, both of them key environmentaland palaeoenvironmental indicators in peatbogs.