Odonata larvae as dispersal vectors of zooplankton resting stages: a preliminary study in the Parana River Foodplain

MANZO, RAMIRO ; BATTAUZ YAMILA; PAGGI, JUAN CESAR; MUZÓN JAVIER

La Plata

Congreso; International Congress of Odonatology; 2015

Different evolutionary strategies enable the zooplankton community to survive the seasonal heterogeneity of aquatic environments, one of the most interesting is the dormancy which includes states of diapauses and inactivity. Currently, it is known that in natural environments eggs that are deposited in the sediments and on different surfaces contribute significantly to the species dispersion. In the Parana River oodplain, one would expect that vectors with a significant presence in the region, such as the Odonata larvae, may play an important role in the dispersion of zooplankton. Our objective is to determine the importance of Odonata larvae associated with aquatic plants in the dispersion of resting stages of zooplankton by exo and endozoochory. Pleustonic larvae of Libellulidae, together with the zooplankton supply, were collected in shallow lakes, classified according to size (small, medium and large), and grouped into 3 replicates of the 11 individuals per size. In order to study the dispersion by exo and endozoochory, the larvae were washed, and left to defecate. The collected material was dried at room temperature and then stored in refrigerator at 4°C for 3 weeks. Then, the samples were placed on trays and incubated at 25°C with a photoperiod of 16/8 (light-dark) hours for 30 days. The supernatant water from each tray was filtered and examined every other day. 87 hatchlings were recorded, of which only 30% were associated with the dispersion by endozoochory. Rotifera, with 16 species, was the only group recorded. The most frequent species found were: Lecane inermis, L. hamata, L. bulla and Bdelloidea. The abundance and richness of hatchings varied with the size of the larvae, in endozoochory a progressive increase of hatchings until the larger size was observed, while in exozoocoria, no pattern was observed. As for the faunal composition, Jaccard index denoted a clear dissimilarity between exo and endozoochory (Jaccard: 0.12). The results show that Odonata larvae could act as vehicles for the dispersion of resting stages of zooplankton. Being the Odonata a very important group in terms of density, they could play a key rolein determining the structure of the zooplankton community.