Abstract
Bees are valuable bioindicators, providing information regarding environmental conditions through different kinds of analyses. Therefore, the effect of cadmium on the morphology of ovaries of Bombus morio workers was used to study a concentration considered environmentally safe (1 ppb) in Brazil. Workers of the same estimated age exposed for 48 h to 1 ppb cadmium showed extensive morphological changes in the germarium and vitellarium compared with the control group. Bees exposed to cadmium showed death of or damage to entire vitellogenic follicles, with chromatin condensation and fragmentation of nurse cell nuclei. In the germarium, the intercellular bridge connecting the primary oocyte to the developing nurse cells was broken. The nurse cells formed a cluster of cells with compacted chromatin, detached from an isolated primary oocyte. In some cases, the cytoblasts were absent from the germarium, leaving an empty space surrounded by collapsed peritoneal sheaths. We further propose that such a hazardous impact of 1 ppb cadmium on the ovaries of B. morio workers is not only mainly due to cadmium itself as an endocrine disruptor, indirect oxidative stress promoter, cytoskeleton destabilizer and mutagenic trace metal, but by disruption of the trophocytes, where perivitelline space filled with eosinophil material in the control group, was totally empty in exposed bees, suggesting interruption of trophocyte vitellogenin production.
Highlights
In addition to the invaluable pollination services of bees, these insects are successful bioindicators
We investigated the effect of 1 ppb cadmium on the ovaries of Bombus morio to verify if the cadmium concentration considered environmentally safe impacts the cells of the reproductive biology of the females
The ovarian cycle and general morphology of the ovarioles of non-exposed bees were typical of polytrophic meroistic ovaries, as described for other bee species (Martins and Serrão, 2004; Tanaka and Hartfelder, 2004; Tanaka et al, 2009; Chapman, 2012), i.e., each ovariole was comprised of a terminal filament, germarium and vitellarium (Fig. 1A, Fig. 1E)
Summary
In addition to the invaluable pollination services of bees, these insects are successful bioindicators. Trace metals are very harmful and their concentrations in the environment have been increasing, making them an important risk factor for bees (Celli and Maccagnani, 2003; Duruibe et al, 2007; Roman, 2010; Carrero et al, 2013). These metals are highly cationic elements in organic systems, given that they are converted into a stable oxidation state in acidic pH, a condition that exists in the stomach of all animals. As the colony biological cycle of B. morio begins with one fecundated solitary queen, or solitary phase, these bees are predisposed to be more susceptible to environmental impacts
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