Effects of pollution on dormant-stage banks of cladocerans and rotifers in a large tropical reservoir

Here, we describe the abundance and composition of the dormant-stage banks of cladocerans and rotifers at two locations in a tropical reservoir (Furnas Reservoir, Minas Gerais, Brazil) that are subject to different anthropogenic impacts. We hypothesized that at the site that received sewage, the density of resting eggs would be higher, but the species richness would be lower. Sediment samples were collected monthly at the two sampling stations. We counted the number of dormant stages and performed hatching experiments in the laboratory. Combining both sampling locations, we found a total of 26 species, 16 cladocerans, and 10 rotifers. Our hypothesis was partially corroborated, since the abundance and richness of dormant stages were significantly higher in the location subjected to wastewater release. Environmental pollution resulting from wastewater release and the cultivation of tilapia in cages is the most likely factor contributing to the higher values of egg density at this location. In contrast, the presence of aquatic macrophytes (a possible result of nutrient enrichment) at the same site may have contributed to the increase in species richness. Finally, our study indicates that the wastewater release in the reservoir can affect the production of dormant stages by cladocerans and rotifers.

Adaptive response to olive cultivation in a generalist parasitic nematode (Meloidogyne javanica)

Cultivated plants usually differ from their wild progenitors in several morphological and/or physiological traits. Their microbe communities might also differ because of adaptation to new conditions related to cultivation. To test this hypothesis, we investigated morphological traits in a parthenogenetic root-knot nematode (Meloidogyne javanica) from natural and agricultural environments. Seventeen populations of M. javanica were sampled on cultivated and wild olives in Morocco, then maintained in controlled conditions for a ‘common garden’ experiment. We estimated the genetic variation based on three traits (stylet size, neck width and body width) by a quantitative genetic design (ten families per population and nine individuals per family were measured), and molecular variation was investigated with a mitochondrial marker to identify the genetic lineages of nematode isolates sampled from wild and cultivated olives. Significant morphological differences were detected between individuals from wild vs. cultivated hosts for the three traits, whereas no phylogenetic clustering was observed among isolates collected on those two hosts. Our results thus suggest an adaptive response of the asexual parasite, possibly related to the deep modification of soil nematode communities between natural olive stands and orchards.