Ten sites (ADE & adjacent reference soil) were sampled for soil fauna, including the assessment of the main ecosystem engineer populations (earthworms, ants, and termites) using ISO standard method (n= five 25 x 25 x 30 cm deep soil monoliths per site). Soil chemical parameters and macromorphology were assessed on samples from the 0-30 cm soil layer. Study sites included old-growth forests, young forests, and agricultural systems in the regions of Belterra (PA), Iranduba (AM), and Porto Velho (RO). Qualitative sampling (~80 sites) along a transect from western Amazonia (Rondonia) to Southern Brazil (Parana) and to North (Roraima) was also accomplished.
Main results achieved so far:
ADE soil species composition is staggeringly different when compared to adjacent soils with a large number of exclusive representatives in ADE, with some newly discovered species. A higher proportion of ecosystem engineers was found in ADEs, closely associated to the presence of bio-aggregates, potsherds and to the soil’s unique physical and chemical properties. Species richness was also lower in agricultural sites and higher in old-growth forest. In total, 530 specimens were selected for DNA analysis, of which the COI was amplified and sequenced, obtaining a successful amplification in ~60% of the cases. These sequences generated a total of 45 MOTUs (Figure 5). The intra-MOTU mean divergence varied between 0 to 3% and between-MOTU from higher than 16%, considering a genetic distance of at least 15% for separation of MOTUs, the identified “barcode gap” (3% - 15%) corresponded to the intervals of divergence generally observed between well-established species in well-known earthworm families, such as Lumbricidae.
The richness of MOTUs in ADEs (24 spp.) was lower than in adjacent reference soils (32 spp.). The number of MOTUs found exclusively in only one of the soils was quite large: 21 in the adjacent reference sites (47% of the total) and 13 spp. in TPIs (29% of the total). The specimens were categorized morphologically into four families (Glossoscolecidae, Rhinodrilidae, Ocnerodrilidae and Acanthodrilidae) and tentatively in several genera, including Righiodrilus, Atatina, Pontoscolex, Martiodrilus, Neogaster and Dichogaster. Among the morphotypes found, most are unknown species, without correspondence in open reference databases (e.g. GenBank/NCBI) or with other species known morphologically. Only three could be identified at the species level: Pontoscolex corethrurus (MOTU5), Dichogaster andina (MOTU6) and Dichogaster modiglianii (MOTU9). These three species are well known to invade and inhabit human disturbed landscapes. Geographically, there were nine MOTUs exclusive found in Porto Velho, 18 in Belterra and 21 in Iranduba (Figure 3B). This indicates that composition is mainly constituted by species from regional groups, which is not surprising as earthworms are known for their limited dispersal capacity, and because most of these species are specialists, which makes them sensitive to environmental filters.
Results suggest that the unique enriched environment of ADEs became so conspicuously different from adjacent land that it developed its own characteristic fauna. We argued that the human impact in this ecosystem is broader than ever before estimated. This is true for the ecosystem engineers which seem to be a main component of ADEs, representing more than half of the total macrofauna and >80% of total biomass. They therefore contribute significantly to the functioning and engineering of these human-modified ecosystems. It is accepted that the ancient human societies that occupied the region adopted sedentary habits and the presence of exclusive representative ADEs species across the sites may reflect these ancient human dynamics, in particular, exchange of crops. This process of human-mediated transport would explain the distributions that are observed in some of the widely-distributed soil fauna in Brazil.
