Periodic Reporting for period 2 - HOOKaWORM (Hook a Worm to Catch a Man: Tracking Historical and Recent Human Settlement, Land use and Migration in Neotropical Rainforests using Ecosystem Engineers)
Reporting period: 2017-05-01 to 2018-04-30
This is being pursued through a three-tier approach with three distinct but complementary objectives, compartmentalized into individual workpackages. Therefore, the main objectives of the project are:
1st objective: Assessment of the extent of the relation between soil biodiversity and human settlements associated with Amazonian Dark Earths (ADEs)
2nd Objective: Tracking recent and historical (i.e. pre-Columbian) land use changes using soil biodiversity assemblages
3rd Objective: Tracking Amerindian migration impacts on genetic diversity from western Amazonia to Southern Brazil using a peregrine earthworm species
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.
Earthworms in particular, display a number of properties that may make them an excellent bioproxy for ancient human dispersal events.
It is important to reveal, that most of the work could not be possible without the established wide collaborative network Terra Preta de Índio Network (TPInet) (TPI Network: http://tpinet.org) implemented during the first year of the project. The available expertise and human resources (associated with the different project workpackages according to various expertise) available in the TPInet is mainly characterized by a multidisciplinary nature, that tends to work by a dynamic interdisciplinary interaction.