Pontoscolex corethrurus:a Homeless Invasive Tropical Earthworm?

Abstract

SummaryThe presence of earthworm species in crop fields is as old as agriculture itself. The earthwormsPontoscolex corethrurus(invasive) andBalanteodrilus pearsei(native) are associated with the emergence of agriculture and sedentism in the region Amazon and Maya, respectively. Both species have shifted their preference from their natural habitat to the cropland niche; however, they contrast in terms of intensification of agricultural land use (anthropic impact to the symbiotic soil microbiome).P. corethrurusinhabits conventional agroecosystems (pesticides, herbicides, and fertilizers are applied to soil), whileB. pearseithrives in traditional agroecosystems (biological management of soil); that is,P. corethrurushas not yet been recorded in soils whereB. pearseidwells. The demographic behavior of these two earthworm species was assessed in the laboratory over 100 days, according to their origin (OE;P. corethrurusandB. pearsei) food quality (FQ; soil only, maize stubble, andMucuna pruriens), and soil moisture (SM; 25, 33, and 42%). The results showed that OE, FQ, SM, and the OE x FQ interaction were highly significant for the survival, growth, and reproduction of earthworms.P. corethrurusshowed a lower survival rate (> mortality).P. corethrurussurvivors fed a diet of low-to-intermediate nutritional quality (soil and corn stalks, respectively) showed a greater capacity to grow and reproduce; however, it was surpassed by the native earthworm when fed a high-quality diet (M. pruriens). Besides,P. corethrurusdisplayed a low cocoon hatching (emergence of juveniles). These results suggest that the presence of the invasive species was associated with the absence of natural mutualistic bacteria (gut, nephridia, and cocoons), and with a negative interaction with the soil microbiota where the native species dwells. These results are consistent with the absence ofP. corethrurusin milpa and pasture-type agricultural niches managed by peasants (agroecologists) to grow food regularly a biological management of soil. The results reported here and the published information jointly (e.g., designation of the neotype and ambiguity of the place of origin) jointly suggest thatP. corethrurusis an invasive species that is neither wild nor domesticated, that is, its eco-evolutionary phylogeny needs to be derived based on its symbionts.