Invasion of the tropical earthworm Pontoscolex corethrurus (Rhinodrilidae, Oligochaeta) in temperate grasslands

The tropical earthworm Pontoscolex corethrurus presents a broad distribution (56 countries from four continents) with climates that resemble the one in its native area of distribution. In invasive earthworms, it is generally assumed that temperature appears to limit the success of tropical exotic species in temperate climates. With the global climate change, the edge of the distribution range of this species could advance towards higher elevations (with lower temperatures) where no tropical species currently occur. The aim of this study was to evaluate the soil and climatic variables that could be closely associated with the distribution of P. corethrurus in four sites along an altitudinal gradient in central Veracruz, Mexico. We tested the hypothesis that the global migration of P. corethrurus appears to be limited only by temperature. Five sampling points (monoliths) were established at each of four sites along an altitudinal gradient: Laguna Verde (LV), Ingenio La Concepción (IC), Naolinco (NA) and Acatlán (AC) at 20, 982, 1542 y 1751 masl, respectively. Our results showed that the climate along the altitudinal gradient ranged from tropical to temperate. Ten earthworm species were found along the gradient, belonging to three families (Rhinodrilidae, Megascolecide and Lumbricidae). Soil properties are associated with the abundance of the earthworm community along the altitudinal gradient. P. corethrurus was recorded at three sites (LV, IC and NA) along the altitudinal gradient. Our results reveal that the premise that low temperature limits the distribution of P. corethrurus in not supported; that is, this species may survive and reproduce at the site NA with an average annual temperature of 17 ºC. These results suggested that P. corethrurus might be colonizing temperate environments.