Range expansion of Kellicottia bostoniensis (Rousselet, 1908) (Rotifera) throughout a biogeographic boundary between the Brazilian savanna and the Amazon

The freshwater rotifer Kellicottia bostoniensis (Rousselet, 1908), native from North America, has been considered invasive in European, Russian and South American waterbodies. More than reporting its presence, for the first time, in Araguaia River, which plays critical role in a set of floodplain systems in the Brazilian savanna, we aim to understand how this invader react to new physical, chemical and hydrodynamics conditions, which can be helpful for predicting its invasiveness and colonization success in other similar non-native ranges. We use population data of K. bostoniensis and environmental variables surveyed across the meandering middle-stretch of the Araguaia River. The highest frequencies of K. bostoniensis were registered in sites of lower mean temperatures, higher pH and dissolved oxygen at sites with higher hydrodynamics. However, the highest abundance was found in a backwater site, a more lentic habitat in which total body size was slightly higher than those with lotic conditions. Both the abundance values and body length were the lowest registered in non-native areas, suggesting the initial phase of the invasion process. Also, the trade-off between abundance and body size may allow population to persist in flowing water conditions, thus playing fundamental role in population recruitment and dispersal, favoring the propagation of this organism in the river curse and adjacent environments. Specifically, stepping stones created by the river meanders would increase population growth and the rapid spread of K. bostoniensis through Araguaia River. Due to its wide environmental tolerance, morphological plasticity and high dispersal ability, we further anticipate continued dispersion of K. bostoniensis to other Brazilian basins highlighting the need for persistent monitoring upstream and downstream of this freshwater ecotone.