Samples issued from intensive sampling in the Netherlands (1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) and from extensive sampling carried out in the context of international campaigns (1998, 2000 and 2001) were revisited. Additional samples from artificial substrates (1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) and other techniques (various periods) were analysed. The combined data provide a global and dynamic view on the Peracarida community of the River Meuse, with the focus on the Amphipoda. Among the recent exotic species found, Crangonyx pseudogracilis is regressing, Dikerogammarus haemobaphes is restricted to the Condroz course of the river, Gammarus tigrinus is restricted to the lowlands and seems to regress, Jaera istri is restricted to the 'tidal' Meuse, Chelicorophium curvispinum is still migrating upstream into the Lorraine course without any strong impact on the other amphipod species. After a rapid expansion Dikerogammarus villosus has continued its upstream invasion between 1998 and 2002 at a rate of 30-40 km per year, but no further progression was noticed in 2003. Locally and temporarily the native species (Gammarus fossarum and G. pulex) and naturalized species (G. roeseli and Echinogammarus berilloni) may have been excluded by the most recent invaders (mainly D. villosus), but none of the native and naturalized species has disappeared completely. Therefore, the number of amphipod species found in the River Meuse has increased. Moreover, the native and naturalized species keep on dominating the tributaries from which the recent invaders seem to be excluded. A changing Peracarida community structure is observed along the course of the River Meuse: four native or naturalized species inhabit the upstream (Lorraine) course, three invasive species dominate in the middle reach (Ardenne-Condroz zone), one exotic species is housed in the Border Meuse and three or four invasive species dominate the assemblages in the lowlands.

No abstract

No abstract

No abstract

Knowing that the workers of the ant Myrmica sabuleti can distinguish different numbers of elements and have a basic notion of zero, we here examine if they can add two numbers of identical elements seen simultaneously. As soon as after three training days, the ants could respond significantly more to the sum of 1 + 1, 2 + 1, 3 + 1, and 3 + 2 elements than to the two initial numbers of elements seen during training and to the wrong sums 3, 4, 5 and 6 respectively. Their ability in giving the correct response seemed to somewhat decrease with increasing numbers to add. Twenty-four hours after the removal of the initial numbers presented during training, the ants no longer responded essentially to the correct sum of these numbers.

The notion of zero is rarely apprehended by animals. We examined if ants possess this ability in four experiments, each time using two colonies and operant conditioning. Ants succeeded in significantly comprehending the absence of a cue, but not as well as learning an existing cue, and they soon lost their learning. Ants thus have a sensory notion of the absence of an item, but not the abstract notion of a sensu stricto mathematical zero.

Using ants as models, the glycoside rebaudioside A, a sweetener extracted from the plant Stevia rebaudiana and commercialized under the name 'stevia', was shown to have no effect on their food consumption, locomotion, precision of reaction, response to pheromones, brood caring, cognition, visual and olfactory conditioning and memory, although this sweetener slightly increased the ants audacity. However, when having the choice between stevia and saccharose, the ants somewhat preferred the latter. Stevia is thus a safe sweetener which does not impact general health, behavior and cognition, but it is generally perceived less pleasant than saccharose.

No abstract