Influence of interspecific interactions on avoidance response to contamination.

An increasing number of studies have shown the ability of organisms to escape from toxic effects due to contamination, by moving spatially towards less contaminated habitats. However, this issue has been investigated in monospecific scenarios, without considering possible interactions between species during the contamination avoidance process. It is widely known that the spatial distribution of one species can be affected by another one, in different ways. Therefore, the main question addressed in the present study was as follows: Might interspecific interaction between the freshwater fish Danio rerio (zebrafish) and Poecilia reticulata (guppy) change their behavior patterns in terms of avoidance in the presence of a copper gradient? Zebrafish and guppies exposed to a copper gradient were tested for avoidance responses in a free-choice, non-forced, static, multi-compartmented exposure system, using two distinct approaches: (1) monospecific tests, in which only one species was exposed to the copper gradient, at two different population densities; and (2) multispecific tests, in which both species were tested simultaneously. In the control (with no copper) monospecific tests, both species were randomly distributed; however, in the control multispecific test, P. reticulata tended to aggregate. In the monospecific tests with a copper gradient, both species avoided copper in a similar way, with AC50 (concentration triggering avoidance in 50% of the exposed population) values between 15 and 18 μg·L-1, irrespective of the population density. However, in the multispecific tests, P. reticulata displaced D. rerio to previously avoided copper levels, consequently increasing the AC50 of D. rerio to 75 μg·L-1. This study shows the importance of understanding the interactions among species in contaminated areas, and the way that one species can prevent the avoidance behavior of another.