Ontogenetic phenomena, temporal aspect, and ecological factors in the successful invasion of round goby Neogobius melanostomus in the River Danube

Abstract

Plasticity in life-history traits is thought to be one of the key factors that contribute to adaptation of invasive species to the novel environment at the beginning of an invasion. It has been found that round gobies Neogobius melanostomus from freshly invaded areas (invasion front) exhibit different life-history traits than individuals from core or central areas with well-established populations. The theory of alternative ontogeny and invasive potential predicts such differences. Nevertheless, it is difficult to distinguish between the effects of intrinsic ontogenetic phenomena and the effects of particular ecological factors on life-history traits of populations at various stages of invasion. Thus, the main aim of this study was to test the prediction that two sub-populations of round gobies from two habitats exposed to a different intensity of anthropogenic pressures in the River Danube, but at the same stage of invasion, will have significant differences in their reproductive parameters. Females from the relatively undisturbed habitat were predicted to have 1) larger oocytes, 2) lower absolute number of oocytes, and 3) lower real absolute fecundity. For two parameters (1 and 3), differences were statistically significant, as predicted. For parameter 2, the difference was as predicted, though not significant. Several studies suggest that changes in life-history traits observed over the progressing invasions of fishes are typical rather than accidental. They appear to be related to the stage of the invasion and closely associated with ontogenetic phenomena (the capability to generate alternative ontogenies). However, ecological factors also play an important role in this process. If the habitat is exposed to permanent disturbances, the established invasive population will probably keep the same life-history traits as at the beginning of the invasion.