Overwinter survival, energy storage and reproductive allocation in the invasive round goby (Neogobius melanostomus) from a river system

The dynamic nature of population density during the invasion process may compromise how a population is able to cope with challenging environmental conditions within their non-native range. In temperate regions, one of the greatest seasonal environmental challenges is winter. We assess overwinter survival, changes in body condition and lipid content, and reproductive allocation of round goby (Neogobius melanostomus) from the point of introduction and the leading edges of an expanding invasive population in a tributary of Lake Ontario. Autumn lipid content was highest in round goby from the downstream edge and lowest at the centre of the invasive range, likely due to lower population density and reduced intraspecific resource competition at the expanding edges of its distribution. After 142days of starvation under simulated winter conditions, round goby exhibited 96% survival. Despite the extended starvation period, the majority of females were able to allocate energy into ovarian development, with 60% of females having a gonadosomatic index of >5% at the end of the overwintering period. Individuals originating from the downstream edge allocated significantly more energy towards reproduction compared with individuals from the upstream and centre locations. The results suggest that the position within an expanding invasive range can influence the autumn energy content and consequently the reproductive effort of round goby in early spring. High overwinter survival and greater allocation of energy to reproduction at the expanding edge of an invasion may contribute to the highly successful expansion of the round goby in the Great Lakes Basin.