Divergent life histories of invasive round gobies (Neogobius melanostomus) in Lake Michigan and its tributaries

Round gobies (Neogobius melanostomus) have invaded benthic habitats of the Laurentian Great Lakes and connected tributary streams. Although connected, these two systems generally differ in temperature (Great Lakes are typically colder), food availability (Dreissenid mussels are more prevalent in Great Lakes), and system size and openness. Here, we compare round goby life histories from inshore Lake Michigan and adjacent tributary systemsan uncommon case study of life-history differences between connected systems. Tributary round gobies grew much faster (average length-at-age of 122.3 vs. 65.7mm for Age 2+ round gobies), appeared to have shorter life spans (maximum observed age of 2 vs. 5) and had lower age-at-50% maturity (1.6 vs. 2.4years; females only) compared to gobies from Lake Michigan. In addition, tributary gobies had greater fecundity at Ages 1-2 than lake gobies, but had fewer eggs for a given body size prior to the first spawning event of the summer. We were not able to determine the cause of the observed life-history differences. Nonetheless, the observed differences in growth, maturation and longevity were consistent with known effects of water temperature, as well as predictions of life-history theory for animals at invasion fronts exposed to novel environmental conditions. The high degree of phenotypic plasticity in connected populations of this invasive species has implications for our understanding of invasive species impacts in different habitats.