Alternative reproductive tactics in Lake Michigan populations of invasive round goby (Neogobius melanostomus): How fish increase fitness by doing less

Understanding the reproductive biology of invasive species is an important step in managing populations. Yet, little is known about the reproductive strategies of invasive round goby (Neogobius melanostomus) in Lake Michigan. For round goby, fertilization occurs externally in nests guarded by large “paternal” males. However, some males pursue alternative reproductive tactics (ARTs), where males sneak into a larger male’s nest and fertilize a portion of the eggs, these males are called “sneakers”. We investigated if the proportion of ARTs varies between sites and how that affects population dynamics of round goby. We caught 264 fish from 4 lakes along Eastern Lake Michigan. We measured their color, morphology, and gonad traits to determine each male’s reproductive type. Our results suggest ARTs represent at least 20% of reproductive round goby males. As predicted, sneaker males had larger testes relative to their body mass, and paternal males had larger accessory glands relative to body mass. The next step in this work is to model how the presence of ARTs within these populations may be impacting population growth estimates of this invasive species around Lake Michigan.