Alternative reproductive tactics, an overlooked source of life history variation in the invasive Round Goby.

Alternative reproductive tactics (ARTs) can generate considerable within species life history variation, but are often overlooked. Here, we use the invasive Round Goby (Neogobius melanostomus) to address a number of ecological and evolutionary questions about ARTs. Making use of a 12-year, multi-site, Laurentian Great Lakes dataset, we show that guarder males were twice as common as sneakers males, but that non-reproductive males were the most common tactic. The ratio of guarder to sneaker males did not vary spatially despite wide ranges of resource density across sites. Guarders and sneakers spanned similar age ranges, suggesting the ARTs are non-sequentially expressed. Based on short term (gut contents) and long term (isotope) diet analyses, both reproductive tactics had fewer numbers and types of food items in their digestive tracts compared to non-reproductive males. Guarder males fed at a higher trophic level based on δ¹⁵N and had a broader isotopic niche. Our results show that ARTs are an important aspect of this invasive species’ mating system and should be accounted for when assessing and managing populations.