Supplementary data to “Alternative reproductive tactics are associated with sperm performance in invasive round goby from two different salinity environments”

During male-male competition, evolution can favor alternative reproductive tactics. This often results in a dominant morph that holds a resource, such as a nest for egg laying, competes with a smaller sneaker morph that reproduces by stealing fertilizations. The salinity environment can influence male growth rates, e.g. via osmoregulatory costs, which in turn may influence the use of sneaker tactics for small males competing for mating opportunities. Salinity can also affect sperm directly; however, little is known of how salinity influences sneaker tactics through sperm performance. We sampled males of the invasive round goby (Neogobius melanostomus) from two environments, a freshwater river and a brackish estuary. This fish has two male morphs: nest-holding dark males and non-nest-holding light males. We examined the role of water salinity of 0, 8 and 16 on sperm performance and found that in estuarine males, a salinity of 0 reduced sperm velocity compared to a salinity of 8 and 16. R...