Alternative reproductive tactics, an overlooked source of life history variation in the invasive round goby

Abstract

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, multisite Laurentian Great Lakes data set, we show that the guarder male tactic was twice as common as the sneaker male tactic but that nonreproductive males were the most common morph. The ratio of guarder to sneaker males did not vary spatially despite a wide range of resource densities across sites. Guarders and sneakers spanned similar age ranges, suggesting that the ARTs are nonsequentially expressed. Based on short-term (gut contents) diet analyses, both reproductive tactics consumed fewer types of food and tended to consume fewer items overall when compared with nonreproductive males. Long-term (isotope) diet analyses showed that guarder males fed at a higher trophic level (higher δ15N) and had a broader isotopic niche. Our results show that ARTs are an important aspect of this invasive species’ breeding system and should be accounted for when assessing and managing populations.

Alternative reproductive tactics are associated with sperm performance in invasive round goby from two different salinity environments

“…(2017) also reported a size‐related birthdate effect, arguing that a fish born late in the season would not have as much time to grow as their competitors that hatched earlier the same year. This has been further supported by less growth during the first year in round goby sneakers than in nest holders (McCallum et al., 2019). However, Somerville et al.…”

“…Other factors that may differ between these sites are unknown, in particular food availability and nest‐site availability. Food availability can drive growth rates, and in round goby, male nest‐holding tactics have been associated with time for growth in the first year between individuals of the same age cohort (McCallum et al., 2019; Somerville et al., 2019). Limited energy availability will also commonly limit reproductive investment.…”

“…The effect of nest availability on sneaking rates is yet to be experimentally tested in round goby. However, observational data suggest that environmental complexity (important for nest‐site availability) does not affect morph ratios (McCallum et al., 2019). In artificial aquarium conditions, round goby males of the light male morph have been reported to occupy a nest and court females when they did not have to compete with a dark, larger male (Meunier et al., 2009), suggesting that nest‐site availability might influence reproductive tactics.…”

Reproductive biology of pioneer round gobies (Neogobius melanostomus Pallas, 1814) at the edge of their invasion front in three small rivers (Lower Danube Basin, Bulgaria)

“…The existence of alternative male reproductive tactics (ARTs) is also considered a factor contributing to the invasion success of this species (Marentette et al 2009, Bleeker et al 2017, Cerwenka et al 2020, Green et al 2020. Over an entire year non-reproducing males dominate in a population, while at the start of the reproductive season (April, May) parental males are more commonly found, followed by sneaker males, which exhibit sexual mimicry (McCallum et al 2018, Cerwenka et al 2020).…”

Cryptic alternative male mating strategies in invasive alien round goby (Neogobius melanostomus) of the upper Danube River

“…However, studies on alternative reproductive strategies have only recently started in the context of biological fish invasions (McCallum et al 2019). The round goby, Neogobius melanostomus (Pallas 1811), has invaded numerous ecosystems worldwide (Kornis et al 2012) and often became highly abundant in invaded areas (e.g.…”