Spawning behaviour of Arctic charr (Salvelinus alpinus): risk of sperm competition and timing of milt release for sneaker and dominant males

Abstract

SummaryA mismatch in timing between the release of male and female gametes in external fertilizers may lead to failed fertilization or, under sperm competition, reduced paternity. To quantify the actual synchrony of gamete release and the level of sperm competition we placed video cameras on two spawning grounds of a naturally spawning population of Arctic charr (Salvelinus alpinus). Females release eggs in response to courting (quivering) in less than 1% of the cases, yet to both dominant and sneaker males. That is, females initiated spawning with dominant males in 73.3% of the recorded spawning events. Although the actual spawning seems to be largely under female control, 55.6% of spawning events occur under sperm competition. The average time delay between dominant and sneaker males milt release under sperm competition is 0.68 s. Thus, female reproductive decisions seem to be strongly influenced by male-male competition and this may have set the stage for the evolution and maintenance of the observed plasticity in ejaculate characteristics of male charr.

Spawning behavior of Arctic charr (Salvelinus alpinus): Spawning synchrony, vibrational communication, and mate guarding

“…Conflicts between males trying to fertilize the eggs are common (Sørum et al., 2011; own unpublished data). Bigger guarding males have the advantage of spawning close to and in synchrony with the spawning female.…”

“…Here, on shallow waters, females ready to release their eggs seem to attract males to their desired spawning site. The spawning males often adopt different size‐dependent mating tactics, either dominant (guarding) or subordinate (sneaker) (Figenschou, Rudolfsen, & Folstad, 2007; Sigurjónsdóttir & Gunnarsson, 1989; Sørum, Figenschou, Rudolfsen, & Folstad, 2011; Supporting information video S1), and their differing tactic is easily distinguished by recognizable behavioral traits (Sigurjónsdóttir & Gunnarsson, 1989). Bigger dominant males often acquire a guarding tactic, protecting and defending the spawning female against other surrounding males by aggressive traits like biting and chasing (Sigurjónsdóttir & Gunnarsson, 1989).…”

“…Bigger guarding males have the advantage of spawning close to and in synchrony with the spawning female. Smaller sneaker males, on the other hand, are forced by the aggressive bigger male to spawn out of synchrony and further away from the released gonadal products of the female (Sørum et al., 2011). Guarding and synchronized spawning by the dominant male may thus leave fewer unfertilized eggs available for the sneaker males, and the eggs will also be more dispersed and difficult to fertilize.…”

“…Guarding and synchronized spawning by the dominant male may thus leave fewer unfertilized eggs available for the sneaker males, and the eggs will also be more dispersed and difficult to fertilize. Yet, sperm competition occurs when sneaker males try to fertilize a limited number of dispersed, unfertilized eggs (Birkhead & Møller, 1998; Egeland, Rudolfsen, Nordeide, & Folstad, 2016; Sørum et al., 2011). …”

“…(2011), guarding and sneaker males of Arctic charr may differ in how synchronous they manage to ejaculate with the spawning female, in situations both with and without sperm competition. That is, the average time delay in gamete release under sperm competition between the guarding male, spawning in synchrony with the female, and the first sneaker was shown to be 0.68 s (Sørum et al., 2011). Females also initiated spawning with guarding males in 73.3% of all observed events, and 55.6% of the spawning events occurred under sperm competition.…”