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

Abstract

A mismatch in synchrony between male and female gamete release in external fertilizers can result in reduced or failed fertilization, sperm competition, and reduced paternity. In Arctic charr (Salvelinus alpinus), males can adopt either a guard or sneak tactic resulting in both pre‐ and postcopulatory competition between males with alternative reproduction tactics. Here, spawning behavior of free‐living Arctic charr was video‐recorded, and their reproductive behavior was analyzed. From evaluating 157 spawning events, we observed that females mainly spawned with a guarding male and that the female and the guarding male synchronized timing of gamete release under sperm competition. Although sneakers spawned with higher synchrony than the guarding male in single‐male spawning events, the average sneaker released his milt less synchronized with the female than the guarding male under sperm competition. Approximately 50% of the recorded spawning events occurred under sperm competition, where each event included an average of 2.7 males. Additionally, sneakers were more exposed to sperm competition than guarding males. An influx of males, in close proximity to the female, occurred during the behavioral sequences leading up to egg release, but this influx seemed not dependent on egg release, suggesting that something else than gonadal product attracts sneaker males to the spawning female. Just before and during the actual release of gametes, the spawning couple vibrates their bodies in close contact and it seems likely that this vibrational communication between the spawning couple, which results in a larger amplitude sound wave than seen under regular courting, reveals time of gamete release to sneaker males. Thus, vibrational communication may enable synchrony between the guarding male and the female, and this might be traded against the cost of higher detectability from surrounding sneaker males, eavesdropping in close proximity.

Contrasting associations between breeding coloration and parasitism of male Arctic charr relate to parasite species and life cycle stage

“…Of note, charr display a striking indifference to human presence during spawning as we and other charr researchers observed (see Supplementary Video kindly donated by Brattli et al . 43 ) indicating increased risk-taking behavior. Thus positive relationships between parasite abundance and secondary sexual ornamentation could be caused by the presence of parasites that stand to benefit from host reproductive maturation (for instance those awaiting trophic transmission) and their putative influence on host behavior and physiology.…”

Cannibalism and protective behavior of eggs in Arctic charr (Salvelinus alpinus)

“…Males have alternative reproductive tactics, and one dominant male always guards the female from other subordinate males by aggressively chasing and biting them (Sørum et al., 2011). The dominant male courts the female frequently by positioning himself alongside her and quivers his body next to hers (Brattli et al., 2018; Fabricius, 1953; Sigurjónsdóttir & Gunnarsson, 1989). Occasionally, the female also quivers along with the male, and this is sometimes followed by “gaping” and simultaneous shedding of gametes (Brattli et al., 2018; Fabricius, 1953; Sørum et al., 2011).…”

No support for cryptic choice by ovarian fluid in an external fertilizer

“…Spawning behavior of charr in the present population has been studied by Sørum et al (2011) and Brattli et al (2018). The studies show that (a) more than 50% of the spawning events occur under sperm competition, (b) mean number of males is 2.9 s at egg release and increases to more than four males within the next 2.0 s, (c) the first male to release milt ejaculated from 0.15 s before to 1.9 s after the eggs are shed, and (d) the average time delay in gamete release under sperm competition between the first and the subsequent males is estimated as 0.68 s (Sørum et al, 2011).…”

“…The studies show that (a) more than 50% of the spawning events occur under sperm competition, (b) mean number of males is 2.9 s at egg release and increases to more than four males within the next 2.0 s, (c) the first male to release milt ejaculated from 0.15 s before to 1.9 s after the eggs are shed, and (d) the average time delay in gamete release under sperm competition between the first and the subsequent males is estimated as 0.68 s (Sørum et al, ). Moreover, some males have the advantage of spawning physically relatively close to the spawning female, whereas the remaining males spawn further away (Brattli, Egeland, Nordeide, & Folstad, ; Sørum et al, ). The exact concentration of OF diluted in water at the time of fertilizations in natural spawning events is not known for this population, but most likely it varies a lot between fertilizations and competing males.…”