On the relative effect of spawning asynchrony, sperm quantity, and sperm quality on paternity under sperm competition in an external fertilizer

How much of a fitness benefit is obtained by dominant males of external fertilizers from releasing ejaculates in synchrony with female egg-release when engaging in sperm competition, and what is the most important sperm trait for paternity in these situations? The Arctic charr (Salvelinus alpinus) is an external fertilizer experiencing intense male-male competition over reproductive opportunities including sperm competition. To compensate for their disadvantage the sneaker males, which often spawn out of synchrony with the female, produce more and faster sperm than the guarding males. We used controlled in vitro fertilization trials with experimentally produced dominant and subordinate, sneaker males to test what effect relative synchrony in gamete release, sperm quality (i.e., motility and velocity) and sperm quantity have on a male’s fertilization success in pair-wise sperm competitions. When the sneaker males released ejaculates after the guarding male there was no overall difference in fertilization success. The quality (i.e., motility and velocity) of a male’s sperm relative to that of the competing male was the best predictor of male fertilization success regardless of their mating tactic and spawning synchrony. The relative number of sperm cells also had an effect on fertilization success, but mainly when the dominant and sneaker male ejaculated synchronously. Our close imitation of natural sperm competition in charr shows that the sneaker males of external fertilizing species may fully compensate for their disadvantaged mating role by producing ejaculates of higher quality—an adjustment strangely not met by dominants

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

From video recordings of spawning events, we quantified protective and cannibalistic behavior of Arctic charr occurring immediately after spawning. The number of fish cannibalizing on stray eggs was examined regarding (a) whether more than one male shed milt during the spawning event, that is, whether sperm competition occurred, (b) whether the sperm competition included few or many males, that is, the intensity of sperm competition, and (c) the density of fish at the spawning site. Response behavior toward egg cannibalism was also examined among females and dominant males in order to determine any parental investment toward protecting the eggs after spawning. Cannibalistic behavior was seen in almost 50% of the spawnings, and the multiple spawning events showed the highest numbers of fish cannibalizing on eggs. Both the number of males releasing milt and the number of fish approaching the spawning site were positively correlated with egg cannibalism. Sperm competition was, however, not a prerequisite for egg cannibalism. Although we also observed partial filial cannibalism, protective behavior of eggs was seen both among dominant males and females, suggesting that charr actually conduct parental care.publishedVersio

Status specific tailoring of sperm behavior in an external fertilizer

Published version. Source at https://doi.org/10.3389/fevo.2016.00135 Why dominant males experiencing intense sperm competition sometimes show low investments in sperm production is not always obvious. One well-documented example is that of the external fertilizing teleost, the Arctic charr (Salvelinus alpinus), where individuals becoming dominant reduce sperm production and sperm swimming speed in water compared to subordinates. Here, we report how ovarian fluid differentially influences sperm velocity of dominant and subordinate male Arctic charr. That is, sperm from dominant males increase their velocity in water diluted ovarian fluid compared to that observed in water, while sperm from subordinates, on the other hand, decrease velocity in ovarian fluid compared to that observed in water. Thus, subordinates, who invest more resources in their sperm and usually show the highest sperm velocity in water, have lower gains from their investment than dominant males when sperm are swimming in ovarian fluid. In sum, our result suggests that ovarian fluid increase sperm velocity more in dominant males than in subordinate males. Although this finding could partly be caused by cryptic female choice exerted by the ovarian fluid for sperm from dominant males, an alternative and more parsimonious explanation is that sperm from dominant males may simply be better designed for swimming in ovarian fluid compared to sperm from subordinate males. Thus, sperm production in the two reproductive roles seems to be adaptively tailored to different external environments

Carotenoids-based reddish pelvic spines in nonreproducing female and male sticklebacks (Gasterosteus aculeatus) – Signalling social dominance?

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Reproduction in Arctic charr – timing and the need for speed

Doctoral thesis (PhD) – Nord University, 2017publishedVersio