Competitive interactions shape offspring performance in relation to seasonal timing of emergence in Atlantic salmon

Abstract

Summary 1.Timing of birth ⁄ hatching may have strong effects on offspring fitness. Breeding time is generally considered to have evolved to match offspring arrival with optimal seasonal environmental conditions, though this is rarely tested experimentally and factors shaping the relations between timing of birth and reproductive success are often poorly understood. 2. By manipulating incubation temperature of Atlantic salmon embryos, and hence controlling for maternal and genetic effects, we obtained offspring emerging from nests prior to (accelerated), during and after (decelerated) normal emergence times, and accordingly experienced widely different seasonal environmental conditions at emergence (stream temperature range 4-16°C). The accelerated group emerged at temperatures that are generally considered to be highly sub-optimal for growth and likely imposes strong constraints on feeding and activity, and during a peak in water discharge which is expected to negatively influence habitat availability. 3. In the wild, overall mortality during the period after emergence was 79%, and was significantly affected by both release density and emergence timing. Accelerated offspring, which emerged earliest and experienced the harshest environmental conditions, had both highest survival and largest final body size. The effect was particularly strong at the high density release site, where survival of accelerated offspring was significantly higher than both the normal and decelerated groups. 4. In more controlled semi-natural environments, all developmental groups were able to perform well, but accelerated offspring had a relatively better performance than the later emerging offspring when density was high. Furthermore, the relative performance of the different groups was not sensitive to water discharge regimes (temporally stable vs. fluctuating). 5. These results suggest that the performance of offspring in relation to seasonal timing of emergence is highly affected by competitive interactions in Atlantic salmon. Although a match between phenology and optimal seasonal environmental conditions may be highly important for organisms depending on specific resources that are only available during a limited period of the season, such resources may be available in variable amounts year around for many organisms. For these, offspring success may to a larger degree be shaped by the timing of their hatching ⁄ birth relative to each other, and particularly so under high population densities.

Maternal Size and Age Shape Offspring Size in a Live-Bearing Fish, Xiphophorus birchmanni

“…Increased size at birth is generally thought to increase survival, competitive ability, or growth in the stages following independence from the female [5] [44]–[46]. However, much is still unknown about the rate at which fitness increases with size, or why it does so [21] [45].…”

Timing matters: species‐specific interactions between spawning time, substrate quality, and recruitment success in three salmonid species

“…A shorter period of development in substratum by DS compared with RBT in the subsequent life stage, that is, the emergence of fry, was shown previously (Sternecker and Geist 2010). Cumulative effects of shorter development times are important to consider, because it has also been shown that an earlier emergence of fry increases competitiveness of species and individual fish, respectively (Skoglund et al 2011). As both life stages (egg-to-fry and emergence of fry) benefit from an accelerated development, the total effect is likely to be even stronger than the one described herein.…”

Genetic variability in reaction norms in fishes

“…Experiments should also be carried out simultaneously to maximize the similarity between common environments and ensure consistency in the execution and timing of measurements, although this can be problematic for many species of fishes in which different populations spawn at different times of year. Some species can be induced to spawn using photoperiod manipulation (e.g., Atlantic silversides; Conover and Present 1990) or degree-day calculations can be used to rear eggs from different populations at different temperatures so that all eggs hatch at the same time (Skoglund et al 2011). When it is not possible to study populations simultaneously, experiments should be replicated at different times to estimate potential temporal differences between experiments (e.g., Hutchings et al 2007).…”