Selection Against Late Emergence and Small Offspring in Atlantic Salmon (Salmo Salar)

Abstract

Abstract. Timing of breeding and offspring size are maternal traits that may influence offspring competitive ability, dispersal, foraging, and vulnerability to predation and climatic conditions. To quantify the extent to which these maternal traits may ultimately affect an organism's fitness, we undertook laboratory and field experiments with Atlantic salmon (Salmo salar). To control for confounding effects caused by correlated traits, manipulations of the timing of fertilization combined with intraclutch comparisons were used. In the wild, a total of 1462 juveniles were marked at emergence from gravel nests. Recapture rates suggest that up to 83.5% mortality occurred during the first four months after emergence from the gravel nests, with the majority (67.5%) occurring during the initial period ending 17 days after median emergence. Moreover, the mortality was selective during this initial period, resulting in a significant phenotypic shift toward an earlier date of and an increased length at emergence. However, no significant selection differentials were detected thereafter, indicating that the critical episode of selection had occurred at emergence. Furthermore, standardized selection gradients indicated that selection was more intense on date of than on body size at emergence. Timing of emergence had additional consequences in terms of juvenile body size. Late-emerging juveniles were smaller than early-emerging ones at subsequent samplings, both in the wild and in parallel experiments conducted in seminatural stream channels, and this may affect success at subsequent size-selective episodes, such as winter mortality and reproduction. Finally, our findings also suggest that egg size had fitness consequences independent of the effects of emergence time that directly affected body size at emergence and, in turn, survival and size at later life stages. The causality of the maternal effects observed in the present study supports the hypothesis that selection on juvenile traits may play an important role in the evolution of maternal traits in natural populations.

Adaptive responses to cool climate promotes persistence of a non-native lizard

“…twofold) increase in survival after emergence (see also [30]). This increased survival of early hatched offspring could be the result of several non-mutually exclusive mechanisms, including increased opportunity for growth and production of fat bodies prior to hibernation ( [49] see also [50]), positive effects of high embryonic temperature on physiological and morphological traits [51,52] or greater ability to capitalize on seasonally available food sources [53]. Earlier emergence and long-term persistence of non-native populations could be further enhanced if non-native lizards also initiated reproduction earlier than their native counterparts.…”

Why climate change will invariably alter selection pressures on phenology

“…Another important assumption of our modelling work was that deviating from the optimal reaction norm (in both elevation and slope) carries a fitness cost for the consumer, which seems to be common in phenological traits [1][2][3][4][5][6][7][8][9][10][11].…”

“…Phenology, the seasonal timing of lifecycle events, has important fitness consequences in seasonal environments as there is generally only a limited period of favourable conditions for carrying out seasonal activities such as reproduction, migration or hibernation [1][2][3][4][5][6][7][8][9][10][11]. These favourable conditions could be set by weather, for example, arriving too early at the breeding grounds when conditions are still harsh [12], or by the phenology of other species [3,13].…”

Milk matters: offspring survival in Columbian ground squirrels is affected by nutrient composition of mother's milk

“…Timing of reproduction impacts reproductive performance for many animals (Festa-Bianchet, 1988;Verhulst and Tinbergen, 1991;Dobson and Michener, 1995;Einum and Fleming, 2000) and may be especially critical for hibernating animals that need to gain fat mass prior to hibernation. By mating earlier, mothers and juveniles have more time to acquire fat reserves before hibernation commences (Murie and Boag, 1984;Millesi et al, 1999).…”