Maternal and environmental influences on egg size and juvenile life‐history traits in Pacific salmon

Abstract

Life-history traits such as fecundity and offspring size are shaped by investment trade-offs faced by mothers and mediated by environmental conditions. We use a 21-year time series for three populations of wild sockeye salmon (Oncorhynchus nerka) to test predictions for such trade-offs and responses to conditions faced by females during migration, and offspring during incubation. In years when their 1100 km upstream migration was challenged by high water discharges, females that reached spawning streams had invested less in gonads by producing smaller but not fewer eggs. These smaller eggs produced lighter juveniles, and this effect was further amplified in years when the incubation water was warm. This latter result suggests that there should be selection for larger eggs to compensate in populations that consistently experience warm incubation temperatures. A comparison among 16 populations, with matching migration and rearing environments but different incubation environments (i.e., separate spawning streams), confirmed this prediction; smaller females produced larger eggs for their size in warmer creeks. Taken together, these results reveal how maternal phenotype and environmental conditions can shape patterns of reproductive investment and consequently juvenile fitness-related traits within and among populations.

Indirect genetic effects underlie oxygen-limited thermal tolerance within a coastal population of chinook salmon

“…While the correspondence between thermal tolerance and environmental conditions suggests local adaptation brought about by selection on additive genetic effects, our study suggests that an indirect genetic effect-mediated by egg size-could instead underlie the variation. Indeed, across many sockeye salmon populations, egg size is populationspecific and positively correlated with natural incubation temperatures [37] and juvenile thermal tolerance [36]. Heart rate varies considerably both within and between fish species, with resting f H being primarily determined by metabolic rate and haemodynamic requirements, and f Hmax being limited by mechanistic constraints such as pacemaker potential, excitation-contraction properties and myocardium structure [38].…”

Local adaptation to cold temperatures by larval coho salmon (Oncorhynchus kisutch) from different populations throughout British Columbia

“…Fecundity of sockeye salmon (Oncorhynchus nerka) has also been found to increase with increased female size (Braun et al 2013), consistent with my findings as large females were found to spawn farther north and at longer migration distances.…”

“…Colder incubation temperatures were also found for the northern interior systems where not only did the eggs incubate at colder temperature, but temperature was colder for spawning and most likely for migration. Braun et al (2013) found that gonadal mass decreased with increased migration difficulties for sockeye salmon -a finding consistent with my study as migration is more difficult for adult salmon at warmer temperatures (Farrell et al 2008). Additionally, less energy is required for metabolic processes at colder temperature, thus there may be limited benefit of producing large eggs, allowing females to allocate energy to other processes such as producing more eggs and somatic growth (Stickland et al 1988;.…”

“…A number of previous studies have examined life-history variation among populations at different latitudes, but the populations have been limited to coastal watersheds or short migration distance into interior river systems (Fleming and Gross 1990;Beacham and Murray 1993;Braun et al 2013). In my study, data were collected from populations of coho salmon that migrate approximately 20 km to stocks that spawn more than 750 km from the ocean.…”

“…Braun et al (2013) found that larger female sockeye salmon produced more large eggs than smaller females -an overall increase in reproductive investment. Informative variables in my model were that female size increased with latitude, increased with spawning temperature, and decreased with size of system.…”