Adaptive variation in senescence: reproductive lifespan in a wild salmon population

Abstract

The antagonistic pleiotropy theory of senescence postulates genes or traits that have opposite effects on early-life and late-life performances. Because selection is generally weaker late in life, genes or traits that improve early-life performance but impair late-life performance should come to predominate. Variation in the strength of age-specific selection should then generate adaptive variation in senescence. We demonstrate this mechanism by comparing early and late breeders within a population of semelparous capital-breeding sockeye salmon (Oncorhynchus nerka). We show that early breeders (but not late breeders) are under strong selection for a long reproductive lifespan (RLS), which facilitates defence of their nests against disturbance by later females. Accordingly, early females invest less energy in egg production while reserving more for nest defence. Variation along this reproductive trade-off causes delayed or slower senescence in early females (average RLS of 26 days) than in late females (reproductive lifespan of 12 days). We use microsatellites to confirm that gene flow is sufficiently limited between early and late breeders to allow adaptive divergence in response to selection. Because reproductive trade-offs should be almost universal and selection acting on them should typically vary in time and space, the mechanism described herein may explain much of the natural variation in senescence.

Does temporal and spatial segregation explain the complex population structure of humpback whales on the coast of West Africa?

“…The timing of reproduction is highly heritable and is thus influenced by genetic as well as (seasonal) environmental factors (Hendry and Day 2005). Under these conditions, gene flow is expected to be limited between early and late reproducers even within populations having a unimodal temporal distribution of reproductive activity (Hendry et al 2004). a temporal, instead of spatial, restriction on gene flow would hence create a pattern of isolation by time (IBT; Hendry and Day 2005); this could be a plausible explanation for the population structure found in BSB stock if the animals arrived in the greater gulf of guinea at slightly different times due to the fact that they had migrated from different feeding areas.…”

Mortality rate acceleration and post-reproductive lifespan in matrilineal whale species

“…Hendry et al 2004;Reznick et al 2006). The benefits from a living post-reproductive female in stable social groups could directly impact the fitness of multi-generations through interactions such as cooperative foraging and food provisioning (e.g.…”

“…Hendry et al 2004;Reznick et al 2006). In species with maternally-dependent offspring, females can have a post-reproductive lifespan equivalent to the length of the time taken to raise the last born offspring to independence (Packer et al 1998).…”

Colour-assortative mating among populations ofTropheus moorii, a cichlid fish from Lake Tanganyika, East Africa

“…McLennan & Ryan 1999), differences in spawning time and/or locality (e.g. Hendry et al 2004;Østbye et al 2004;Fraser & Bernatchez 2005;Hendry & Day 2005;McLean et al 2005), or size (e.g. McLean et al 2005).…”