BIO2242 Lecture Notes - Lecture 21: Chinook Salmon, Pacific Life, Ectotherm
Lecture 21 – Vertebrate Life Histories II
Rapid Life History Evolution in Captive Chinook Salmon
• Artificial selection
• Largest salmon species (adult size 18-61 kg)
• Arctic, northwest and northeast Pacific
• Life cycle (life span 4-8 years)
o Adults live in ocean but come to freshwater to breed
▪ 3-6 years at sea, return to river to spawn
o Mate and lay eggs
o Females guard eggs for up to 1 month, then die (semelparous)
o Eggs hatch 3-5 months later → all adults are dead
o Up to two years in freshwater before moving to estuary
• Commercial hatchery
o Adults reutnr to hatchery
o Harvest eggs from females, fertilise with sperm from males
o Fry hatch and grow at hatchery → released into natural rivers
• Egg size vs fecunditiy trade off
o Larger the egg size, the smaller the number (fewer) → higher survival
o Or lots of small eggs
o Don’t want eggs too large: intermediate sized eggs is favoured
(maternal fitness)
▪ Depends on environmental conditions
▪ Optimal egg size at hatchery: 0.15 g
• Optimal egg size: decreases at hatchery vs natural
populations
o Hatchery provides safe environment (increases
survival)
• Increased female fitness: many smaller eggs
• Hatchery eggs used to supplement natural populations
o Artificial selection
• Decreased egg size in natural population
Life History Evolution in Reptiles
• Influence of terrestrial ectothermy and low metabolic rate
o Low metabolic rate (low energy needs)
o Behavioural control of body temperature
o Can maintain higher body temperatures than endotherms
• Lift history traits differ from endothermic vertebrates
o Smaller offspring size
o Larger litter size
▪ Total litter mass is larger
o Lower growth rate
o Infrequent reproduction → some longer life spans
• Phenotypic plasticity and life history variation
o Females can manipulate incubation temperature
▪ Endotherms have stable body temperatures (limited flexibility)
▪ Fish (stable environment), amphibians (hydric constraints)
o Flexibility to match local conditions
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