Sex Allocation

• Resource allocation has tradeoffs between parent and offspring - growth and survival vs reproduction, number and size of offspring, offspring sex ratio
• Species either have few big offspring that require a lot of resources, or lots of small offspring with barely any resources
• Sex allocation - the allocation of resources by parents to offspring of each sex
• If one female is founding the population, it makes sense to only produce one male and lots of females, but more grandchildren are granted if give birth to more males (rarer)
• Sex ratio fluctuates over time, as depends on how much it costs to produce sons vs daughters, the rarer sex will do better and be produced more
• Fisher: reproductive value of all females = that of all males for equal expenditure - if sex ratio not 1:1 then reproductive success higher for rare sex and are overproduced
• Fitness is frequency dependent, as in female biased population males will do better and vice versa
• Unequal costs, as when males cost less to produce ESS is not 1:1 as it requires equal investment in the 2 sexes, 2:1 is ESS sex ratio biased in favour of cheaper sex
• Fitness of sons and daughters varies with mother's fitness, as male reproductive sex more variable than a females - male competition
• Size is more important for males than for females in reproductive success
• The more dominant a mother red deer was, the more her sons had reproductive success, and when she was subordinate her sons barely succeeded
• Red deer sex ratio is around 55% male biased - dominant mothers will produce sons and subordinate males produce daughters
• Women who had children with billionaire fathers had more sons (65% vs 50%)
• Mother can adjust offspring sex according to need for help - when helpers rare more of helping sex produced, or fewer if too many helpers competing for resources
• In a high quality territory, daughters help and increase parental fitness and sibling survival so mostly females produced
• In a low quality territory, daughters will decrease parental fitness and 80% males are produced