Brent Cornell

    
Breeding Strategies

Male coho salmon form two different breeding populations according to the strategy used for passing on genes:

• All males initially undergo a development phase as juveniles in which they grow within freshwater rivers (~12 months)
• Following that, the males migrate out to the ocean for a period of maturation, whereby they differentiate into two populations

Some of the male salmon develop into ‘jacks’, while other male salmon will develop into ‘hooknoses'

• Jacks are smaller and well camouflaged – they only require ~ 6 months in the seawater to reach maturity
• Hooknoses are larger and brightly coloured – they require ~ 18 months in the seawater to reach maturity

Jacks and hooknoses employ different breeding strategies in order to successfully reproduce with female coho salmon:

• Jacks sneak out from behind rocks or recesses in the riverbed and attempt to stealthily mate with a female
• Hooknoses swim within the open water and fight aggressively amongst one another for the opportunity to mate

Having two breeding pathways improves the rates of successful reproduction and also increases levels of genetic variation

• Jacks have higher rates of survival (as they spend less time in seawater), but have more competition for reproduction
• Hooknoses have lower rates of survival but consequently experience less direct competition for successful mating

Breeding Strategies in Coho Salmon Populations

 

    
Mate Selection

Courtship describes a set of behavioural patterns whereby potential mates inform each other of a readiness to reproduce

• Courtship stimuli may be species-specific and will be performed differently by different individuals
• Courtship stimuli are often competitive among males and form the basis of assessment by females

Courtship behaviour is especially pronounced in the different species of birds of paradise

• Whereas females appear drab, males will have bright plumage and display fancy behaviours to demonstrate their virility
• While these features make them a target for predators, they improve chances of attracting female attention (mate selection)
• Any exaggerated trait that improves reproductive fitness will become more prominent in future generations (sexual selection)

Courtship Behaviour in Birds of Paradise

    
Synchronised Oestrus

Female lions synchronise their sexual receptiveness (oestrus) to increase chances of survival and reproduction of offspring

• Lionesses remain in the same pride their entire lives, living with genetic relatives (sisters, aunts, nieces)
• Male lions leave their birth group at a young age and in order to reproduce must replace males in existing prides
• Upon establishing dominance within a pride, a male lion will kill all cubs already present
• The loss of cubs triggers an innate, synchronised response whereby all lionesses enter a period of oestrus
• This synchronised oestrus is mediated by pheromone signals

There are many advantages to synchronising oestrus:

• It increases the number of offspring the male lion can produce (risks of displacement are always present)
• It allows for shared lactation and nursing of cubs within the pride (all female lions nurse indiscriminately)
• It is easier for the lionesses to hunt and defend the pride if all cubs are of a comparable age

A Pride of Lions