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Lecture 5

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Todd Ferretti

 social behaviour evolves when cooperating conspecifics achieve higher rates of survival and reproduction than if they had lived alone (ants, bees, wasps, lions)  many degrees of social system complexity exist among living species  social systems are dynamic; individuals repeatedly communicate with one another and adjust relationships b/c costs and benefits experienced by individuals change with age, sex, physiological condition, status  must understand how individuals that join together benefit from doing so  groups may confer many types of benefits (hunting success, expand food range) [hawk most successful when attacked solitary pigeons)  but costs a lotinterferes with food (pigeons’ seeds) and inhibit others’ attempts to produce or injure offspring; higher exposure to diseases and parasites  most widespread form of social system (SS) is association btwn 1/2 parents with immature, independent offspring; some have more adult individuals  simple mammalian SS, solitary females pairs care for young, older offspring may still be present when next generation is bornhelp rear newborns; females stay in group but men usually leave. Thus most helpers are females  altruistic acts: behaviours that reduce helper’s reproductive chances but increases fitness of helped individual; favoured by natural selection  animals offspring can contribute to its individual fitness. By helping relatives, individual can increase representation of own alleles in population. Inclusive fitness of individual involves individual fitness plus fitness gained by increasing reproductive success of nondescendant kin  altruistic acts may evolve into altruistic behaviour patterns if benefits (inclusive fitness) exceed costs (decreases in giver’s own reproductive success)  some species recognize relatives + adjust behaviour accordingly (white-fronted bee-eaters)  species whose social groups include sterile individuals are said to be eusocial (ex termites); most females are nonreproductive workers that forage or defend colony; workers may include soldiers with large defensive mechanisms; few females (queens) are fertile  both genetic and environmental factors may facilitate eusociality. Since workers are more genetically similar to sisters than to own offspring, they can potentially increase fitness by caring for sisters than by caring for own offspring  eusociality may be favours if it is difficult or dangerous to es
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