Aging and social homeostasis in social insects

Main topics of this thesis are aging and social homeostasis in eusocial insects in light of the evolutionary biology. The keystone of studies presented here are questions how eusociality evolved and is maintained. Chapter 1 comprises a review of theories concerning evolution of eusociality, evolutionary theories of aging, as well as major issues regarding aging of eusocial insects and social homeostasis. Chapter 2 presents studies on sexual cooperation and longevity in honeybee (Apis mellifera). Contrary to solitary insects, in eusocial species insemination itself is expected to increase lifespan of a female. However testing this prediction on honeybee turned out to be impossible as (1) queens inseminated with non-viable sperm are recognized and killed by workers, and (2) they experience increased mortality when kept in semi-isolation (queen bank approach). Studies presented in chapter 3 exemplify mechanism protecting social insect colonies from the spread of pathogen. Moribund workers of the ant Temnothorax unifasciatus (Myrmicinae) show striking adaptation on the individual level: they cease all social contacts and leave nest to die in isolation. Chapter 4 presents how functional sterility of workers is achieved in colonies of different size and relatedness among individuals. In the ant T. unifasciatus the sterility is enforced by policing: reproducing workers are attacked by their nestmates, that induce workers to refrain from reproduction. I show that policing effectiveness (proportion of reproducing workers which are policed) is influenced by the group size and relatedness among colony members in manifold way. Chapter 5 discusses proximate and ultimate factors influencing evolution of labour division. I present data indicating that workers of the ant T. unifasciatus divide into low fecund foragers and high fecund intra-nidal workers. The reproductive aging of workers is not dependent on chronical age, but is an effect of phenotypic plasticity. The findings shed light on the evolution of eusociality suggesting that reproductive labour division could have evolved from differences in fecundity among related cooperative breeders