Eusociality: Cooperation to the extreme Groups form colonies with reproductive and worker castes. Eusociality has evolved most often in insects: Ants Eusocial species Honeybees Termites Wasps Phylogeny showing only eusociality Eusocial insects Hymenoptera - ants, bees, wasps Isoptera - termites Hemiptera - aphids Eusociality 1
Eusociality Eusocial crustaceans: snapping shrimp colonies are located within sponges Colonies are not uncommon in animals Soldier shrimp Range of sociality in bees Definition of eusociality 1. Sterile castes 2. Young raised cooperatively 3. Overlapping adult generations 2
Queen termite pic of bee queen Queen bee male Reproductives queen Worker caste in eusocial colonies Tending queen Tending larvae Honeybee worker activity and age Sharing food Foraging Defending Storage 3
Light feeding Differentiation in honeybees Fertilized Egg Heavy feeding + Royal jelly Unfertilized Differentiation in eusocial colonies How bees differentiate into queen vs workers? Differential feeding Epigenetics DNA methylation, 20+% of genes have differential expression in bees Worker Queen Drone Queen larvae in royal jelly Coordination of colony members can create remarkably complex structures Ant agriculture weaver ant nest honeybee hive inside a weaver ant nest 4
Queen termite Reproductives pic of bee queen Queen bee Complexity in cooperation Communication within colonies relies on chemical, tactile and visual signals Activities are coordinated without any centralized overseer Queen signals only control new queen production Queen pheromone controls queen rearing Coordination comes from workers and external cues leaf damage recruits carriers honeybee foragers dance to recruit more foragers high colony humidity, temperature increases worker fanning ants following pygidial gland extract time to unload nectar indicates colony nutritional status 5
Ant recruitment Honeybee dance communication Sound cues and dance provide information on distance and direction of food Honeybee communication Honeybee dance communication Controversy regarding true function of bee dances was resolved with use of robot bee Robot needed dance and sound to recruit foragers Colony decision making Voting for a new colony site Scouts communicate locations and site quality Eventually one dance wins out 6
Life in an ant colony Text uses black garden ant as example: How does eusociality start? Colony founding First generation of workers Eventual reproductive generation Death of queen How did species evolve to form such high sociality (eusociality)? rb C > 0 Pathways to eusociality 1. Subsocial route ( staying at home ) supported by intermediately social Polistes wasps, hover wasps Like helpers at the nest species 2. Parasocial route ( sharing a nest ) supported by allodapine bees, some paper wasps, Like communal breeding groups Subsocial route rb C > 0 more likely (with subsocial route) Can involve parental manipulation or mutualism Solitary Parental Offspring Sterile care may stay castes 7
Subsocial route Halictid (sweat) bees have a range of sociality In some spp, founding female lays an initial set of offspring that are manipulated to be workers Haplodiploidy hypothesis Hamilton: Haplodiploid species are predisposed for eusociality Indirect fitness can still be high when raising siblings and mom lays tons of eggs Female Male An underappreciated point diploid haploid Monogamy is crucial for eusociality to evolve When a parent refrains from mating with any additional mates, their offspring are free to stop mating at all Koos Boomsma Male offspring Mother-Son.5 Mother-Daughter.5 Sister-Sister.75 Sister-Brother.25 Female offspring Trivers and Hare (1976) make an important point High sibling r from Hd is not so necessary 8
Haplodiploid (Hd) inheritance and eusociality High sister relatedness from Hd can help eusociality arise but there is more to it Consider other haplodiploid species What about termites? Monogamy How haplodiploid inheritance can encourage helping > > B r (donor to own offspring) B 0.5 or 2 C r (donor to recipient) C 0.75 3 They have different siblings though, 0.75 and 0.25 The above assumes monogamy 9