‘Beeing’ part of a group:Group and individual decision-making in honeybeesKatie WhartonMarch 2007Group decision-makingGroup decision-makingSocial insect colonies – superorganismsOverview Social insect colonies: investment in reproduction Does the queen influence male production?- a study with honeybees Do workers influence male production?- future work with honeybeesOrganisms invest in survival and reproduction…so do social insect colonies!Virgin queens MalesWorkersOrganisms invest in survival and reproduction…so do social insect colonies!Virgin queens MalesWorkersHow do colonies appropriately regulate investment in reproduction?Queen Produces eggsWorkersRear larvaeFertilize egg?Female Maleyes noStudying how colonies invest in reproduction Just observe the actions of the queen and the workers -- simple, right? Figure adapted from Queller & Strassmann 2002unrelated male0.750.250.25Haplodiploidy – patterns of relatednessMost ants, Polistine wasps, stingless bees, bumblebeesVespula germanica, squamosaVespula maculifronsPogonomyrmex(harvester ants)African army antsHoneybees Just observe the actions of the queen and the workers -- simple, right? If queen or workers can influence investment in males, why did that ability evolve? Cooperation over allocation to reproduction? Conflict over sex ratio?Studying how colonies invest in reproductionIs interest in queen-worker conflict growing?Overview Social insect colonies: investment in reproduction Does the queen influence male production?- a study with honeybees Do workers influence male production?- future work with honeybeesOrganisms invest in survival and reproduction…so do social insect colonies!Virgin queens MalesWorkersHow do colonies appropriately regulate investment in reproduction?What are we missing by concentrating on conflict?The queen’s ability to influence colony male production: queen-worker conflict or colony-level cooperation?QueenWorkersFire ants, Pheidole pallidulaCan queens influence colony male production?YESCooperation?Conflict?Honeybees ???Cooperation?Conflict?(x 17)Honeybee drone production15-20% droneFertilize egg?Worker Droneyes noHoneybee drone production15-20% droneEnvironmental factors that influence colony drone production: Season Colony size Food availability Amount of drone brood already presentdata from Free & Williams 1975Hypothesis:Queens can use oviposition history as an indicator of subsequent investment in dronesPredictions:Relative to queens who have recently invested in drones, queens who have been prevented from laying drone eggs for a short period of time should:1. Lay more drone eggs, or2. Lay a more drone-biased egg sex ratio Summers of 2004 and 2005 East Lansing, MI 24 colonies total-same size- same food availability(12 colonies)4 days 1 day(12 colonies)DWDWWDQueen decisions030060090012000 300 600 900 1200Eggs on w ork e r com bEggs on drone combWC queensDC queensDWF2,21= 4.139P = 0.031Queen decisions030060090012000 300 600 900 1200Eggs on w ork e r com bEggs on drone combWC queensDC queensDWF2,21= 6.950P = 0.015Queen decisions030060090012000 300 600 900 1200Eggs on w ork e r com bEggs on drone combWC queensDC queensDWF1,22= 0.995P = 0.329Hypothesis:Queens can use oviposition history as an indicator of subsequent investment in dronesPredictions:Relative to queens who have recently invested in drones, queens who have been prevented from laying drone eggs for a short period of time should:1. Lay more drone eggs, or2. Lay a more drone-biased egg sex ratio030060090012000 300 600 900 1200Eggs on worker combEggs on drone combWC queensDC queens030060090012000 300 600 900 1200Worker pupaeDrone pupaeWC coloniesDC coloniesPatterns of brood-rearing at the colony level are notdue to the workers alone. Instead, the patterns are due to the workers and the queen.Fire ants, Pheidole pallidulaCan queens influence colony male production?YESCooperation?Conflict?Honeybees YESCooperation?Conflict?What are we missing by concentrating on conflict?The queen’s ability to influence colony male production: queen-worker conflict or colony-level cooperation?QueenWorkersOverview Social insect colonies: investment in reproduction Does the queen influence male production?- a study with honeybees Do workers influence male production?- future work with honeybeesWhat are we missing by concentrating on conflict?The workers’ ability to influence colony male production: queen-worker conflict or colony-level cooperation?QueenWorkersFire ants, Wood ant, Argentine ant, Pheidole pallidulaYESCooperation?Conflict?Can workers influence colony male production?“Workers thus exert a control on the secondary sex ratio by eliminating a proportion of the male brood during the period of sexual production and eliminating all the males during the remainder of the cycle. These data are consistent with workers preferring a more female-biased sex ratio than queens.”Aron et. al. 1994Proportion of male eggsProportion of broodWorkers eliminating males: conflict or cooperation? Is selective elimination of males evidence for queen-worker conflict? My hypothesis: Not always. Sometimes it may reflect queen-worker cooperation over the colony’s allocation to reproduction.  Test: Do we find examples of selective elimination of males in species without queen-worker conflict? Fire ants, Wood ant, Argentine ant, Pheidole pallidulaYESCooperation?Conflict?Honeybees ???Cooperation?Conflict?Can workers influence colony male production?Does selective male elimination by the workers help to regulate colony brood production?Rationale:1. After the queen lays eggs, environmental conditions can change; opportunity for workers to modify queen’s decisions accordingly2. Relative cannibalization rates of drone and worker larvae are unknownEnvironmental factors that influence colony drone production: Season Colony size Food availability Amount of drone brood already presentdata from Free & Williams 1975General strategyDWDrone brood - Drone brood + Drone brood DWDWPredicted results: do workers regulate drone rearing?H0: noH1: yesOrganisms invest in survival and reproduction…so do social insect colonies!Virgin queens MalesWorkersHow do colonies appropriately regulate investment in reproduction?Most ants, Polistine wasps, stingless bees, bumblebeesVespula germanica, squamosaVespula maculifronsPogonomyrmex(harvester ants)African army