Reuter, Isabel

Roces, Flavio

Romer, Daniela

English

Sydney eScholarship

University of Würzburg, GermanyDepartment of Behavioral Physiology and SociobiologyDaniela Römer*, Isabel Reuter & Flavio Roces *Daniela.Roemer@uni-wuerzburg.deWorker aggregation leads to collective chamber excavationin leaf-cutting antsAim of the studyOur aim was to evaluatewhether the excavationof either chambers ortunnels depends on localworker aggregation, i.e.the concentration of‚workforce‘ at one placewithin the nest.IntroductionThe underground nests of the leaf-cuttingants (genus Atta and Acromyrmex) consistof a complex system of round, sphericalchambers and oblong, narrow tunnels. Themechanisms leading to the excavation ofthese morphologically different structuresare yet to be discovered. It is known,however, that the building of nests is a self-organized process where workers onlyhave access to local information andexcavate accordingly.aCement castof nest: Atta laevigatab The different structures of an ant nest: chambers and tunnelswithoutreflectorwithreflectorSmall groupLarge groupReduced space Ample spaceExperimentalseriesMethodsEvaluation of worker aggregationInterval photo of digging arena every30 minutes during the experiment. A portion of workers were marked withreflective tape (50 % - 100 setup, 33.3 % -300 setup) to increase countability. Onlymarked ants were counted in each photo(and multiplied times 2 or 3 for evaluation).Four experimental series were performedEvaluated parameters:• Worker aggregation• Size of excavated chamber/chamber enlargement• Size of excavated tunnel• Time of tunnel emergenceResults: Worker aggregationentranceDigging arenacentral quadrantExcavation setup:2-D digging arena (50x50 cm, 1 cm high),filled with moist clayArena virtually divided by grid (10x10 cmquadrants, drawn on covering glas plate forassessment of worker aggregation48 h excavation time50 pieces of worker-attracting brood per setup(which were deposited in the central quadrant by the ants)areduced spacebample spaceWe manipulated worker aggregation in two ways:1. Using different group sizes300Large group2. Offering different space• Worker aggregation was higher in the large group,independent of available space.• At any given time only a portion of the workersaggregated inside the arena.• Worker aggregation in the central quadrant decreasedwith time and leveled out at comparable levels.Does worker aggregation depend on group size? Does worker aggregation depend on available space?duration of experiment [h]0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48ant aggregation in central quadrant0102030405060ant aggregation in central quadrant051015202530duration of experiment [h]12 24 36 486 18 30 42Results: Emergence of chambers and tunnels• Worker aggregation was not increased, when ants hadaccess to ample space, but the peak of worker aggrega-tion was reached earlier. • Worker aggregation increased slower in the reducedspace setup (because the ants had to create the space themselves).• Worker aggregation decreased rapidly in ample spaceChamber emergenceThe self-excavated chamber volume emerging in the reducedspace setup (a) was offered in the ample space setup (b)In reduced space chambers were excavated by both groups,but the large group excavated bigger chambers.Worker aggregation was higher in the large group.In ample space the small group enlarged the existing chamberby the same volume of their formerly self-excavated chamber,while the large group excavated less chamber volume andenhanced the offered chamber only marginally.Steeper and quicker decrease of worker aggregation inample space.Tunnel emergenceexcavated tunnel volume [cm³]050100150200250300350n.s.***Both groups excavatedtunnels (as well as chambers.),but large groups excavatedmore tunnels (as well aslarger chambers).More ‚workforce‘can engage in diggingactivityMore tunnels were excavatedwhen a chamber was allreadyavailable.Marginal chamber enlarge-ment and switch to tunnel exca-vationBy offering ample space,worker aggregation was reduced(equal number of workers present in alarger volume)time of first tunnel emergence [h]02468101214161820*** *****Timing of tunnel emergenceThe large group engaged earlier in tunnel excavationAggregation in- and decreased quickly here, while in thesmall group aggregation decreased not as rapidly.In ample space both groups engaged earlier in tunnelexcavation.Low worker aggregation in central quadrant early in thedigging process.Workers aggregated first in the centralquadrant of the digging arena (yellowsquare). Therefore aggregation in thisquadrant was evaluated. 6 12 18 24 30 36 42 486 12 18 24 30 36 42 48from Bollazziet al., Insect. Soc (2012)chambertunnelPhoto credits:Background photo ©Alex WildAnt photo ©James WatersConclusionsA high worker aggregation during nest excavationleads to chamber emergence.Low worker aggregation, i.e., dispersed workersduring excavation, leads to the excavation oftunnelsThere is a timed sequence during nest excavation. First chamber excavation (high aggregation), thenswitch to tunnel excavation (low aggregation).Acromyrmex lundiexcavated/enlarged chamber volume [cm³01020304050n.s.n.s. ****e]duration of experiment [h]0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48ant aggregation in central quadrant0102030405060ant aggregation in central quadrant01020304050duration of experiment [h]0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 486 12 18 24 30 36 42 486 12 18 24 30 36 42 48t100Small grouptunnelofferedchamber

Worker aggregation leads to collective chamber excavation in leaf-cutting ants

https://ses.library.usyd.edu.au/bitstream/2123/11238/4/Poster139.pdf

Worker aggregation leads to collective chamber excavation in leaf-cutting ants

Abstract

Similar works

Full text

Available Versions

Sydney eScholarship