TY - JOUR

T1 - The economy of worker reproduction in Acromyrmex leafcutter ants

AU - Dijkstra, Michiel B.

AU - Boomsma, Jacobus J.

N1 - Funding Information: We thank Sylvia Mathiasen, Sandra South, and Bill Hughes for help with monitoring the colonies, Sylvia Mathiasen for genotyping most of the males, Charlotte Andersen for help with the DNA extractions, and David Nash for advice on the statistics. We also thank Lisbeth Børgensen, Boris Baer, David Nash, and Jes Pedersen for comments on the manuscript. This study was funded by a Ph.D. fellowship from the University of Copenhagen to M.B.D. and by a research grant from the Danish National Research Council to J.J.B.

PY - 2007/9

Y1 - 2007/9

N2 - Workers of most eusocial Hymenoptera can produce sons but rarely do so in the presence of the queen, despite the potentially high fitness payoff of direct reproduction. It has often been suggested that colony-level productivity costs may outweigh the fitness advantages of worker reproduction, but this has never been shown. We estimated these costs in two ant species with large complex societies, the leafcutter ants Acromyrmex echinatior and Acromyrmex octospinosus, by splitting 16 laboratory colonies and comparing the dynamics of the fungus garden volume between orphaned and queenright nests (with and without laying workers, respectively). Apart from fungus volume as a longitudinal measure of colony productivity, we estimated sex allocation, the timing of the switch between raising queen offspring and worker sons, and differences in body mass between queen and worker sons. We showed that orphaned nests give priority to raising dispersing queen-derived sexuals (virgin queens, haploid and diploid queen sons) over raising worker sons. Worker sons could be heavier than, equally heavy as, or lighter than queen sons, depending on the condition of the colony. The reduction in colony productivity of orphaned nests compared to their queenright counterparts was negligible (≤1.2%), at least during the first 9 weeks after queen loss when these costs could be estimated. Such low costs could only outweigh the benefit of worker laying if the survival of worker sons is low, for example if workers show efficient worker policing, or discriminate against all male brood outside the brief reproductive season.

AB - Workers of most eusocial Hymenoptera can produce sons but rarely do so in the presence of the queen, despite the potentially high fitness payoff of direct reproduction. It has often been suggested that colony-level productivity costs may outweigh the fitness advantages of worker reproduction, but this has never been shown. We estimated these costs in two ant species with large complex societies, the leafcutter ants Acromyrmex echinatior and Acromyrmex octospinosus, by splitting 16 laboratory colonies and comparing the dynamics of the fungus garden volume between orphaned and queenright nests (with and without laying workers, respectively). Apart from fungus volume as a longitudinal measure of colony productivity, we estimated sex allocation, the timing of the switch between raising queen offspring and worker sons, and differences in body mass between queen and worker sons. We showed that orphaned nests give priority to raising dispersing queen-derived sexuals (virgin queens, haploid and diploid queen sons) over raising worker sons. Worker sons could be heavier than, equally heavy as, or lighter than queen sons, depending on the condition of the colony. The reduction in colony productivity of orphaned nests compared to their queenright counterparts was negligible (≤1.2%), at least during the first 9 weeks after queen loss when these costs could be estimated. Such low costs could only outweigh the benefit of worker laying if the survival of worker sons is low, for example if workers show efficient worker policing, or discriminate against all male brood outside the brief reproductive season.

KW - Acromyrmex echinatior

KW - Acromyrmex octospinosus

KW - cost of worker reproduction

KW - leafcutter ants

KW - orphaned colonies

KW - queen loss

KW - worker sons

UR - http://www.scopus.com/inward/record.url?scp=34548612415&partnerID=8YFLogxK

U2 - 10.1016/j.anbehav.2006.11.020

DO - 10.1016/j.anbehav.2006.11.020

M3 - Journal article

AN - SCOPUS:34548612415

VL - 74

SP - 519

EP - 529

JO - Animal Behaviour

JF - Animal Behaviour

SN - 0003-3472

IS - 3

ER -