Conditional manipulation of sex ratios by ant workers: A test of kin selection theory

Science

Volumn 274, Issue 5289, 1996, Pages 993-995

  Sundström, Liselotte ^a,b,c,e   Chapuisat, Michel ^a,d   Keller, Laurent ^a,b  

^a UNIVERSITY OF LAUSANNE   (Switzerland)

^b UNIVERSITY OF BERN   (Switzerland)

^c AARHUS UNIVERSITY   (Denmark)

^d Musee de Zoologie Lausanne   (Switzerland)

^e UNIVERSITY OF HELSINKI   (Finland)

Author keywords

[No Author keywords available]

Indexed keywords

ANT; ARTICLE; FEMALE; MALE; MATING; NONHUMAN; PRIORITY JOURNAL; REPRODUCTION; SEX RATIO;

BIOLOGY; ECOLOGY; GENES; LIVING SYSTEMS STUDIES;

ANT WORKERS; INSECTS; KIN SELECTION THEORY;

BIOLOGICAL MATERIALS;

ANT; INCLUSIVE FITNESS; KIN SELECTION; SEX RATIO;

FORMICA EXSECTA; FORMICIDAE; HYMENOPTERA;

EID: 0029659187     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.274.5289.993     Document Type: Article

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36. To determine primary sex ratios, approximately 50 eggs (a small fraction of the total number of eggs) were collected at the onset of egg laying, between late April and mid-May, when sexual brood is produced [K. Gösswald, Die Waldameise Vol. 1 (AULA-Verlag, Wiesbaden, Germany; 1989)]. The number of chromosomes (2n = 52) [E. Hauschiteck-Jungen, and H. Jungen, Insect Soc. 23, 513 (1976)] was assessed (11) (blind with respect to colony identity and queen mating frequency) in at least 5 but usually 10 cells per egg. The large number of chromosomes sometimes precluded counts of all chromosomes, so eggs in which fewer than 26 chromosomes were consistently found were classified as males, whereas those with more than 40 chromosomes were classified as females. Only nests with at least 20 successfully sexed eggs were included in the analyses, so that two nests in 1994 and three in 1995 were discarded.
37. To determine primary sex ratios, approximately 50 eggs (a small fraction of the total number of eggs) were collected at the onset of egg laying, between late April and mid-May, when sexual brood is produced [K. Gösswald, Die Waldameise Vol. 1 (AULA-Verlag, Wiesbaden, Germany; 1989)]. The number of chromosomes (2n = 52) [E. Hauschiteck-Jungen, and H. Jungen, Insect Soc. 23, 513 (1976)] was assessed (11) (blind with respect to colony identity and queen mating frequency) in at least 5 but usually 10 cells per egg. The large number of chromosomes sometimes precluded counts of all chromosomes, so eggs in which fewer than 26 chromosomes were consistently found were classified as males, whereas those with more than 40 chromosomes were classified as females. Only nests with at least 20 successfully sexed eggs were included in the analyses, so that two nests in 1994 and three in 1995 were discarded.
38. We made efforts to collect eggs immediately after the onset of egg laying in April/May, when only sexual brood is laid. However, worker-destined eggs are laid from mid-May onward, causing a slight overlap in worker and sexual brood, so a few worker-destined eggs may have been included in the primary sex ratio sample. Hence, the primary sex ratios obtained here may slightly overestimate the proportion of females among the eggs, and consequently provide a conservative test of differences in primary and secondary sex ratios in the singly mated class. The sample sizes differ from those given in Table 1, because three colonies that were scored for primary sex ratios only produced worker brood in 1994.
39. We thank J. J. Boomsma, A. F. G. Bourke, W. D. Brown, E. A. Herre, M. Milinski, D. Nash, T. Reuter, F. L. W. Ratnieks, P. Sherman, and three anonymous referees for comments on the manuscript; C. Chang, R. Forsman, P. Gertsch, A.-M. Mehmeti, I. Schmidt, and H. Åberg for assistance: and Tvärminne Zoological Station in Finland for working facilities. The study was funded by the Academy of Finland; Svenska Kulturfonden; Société Vaudoise des Sciences Naturelles; Swiss National Science Foundation; and Fondation du 450e anniversaire, University of Lausanne.