Genetic influence on caste in the ant Camponotus consobrinus |
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Authors: | V S Fraser B Kaufmann B P Oldroyd R H Crozier |
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Institution: | (1) Department of Genetics and Evolution, La Trobe University Bundoora, Victoria 3083, Australia e-mail: r.crozier@gen.latrobe.edu.au Tel.: +61-3-94792255, AU;(2) School of Biological Sciences, Sydney University, Sydney, NSW Australia, AU |
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Abstract: | Genetic influences on polyethism within social insect colonies are well known, suggesting that the determination of caste
(soldiers and minor workers) may also be genetically mediated. The Australian sugar ant Camponotus consobrinus is suitable for such a study, having soldiers and minor workers that follow a complex allometry. Further, although most C. consobrinus colonies are monogynous, 13 of 42 surveyed using microsatellites were found to be polygynous. Thus, although a minority of
colonies were polygynous, the great majority of queens live in polygynous colonies. From the 29 monogynous colonies studied,
we inferred that the queens are monandrous. Ants from four polygynous colonies were assigned to families on the basis of microsatellite
genotypes, after measurements had been taken of head width and scape length. These measurements reflect a complex allometry
interpretable as soldier and minor worker growth curves with a large changeover zone. Genetic influence on caste determination
was examined by testing for differences between families within colonies in the distribution of scape lengths, residuals from
the overall colony allometric curve, and proportions of soldiers and minor workers (as determined by head width falling above
or below the inflection point of the overall colony allometric curve). Families in all four colonies differed significantly
in caste proportions and in head-width distributions, and three of the four colonies showed significant differences between
families in residuals from the overall colony growth curve. Nested ANOVAs using head widths and scape-length residuals showed
that when the effect of family is removed, intercolony differences in allometry are negligible. This evidence indicates genetic
rather than environmental causes for the observed differences between families. We speculate that this variation may reflect
some selective advantage to within-colony heterogeneity between families or that selective differences are few between a wide
array of family growth patterns.
Received: 16 June 1999 / Received after revision: 13 September 1999 / Accepted: 25 September 1999 |
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Keywords: | Caste determination Camponotus ants Morphometrics Microsatellites Allometry Polygyny |
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