Sex allocation in the polydomous leaf-cutting ant <Emphasis Type="Italic">Acromyrmex</Emphasis><Emphasis Type="Italic">balzani</Emphasis> |
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Authors: | Katsuya Ichinose Luis C Forti Denis R Pretto Gösta Nachman Jacobus J Boomsma |
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Institution: | (1) Japan International Research Center for Agricultural Sciences, Ohwashi 1-2, Tsukuba, Japan;(2) Department of Agriculture, UNESP, Botucatu, SP, Brazil;(3) Department of Population Biology, Institute of Biology, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark;(4) Present address: Okinawa Subtropical Station, Japan International Research Center for Agricultural Sciences, Maesato Kawarabaru 1091-1, Ishigaki, Okinawa 907-0002, Japan |
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Abstract: | Logistic regression analysis was used to analyse sex allocation in a population of the leaf-cutting ant Acromyrmex
balzani occurring in a pasture in southern Brazil. The field sample consisted of 151 fungus-garden chambers (18 queenright and 133
queenless), belonging to 50 nests with three vertically stacked chambers per nest on average. Taking nest chamber as the unit
of analysis, seven predictor variables were considered: sampling date, chamber depth, chamber volume, weight of fungus garden,
presence of a queen, number of large workers, and number of small to medium workers. The population-level numerical proportion
of females was 0.548 and the inferred proportional energetic investment in females 0.672. The former was not significantly
different from 0.5 (P=0.168), but the latter was (P=0.0003). The proportional investment in females per fungus garden increased with the number of large workers present (P=0.0002) and decreased with the dry weight of the fungus garden (P=0.012). This implies that resource acquisition through foraging is likely to be a major proximate determinant of sex allocation.
The negative correlation between female bias and fungus garden weight might be due to developing adult females requiring more
food than males, but this hypothesis could not be confirmed by direct statistical evidence. |
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Keywords: | Logistic regression Queen-worker conflict Sex ratio Symbiosis |
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