The sex in short supply for matings varies over small spatial scales in a katydid (Kawanaphilanartee, Orthoptera: Tettigoniidae) |
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Authors: | Darryl T Gwynne Winston J Bailey Amanda Annells |
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Institution: | (1) Department of Zoology, Erindale Campus, University of Toronto, Mississauga, Ontario L5L 1C6, Canada Tel.: (905) 828-3892; Fax: (905) 828-3792; e-mail: dgwynne@credit.erin.utoronto.ca, CA;(2) Department of Zoology, University of Western Australia, Nedlands 6009, Western Australia, AU |
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Abstract: | In katydids such as Kawanaphilanartee, a female bias in the operational sex ratio (OSR) results in female competition for mates and male choice of mates. Previous
work showed that the excess of sexually active females occurs when food availability is low, in part because less food increases
the propensity of females to mate as they forage for the large edible spermatophores produced by males. In this study with
K.nartee, a pollen-feeding species, we estimate natural variation in numbers of sexually active males and females by assessing male
calling activity and the propensity of females to respond to experimental calling males. We found an excess of sexually active
males at a site with many flowers and an excess of sexually active females at a site with few flowers about 900 m away. Between-site
differences in gut masses of calling males were consistent with the hypothesis that pollen availability controls OSR. Finally,
at a third site where flowers were at first scarce, we found that the initial excess in sexually active females changed to
an excess of sexually active males after a clump of grass-trees flowered. The mean gut mass of all sampled males from this
site increased after flowering. The large variation in OSR that we document for K. nartee highlights the importance of identifying the appropriate spatial and temporal scales over which OSRs are measured in studies
of factors controlling sexual selection.
Received: 13 May 1997 / Accepted after revision: 27 October 1997 |
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Keywords: | Orthoptera Tettigoniidae Operational sex ratio Food availability |
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