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Intrasexual Competition Alone Favors a Sexually Dimorphic Ornament in the Rubyspot Damselfly Hetaerina americana

Gregory F. Grether
Evolution
Vol. 50, No. 5 (Oct., 1996), pp. 1949-1957
DOI: 10.2307/2410753
Stable URL: http://www.jstor.org/stable/2410753
Page Count: 9
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Intrasexual Competition Alone Favors a Sexually Dimorphic Ornament in the Rubyspot Damselfly Hetaerina americana
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Abstract

I studied the sex-limited red spots on the wings of male rubyspot damselflies (Hetaerina americana) in relation to territoriality and fitness in the wild. Both observational and experimental (wing spot manipulation) studies indicated that wing spots were selected through competition among males for mating territories, not through female choice or direct competition for females. Males with naturally or artificially large wing spots were more successful at holding territories and consequently mated at higher rates than males with relatively small wing spots. In contrast, sexual selection on male body size appeared to operate among nonterritorial males at the clasping stage of the mating sequence, perhaps because larger males were better at clasping females forcibly. Of four models proposed to explain the evolution of ornaments through territory competition, only the agonistic handicap model makes predictions consistent with the results of this study.

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