Patterns of fluctuating asymmetry in beetle horns: an experimental examination of the honest signalling hypothesis |
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Authors: | John Hunt Leigh W Simmons |
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Institution: | (1) Department of Zoology, University of Western Australia, Nedlands, WA 6009, Australia Tel.: (09) 380 2221; Fax: (09) 380 1029; e-mail: lsimmons@cyllene.uwa.edu.au, AU |
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Abstract: | Recent theoretical arguments have claimed that negative relationships between the size and symmetry of secondary sexual traits
are indicative of honest signalling of male quality. The patterns of fluctuating asymmetry in beetle horns have been proposed
to support the honest signalling hypothesis. Here we examine three assumptions of the hypothesis, (1) that traits are costly
to produce; (2) the levels of fluctuating asymmetry are indicative of stress imposed during development; and (3) that males
with larger traits should have more symmetrical traits, using the horned beetle, Onthophagus taurus. Experimental manipulations of brood mass were used to manipulate horn size and asymmetry. The development of horns was found
to be environmentally determined and costly in terms of delayed development and increased risk of pre-adult mortality. Decreasing
resource availability increased relative horn asymmetry. However, horn height was positively related to absolute horn asymmetry.
While the results do support the hypothesis that sexual selection on secondary sexual traits should increase levels of fluctuating
asymmetry, they provide no support for the notion that the patterns of asymmetry honestly signal male quality. Horns are used
in disputes between males and may be indicative of male parental investment. Thus, we conclude that while horn size may be
an indication of male quality, the patterns of fluctuating asymmetry are not.
Received: 16 December 1996 / Accepted after revision: 5 May 1997 |
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Keywords: | Fluctuating asymmetry Beetle horns Onthophagus taurus Sexual selection Honest signalling |
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