The evolution of empty nuptial gifts in a dance fly, Empis snoddyi (Diptera: Empididae): bigger isn't always better |
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Authors: | Jennifer A Sadowski Allen J Moore Edmund D Brodie III |
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Institution: | (1) Center for Ecology, Evolution, and Behavior School of Biological Sciences, 101 T.H. Morgan Building University of Kentucky , KY 40506-0225, USA e-mail: jen@ceeb.uky.edu Tel.: +1-606-2577472, Fax: +1-606-2571717, US;(2) School of Biological,;(3) Department of Biology, Indiana University, Bloomington, IN 47405, USA, IN |
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Abstract: | Adaptive female choice is thought to have led to the evolution of nutritionally valuable nuptial gifts in many insect species.
However, in several dance fly species, males offer and females accept “empty gifts” with no nutritional value. In the species
studied here, Empis snoddyi Steyskal, males produce empty balloons comprised of hundreds of silk bubbles and form mating swarms that females approach
to investigate males. Males within the swarm engage in agonistic interactions. The empty balloon has been hypothesized to
be an indicator of male condition such that males with larger balloons are predicted to have higher mating success and be
more successful in male-male interactions than males with smaller balloons. We examined the role of male body size and balloon
size in the context of intersexual and intrasexual selection. We found that neither male body size nor balloon size affected
the outcome of pairwise male-male interactions. Using multiple-regression techniques, we found significant linear selection
for increasing male body size and decreasing balloon size associated with mating success, a surprising result given a positive
relationship between male body size and balloon size. A visualization of selection showed the highest peak of male mating
success for larger males with intermediate-size balloons. These results can be explained by a trade-off between long-range
attraction of females using large balloons and close-range attraction of females via improved flying efficiency associated
with smaller balloons. Both male body size and balloon size are important components in determining male mating success; however,
the empty balloon does not appear to play a typical role as a sexually selected ornament.
Received: 29 December 1997 / Accepted after revision: 7 October 1998 |
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Keywords: | Sexual selection Mating behavior Balloon flies Selection analyses Empis snoddyi Nuptial gifts |
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