L05-zuk-06 - Biol. Lett. (2006) 2, 521524...

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Biol. Lett. (2006) 2 , 521–524 doi:10.1098/rsbl.2006.0539 Published online 19 September 2006 Silent night: adaptive disappearance of a sexual signal in a parasitized population of Feld crickets Marlene Zuk * , John T. Rotenberry and Robin M. Tinghitella Department of Biology, University of California, Riverside, CA 92521, USA * Author for correspondence ( marlene.zuk@ucr.edu ). Sexual signals are often critical for mate attrac- tion and reproduction, although their conspicu- ousness exposes them to parasites and predators. We document the near-disappearance of song, the sexual signal of crickets, and its replacement with a novel silent morph, in a population subject to strong natural selection by a deadly acoustically orienting parasitoid Fy. On the Hawaiian Island of Kauai, more than 90% of male ±eld crickets ( Teleogryllus oceanicus ) shifted in less than 20 generations from a normal-wing morphology to a mutated wing that renders males unable to call (Fatwing). ²latwing morphology protects male crickets from the parasitoid, which uses song to ±nd hosts, but poses obstacles for mate attraction, since females also use the males’ song to locate mates. ²ield experiments support the hypothesis that Fatwings overcome the dif±culty of attract- ing females without song by acting as ‘satellites’ to the few remaining callers, showing enhanced phonotaxis to the calling song that increases female encounter rate. Thus, variation in behaviour facilitated establishment of an other- wise maladaptive morphological mutation. Keywords: phonotactic parasitoid; rapid evolution; satellite 1. INTRODUCTION Sexual signals such as colourful plumage are critical for mate attraction and hence reproduction, even though their conspicuousness exposes them to parasites and predators ( Zuk & Kolluru 1998 ). Such signals often represent compromises between natural and sexual selection. Since 1991, we have been examining the responses to such conFicting selective pressure in populations of the ±eld cricket Teleogryllus oceanicus , an Australian and Paci±c Island species introduced to three Hawaiian Islands (Oahu, the Big Island of Hawaii and Kauai), where it is subject to an acoustically orienting parasitoid Fy, Ormia ochracea ( Zuk et al . 1993 ). The parasitoid is North American in origin and overlaps in range with T. oceanicus only in Hawaii ( Lehmann 2003 ). The Fy ±nds its host using the same signal (the calling song) that males produce to attract mates; Fy larvae burrow into the cricket and develop inside, killing the host upon emergence. Previous work demonstrated that parasitized popu- lations have altered song structure, response to disturbance and calling behaviour compared with unparasitized populations ( Zuk et al . 1993 , 1995 , 1998 , 2001 ; Rotenberry et al . 1996 ; Lewkiewicz & Zuk 2004 ). Here we document a much more extreme and rapid adaptive change, near-complete loss of calling, in the Kauai population, and examine its consequences for mate location and the evolution of mate choice in the context of interaction between behavioural plasticity and morphological adaptation.
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L05-zuk-06 - Biol. Lett. (2006) 2, 521524...

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