Ritual Jousting by HornedParisoschoenus expositusWeevils (Coleoptera, Curculionidae, Baridinae)

William G Eberhard,J Mauricio Garcia-C

doi:10.1155/2000/16361

Abstract

Males of the weevilParisoschoenus expositususe their prothoracic horns as weapons in stylized battles with other males over females that are drilling oviposition holes in palm leaves. The unusual sheath-like structures that penetrate deep into the male prothorax function to receive the horns of opponents during battles. Horn size is dimorphic with respect to body size, and small and large males also differ behaviorally. Small males that have mated with a drilling female are sometimes able to impede a large male's access to the female until after she has oviposited, but they are not able to take over females from larger males.

Highlights

Beetle horns are extremely diverse in size and shape (e.g., Arrow 1951; Eberhard 1979)
Morphology All but the very smallest males of Parisoschoenus expositus had a pair of rigid, pointed homs projecting anteriorly from the ventral portion of the anterior surface of the prothorax (Fig. 2)
Functional morphology Our observations strongly suggest that the horns of male Parisoschoenus expositus function as weapons to lock the male to his opponent and allow him to tilt him during horn-locking battles, and not in other contexts

Summary

Introduction

Beetle horns are extremely diverse in size and shape (e.g., Arrow 1951; Eberhard 1979). Despite occasional claims to the contrary (Moller 1992), observations of their use in natural contexts suggest that they function as weapons in battles between conspecifics (Mor6n 1976; Bechtle 1977; Eberhard 1977, 1979, 1981, 1987; Palmer 1978; Brown and Siegfried 1983; Otronen 1988; Connor 1988; Siva-Jothy 1989; Rasmussen 1994; Emlen 1994, 1997), rather than as visual display devices as do the horns and antlers of some ungulates (Geist 1966, 1978; Lincoln 1994). In many species the winning male physically removes the loser from the vicinity of the female (i.e., tosses him to the ground), or blocks his access to her (i.e., pushes .him from the tunnel leading to her and defends against reentry)

Methods

Results

Conclusion