Function of male genital titillators in mating and spermatophore transfer in the tettigoniid bushcricket Metrioptera roeselii NADJA C. WULFF and GERLIND U. C. LEHMANN* Department of Biology, Humboldt-University Berlin, Behavioral Physiology, Invalidenstrasse 43, 10115 Berlin, Germany Received 30 May 2015; revised 8 July 2015; accepted for publication 8 July 2015 Males of certain bushcrickets (Orthoptera: Ensifera: Tettigoniidae) possess sclerotized internal genital devices termed titillators. These titillators are paired chitinized structures for which the function remains to be completely determined. We studied the role of the titillators during copulation in the bushcricket Metrioptera roeselii (Hagenbach, 1822), in the context of four a priori hypotheses for their function during mating and insemination: (1) bushcricket titillators act as anchors to secure matings; (2) titillators facilitate sperm removal or sperm dumping in the polyandrous females; (3) titillators stimulate the females during copulation; and/or (4) titillators are organs that assure an accurate spermatophore transfer. To distinguish between those hypotheses, virgin females were mated with males of five groups: unmanipulated (Control), males with titillator tips removed (T-tips); males with both titillator arms cut in half (T½); and males with titillator arms completely ablated on one side (T-1); or on both sides (T-2). These manipulations were chosen to test the response towards an increasing removal of the titillator processes (T-tips, T½, T-2) and to include a strongly asymmetric manipulation for comparison (T-1 vs. T-2). Male titillators were observed to be rhythmically inserted into the female’s genital chamber during copulation. Females generally stayed motionless during titillation, with resistance behaviours observed at a low rate but increasing to 38% when females mated with T-1 males. In some cases, female resistance behaviour resulted in severe male damage, although pairs never separated. After remating of females, we traced no sperm attached to titillators of the second mate. This fact contradicts any sperm removal function. Titillator manipulation reduced the capacity of a male to attach the spermatophore. This spermatophore detachment was a result of titillator ablation without a significant relation to rhythmical titillator movements or correlation with female resistance behaviour. We therefore conclude that titillators in M. roeselii function as tools to stimulate the females and accurately place the spermatophore. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2016, 117, 206–216. ADDITIONAL KEYWORDS: copulation – copulatory courtship – genital function – genitalia – mat- ing – Metrioptera – nuptial gifts – Orthoptera – sexual selection – Tettigoniidae. INTRODUCTION In most animal taxa with internal insemination, structures involved in mating and sperm transfer, such as the genitalia, evolve faster than other body parts (Eberhard, 1985, 2010a; Shapiro & Porter, 1989; Rowe & Arnqvist, 2012). In many cases, geni- talia are thus the only attributes by which closely-re- lated species can be distinguished (Eberhard, 1985, 2010b; Hosken & Stockley, 2004). Animal genitalia are highly diverse and act at different stages of the mating process (Eberhard, 1985).To determine which selective forces may be implicated in the evolution and maintenance of genital traits, it is crucial to understand their function during mating and sperm transfer. Although ablation experiments have been discredited in terms of explaining the that way selec- tion acts on genital morphology, they are rated as being useful for identifying the impact of male geni- talia on mating and/or insemination success (Sim- mons, 2014) and it is argued that manipulation of genitalia is a way to test adaptive hypotheses (Eber- hard, 2011; Friesen et al., 2014). *Corresponding author. E-mail: gerlind.lehmann@t-online.de 206 © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2016, 117, 206–216 Biological Journal of the Linnean Society, 2016, 117, 206–216. With 4 figures. Downloaded from https://academic.oup.com/biolinnean/article-abstract/117/2/206/2440323 by guest on 15 June 2020