Interactions Between Multiple Forms of Nuptial Feeding in the Wood
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Ethology Interactions Between Multiple Forms of Nuptial Feeding in the Wood Cricket Nemobius sylvestris (Bosc): Dual Spermatophores and Male Forewings Pavol Prokop*, & Michael R. Maxwellà * Department of Biology, University of Trnava, Trnava, Slovakia Institute of Zoology, Slovak Academy of Sciences, Bratislava, Slovakia à Department of Mathematics and Natural Sciences, National University, La Jolla, CA, USA Correspondence Abstract Michael R. Maxwell, Department of Mathematics and Natural Sciences, National Nuptial feeding is widespread in insects, with many species showing one University, 11255 North Torrey Pines Road, form of feeding. In the wood cricket Nemobius sylvestris, the male may La Jolla, CA 92037, USA. provide multiple forms of feeding during an encounter: two kinds of E-mail: [email protected] edible spermatophores (microspermatophore and macrospermatophore) and forewing secretions. We examined the roles and interactions of the Received: August 16, 2007 spermatophores and forewing exposure in the mating sequence of this Initial acceptance: January 14, 2008 Final acceptance: July 4, 2008 species. The small microspermatophore was not found to contain sperm, (S. Forbes) whereas the larger macrospermatophore contained sperm. In mating tri- als, the microspermatophore may be transferred to the female early in doi: 10.1111/j.1439-0310.2008.01562.x the trial. Transfer of the microspermatophore was not a necessary prere- quisite to the subsequent transfer of one or more sperm-filled macro- spermatophores. Forewing exposure increased male mating success, as males with exposed forewings were more successful in transferring the macrospermatophore than males with experimentally covered fore- wings, both in terms of occurrence of successful transfer and the num- ber of macrospermatophores transferred. Male mating success was very low when the male’s forewings were covered and when the male did not transfer a microspermatophore. The sperm-filled macrospermato- phore may have nutritional value, as females eventually consumed all transferred macrospermatophores, and males consumed all rejected mac- rospermatophores. Somewhat unexpectedly, this study casts doubt on the role of the forewings in nuptial feeding. Although males with exposed forewings were more successful in macrospermatophore trans- fer, females actually palpated these males’ forewings less. We posit the alternative hypothesis that the forewing secretions play a role in chemi- cal communication to the female (e.g., signaling male quality), possibly instead of female nourishment. male, glandular secretions by the male, edible sper- Introduction matophores, and even the male’s body parts Nuptial feeding, a male’s provision of nourishment (reviewed in Gwynne 1997; Vahed 1998, 2007). to his mate, occurs in many arthropods (Thornhill & Research over the past few decades points to male Alcock 1983; Zeh & Smith 1985; Parker & Simmons mating benefits via nuptial feeding, as well as 1989; Simmons & Parker 1989; Boggs 1995; Vahed potential male paternal investment and reproductive 2007). This nourishment has been observed in vari- benefits and costs to the female (Gwynne 1997; ous forms including food items captured by the Vahed 1998, 2007). Ethology 114 (2008) 1173–1182 ª 2008 The Authors Journal compilation ª 2008 Blackwell Verlag, Berlin 1173 Nuptial Feeding in the Wood Cricket P. Prokop & M. R. Maxwell For many species, males provide a single form of opening. The female may eat the microspermato- nuptial feeding (Gwynne 1997; Vahed 1998). In phore, and then palpate liquid secretions on the dor- some insects, however, males offer multiple modes sal surface of the male’s right forewing (tegmen), of nuptial feeding. On the one hand, males may which overlaps and covers the left forewing when present different gift items to successive females. the male is not stridulating. This behavior is similar Male scorpionflies, for example, may offer either to female palpations of male metanotal secretions in dead arthropod prey or salivary secretions to a other gryllids (e.g., Ono et al. 1995; Brown 1997; female (reviewed in Sauer et al. 1998). Alterna- reviewed in Gwynne 1997). After palpations, the tively, a male may provide two or more forms of female may remount the male, who then passes a feeding during an encounter with a female. Exam- larger macrospermatophore to the female’s genital ples include the sagebrush cricket Cyphoderris strepi- opening. The macrospermatophore is approx. 1 mm tans, wherein the female may consume the in diameter, being 3· wider than the microspermato- spermatophylax (gelatinous component of the sper- phore (Gabbutt 1954; Campan & Demai 1983). The matophore) as well as portions of the male’s hind female typically eats the macrospermatophore after wings (Dodson et al. 1983; Eggert & Sakaluk 1994; it has been attached to her genital opening for a per- Gwynne 1997). Similarly, a female of the striped iod. The male may pass multiple macrospermato- ground cricket Allonemobius fasciatus may eat the phores to the female, and the female may perform spermatophore in addition to feeding on a glandular multiple bouts of palpations on the male’s forewing. spur on the male’s hind tibia (Mays 1971; Bidochka Interactions between the transfer of the dual sper- & Snedden 1985). matophores and the forewing secretions remain Multiple forms of nuptial feeding within a species unclear in this species, as well as their influences on raise intriguing questions. The male faces decisions male mating success. We address these questions regarding energy and nutrient allocation between experimentally. First, we examine the roles of the the different forms. For the female, multiple offer- microspermatophore and macrospermatophore. We ings broaden information relevant to mate choice, ask whether both contain sperm, as spermless micro- while simultaneously broadening the arena for sex- spermatophores have been found in the gryllids ual conflict regarding male investment and poten- Laupala spp. (Shaw & Khine 2004; deCarvalho & tial manipulation (Arnqvist & Rowe 2005; Vahed Shaw 2005). Through mating trials, we ask whether 2007). Nevertheless, the interaction between differ- successful transfer of the microspermatophore is ent modes of nuptial feeding has received relatively necessary for successful transfer of the macrosperma- little attention. In this study, we examine the roles tophore, as suggested by Gabbutt (1954) and Mays of the forewings and edible spermatophores in the (1971). Second, we examine the influence of expo- mating behavior of the wood cricket Nemobius syl- sure of the male’s forewings on mating success. We vestris.InN. sylvestris, females palpate secretions on experimentally cover the forewings of males, and the males’ forewings (Richards 1952, 1953; Gabbutt ask how this treatment affects mating success. 1954). This species is also notable for having two kinds of spermatophores: small ‘microspermato- Methods phores’ and larger ‘macrospermatophores.’ Such dual spermatophores have been recently studied in Rearing and Mating Trial Protocol other gryllids (e.g., Shaw & Khine 2004; deCa- rvalho & Shaw 2005). In early July 2006, subadult wood crickets were col- The mating sequence of N. sylvestris is complex, lected from leaf litter in mixed oak-pine woodland consisting of stridulation by the male, the passage of near Trnava, Slovakia (48°37¢ N and 17°58¢ E). two kinds of edible spermatophores to the female, Crickets were briefly anaesthetized with CO2, sexed, and the female’s palpations of the male’s forewing and group-reared in single-sex containers housed at secretions (Richards 1952, 1953; Gabbutt 1954; Mays room temperature (approx. 20°C) and exposed to 1971; Campan & Demai 1983; Dombrowski & Dam- natural photoperiod. Crickets were fed ad libitum bach 1994). After attraction via male stridulation, with crushed dog food, oat flakes, fresh fruit, and tactile exchange occurs between the sexes including dry Daphnia sp. Each rearing container contained antennation of the male by the female (Gabbutt pieces of paper to serve as concealment, and several 1954; Campan & Demai 1983). If the female is water reservoirs consisting of wet cotton placed in receptive, the male typically passes a small micro- Petri dishes. Crickets were checked daily for adult spermatophore, affixing it to the female’s genital molting. New adults were identified as belonging to Ethology 114 (2008) 1173–1182 ª 2008 The Authors 1174 Journal compilation ª 2008 Blackwell Verlag, Berlin P. Prokop & M. R. Maxwell Nuptial Feeding in the Wood Cricket subweekly cohorts by means of white paint marked water to create a diluted sperm solution (Laird et al. on the legs. Paint patterns changed every 4–5 d, so 2004). The entire glass slide was searched under a adult age is known to 4–5 d. New adults were main- compound microscope (400· total magnification) for tained in the single-sex containers. the presence of sperm cells. The presence of sperm Virgin adults were used in mating trials at 8–15 d cells was checked for macrospermatophores using post-molting. Mating trials were conducted between similar methods in 10 trials. To get macrospermato- 19 and 28 July 2006. To control for potential diur- phores, males were anaesthetized with CO2 at the nal effects on spermatophore production (e.g., appearance of the trial’s first (five trials), second deCarvalho & Shaw 2005), each mating trial started (three trials) or third (two trials) macrospermato- at 10:00 and finished at 16:00. Each mating trial phore on the surface of the male’s