Ecological Entomology (2012), 37, 244–251 DOI: 10.1111/j.1365-2311.2012.01361.x Trade-off between flight capability and reproduction in male Velarifictorus asperses crickets YANG ZENG1 andDAO-HONG ZHU1,2 1Laboratory of Insect Behavior & Evolutionary Ecology, Central South University of Forestry and Technology, Changsha, China and 2Laboratory of Zoology, Hunan First Normal University, Changsha, China Abstract. 1. There are numerous data that support the trade-off between flight capability and reproduction in female wing polymorphic insects, but the relationship between wing form and fitness remains poorly investigated in males. 2. In the present study, the development of flight muscle and gonads, spermatophore size, and multiple copulation ability were investigated in both long-winged (LW) and short-winged (SW) males to verify this trade-off, using a wing dimorphic cricket species Velarifictorus aspersus (Walker). 3. The LW males had better-developed wing muscles than the SW males on the day of emergence, and both of them developed wing muscles after emergence, but the peak of weight in SW males was achieved 4 days later than that of the LW males. The accessory glands (AG) of the LW males developed significantly slower than that of the SW males. These results suggest that development and maintenance of flight muscles have a cost on the development of reproductive organs in male V. asperses. 4. The SW males produced significantly heavier spermatophores in a single copulation and mated more often than LW males. This indicates the SW males have a higher mating success than the LW males, thereby increasing their chance of siring offspring. Key words. Accessory gland, flight muscle, multiple mating, spermatophore, trade- off, Velarifictorus aspersus, Wing dimorphism. Introduction a trade-off exists between flight capability and reproduction in wing dimorphic insects (Roff & Fairbairn, 1991). A general Wing dimorphism occurs in many insect orders (Johnson, observation, derived from many previous studies, is the ear- 1969; Harrison, 1980; Dingle, 1985; Roff, 1986, 1990; Zera lier onset of oviposition and enhanced reproductive output of & Denno, 1997; Zera, 2004). In general, there are two dis- flightless females (Anderson, 1973; Tanaka, 1976; Walters & tinct morphs, either with long or short wings. The long-winged Dixon, 1983; Roff, 1984; Zera, 1984, 2009; Guerra, 2011), (LW) adults usually have well-developed flight muscles, and which supports this trade-off in female insects. are flight-capable. In contrast, the short-winged (SW) adults Understanding the ecological significance of dispersal poly- usually have poorly-developed flight muscles, and are flight- morphism requires that fitness differences be documented less (Zera & Denno, 1997). The advantage of flight is obvi- between the wing forms of both sexes (Langellotto et al., ous as it gives the organism the ability to move away from 2000). However, the relationship between wing form and com- unfavourable or move towards favourable habitats, and many ponents of fitness in males has been much less studied. Some insects also use flight for smaller-scale foraging and courtship published studies on male crickets have suggested the absence flights (Roff, 1990). However, there are large energetic costs of the trade-off, e.g. no paternity difference (Holtmeier & Zera, associated with the production and maintenance of flight mus- 1993; Roff & Fairbairn, 1993), similar gonad size (Roff & Fair- cles (Roff, 1986; Zera, 2009). A well-known hypothesis is that bairn, 1993; Zera & Denno, 1997), and no difference in calling song structure (Souroukis et al., 1992). However, others have Correspondence: Dao-Hong Zhu, Laboratory of Zoology, Hunan shown differences between wing morphs that are suggestive First Normal University, Changsha 410205, China. of the trade-off, e.g. differences in calling and courtship songs E-mail: [email protected] (Crnokrak & Roff, 1995, 1998a,b, 2000; Guerra & Pollack, © 2012 The Authors 244 Ecological Entomology © 2012 The Royal Entomological Society Trade-off in male cricket 245 2007), differences in gonad size (Tanaka, 1999; Crnokrak & Materials and methods Roff, 2002), difference in aggression (Guerra & Pollack, 2010), and differences in male nuptial gift size (Sakaluk, 1997). Vary- Insects and rearing method ing conditions under which the insects were raised to assess Adults of V. aspersus were collected from Taian City, fitness differences between wing forms may have contributed ◦ ◦ to the conflicting evidence of the trade-off (Denno, 1994; Shandong Province (35 38 N, 116 20 E) in August 2007, and × × Zera & Denno, 1997). In addition, any reproductive penal- maintained in plastic containers (30 cm 18 cm 20 cm) ties selectively imposed on macropterous males may be more to establish a laboratory strain. Eggs, nymphs, and adults were handled as described in previous studies (Zeng et al., difficult to detect (Ott, 1994; Zera & Denno, 1997) because ◦ 2010). The eggs collected were exposed to 8 C for 60 days reproduction costs are generally much lower in males than in ◦ females (Trivers, 1972). However, males often spend a great to terminate their diapause, and then incubated at 25 C deal of energy on different reproductive behaviours besides for hatching. Newly hatched nymphs were raised in groups (50 nymphs) in plastic containers (30 cm × 18 cm × 20 cm) gonad development. For example, calling requires a 10-fold ◦ increase in metabolic rate (Crnokrak & Roff, 1998a). Thus, under LD 16:8 h and 25 C. After emergence, the adults × × different results would also arise when different reproductive were moved to another container (10 cm 10 cm 10 cm) traits are examined. For instance, the testes size and paternity and kept separately under the same condition for the next of the LW and SW Gryllus firmus males are not significantly experiments. different (Roff & Fairbairn, 1993), but SW males do call longer and attract more females than the LW male (Crnokrak Development of flight muscles and reproductive organs in LW & Roff, 1998a). Generally, male reproduction includes three and SW adults steps: the first step is pre-copulatory behaviour, such as calling and courtship songs, (Hedrick, 1986; Simmons, 1988; Nelson Every 2 days for 14 days and then on the 17 and 20 day & Nolen, 1997), aggression towards the rival males (Langel- after emergence, LW and SW males (10 males for each) were ◦ lotto et al., 2000; Guerra & Pollack, 2010), and pre-copulatory frozen at −20 C for 12 h. The frozen insects were thawed at mounting (Zhu & Tanaka, 2002). The second step is copula- room temperature for 5 min. The dorso-longitudinal muscles tion, including prolonged copulation (Carroll, 1991; Michiels, (DLM) and testes of the males were dissected out under a 1992) and spermatophores transformation (Hayashi, 1998; binocular dissecting microscope (Leica Camera AG, Solms, Wedell & Ritchie, 2004). The last step is the post-copulatory Germany), and weighed using an electronic balance (Mettler- behaviour, such as post-copulatory guarding (Parker, 1970; Toledo Group, Zurich, Switzerland; 0.0001 g). Because the Tanaka & Zhu, 2003) and multiple copulation (Evans, 1987; accessory gland is important for crickets and other insects Hissmann, 1990; Fox, 1993). Therefore, all energy investments to form spermatophores (Kaulenas, 1992), the weights of in those three aspects should be considered when verifying reproductive accessory glands (AG) were also examined. To whether the trade-off really exists in male insects. Moreover, examine the effect of histolysis of flight muscles on the in some wing dimorphic insects, LW adults histolyse their expression of the trade-off, the LW males were classified flight muscles, and have increased investment into reproduc- by status of flight muscles and the weights of gonads were tion (Guerra & Pollack, 2007; Mitra et al., 2011). Thus, the compared between LW with fully developed flight muscles status of flight muscles may also influence the expression of (LWF), LW with histolysed flight muscles (LWH), and the trade-off. SW males. Velarifictorus aspersus (Walker) is a common cricket species found in fields, and is widely distributed throughout China (Yin & Liu, 1995), which means that flight may play a Comparative mating success in males between two wing forms very important role in dispersal of this species. This cricket species displays distinct wing dimorphism, and exposure to To examine the effects of wing morphs and age on the long-day, high-temperature, and high-density conditions induce spermatophore size of males, copulation experiments were macroptery (Zeng et al., 2010). Like the other wing dimorphic conducted on days 3, 5, 7, and 9 after male emergence. An insects, the flight capable female V. aspersus has a longer pre- individual male of either morph was placed with a virgin oviposition period and less fecundity than the SW female (Zeng 12- to 15-day-old adult SW female. The spermatophores were et al., 2012). Thus, this trade-off may underlie the differenti- removed and weighed immediately after they were transferred ation of life history strategy that is the LW individuals are to the females. capable of flight and SW ones benefit more in reproduction. To determine whether SW males have a higher capacity To verify the trade-off between flight capability and reproduc- for multiple copulation than LW males, an individual male of tioninmaleV. asperses, we investigated: (i) development of either morph was placed with a 12- to 15-day-old virgin adult testes and reproductive accessory glands that reflects