Atypical Mating in a Scorpionfly Without a Notal Organ

Contributions to Zoology, 84 (4) 305-315 (2015)

Atypical mating in a scorpionfly without a notal organ

Wen Zhong1, Zi-Yi Qi1, Bao-Zhen Hua1, 2 1 State Key Laboratory of Crop Stress Biology for Arid Areas, Key Laboratory of Plant Protection Resources and Pest Management, Ministry of Education, Entomological Museum, Northwest A & F University, Yangling, Shaanxi 712100, China 2 E-mail: [email protected]

Key words: Mecoptera, Panorpidae, Furcatopanorpa longihypovalva, mating behaviour, nuptial feeding, salivary glands, genitalia, functional morphology, copulation

Abstract Results ...... 307 Mating behaviour ...... 307 Gross morphology of the salivary glands ...... 307 Firm coupling of genitalia is critical for copulation in most Male abdominal segments ...... 309 groups of insects. To counter female resistance that usually Male genitalia ...... 309 breaks off genital connection, male scorpionflies (Mecoptera: Female genitalia ...... 310 Panorpidae) usually provide nuptial gifts for the female and Coupling of the genitalia ...... 311 seize their mates with grasping devices. The notal organ, a Discussion ...... 311 modified clamp on tergum III of male scorpionflies, plays a sig- Acknowledgements ...... 313 nificant role in seizing the female wings and helping maintain References ...... 314 mating position during copulation. The mating behaviour re- mains unknown for the scorpionfly Furcatopanorpa longihypovalva (Hua and Cai, 2009) whose male lacks a notal organ. In this paper, we first attempt to study the mating behaviour of F. Introduction longihypovalva. The results show that the male provides liquid salivary secretion through a mouth-to-mouth mode for the female, and maintains copulation mainly by continuous provision The firm coupling of genitalia is critical for successful of salivary secretion rather than by seizing the female with copulation of internally inseminating insects (Matthews grasping devices. Thus the male copulates with the female in an and Matthews, 2010; Chapman, 2013). This process, atypical O-shaped position, with only their mouthparts and however, is frequently interrupted or terminated by genitalia connected to each other. The salivary glands exhibit the female during copulation due to sexual conflict remarkable sexual dimorphism: short and bifurcated in the female, but well-developed and multi-furcated in the male. The (Parker, 2006). To counter female resistance, males extremely developed salivary glands of the male lay a structural usually seize their mates with modified grasping de- foundation for the male to continuously provide liquid salivary vices, including claspers and other non-genital struc- secretion, and to help the male to mediate female resistance, tures (Eberhard, 2010). In some species of insects, in- being likely to serve as a compensation to his absence of the cluding scorpionflies (Mecoptera: Panorpidae), males notal organ. We also investigated the functional morphology and copulatory mechanism of the male and female genitalia. provide edible gifts for the female to help obtain copu- The evolution of the atypical mating pattern of F. longihypo- lation and mediate female resistance (Gwynne, 2008). valva is putatively discussed as an adaptation in the context of Scorpionflies are intriguing insects for their males sexual conflict. having a genital bulb that is enlarged and recurved antero-dorsally, superficially resembling the tail of a scorpion (Byers, 2002). The male of scorpionflies usu- Contents ally employs elaborate nuptial feeding behaviour to obtain copulation with the female. Males of some Introduction ...... 305 Panorpidae species bear well-developed salivary Material and methods ...... 306 glands (Grell, 1938; Ma et al., 2011), thus they can se- Adult collecting ...... 306 crete gelatinous salivary masses from their salivary Observation of the mating behaviour ...... 306 Light and scanning electron microscopy ...... 307 glands as nuptial gifts to lure a female into copulation Morphology of the salivary glands ...... 307 (Byers and Thornhill, 1983; Engqvist, 2007). If a male

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Fig. 1. Copulation of F. longihypovalva (close-up photograph).

fails to offer salivary secretions, he alternatively pro- ous species of Panorpidae (Issiki, 1933; Cheng, 1957). vides a dead arthropod as a nuptial gift (Sauer et al., This important organ, however, is absent in the males 1998; Engqvist and Sauer, 2003). In some cases, the of the scorpionfly Furcatopanorpa longihypovalva male can obtain copulation by seizing the female with (Hua and Cai, 2009; Ma and Hua, 2011a). Here a ques- his claspers and other grasping devices, rather than by tion arises: how does such a male scorpionfly without provisioning nuptial gifts, the so-called ‘forced mat- a notal organ mate with the female? In this study, we ing’ or ‘coercive copulation’ (Thornhill, 1981; Engqvist investigate the mating behaviour and copulatory and Sauer, 2003). mechanism of F. longihypovalva to unravel the mating In both the gift- and non-gift-providing copulations, pattern of the scorpionfly without a notal organ. the notal organ (a modified abdominal clamp on tergum III) of male scorpionflies is utilized to seize the female to maintain mating position (Thornhill, 1981; Material and methods Thornhill and Sauer, 1991). In many Panorpa species, males clamp the anterior margin of wings of the fe- Adult collecting male with the notal organ (Mickoleit, 1971), which is regarded as helpful to prolong copulation, especially Adults of F. longihypovalva were collected along the against female interests (Thornhill and Sauer, 1991). Jialing River source (34°13’N, 106°59’E, elev. 1500- Kock et al. (2009) contend this view because the notal 1800 m) in the Qinling Mountains, Shaanxi Province, organ of male Panorpa vulgaris Imhoff and Labram, China from the middle of May to the late June in 1836 does not prolong copulation after the last nuptial 2013. All adults were caught at least a few days after gift has been delivered. In Neopanorpa longiprocessa eclosion because their bodies and wings were deeply Hua and Chou, 1997, the extremely developed notal pigmented. organ is utilized to steadily seize the female’s wings of one side, enabling the male to obtain copulation exclu- Observation of the mating behaviour sively by seizing (Zhong and Hua, 2013b). The notal organ not only plays a significant role in The mating behaviour of F. longihypovalva was ob- copulation (Thornhill and Sauer, 1991; Zhong et al., served in the field, including the courtship, provision- 2015), but also exhibits a great diversity among vari- ing of nuptial gift, nuptial feeding, and copulation.

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Photographs of mating behaviour were taken with a process of mating can be divided into two phases: Nikon D200 digital camera (Nikon, Tokyo, Japan). courtship and copulation. During courtship, the male vibrates his wings and Light and scanning electron microscopy swings his abdomen up-and-down rhythmically. Meanwhile, he releases sex pheromones from a pouch- For light microscopy, live adults were fixed in Car- like gland in the genital bulb to attract potential mates noy’s solution for 12 h before being preserved in 75% nearby (see Kock et al., 2007). Once the male lured a ethanol. Specimens were dissected under a Nikon female, he terminates the olfactory releasing, and se- SMZ1500 stereoscopic zoom microscope (Nikon, To- cretes a drop of liquid salivary secretion, which ad- kyo, Japan). Male and female genitalia dissected were heres to his mouthparts. Then he moves to the lateral macerated in cold 5% sodium hydroxide solution for side of the female, seizing her abdominal segment IX several hours and rinsed in distilled water. Micro- with his gonostyli when she attempts to feed on the graphs were taken with a QImaging Retiga-2000R salivary secretion. Thus the male and female form an Fast 1394 Scientific CCD Camera (QImaging, Surrey, O-shaped mating position: the male and female only Canada) attached to a Nikon SMZ1500 microscope contact to each other with their mouthparts and genita- and were stacked with Syncroscopy Auto-Montage lia (Fig. 1). software (Syncroscopy, Cambridge, UK). During copulation, the male continuously transfers For scanning electron microscopy (SEM), ethanol- liquid salivary secretion to the female by a mouth-to- preserved specimens were dissected in 75% ethanol mouth mode. The female usually cooperates with the under a Nikon SMZ1500 microscope. The dissected male to maintain stable mating position when feeding genitalia and other genital components were dehydrat- on salivary secretion. After the male stopped provided in a graded ethanol series after ultrasonic cleaning ing salivary secretion, the female terminates copula- for 60 s. Then the samples were dried with liquid car- tion by lashing her abdomen to break off the genital bon dioxide in a critical-point dryer, sputter-coated coupling and then leaves the male. with gold, and examined in a Hitachi S-3400N scanning electron microscope (Hitachi, Tokyo, Japan). Gross morphology of the salivary glands Morphology of the salivary glands The salivary glands are tubular labial glands, opening A total of 33 individuals of F. longihypovalva (18♂♂, at the bottom of the salivarium between the labium 15♀♀) were dissected to study the morphology of the and hypopharynx. They are similar to those of Pan- salivary glands. The salivary glands were rapidly dis- orpa species (see Grell, 1938). The salivary glands ex- sected in Ringer’s solution, and then fixed in Carnoy’s hibit spectacular sexual dimorphism between the sex- solution for 12 h before being preserved in 75% etha- es: simply bifurcated and short in the female, but well- nol. In addition, to avoid low nutritional status that developed and multiple-furcated in the male (Fig. 2). may impede the development of salivary glands of The salivary glands are undeveloped and short in the males (Engqvist and Sauer, 2001; Engels and Sauer, females, extending only to the prothorax, and consist of 2008), we supplied the field-caught F. longihypovalva a salivary pump, a common salivary duct, and a pair of adults with sufficient dead arthropods before dissec- short secretory tubes. The salivary pump is swollen, and tion and morphological investigation. connects ventrally with the labium. The common salivary duct extends from the posterior end of the salivary pump, and runs along the rostrum, finally bifurcating to Results form a pair of secretory tubes (Fig. 2a). The salivary glands are extremely well-developed Mating behaviour in the males (Fig. 2b), usually extending to abdominal segment VI. The male salivary pump is very similar Seven pairs of F. longihypovalva were observed to to that of the female. The common salivary duct ex- mate in the daytime: six in the afternoon and one in tends posteriorly from the salivary pump along the the morning. All of these matings were accompanied rostrum of head and divides into two branches (sali- with nuptial feeding behaviour. The male exclusively vary ducts) above the suboesophageal ganglion. Each provided liquid salivary secretion for the female. The of the branches expands into a sac and is subdivided

Downloaded from Brill.com10/04/2021 12:08:36AM via free access 308 Zhong et al. − Atypical mating in a scorpionfly into three secretory tubes subsequently, resulting in ing 24 distal secretory tubules that are convoluted in six secretory tubes in the thorax. The subsequent abdominal segments V and VI (Fig. 2b). In the male parts of the salivary glands twine around the gut and salivary glands, no prominent reservoirs were ob- branch twice in a dichotomous way, eventually form- served.

Fig. 2. Sexual dimorphism on salivary glands of F. longihypovalva (drawings). a, simple and undeveloped female salivary glands; b, well-developed male salivary glands. CSD, common salivary duct; DSTu, distal secretory tubule; SP, salivary pump; ST, secretory tube; STu, secretory tubule. Scale bar = 2.0 mm.

Fig. 4. Male genital bulb of F. longihypovalva, ventral view Fig. 3. Abdominal segments of male F. longihypovalva (micro- (SEMs). BP, basal process; Gcx, gonocoxite; Gs, gonostylus; photographs). a, dorsal view, scale bar = 0.5 mm; b, lateral view, Hyp, hypovalve; Pm, paramere; VV, ventral valve of aedeagus; scale bar = 1.0 mm. *, pheromone gland. Scale bar = 300 μm.

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Male abdominal segments The epandrium and hypandrium are fused at base, cupping the median aedeagal complex and the lateral The abdominal segments of males are simple in struc- gonopods. The epandrium is broad at the base and nar- ture for terga II-V. It can be clearly seen that tergum III rower toward the apex. The hypandrium is composed is devoid of a notal organ both from dorsal and lateral of a very short stalk and a pair of elongated hypo- views (Fig. 3). Abdominal segments VI-VIII are great- valves, each of which bears 8-10 thick bristles along ly sclerotized into a ring. Tergum VI lacks any anal the inner margin (Fig. 4). horn, and segments VII and VIII are thick and short- The gonopod is composed of the basal gonocoxite ened, not constricted at the basal part (Fig. 3b). and the distal gonostylus. The paired gonocoxites are fused together at the base, forming a deep U-shaped Male genitalia cavity, in which the aedeagal complex is inserted cen- trally (Fig. 4). The distal gonostyli serve as claspers The male genitalia consist of the dorsal epandrium during copulation. Each gonostylus has a broad basal (tergum IX), the ventral hypandrium (sternum IX), the process, which bears numerous setae and is serrate in paired lateral gonopods, and the central aedeagal com- distal margin. The median tooth is also broad and ser- plex (Fig. 4). rate in apical margin.

Fig. 5. Aedeagus and parameres of F. longihypovalva (SEMs). a, ventral view; b, dorsal view; c, lateral view; d, caudal view. DB, dorsal branch of paramere; DL, dorsal lobe of dorsal branch; DV, dorsal valve of aedeagus; PG, pheromone gland; Pm, paramere; Pt, phallotreme VB, ventral branch of paramere; VL, ventral lob of dorsal branch; VV, ventral valve of aedeagus; *, ventral pouch of aedeagus. Scale bars = 200 μm.

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Fig. 6. Female genitalia of F. longihypovalva (SEMs). a, abdominal segments VIII-XI, lateral view; b-d, genital plate in ventral, dorsal, and lateral views. Ax, axis; Ce, cercus; CP, copulatory pore; DF, distal fork; GP, genital plate; Mu, muscles; PA, posterior arm; SP, subgenital plate; VIII and IX, tergum VIII and IX. Scale bars = 200 μm.

ventral valves produces caudally from the base of aedeagus, being mesally fused to form a deep cuculiform pouch (Figs 5a, c, d). The weakly-developed distal parts of ventral valves are mesally fused with each other and are concealed behind the dorsal branch of parameres in ventral view, surrounding the phallotreme with dorsal valves to form a concavity (Figs 5a, d). The dorsal valves are slender and narrower toward the apex, and separated from each other (Figs 5b, d). The paramere is Y-shaped in ventro-lateral view: a single basal stalk bifurcates into a slender ventral branch and a well-developed dorsal branch. The basal stalk is fused with the opposite one at the base (Figs 5a, b). The dorsal branch consists of a mesally curved ventral lobe and a broad dorsal lobe (Fig. 5c). The ventral Fig. 7. Schematic drawing of the male grasping the abdomen of branch is slender, twists in an S-shape at the distal half, female with claspers and other grasping devices in copulation. which is densely set with long setae and is concealed Ce, cercus; Ep, epandrium; Gcx, gonocoxite; Gs, gonostylus; behind the ventral lobe of dorsal branch in ventral view Hyp, hypovalve; SP, subgenital plate; VII, VIII, and IX, abdominal segment VII, VIII, and IX; *, everted swollen pheromone (Figs 5a, d). gland. Female genitalia

The aedeagal complex consists of an aedeagus and The female genitalia are located on the ventral side of associated parameres. The aedeagus is composed of abdominal segment IX, and consist of a subgenital plate paired bilobed ventral and dorsal valves, basally fused and a genital plate (Fig. 6a). The subgenital plate curves with a pair of parameres (Figs 5a-c). The basal part of dorsally on posterior and lateral sides to form a shallow

Downloaded from Brill.com10/04/2021 12:08:36AM via free access Contributions to Zoology, 84 (4) – 2015 311 genital chamber above, in which the genital plate is situ- grasping devices or both to obtain copulation with the ated. The genital plate consists of a main plate and a female (Engqvist and Sauer, 2003; Ma and Hua, 2011b). central axis. The broad main plate curves ventrally on For both tactics, the male seizes the female with his lateral sides and extends caudally to form a pair of thick notal organ to sustain mating position (Thornhill and posterior arms. The axis passes through the main plate Sauer, 1991). In our present research of mating behav- from dorsal to ventral side, and extends beyond the iour in F. longihypovalva, whose male is devoid of a main plate slightly less than half its length. The poste- notal organ, we found a novel, atypical mating pattern rior end of the axis protrudes beyond the main plate, in the Panorpidae for the first time. The male and fe- with regular sculpturing on the ventral surface and a male copulate in an O-shaped manner with their small copulatory pore (the orifice of the spermathecal mouthparts and genitalia connected to each other (Fig. duct) situated medially at the posterior apex. The main 1), remarkably different from the V-shaped mating po- plate covers the posterior end of the axis from dorsal sition in other scorpionflies studied (Ma and Hua, side, and bifurcates to form a pair of branches, the distal 2011b; Zhong and Hua, 2013b; Zhong et al., 2015). fork sensu Ma and Hua (2011a) (Figs 6b, c). In addition, Owing to the absence of the notal organs in male F. bundles of longitudinal muscles attach to the anterior longihypovalva (Ma and Hua, 2011a), it is reasonable part of the axis as well as the dorsal surface of the main for the male not to seize the female with that kind of plate (Figs 6c, d). These muscles can stretch the genital clamping device. Instead, the male mediates the fe- plate out of the genital chamber, and allow the female male resistance mainly by providing liquid salivary copulatory pore to connect to the phallotreme of the secretion as a nuptial gift through a mouth-to-mouth male aedeagus. feeding during copulation, resembling the trophallaxis of social termites and ants to a great extent (Matthews Coupling of the genitalia and Matthews, 2010). This nuptial feeding behaviour is greatly different from that of other Panorpidae spe- Stable coupling of the genitalia between the sexes en- cies whose male adheres solid or gelatinous salivary sures continuous sperm transfer, which is vital for a suc- secretions on a leaf surface for the female (Thornhill cessful copulation. The structures of male genitalia can and Alcock, 1983; Zhong et al., 2015). Based on mor- be divided into a central intromittent organ (the aedea- phological studies by this investigation and others gal complex in this context) and associated grasping (Hua and Cai, 2009; Ma and Hua, 2011a), we assume devices. In scorpionflies the aedeagal complex is em- that the formation of this atypical mating pattern is ployed to connect to the orifice of the female spermath- related to the well-developed salivary glands of the ecal duct on the distal end of the genital plate to form a male and the genitalia of the male and female. pathway for sperm transfer during copulation. The The greatly developed salivary glands of male F. grasping devices include the gonostyli, epandrium, and longihypovalva provide a structural basis for this par- hypovalves, and are used to grasp the particular part of ticular nuptial feeding behaviour, in which the male the female body to ensure genital coupling. During cop- continuously provides liquid salivary secretion to the ulation, the male seizes the basal abdominal segment female. It is different from many other species of Pan- IX of the female with his gonostyli, to open her genital orpidae, whose males provide solid or gelatinous sali- chamber and to compel her to stretch out her genital vary secretion. This solid or gelatinous salivary secre- plate. In addition, he uses his hypovalves to seize the tion may be attributed to the male salivary glands of abdominal segment IX or the cerci of the female, and these species that include a dilated middle salivary keeps his pouch-like pheromone gland to swollen. This reservoir to dehydrate liquid salivary secretion pro- gland pushes up the abdominal segments X and XI of duced by the posterior secretory region (Ma et al., 2011). the female, thus opening the female genital chamber We assume that the dehydrated solidified salivary se- and enabling the phallotreme of the male aedeagus to cretions can lead the female to spend more time to con- contact to the copulatory pore of the female (Fig. 7). sume the nuptial gifts, thus prolonging the copulation duration. In male F. longihypovalva, the middle salivary reservoir of the salivary glands is reduced or even Discussion absent. Furthermore, the secretory region is extremely elongated and each secretory tube bifurcates twice to In the panorpid species whose mating behaviours have form 24 distal secretory tubules totally. The combina- been studied to date, all the males use nuptial gifts and tion of developed secretory region and undeveloped

Downloaded from Brill.com10/04/2021 12:08:36AM via free access 312 Zhong et al. − Atypical mating in a scorpionfly middle dilated salivary reservoirs likely result in the other clasping devices can have little help in obtaining failure of the male to dehydrate salivary secretion and copulation, which needs cooperation between the to produce solidified salivary secretions. As a compen- male and female. Thus we assume that in male F. sation, the developed secretory region of salivary longihypovalva, continuous provisioning of salivary glands is likely to greatly improve the male’s ability to secretion as nuptial gifts is likely used to ‘buy’ the produce salivary secretion, enabling the male to con- female’s cooperation to obtain and sustain copula- tinuously provide liquid salivary secretion to sustain tion. The salivary glands, notal organ, and genitalia copulation. This is one of the possible explanations of male and female likely play essential roles in the why the male continuously provides liquid salivary se- formation of the mating behaviour of F. longihypo- cretion through a mouth-to-mouth feeding. valva. We summarized the morphological differenc- In scorpionflies nuptial-gift-providing mating is es of these structures between F. longihypovalva and much more effective to copulation than coercive mat- the ‘typical’ panorpids as exemplified by Panorpa ing (Sauer et al., 1998; Kullmann and Sauer, 2009). On dubia Chou in Table 1. the other hand, seizing the female with his notal organ Sexual conflict is caused by divergent reproductive, is likely not effective to mediate the female resistance evolutionary, and genetic interests between the sexes or prolong copulation duration, as in Panorpa vulgaris (Chapman et al., 2003; Parker, 2006), and may also (Kock et al., 2009). The modified complex female gen- contribute to the formation of this atypical mating be- italia of F. longihypovalva may reduce the ability of haviour in F. longihypovalva. In the mating of scorpi- the male to copulate against female interests. The dis- onflies, sexual conflict is mainly expressed as the tal fork of the female genital plate increases the diffi- fierce contest on control over nuptial gifts (Engqvist, culty of coercive copulation by obstructing the cou- 2011). Because providing salivary masses requires a pling of genitalia. Based on morphological investiga- huge nutrient investment for the male (Sauer et al., tion, we assume that a male has to accurately locate the 1998; Engels and Sauer, 2006), it is the male’s interest distal fork of the female genital plate into the ventral to avoid wasting his salivary secretion so as to maxi- pouch of his aedeagus, thus he could correctly connect mize the number of his mates and guarantee his mat- his phallotreme with the female copulatory pore to en- ing success rate (Zhong et al., 2015). On the other sure sperm transfer. The female, however, can still eas- hand, the female struggles to consume maximum sali- ily break off the coupling of genitalia to terminate the vary masses, probably impeding subsequent matings copulation through retreating her genital plate. In this of the male (Engqvist, 2009). The males of F. longihy- case, seizing the female only with his notal organ or povalva have successfully solved this problem by con-

F. longihypovalva ‘Typical’ panorpid Panorpa dubia Chou

Male notal organ lacking (Fig. 3a) moderately- or well-developed

Male salivary glands secretory tubes secretory tubes bifurcated twice; , bifurcated once or not; reservoirs undeveloped reservoirs developed, not expanded (Fig. 2b) usually expanded

Male aedeagus with a ventral pouch without a ventral pouch (Figs 5a, d)

Table 1. + + + + + + + +

+ + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + + + + + +

+ Morphological differ- + + + + + + + + + + + +

+ + + + + + + + + + + + +

+ + + + + + + + + + + +

+ + + + + + + + + + + + + + + + + + + + + +

+ Female genital plate with a distal fork + + + + + + + without a distal fork F. longihypo- ences between (Fig. 6b) valva and ‘typical’ panorpids.

Downloaded from Brill.com10/04/2021 12:08:36AM via free access Contributions to Zoology, 84 (4) – 2015 313 tinuously providing liquid salivary secretion to the fe- 2013b). This hypothesis may help understand the for- male through mouth-to-mouth feeding during copula- mation and diversity of mating patterns of Panorpidae tion. It enables the male to terminate provisioning species in morphological aspect. nuptial gift immediately if the female terminates cop- From a phylogenetic point of view, F. longihypo- ulation, thus avoiding wasting salivary secretion in valva may evolve early in Panorpidae based on mor- fruitless courtship and failed matings that are too short phological characters (Ma and Hua, 2011a; Ma et al., to transfer enough sperm. Furthermore, continuous 2012). The morphological phylogenetic analysis indi- provisioning of liquid salivary secretion invalidates cates that the genus Furcatopanorpa forms a sister snatching of nuptial gifts by the female or conspecific taxon to all the other genera in Panorpidae (Ma et al., males. 2012). This probably explains why the mating behav- Based on the developmental degrees of the male no- iour of F. longihypovalva differs markedly from that tal organ and salivary glands, the nuptial feeding be- of other panorpids in phylogenetic aspect. The recent haviour of scorpionflies can be broadly divided into molecular phylogenetic study, however, shows that F. four types: solid-salivary-mass-dominant mating, prey- longihypovalva forms a sister-group relationship with gift-only mating, coercive copulation, and liquid-sali- Panorpa liui based on mitochondrial and nuclear gene vary-only mating. In the first type of mating, males of sequences (Hu et al., 2015). From a behavioural point many Panorpa species mainly provide salivary secre- of view, this conclusion seems strange because the tions to obtain copulation, sporadically employing co- mating behaviours of F. longihypovalva and P. liui ercive copulation. These species bear a moderately differ remarkably from each other as mentioned above. developed notal organ (Zhong and Hua, 2013a: Fig. Further research is needed to solve this contradiction 1F), and have developed salivary glands (Ma et al. problem. 2011: Fig. 1), which are able to produce enough sali- A similar mating pattern is also present in the vary secretions as nuptial gifts (Grell, 1938; Engqvist, mecopteran family Choristidae (Tillyard, 1926; Riek, 2007; Kock et al., 2009; Zhong et al., 2015). In the 1970). According to R. Thornhill (personal communi- second type, males of some Panorpa species, as exem- cation), the males of Chorista australis Klug, 1836 in plified inP. liui Hua and Chou, 1997, P. nuptialis Ger- New South Wales, Australia, also lack a notal organ. staecker, 1863, and P. japonica Thunberg, 1784, have a The male and female C. australis form the O-shaped moderately developed notal organ and reduced or mating position and contact each other with mouth- weakly-developed salivary glands (Ma and Hua, parts during copulation. This behaviour is regarded as 2011b: Figs 1, 2). They can only provide dead arthro- a transfer of liquid salivary secretion from the male to pods as nuptial gifts to the female or employ a coercive the female through a mouth-to-mouth mode. In addi- copulation since they are unable to produce enough tion, Thornhill’s observation shows that male C. aus- salivary masses (Byers, 1963; Thornhill, 1992; Ma and tralis does not provide salivary masses or putting sali- Hua, 2011b). In the third type, males of Neopanorpa vary secretions on the substrate as nuptial gifts as in longiprocessa exclusively employ coercive copulation most other panorpids (R. Thornhill, personal commu- and provide no nuptial gifts. They bear a greatly devel- nication). Since Choristidae is the sister group of Pan- oped notal organ (Zhong and Hua, 2013b: Figs 1, 3) orpoidea (Panorpidae + Panorpodidae) (Willmann, and moderately developed salivary glands (Ma et al. 1987), the absence of a notal organ and the O-shaped 2011: Figs 2F, G), which are also unable to produce mating behaviour are very likely plesiomorphic char- enough salivary secretions (Zhong and Hua, 2013b). In acters in scorpionflies, suggesting that mating behav- F. longihypovalva, owing to the absence of a notal or- iour is closely related with morphology and may play a gan, the male exclusively relies on a unique liquid- significant role in evolutionary and phylogenetic anal- salivary-only nuptial feeding through a mouth-to- yses in Mecoptera. mouth transfer. Concomitantly, the male has extremely developed salivary glands to provide sufficient liquid salivary secretion to the female during copulation. Acknowledgements This atypical mating behaviour of F. longihypovalva provides additional new evidence to support our re- We are indebted to Guo Ding for assistance in insect collection cently proposed hypothesis that the developmental de- and observation. We are grateful to Randy Thornhill for kindly sharing unpublished information on the mating behaviour of gree of salivary glands is negatively correlated with Chorista australis. We appreciate Lu Jiang for providing infor- the notal organ in male scorpionflies (Zhong and Hua, mation on the morphology and biology of scorpionflies. We also

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