ZOOSYSTEMATICA ROSSICA

ISSN 2410-0226 Zoological Institute, Russian Academy of Sciences, St Petersburg ▪ https://www.zin.ru/journals/zsr/ [ onl ine] 0320-9180 Vol. 28(1): 3–18 ▪ Published online 7 March 2019 ▪ DOI 10.31610/zsr/2019.28.1.3 [ print] RESEARCH ARTICLE

An instance of intergeneric copulation in the family Rhopalidae (Heteroptera): structure, functioning and congruence of the genitalia in two different species from the standpoint of the lock-and-key hypothesis Случай межродового спаривания в семействе Rhopalidae (Heteroptera): структура, функционирование и конгруэнтность гениталий двух разных видов с точки зрения гипотезы «ключ-замок»

D.A. Gapon Д.А. Гапон

Dmitry A. Gapon, Zoological Institute, Russian Academy of Sciences, 1 Universitetskaya Emb., St Petersburg 199034, Russia. E-mail: [email protected]

Abstract. An event of mating between specimens of Corizus hyoscyami and Rhopalus parumpunctatus, registered in the Novgorod Province of Russia is considered. The structure of the aedeagi in their completely inflated state and the female genitalia, as well as the functioning of the genitalia, are described and illustrated. The process of unfolding and swelling of the aedeagi is traced using the method of hydraulic inflation of the membranous parts with glass microcapillaries. The congruence of the genitalia is discussed for each species, and also for the interspecific crosses in both combinations of sexes and species. Structures of insect terminalia are divided into three groups according to their functions: 1) auxiliary structures; 2) structures providing the mutual fixation of the genitalia; and 3) structures directly performing the function of transferring seminal fluid. It is shown that in the considered variants of interspecific crosses, the parts of the genitalia belonging to the second group have almost the same structure and functioning, and most likely cannot perform the function of structural isolation. The structures of the third group have taxon-specific morphological and functioning traits and a high degree of congruence within each species. Schemes of the functioning of the genitalia in interspecific crosses, speculatively showing the impossibility of normal insemination, are proposed. Резюме. Рассмотрен случай спаривания между Corizus hyoscyami и Rhopalus parumpunctatus, зарегистрированный в Новгородской области России. Описано и проиллюстрировано строение эдеагусов в полностью раздутом состоянии и гениталий самок, а также их функционирование. Прослежен процесс расправления и раздувания эдеагусов при помощи метода гидравлического их раздувания с использованием стеклянных микрокапилляров. Рассмотрена конгруэнтность гениталий для каждого вида, а также в межвидовых скрещиваниях в обеих комбинациях полов и видов. Структуры терминалий разделены на три группы по их функциям: 1) вспомогательные структуры; 2) структуры, обеспечивающие взаимную фиксацию гениталий; и 3) структуры, выполняющие функцию передачи семенной жидкости. Показано, что структуры второй группы в рассматриваемых вариантах межвидового спаривания имеют почти одинаковое строение и, скорее всего не могут выполнять функцию структурной изоляции. Структуры третьей группы имеют специфическое для каждого таксона строение и особенности функционирования, обладая высокой степенью конгруэнтности внутри каждого вида. Предложены схемы функциони- рования гениталий в межвидовых спариваниях, умозрительно показывающие невозмож­ность нормального осеменения.

© 2018 Zoological Institute RAS and the Author(s) D.A. Gapon. An instance of intergeneric copulation in the family Rhopalidae

Key words: genitalia, aedeagus, gynatrium, functioning, congruence, structural reproductive isolation, lock-and-key hypothesis, insects, Heteroptera, Rhopalidae Ключевые слова: гениталии, эдеагус, гинатриум, функционирование, конгруэнтность, структурная репродуктивная изоляция, гипотеза «ключ-замок», насекомые, полужестко- крылые, Rhopalidae ZooBank Article LSID: urn:lsid:zoobank.org:pub:6C796633-E732-4F3C-8114-D123D5073588

Introduction 1829. According to the author of the photos, E.Yu. Kirtsideli, the mating was lasting during The lock-and-key hypothesis has been proposed about 20 minutes while photographing and by Dufour in 1844 in an extravagant statement, was continued thereafter, although no further ‘L’armure copulatrice est un organe ou mieux un observations were carried out and the material instrument ingénieusement compliqué, destiné was not collected. This event of intergeneric à s’adapter aux parties sexuelles externes de la copulation is curious per se and interesting femelle pour l’accomplissement de l’acte copulatif; from the standpoint of the lock-and-key rule. elle est la garantie de la conservation des types, Obviously, the reproductive isolation mechanism la sauvegarde de la légitimité de l’espèce’. Since of genitalia did not operate in this case, since the then, quite a lot of data has been accumulated for copulation began and lasted for rather a long time different groups of animals, both confirming and (unfortunately, it is not known how long it lasted disproving this hypothesis; review of these data as a whole and how long the normal copulation is given, for example, by Mayr, 1963; Shapiro & continues for each of these species). Therefore, it Porter, 1989; and Masly, 2012 (I deliberately seems to me interesting to consider the structure shy away from the consideration of particular of the genitalia in these species for understanding examples and theoretical considerations proposed why copulation between these rather strongly in the literature, since otherwise the volume of the diverged species from the group having a complex article would have increased by several times). It structured aedeagus turned out to be possible; seems more correct to designate this concept not and whether the mechanism of structural isolation as a hypothesis, but as the lock-and-key rule or which is supposed to prevent insemination was Dufour’s rule, which can be formulated as follows: implemented. complex structured genitalia of various animal Thus, the purpose of this work was to exa­ species are congruent in the sexes inside the mine the structure of male and female internal species and operate like a key and lock, preventing ectodermal genitalia in C. hyoscyami and hybridisation between individuals of different Rh. parumpunctatus, the functional morphology species. The challenge for researchers is to test of these structures and to evaluate a degree of the applicability of this rule to as many taxonomic their morphological and functional congruence in groups as possible, taking into account past the interspecific cross, both direct and reciprocal. methodological errors, when only the external and auxiliary, not participating in closest contact parts Material and methods of genitalia were involved in the analysis (for more on this, see below in the Preliminary reasoning The photographs of mating true bugs were section). One of model objects convenient for taken on 29 May 2013 in a meadow near particular testing of the lock-and-key rule is Terekhovo Village, Novgorod Province, Russia. considered in this article. The genitalia of dry specimens of C. hyoscyami and Some time ago I have received photos of Rh. parumpunctatus were examined basing on the copulating true bugs (Fig. 1; Figs 13–15 as material from collection of the Zoological Institute, electronic supplementary material) which were Russian Academy of Sciences. The structure and identified by me asCorizus hyoscyami (Linnaeus, functional morphology of the aedeagi was studied 1758) and Rhopalus parumpunctatus Schilling, by the method of hydraulic inflation using glass

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Fig. 1. Copulation of Corizus hyoscyami (male) and Rhopalus parumpunctatus (female), Novgorod Province. Photograph by E.Yu. Kirtsideli. microcapillaries (Gapon, 2001). Female terminalia 1 female. Russia: Ryazan’ Rrov., Miloslavskiy were anatomised by the standard method after Distr., Gremyachka Settlm., 13, 27.V.1908 (A. & Z. boiling for 2–3 minutes in 15–20% KOH solution; Semenov), 1 male, 1 female; Nizhniy Novgorod Prov., when necessary, gynatrial membranes were Arzamas Distr., Staraya Pustyn’, 12,16,22.VIII.1939 stained with methylene blue. In all cases, including (Kiritshenko), 2 males, 3 females; Samara Rrov., Kinel’ Distr., Kinel’, 23–24,26.VII.1927 (Lubischew), 1 consideration of the functional morphology, the male, 1 female; Volgograd Prov., Sarepta [Volgograd], aedeagi are described according to their position in 30.V.1926 (Obolenskiy), 1 male; Irkutsk Rrov., Tayshet an inverted pygophore, i.e. in copula. Thus, the right Distr., Yurty Settlm., 23.V1912 (Mishin & Verkhovsk. side of the aedeagus in the descriptions corresponds [iy]), 1 male. Kyrgyzstan, 1928, 1 male (collector to the left side of the gynatrium. Terminology for unknown). parts of the endosoma is based on the topographic principle and follows Konstantinov & Gapon Rhopalus parumpunctatus Schilling, 1829 (2005) and Gapon (2007); terminology for parts of (Figs 1, 7–9, 12; Figs 13–16 as electronic the internal ectodermal genitalia of females follows supplementary material) Štys (1961) and Gapon (2007). Material examined. Russia: Tver’ Prov.[?], Mele­ Structure of the genitalia dikha Settlm., 16.VII.1912 (S. Rodionoff), 1 female; Moscow Prov., Zaraysk Distr., Gremyachevo Settlm. Corizus hyoscyami (Linnaeus, 1758) (L. Bianki), 1 female; Ryazan’ Prov., Ryazan’ Distr., (Figs 1–6, 10, 11; Figs 13–16 as electronic Sten’kino Settlm., 14.VII.1913 (L. Bianki), 1 male; supplementary material) Nizhniy Novgorod Prov., Arzamas Distr., Staraya Pustyn’, 11.VIII.1939 (Kiritshenko), 1 male, 1 Material examined. Ukraine: Volyn Prov., Loka­ female; Voronezh Rrov.: Voronezh env., 9.VIII.1929 (I. chi Distr., Markovichi Settlm., 11.V1899, 4 males, Gudim), 1 male; Kalacheevskiy Distr., Kalach, 24–25.

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Figs 2, 3. Aedeagus of Rhopalus parumpunctatus. 2, at rest; 3, at very beginning of inflation. Wet preparations in dorsal view. a.p.v, apical part of vesica; ar.s, articular sclerite; d-l.l, dorso-lateral lobes of conjunctiva; ej.r, ejaculatory reservoir; l.l.v, left lobe of basal part of vesica; r.l.v, right lobe of basal part of vesica; s.gp, secondary gonopore. Scale bar: 0.14 mm.

VII.1937 (Lukjanovitsh), 1 male; Ternovska Distr., margin, connected with rather short dorsal Saval’skoe lesnichestvo [forestry], 3,25.V.1954 (Stark), connectives. Capitate processes rather small, oval, 1 male, 1 female; “Kubanskaya Prov., Maykopskiy with very short stalk. In medial part of phallobase, okrug, Mogilki”, 9.VII.1911 (Bogdanov-Katjkov), 1 anterio-dorsal margin of its basal plates with two female; Krasnoyarsk Terr., Kuragino Distr., Mazharka [Settlm.], 19.VI.1925 (Serebrennikov), 2 males; Irkutsk contiguous, rather large triangular protrusions Prov., Irkutsk, 9.VI.1912 (S. Rodionoff), 1 female. with rounded apices and medial to them with Aedeagus. Phallobase (Figs 2, 7) with relati­ two narrow sclerotised processes splitting at vely narrow basal plates and short arms forming apex and connected with anterior ends of hyaline small acute-angled protrusion at posterior-dorsal bands. Transversal bridge wide and short. Ventral

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Figs 4, 5. Aedeagus of Rhopalus parumpunctatus in intermediate stages of inflation.4, earlier stage of inflation; 5, somewhat later stage of inflation. Wet preparations in dorsal view.b.p.v ., basal part of vesica; h.bd, hyaline band. Scale bar: 0.14 mm.

(anterior) processes of phallobase not developed, strongly sclerotised and covered with sculpture and ventral connectives joining directly to margin of smallest transverse ridges; ventral wall with of basal plates. Pump of erection fluid rather small, two wide and somewhat more sclerotised areas membranous, rounded sac. percurrent almost from base of theca but not Theca (Figs 2, 6–9) uniformly cylindrical, reaching its apical margin, with rounded distal relatively short and wide, about 1.3 times as ends. Extreme base of theca membranous at its long as wide. Walls of theca as a whole weakly dorsal and lateral sides, forming rounded, large sclerotised; large part of dorsal wall in its basal but weakly convex lateral tubercles at sides, and half convex, rounded at distal margin, more capable of being swelled.

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right tubercle is directed dorso-laterally, while left tubercle is directed posteriad (Fig. 6). In C. hyoscyami, apex of each lobe at inner side with large rectangular membranous protrusion (Fig 9); lobes in Rh. parumpunctatus smooth at inner sides. Ejaculatory reservoir (Figs 2–9) in its posterior part weakly sclerotised and having shape of rather large, flattened dorso-ventrally cone with truncated apex directed posteriad. Anterior- ventral margin of this cone continued as wide, thickened and strongly sclerotised plate curved at ventral side. Anterior wall of reservoir is represented by two wide and convex sclerotised plates. These plates movably connecting with anterior lateral angles of reservoir and with lateral part of its deflexed ventral plate, and also connecting to each other and to dorsal and ventral posterior margins of reservoir through membrane. Outer parts of these plates continuing into long rod-shaped articular sclerites slightly curving ventrally and diverging by their apices. Wall of endosome inter- growing with posterior margins and apices of articular sclerites and also with both anterior dorsal and deflexed ventral margins of ejaculatory reservoir along their entire length; line of this intergrowth separating conjunctiva and Fig. 6. Completely inflated aedeagus ofRhopalus parumpunctatus. vesica. Posterior ends of two narrow Dry preparation in dorsal view. Scale bar: 0.14 mm. hyaline bands connecting to anterior ventral deflexed margin of reservoir at Conjunctiva (Figs 6, 9) rather short, having some distance from each other. Dorsal wall of convex dorsal wall and bearing a pair of large reservoir near posterior margin with rounded, membranous dorso-lateral lobes. Each lobe with weakly sclerotised area having in middle narrow, cone-shaped apex, membranous tubercle on highly sclerotised strip, which splitting and posterior wall and elongated sclerite on posterior- reinforcing place where ductus seminis attaching ventral wall; sclerite reaching apex of lobe and to ejaculatory reservoir. Ductus ejaculatorius protruding by its ventral margin beyond wall originating from posterior wall of reservoir. of lobe as sharp ridge; proximal end of sclerite Vesica (Figs 6, 9) consisting of two parts connecting with prominent small conical and strongly differing in their structure. Basal part sclerotised tubercle. Membranous tubercles on of vesica as more or less large membranous sac posterior walls of lobes asymmetrical: left tubercle curved to the left. Right wall of basal part of smoother. Both tubercles in Rh. parumpunctatus vesica distal to its base forming large navicular slightly longer than those in C. hyoscyami, and lobe with pointed apex, convex sclerotised outer

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Figs 7–9. Aedeagus of Corizus hyoscy­ ami, sequential stages of inflation.7 , most initial stage; 8, intermediate stage; 9, final stage of complete inflation. Wet (7, 8) and dry (9) preparations in ventral (7) and dorsal (8, 9) views. a.p.v, apical part of vesica; ar.s, articular sclerite; d-l.l, dorso-lateral lobes of conjunctiva; ej.r, ejaculatory reservoir; l.l.v, left lobe of basal part of vesica; r.l.v, right lobe of basal part of vesica; s.gp, secondary gonopore. Scale bar: 0.14 mm.

( Zoosystematica Rossica, Vol. 28, No. 1, pp. 3–18 9 D.A. Gapon. An instance of intergeneric copulation in the family Rhopalidae and concave membranous inner walls. Similar, but of which arcuate curved and fused with lamellar much smaller lobe lying at left wall of basal part of process of laterotergite IX (part of gonangulum), vesica near its base. At dorsal wall of basal part of and posterior end significantly short of reaching vesica near place where endosomal wall adhering apex of gonapophysis. to anterior margin of ejaculatory reservoir, apical Laterotergites IX rather large, transverse, close part of vesica originating. It looking like narrow, to rhomboid in shape; their inner angle short, wide long tube straight or curved to the left at base and and rounded; outer angle long, strongly elongated twisted spirally in remaining part. For most of and directed laterally and anteriad. Outer- its length, this tube possesses a membranous wall anterior margin of each laterotergite thickened closely adjoining the strongly sclerotised wall of at dorsal side; anterior angle continuing anteriad ductus ejaculatorius located inside; only the outer as sclerotised, dorso-ventrally flattened process portion of membranous wall capable of swelling. almost reaching under gonocoxites VIII to its Secondary gonopore lying at apical part of vesica concave anterior margin. Outer angle, thickening terminally. In Rh. parumpunctatus, spiral part of outer-anterior margin, and lamellar process forming one small and one significantly larger turn of each laterotergite IX together entering into oriented clockwise in rest and lying anticlockwise composition of gonangulum. Outer-posterior in completely inflated aedeagus (see the section margins of laterotergites IX fused with margins ‘Functional morphology of the genitalia’ below); of rather long tergite of corresponding segment. remaining distal section curving slightly outward, Laterotergites VIII rather small, transverse, with straight behind bend and curved slightly ventrally widely rounded internal angle, overlying outer before extreme apex; secondary gonopore small parts of laterotergites VIII and bearing spiracles; (Figs 2–6). In C. hyoscyami, spiral part with two their outer margins connecting to margins of small and one significantly larger turn, oriented tergite VIII without suture in anterior part. clockwise, at rest and when in completely inflated Reduced gonocoxite IX lying along anterior- condition of aedeagus; secondary gonopore large, inner margin of laterotergite IX and having due to spoon-like expanding walls of vesica (Figs the appearance of a rod-shaped sclerite slightly 7–9). widened in middle of length; reaching apex of Terminalia of females (Figs 10–12), as in all lamellar process of laterotergite IX and lying rhopalids, drawn into abdomen and covered by dorsally to it. Gonocoxite IX rigidly connecting ventrite VII. Gonocoxites VIII, being the largest with anterior margin of laterotergite IX and its genital plates, transverse, with slightly elongated lamellar process, but not completely fused with and rounded posterior-inner angle and more them. Gonapophyses II as longitudinal, rather elongated, pointed and curved dorsally anterior- wide membranous swellings located diagonally inner angle; inner margin between them convex. under gonapophyses I, their posterior ends Gonapophyses I slightly shorter than the latter; converging and contiguous, and anterior ends their inner parts, located between gonocoxites widely diverging. Posterior ends of gonapophyses VIII and visible from outside, longitudinally oval, II forming small convex sclerites visible from convex and sclerotised, attached by anterior end to outside at rest. Middle of each gonopophysis II anterior inner angle of gonocoxites VIII; located with thin sclerotised band, anterior end of which under gonocoxites VIII, their outer parts and arcuately curving and is fused with anterior end apices lamellar; apices directed posteriad, pointed of gonocoxite IX. Part of gonapophysis inside this and sclerotised. Inner margins of gonapophyses band, membranous, lamellar, with convex margin; I connected to each other by wide membrane part outside band with form of weakly sclerotised reinforced in middle by large sclerotised incomplete plate curved dorsally and posteriad at anterior ring opened at dorsal side; parts of membrane on end, where it forms a sclerotised area on ventral sides of incomplete ring long, forming a deep fold, wall of gynatrial sac; this area by its outer margin concave in the dorsal direction. Dorsal wall of each is fused with process of gonocoxite IX, and its gonopophysis I along its outer margin reinforced inner margin forming a rather short and wide with narrow thin sclerotised band, anterior end sclerotised band directed medially and posteriad.

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Proctiger as wide elliptical sclerotised tube plane almost perpendicular to longitudinal plane somewhat flattened dorso-ventrally, with dorsal of proximal half and ventrally to transverse plane wall longer than ventral one, and sclerotised valve of the latter (Fig. 11). In C. hyoscyami, apical part inside with lips-shaped flaps. All visible from of gynatrial cone with appearance of simple, short, outside parts of terminalia covered with dense, rather wide tube (Fig. 12). rather long setae. Slightly sclerotised spermathecal duct atta­ Gynatrial sac large (Figs 11, 12). Its posterior ched terminally to apical part of gynatrial cone, part posteriorly resembling a wide and rather long uniformly wide and very long, forming 5–6 turns semicircular fold with a convex dorsal wall and a of small radius basally and of larger radius distally, flat ventral one. Transverse ring sclerites lying on with part of turns oriented clockwise and part ventral wall of this fold with thin edging; relatively against. Distal turns of duct embracing base of small in Rh. parumpunctatus (Fig. 11) and relatively large, slightly sclerotised spermathecal capsule, larger in C. hyoscyami (Fig. 12). Anterior to this with ellipsoid shape. fold, between anterior ends of laterotergites IX, gynatrial sac widening and forming a pair of lateral Functional morphology of the genitalia pouches with convex dorsal walls; ventrally these pouches reinforced with bends of weakly sclerotised The functioning of the genitalia in their mutual lamellar parts of gonapophyses II, described above. contact can only be described speculatively, since Anterior part of gynatrial sac wide, its anterior it is almost impossible to observe their contact angles sharply elongated, set apart, rather short and directly in living insects. Thus, the processes wide in Rh. parumpunctatus (Fig. 11) and narrow, occurring inside the body of a living female are long and having connivent bases in C. hyoscyami reconstructed by comparing the structure and (Fig. 11). Gynatrial cone lying closer to base of functioning of the aedeagus with the structure of common oviduct, large and consisting of two parts. the internal genitalia of the female. Its basal part lying in inclined position, more or Rhopalus parumpunctatus. At rest, the con­ less close to transverse plane, subconical in shape, junctiva and vesica are drawn into the theca flattened dorso-ventrally, with broad base and (Fig. 2); only the apices of dorsal-lateral lobes directed to the right apex. Anterior wall of basal and a small portion of the big turn and apex of part of cone as triangular protrusion continuing the distal part of vesica protrude inside. After anteriad and reaching base of common oviduct. In penetration of the aedeagus into the gynatrium, Rh. parumpunctatus, dorsal wall of basal part of the conjunctiva begins to swell and pushes the gynatrial cone at some distance from its base with vesica outside. Then the dorso-lateral lobes of broad and deep semicircular fold (Fig. 11); basal conjunctiva emerge, swell slightly and unfold part of cone in C. hyoscyami without such a fold, about 140 degrees, so that their apices turn out but with triangular prominence at left side and to be directed laterally and anteriad (Fig. 3). At furthermore with shallow fold on anterior-right the same time, they enter the lateral pouches of wall. Internal surface of dorsal wall of basal part of the posterior part of gynatrial sac, hooking by cone bearing narrow, arcuately curved groove with their sclerotised tubercles and protruding ventral thickened margins forming shallow folds; one end margins of sclerites to the anterior margin of the of this groove reaching mouth of common oviduct, ventral wall of posterior part of the gynatrial sac and other end going into apical part of gynatrial and simultaneously their swelling membranous cone. In Rh. parumpunctatus, radius of curvature parts function as transversal struts. The apex of and relative length of this groove larger than in the apical part of the vesica enters the basal part C. hyoscyami. Apical part of gynatrial cone tubular of the gynatrial cone and sets against its anterior and extending from apex of basal part. In Rh. wall. The apex of the right (large) sclerotised parumpunctatus, proximal half of this part rather lobe of the basal part of the vesica is still directed narrow and continuing the curvature of groove on posteriad and is stuck into the fold of the dorsal dorsal wall of basal part of cone; distal half wider, wall of the basal part of gynatrial cone. Further also arcuately curved, but located in longitudinal swelling of the aedeagus leads to the release of

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Figs 10, 11. Female terminalia in Rhopalus parumpunctatus. 10, external terminalia, ventral view; 11, internal ectodermal genitalia, dorsal view. b.g.c, basal part of gynatrial cone; a.g.c, apical part of gynatrial cone; gon, go- nangulum; gp.I, gonapophysis I; f.d.w, fold on dorsal wall of basal part of gynatrial cone; gp.II, gonapophysis II; gx.VIII, gonocoxite VIII; gx.IX, gonocoxite IX; l.p.g, lateral pouches of gynatrial sac; lt.VIII, laterotergite VIII; lt.IX, laterotergite IX; prg, proctiger; sp.d, spermathecal duct. At fig. 10, the genital plates are shown somewhat driven apart and the inner margins of laterotergites IX are shown slightly turned ventrally; at fig. 11, the basal part of gynatrial cone is shown in more or less dorso-ventral plane. Scale bar: 0.14 mm.

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Fig. 12. Female internal ectodermal genitalia in Corizus hyoscyami. b.g.c, basal part of gynatrial cone; a.g.c, apical part of gynatrial cone; l.p.g, lateral pouches of gynatrial sac. The basal part of gynatrial cone is shown in more or less dor- so-ventral plane. Scale bar: 0.14 mm. the basal part of the conjunctiva from the theca approximately 140 degrees under the action of and complete swelling of the dorso-lateral lobes the right lobe, and the turns became oriented which become firmly fixed in the lateral pouches, anticlockwise. At the same time, the apex of distal and to swelling of the membranous parts of the part of vesica is pushed into the narrow apical vesica, which are already completely extruded part of the gynatrial cone due to the tension of from the conjunctiva (Fig. 4). Due to swelling the dorsal wall of the basal part of the latter under of the basal part of vesica, its right (large) lobe the action of the right lobe of the vesica. Herewith bends to the left, then moves to the left side and the bend at the apex of the apical part of vesica bends by its apex anteriorly and to the right, at first corresponds to the bend of the channel describing a semicircle (Fig. 5). At the same time, in base of the apical part of gynatrial cone, and the lobe entrains the dorsal wall of the basal part after the flip-over, this vesical bend corresponds of gynatrial cone (in the fold of which it is placed) to the bend in the distal part of the channel; i.e., and presses it to the wall of the left (small) lobe of the apex of vesica screws into the apical part of the basal part of vesica. The distal part of vesica, the gynatrial cone like a corkscrew. In the end, the which at the beginning of the erection of the apex of the apical part of the vesica is found to be aedeagus was located in the dorso-ventral plane directed to the right and entrains the apical part so that its turns were oriented clockwise, rotating of gynatrial cone, which is filled entirely by the

( Zoosystematica Rossica, Vol. 28, No. 1, pp. 3–18 13 D.A. Gapon. An instance of intergeneric copulation in the family Rhopalidae vesical apex. Probably, the presence of turns in the mating and post-mating mechanisms, and spermathecal duct is connected with this: these attributed structural or mechanical isolation to turns have the function of a spring, straightening the first group. In my opinion, a more rigorous when the apical part of the gynatrial cone moves. approach would be to consider a separate group of The function of the groove on the dorsal wall of copulation mechanisms, which includes structural the basal part of gynatrial cone remains unclear; and sensory isolation; the latter in the sense of either it serves to direct the extreme apex of vesica De Wilde (1964) and Eberhard (1985) is hardly into the channel of distal part of the cone, or it discussed in this work. performs the function of the duct through which Often, the presence or absence of the function the spermatozoa migrate from the spermatheca to of structural isolation in genitalia are judged by the common oviduct to fertilise the eggs there. the degree of their morphological differences The main stages of swelling of the aedeagus between species, and only parts of the genitalia, in Corizus hyoscyami are the same as those in visible from the outside and usually not coming Rh. parumpunctatus. The differences are that, into direct contact as congruent structures, are due to the less developed membranous portion of considered. Such structures in the true bugs the basal part of the vesica, its right lobe bends and many other insects are the endosome (or less strongly to the right. Apparently, this lobe endophallus) which is indrawn into the theca at does not hook onto the wall of the basal part of rest, and the gynatrial sac (or bursa copulatrix, also the gynatrial cone, since there is no fold in the sometimes called the vagina). In essence, these are corresponding part of the wall, in contrast to the “key” and “lock”. In general, the structures of Rh. parumpunctatus; the right wall of the basal the terminalia in insects, involved in copulation, part of the cone forms a triangular protrusion, in can be divided into three groups according to which, apparently, a relatively small membranous their functions: 1) auxiliary structures involved in portion of the vesica takes a place. The right lobe the initial contact, performing a sensory function of the vesica constantly tightly fits the wall of the and serving to prepare the genitalia for contact distal part of the vesica posteriorly, guides it and (parameres, phallobase and theca in heteropteran promotes its movement around the circumference. males; genital plates, gonapophyses, triangulum The apex of the left lobe, on the contrary, goes and other parts of the vestibulum in females); 2) into the fold of the anterior right wall of the basal structures that serve to the mutual fixation of part of gynatrial cone, pulls it up and presses it to the genitalia during copulation (membranous the anterior wall of the distal part of vesica in the and sclerotised lobes of the conjunctiva and place where the right lobe is adjacent to it. Thus, vesica, spicules, denticles, spine fields, etc. in the distal part of vesica does not turn over, but males; pouches and folds of the gynatrial sac in describes an almost complete circle in almost the females); and 3) structures directly providing the same plane but only somewhat inclined to the left transmission of seminal fluid or spermatophores side. At the beginning of the aedeagus erection, from male to female (the apex of vesica in males; the extreme apex of the vesica is directed to the the gynatrial cone in females). The auxiliary left and enters the wide opening of the apical part structures of one sex do not necessarily have to of gynatrial cone; at the point of complete inflation be congruent in their morphology to those of the of the aedeagus, the apex of the vesica is directed opposite sex within the same species. However, the posteriad, and the apical part of gynatrial cone is structures that serve to anchor of the genitalia and bent correspondingly. transfer seminal fluid must have a high degree of congruence so that these functions are performed Congruence and possibility successfully. Of course, these structures can also of structural isolation have a sensory function and implement the so- called sensory reproductive isolation. Preliminary reasoning. Mayr (1963), in his It is not enough to simply state the differences classification of the mechanisms of reproductive in the morphology of these structures in order to isolation, divided them into two groups: pre- judge whether they have the function of structural

14 ( Zoosystematica Rossica, Vol. 28, No. 1, pp. 3–18 D.A. Gapon. An instance of intergeneric copulation in the family Rhopalidae isolation, since, using the terminology of the due to the elastic hyaline bands which are strongly lock-and-key metaphor, sometimes one key can strained in the erect aedeagus. Many insects are open several different locks and one lock can be adapted to interrupt copulation very quickly in opened with several different keys. It is necessary cases of danger. The exceptions are groups with to compare the structure of those organs from strongly sclerotised structures in the genitalia of the second and third groups listed above, which both sexes, which take time to disengage. may come into direct contact during interspecific Therefore, it is often possible to judge the mating. In addition, not only morphological, but presence of the structural isolation between also functional congruence should be considered, different species only indirectly by comparing the since similar structures of the genitalia can structure of gynatrium and the completely inflated function differently, and different structures can aedeagus, finding the correspondence of these produce the same functional effect. Obviously, structures within the same species and comparing the function of structural isolation is carried out them for different species. An examination of only when at least one of the following conditions completely inflated aedeagi is made possible by is fulfilled: 1) the genitalia of opposite sexes are the method of their hydraulic inflation proposed so different that copulation cannot begin: the by the author (Gapon, 2001); this method makes it aedeagus (or penis) cannot be inserted into the possible to change the pressure of water entering female genital opening (as, for example, in insects through a glass microcapillary into an aedeagus, having a paired penis: even a small change in creating the negative pressure and thus tracing the angle between the copulatory appendages of the successive stages of unfolding and swelling males or the distance between the genital opening of an endosome, movement of its lobes, spicules, of females makes penetration impossible); 2) the vesica and other structures. aedeagus is inserted into the female genital tract, Testing the possibility of structural repro­ but cannot be fixed there because the soft and ductive isolation in the species examined. In swelling part of the aedeagus cannot completely a case of the intergeneric mating, the subject of unfold or because its parts do not correspond to this article, the biotopical and seasonal premating parts of the gynatrium; 3) the aedeagus swells and modes of reproductive isolation (according to the becomes fixed in the gynatrium, but its structures classification of Mayr (1963)) are not realised, damage the gynatrium and this leads to the since both species are sympatric and rather similar impossibility of a normal egg-laying or to the death in their ecological characteristics. According to of the female; 4) the aedeagus during the process of Puchkov (1986), adult individuals of Corizus unfolding and swelling inside the female genitalia hyoscyami hibernate among various plant residues is damaged, and this makes its further functioning along edges of fields, roadsides, on fallow lands, at impossible; 5) the aedeagus is normally swelled forest edges, in forest belts, parks, on ravine slopes and fixed in the gynatrium, but the structures that and river terraces; in the conditions of the forest- perform the function of direct transfer of seminal steppe of Ukraine, they migrate from wintering fluid do not come into proper contact, and as a result places to new biotopes in early May, where they this function is not performed; and 6) copulation feed on species of Matricaria, Arctium, Sonchus, cannot be completed because the aedeagus is Linaria, Silene, Taraxacum, Euphorbia and many stuck in the female genitalia, and the male cannot others. And from mid-May, bugs accumulate on withdraw it. In most cases, it is almost impossible Hyoscyamus niger, Ononis spinosa and Erodium to directly observe the contact of congruent parts spp. Rhopalus parumpunctatus also inhabits of the genitalia that takes place inside the body of various mesophilous and moderately xerophilous female, and any intervention leads to disruption or biotopes: glades and forest edges, thickets of termination of this process. This is determined by ruderal-grass vegetation near roadsides, along the fact that the aedeagus is in a state of erection ditches, forest belts, on slopes of ravines and river under the pressure of an erection fluid, and this terraces and other similar places. The trophic links pressure can be changed rapidly; in addition, the of this species are extremely extensive and include rapid retraction of the endosome into the theca is plants of the families Caryophyllaceae, Lamiaceae,

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Brassicaceae, Asteraceae, and others. Females of aedeagus of C. hyoscyami in the corresponding both species in the forest-steppe zone lay eggs in cross cannot be excluded. However, it is very the second half of May. It is worth noting that in difficult to assess the possibilities of stretching the Great Britain, according to Max Barclay (pers. walls of the gynatrium in living insects. Several comm.), the two species occur in different habitats photographs show that the female abuts with its and in general association with different plant hind legs against the abdomen of the male (Figs genera, and C. hyoscyami has recently hugely 13–16 as electronic supplementary material), expanded its distributional range, going from apparently trying to interrupt the copulation, rare and local to quite common and widespread which may indicate its discomfort, possibly caused in only the last 10–15 years. However, according by injuries to the gynatrium. This does not support to my observations, both species are common and the hypothesis of sensory isolation: the male found in the same biotopes in different regions of does not interrupt copulation with the female of the European part of Russia. Since they are not another species, and the female cannot interrupt separated in space and time on a significant part the process. In any case, traumatically or not, the of the common range, they must have some other function of anchoring the aedeagus was carried isolating mechanisms. out. And, judging by the very similar structure of Obviously, in the instance considered the the dorso-lateral lobes of the conjunctiva and the premating ethological isolation mechanism also lateral pouches of the gynatrial sacs in the both did not operate and in one way or another neither species, this function is performed identically in did the mechanism of structural isolation. Since them, but the same cannot be said of the function mating began and lasted for a rather long time, the of the structures that realise the transfer of genitalia of the male and female would appear to seminal fluid. The complicated implementation be rather congruent for this. It is also obvious that of this function is characteristic for both species, this mating could not lead to intergeneric hybrids, and in Rh. parumpunctatus it is more complicated since no hybrids of the taxa under consideration than in C. hyoscyami. have been found in nature. So, in this case either In mating of the male of C. hyoscyami and one of the post-mating isolation mechanisms female of Rh. parumpunctatus, the incongruence was activated or, nevertheless, the mechanism of of the apical part of the vesica and the apical part structural isolation partially worked: the aedeagus of the gynatrial cone may have the following was able to penetrate and fix itself in the gynatrium, consequences. Because of the wide secondary but the genitalia may not have been sufficiently gonopore, the vesica is not able to penetrate congruent for insemination. Consideration of through the narrow opening of the apical part the post-mating isolation mechanisms is beyond of the gynatrial cone. In addition, it is obvious the scope of this work and there are no data to that in order to overcome the bend of the apical judge the possibilities of such isolation, except part of gynatrial cone, the vesica must have a for information on the chromosome complement, corresponding bend before its apex and carry out which includes the same number of autosomes, the flip-over taking place inRh. parumpunctatus. microchromosomes and sex chromosomes in both As a result, the inability of the vesica to normally species: 5A + m + X0 (Ueshima, 1970). penetrate into the channel of the distal part of The photographs show that the copulating pair gynatrial cone should lead to perforation of the consists of the male of Corizus hyoscyami and the channel wall or injury to the vesical apex (taking female of Rhopalus parumpunctatus. However, into account that the aedeagus is larger than in addition to this registered combination, I will the gynatrium), or at least to plugging of the consider the opposite variant of reciprocal mating. secondary gonopore because it abuts against the The first thing that attracts attention is the wall of the gynatrial cone in the place of its bend. somewhat larger genitalia of the male and female In the hypothetical case of the mating of a male of C. hyoscyami, which has a larger body size. Rh. parumpunctatus with a female C. hyoscyami, Therefore, the possibility of injury to the gynatrium it seems that nothing prevents the apical part of Rh. parumpunctatus by the completely swelled of vesica from penetrating into the apical part

16 ( Zoosystematica Rossica, Vol. 28, No. 1, pp. 3–18 D.A. Gapon. An instance of intergeneric copulation in the family Rhopalidae of gynatrial cone, having a wide lumen of the crosses in both combinations, and, as a result, the channel, and making the flip-over in it. However, impossibility of normal insemination. It is difficult the right lobe of the basal part of vesica in this to say whether the described mechanisms are case will not be able to cling to the fold on the actually realised in the considered species, but at wall of the basal part of gynatrial cone (since least they are possible. this fold is absent in C. hyoscyami) and will not entrain this wall. As a result, the long apical Addenda portion of the apical part of vesica cannot enter the apical part of gynatrial cone but having Electronic supplementary material. Image files: turned over it will be directed to the right inside Fig. 13, Fig. 14, Fig. 15, and Fig. 16. File format: the basal part of the cone. This cannot completely JPEG. Available from: https://www.zin.ru/jour- exclude the possibility of sperm penetration into nals/zsr/publication.asp?id=1319 the spermatheca because, as Pluot (1970) showed Explanation note. Additional photographs of for the genus Dysdercus Audinet-Serville, 1835, mating Corizus hyoscyami (male) and Rhopalus the spermatozoa can migrate from the part of the parumpunctatus (female), Novgorod Province. gynatrial cone, located close to the opening of the Photographs by E.Yu. Kirtsideli. spermathecal duct, into the spermathecal capsule under the action of the secretion of its apical cells. Acknowledgements However, in the case of such mating, the number of spermatozoa reaching the capsule would be I heartily thank Evgeniy Yu. Kirtsideli and Maria A. Berlina (St Petersburg) for providing the small, taking into account the volume of the basal photographs that underpin this work. I am also very part of gynatrial cone in C. hyoscyami, and the grateful to Max Barclay (Natural History Museum, fact that the cone is widely opened ventrally. Such London) for the linguistic correction of the text migration is probably difficult for the spermatozoa, and valuable comments. The work was performed since for their migration from the spermathecal in the frameworks of the state research project capsule to the common oviduct through the basal No. АААА-А19-119020690101-6 and supported by part of gynatrial cone serves the special groove the Presidium RAS program No. 41 “Biodiversity of on its dorsal wall (at least, this is the most likely natural systems and biological sources of Russia”. function of this groove). Thus, it is unlikely that insemination will succeed. References As a result of the purely speculative comparison of the structure and functioning of the male and Dufour L. 1844. Anatomie générale des diptères. female genitalia in the two species considered, Annales des Sciences Naturelles. Troisième série. Zoologie, 1: 244–264. it can be concluded that the genital structures Eberhard W.G. 1985. Sexual selection and animal of both species, which serve for anchoring, are genitalia. Cambridge: Harvard University Press. completely congruent to each other in both 244 p. variants of interspecific crosses (although Gapon D.A. 2001. Inflation of Heteropteran aedeagi corresponding parts of the aedeagi somewhat using microcapillaries (Heteroptera, Pentatomi- differ in the examined species), and if their dae). Zoosystematica Rossica, (2000), 9(1): 157– contact does not result in injury to a female of 160. Rh. parumpunctatus when mating with a male of Gapon D.A. 2007. Structure, function, and morpholo­ C. hyoscyami, then these organs do not have the gical conformity of the male and female genitalia in function of structural isolation. The situation with the true bug genus Pyrrhocoris Fall. (Heteroptera, Pyrrhocoridae). Entomologicheskoe Obozrenie, the structures that serve for the transfer of seminal 86(4): 729–741. (In Russian. English translation: fluid is different; in both species, these structures Entomological Review, 2007, 87(9): 1099–1108. have different morphology and functioning. The https://doi.org/10.1134/S0013873807090011) proposed schemes of the functioning of these Konstantinov F.V. & Gapon D.A. 2005. On the struc- structures indicate their not only morphological, ture of the aedeagus in shield bugs (Heteroptera, but also functional incongruence in interspecific Pentatomidae): 1. Subfamilies Discocephalinae and

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Phyllocephalinae. Entomologicheskoe Obozrenie, grad: Nauka. 132 p. (In Russian). 86(2): 334–352. (In Russian. English translation: Shapiro A.M. & Porter A.H. 1989. The lock-and-key Entomological Review, 2005, 85(3): 221–235). hypothesis: evolutionary and biosystematic inter­ Masly J.P. 2012. 170 years of “lock-and-key”: genital pretation of insect genitalia. Annual Review of En- morphology and reproductive isolation. Interna- tomology, 34: 231–245. https://doi.org/10.1146/ tional Journal of Evolutionary Biology, 2012: 1–10. annurev.en.34.010189.001311 https://doi.org/10.1155/2012/247352 Štys P. 1961. Morphology of the abdomen and female Mayr E. 1963. Animal Species and Evolution. Cam­bridge: ectodermal genitalia of the Trichophorous Hetero- Belknap Press of Harvard University Press. 797 p. ptera and bearing on their classification. In: Strouhal Pluot D. 1970. La spermathèque et les voies genitals H. & Beier M. (Eds). XI. Interna­t­ionaler Kongress femelles des Pyrrhocoridés (Hemiptera). Annales de für Entomologie, Wien, 17. bis 25: verhandlungen, la Société entomologique de France, 6(4): 777–807. 1: 37–43. Wien : Organisa­tionskomittee des XI. Putshkov V.G. 1986. Poluzhestkokrylye semeystva Internationalen Kongresses für Entomologie. Rhopalidae (Heteroptera) fauny SSSR [Bugs of the Ueshima N. 1979. Hemiptera II: Heteroptera. In: John family Rhopalidae (Heteroptera) of the fauna of the B. (Ed.). Animal cytogenetics, 3(6). Berlin & Stutt- USSR]. Opredeliteli po Faune SSSR, 146. Lenin- gart: Gebrüder Borntraeger. 113 p.

Received 30 November 2018 / Accepted 24 December 2018. Scientific editor: I.A. Gavrilov-Zimin

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