Structure, function, and morphological conformity of ...

ISSN 0013-8738, Entomological Review, 2007, Vol. 87, No. 9, pp. 1099–1108. © Pleiades Publishing, Inc., 2007. Original Russian Text © D.A. Gapon , 2007, published in Entomologicheskoe Obozrenie, 2007, Vol. 86, No. 4, pp. 729–741.

Structure, Function, and Morphological Conformity of the Male and Female Genitalia in the True Bug Genus Pyrrhocoris Fall. (Heteroptera, Pyrrhocoridae) D. A. Gapon Chair of Zoology, Rostov State University, Rostov-on-Don, Russia Received May 27, 2005

Abstract—In representatives of the genus Pyrrhocoris examined, the male and female genitalia are highly congruent and possess a number of structures providing firm fixation of copulating individuals, at the same time ensuring a quick release of partners when necessary. Mechanic prevention of interspecific hybridization is realized in sympatric species and absent in allopatric ones. DOI: 10.1134/S0013873807090011

In many insects, the male genitalia possess a complicated structure and, in some groups, differ well in closely related taxa; in this connection, their structural characters are widely used in modern taxonomy. Analysis of diversity and structure of the aedeagus resulted in an assumption that male and female genitalia in insects fit each other as lock and key (Dufour, 1944), i.e., are congruencies. This assumption allows supposing two more functions of the insect genitalia, together with the transfer of sperm or spermatophores, namely (1) providing a strong fixation of copulating specimens, and (2) preventing hybridization between specimens of different species. Ideally, the study of the morphological conformity (congruency) between genitalia of different sexes and its biological significance should be conducted under direct observation of these structures in relation to each other in the process of copulation. The existing descriptions of mutual disposition of genitalia were performed for representatives of the family Lygaeidae (Ludwig, 1926; Bonhag and Wick, 1953), possessing a transformed spiral aedeagus screwing into the similarly spiral inner genitalia of the female. In insects with such genital structure, copulation lasts for rather a long time, significantly facilitating the study of mutual disposition of the genitals. A membranous non-screwed endosoma (the endophallus), retracted into the sclerotized theca in the resting state and swelling in the female reproductive duct during copulation (due to pumping of the haemolymph into the endophallus) is characteristic of virtually all the rest hemipterans and also of many other insect groups. It is very hard or even impossible to fix such structures in copula; therefore, we can estimate the

degree of morphological congruence only indirectly, by comparison of male and female structural details analyzed separately. The assumption on the function of mechanical isolation characteristic of the insect genitalia was discussed in many publications, both pro and contra. Some of these publications were reviewed by Mayr (1968). It should be noted that the majority of these works is devoted only to the external sclerotized parts of copulatory organs, acting only at the very beginning of the copulatory process and performing an accessory function. At the same time, the question of the existence of the mechanical isolation requires the study of inner membranous and sclerotized structures coming in direct contact with each other during the entire copulation. On the one hand, the study of this question is associated with significant difficulties in dissecting the inner structures of the aedeagus; investigation of these structures began only recently and covers only a small number of taxa. On the other hand, it is associated with our poor knowledge of the inner ectodermal structures of the female genitalia; usually, only the structure of the spermatheca is analyzed for taxonomic purposes. In the present work, the method of hydraulic distension of the aedeagi with micro capillaries and the subsequent drying of these structures in a hot air stream (Gapon, 2001) was used. This method allows obtaining preparations completely corresponding to the state of the aedeagus in the female reproductive duct; it allows studying the shape and structural details of the aedeagus and also to trace the process of erection and

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retraction of its inner structures. Standard methods of hand dissection and staining with methylene blue were used for the study of the structure of inner ectodermal female genitals.

the resting state (in hemipterans, the pygophore turns by 180° during copulation; therefore, the ventral surface of the aedeagus in the resting state turns into the dorsal one, and vice versa).

Dry specimens of Pyrrhocoris apterus (Linnaeus, 1758), P. fuscopunctatus Stål, 1858, P. marginatus (Kolenati, 1845), P. sibiricus Kuschakewitsch, 1866, and P. sinuaticolis Reuter, 1885 from the collection of the Zoological Institute, Russian Academy of Sciences, and also living specimens of P. apterus collected in Rostov-on-Don in 2002 were used in this work.

In P. apterus, the aedeagus is elongated and slightly bent ventrally near the middle of its length (Figs. 1, 2). The phallobase is small, without ventral processes. Long triangular outgrowths of the ventral wall of the pygophore are situated at sides of the phallobase (Fig. 20). Very short suspensory apodemae are attached to apices of these outgrowths. Dorsal connectives are moderately long. Mushroom bodies are large and disk-shaped.

STRUCTURE OF MALE AND FEMALE GENITALIA The Aedeagus of Pyrrhocoris apterus Three following parts are traditionally distinguished within the aedeagus (or the phallus) of hemipterans: the phallobase, the theca, and the endosoma. The phallobase lies on the membrane of the genital chamber of the pygophore and is represented by a horseshoe-shaped sclerite enveloping the base of the theca. The phallobase is attached to walls of the pygophore by suspensory apodemae. Protractors are attached to the phallobase from the ventral side and retractors, from the dorsal side (by dorsal connectives terminating as mushroom bodies). The theca is tubular, more or les strongly sclerotized. Apically, it passes into the thin-walled endosoma, differentiated into the eversible conjunctive and non-eversible (sclerotized in the majority of Pentatomomorpha) vesica, bearing the secondary gonopore. The semen duct passes through the entire cavity of the aedeagus from the phallobase to the secondary gonopore; in Pentatomomorpha, this duct forms the ejaculatory reservoir, dividing it into the proximal semen duct and distal ejaculatory duct. Usually in the resting state, the endosoma is retracted into the theca. A detailed terminological review of hemipteran aedeagal structures is given by Dupuis (1955). Hereinafter, original terms are given in italics. The structure of the aedeagus in P. apterus was analyzed by Ludwig (1926), Merle (1968), and Pluot (1978). In these works, some structural details of the aedeagus were described incompletely or not described at all, because, as was mentioned by the latter author, some structures can be seen only in the erected state (although she had studied the aedeagus stretched with forceps). Then, a completely swollen aedeagus is described but its structures and surfaces are given for

The theca is cylindrical, weakly sclerotized, and semitransparent at the base. More distally, its wall forms a stronger sclerotized ring with indistinct borders. The distinctly convex and sclerotized carina with transverse ribs is situated on the ventral surface of the theca. Distally to this ring, the wall of the theca forms a small weakly sclerotized convexity. The theca somewhat narrows apically and smoothly passes into the wider and convex conjunctive. The border between these two parts runs along the place of flexure of the wall of the conjunctive during its retraction and stretching (Fig. 3), strengthened by apical margins of a Y-shaped sclerotized spot situated on the dorsal wall of the theca. Paired basal and parabasal lobes are situated at the base of the conjunctive on its ventral side. Each blade is a flattened dorso-ventral fold of the conjunctive; the ventral surface of each lobe is sclerotized and the dorsal one, membranous. Basal lobes are wide oval plates. Parabasal lobes are narrower; they are attached distally to the basal lobes closely to them. A narrow sclerotized ventral band passes from each parabasal lobe over the wall of the conjunctive apically. Apices of lobes of each pair are directed to the base of the aedeagus, slightly diverging. Dorsal walls of parabasal lobes are nearly pressed to ventral surfaces of basal lobes. Dorsally to the base of parabasal lobes, lateral wall of the conjunctive forms a pair of small lateral tubercles. A fine sclerotized line passes obliquely along the lateral wall of the conjunctive distally to lateral tubercles. Apically, the conjunctive widens, forming a pair of large latero-apical tubercles. A large complicated vesica is situated at the apex of the conjunctive (Figs. 4, 5). The base of the vesica is retracted into the conjunctive. A small rounded chamber is situated in the base of the vesica; the semen duct ENTOMOLOGICAL REVIEW Vol. 87 No. 9 2007

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Figs. 1, 2. Pyrrhocoris apterus L., entirely swollen aedeagus in (1) ventral; and (2) lateral view; phb, phallobase; pro c, mushroom bodies; th, theca; lob. b, basal lobe of conjunctive; lob. pb, parabasal lobe of conjunctive; tr. v, ventral rod; tub. I, lateral tubercle; tub. la, latero-apical tubercle; ves, vesica; lob. gon, gonoporallobe of vesica; lob. d, dorsal lobe of vesica; gon, gonopore; d. s, semen duct.

approaches this chamber. This chamber is a homologue of the ejaculatory reservoir of Pentatomoidea, because a hyaline band is attached to its walls (Fig. 5).In this case, the part of the semen duct situated in the cavity of the theca and the conjunctive is the semen duct (ductus seminis), whereas the entire ejaculatory duct (ductus ejaculatorius) is situated in the vesIca. Two lobes (gonoporal and dorsal ones) go from the base of the vesica. The gonoporal lobe is sclerotized, flattened laterally; the ejaculatory duct runs inside it. It is rather thin in the median part and widened and hooked apically; the apex of a large hook is directed ventrally. The ejaculatory duct opens at the base of a groove running along the dorsal margin of the hooked part of the vesica. Margins of this groove are membranous, overlapping each other along the entire length (this closed groove opens after boiling in alkaline). This closed groove forms a kind of a channel finishing in the pointed apex of the lobe as the secondary gonopore. The dorsal lobe of the vesica is flattened dorso-ventrally; narrow at the base; and dilated (eggshaped) in the distal part. Approximately in the middle of its length, the dorsal lobe is connected with the ENTOMOLOGICAL REVIEW Vol. 87 No. 9 2007

gonoporal lobe by a sclerotized bridge. The apex of the dorsal lobe adjoins the wall of the gonoporal lobe at the level of the orifice of the ejaculatory duct at the bottom of the aforementioned groove. Small stickshaped articular sclerites (inner and outer thickenings of the wall of the conjunctive) are situated on the dorsal wall of the conjunctive near the base of the vesica. One end of each of these sclerites is movably attached to the ejaculatory reservoir; at the other end, sclerites pass into small sclerotized areas on the dorso-ventral surface of the conjunctive. The hyaline band (processus ligamentaires) is very elastic; in the resting state, it looks like a plate with marginal plait-like thickenings (Fig. 4). It runs from the ventral margin of the phallobase and is attached to the base of the vesica at the level of the ejaculatory reservoir. In the erected aedeagus, this stretched band looks like a thread (not shown in Figs. 1,2). The Inner Ectodermal Genitalia of the Pyrrhocoris Apterus Female

The ectodermal genitalia of females of another genus of the family Pyrrhocoridae (Dysdercus), and also

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lob. pb

I:

ej

3

Figs. 3-5. Pyrrhocoris apterus L.: (3) aedeagus in resting state; (4-5) vesica [(4) lateral, (5) dorsal view]. In Fig. 4, the dorsal lobe of the vesica and the wall of the conjunctive are shown in the parasagittal section; bas, base of vesica; r. ej, ejaculatory reservoir; s. a, articulator sclerite; d. ej., ejaculatory duct; pro Zig, hyaline rod. For other designations, see Figs. 1-2.

a review of the literature on this subject are given in the work ofPluot (1970). In P. apterus, the female genitalia (Figs. 6, 7) belong to the coreoid type, with the lamellar ovipositor and undeveloped vagina (Stys, 1960). The entrance to the gynatrium is covered with large movable anterior outer genital plates (gonocoxites VIII). Gonapophysae VIII and IX, situated under them, are represented by fine semitransparent plates with small areas of sclerotization. Gonapophysae IX are divided into two parts by a sci erotized line. A wide and rather long gynatrium opens immediately beyond the rudiments of the ovipositor. The dorsal wall of the gynatrium is stretched between the inner genital plates (gonocoxites IX) and fibulae (fibulae anteriores et posteriors: Ludwig, 1926). In its anterior part, the gynatrium smoothly passes into the unpaired ovipositor. The dorsal wall of the gynatrium forms a voluminous and rather complicated dilatation (the gynatrial sack) (Sty, 1960). Two pairs of pockets (basal and parabasal ones) are situated in its posterior part. Basal pockets are large depressions in the dorsal wall of the gynatrial sack, limited posteriorly and laterally by a shallow fold; their shape is similar to that of the basal lobes of the conjunctive. The ventral wall of basal pockets is functionally formed by proximal parts of gonapophysae IX strengthened by a sclerotized line. The parabasal pockets are smaller than basal pockets; they are situated close to the latter and anterior to them, pressing against basal

pockets dorsally. The fold bordering parabasal pockets is pronouncedly deeper than those bordering basal pockets, forming their ventral wall. The gynatrial cone represented by a large conical pocket directed forward apically and pressed over the wall of the unpaired ovipositor is situated in the anterior part of the gynatrial sack. It possesses solid (but not sclerotized) walls, except for a narrow median membranous strip on the ventral side. The duct of the spermatheca begins on the apex of the gynatrial cone. A pair of large gynatrial glands (Stys, 1960) framed by a fine sclerotized band or rounded sclerites is situated on the lateral sides of the gynatrial sack between parabasal pockets and the gynatrial cone (Bonhag and Wick, 1953). Genitalia in Other Species ofPyrrhocoris Pyrrhocoris sibiricus. The conjunctive is elongate (Figs. 8, 9). The basal lobes are wide and rather short. The parabasal lobes distinctly project beyond the apices of the basal lobes; they are strongly bent medially at the apex. The mentioned lobes nearly adjoin each other. Small lateral and latero-apical tubercles are present. The gonoporal lobe is long, narrowing distally, S-shaped; the apex of the dorsal lobe adjoins the base of its upper bending. The secondary gonopore opens at the apex of the gonoporal lobe, the latter beENTOMOLOGICAL REVIEW Vol. 87 No. 9 2007

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6 Figs. 6, 7. Pyrrhocoris apterus L.: (6, 7) gynatrium [(6) dorsal and (7) ventral view]. Ventral folds of the gynatrial sack, sclerotized areas, and borders of gonocoxites Vlll are shown in dotted lines. In Fig. 7, gonocoxites Vlll and the left gonapophysa Vll with a part of the ventral wall of the gynatrium are not shown; gc, IX, gonocoxites IX; fib. ant, anterior fibula; fib. post, posterior fibula; gpo VIII, gonapophysae Vlll; gpo IX, gonapophysae IX; g. s, gynatrial sack; bur. b, basal pouches of gynatrial sack; bur. pb, parabasal pouches of gynatrial sack; con. g, gynatrial cone; c. s, capsule of spermatheca; sp. d, duct of spermatheca; g. g , gynatrial glands; odv. m, unpaired oviduct.

ing elongate at the apex, looking like a fine elastic thread. The gynatrium possesses a wide and long gynatrial sack (Fig. 16). The basal pouches are distinct. The parabasal pouches are large. The gynatrial cone possesses a rather strongly convex dorsal wall; without any distinct border, the cone passes into a wide and short duct of the spermatheca with walls thickened in the proximal part.

conjunctive (they are situated in the same place, where lateral tubercles are found in P. apterus). A fine sclerotized band passes from them along the lateral surface of the conjunctive. Latero-apical tubercles are absent; a single large ventro-apical tubercle is present. The gonoporal lobe is fine, C-shaped. The secondary gonopore opens at the apex of the gonoporal lobe; the dorsal lobe adjoins the latter in the same place.

The structure of the genitalia in P. sibiricus is similar to that revealed in specimens with the red label distinguished as a separate species P. jieberi Kuschakewitsch, 1866 (synonymized by 10sifov and Kerzhner (1978).

The gynatrial sack is short and wide (Fig. 17). Basal pouches are separated indistinctly. Parabasal pouches are not very wide. The gynatrial cone is moderately large; at the base, it possesses a strongly convex dorsal wall. A fine and long duct of the spermatheca opens on the cone more or less ventro-apically.

Pyrrhocoris fuscopunctatus. The conjunctive is

Pyrrhocoris marginatus. The conjunctive is rather

wide, short in the basal part and narrowing apically (Figs. 10, 11). The basal lobes are small and rather narrow. The parabasal lobes slightly project beyond the apices of the basal lobes. The lobes nearly adjoin each other. Raised sc1erotized triangular plates are situated on the dorso-Iateral surface at the base of the

short and wide (Figs. 12, l3). The basal lobes are short, of irregular shape; they are nearly pressed to the sides of the conjunctive. The parabasal lobes are long; they strongly project beyond apices of the basal lobes and are bent toward each other at the apex. Wide rods run from the bases of the parabasal lobes. Long tuber-

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11

9

13

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Figs. 8-15. Pyrrhocoris Fall., aedeagi [(8, 10, 12, 14) ventral, (9, 11 , 13, 15) lateral view]. The basal part of the theca and the phallobase are not shown; (8, 9) P. sihiricus; (10, 11) P. Juscopunctatus; (12, 13) P. marginatus; (14, 15) P. sinuaticollis.

c1es with apices pointed laterally and somewhat apically are situated directly near the base of the parabasal lobes. They evidently correspond to the lateral tubercles of P. apterus. The conjunctive narrows toward the apex and does not form any latero-apical tubercles. The ventro-apical tubercle is present. The vesica is rather short. The apex of the gonoporal lobe is widened in the sagittal plane. The secondary gonopore opens on its dorsal wall; the apex of the dorsal lobe adjoins the dorsal side of the gonoporal lobe nearby. The gynatrial sack is wide (Fig. 18). The basal pouches are separated indistinctly. The parabasal pouches are wide. The gynatrial cone is small, with a weakly convex dorsal wall at the base; the duct of the spermatheca opens on the cone ventro-apically.

Pyrrhocoris sinuaticollis. The conjunctive is short and wide (Figs. 14, 15). The basal lobes are small, slightly adjoining the wall of the conjunctive. The parabasal lobes are wider than in the previous species; they slightly project beyond the apices of the basal lobes and are bent toward each other at the apex. Two small rounded tubercles, similar to those found in P. marginatus, are situated above the base of the basal lobes. A sci erotized band runs obliquely along the lateral surface of the conjunctive; dorsally, it passes into free processes. Small ventro- and latero-apical tubercles are situated on the apex of the conjunctive. The latter tubercles are bimodal; articulator sclerites are connected with one of these apices. The vesica is similar to that found in P. marginatus but its gonoporallobe is wider. ENTOMOLOGICAL REVIEW Vol. 87 No. 9 2007

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Figs. 16-19. Pyrrhocoris Fall., gynatria in dorsal view. (16) P. sihiricus; (7) P.juscopunctatus; (18) P. marginatus; (19) P. sinuaticollis.

The gynatrial sack is rather wide (Fig. 19). The basal pouches are separated indistinctly. The parabasal pouches are rather small. The gynatrial cone is small, with the convex dorsal wall at the base; the duct of the spermatheca opens on the cone ventro-apically. FUNCTIONING AND MORPHOLOGICAL CONGRUENCY OF THE MALE AND FEMALE GENITALIA IN PYRRHOCORIS APTER US On the basis of the data on the shape and structure of the entirely swollen aedeagus, on the structure of the gynatrium, and on the process of extroversion of the endosoma of the dissected aedeagus during microcapillary pumping of water into its cavity, it is possible to reproduce the pattern of the mutual disposition of these structures during copulation. The question of the mutual disposition of the genitalia in P. apterus during copulation was analyzed by Ludwig (1926). His views, however, are erroneous in some aspects (in ENTOMOLOGICAL REVIEW Vol. 87 No. 9 2007

particular, he shows that basal and parabasal lobes of the conjunctive do not project beyond the pygophore during copulation, see below). Directly before the copulation, a male is situated on the back of a female in the head-to-head position. Later, it moves laterad in such a way, that its ventral side appears turned to the ventral side of the female. After that, the genital segment of the male is turned by 1800 and bent toward anterior genital plates of the female due to stretching of membranes between segments VII and VIII and segment VIII and the pygophore. In the resting state, the aedeagus is arranged inside the genital segment in such a way that the hook of the vesica is directed ventrally and backwards. After the tum of the genital segment, the apex of the vesica is directed dorsally. Due to contraction of the protractors attached to the phallobase, the aedeagus protracts from the genital segment, being placed between the opened anterior genital plates of the female.

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Fig. 20. Pyrrhocoris apterus L., posterior ends of the abdomen of copulating individuals in cross-cut; pgph, pygophore; par, base of parameres; VllI, male abdominal segment Vlll; gc. VIII, gonocoxites VIII. For other designations, see Figs. 1,2,6, 7.

After fixation of the endosoma in the gynatrial sack, the male turns around; as a result, copulating specimens appear in tail-to-tail position (Fig. 20). At the same time, the genital segment does not tum back. Copulation can last for several hours, but in emergency, the endosoma rapidly retracts into the theca and copulation stops. After introducing the apex of the theca into the base of the gynatrium, haemolymph is pumped into the cavity of the conjunctive and the latter everts in the theca. Apices of basal and parabasal lobes and of the vesica protract from the theca. Entirely appearing out of the theca, lobes of the endosoma describe an arch of nearly 180 0 • At the same time, basal lobes are situated in wide basal pouches of the gynatrial sack and parabasal lobes enter parabasal pouches. The walls of both pouches become tightly clutched between the basal and parabasal lobes. Thus, two mechanisms of fixation of the endosoma in the gynatrial sack are realized, making the fixation stronger: its lobes are caught by pouch walls and the walls are jammed between the lobes. The rest of the conjunctive and the vesica retract from the theca simultaneously with the tum-off of lobes. When the aedeagus is completely swollen the vesica enters the gynatrial cone and the gonopore directly contacts the orifice of the duct of spermatheca. When the conjunctive bulges, articular sclerites tum; these sclerites, being elastically tensed, evidently promote more complicated retraction of the vesica and stabilize its position in relation to the longitudinal axis

of the conjunctive. The question on the position of the dorsal wall of the vesica is not clear: it either enters the gynatrial cone together with the rest of the vesica or is situated more ventrally and presses its wall (it can be assumed taking into account the fact that the dorsal lobe is supplied by a rigid rod and swells when the haemolymph is pumped in). Observation of the copulation under a binocular microscope demonstrates that parameres do not participate in clutching of the pygophore with the female genitalia during the entire copulation. This function completely passes to the structures of the endosoma. In the resting state, the gynatrial sack is distinctly smaller than the erected aedeagus (the conjunctive and the vesica inside it) but it can significantly dilate, which seems to occur during copulation. Pavlovskii (1949) assumed that the shape of the artificially everted endosoma ("the inner sack") of insects does not correspond to its shape during copulation because in the latter case the endosoma does not swell completely. The example of P. apterus demonstrates quite a different situation: if the aedeagus is carefully removed from the female genitalia with a needle, without distributing the male (and keeping the female fixed). The aedeagus which stays erected for some time completely corresponds to that shown in Figs. 1 and 2 in shape and size. Retraction of the endosoma into the theca is evidently provided by the elasticity of the hyaline rod ENTOMOLOGICAL REVIEW Vol. 87 No. 9 2007

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Possibility of copulation of Pyrrhocoris species according to the structure of the genitalia Males

Females

P. apterus

P. apterus P. sibiricus P. fuscopunctatus

CI

P. marginatus

CI

P. fuscopunctatus

P. marginatus

P. sinuaticollis

CI Cp*

CI CP

Cp*

Notes: CI, copulation is impossible; CP, copulation is possible. Species with allopatric ranges are marked with an asterisk.

connecting the base of the vesica with the phallobase. The presence of muscles inside the aedeagus can also be assumed because the conjunctive does not retract completely during pumping of water from the cavity of a swollen aedeagus with a syringe (sclerotized rods running from parabasallobes hamper this process). As seen in vivo, the vesica and the apical part of the conjunctive up to apices of ventral rods are the first to retract into the cavity of the conjunctive. It probably occurs due to the decrease of haemolymph pressure and the elasticity of hyaline rods. Then, the median part of the conjunctive down to the bases of parabasal lobes is also retracted. Very likely it occurs due to some additional effort. DISCUSSION

As seen from descriptions and pictures mentioned above, the male and female genitalia in the species analyzed correspond to basic structural schemes. In males, the weakly and partly sclerotized theca passes into the thin-walled conjunctive without any distinct border; the basal and parabasal lobes directed toward the base of the aedeagus are situated at the base of the conjunctive. In females, the scheme includes the presence of basal pouches in the posterior part of the gynatrial sack, ventrally concealed by gynapophysae; the presence of parabasal pouches immediately before the gonapophysae; and the presence of the gynatrial cone with the duct of the spermatheca. Within the limits of these schemes, interspecific differences in the structure of and shape of the endosoma are more pronounced than those in the structure of the female genitalia. In spite of this, in each species, the degree of congruency of genital structures directly contacting during copulation can be estimated as a high one. Basal pouches correspond to basal lobes; parabasal pouches correspond to parabasal lobes; the gynatrial cone, to the vesica; and the shape and structure of the gynatrial sack, to the shape of the endosoma. The deENTOMOLOGICAL REVIEW Vol. 87 No. 9 2007

gree of development of basal pouches depends on the size and arrangement of basal lobes: the presence of the largest basal lobes corresponds to the presence of the largest and distinctly separated basal pouches (P. apterus), whereas small basal lobes of P. sinuaticollis pressed to walls of the endosoma, agree with weakly developed basal pouches. The size of parabasal pouches also distinctly depends on the length of parabasal lobes that stretch in these pouches during swelling of the conjunctive: the longest parabasal lobes correspond to the widest parabasal pouches (P. sibiricus) and rather small parabasal lobes (P. Juscopunctatus and P. sinuaticollis), to similarly small parabasal pouches. The shape of the gynatrial cone repeats the curves of the gonoporal lobe of the vesica; the position of the orifice of the duct of the spermatheca on the gynatrial cone more or less correlates the position of the secondary gonopore on the gonoporal lobe. In P. apterus, the gonopore is oriented dorsally in the erection state; the orifice of the duct of the spermatheca in the gynatrial cone is also oriented dorsoapically; in P. marginatus, P. sinuaticollis, and P. Juscopunctatus, it is oriented ventrally during erection and the duct of the spermatheca also opens ventroapically. In P. sibiricus, the gonopore opens on the apex of the thin and bent gonoporal lobe elongated into a long thread, and the gynatrial cone smoothly passes into the widened basal part of the duct of the spermatheca possessing thickened walls. Analysis of the described structural features of the male and female genitalia, however, demonstrates that the possibility of interspecific hybridization can be excluded only in some cases (see table). Impossibility of insemination during genital contact can be explained by several reasons. In species of Pyrrhocoris, the introduction of sperm into the spermatheca evidently needs a direct contact between the gonopore and the orifice of the duct of the sper-

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matheca. The introduction of sperm into the spermatheca is impossible when the orifice of the duct of the spermatheca is situated ventro-apically and the gonopore is oriented dorso-apically and vice versa but it is possible in species with the gonopore oriented ventro-apically and in P. sibiricus, possessing a strongly dilated proximal part of the duct of the spermatheca. It is associated with the fact that the strongly swollen aedeagus significantly dilates the gynatrium and the tensed walls of the gynatrial cone appear to be closely pressed to the walls of the vesica, closing the gonopore, if only the latter does not directly contact the orifice of the duct of the spermatheca. P. sibiricus males cannot probably inseminate females of other species because of the presence of a long thread on the apex of the gonoporal lobe which is not introduced into a narrow duct of the spermatheca and can simultaneously close the gonopore. Besides, in both P. apterus and P. sibiricus, the aedeagus is significantly larger then that in the other species examined and, probably, is unable to swell in the gynatrial sack of these species. It should be especially noted that species with genitals allowing all cross-breeding combinations (P. fuscopunctatus, P. marginatus, and P. sinuaticollis) are characterized by non-overlapping ranges, whereas species unable to copulate with each other possess, as a rule, sympatric ranges (see Table). The overlapping ranges of P. sibiricus and P. fuscopunctatus and P. sibiricus and P. sinuaticollis correspond only to one-way cross-breeding, when males of P. fuscopunctatus and P. sinuaticollis are able to inseminate P. sibiricus females. The data on the species distribution are given in the catalogue of Palaearctic Heteroptera (Aukema and Rieger, 2001). Thus, the male and female genitalia in the Pyrrhocoris species examined are characterized by a high degree of congruency; they possess some adaptations for strong fixation of copulating individuals, at the same time allowing rapid interruption of the copulation. The function of mechanical preventing of interspecific hybridization can be realized in sympatric species and most frequently is absent in allopatric ones.

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