Grylloidea, General, General

Josse, Hugo, Faberon, Léo, Schubnel, Thomas, Nel, André & Desutter-Grandcolas, Laure, 2023, Reconciliation between neontology and paleontology in the Gryllidea (Orthoptera, Ensifera): reinterpreting the venation of the stridulatory apparatus in crickets, Zoosystema 45 (24), pp. 769-801 : 774-777

FOREWING VENATION PATTERN IN THE MODERN GRYLLOIDEA

General venation pattern of male Grylloidea

The overall venation pattern of crickets is shown here on four species, having a stridulatory apparatus considered as ‘complete’ (file, harp and mirror) and a lanceolate cell: Natula longipennis (Serville, 1838) ( Trigonidiidae , Trigonidiinae Saussure, 1974 : Fig. 3A ), Lerneca fuscipennis (Saussure, 1874) ( Phalangopsidae , Luzarinae Hebard, 1928 : Fig. 3B ), Phyllogryllus sp. ( Oecanthidae , Podoscirtinae Saussure, 1878 : Fig. 4A ), and Brachytrupes membranaceus (Drury, 1773) ( Gryllidae , Gryllinae Laicharting, 1781 : Fig. 4B ).

Lateral field. The lateral field is delimited by the anterior edge of the wing and the median fold located between M+CuA and CuPa ( Figs 3 ; 4 ). At their bases, the veins of this field can be identified, from the most anterior to the most posterior, as C, Sc, R, and M+CuA, originating from often closed or even fused basivenal bullae. Orthoptera are characterized by the presence of a large costal field. In Grylloidea , a C vein is almost always present, even though the number and shape of its bifurcations vary. In some cases, C and Sc bullae are joined, and it can be very hard to distinguish them, and their related branches. The separation between C and Sc is particularly clear in male Ectotrypa olmeca Saussure, 1874 ( Appendix 3: Fig. S2C ) or female Brachytrupes membranaceus ( Appendix 3: Fig. S4C ). In Orthoptera , a rather long ScA and a long pectinate ScP may be both present. In Grylloidea , ScA and ScP are relatively difficult to distinguish. For sake of clarity, we consequently consider the Sc vein s.l., and do not always differentiate C and Sc (then indicated in figures as C+Sc). The shape and bifurcations of C and Sc do not seem related to the presence / absence of a stridulatory apparatus. R is very strong and convex, especially at its base, basally merged with Sc: these two veins are always almost parallel. Basally, the R and M+CuA veins are also very close or even fused in the most basal part of the wing. Distally, the closed lanceolate cell is present ( Figs 3 ; 4 ). The short vein between M+CuA and R, at the base of the lanceolate cell, is here interpreted as a secondary crossvein called ‘r-m’. This vein is sometimes very short (as in Brachytrupes membranaceus , Fig. 4A ) or even totally absent due to the partial fusion of M+CuA with R (as in Phyllogryllus sp. , Fig. 4B ). This last configuration of the r-m may be an aberration, but it has also been observed in other specimens (for example in Acheta domesticus Linnaeus, 1758 ). More distally, the lanceolate cell is closed by the concave RP: the posterior branch of R emerges very distally compared to the situation in other Orthoptera , but can still be identified in some Grylloidea by its basal concavity (as in Brachytrupes membranaceu s, Appendix 3: Fig. S1C ). RP is strongly bent proximo-posteriorly, and merges with MA over a short distance, these veins separate again and both have a longitudinal trajectory to the wing apex ( Fig. 4 ). RA is convex and often joins the distal edge of the wing. It can also be strongly reduced or shortened (as in Lerneca fuscipennis , Fig. 3B ). In many crickets, R is strongly curved just basally to RA/RP fork, thus making the base of RP to have a reverse longitudinal trajectory in the continuity of MA ( Figs 3 ; 4 ). RP sometimes has the same polarity and ornamentation as the latter vein. The distal part of RP (after its separation with MA), MA and MP often have a rather neutral polarity in modern crickets, which may be related to the thinness of the wing membrane in this folded area. MA and MP can therefore be identified by a slight polarity at their base (MA convex and MP concave) and by their relative positions. Note that RP can be reinforced in the continuity of M so that it resembles an anterior branch of the latter, as in Phyllogryllus sp. ( Appendix 3: Fig. S2D ) for example.

CuA separates from M at the same level or slightly distad the base r-m of the lanceolate cell. It is very short and merges with CuPaα by crossing the median fold ( Figs 3 ; 4 ). The combination of the transverse vein r-m, of the emerging M and CuA, and of the fusion of CuA with CuPaα results in a composite transverse structure in the mid part of wing. Its function, if any, remains unknown, but it could be a kind of ‘arculus’ sensu Wootton (1992), i.e., a reinforcement of the wing structure in a zone of great functional constraint. Other short veins sometimes cross the median fold between M and CuA+CuPaα, but these are not regularly present in all the species and are often much less marked than the CuA (as in Natula longipennis , Fig. 3A and Brachytrupes membranaceus , Fig. 4A ). Therefore, they are here considered as secondary transverse veins.

The median fold marks the boundary between the two fields. Distally, it bifurcates into two distal folds, both making the fan; one of the folds crosses M+CuA (between r-m and the bifurcation of M and CuA) and the lanceolate cell longitudinally, while the other runs along the stem vein of CuA+CuPaα.

Dorsal field. At the base of the dorsal field, from the most anterior to the most posterior veins, there are six veins: CuPa, CuPb, PCuA, PCuP, and two anal veins (AA and AP) ( Figs 3 ; 4 ). CuPa is very thin, concave and continuous toward the wing distal margin. Following Desutter-Grandcolas et al. (2017), we consider that Grylloidea have a shortened CuPb. Indeed, between CuPa and PCuA, we can easily notice a very short vein radiating from the Cu basivenal bulla. CuPb is usually easily observed in Phalangopsidae , Oecanthidae and some Gryllidae , as a most often faint vein, that can reach at most half wing length in some specimens (see for example Lerneca fuscipennis , Fig. 3B ). However, in observed Trigonidiidae, CuPb is extremely thin and tangy to the file (PCuA) ( Figs 3A ; Appendix 3: S1A). An intercalary vein can also be present between CuPa and CuPb, which we named here ‘cup spl’ (supplementary cubital posterior) although its homology with that of other families is questionable (see Discussion). This vein differs from CuPb in that it is not connected to any main vein base, which is our strongest argument for primary venation homology between the main veins. PCu can be identified thanks to its strong and curved base, and divides from its base into two branches, PCuA and PCuP. PCuA bears the stridulatory teeth ventrally; it is rather strong, convex basally then concave (reversed polarity in connection with the stridulation process); PCuP is slightly concave. PCuA and PCuP are relatively parallel at their base; they join more posteriorly in the anal node, near the plectrum. The common base of AA (slightly convex) and AP (slightly concave) is more posterior to that of the PCu ( Figs 3 ; 4 ). The configuration of the anal veins is quite variable among the species, and presents a strong intraspecific, or even intraindividual, variation. AA is generally well-differentiated whereas the AP vein can be reduced to a network of several veins. AA usually joins the two branches of the PCu in the anal node, whereas the very thin AP often runs along the posterior edge of the wing. In the specimens we studied, a reinforced crossvein ‘a’ joins AA and AP proximally to the plectrum, closing an anal cell (ac) basally ( Figs 3 ; 4 ).

Distally to the file, the Grylloidea have a large triangular cell called the harp, bounded proximally by the PCuA (the file), anteriorly by CuPa and distally by the beginning of the CuPaβ and a reinforced crossvein (named here the diagonal 2 (d2)), aligned with the first part of CuPaβ, and joining the plectrum ( Figs 3 ; 4 ); d2 corresponds to half of the traditional ‘diagonal’ of the cricket wing (e.g., Vicente et al. 2015), or to the ‘column’ sensu Béthoux (2012). The harp is often crossed by a variable number of transverse or oblique crossveins, except in the Trigonidiidae , where it is crossed by a unique longitudinal crossvein. The CuPaβ configuration could result from a capture of its base by the crossvein diagonal 1 (d1) in modern Grylloidea (see sections on fossil families and Discussion).

The antero-distal area of the dorsal field is occupied by CuPa and its branches. Some particular cells are observed in the different species. A large rounded cell is present between the CuPaβ and CuPaα2: it corresponds to the mirror sensu stricto (mi, Figs 3 ; 4 ) and is bounded by two crossveins, the diagonal crossvein d1 anteriorly and a crossvein that we called septum 1 (s1) distally. The contour of the mirror is often uniformly reinforced, complicating the differentiation between main and secondary veins; they are here identified according to their relative positions. Anteriorly to d1, a very little cell may separate CuPaβ and CuPaα 2 in some species: this cell is named here the ante-mirror (ant-mi, in Brachytrupes membranaceus and Phyllogryllus sp. , Fig. 4 ). In Lerneca fuscipennis ( Fig. 3B ), ant-mi and d1 are totally absent and the bases of CuPaβ and CuPaα2 are fused. Posteriorly to the mirror but still between CuPaβ and CuPaα2, there is another cell, named sub-mirror (sub-mi, Figs 3 ; 4 ), limited by s1 and by septum 2 (s2). The sub-mirror is more or less elongate, long in Lerneca fuscipennis and Phyllogryllus sp. ( Figs 3B ; 4B ), shorter and wider in Brachytrupes membranaceus ( Fig. 4A ).

The short CuA vein fuses with CuPaα1 (anterior branch of CuPaα) after its bifurcation with CuPaα2. While CuPa is relatively thin and concave on the first half of the wing, it becomes much thicker after its fusion with CuA and becomes rather convex. CuA+CuPaα1 is distally branched with a strong ‘stem-vein’ in the continuity with CuPa (and the base of CuPaα) and a series of weaker branches directed postero-distally. In Lerneca fuscipennis and Phyllogryllus sp. CuPaα2 merges very partially (just as a contact point) with CuA+CuPaα1 and closes a well-delimited cell between CuA+CuPaα1 and CuPaα2, located anterior to the mirror and named here the para-mirror (‘para-mi’, Figs 3B ; 4B ). Para-mi is present in the species with a long sub-mi.

The distal part of dorsal field is very variable between species, individuals, and even between the two forewings of the same individual, notably because of a non-stable number of branches of CuA+CuPaα1, making their identification little informative, except for the first ones. In some species, the branches of CuA+CuPaα1 are partially fused (often in their middle), giving a pectinate aspect of distally oriented veins, with some closed cells between bases of the branches and their fused part (as in Lerneca fuscipennis , Fig. 3B ).

On the posterior area of the wing, distad the anal node and the plectrum, PCuA, PCuP and AA separate again. The distal parts of PCuA (generally named first chord, as the most anterior chord) and PCuP (generally named second chord) have curved trajectories. AA may also be curved and forms a third chord, i.e., the most posterior chord. Some stable cells can here be identified. A large cell c1 is located between CuPaβ (posterior edge of the mirror) and PCuA. It is bounded basally by d2 and distally by the crossvein t1. The configuration of c1 crossveins is variable, but one reinforced crossvein, here named the ‘pilar’ (pi), is often present in the middle of c1, often very close to the bend of CuPaβ and its contact point with d2. The pilar exists in Lerneca fuscipennis and Phyllogryllus sp. ( Figs 3B ; 4B ). Distally to c1, another cell, herein named sub-c1, is distally bounded by t2. This cell is located posteriorly to the sub-mi. Posteriorly to c1, a large cell c2 is situated between the first and second chords, and distally bounded by the crossvein t3. Distally to c2, between PCuA and PCuP (and sometimes also AP, as in Phyllogryllus sp. or Lerneca fuscipennis (in which there seem to be more vein fusions than in Brachytrupes membranaceus )), a sub-c2 cell is bounded distally by t4. A cell c3 is located between PCuP and AA, bounded distally by t5. Distad this last vein, a sub-c3 cell is present between PCuP and AA, just before these two veins go into AP. A last cell (anal cell, ac) is located between AA and AP and is bounded basally by a supposed reinforced crossvein a ( Figs 3 ; 4 ). More distally, AA and PCuP merge with AP (which runs along the posterior margin of the wing). PCuA can continue its trajectory to the distal edge (as in Brachytrupes membranaceus , Fig. 4A ) or join the end of AP (as in Lerneca fuscipennis or Phyllogryllus sp. , Figs 3B ; 4B ).

Grylloidea : special venation patterns

We do not aim to exhaustively list all the venation patterns of crickets, which are extremely diversified, but we present some cases for which the general venation pattern needs to be adapted.

In all families of Grylloidea , many species have ‘shortened’ forewings. In these species, the base of the wing has often nearly the same configuration as in the species with long forewings. But their more distal structures (fan, lanceolate cell, and sometimes cells of the mirror) are variously reduced, as in Landreva sp. ( Gryllidae , Landrevinae Saussure, 1878; Fig. 5A ), or even absent as in Nemobius sylvestris (Bosc, 1792) ( Trigonidiidae , Nemobiinae Saussure, 1877 ; Fig. 5B ).

In many species, males do not have a complete singing apparatus ( Fig. 5C, D ). The apparatus can be reduced to the file, the rest of the venation being very similar to that of the female ( Oecanthidae , Tafaliscinae Desutter-Grandcolas, 1988, e.g., Tafalisca lineatipes Bruner, 1916 ; Fig. 5C ). Or venation can be identical in males and females ( Oecanthidae , Podoscirtinae , Aphonomorphus sp. ; Fig. 5D ). Males with a strongly reduced apparatus, as well as the females ( Appendix 3: Fig. S3 ), do not have a lanceolate cell on the lateral field: the identities of the veins located in the lateral field and in the fan thus remain uncertain, because the relative convexity of the veins is hardly visible on the dorsal edge of their wings, while the median fold is strongly marked. However, following the hypothesized venation of the stridulatory apparatus, and thanks to the low relative convexity of veins, RA seems to follow a straight path to the distal edge of the wing, while RP merges with M. The fusion of RP with M would thus occur before its bifurcation into MA and MP, contrary to males with complete stridulatory apparatus. In the males devoid of a stridulum, the fan is also clearly longer and starts much more basally than in the singing males. If the fan is assumed to be homologous between males and females, the two veins inside these long fans must be MA and MP. RP would then be in the continuity with M, while the latter usually separates from RP and extends into the fan where it branches into MA and MP: RP thus strongly resembles an anterior branch of M ( Fig. 5C, D ). Indeed, the vein identified here as RP is slightly concave in females (in ventral view). The strongly marked median fold between the lateral and dorsal fields leads to a strongly reduced CuA, which is hard to see. CuA merges with CuPa, i.e., the most anterior vein of the dorsal field. The latter is concave at its base and becomes convex distally close to M+CuA, suggesting a fusion of CuA with CuPaα as in singing males. Males without an apparatus have no CuPb at all. The veins posterior to the CuPa are PCu, notably curved at base and always with two branches PCuA and PCuP, and A, divided into AA and AP.

Figures

FIG. 3. — Hypothesis of primary homology of venation of male Grylloidea:A, Natula longipennis (Serville, 1838) (MNHN-EO-ENSIF9933, Trigonidiidae);B, Lerneca fuscipennis (Saussure, 1874) (MNHN-EO-ENSIF9780, Phalangopsidae). Abbreviations and colour code: see text. Scale bars:1 mm.

FIG. 4. — Hypothesis of primary homology of venation of male Grylloidea: A, Brachytrupes membranaceus (Drury, 1773) (MNHN-EO-ENSIF9769, Gryllidae); B, Phyllogryllus sp. (MNHN-EO-ENSIF9768, Oecanthidae). Abbreviations and colour code: see text. Grey dash lines represent folds. Scale bars: 5 mm.

FIG. 2. — Main fields (A, C) and functional structures (B, D) of a male grylloid forewing (A, B: Brachytrupes membranaceus (Drury, 1773), MNHN-EO-ENSIF9769) and a male gryllotalpid forewing (C, D: Scapteriscus sp., MNHN-EO-ENSIF3068). Abbreviations: lc, lanceolate cell; ha, harp; mi, mirror. Scale bars: 5 mm.

FIG. 1. — Theoretical pattern of venation of a gryllidean forewing (terminology after Béthoux & Nel [2002], modified after Schubnel et al. [2020]). Abbreviations and colour code: see text.

FIG. 5. — Hypothesis of primary venation homology in male Grylloidea with particular forewing venation:A, B, species with ‘shortened’ wings; B, C, species with ‘reduced’ stridulatory apparatus.A, Landreva sp. (MNHN-EO-ENSIF9775, Gryllidae); B, Nemobius sylvestris (Bosc, 1792) (MNHN-EO-ENSIF9786, Trigonidiidae); C, Tafalisca lineatipes Bruner,1916 (MNHN-EO-ENSIF9760, Oecanthidae);D, Aphonomorphus sp.(MNHN-EO-ENSIF9764, Oecanthidae).Abbreviations:‘ha’, distally opened harp; ‘mi’ distally opened mirror; others and colour code: see text. Grey dash lines represent folds. Scale bars: 1 mm.