Griburius consanguineus, Sassi, 2024

Sassi, Davide, 2024, Revision of the Griburius posticatus (Suffrian, 1866) species group (Coleoptera: Chrysomelidae: Cryptocephalinae), Zootaxa 5406 (2), pp. 201-237 : 229-236

Griburius consanguineus sp. nov.

urn:lsid:zoobank.org:act:2E93B922-632D-456A-A47B-C42E5BE1D03D

(Figs 10; 11a; 13d)

Types. HOLOTYPE: ( MNHN) ♂, body and detached abdomen glued on the same card, aedeagus glued on a different card // “ Jatahy Etat de Goyaz Ch. Pujol 1895-96” [white label, printed] // “ Griburius consanguineus sp. nov . HOLOTYPUS D. Sassi des.” [red label, printed] //. PARATYPES (16): ( MNHN) 1♀, same data of the holotype; ( USNMNH) 1♂ // “ Goiás Jataí 1/9” [white label, partly printed] // “ F. Monros Collection 1959” [white label, printed] //; ( MNHN) 1♂ // “ Jatahy Etat de Goyaz Ch. Pujol 1898” [white label, partly printed] //; ( NMPC) 1♂ // “Brésil Goyaz Rio Verde ” [white label, printed] // “ex coll. J. Achard National Museum Prague, Czech Republic ” [white label, printed] //; ( NMPC) 1♂ // “ Mineiro Goyaz Brésil” [white label, printed] // “ Metallactus Griburius posticatus Suff ,” [white label, handwritten] // “ex coll. J. Achard National Museum Prague, Czech Republic ” [white label, printed] //; ( NMPC) 1♂ // “ Mineiro Goyaz Brésil” [white label, printed] // “ Gr posticatus S.” [white label, handwritten] // “ex coll. J. Achard National Museum Prague, Czech Republic ” [white label, printed] //; ( USNMNH) 1♀ // “Jatahy (Goyaz) [white label, printed] // “gift of F. C. Bowditch ” [white label, printed] // “498” [pink label, printed] // “ Metallactus posticatus Suffr ” // [white label, handwritten] //; ( CEMT, BMNH) 4♂ 2♀ // “ Brazil: Mato Grosso Cuiabá, near Belvedere 15°36´06´´S 56°01´45´´W ca. 200 m, 25.XI.2018 M. Geiser & J. Cristovão leg. Sweeping & beating Cerrado” [white label, printed] // “BMNH {E} 2018-179” [white label, printed] //; ( MNHN) 1♀ // “Jatahy (Goyaz) [white label, printed] // “Museum Paris 1937 Coll. Ch Demaison ” [white label, printed] //; ( MNHN) 2♀ // “Trindade (Goyaz) Ch. Pujol ” [white label, printed] //. All paratypes are also labelled: // “ Griburius consanguineus sp. nov. PARATYPUS D. Sassi des.” [red label, printed] //.

Type locality. Jataí (Goiás, Brazil).

Etymology. The specific name is the Latin adjective consanguineus (- a, - um), meaning “kindred”, given the strong external similarity with G. posticatus .

Distribution. Brazil (Goiás, Mato Grosso).

Diagnosis. The species is clearly very close to G. posticatus to the point that it cannot be clearly distinguished based on external traits, however the shape of the apex of the aedeagus is rather significantly different, being less squared in the new species. Furthermore, in G. posticatus on each side the setose depression is separated from the glabrous depression by a tiny but prominent septum, which sharply separates the two structures (Figs 4k–m). In G. consanguineus , such separation is very uncertain, as a dividing septum prominent on the ventral surface is basically lacking (Fig. 10k). Additionally, the spermatheca duct is clearly coiled, unlike what is observed in G. posticatus . The evaluation is unfortunately made on a limited number of specimens, but the shape (straight or coiled) of the spermatheca duct seems to represent, at the current state of knowledge, a trait generally very significant for the distinction at the species level in South American Pachybrachina .

Description of male. Habitus in figs 10a–b (HT). BL = 4.3–4.7 mm, BW = 2.7–3.0 mm, PL = 1.5–1.6 mm, PW = 2.5–2.9 mm. Interocular distance 9.3–10.6 % of BL.

Head entirely black, labrum brownish.Vertex and frontoclypeal surface covered with almost regularly distributed punctation, only a little denser between the ocular canthi. Setosity sparse except for a transverse band between ocular canthi, where rather dense, appressed, and silver-coloured. Mid-cranial suture barely noticeable to totally obliterated. Upper lobes of eyes well separated from each other. Ocular lines barely visible, strictly adhering to ocular rim. Antennae normal in shape, first five antennomeres yellowish, bright, 3–5 subcylindrical, the subsequent ones gradually darker, dull, moderately flattened and more diffusedly setose.

Pronotum reddish or chestnut with four rounded black spots just beyond middle of disc, two median ones larger. Sometimes black spots reduced or missing. Pronotal shape elliptical, scarcely transverse, with regularly curved, narrow lateral margins. Maximum width at around middle. Surface moderately convex, flattened above all behind midline. Surface relatively shiny, covered with fine punctation, denser along sides, almost obliterated at center of disc. Posterolateral impressions short and shallow, but usually perceptible.

Scutellum black, sometimes reddish at middle, clearly raised, minutely punctured, covered with whitish setae, subtriangular with apex cut in sharp line.

Elytron reddish as well, sometimes slightly lighter than pronotum, with single rounded spot just behind midpoint of elytron, approximately between second and fourth interstices. At times, suture, epipleuron and humeral calli weakly darkened as well. Elytral outline with short dorsal profile, not curved at the sides. Sides weakly converging towards apex. Lateral margins rather narrow, barely visible simultaneously from above. Scutellar area perceptibly raised. Humeral callus prominent, impunctate. Surface with dense punctation rather confusedly arranged on anterior half, finer and distributed in almost regular rows toward apex. Epipleuron shiny, not punctured, with flat surface.

Pygidium brownish, with margins sometimes slightly lighter. Surface matt, covered with very fine punctation and short, rather sparse setae.

Hypomera red-brown, remainder of ventral surface ranging from dark brown to black. Hypomera shiny not punctured, essentially glabrous. Remainder of ventral surface matt, covered with fine punctation and short, whitish setae. Prosternal process moderately wide, depressed along the midline, with surface covered with coarse punctures and rather long, partly semi-erect setae. Apex of prosternal process triangular, ending with blunt tip. Legs entirely black, anterior tarsi stout and widened.

Median depression on fifth abdominal ventrite shallow, diffusedly setose, barely distinguishable from remainder of ventrite surface but for lighter coloration. Posterior margin of fifth abdominal ventrite straight. In lateral view median lobe of aedeagus (Figs 10h–m) scarcely compressed dorso-ventrally, then noticeably narrowed towards apex, terminated with rather wide, blunt, apical denticle, with sloping sides towards the anterior margin of the shaft. Apex straight, i.e., not bent ventrally in lateral view. Setose depressions narrow, shifted on sides, setose only along external margins, barely separated from glabrous depressions due to lack of evident partition septum (Figs 10h–k). Aedeagal ventral surface with long sharp median carina, often slightly concave at middle in lateral view.

Female. BL = 5.1–5.8 mm, BW = 3.2–3.8 mm, PL = 1.6–1.7 mm, PW = 3.0– 3.4 mm. Interocular distance 12.1–13.7 % of BL.

In females, both the “ posticatus form” and the “ rufomarginatus form” have been observed with approximately the same frequency. In the “ rufomarginatus form”, the pronotum is entirely black or, more rarely, reddish along margins. The elytron is reddish with a large black patch extending from the suture to the lateral margin. This spot leaves a wide reddish band along the anterior margin and a circular area, reddish as well, at the elytral apex. In some cases, the black patch is narrower, not reaching the lateral margin. The “ posticatus form” in females does not differ significantly from males in dorsal coloration.

The fifth abdominal ventrite in females has a large, almost circular, deep pit. The bottom of the pit is bald, covered by tiny punctures and wrinkles. The vasculum of spermatheca (Fig. 11a) is scarcely pigmented, slender, with the proximal lobe slightly bent at base, scarcely swollen. The distal lobe is slender as well, long, almost straight, often with a sharp apex bent downward. The ampulla is short, not pigmented. The duct insertion and the sperm gland insertion are well separated. The duct is rather short, slender, coiled, with the coils never forming a real tangle outside or close to the vasculum. The insertion on bursa copulatrix is usually slightly enlarged, not pigmented but in a single specimen from Ponta Grossa (Paraná) it is strongly pigmented. It would be premature to attribute a particular taxonomic value to this single piece of data.

Remarks. The morphology of the median lobe of the aedeagus in the type series is different from that of G. posticatus , (Figs 10h–m and figs 4k–n) in a way that is sufficient to justify the belief that we are dealing with two distinct taxa. This is confirmed in females by the structure of the spermathecal ductus (Fig. 11a and Fig. 11d). However, it should be noted that in most of the Brazilian specimens available for study the two sexual characteristics mentioned above can show quite a strong variability, and in some cases, there may be some difficulty in confidently attributing the specimens to G. posticatus or G. consanguineus . This could suggest a local incomplete genetic isolation of the two species and the presence of intermediate forms. This situation has long led me to refrain from formally proposing a new taxon and, instead, report the presence of unusual morphological plasticity within a highly variable G. posticatus . However, it is undeniable that this variability has a strong geographical component, as in the Jataí and Cuiabá areas, the morphological peculiarities seem well characterized and sufficiently stable, while in many examined specimens from the westernmost portion of the G. posticatus range ( Paraguay and Bolivia but also Argentina), no evident variations from the typical G. posticatus configuration have ever been observed. For this reason, it was deemed appropriate to formally describe the new species. Indeed, considering what has been stated above, G. consanguineus might have been assigned a subspecific rank, but, given the limited knowledge of population dynamics, it is believed that, at present, the rank of a distinct species represents the hypothesis that requires fewer unproven assertions.

Unfortunately, it was not possible for the new taxon to retain the name G. distigma , described from Brazil ( Suffrian, 1866) and here synonymized with G. posticatus , because the lectotype, although showing some slight difference in the aedeagal apex compared to the populations from Paraguay, Bolivia, and Argentina, cannot be considered representative of the form from Jataí and Cuiabá.

The proposal of the new species, well characterized and decidedly stable in aedeagal morphology, unfortunately does not completely resolve the problem of how to taxonomically interpret the many Brazilian specimens attributable to G. posticatus but showing quite a strong variability in the morphology of the aedeagal apex compared to the form observed in the lectotype and, generally, in the Paraguayan, Argentine and Bolivian populations. The morphology of the spermathecal duct further complicates the problem, because in these possible transition forms the “conformation” observable in G. consanguineus seems to be the most common across the Brazilian territories. The decision taken was therefore, regarding the males, to consider as belonging to G. consanguineus only the specimens from Goiás and Mato Grosso with characteristics clearly referable to what is reported in the diagnosis and description of the new species (see also figs 10h–m) and attributing all specimens of uncertain determination to G. posticatus . Regarding the females, since, as mentioned, the spermathecal duct morphology shows an unexpected “convergence” in the Brazilian populations of the two species, only those specimens whose “coexistence” with G. consanuineus males seemed more certain were assigned to the type series.

Based on what has been said, it goes without saying that the complex of species G. posticatus , G. consanguineus and G. bicoloratus , together with the taxonomic entities synonymized here ( G. distigma and G. rufomarginatus ) constitutes a particularly complex taxonomic problem, centered on an aggregate of widely distributed South American species morphologically very close and extremely variable in coloration and in some morphological traits.Additionally, besides the forms discussed in this work, other studied specimens suggest the presence, in Minas Gerais and Mato Grosso, of at least two other taxa very similar to the species treated here, but with particularly distinct aedeagal traits, however the limited data (no more than two males for each possible further distinct taxon) suggests for the moment to abstain from proposing their taxonomic treatment.

The limitation of the available data unfortunately does not allow for a definitive clarification and therefore the decisions made in this work could reveal themselves as not completely shareable in the light of future research. It is hoped, however, that this study will stimulate further studies on this extremely difficult group of species.