Aglaothorax sphenosternum Cole, Weissman, and Lightfoot, 2025

Cole, Jeffrey A., Weissman, David B., Lightfoot, David C., Ueshima, Norihiro & Warchałowska-Śliwa, Elżbieta, 2025, A revision of the shield-backed katydid genus Aglaothorax (Orthoptera: Tettigoniidae: Tettigoniinae: Nedubini), Zootaxa 5667 (1), pp. 1-104 : 67-70

Aglaothorax sphenosternum Cole, Weissman, and Lightfoot , sp. nov.

Fig. 15 (distribution), Fig. 27 (male and female habitus, calling song, male and female terminalia, karyotype), Plate 5 (male terminalia), Plate 8 (female subgenital plate), Plate 12 (male titillators), Plate 15 (male calling song).

Common name. Wedge-breasted Shieldback.

History of recognition. None.

Type material. HOLOTYPE MALE: México, Baja California, 11 miles east of Ojos Negros on road to Laguna Hanson , 31.90864N, 116.07022W, 1160 m, 9-VIII-1988, DB Weissman, DC Lightfoot, S 88-85, R88-124 , T88-58 , 3.0 [stridulatory file length, mm], 104 [stridulatory file tooth count], excised tegmen in gelcap below specimen, deposited in CAS, Entomology type #20376 . PARATYPES: (n=8) México, Baja California, 11 mi. E of Ojos Negros on road to Laguna Hanson , 31.908643, -116.070218, 1160 m, 9-VIII-1988, DB Weissman, DC Lightfoot, CAS, 2♂, 3♀ ; Laguna Hanson Road, 18 km east of Ojos Negros , 31.91139, -116.11694, 1033 m, 28-VI-2019, JA Cole, DB Weissman, LACM, 3♂ .

Measurements. (mm, ♂ n=7, ♀ n=1) Hind femur ♂ 12.78–13.80, ♀ 15.13, pronotum total length ♂ 7.65–8.47, ♀ 7.25, prozona length ♂ 3.42–4.56, ♀ 3.63, metazona dorsal length ♂ 3.80–4.63, ♀ 3.62, pronotum constriction width ♂ 2.60–2.84, ♀ 2.69, metazona dorsal width ♂ 5.26–6.57, ♀ 5.05, head width ♂ 3.46–3.90, ♀ 4.05, ovipositor length ♀ 9.01.

Distribution. Northern Baja California, México.

Habitat. Chaparral. On Yerba Santa, Laurel Sumac, and Salvia spp.

Seasonal occurrence. Sparse records span summer (28-VI-2019, JA Cole & DB Weissman, CAS to 9-VIII-1998, DB Weissman & DC Lightfoot, CAS) .

Stridulatory file. (n=3) length 2.90–3.10 mm, 92–107 teeth, tooth density 33.6±1.7 (31.7–34.7) teeth/mm.

Song. (n=6) Standard small Aglaothorax song type with a slow pulse train rate. Pulse trains 70±10 ms are repeated at a rate of 6.08± 0.44 s- 1. Mean peak frequency is 15.48±0.35 kHz. Echemes contain a variable number (mean 14 ± 7, range 4–26) of pulse trains repeated at rates between 7 and 14 min-1.

Karyotype. (n=5) 2n ♂ =22 (2m + 18t +XtYt), holotype T88-58 (S88-85). The presence of one pair of metacentric autosomes, combined with an autosome number reduction from 22 to 20 when compared with other widespread Morsei Group members, is most easily explained by a Robertsonian fusion involving two telocentric pairs.

Recognition. Morphology, karyotype. Both sexes may be diagnosed by the broad, conical prosternal spines, in contrast to the long, thin, spines typical of other Morsei and Diminutiva Group species. In addition, males have a concave supra-anal plate, which contrasts with the flat, square plate of A. nesiazo to the north. Male A. sphenosternum also have long, thin, cylindrical paraproct processes, unlike San Diego County , California A. nesiazo or the two other Baja California species A. bufonoides and A. kelainops . The apical paraproct tooth eliminates A. costalis , A. morsei , and A. hulodomus from consideration. The male titillator arms are short and nearly straight, unlike the arms of A. bufonoides that are smoothly curved laterally. The male stridulatory file tooth density is higher than both other Baja California species at 33.6 ± 1.7 teeth/mm versus 29.3 ± 3.2 in A. bufonoides and 26.2 ± 0.9 in A. kelainops . Female A. sphenosternum have the subgenital plate lateral processes as long as wide, whereas A. kelainops females have those processes slightly longer than wide. This is the only Aglaothorax with a 2n ♂ =22 karyotype.

Etymology. G. spheno wedge + sternum breast, breastbone. Descriptive of the conical prosternal spines that help diagnose this species.

Notes. Like A. kelainops (see species account above p. 64), this species is genetically related to a subset of A. bufonoides , albeit to a different subset of populations ( Figs. 3–4 ). A chromosome evolution hypothesis that explains the reduction in chromosome number from 2n ♂ =24 to 2n ♂ =22 is Robertsonian fusion, during which two pairs of telocentric autosomes underwent centric fusion. Once evolved, such divergent karyotypes may create reproductive isolation through reduction in hybrid fitness ( Shaw et al. 1998; White 1978). Reproductive isolation via chromosome differences may explain the biogeography, where closely situated populations do not overlap in sympatry ( Fig. 15 ). Songs are statistically identical, thus reinforcement of premating isolation via calling songs has not occurred as in other nedubines with ( Neduba duplocantans Cole, Weissman, and Lightfoot 2021 ; Cole et al. 2021) and without ( Aglaothorax costalis ; Cole 2016, also see species account above p. 43) chromosome differences.

Material examined. See Type Material above. QUESTIONABLE PLACEMENT: (n=2) México, BCN , 11.2 km E Ojos Negros on road to Laguna Hanson , 31.908726, -116.139372, 1200 m, 2-VIII-1981, DB Weissman, DC Lightfoot, CAS, 1♂ ; 17.9 km E Ojos Negros on road to Laguna Hanson , 31.90864, -116.068237, 1463 m, 29-VII-1978, DB Weissman, DC Lightfoot, CAS, 1♂ .

Diminutiva Group

The Diminutiva Group is, like the Morsei Group, a clade of small Aglaothorax . The prosternal spines are typically long and divergent, occasionally reduced and nipple-like. Like the other Aglaothorax species Groups, chaetotaxy is more variable within species than between ( Table 4). The male supra-anal plate of this group is characteristically heart-shaped, indented along the posterior margin and expanded posterolaterally into two lobes ( Figs. 28–33 , Plate 6). The male subgenital plate has a wide posterior margin that is rounded to transverse and with long cylindrical styli ( Figs. 28–33 ). The male paraprocts have the internal tooth situated apically ( Figs. 28–33 , Plate 6). In all but one species ( A. constrictans ) the male titillator arms are long, slender, and strongly curved laterally, often bowed (Plate 13). The female subgenital plate in all but one species (again A. constrictans ) has long, digitiform lateral processes ( Figs. 28–33 , Plate 9). The female ovipositor is shorter than the hind femur, approximately 3/4 its length, and regularly upcurved ( Figs. 28–33 ).

Diminutiva Group males produce a calling song with irregular, often long echemes (bouts) of widely spaced pulse trains (Plate 15). Male choruses may synchronize or alternate pulse train production. The acoustical activity of several species may begin late at night and continue until dawn, becoming more frequent as the night progresses.

The Diminutiva Group is most speciose in the South Coast Ranges of California, but a widespread species occurs in the Tehachapi Mountains at the eastern extreme of the Transverse Ranges where they join the southern Sierra Nevada ( Fig. 28 ). The Transverse Ranges represent a region of sympatry with members of the Morsei Group marked by extensive mitochondrial capture ( Fig. 3 ). Apart from incidences of capture, the Diminutiva Group species are well resolved phylogenetically ( Figs. 2–4 ).

Figures

FIGURE 2. Bayesian consensus tree of nDNA matrix. Nodes with less than 85% posterior probability are collapsed. Terminals in red show mitochondrial capture in Fig. 3.

FIGURE 3. Bayesian consensus tree of mtDNA matrix. Nodes with less than 85% posterior probability are collapsed.Terminals in red are Diminutiva Group exemplars that experienced mitochondrial capture into the Morsei Group.

FIGURE 4. Bayesian consensus tree of concatenated matrix. Terminals in red show exemplars involved in mitochondrial capture.

PLATE 5. Male terminalia of Morsei Group, dorsal view.

FIGURE 15. Distribution of Morsei Group species.

FIGURE 27. A. sphenosternum male and female habitus, calling song, male and female terminalia, and idiogram A. Karyotype 2n♂=22 showing largest autosomal pair M composed of metacentric chromosomes; B. Sex chromosomes X and Y, in same male, are marked and associated (without apparent chiasmata), to ensure proper segregation at anaphase.

FIGURE 28. Distribution of Diminutiva Group species.

FIGURE 29. A. diminutiva male and female habitus, calling song, male and female terminalia, and karyotype.A. Idiogram, A. diminutiva, type locality T82-114 (S82-113) showing X1X2Y sex chromosome system; B. Metaphase I in same male showing association of all 3 sex chromosomes, with submetacentric X1 and submetacentric Y apparent.

FIGURE 30. A. constrictans male and female habitus, calling song, male and female terminalia, and karyotype. Idiogram shows karyotype 2n♂=24.

FIGURE 31. A. dactyla male and female habitus, calling song, male and female terminalia, and karyotype. Idiogram shows karyotype 2n♂=24.

FIGURE 32. A. acrolophitus male and female habitus, calling song, male and female terminalia, and karyotype. Idiogram shows karyotype 2n♂=24.

FIGURE 33. A. oreibates male and female habitus, calling song, male and female terminalia, and karyotype. Idiogram shows karyotype 2n♂=24.