Four New Katydid Species Hidden in Sichuan’s Mountains Revealed by DNA and Anatomy

Taxonomists working in the mountains of western Sichuan, China have doubled the known diversity of a little-known genus of bush crickets, describing four new species of Sichuana and refining the genus’s diagnosis in a study that combines detailed morphological comparison with mitochondrial DNA analysis. The genus, previously known from just two species, now contains six, all of them apparently confined to a small corner of Sichuan Province.

Sichuana Shen & Yin, 2020 belongs to the subfamily Tettigoniinae, tribe Drymadusini, and was originally erected on the strength of two species, S. cryptospina and S. feicui, found in Wenchuan County and Mao County of western Sichuan. The genus is set apart from its relatives by a distinctive suite of traits: lateral carinae on the pronotum that are distinct in the metazona but only faintly indicated on the prozona, a pair of spines on the prosternum, female tegmina only slightly longer than the pronotum, and male cerci that are strongly incurved in the middle with acute tips and an inner tooth near their base.

The new species, named S. planicercata, S. curvicercata, S. longilamina and S. magnicerca, were all collected in August 2022 in Xiaojin County and Li County within the Ngawa Tibetan and Qiang Autonomous Prefecture, at altitudes ranging from roughly 2000 to 2800 meters. The specimens, including holotypes, are deposited in the collection of the Department of Plant Protection of Sichuan Agricultural University in Chengdu. Each species was separated from its relatives by a combination of characters in the male terminalia, the female tenth abdominal tergite, the stridulatory apparatus and the shape of the ovipositor.

S. planicercata, whose name reflects its flat, unbent male cerci, is distinguished by a pair of very short round projections on the posterior margin of the male tenth abdominal tergite and an inner cercal tooth that rises far above the top of the cercus in lateral view. Its closest relative, S. curvicercata, instead has male cerci that curve ventrally with the apex pointing dorsally, a thick, nearly straight inner tooth that becomes sharp only at its tip, and a wide trapezoidal projection on the female tenth abdominal tergite. The two species were collected at nearby sites in Xiaojin County, at about 2700 and 2800 meters respectively.

S. longilamina, from Guergou in Li County at about 2400 meters, takes its name from the elongated male subgenital plate, whose long styli measure about one-third of the plate’s length. Its male cerci are strongly incurved at an acute angle and point dorsally, and its stridulatory file carries roughly 34 teeth, notably more than the approximately 20 teeth of S. planicercata or the 18 of S. curvicercata. S. magnicerca, from Zagunao town in Li County at about 2000 meters, is defined by unusually large and long male cerci that extend beyond the subgenital plate, a small inner tooth inserted at the very base of the cercus, and a U-shaped notch on the male tenth abdominal tergite.

To test whether these morphological differences correspond to genuine species boundaries, the team extracted genomic DNA from hind-leg muscle and sequenced two mitochondrial markers: the cytochrome c oxidase subunit I gene, COI, and the large-subunit rRNA gene, 16S. Genetic distances were estimated in MEGA11 using the Kimura-2-parameter model with 1000 bootstrap replicates. The COI sequence divergences among Sichuana species ranged from 2.208% to 15.688%, and divergences between most species exceeded 8%. The single exception was the pair S. planicercata and S. curvicercata, which showed a mean divergence of 2.208% — low by comparison with other species pairs, but still well above their own intraspecific means of 0.586% and 0.305%.

That pattern matters because previous work on insects has shown that COI divergences within species are rarely greater than 2% and are mostly below 1%. The 16S marker, which evolves more slowly, showed correspondingly lower divergences, ranging from 0.830% between S. planicercata and S. curvicercata to 5.900% between S. curvicercata and S. feicui. Together, the two markers support the recognition of six distinct lineages within the genus.

For the phylogenetic analysis, the team used COI sequences with two related species, Mongolodectes huangxinleii and Atlanticus fengyangensis, as outgroups. Bayesian inference was run in MrBayes 3.2.7 for 1,000,000 generations with four chains, and maximum-likelihood analysis was performed in IQ-tree 1.6.2 under the TVM+F+I model with 10,000 ultrafast bootstrap replicates. The two methods produced almost identical topologies. S. feicui occupies the earliest position, sister to all other Sichuana species. The remaining species split into two clades: one containing S. magnicerca, S. cryptospina and S. longilamina, and another containing S. planicercata and S. curvicercata. Within the latter pair, the maximum-likelihood tree resolved some samples of S. curvicercata as sister to the clade containing S. planicercata and the remaining S. curvicercata samples, whereas the Bayesian tree resolved the two species cleanly — a small discrepancy the authors note between methods.

Beyond the species descriptions, the large sample size allowed the researchers to document something rarely quantified in living orthopterans: substantial variation in wing venation within species. The position where the radius vein forks into RA and RP, the branching point of the media vein, the end of ScA, and even the fusion of certain longitudinal veins proved unstable among individuals — and in some cases between the left and right tegmina of a single individual. In S. planicercata, for example, R sometimes fuses distally with ScP and separates again immediately, while in S. magnicerca RP occasionally fuses with M. By contrast, the bifurcations of R and M are usually stable in fossil ensiferans, a group where wing venation is heavily used in classification. The authors argue that more documentation of venational variation in extant orthopterans would provide a better reference for interpreting fossil material.

The male subgenital plate also varied between individuals, particularly in the shape and width of the notch on its posterior margin, most noticeably in S. planicercata. Taken together, the morphological comparisons and molecular results led the authors to conclude that assigning the specimens to four new species is justified, bringing Sichuana to six species and sharpening the diagnostic characters that separate it from related Drymadusini genera such as Uvarovina, Ptosoproctus, Eulithoxenus and Atlanticus. The study also maps the distributions of all six species across western Sichuan, underscoring how much insect diversity can remain undocumented in a single mountainous province — and how combining classical anatomy with DNA barcoding can bring it to light.

Subject of Research: Taxonomy and molecular phylogeny of the katydid genus Sichuana with four new species from Sichuan, China

Article Title: Phylogeny of genus Sichuana Shen & Yin, 2020 ( Orthoptera , Tettigoniidae , Tettigoniinae ) with four new species from Sichuan, China

Article References: Gu, J.-J., Zheng, C., Jiang, S.-R., & Yue, Y. (2023). Phylogeny of genus Sichuana Shen & Yin, 2020 (Orthoptera, Tettigoniidae, Tettigoniinae) with four new species from Sichuan, China. Deutsche Entomologische Zeitschrift, 70(2), 337-355. https://doi.org/10.3897/dez.70.105870

Image Credits: AI Generated

DOI: 10.3897/dez.70.105870

Keywords: Sichuana, Tettigoniidae, Orthoptera, new species, taxonomy, mitochondrial DNA, COI, 16S, phylogenetics, Sichuan, China, bush crickets