Perlesta sublobata South & DeWalt

South, Eric J., DeWalt, R. Edward, Davis, Mark A. & Thomas, Michael Jared, 2019, A new stonefly species (Plecoptera, Perlidae) from the Interior Highlands USA, with morphological and molecular comparison to other congeneric species, ZooKeys 858, pp. 45-70 : 48-59

Perlesta sublobata South & DeWalt sp. nov. Figs 1, 2, 3, 4, 5, 6

Diagnosis.

Males are distinguished by a combination of a prominent ventral caecum with a broad ventral setal patch and a distinct dorsal extension of the lateral sclerites of the aedeagus. Females possess a subgenital plate with a deep V-shaped notch and truncate lobes. Eggs have a smooth chorion and a well-developed, distally flanged collar.

Male. Habitus moderately dark (Fig. 2A). Wings: Membrane brown with dark brown venation and pale intercostal margin (Fig. 2B, C). Forewing: Length 8-9 mm (mean = 8.3 ± 0.3 SD, n = 95); membrane with two lightly pigmented longitudinal bands: one posterior to the posterior cubital vein and a second anterior to the median vein (Fig. 2B). Head: Pale with dark brown quadrangular patch covering interocellar region; brown subtriangular patches anterolateral and anteromedial to median ocellus (Fig. 2D, E); diffuse brown pigmentation posterior to ecdysial suture (Fig. 2D); ecdysial suture extends slightly to moderately beyond ocelli as a distinct dark line; antenna darkly pigmented on ca. distal 2/3 of flagellum and dorsomedian region of scape; proximal antennal segments pale with tan dorsal pigmentation. Thorax: Pronotum brown with vermiculated rugosities and faint, pale median stripe (Fig. 2D, E); mesothoracic and metathoracic nota brown; mesothoracic and metathoracic basisterna pale; femur and tibia pale, brown dorsally. Abdomen: Sterna pale; terga pale medially and light brown laterally, or uniformly brown. Terminalia: Tergum 10 with dark subquadrate pigment patch (Fig. 3A) and 10-20 small, sensilla basiconica (visible at 80 × magnification); cercus long (holotype = 15 segments), pale proximally and dark brown distally; paraprocts broad basally and narrowed distally in caudal aspect (Fig. 3B); anteapi cal paraproct spine and carina directed anteromedially—best visible in oblique lateral view of unextruded individuals (Fig. 3C, D). Aedeagus: Dorsal caecum moderately produced, ca. as long as wide and broad apically (Fig. 4A, B); dorsal patch broad over sac, moderately expanded proximally, constricted subapically, and broadly expanded over caecum; prominent lateral sclerites merge dorsally to form a distinct V-shaped pattern extending more than 1/2 tube length (Fig. 4C, D); prominent ventral caecum, narrowed apically, with a broad patch of fine seta-like spines covering venter and apex, length ca. 2/5 sac width; sac with fine seta-like spines covering venter (Fig. 4E, F).

Female. Female habitus similar to male, but of larger size and wings of lighter pigmentation (Fig. 5A). Pronotum tan with brown vermiculated rugosities and pale median stripe (Fig. 5B). Wings with subhyaline membrane, tan venation, and pale intercostal margin (Fig. 5C, D). Forewing length 9-11 mm (mean = 9.8 ± 0.6 SD, n = 40); often with two unpigmented longitudinal bands: one posterior to the posterior cubital vein and a second anterior to the median vein (Fig. 5C). Subgenital plate lobes truncate medially and truncate to slightly rounded laterally, slightly to moderately pigmented, covered with long bristle-like hairs, and separated by a deep V-shaped notch (Fig. 5E, F).

Egg. Length ca. 360 µm, width ca. 280 µm. Chorion smooth with fine pitting (Fig. 6A). Collar well developed, ribbed, and flanged distally (Fig. 6B). Micropylar orifices distinct near anterior pole (opposite collar) (Fig. 6C).

Molecular analyses.

Perlesta sublobata formed a monophyletic group with strong support (ML bootstrap support = 97%, Bayesian posterior probability = 92%). The nearest neighbor species to P. sublobata was P. decipiens (Walsh, 1862) at 1.8% sequence divergence. Maximum intraspecific COI genetic distances were less than minimum interspecific distances within all tested Perlesta (Table 2). All intraspecific distances were less than the arbitrary threshold of 3.5%, suggesting that the new species was monophyletic without other cryptic species present within the new taxon ( Hebert et al. 2003, Zhou et al. 2010). All haplotypes (total = 47) were confined to their respective genera and presumptive species in the ML and Bayesian analyses (Figs 7, 8, respectively). The three tested species within the P. frisoni group, consisting of five Nearctic species that lack an aedeagal dorsal caecum, formed a monophyletic grouping. Four of the five “dark” species studied in Grubbs and DeWalt (2018) also formed a monophyletic grouping. The placement of P. adena Stark, 1989 outside this group may be spurious, indicating additional genes or populations are needed for further refinement. The relatively distant placement of P. golconda DeWalt & Stark, 1998 from P. sublobata is congruent with the species’ distinctly different morphologies, apart from the male genitalic similarities.

Remarks.

The shape and armature of the aedeagus are the most distinct morphological features of P. sublobata . Stark (1989) illustrated a lateral view of an undetermined species from Arkansas ( P. sublobata ), demonstrating spinule patterns and shape of the aedeagal telescoping sections: envelope, tube, and sac. He noted that lateral sclerites of the tube joined dorsally. This dorsal extension of the lateral sclerites was not illustrated or specified in the literature for any other Perlesta . Furthermore, a ventral caecum is present in P. sublobata and only one other described congener, P. golconda . However, the ventral caecum of P. golconda is less prominent and without a distinct ventral patch of fine seta-like spines. Additionally, the dorsal caecum of P. sublobata is moderately developed, compared to the poorly developed dorsal caecum of P. golconda (Fig. 9).

The known distribution of P. golconda , originally limited to Illinois (DeWalt and Stark 1998), has expanded to include Iowa, Indiana, Michigan, and Nebraska ( DeWalt et al. 2019), as well as Missouri ( Stark 2004) and Louisiana (INHS Insect Collection 564765). Arkansas is bordered by Missouri to the north and Louisiana to the south. A sympatric distribution with P. sublobata is expected due to this geographic adjacency and overlap of the Interior Highlands’ habitat. Consequently, re-examination of some museum specimens may be required. The male and female habitus easily distinguish P. golconda from P. sublobata . The ocelli of P. golconda are usually connected by a moderately dark V-shaped pattern on a pale background (Fig. 10A, B), whereas P. sublobata has a dark subquadrate interocellar region. The pronotum of P. golconda is primarily pale with light tan rugosities on the lateral margins, whereas P. sublobata has a dark pronotum with a pale narrow median stripe. Additionally, P. golconda females are dis tinguished by a very short egg collar ( Grubbs and DeWalt 2008, their fig. 17) and rounded subgenital plate lobes (Fig. 11A, B).

The female habitus of P. sublobata resembles two Interior Highlands congeners, P. decipiens and P. ephelida Grubbs and DeWalt, 2012. However, P. sublobata differs from P. decipiens and P. ephelida by subgenital plate morphology. Perlesta decipiens has a deep U-shaped notch bordered by truncate lobes, typically with darker pigmentation on the posterior margins (Fig. 12). Perlesta ephelida has a shallow V-shaped notch enclosed by truncate lobes, usually pale to lightly pigmented with posteromedially upturned margins (Fig. 13; Grubbs and DeWalt 2012, their fig. 7). These characters are contrasted to the deep V-shaped notch and moderately pigmented, truncate lobes of P. sublobata . Furthermore, P. sublobata has a shorter forewing length than P. decipiens ( P. sublobata = 9-11 mm; P. decipiens = 12-13 mm, Stark 2004). Egg chorion and collar are similar to P. decipiens ( Stark 2004, his figs 7.397-7.399) and P. ephelida ( Grubbs and DeWalt 2012, their figs 14-21).

Habitat.

With the exception of one locality (OK, Washington Co., Caney River), all collection sites for P. sublobata are within or closely adjacent to the Interior Highlands, a region containing four contiguous U. S. Environmental Protection Agency (EPA) Level III Ecoregions: Ozark Highlands, Boston Mountains, Arkansas Valley, and Ouachita Mountains. Collection sites for P. sublobata within the Interior Highlands are partially canopied, hardwood forested, wadeable, low gradient streams (ca. 15-20 m wide) with substrata composed mostly of sand, gravel, and cobble. The type locality is a low gradient run (ca. 25 m wide) of the Little Missouri River (Fig. 14), located 45 km downstream of Lake Greeson and 65 km upstream from its confluence with the Ouachita River in the extreme north EPA Level III Ecoregion 35 (South Central Plains). The substrate is primarily gravel and sand, with some large woody debris. Other stonefly species collected with the new species at the type locality included Acroneuria frisoni Stark & Brown, 1991, Acroneuria nr. ozarkensis Poulton & Stewart, 1991, Agnetina flavescens (Walsh, 1862), Neoperla falayah Stark & Lentz, 1988, N. robisoni Poulton & Stewart, 1986, P. decipiens , and Perlinella ephyre (Newman, 1839).

Etymology.

The specific epithet is derived from sub, Latin for under, and lobata, the feminine adjectival form of lobus, Latin for a rounded projection or protuberance ( Brown 1956). The name references the ventral caecum of the aedeagus, a character shared by only one other described congener, P. golconda , though it is most prominent in P. sublobata .