Dromochorus belfragei, Duran & Herrmann & Roman & Gwiazdowski & Drummond & Hood & Egan, 2019

Duran, Daniel P., Herrmann, David P., Roman, Stephen J., Gwiazdowski, Rodger A., Drummond, Jennifer A., Hood, Glen R. & Egan, Scott P., 2019, Cryptic diversity in the North American Dromochorus tiger beetles (Coleoptera: Carabidae: Cicindelinae): a congruence-based method for species discovery, Zoological Journal of the Linnean Society 186, pp. 250-285 : 269-271

DROMOCHORUS BELFRAGEI SALLÉ, 1877

( FIGS 7B , 9B )

Common name

Loamy-ground tiger beetle.

Type locality

‘Texas–Dallas, Wasco (presumed to be a misspelling of Waco), etc., on the banks of the Trinity River’ (English translation). Syntypes unknown, probably in MHNP ( Bousquet 2012).

Synonymy

Dromochorus bellefragei Heyne, 1893 (unjustified emendation).

Dromochorus sericeus Casey, 1897: 294 .

Type locality

‘Texas’. Two syntypes in USNM, Washington DC (synonymy established by Leng, 1902).

Taxonomic history

Dromochorus belfragei has been a catch-all taxon, and many populations of Dromochorus were lumped under this name in the literature or in museum collections prior to this revision. Dromochorus pilatei and D. velutinigrens are the only nominal taxa that have never been considered conspecific with D. belfragei . Based on morphology, ecology, biogeography, mtDNA genealogy and multilocus genetic data, D. belfragei (sensu stricto) is circumscribed as a separate species from three other distinct species, D. pruininus , D. knisleyi sp. nov. and D. minimus sp. nov. Occasional hybridization with D. knisleyi has been observed where their ranges come in contact, and this is further supported by evidence of mtDNA introgression.

Distribution

Dromochorus belfragei is known to occur from the north-western panhandle of Texas and southern Oklahoma to south-eastern Texas. Previous literature described a more extensive range from south-eastern Colorado ( Michels et al., 2008) to Tamaulipas, Mexico ( Cazier, 1954). The former record now appears to be an error (Michels, pers. comm., 2015), and the latter would appear to belong to D. chaparralensis sp. nov. One specimen from the AMNH was labelled ‘St. George, Utah’, although this locality would not appear plausible. The range of D. belfragei comes close to several other species. In particular, D. belfragei is nearly sympatric with D. pruininus in several places ( Fig. 3 ; see D. pruininus account). In eastern and southern Bexar County, TX, this species is found sympatrically with D. knisleyi , and possibly D. minimus .

Diagnosis

This species can be distinguished from all other similar Dromochorus by the presence of finely to coarsely pitted black elytra that are not frosted in texture, in conjunction with maxillary palpi that have the apical segment darkest, with dark yellow-ochre to dark amber coloration in other segments ( Fig. 8 ). Most populations of D. belfragei possess at least small subsutural foveae, but these lack metallic reflections. Southern and eastern populations may have subtle dark infuscations on the elytra.

Dromochorus belfragei is most likely to be confused with D. pruininus , knisleyi or welderensis . It can be separated from these taxa by the following:

1. Dromochorus pruininus has a frosted blue sheen on the elytra and the entire dorsal surface, and it lacks any pits or subsutural foveae. The maxillary palpi in D. pruininus are pale yellow-ochre with a dark apical segment, whereas D. belfragei has darker yellow-red to red testaceous palpi with a dark apical segment.

2. Dromochorus knisleyi is similar to D. belfragei , but has more prominent subsutural foveae, often with bright metallic blue, green or gold reflections. In D. knisleyi , the maxillary palpi are always dark in all segments, whereas in D. belfragei , the apical segment is darker than the preceding. Infuscations are always present in D. knisleyi and are usually absent in D. belfragei . Ecologically, D. knisleyi is found in upland juniper woodland in the Edwards Plateau, and D. belfragei is found outside of this region, in clay soils associated with larger riparian systems. The two species appear to hybridize along a narrow contact zone at the edge of the Balcones Escarpment in south-eastern and south-central Texas. Both species and their hybrids may be found in this area. The existence of a hybrid zone was further supported by mtDNA data ( Fig. 2 ).

3. Dromochorus welderensis has a smooth velvety black elytral surface (may have metallic blue-violet reflections), and never has pitting or subsutural foveae. The maxillary palpi are always dark in all segments, whereas in D. belfragei , the apical segment is darker than the preceding.

Description

Medium- to large-sized Dromochorus . Body length 11.6–15.2 mm, mean ♀ 14.5 mm, mean ♂ 13.2 mm. Head slightly wider than pronotum. Head predominantly black with blue reflections mostly concentrated near the anterior margin and edges of the supraorbital region. Fine rugosity often present on the frons and vertex. All head portions glabrous except for two supraorbital setae next to each eye. Frons concave in median area, especially in male, bulging towards slightly convex near anterior margin, clearly delimited from clypeus, gradually blending into vertex. Genae bright polished metallic violet to blue, with shallow, longitudinal striae gradually ending at border of vertex. Clypeus mostly black, with patches of metallic blue or violet reflections; clypeus may be nearly entirely blue to violet in females. Male labrum tridentate with 6–8 setae, central area pale ochre-testaceous, with a thin dark-brown to black bor- der posteriorly and sometimes anteriorly, dark-brown to black laterally; in some populations, the pale central area of the labrum may exist as a small spot, in others the pale area may cover more than two-thirds of the total labrum surface; female labrum tridentate with 6–8 setae, entirely dark-brown to black with polished metallic cupreous to green reflections. Maxillary and labial palpi with apical segment darker than other segments; basal to penultimate segments yellow-ochre to dark red-amber, often with metallic purple and green reflections. Antennae normal length, reaching back to humerus and basal third of elytron, slightly longer in male than female; scape dark testaceous to black with metallic reflections of violet, cupreous and green, with 2–3 apical setae; pedicel dark testaceous with metallic reflections of violet, cupreous and green, lacking any setae; flagellum dark testaceous, antennomeres 3–4 with metallic violet and green reflections, densely clothed in short white setae, antennomeres 5–11 dulltextured without metallic reflections and possessing erect setae in apical rings only, covered with fine pubescence throughout.

Thorax: Pronotum 2.5–3.4 mm in length, mean ♀ 3.1 mm, mean ♂ 2.8 mm; width 2.8–3.6 mm, mean ♀ 3.4 mm, mean ♂ 3.1 mm. Pronotum black, with some dark-blue reflections, especially in sulci, slightly wider than long, widest near anterior margin, width to length ratio 1.0 to 1.2, setae sparse to regularly spaced, mostly present along lateral third of dorsal surface; disc finely rugose, with thin but distinct median line, with well-defined shallow sulci present anteriorly and posteriorly; notopleural sutures clearly defined, not visible from dorsal view; proepisternum black with weak to strong iridescent blue reflections, glabrous. Elytra convex, elongate, 7.1–9.7 mm length, mean ♀ 8.8 mm, mean ♂ 8.2 mm, shape similar in both sexes, but slightly wider in female, especially toward apical third; sutural spine absent, microserrations not present on elytral apices; elytral texture dull, with regular small pits present throughout disk, elytral coloration black, often with blue reflections near humeral region; elytral maculations absent; infuscations rarely present; subsutural foveae, when present, only slightly more prominent than other pits on the elytral disk; subsutural foveae lacking bright metallic reflections, except rarely in basal area.

Legs: Pro-, meso- and metacoxae dark testaceous to black with iridescent blue to violet and cupreous reflections, with numerous setae; pro- and meso- trochanters with a single erect seta, metatrochanter glabrous, trochanters dark brown-testaceous, dark brown-testaceous; femora black with metallic violet and green reflections, densely clothed in decumbent white setae; tibiae testaceous brown, clothed with setae of two types: sparser brown-testaceous long setae and dense short decumbent white setae; two tibial spines present; tarsi brown-testaceous, first three dilated protarsomeres in male with dense greyish-white setal pad.

Abdomen: Venter mostly black with occasional metallic violet reflections. Decumbent white setae present on ventrite 1. Ventrites 2–6 have sparse, short, brown erect setae present throughout, but often abraded.

Ecology/natural history

Dromochorus belfragei adults are active between mid- May and early July in most of its range (e.g. central to north TX) and late June to late July in northern part of its range (e.g. OK to panhandle of TX).

Dromochorus belfragei can be found in natural and managed forested and agricultural areas (e.g. pecan groves) that have semi-open shaded areas or trails beneath the canopy. Soils in these areas can be dark, red to black in color, clay to clay-loam, cracked and sometimes moist in low areas that are heavily trampled by cattle. Adult beetles tend to avoid the lighter coloured sandy areas that are exposed to full sunlight on the forest edges. Despite the common name, this species appears more closely associated with soils that possess high clay content, more so than loam. The preferred habitat of D. belfragei is generally associated with larger riparian systems, although the beetles are not typically found near the water’s edge and we have found them over 3 km from water. They appear to have a wider ecological niche than most Dromochorus ; their habitat and geographic distribution encompass a larger number of ecoregions than other species ( Fig. 3 ; Table 1).

Dromochorus belfragei and D. pruininus have similar but non-overlapping ranges, and they may be separated by ecological barriers, at least in some areas. In the DFW area of North Texas, the species has been reported a few kilometers from D. pruininus ( Pearson et al., 2006) , but the two appear to be separated by a narrow extension of the EPA Level IV Eastern Cross Timbers ecoregion, which is not suitable for either species. The forested undergrowth of this area is extremely dense in many areas, and may not possess the necessary surface soil conditions for either species to persist. Dromochorus belfragei may be more susceptible to urbanization than D. pruininus , as none have been collected in the DFW area (Tarrant Co.) since the 1970s, whereas D. pruininus appear much more tolerant to these disturbances and may be abundant in semi-open grassy areas where trails have been established in riparian parks (Dallas, Collin Co.).

Thought to be crepuscular, this species is active throughout the day in shady areas or when overcast. Similar in behaviour to D. pruininus and D. pilatei , this species has been observed using soil cracks for escape, especially during dry conditions when virtisolic cracks are pronounced. Like other Dromochorus , D. belfragei frequently moves to vegetated cover to escape when pursued.

Figures

Figure 2A. Mitochondrial DNA (mtDNA) cytochrome oxidase b (Cytb) Bayesian genealogy of all members of the genus Dromochorus. Outgroups include North American representatives of Cylindera and Cicindelidia. On the left is a reduced version of the full tree indicating clades shown, in detail, in each figure. Colours are arbitrarily chosen to show distinctions among the taxa, and directly correspond to populations shown in Figure 3. Only posterior support values above 60 are displayed, and the scale bar at bottom shows a branch length representing nucleotide substitutions per site. Taxon names include the unique specimen number (see also Supporting Information, Table S1), along with the state and collection locality; genomic material from specimens marked with a ~ were also used in the multilocus analysis (Figure 4), and holotypes of species described in this work are marked with an ‘H’. The longitudinal bars on the right identify specimens and clades historically considered to be a single species.

Figure 3. Distributionof sampled Dromochorus populations.Colours correspondto those used in Figure 1. Green = D.pilatei, pink = D. welderensis sp. nov., sky blue = D. velutinigrens, red = D. chaparralensis sp. nov., blue = D. pruininus, lime green = D. knisleyi sp. nov., orange = D. minimus sp. nov., black = D. belfragei.

Figure 7. Labial palps of: A, D. pruininus; B, D. belfragei; C, D. knisleyi sp. nov. A and B illustrate labial palps with a contrasting darker apical segment, and C illustrates labial palps that are consistently dark throughout.

Figure 8. A, Elytra showing distinct punctures (foveae) running parallel to the suture of the elytra (D. knisleyi sp. nov.). B, lack of distinct subsutural foveae (D. welderensis sp. nov.).

Figure 9. Dorsal habitus for species of Dromochorus. A, D.pruininus; B, D.belfragei; C, D. knisleyi sp. nov.; D, D. minimus sp. nov.; E, D. chaparralensis sp. nov.; F, D. welderensis sp. nov.; G, D. velutinigrens; H, D. pilatei.