Hexurella apachea Gertsch & Platnick, 1979

Monjaraz-Ruedas, Rodrigo, Mendez, Raymond Wyatt & Hedin, Marshal, 2023, Species delimitation, biogeography, and natural history of dwarf funnel web spiders (Mygalomorphae, Hexurellidae, Hexurella) from the United States / Mexico borderlands, ZooKeys 1167, pp. 109-157 : 109

Hexurella apachea Gertsch & Platnick, 1979

Figs 5 , 6

Hexurella apachea Gertsch and Platnick (1979): 29, figs 81, 83-85 (Dmf).

Material examined.

Near-type locality material: USA - Arizona, Cochise Co. • 1♂, 1 imm; Chiricahua Mtns., Cave Creek Canyon, 31.8815, -109.1978; 15 Mar. 2021; R.W. Mendez leg. - Cochise Co. • 1♂; Chiricahua Mtns., Cave Creek Canyon , 1 mi. E Southwest Research Station, FR 42, 31.8809, -109.1890; 12 Oct. 2021; R.W. Mendez leg.; RWM 21_050. - Cochise Co. • 5♂, 1♀, 2 imm; Chiricahua Mtns., Cave Creek Canyon , FR-42, Snowshed Trailhead, 31.8811, -109.1968; 20 Oct. 2021; R.W. Mendez, R.A. Mendez leg; RWM 21_057 .

Non-type material.

H. apachea Eastern Lineage - Arizona, Cochise Co. • 3♂, 4♀, 7 imm; Chiricahua Mtns., Price Canyon, 31.7266, -109.2387; 16 Mar. 2021; R.W. Mendez leg. - Cochise Co. • 3♂, 6♀; Dragoon Mtns, 1 mi E West Stronghold trailhead, Cochise Trail 279, 31.9223, -109.9899; 30 Oct. 2021; R.W. Mendez, K. Silvestre-Bringas, E. Ciaccio leg.; RWM 21_061. - Cochise Co. • 5 imm; Dragoon Mtns, 2.8 mi up NF-345A, 0.4 mi down ravine, 31.9036, -109.9830; 21 Aug. 2021; R.W. Mendez, M.A. Leimroth leg.; RWM 21_027. - Cochise Co. • 3♂, 3♀, 2 imm; Dragoon Mtns, 2.8 mi up NF-345A, 31.8997, -109.9835; 17 Nov. 2021; R.W. Mendez, C.A. Hamilton leg.; RWM 21_076. - Cochise Co. • 1♀, 4 imm; Dragoon Mtns., Middlemarch Canyon, E of Middlemarch Pass, W of Pearce, 31.8729, -109.9399; 23-24 Jul. 2021; M. Hedin, R.W. Mendez leg.; MCH 21_084. - Cochise Co. • 1♂, 2♀, 4 imm; Pedregosa Mtns., Prune Canyon, 31.5668, -109.3800; 17 Apr. 2021; R.W. Mendez leg.

H. apachea Central Lineage - Cochise Co. • 1♂, 1♀, 1 imm; SW of Winchester Mtns, Johnny Lyon Hills, W of Keith Peak, 32.1154, -110.2237; 17 Jan. 2022; R.W. Mendez, M.A. Leimroth leg.; RWM 22_009. - Cochise Co. • 3♀; Whetstone Mtns, French Joe Canyon, 31.8092, -110.3976; 23 Aug. 2021; R.W. Mendez leg. - Cochise Co. • 6♂, 3♀, 4 imm; Whetstone Mtns, French Joe Canyon, E French Joe Spring, 31.8107, -110.3945; 14 Nov. 2021; R.W. Mendez, C.A. Hamilton, M.A. Leimroth leg.; RWM 21_075. - Pima Co. • 4♀, 3 imm; Whetstone Mtns, 0.5 mi SE Willow Spring, Apache Canyon, 31.8193, -110.4571; 22 Aug. 2021; R.W. Mendez leg; RWM 21_030. - Pima Co. • 3♀, 3 imm; Whetstone Mtns, 0.75 mi E Willow Spring, Apache Canyon, 31.8252, -110.4487; 22 Aug. 2021; R.W. Mendez leg; RWM 21_029. - Santa Cruz Co. • 4♂, 8♀, 2 imm; Mustang Mtns, NW Mustang Peak, 31.6852, -110.4709; 14 Nov. 2021; R.W. Mendez, C.A. Hamilton, M.A. Leimroth leg.; RWM 21_074.

H. apachea Western Lineage - Pima Co. • 2♂, 2♀, 8 imm; Santa Catalina Mtns, Redington Pass, 1 mi W Youtey Pasture Tank., Redington Road, 32.3107, -110.5508; 2 Oct. 2021; R.W. Mendez, D. Roth leg.; RWM 21_044. - Pima Co. • 1♀; Santa Catalina Mtns, Nugget Cyn., E Peppersauce Cave, 32.5249, -110.7106; 11 Jul. 2021; R.W. Mendez leg. - Santa Cruz Co. • 4♂, 7♀, 1 imm; Patagonia Mtns, 0.5 mi N Harshaw/Duquesne Road jnct, 31.3917, -110.6885; 6 Nov. 2021; R.W. Mendez, M.A. Leimroth leg.; RWM 21_062. - Santa Cruz Co. • 1 imm; Patagonia Mtns, 1 mi E Harshaw Road, 31.4659, -110.7099; 5 Sep. 2021; R.W. Mendez, M.A. Leimroth leg.; RWM 21_035. - Santa Cruz Co. • 3♂, 3♀, 1 imm; Patagonia Mtns, 1.5 mi W Harshaw/Duquesne jct., Duquesne Wash, 31.3856, -110.7114; 18 Nov. 2021; R.W. Mendez, C.A. Hamilton leg.; RWM 21_078. - Santa Cruz Co. • 1♀, 3 imm; Santa Rita Mtns, Adobe Canyon, 0.5 mi S Bathtub Tank, 31.6730, -110.7601; 16 Sep. 2021; R.W. Mendez leg.; RWM 21_040. - Santa Cruz Co. • 1 imm; Santa Rita Mtns, Madera Canyon; date unknown; M. Hedin leg.; MCH 99_010. - Santa Cruz Co. • 2♂, 3 imm; Santa Rita Mtns., Aliso Springs, 31.7355, -110.8040; 6 Mar. 2021; R.W. Mendez leg.

H. apachea Mule Lineage - Cochise Co. • ♂, 1 imm; Mule Mtns, 0.5 mi S Mule Pass, Bisbee, 31.4528, -109.9403; 13 Nov. 2021; R.W. Mendez, C.A. Hamilton, M.A. Leimroth leg., RWM 21_073. - Cochise Co. • 2♂, 3♀, 3 imm; Mule Mtns, drainage off Escabrosa Ridge, 31.4530, -109.9634; 9 Mar. 2021; R.W. Mendez leg. - Cochise Co. • ♂; Mule Mtns, Fissure Peak, 31.4473, -109.9631; 9 Mar. 2021; R.W. Mendez leg.

Diagnosis.

This species differs from all other congeners in possessing a diagnostic comb of robust spines distally on the prolateral surface of the male I patella, with a dorsal-most spine that is long and distinctively curved (Fig. 5A-D ). The patellar comb is combined with a conspicuous brush of robust prolateral spines on tibia I, again with a dorsal-most spine longer than the others (Fig. 5A-D ).

Variation.

Representative variation in male leg I patella/tibia spine counts (including some spines tending towards the ventral surface on the patella) is as follows: Mule Lineage - Mule Pass (7, 10), Fissure Peak (6, 10); Western Lineage - Redington Pass (5, 8), Duquesne Wash (6, 11), Aliso Springs (5, 7); Central Lineage - Johnny Lyon Hills (3, 15), French Joe Canyon (6, 12), Mustang Mtns (7, 12); Eastern Lineage - Cave Creek Canyon (5, 10), Price Canyon (4, 12), Cochise Trail (5, 9).

Distribution.

Hexurella apachea is represented by a series of four phylogeographic lineages distributed north-south through the Cordilleran Gap of southeastern Arizona. COI suggests divergence times between the four clades spanning from the late Miocene to the early Pliocene (Fig. 4 ); these time estimates are slightly younger ( Masta 2000; Derkarabetian et al. 2016) or approximately coincident (Bryson et al. 2013b) with sky island divergence times for other co-distributed arachnid groups. These estimated times are much earlier than the last glacial maximum, when potentially suitable oak and pinyon-juniper forest connected the sky islands (summarized in Moore et al. 2013). With two exceptions (discussed below), populations from individual sky islands form monophyletic genetic groups (Figs 1 , 2 , 4 ), suggesting little movement between ranges.

Vaejovis vorhiesi and Pseudouroctonus apacheanus group scorpions, often collected with H. apachea , were diverging in this area throughout the Miocene (with occasional Pleistocene divergences between geographically adjacent ranges) and were dispersing from south to north and east to west, respectively (Bryson et al. 2013a, b). Vaejovis Koch, 1836 exhibits a similar pattern to H. apachea ; a series of lineages oriented north south, but most extending much further north in Vaejovis . The biogeographic origin for H. apachea remains unclear, and material from northern Sonora and the gap between H. apachea and H. zas sp. nov. (Fig. 3 ) will be needed to clarify this directionality.

A comparison can be made with Yarrow’s Spiny Lizard, Sceloporus jarrovii jarrovii Cope, 1875 regarding the Central and Eastern Clades in H. apachea . Hexurella apachea often live at lower elevations than S. j. jarrovii , but both utilize rock outcrops and canyons in Madrean Oak Woodlands. Wiens et al. (2019) find a similar east-west split around 4.5 million years ago in S. j. jarrovii , divided by the San Pedro River other than Mule Mountains specimens (which fell sister to their western clade). The San Pedro River can be an important barrier resulting in separate lineages inhabiting the sky islands to either side, again seen in the Vaejovis vorhiesi group. The rarely sampled Johnny Lyon Hills (RWM22_009), east of the river, should receive more attention to see where their biogeographic affinities typically lie.

The Santa Rita and Patagonia Mountains are closely adjacent, divided by the headwaters of Sonoita Creek. Oak forest comes very low here, connecting the ranges with suitable or near-suitable Hexurella habitat. As a result, it is not surprising that H. apachea populations may have had contact between these ranges, although the divergences in the Western Clade are not recent (Fig. 4 ). Similarly, the Pedregosa Mountains are a subrange of the Chiricahuas. This emphasizes the need to include samples from multiple locations per sky island when studying regional species.

Natural history.

Hexurella apachea is primarily found in low elevation Madrean oak communities between 1400-2075 meters. Nearly all collections have come from flipping small to medium-sized rocks in oak litter (Fig. 6E ). Common oak species include Quercus arizonica Sarg., Q. emoryi Torr., Q. rugosa Née, and Q. toumeyi Sarg.. Other plants that can also provide suitable litter include the sumacs Rhus trilobata Nutt. and R. virens Lindh. ex A. Gray, and rarely Cercocarpus montanus Raf. (Mountain Mahogany) or Celtis reticulata Torr. (Netleaf Hackberry.) Additionally, Piptochaetium fimbriatum (Kunth) Hitchc. (Pinyon Ricegrass) and Juniperus deppeana Steud. (Alligator Juniper) are useful indicator species, although they are not used in web construction. Aggregations of spiders are usually found along gentle slopes above low riparian corridors or rock outcrops; at the upper end of their elevational range spiders also inhabit north-facing ridgelines.

The litter utilized by H. apachea is generally compacted and dense, yet well-draining and without much active fungal activity. Webs are constructed at the transition between litter and soil, consisting of numerous short and interconnected branching tunnels that open into small, space-filling funnel webs wherever voids are present in the leaf matrix (Fig. 6F ). Hexurella in general are capable of excavating burrows in the top few centimeters of substrate, and often construct a shallow retreat.

Despite their small size, H. apachea are typically found in fairly dry microhabitats, especially when compared to the commonly syntopic funnel-web spider Euagrus chisoseus Gertsch, 1939. In captivity, H. apachea has proven to be remarkably desiccation tolerant, requiring no substrate moisture as long as the temperatures remain stable between 20-25 °C and the room has some ambient humidity (10-20%). Like western taxa, H. apachea must survive high temperatures and low humidity in the dry season. Egg sacs (laid in late March) have invariably molded when enclosures are kept moist, and the sacs observed in the field are usually placed above the webs, away from the soil in cracks under rocks. In captivity and in the wild, egg sacs are coated with debris, behavior like E. chisoseus (RWM, personal observation). Adults likely take two years to mature based on the two overlapping size classes of juveniles usually seen in the wild and captive growth rates, with mature females living for at least two years after maturing.

While patchily distributed throughout their range, H. apachea can be dense in appropriate habitats, with 8 males and>75 immatures and females observed (not all collected) in 2 m2 in one collection (RWM 21_057) from the type locality in Cave Creek Canyon, Chiricahua Mountains. Small rocks will often have at least one adult female and three or four subadults under them. Despite their proximity in the wild, H. apachea (and Hexurella in general) do not tolerate cohabitation and readily cannibalize. Mature males have been collected in the field from early October through April; it is unknown if these are overwintering or a different set of males. Males are found running through litter, in 4-5 cm temporary retreats that may function as sperm webs, and the webs of females. Males and juveniles will descend via draglines, permitted by their small size.

Discussion.

Because of an overall shared male palpal (Fig. 6A-D ) and leg I patella/tibia morphology (see above), we did not explicitly test a multiple species hypothesis for H. apachea using genomic algorithmic analyses. However, given the depth of nuclear and mitochondrial divergence and consistently recovered phylogeographic clades (Figs 1 , 2 , 4 ), we suspect that such analyses (DELINEATE in particular) would indicate multiple species in this complex. We here favor the more conservative single-species hypothesis, pending additional collecting efforts to the south, north, and east.

Conservation status.

Widely distributed and sometimes common in mostly mid-elevation habitats, viewed as secure.

Figures

Figure 1. Ingroup-only UCE concatenated ML tree. Specimen numbers correspond to those in Suppl. material 1. Nodal values correspond to bootstrap / gCF / sCF (gCF and sCF values rounded to nearest integer). Inset upper left - Rooted ML tree with bootstrap values shown for primary lineages (see also Suppl. material 4). Inset upper right - adult male Hexurella rupicola (San Diego County, CA).

Figure 2. Ingroup-only UCE ASTRAL species tree. Specimen numbers correspond to those in Suppl. material 1. Included are local posterior probability values. Branch lengths in coalescent units for internal branches only, terminal branch lengths arbitrary.

Figure 3. Map of all collection localities. Phylogeographic lineage names for H. apachea as in text. The unsampled type locality of H. pinea is designated with a special symbol; all other type (or near type) localities were sampled, see text.

Figure 4. Mitochondrial COI time tree, based on 2.5 % substitution rate analysis. Bootstrap values from whole mitogenome phylogenetic analysis (see Suppl. Material 5). Upper left inset: Density plot of tree root heights estimated using different COI substitution rate values.

Figure 5. H. apachea A ♂ leg I, prolateral view, Mule Mtns (SDSU _ TAC 000684) B ♂ leg I, prolateral view, Cave Creek Canyon (SDSU _ TAC 000685) C ♂ leg I, prolateral view, Mustang Mtns (SDSU _ TAC 000686) D ♂ leg I, prolateral view, Redington Pass (SDSU _ TAC 000687) E ♀ spermathecae (Mustang Mtns, SDSU _ TAC 000688) F live ♀, Johnny Lyon Hills (RWM 22 _ 009).

Figure 6. H. apachea A ♂ palp, retrolateral view, Mule Mtns (SDSU _ TAC 000684) B ♂ palp, retrolateral view, Cave Creek Canyon (SDSU _ TAC 000685) C ♂ palp, retrolateral view, Mustang Mtns (SDSU _ TAC 000686) D ♂ palp, retrolateral view, Redington Pass (SDSU _ TAC 000687) E habitat, Whetstone Mtns (RWM 21 _ 029) F web, French Joe Canyon (RWM 21 _ 075).