Nesticus roanensis, Hedin & Milne, 2023

Hedin, Marshal & Milne, Marc A., 2023, New species in old mountains: integrative taxonomy reveals ten new species and extensive short-range endemism in Nesticus spiders (Araneae, Nesticidae) from the southern Appalachian Mountains, ZooKeys 1145, pp. 1-130 : 1

Nesticus roanensis sp. nov.

Fig. 28A-G

Material examined.

Type material: Holotype: USA - North Carolina, Mitchell Co. • ♂; Roan Mountain, below Roan High Bluff ; 36.0931°N, - 82.1459°W; 22 Aug. 2001; M. Hedin, M. Lowder leg.; MCH 01_150 (SDSU_TAC000675) ; Paratype: - North Carolina, Mitchell Co. • ♀; Roan Mountain, below Roan High Bluff ; 36.0931°N, - 82.1459°W; 22 Aug. 2001; M. Hedin, M. Lowder leg.; MCH 01_150 (SDSU_TAC000676); Non type material: USA - North Carolina, Avery Co. • ♂, 1 imm; Henson Creek at Henson Creek Baptist Church , on Henson Rd , N of Ingalls; 36.0374°N, - 82.042°W; 21 Aug. 2007; M. Hedin, M. McCormack, S. Derkarabetian leg.; MCH 07_138 ; - North Carolina, Mitchell Co. • 2♂, 2♀; Roan Mountain, below Roan High Bluff ; 36.0931°N, - 82.1459°W; 22 Aug. 2001; M. Hedin, M. Lowder leg.; MCH 01_150; • ♂, 2♀, 6 imm; upper Roan Valley, Hwy 261; 36.0929°N, - 82.0932°W; 21 Aug. 2001; M. Hedin, M. Lowder leg.; MCH 01_148 ; - Tennessee, Carter Co. • 5♂, 15♀; Hwy 143, NE Roan Mountain , 3 mi. N Carvers Gap; 36.1184°N, - 82.0818°W; 9 Aug. 2004; M. Hedin, R. Keith, J. Starrett, S. Thomas leg.; MCH 04_034; • 3♂, 3♀; Hwy 143, NE Roan Mountain , 3 mi. N Carvers Gap; 36.1094°N, - 82.0961°W; 31 May. 2016; M. Hedin, S. Derkarabetian, J. Starrett, D. Proud leg.; MCH 16_033 .

Diagnosis.

Male Nesticus roanensis possess a distinctive fork at the base of the tegulum unlike any other species in the species group (Fig. 28A-D ). Like the sister species N. paynei the distal end of the paracymbial dorsal process is relatively rounded, vs. truncate. Females of N. roanensis are very similar to females of sister species N. paynei .

Description of ♂ holotype

(SDSU_TAC000675). Carapace dusky cream, faint dark pigment behind ocular area. Legs pale yellow / cream. Abdomen dirty pale cream with darker paired lateral pigmentation blotches. All eyes approximately equal in size, except for AMEs, ~ 1/4 width of ALEs. Eyes with rings of dark pigment. CL 1.6, CW 1.5, abdomen length 2.25, total body length 3.85. Leg I total length 11.35 (3.05, 0.75, 3.4, 2.95, 1.2), leg formula 1423, leg I / CW ratio 7.6. Paracymbium with a knob-shaped ventral process with a sclerotized retrolateral keel, a dorsal process with a rounded serrate, distal portion, a rectangular paradistal process, and a translucent, elongate, prolaterally-directed dorsal process. Median apophysis rectangular with an anteriorly directed edge coming to a point, translucent proximal spatulate edge lying above distal tegular process. Tegular process with arrowhead-like basal fork, distal process nearly as broad as long with apical point, nose-like bulge at the base of the distal process. Distal tip of conductor bent and directed prolaterally.

♂ Variation.

Adult males from multiple collection events, including the lower elevation Henson Creek specimens, all closely approximate the holotype male. The distal portion of the tegular apophysis for the male from upper Roan Valley (MCH 01_148) is broken (Fig. 28C ).

Description of ♀ paratype

(SDSU_TAC000676). Carapace dusky orange, conspicuous faint dark pigment behind ocular area. Legs pale orange. Abdomen dirty pale cream with darker paired lateral pigmentation blotches. All eyes approximately equal in size, except for AMEs, ~ 1/4 width of ALEs. Eyes with rings of dark pigment. CL 1.5, CW 1.4, abdomen length 2.35, total body length 3.85. Leg I total length 9.35 (2.65, 0.7, 2.65, 2.3, 1.05), leg formula 1423, leg I / CW ratio 6.7. Epigynum short, wider than long. Broad proximal median septum, narrowing slightly posteriorly. Lateral to proximal septum lie obliquely oriented, oval-shaped shallow pockets outlined by circular rings. Short, banana-shaped spermathecae visible lateral to distal septum, approximately perpendicular to septum. Viewed dorsally, circular internal lobes with interior margins bulging inwards and touching along the midline.

♀ Variation.

The epigyna of females from multiple locations closely approximate the paratype female.

Distribution and natural history.

Restricted to Roan Mountain and immediate vicinity at elevations near or above 1800 meters, except for the Henson Creek location (~ 900 meters) on the southeastern flanks of Roan Mountain (Fig. 13 ). At high elevations spiders were found to be reasonably common under large stones in extensive north-facing talus habitat.

We have collected comprehensively in this region, finding the sister species Nesticus paynei to the north and west, other Nesticus tennesseensis group species to the east and southeast (Fig. 13 ), and other Nesticus further southwest. We believe that we have the small geographic distribution of N. roanensis well-circumscribed. The lower elevation Henson Creek sample location (~ 900 meters) has important conservation implications for this species, but more extensive regional sampling is needed to fully understand the distribution and abundance of this species.

Etymology.

Named after the highlands of Roan Mountain along the North Carolina / Tennessee border.

Remarks.

While male morphological evidence clearly supports this species as distinct in a "morphology first" framework (unique forked base of tegular apophysis), the UCE phylogenomic evidence is mixed. Concatenated likelihood supports the two sampled Nesticus roanensis populations as monophyletic (bootstrap = 100), but nested within a larger N. paynei clade (Fig. 3 ). However, this N. paynei paraphyly is weakly supported, with a bootstrap value of 59 and a sCF value of only 30.5. Collapsing this node results in a topology where N. roanensis shares a polytomous node with N. paynei populations (i.e., there is not strong support for N. paynei paraphyly). The ASTRAL topology more clearly favors reciprocal monophyly of N. roanensis and N. paynei , the former with a posterior probability of 0.99, the latter with a posterior probability of 1.0 (Fig. 4 ). This recovered monophyly, in combination with morphological diagnosability, would be consistent with our species criteria.

Mitochondrial data fail to support Nesticus roanensis as distinct from N. paynei (Fig. 6 ), with N. roanensis haplotypes intermixed with N. paynei haplotypes, and sometimes sharing nearly identical haplotypes. Because these taxa are closely parapatric it is possible that this reflects mitochondrial introgression at areas of contact on the northern slopes of Roan Mountain (Fig. 13 ). A combination of introgression and incomplete lineage sorting (or ILS alone) is also a possibility.

Overall, this taxonomic situation illustrates patterns of nuclear vs. mitochondrial vs. morphological discordance as also found elsewhere in Appalachian Nesticus . The male morphology of N. roanensis is as divergent as any taxon in the species group (Fig. 12C ), female morphology and mitochondrial haplotypes are shared with N. paynei , while nuclear phylogenomic divergence is mixed. Rates of evolution in these different character classes appear to vary in this group of populations.

Figures

Figure 3. UCE concatenated maximum likelihood tree. Distant outgroups removed (for graphical purposes), specimen numbers correspond to those in Suppl. material 3 (with detailed location provided in Suppl. material 1). Node numbers correspond to bootstrap (bold text) / gCF / sCF. Only bootstrap values below 100 shown, all others 100. gCF and sCF values rounded to nearest integer; sCF values below 38 highlighted with red text.

Figure 4. UCE ASTRAL species tree. Distant outgroups removed (for graphical purposes), specimen numbers correspond to those in Suppl. material 3 (with detailed location provided in Suppl. material 1). Included are quartet support values (rounded to nearest integer), and local posterior probability values (if less than 1.0, red text). Branch lengths in coalescent units for internal branches only, terminal branch lengths arbitrary. Internal branch to Nesticus cressleri truncated for graphical purposes.

Figure 6. COI IQT gene tree. Distant outgroups trimmed. Specimen numbers correspond to those in Suppl. material 3 (with detailed location provided in Suppl. material 1). Sequences from UCE capture denoted with " NODE ". Populations with a " Nesticus cooperi - like " male paracymbium denoted by small circles. Not all tip bootstrap values shown (see Suppl. material 4 for. tre file with all bootstrap values).

Figure 12. Comparative ♂ palps of Nesticus tennesseensis group A Nesticus silvanus B N. cherokeensis C N. holsingeri D N. mimus E N. tennesseensis F N. dilutus G N. carolinensis H N. paynei, and I N. roanensis. All views are ventral. See subsequent figures for specimen locations and voucher details.

Figure 13. Distribution of Nesticus tennesseensis group species. Type localities designated with yellow circles. State boundaries and major cities shown for geographic context. Dashed lines circumscribe known species distributions.

Figure 28. Nesticus roanensis sp. nov. genitalia. North Carolina, Mitchell Co., Roan Mountain, below Roan High Bluff, holotype male (SDSU _ TAC 000675) palp, dorsal (A), ventral (B) C North Carolina, Mitchell Co., upper Roan Valley, MCH 01 _ 148, palp, ventral D North Carolina, Avery Co., Henson Creek at Henson Creek Baptist Church, MCH 07 _ 138, palp, ventral. Epigynal variation. North Carolina, Mitchell Co., Roan Mountain, below Roan High Bluff, paratype ♀ (SDSU _ TAC 000675) epigynum, ventral (E), dorsal (F) G North Carolina, Mitchell Co., upper Roan Valley, MCH 01 _ 148, ventral. Scale bar: 0.5 mm.