Dixa elkmontensis, Moulton, John K., 2017

Moulton, John K., 2017, The true identity of Dixa modesta Johannsen (Diptera: Dixidae) resolved: synonymy of Dixa similis Johannsen, designation of the Dixa ubiquita species group, and description of three new eastern Nearctic species, Zootaxa 4216 (3), pp. 247-260 : 254-255

Dixa elkmontensis sp. nov.

( Figs 15–17 , 22 )

Type material. HOLOTYPE, ♂ labeled: “ USA: TN: SEVIER COUNTY / Middle Frk. Little River /ds of Elkmont CG / N35°39′59.52″ W83°35′27.89″, 626 m / 26.vii.2005 / J.K. Moulton ”; “ HOLOTYPE / Dixa / elkmontensis / J.K. Moulton [red label]” ( CNC) . PARATYPES: Same data as holotype, 4♂ and 5♀ to CNC and 5♂ and 5♀ to USNM.

Additional material examined. USA: TN: SEVIER COUNTY, Middle Frk. Little River , d/s of Elkmont CG, N35°39′59.52″ W83°35′27.89″, 626 m, 26.vii.2005, JKM (15♂, 2♀) ; Same data, 16.vii.2011 (7♂, 4♀, 1L); Same data, 15.vi.2012 (57♂, 13♀, 5L).

Diagnosis. This species can be distinguished from D. ubiquita sp. nov. and D. vockerothi sp. nov. by the following characters: Morphological. Basal gonocoxal lobe with apex subovoid, directed posterodorsally; proximal lobe of SES acute, with thin, strap-like connection to proctiger; apical lobe of SES broad, with apex directed ventrally. Molecular. Within the 66 nucleotides (22 codons) shown ( Fig. 35 ) a thymine at position 26 (vs. adenine) and a thymine at position 38 (vs. cytosine) serve to distinguish this species from the other two. Within the encompassing amplified fragment of BZF, D. elkmontensis sp. nov. is 4.5% divergent from D. ubiquita sp. nov. and 9.1% divergent from D. vockerothi sp. nov. (JK Moulton, unpublished).

Description. Male. Same as D. ubiquita sp. nov., except as follows: Wing length (n =10) 3.4–4.1 (avg=3.7) mm. Terminalia ( Figs 15–17 ): Apex of basal gonocoxal lobe narrower (ca. 1/3–2/ 5X depth of gonocoxite at midpoint in lateral view; Fig. 15 ) and less squared.

Female. Wing length (n =10) 3.4–3.9 (avg=3.7) mm. Not reliably separated from D. ubiquita sp. nov. or D. vockerothi sp. nov.

Etymology. Named for the Elkmont area of Great Smoky Mountains National Park (GSMNP), location of the type and only known locality.

Distribution. Known only from the upper reaches of Little River (East Prong) in the Elkmont region of GSMNP ( Fig. 34 ).

Remarks. This species inhabits the widest lotic watercourse (10+m; Fig. 31 ) of any known eastern Nearctic Dixa species and is the only dixid found in this section of Little River. During warm summer evenings, individuals of this species, particularly males, are readily attracted to UV lights, likely the result of swarming behavior. Morphologically and molecularly, this species is more closely related to D. ubiquita sp. nov. than to D. vockerothi sp. nov. The shape of the basal gonocoxal lobe is intermediate to the character states observed in D. ubiquita sp. nov. and D. vockerothi sp. nov.

Figures

FIGURE 34. Known distributions of the three recognized members of the Dixa ubiquita species group.

FIGURE 35. Selected portion of big zinc finger (BZF) gene useful for distinguishing the three recognized species of the Dixa ubiquita species group.

FIGURES 12 – 20. Male terminalia (rotated orientation), 12, Dixa ubiquita sp. nov., lateral view; 13, D. ubiquita sp. nov., ventral view; 14, D. ubiquita sp. nov., terminal view; 15, D. elkmontensis sp. nov., lateral view; 16, D. elkmontensis sp. nov., ventral view; 17, D. elkmontensis sp. nov., terminal view; 18, D. vockerothi, lateral view; 19, D. vockerothi, ventral view; 20, D. vockerothi, terminal view. Scale bar = 50 µm.

FIGURES 21 – 23. Male terminalia, dorsal view; 21, Dixa ubiquita sp. nov.; 22, D. elkmontensis sp. nov.; 23, D. vockerothi sp. nov. Abbreviations: gcx = gonocoxa; S = sternite; ses = subepandrial sclerite (distal lobes); T = tergite. Scale bar = 50 µm.

FIGURES 29 – 33. Examples of Dixa ubiquita group habitats. 29 – 30, D. ubiquita sp. nov., 29, Lackey Creek, Blount County, TN; 30, Cosby Creek, GSMNP, Cocke County, TN; 31, D. elkmontensis sp. nov., type and only known locality, East Prong Little River, Elkmont area of GSMNP, Blount County, TN; 32 - 33, D. vockerothi sp. nov., 32, type locality, Mulvihill Brook, Old Chelsea, QC; 33, Woodfin Cascades, Blue Ridge Parkway NP, Haywood County, NC.