Leptothorax athabasca

This species was discovered nesting in rock crevices.

Identification
Buschinger & Schulz (2008) - A detailed differential diagnosis cannot be provided because of the desolate condition of Leptothorax taxonomy in North America. A comparison is possible only with a few well-known species and with the sympatric forms in the vicinity of the type locality.

The measured values are by no means unusual among related Leptothorax species. Leptothorax athabasca is a bit larger than the European Leptothorax muscorum and the syntopic Leptothorax retractus, but smaller than Leptothorax acervorum and the North American Leptothorax “sp. B” sensu Heinze & Buschinger (1987), Heinze (1989b) and Loiselle & al. (1990).

Propodeal spine length (PSL, Gusten & al. 2006) has not been measured in other species of Leptothorax. The propodeal spine index (PSI; Epinotal Spine Index in Buschinger 1966) can be compared among a few species. In L. athabasca gynes it is 1.3 - 1.6; in L. acervorum (Europe) 1.87 ± 0.06 (Buschinger 1966); in L. muscorum (Europe) 1.73 ± 0.09 (Buschinger 1966); in Leptothorax gredleri (Europe) 1.48 ± 0.06 (Buschinger 1966); in Leptothorax scamni (Caucasus and northern Turkey) c. 2.0 (Heinze & al. 1993); in Leptothorax pocahontas (Canada) 1.7 - 1.8 (Buschinger 1979); and in Leptothorax faberi (Canada) 1.5 - 1.8 (Buschinger 1983).

The color of L. athabasca gynes and workers is evenly dark brown, similar to L. acervorum (but lacking the lighter areas on the body of that species), lighter than in the sympatric Leptothorax “sp. B”, and darker than in L. retractus from the same site.

Sculpture and pilosity are quite similar to other North American species of Leptothorax. Some negative characters may be helpful for identification, though:

Leptothorax pocahontas has long, tapering hairs and, in the typical case, a smooth and shiny surface (however, "dull" gynes with shorter hairs have been found and provisionally attributed to this species, cf. Buschinger & Heinze 1993).

Leptothorax retractus is characterized by a small but clearly visible notch in the anterior margin of the clypeus. This notch lacks in L. athabasca.

Leptothorax sp. C (sensu Heinze & Buschinger 1987, Heinze 1989b and Loiselle & al. 1990), supposed to be the host species of L. pocahontas, is much lighter in coloration. Higgins (year unknown) suggested that Leptothorax sp. C from Jasper NP is identical to Leptothorax muscorum var. septentrionalis Wheeler, 1917, though this taxon still is considered a junior synonym of L. muscorum according to antbase.org and Bolton & al. (2007).

What remains as characteristic for L. athabasca is the very sharp crest on top of the petiole, the flat mesosoma in the female castes, and the dorsolateral small outgrowths of the worker mesonotum.

Distribution
Known from a single location: a south-exposed river bank just upriver from Athabasca Falls of Athabasca River, Jasper National Park (Alberta, Canada).

Distribution based on Regional Taxon Lists
Nearctic Region: Canada.

Biology
Buschinger & Schulz (2008) - The habitat is the river bank that sometimes is evidently flooded. A horizontally split, schist-like sandstone cliff is exposed there. The ants were exclusively found in rock crevices, whereas above the flood line a number of related species of Leptothorax were dwelling dead wood, or a layer of conifer needles and debris beneath small flat rocks. Mainly Leptothorax retractus could be found there. Close to the river and in the collecting site the coniferous forest was comparatively open.

Two among the seven colonies that were collected were polygynous with two and four reproductive queens (checked by dissection; spermathecae full of sperm and ovaries well developed, yolky oocytes present); the species thus is probably facultatively polygynous like most other congenerics. The colonies collected on 27 July 1993 had sexual pupae in various states of pigmentation, and a few adult males. Colony size was about 50 to 100 adults.

The flat and slender mesosoma in the female castes probably represents an adaptation to life in narrow rock crevices. This character corresponds well with the fact that practically all other Leptothorax species both in Europe and in North America preferably are nesting in dead wood or bark (Leptothorax acervorum in some places also in rock crevices), where nest entrances and galleries usually are tubular. The new species seems to have an extremely limited range as far as is known, a phenomenon, however, that appears to be not unusual among the Formicoxenini. Intensive search in Alberta did not reveal any other site where L. athabasca would occur.

Nomenclature

 *  athabasca. Leptothorax athabasca Buschinger & Schulz, 2008: 244, figs. 1-8 (w.q.m.) CANADA.

Worker
(n = 13). HL 697 ± 30 (656 - 760); HW 598 ± 23 (570 - 637); SL 457 ± 14 (437 - 475); MW 416 ± 23 (390 - 456); PSL 119 ± 15 (95 - 143); PEL 239 ± 13 (219 - 257); PEW 180 ± 10 (162 - 190); PPW 255 ± 14 (228 - 285); ML 864 ± 41 (808 - 931); PEH 264 ± 14 (247 - 290); HS 647 ± 26 (613 - 698); SL / HS 0.706 ± 0.019 (0.676 - 0.737); HW / HL 0.858 ± 0.020 (0.822 - 0.884); MW / ML 0.482 ± 0.008 (0.466 - 0.495); PSL / ML 0.138 ± 0.013 (0.113 - 0.158); PEH / PEL 1.107 ± 0.057 (1.000 - 1.217); PEW / PEL 0.755 ± 0.047 (0.667 - 0.833); PEW / PPW 0.707 ± 0.028 (0.667 - 0.760). PSI 1.3 - 1.6 (n = 3).

Total length 3.2 - 3.3 mm; 11 antennomeres, as characteristic for the genus. Head subrectangular, with evenly rounded occipital corners. Head width equal in front of and behind the eyes. Eyes comparatively small, situated at midpoint of head. Frontal triangle distinctly delimited and well depressed. Scapes short, not reaching occipital corners. Mesosoma flat, outline in lateral view over a long distance straight, with shallow mesometanotal depression. Mesonotum at place where wings of alate would insert with slight, but in dorsal and lateral aspect well visible crests; more prominent than in congeners. Propodeal spines broadly attached, longer than broad, in lateral view more or less straight caudad oriented, with pointed tips. In dorsal view, spines slightly convex, distally only minimally divergent. Propodeal spine index (cf. BUSCHINGER 1966) 1.3 - 1.6, the spines thus being comparatively short. Petiole short and high, node triangular, its anterior face markedly concave in lateral view, its posterior face also slightly concave, straight, or appearing a little bit convex with straight or slightly concave outlines. Top of node acute. In dorsocaudal view, upper part of node distinctly convergent, with sharp, medially distinctly impressed ridge. Anterior part of dorsal petiolar outline with prominent corners, well visible in dorsal or lateral view. Subpetiolar process well developed, pointing anterioventrad. Postpetiole rounded and lacking any conspicuous ventral appendage. Erect hairs relatively short (60 - 80 μm). Scapes only with subdecumbent, not erect hairs. Tips of hairs blunt. Petiole with a total of c. 8, postpetiole with c. 10 erect setae. Sculpture of head, mesosoma and waist mainly densely reticulate, without any stronger rugae or other sculpture elements. Color of body evenly dark brown, without any lighter spots, appendages distinctly lighter, mainly light brown to orange-brown.

Queen
(n = 10. Holotype in square brackets). HL 713 ± 18 (675 - 732) [675]; HW 600 ± 19 (570 - 618) [570]; SL 457 ± 13 (437 - 475) [447]; ED 166 ± 19 (133 - 190) [147]; MW 495 ± 13 (475 - 513) [475]; PSL 114 ± 8 (105 - 124) [109]; PEL 264 ± 16 (233 - 285) [233]; PEW 184 ± 9 (171 - 200) [171]; PPW 267 ± 16 (238 - 285) [238]; ML 1009 ± 31 (944 - 1042) [944]; PEH 279 ± 9 (266 - 295) [266]; HS 656 ± 17 (622 - 670) [622]; SL / HS 0.696 ± 0.015 (0.667 - 0.718) [0.718]; ED / HS 0.253 ± 0.028 (0.199 - 0.286) [0.237]; HW / HL 0.843 ± 0.016 (0.818 - 0.867) [0.845]; MW / ML 0.491 ± 0.011 (0.474 - 0.507) [0.503]; PSL / ML 0.113 ± 0.008 (0.100 - 0.122) [0.116]; PEH / PEL 1.060 ± 0.040 (1.033 - 1.143) [1.143]; PEW / PEL 0.698 ± 0.022 (0.655 - 0.735) [0.735]; PEW / PPW 0.689 ± 0.033 (0.650 - 0.750) [0.720]. PSI 1.3 - 1.6 (n = 4).

Total length 3.0 - 3.8 mm; head as in worker, outline below eyes more parallel sided than in worker. Occipital corners distinctly rounded. Mesosoma slender, not bulky, particularly flat as compared to other congenerics. Dorsal outline straight. Propodeal spines as in worker. Petiole and postpetiole similar to worker, but in dorsocaudal view ridge medially only slightly impressed. General sculpture as in worker; but frons of head with many fine striae, only with scattered reticulate ground sculpture. Occipital corners nearly unsculptured and shining. Mesonotum longitudinally diffusely striate, with some reticulation and larger unsculptured parts. Scutellum reticulate, unsculptured and shining in medial part. Color and hairs as in worker.

Male
(n = 7). HL 609 ± 28 (570 - 656); HW 633 ± 29 (589 - 675); SL 238 ± 11 (219 - 247); 2FL 221 ± 9 (209 - 238); ED 249 ± 24 (209 - 276 ); MW 677 ± 58 (580 - 732); PEW 214 ± 19 (190 - 238); PPW 269 ± 23 (238 - 304); ML 1250 ± 96 (1102 - 1359); HS 621 ± 28 (580 - 665); HW / HL 1.039 ± 0.023 (1.015 - 1.077); SL / 2FL 1.079 ± 0.076 (0.960 - 1.182); SL / HS 0.383 ± 0.026 (0.329 - 0.410); PEW / HS 0.345 ± 0.032 (0.286 - 0.378); PPW / HS 0.433 ± 0.041 (0.371 - 0.474); MW / ML 0.543 ± 0.048 (0.441 - 0.579); PEW / PPW 0.797 ± 0.059 (0.741 - 0.920).

Total length 3.7 - 4.1 mm; 12 antennomeres, as characteristic for the genus. Head wide, behind eyes distinctly wider than anterior. Eyes large and slightly oval. Mesosoma dorsally rounded, pronotum low and small.Mesonotum and scutellum strongly vaulted, metanotum short, propodeum rounded, without any angles or spines. Petiole variable, mainly flat and long, sometimes higher and shorter, node evenly rounded. Postpetiole shorter than petiole, with rounded semicircular dorsal outline. Waist segments without ventral appendages. Color of body totally dark brown to black, antennae dark brown, legs light brown to orange-brown. Body surface mostly smooth and shining except for head being roughly and irregularly rugoreticulate; scutellum and dorsal surface of propodeum slightly reticulate, with shiny parts; in general, lateral surfaces of mesosoma very diffusely reticulate, but always shiny.

Type Material
On 27 July 1993, seven colonies have been collected in rock crevices on the south-exposed river bank just upriver Athabasca Falls of Athabasca River, Jasper National Park. The site is at 52° 39' 55"’ N, 117° 52' 58" W, at an elevation of c. 1200 m a.s.l. (as indicated by Google Earth). Holotype gyne, 11 paratype gynes, 16 paratype workers, 10 paratype males. , holotype gyne; 4 paratype workers; 1 paratype male;, 2 paratype gynes; 3 paratype workers; 2 paratype males; PCAB – personal collection of Alfred Buschinger, Reinheim, Germany (3 paratype gynes; 3 paratype workers; 3 paratype males); PCAS – personal collection of Andreas Schulz, Dormagen, Germany (3 paratype gynes; 3 paratype workers; 2 paratype males); –  3 paratype gynes; 3 paratype workers; 2 paratype males.

Etymology
The name refers to the type locality. The specific epithet is to be treated as a noun in apposition.