Arostrilepis macrocirrosa Makarikov, Gulyaev & Kontrimavichus 2011

Arostrilepis macrocirrosa Makarikov, Gulyaev & Kontrimavichus, 2011

(Fig. 9)

Hosts in Nearctic: Myodes rutilus (Pallas); rarely Microtus xanthognathus (Leach), Microtus pennsylvanicus (Ord) and Tamiasciurus hudsonicus (Erxleben).

Localities in Nearctic: Alaska - N Central region, SE region; Seward Peninsula (Bering Landbridge National Preserve); Brooks Range (Kobuk Valley National Park, Noatak National Preserve); Wrangell-St Elias National Preserve; Yukon Charley Rivers National Preserve; and Lake Clark National Park, northern Alaska Peninsula.

Material examined: Vouchers include 4 specimens in Myodes rutilus: MSB 1306 (field number- AF 55147, 2 slides/ cyt- b sequence ) by E.P. Hoberg et al., at Braye Lakes in the Wrangell-St. Elias National Preserve, Alaska (62o01’52”N, 141o07’46”W), 26 July 2001; MSB 1285 (AF 37468, 2 slides) by H. Henttonen near Bonanza Creek Research Station, Alaska (62o42’N, 148o16’W), 1 August 2000; MSB 1302, 1303 (AF 49374, 1A and 1B, 3 slides/ cyt- b sequence ) by H. Henttonen et al., from Yukon Charley Rivers National Preserve, Alaska, NW of Mt. Kathryn on Yukon River, S of Woodchopper (65o12’16”N, 143o34’22”W), 3 August 2001; MSB 1307 (AF 55196, 2 slides) by E.P. Hoberg et al., at Rex Creek, northwestern slope of Mt. Holmes in the Wrangell-St. Elias National Preserve, Alaska (61o18’37”N, 142o30’56”W), 30 July 2001; MSB 1304 (AF 49977) ex Tamiasciurus hudsonicus by H. Henttonen et al., from the Yukon Charley Rivers National Preserve, Alaska at Glenn Creek Cabin (65o18’07”N., 142o05’23”W), 12 August 2001; MSB 1351 (RLR 15515, 2 slides) ex T. hudsonicus by R.L. Rausch near Chitina, Alaska (31.6 miles west on highway), 8 October 1955. Palearctic specimens: MSB 1221 (H-15/ cyt- b sequence ) ex M. rutilus, by A. Lavikainen, on the Tunguska River, Irkutsk Oblast’, Russia (59o06’36”N, 108o23’54”E), 8 August 2003. See Appendix 1 for listing of additional identified voucher specimens from the Nearctic and Palearctic.

Description: Based on 4 specimens. Fully developed strobila 145–196 mm long, with maximum width at pregravid or gravid proglottides, 0.9–1.3 mm. Scolex slightly compressed dorso-ventrally, 275–385 (321, n = 3) wide, clearly wider than neck. Suckers ovoid in surface view, 162–210 × 130–191 (182 × 162, n = 8), with thick walls, prominent (Fig. 9 A). Neck relatively long and narrow, 130–185 (157, n = 3) wide.

Dorsal osmoregulatory canals thin, 1–2.5 (1.7, n = 10) wide, situated predominantly in same sagittal plane as ventral canals. Ventral osmoregulatory canals 35–70 (53, n = 10) wide. Genital ducts may pass dorsally or between longitudinal osmoregulatory canals within same strobila; intersegmental variation without regularity. Development of proglottides gradual, protandrous.

Mature proglottides 167–240 × 670–980 (205 × 825, n = 15), transversely elongate, trapeziform (Fig. 9 C). Testes usually 3 in number, almost of equal size, 125–210 × 90–132 (161 × 107, n = 15), round or oval, commonly situated in triangle; poral testis separated from 2 antiporal testes by female gonads. Cirrus sac relatively large, 208–245 × 39–48 (229 × 43, n = 15), commonly overlapping ventral longitudinal canal (Fig. 9 C). Genital atrium simple, cup-shaped, deep, opens laterally about middle of lateral proglottis margin. Cirrus large, 95–123 (106, n = 20) long, conical, with relatively wide basal region, 27–34 (30, n = 20) in diameter, and narrow distal region, 17–24 (19, n = 20) wide; armed along entire length with relatively small (up to 4 long) rosethorn-shaped spines (Fig. 9 B). Internal seminal vesicle, ovoid, 86–113 × 30–40 (101 × 36, n = 15), shorter than half of cirrus sac length (Fig. 9 C). External seminal vesicle 88–145 × 35–72 (115 × 53, n = 8), with size approximately equal to that of seminal receptacle.

Ovary 270–395 (342, n = 10) wide, median, fan-shaped, irregularly lobed, slightly overlapping testes (Fig. 9 C). Vitellarium 70–115 × 140–195 (92 × 167, n = 8), postovarian, median, scarcely lobed. Vagina tubular, clearly distinct from seminal receptacle; ventral to cirrus sac. Distal part of vagina 105–112 × 15–25 (107 × 19, n = 8), thick-walled. Seminal receptacle relatively small, 135–155 × 18–33 (147 × 72, n = 8).

Gravid proglottides 490–611 × 815–1240 (552 × 987, n = 10). Fully developed uterus labyrinthine, occupying entire median field and extending bilaterally beyond longitudinal osmoregulatory canals. Eggs 23–26 × 38–43, elliptical, with thin outer coat; oncosphere 11–13 × 14–15 (Fig. 9 D). Embryophore fusiform, 12–15 × 23–26, with straight polar processes. Embryonic hooks small, 7.5–8.2 long.

Remarks: Results of the present morphological analysis of specimens of A. macrocirrosa do not indicate a high degree of differentiation between cestode populations from the Nearctic and the Palearctic now isolated by the Bering Strait. Similar to observations in A. beringiensis, we noted differences in egg dimensions between conspecific cestodes in the Nearctic and Palearctic (Makarikov et al. 2011). We attribute these minor differences to methods of specimen preparation and mounting medium. Otherwise, specimens we examined representing populations of A. macrocirrosa in red backed voles and limited numbers of cestodes in red squirrels across the Holarctic do not appear to be differentiated morphologically relative to specific geographic localities (Makarikov et al. 2011). These constitute the first confirmed geographic records for A. macrocirrosa from eastern Beringia and the Nearctic. Arostrilepis macrocirrosa is a dominant cestode of Myodes voles at high latitudes across the Holarctic. Occurrence in other arvicolines and sciurids appear to represent incidental infections; A. macrocirrosa in red squirrels from Alaska is known based on multiple hosts and specimens collected at the Yukon Charley Rivers National Preserve, Lake Clark National Park and near Chitina (Appendix 1). Records in Myodes voles are currently limited to M. rutilus from North America, and further collections will be necessary to determine if there is a broader geographic range extending to temperate latitudes in the Nearctic. It is not known if A. macrocirrosa and A. cooki are parapatric and restricted to different species of Myodes, or whether populations of these cestodes occur in sympatry.