Caddisflies of the Yukon - Department of Biological Sciences ...

Caddisflies of the Yukon 839
years, however, isolated collections of the species have been made in Saskatchewan and
northern Ontario (Fuller 1987). Based on the broad distribution of M. tinctus in northern
Europe and Asia, and on phylogenetic evidence for the origin of Molannodes in Asia (Fuller
1987), an eastward dispersal by way of the Bering land bridge is inferred. Evidence is
equivocal as to whether dispersal occurred in Pleistocene time or earlier.
Phryganeidae
Agrypnia colorata Hagen (129)
Material from Asia has been referred by most authors to A. principalis (Martynov), but
this name is a junior subjective synonym of A. colorata Hagen (Wiggins in press). All
Beringian specimens examined and all from the Palaearctic portion of the range are dark in
colour on the thorax, legs, and wings; and all have fully developed tibial spurs of 2,4,4,
typical for the family Phryganeidae (Fig. 18). The single exception in Palaearctic material
that we examined is a light-coloured female from the Keriya River area of China (Sinkiang
Prov.; ZMAS), although the tibial spurs were fully developed. In contrast, most North
American specimens taken outside Beringia are light in colour on the thorax, legs, and wings,
and have the tibial spurs reduced in some way. The pattern of reduction is variable—some
spurs may be absent, others reduced to tiny knobs; and in any pair of spurs, one might be
reduced or lacking and the other normal; opposite members of a pair of legs often have
different spur conditions. Exceptions occur in series from Fort McPherson, Northwest
Territories and Kamloops, British Columbia (ROME), in which specimens are dark as in
Beringian and Palaearctic material, but the tibial spurs are variable as in most North
American populations. No congruent variation was found in genitalic characters. [Specimens
examined: N. Am.—58 #, 55 !]
The sister species of A. colorata is A. legendrei (Navas) known only from China. We
interpret the light-coloured A. colorata to be a vicariant Nearctic form derived from dark
ancestral stock with unmodified spurs following separation of Asia from North America,
perhaps in Pliocene time. Nearctic populations would have been isolated to the south of the
Pleistocene glaciers when light colour and unstable tibial spurs could have been established;
disjunct montane populations of the light-coloured form in Wyoming and Utah are consistent
with this interpretation (Wiggins in press). The plesiomorphic dark Palaearctic form with
stable tibial spurs would have dispersed to Nearctic Beringia across the land bridge.
Following retreat of the ice, contact between the 2 forms in North America could have given
rise to intergrading populations such as those near Kamloops and Fort McPherson.
Agrypnia pagetana Curtis (135)
No close relative of this species is known (Wiggins in press). We infer that A. pagetana
is a Eurasian species that reached North America across the Bering land bridge, perhaps
during the Pleistocene, and dispersed through northern North America following recession
of the glaciers. It has not been recorded east of Hudson Bay. Populations of A. pagetana in
Europe range farther south to more temperate climates than in North America. Larvae of this
species live in small tundra ponds and slow-flowing streams; they are univoltine at
Tuktoyaktuk, Northwest Territories (lat. 69°29′N) (Winchester 1984).
III. Palaearctic-East Beringian Species
Because of their broad Eurasian range and restricted North American distribution, these
species are inferred to be of Palaearctic origin. Dispersal to North America across the Bering
land bridge during the Pleistocene seems the most likely route for a number of these species.
The 13 species in category III constitute about 10 per cent of the Yukon fauna.