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

Caddisflies of the Yukon 837
been brought about by segregation of a portion of the Nearctic population of A. iteratus to
the south of the advancing glaciers, giving rise to A. aldinus, while A. iteratus became
confined to Beringia as a glacial relict. If that were so, A. iteratus or its ancestor probably
reached North America from Asia before the land bridge between the 2 continents was
overrun by the sea during the Pliocene.
Asynarchus lapponicus (Zetterstedt) (75)
Variation in the superior and intermediate appendages of the males showed no coherent
pattern correlated with geographic distribution. Among the species assigned to the lapponicus
group (Schmid 1954b), the sister species of A. lapponicus would be the northern North
American species A. montanus Banks. Prominent morphological differences in the genitalia
of the 2 species suggest that they have been separate for some time, perhaps through
inter-continental vicariant speciation, with A. lapponicus dispersing from Asia to North
America across the Bering land bridge during the Pleistocene. Disjunct distribution between
northern and central populations of this species in Europe (Malicky 1988, fig. 11) suggests
that it was widely distributed in Europe and Asia before the glacial advances of the
Pleistocene. If A. lapponicus was confined to Beringia during Pleistocene glaciation, it has
spread widely in North America following recession of the ice, in contrast to some other
Nearctic Beringian species (see category III). The larval habitat for A. lapponicus is littoral
areas of lakes, tundra pools, and slow streams (Winchester 1984), and the species is
univoltine at the latitude of Tuktoyaktuk, Northwest Territories (69°29′N).
Limnephilus dispar McLachlan (97); L. externus Hagen (98); L. femoralis Kirby (100);
L. nigriceps (Zetterstedt) (108); L. picturatus McLachlan (113); L. rhombicus (Linnaeus)
(114); L. sericeus (Say) (117).
Phylogenetic relationships within the large genus Limnephilus have not been investigated
in sufficient depth to support inferences about the geographic origin of the species.
All of these species have a transcontinental distribution in North America, and probably
occurred on this continent before glaciation in the Pleistocene. We found morphological
variation in several of the species, but a congruent pattern was evident only in L. picturatus.
Comparison of specimens of L. picturatus from all parts of the range in North America
[64 #, 85 !] with Eurasian material indicates genetic continuity between Nearctic Beringia
and Eurasia, and restriction in gene flow between Beringian populations and those from
other parts of North America. This argues for isolation of Nearctic populations of L. picturatus
south of the glaciers while Palaearctic immigrants of the species entered Beringia.
Accordingly, L. picturatus probably would have occurred in North America before the
Pleistocene, and its Holarctic distribution would pre-date the Pliocene separation between
North America and Asia. On melting of the glaciers, the more southerly Nearctic populations
appear to have been more successful in colonizing deglaciated territory than have the
Beringian populations. Analysis of Greenland populations for these variable characters
might shed light on their origin.
Thus, the patch of stout setae on the ventral surface of the hindwing R2 in males is well
developed in all Eurasian specimens examined and in about 95 per cent of Beringian
specimens, but equally well developed in only about one third of other North American
specimens. The pterostigma is light in colour in 90 per cent of Beringian and Palaearctic
specimens examined, but light in about 50 per cent of other North American specimens.
Inferior appendages in the male genitalia are triangular in dorsal aspect in about 86 per
cent of Nearctic Beringian specimens; about 4% of specimens from other parts of North
America are similar in this character, where the predominant condition is for parallel dorsal