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

836 G.B. Wiggins and C.R. Parker
Ceraclea excisa (Morton) (†)
Although not known from the Yukon, this species probably occurs there because it is
recorded from Alaska (Milne 1934; Morse 1975), Wisconsin, and Michigan to Quebec and
Massachusetts; and it extends through northern Europe and Siberia to the Amur region
(Lepneva 1966). It is considered to be the sister taxon of the group of 4 species that includes
C. annulicornis (Yang and Morse 1988); its widespread occurrence in North America leads to
the same interpretation as for the preceding species.
Ceraclea nigronervosa (Retzius) (56)
Although most species of the nigronervosa group are confined to North America (Morse
1975), C. nigronervosa is the sole Holarctic species. Larvae live in large rivers, where they
feed on colonies of freshwater sponge (Resh 1976; Solem and Resh 1981). In addition to
typical nigronervosa specimens that are consistent with most others examined from Europe
and Asia, our North American material reveals a brown-winged variant with distinctive male
genitalic characters (Fig. 4) which is also represented in Europe (Taxonomic Note 3). Thus
the 2 forms appear to be broadly sympatric and could have reached North America during
the Pleistocene by way of unglaciated Beringia, and spread southward following glacial
retreat. This interpretation would require that sponges, the food of the larvae, occurred in
waters of the Bering land bridge; and this is feasible because C. nigronervosa now occurs
in the far northern Yukon (Fig. 1, region 4). However, this species might have been in North
America before the Pliocene separation from Asia because the range of C. nigronervosa now
extends to Wyoming.
Oecetis ochracea (Curtis) (63)
This is the only Holarctic species in Oecetis, and no phylogenetic analysis of the genus
has been made. The subspecies O. o. carri Milne (1934) was segregated to discriminate
between North American and European populations by genitalic characters. We found no
evidence to support this interpretation; variation in genitalic characters was evident, but
showed no geographic correlation. However, specimens from northern Europe and the
Yukon are darker brown in colour overall than those from other parts of North America.
Although slight, this indication of genetic continuity in O. ochracea through Nearctic
Beringia and Europe suggests that the light-coloured Nearctic populations were derived from
ancestors forced to the south of the continental glacier; if so, this species probably was
present in North America before the Pleistocene glaciation.
Ylodes reuteri (McLachlan) (68)
In discussing the Nearctic range of this species, Ross (1965, as Triaenodes griseus)
alluded to morphological variants in the Rocky Mountains, the western part of the Northwest
Territories, and the Hudson Bay area. Highly variable populations in southern Saskatchewan
were interpreted as an intergrading blend from all 3 areas—an example of caddisfly species
that passed the last glaciation in discrete areas in the Rocky Mountains, in eastern North
America, and in Beringia. If so, Y. reuteri or its ancestor must have occupied North America
early enough, before Asia and North America were separated in the Pliocene, to have become
established to the south of the glaciers.
Limnephilidae
Asynarchus iteratus McLachlan (74)
This species was assigned to the lapponicus group (Schmid 1954b), and was considered
to be so close to A. aldinus (Ross) from Alberta that the two could be geographic variants
of the same species. The close similarity suggests that separation between them might have