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

814 G.B. Wiggins and C.R. Parker
brown- and gray-winged specimens. Thus females can be identified only by the brown
membrane of the forewings and by association with males.
In North America material of the brown-winged form was examined from the Yukon
(10, 12, 17; ROME, SMDV), Alaska, and British Columbia; the gray-winged form was
collected only in the Yukon (4, 10, 12; ROME). Adult specimens were collected along lakes
and streams and on the banks of the Yukon River. However, we received a series of the
brown-winged form collected near St. Petersburg, Russia, by V.D. Ivanov; genitalic structure
of males is entirely consistent with our Beringian variant (Fig. 4). Consequently, we infer
that two morphs may occur sympatrically over much of the range attributed to C. nigronervosa,
and perhaps the two differ in preferred habitat or life cycle. The issue has to be resolved
by a worker with access to populations in Europe and Asia.
Note 4. Mystacides sepulchralis (Walker) (60)
Although this species is common and widely distributed over much of North America
including the Yukon and Alaska (Yamamoto and Wiggins 1964), its status beyond North
America requires clarification. Holarctic distribution was attributed to M. sepulchralis by
Yamamoto and Ross (1966), even while recognizing as valid the Siberian species M. bifidus
Martynov (1924b); supporting evidence was not given, and we know of none apart from a
record from Siberia attributed initially to M. sepulchralis (Martynov 1910) but later assigned
to M. bifidus (Martynov 1935).
There is considerable variation in genitalic characters of M. sepulchralis. Through the
assistance of V.D. Ivanov, we have obtained information on genitalic characters of the
holotype of M. bifidus in the Zoological Institute, St. Petersburg; and we have examined
other specimens, indicating that there is at least some variation in this species, too. The two
forms are very close, and clearly are sister taxa; but Martynov affirmed his view (Betten and
Mosely 1940) that the Siberian M. bifidus Martynov and the North American M. sepulchralis
(Walker) are separate species. We follow that interpretation here because small morphological
differences in other species are used here as the basis for inferring separation during
glacial periods. Detailed analysis of the variation in populations within each continent might
reveal evidence of a Beringian interchange; whether such differences would confirm status
as species or as intraspecific variants would emerge from the analysis. For the present, we
interpret M. sepulchralis as a strictly North American species.
Larvae of M. bifidus, for which we have no information, could be relevant to this
question. In recent years, distinctive larvae in some populations of M. sepulchralis from
eastern North America have been found with head markings of discrete spots similar to those
in M. alafimbriata, and quite unlike the largely black heads characteristic of most sepulchralis
populations in North America (cf. figs. 3 and 4, Yamamoto and Wiggins 1964).
Association of these larvae with adults confirms that they are M. sepulchralis. This larval
dimorphism could have been established in populations isolated during the glacial period to
the southeast of the continental ice mass, although it does not appear to be reflected in
characters of the adults.
The sister species of M. sepulchralis/bifidus is M. alafimbriata, confined to western
North America including the Yukon and Alaska (Yamamoto and Wiggins 1964). Mystacides
alafimbriata and sepulchralis are only slightly different morphologically; and although there
appears to be little overlap in their ranges, the two have been taken in the same collections
in a few localities, all in the Yukon and Alaska. Possibly M. alafimbriata was derived from
populations isolated to the south of the Cordilleran glacier in the mountains of western North
America. Outlying montane glaciers along the Rocky and Cascade Mountain ranges served