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

Caddisflies of the Yukon 835
Micrasema gelidum McLachlan (45)
An intensive taxonomic analysis of this species complex was carried out by
BotojAneanu (1988), who concluded from a study of male genitalic morphology that
M. gelidum represents a polytypic superspecies of 6 prospecies, allopatrically distributed
over a large part of northern Eurasia and North America. Three of the prospecies are
represented in the Yukon and Alaska and in the Far East of Russia: M. (gelidum) gentile
McLachlan (junior synonym M. scissum McLachlan, Kimmins and Denning 1951);
M. (gelidum) extremum BotojAneanu; and M. (gelidum) gelidum McLachlan which also
extends across the whole of northern Eurasia to Norway (junior synonyms: M. kluane Ross
and Morse 1973; M. subscissum Martynov; M. sibiricum Martynov). Because M. gelidum
is a member of a Nearctic group comprising M. bactro Ross, M. diteris Ross, M. onisca
Ross, and M. sprulesi Ross, its origin was believed to have been in western North America
(BotojAneanu 1988); and the mosaic of prospecies constituting M. gelidum was attributed
to the isolation of populations during Pleistocene glacial periods and their recolonization
following glacial retreat. Complexity within the superspecies M. gelidum was interpreted to
indicate that glacial intervals preceding the last Wisconsinan period were effective in
isolating populations for periods sufficient to effect morphological divergence. One form in
the complex, M. (gelidum) canusa BotojAneanu (1988), occurs in central North America,
and probably was isolated along the southern margin of the glacial ice; but the more northerly
Nearctic forms were inferred to have passed periods of glacial advance in the Beringian
refugium. As with species of Apatania, larval habitats for members of the gelidum complex
broaden with increasing latitude—those in the most southerly localities living in spring
streams, but northward habitats include rivers and also lakes in the most northerly localities
(BotojAneanu 1988). Consequently larval habitat probably would not have been a
deterrent to dispersal of the northern populations across the Bering land bridge during the
Pleistocene, an inference further supported by occurrence of M. gelidum on the Arctic coastal
plain (Fig. 1, region 1).
Goeridae
Goera tungusensis Martynov (47)
The range of this species known originally from Siberia must now be extended to
northern Quebec, the Northwest Territories, and almost certainly the Yukon (see Taxonomic
Note 2). We also have from Alaska a pharate male that may represent a morphological
variant of this species, or perhaps an unnamed sister taxon. If Pleistocene dispersal of
G. tungusensis across the Bering land bridge to North America is indicated, the species
could have extended eastward in North America after withdrawal of the glaciers. However,
the widely scattered North American records suggest the possibility of repopulation
of deglaciated areas from south of the ice where a pre-Pliocene circumboreal
ancestor took refuge, and from which a disjunct Alaskan population has begun to
diverge.
Leptoceridae
Ceraclea annulicornis (Stephens) (54)
Phylogenetic analysis (Yang and Morse 1988) indicated that C. annulicornis is one of
an unresolved group of 4 species—2 in China, and C. ruthae (Flint) from eastern North
America. Species that are now transcontinental in North America, such as C. annulicornis,
probably passed the Pleistocene to the south of the ice mass and if so, would have occurred
in North America before glaciation.