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

828 G.B. Wiggins and C.R. Parker
along the southern margin of the ice, or it may have entered North America for the first time
during the Pleistocene. This shared pattern of postglacial distribution might indicate that
each of these species passed the Wisconsinan glaciation as disjunct eastern populations;
larvae of each of them usually occur in cool lotic habitats.
Greenland Trichoptera. Species of Trichoptera occurring in both North America and
Greenland pose relevant distributional questions arising from glaciation because most of
them occur in the Yukon as well. Some are Holarctic species, and some are strictly Nearctic,
but the fact that all of them occur in Greenland raises the possibility that they illustrate some
general principles of high-latitude distribution. Since the insect fauna of Greenland includes
few if any endemic species, and was derived to a large extent by postglacial dispersal from
North America (Downes 1966), we infer that these Nearctic species of Trichoptera reached
Greenland after recession of the glaciers. Occurrence of a Palaearctic species, Limnephilus
griseus (Linnaeus), in Greenland (Fristrup 1942) raises a further possibility that some of
the Holarctic species might have reached Greenland from Europe; records for a second
Palaearctic limnephilid from Greenland, Halesus radiatus (Curt.), are believed to be in error
(N.P. Kristensen, pers. comm.). Ice rafting from western Norway has been postulated as a
sweepstakes route for the repopulation of Iceland and other North Atlantic islands by insects
about 10 000 years ago (Buckland et al. 1986). Although adult Trichoptera are generally
short-lived, an adult diapause in species of Limnephilus adapted to transient waters could
prolong the life span, perhaps enabling these species to endure such a passage; their egg
masses embedded in gelatinous matrix are resistant to desiccation (Wiggins 1973). All of
the Greenland Trichoptera are case-making species of the Integripalpia whose larvae live in
lentic waters or in slow currents of streams.
Common patterns in the far northern distribution of Lepidoptera and of several other
groups of insects reveal 2 elements in the fauna of Greenland (Downes 1966). Species of
the high arctic occurring on adjacent Ellesmere Island are very largely shared with northern
Greenland. In the Trichoptera, only 2 species of the Greenland fauna can be considered
high-arctic forms—Apatania zonella (43) and Grensia praeterita (87). The first occurs on
Ellesmere Island (Corbet 1966) where it is the most northerly species of Trichoptera known
in North America, although it is an Holarctic species and is recorded also from Yukon to
Quebec; Grensia praeterita is a circumpolar species recorded mainly above treeline although
not from Ellesmere Island. The high-arctic species are held to have reached Greenland by
way of a far northern route across the Arctic Archipelago (Downes 1966), raising the
possibility that they could have passed the Wisconsinan glaciation in a Peary Land refugium
along the northern edge of Greenland (e.g. Danks 1981, fig. 5). The relatively small number
of high-arctic Trichoptera indicates that these insects are not well adapted to the rigours of
existence at high latitudes.
The second element in the Greenland insect fauna comprises species of more southerly
distribution that are of low-arctic or boreal origin (Downes 1966). Most of the Greenland
Trichoptera appear to be of this group because they range widely across the boreal forest
and often farther to the south. These species are likely to be postglacial dispersants to
Greenland, although probably by way of the Arctic Archipelago and Baffin Island. It appears
that most of them moved into deglaciated North America from refuges in the central part of
the continent, finally reaching Greenland.
Evidence relevant to category I species in Greenland is outlined below, and for other
species under the category indicated; 2 of the Nearctic species known from Greenland have
not been recorded from the Yukon (†).