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

830 G.B. Wiggins and C.R. Parker
Britain and Iceland. We infer that this evidence indicates vicariant speciation from a
circumboreal ancestor. Outlying records of A. glacialis in Idaho, Utah and California suggest
relict montane populations from the time when the species occurred south of the Pleistocene
glacial ice. In these populations, and also in the Greenland material, variations in male
genitalic structure are more common than in the populations of northern North America
(Wiggins in press).
II. Holarctic Species Widespread in North America
Each of these species is now widely distributed in both North America and Eurasia; 28
of them are known in the Yukon, constituting about 18 per cent of the Trichoptera. Many
are now transcontinental, and these broad Nearctic ranges seem more likely to follow from
glacial refuge along the southern margin of the ice. Thus, a number of these Holarctic species
probably occurred in North America before the Pleistocene, and probably have been on this
continent for at least the past 3 million years, before the connection between Asia and North
America was overrun by the sea in mid-Pliocene time. However, southward movement of
any of these species from Beringia through the ice-free corridor between the Laurentide and
Cordilleran glaciers might have occurred during interglacial periods of the Pleistocene (see
Biological Aspects), and is difficult to detect. For some category II species, sister relationships
between Nearctic and Palaearctic species pairs suggest origin from common circumboreal
ancestors, and perhaps arose from intercontinental vicariance in the Pliocene or
earlier. Evidence indicates that for the most part species involved in recent dispersal moved
from Asia to North America (see Biogeographic Analysis). A few species, e.g. Brachycentrus
americanus and Onocosmoecus unicolor, appear to have originated in North America
and dispersed to Asia across the Bering land bridge.
Evidence from intraspecific morphological variation suggests that some Nearctic species
were divided, with populations confined to the south of the advancing glacial front while
disjunct conspecific populations were restricted to Beringia: e.g. Brachycentrus americanus
(44), Micrasema gelidum (45), Oecetis ochracea (63), Ylodes reuteri (68), Limnephilus
picturatus (113), Onocosmoecus unicolor (122), and Agrypnia colorata (129). For the
remaining species of category II, evidence available now is inadequate to support any
inference about their origin and direction of dispersal.
Although several of these species now occur in arctic tundra habitats, most of them are
also widely distributed in forest and grassland biomes at more temperate latitudes. Consequently,
these species do not comply with the general pattern in some other groups that the
arctic and treeline species were derived from Beringia, while the boreal and subarctic fauna
moved northward from refugia below the glacial front. The most northerly species of
category II are Asynarchus iteratus (74) and Apatania zonella (43).
Two species (†) known from Alaska or the Northwest Territories are also considered
under this category; although not yet recorded from the Yukon, they probably occur there.
Spicipalpia
Glossosomatidae
Glossosoma intermedium (Klapalek)
Hydroptilidae
Oxyethira ecornuta Morton (†)
Rhyacophilidae
Rhyacophila narvae Navas
Annulipalpia
Hydropsychidae
Arctopsyche ladogensis (Kolenati)
Polycentropodidae
Neureclipsis bimaculata McLachlan