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

other reasons, most Palaearctic-East Beringian species of category III have functioned
neither as aggressive colonists nor ecological generalists in North America; but quite clear
is the contrast with Europe and Asia where most of them are widely distributed, and
apparently are successful generalists. It is one of the striking paradoxes of Beringian distributions
that wide-ranging, and evidently competitively successful, Eurasian species remain
confined to their East Beringian outpost, evidently unable to disperse much beyond their
former glacial refuge. This distributional paradox can be added to the productivity paradox
(e.g. Hopkins et al. 1982) as significant questions about the biological history of Beringia.
This issue focusses on species of category III because they may differ from category II
essentially in lacking the competitive ecological edge required in new communities;
Palaearctic species having that competitive edge now meet the distributional criterion of
category II.
For several of them (Ylodes kaszabi, Arctopora trimaculata, Grammotaulius signatipennis,
Limnephilus stigma, and Agrypnia obsoleta), sister-group relationships suggest
intercontinental vicariance, perhaps during the Pliocene or earlier, followed later by dispersal
of the Palaearctic form to East Beringia, probably across the Pleistocene land bridge.
In Agraylea cognatella and Limnephilus fenestratus, morphological similarity to their
respective Nearctic sister species is so close that dichotomy during the Pleistocene could be
reasonably inferred. Subdivision of the range by glacial ice seems likely, with the Nearctic
sister species originating in isolation to the south of the glaciers.
Spicipalpia
Hydroptilidae
Agraylea cognatella McLachlan
Rhyacophilidae
Rhyacophila mongolica Schmid, Arefina
and Levanidova
Integripalpia
Leptoceridae
Ylodes kaszabi Schmid
Hydroptilidae
Agraylea cognatella McLachlan (4)
The Palaearctic range of A. cognatella appears to be circumscribed by A. multipunctata
Curtis which is widely distributed through Europe and western Asia (BotojAneanu and
Levanidova 1988); in North America, A. cognatella is evidently circumscribed to the south
of Beringia, not by A. multipunctata as has been the traditional interpretation (e.g. Ross
1944), but by a sibling species A. fraterna Banks apparently now widely distributed on this
continent (Vineyard and Wiggins in prep.). It seems reasonable to infer from present
evidence that A. cognatella is a Palaearctic-East Beringian species now confined in North
America to the refugium, and that A. fraterna passed the glacial period to the south of the
ice where it may have arisen.
Rhyacophilidae
Rhyacophila mongolica Schmid, Arefina and Levanidova (14)
Caddisflies of the Yukon 841
Limnephilidae
Arctopora trimaculata (Zetterstedt)
Dicosmoecus obscuripennis Banks
Grammotaulius signatipennis McLachlan
Grensia praeterita (Walker)
Limnephilus diphyes McLachlan
Limnephilus fenestratus (Zetterstedt)
Limnephilus stigma Curtis
Phryganeidae
Agrypnia obsoleta (Hagen)
Agrypnia sahlbergi (McLachlan)
Oligotricha lapponica (Hagen)