the cynipoid genus paramblynotus - American Museum of Natural ...

2007 LIU ET AL.: REVISION OF PARAMBLYNOTUS (HYMENOPTERA) 23
notus and Kiefferiella may have been caused
by the formation of the Rocky Mountains in
western North America. The Rocky Mountains
were mainly formed during the latest
Paleocene to early Eocene (ca. 56–40 Ma)
(Leopold and MacGinitie, 1972), and they
created direct topographic barriers to plant
movement between southwestern North
America and the rest of the then continuous
land mass Asiamerica (Briggs, 1987).
The endemic distribution of Kiefferiella in
western and southwestern North America
(Idaho, California, and Texas) is apparently
also due to the formation of the Rocky
Mountains, which caused the interior of
North America to become increasingly drier.
The remnants of the earlier, moistureadapted
boreotropical flora were largely
confined to the western slopes or retreated
southward (Leopold and MacGinitie, 1972;
Tiffney, 1985). Kiefferiella might have been
associated with the earlier boreotropical flora
and represents a relic taxon that has retreated
to the south. The fossil species K. connexiva
from Upper Eocene beds in Colorado
(34.1 Ma) (Ronquist, 1995a) indicates that
the genus was once more widespread in
interior North America than it is today.
The disjunction within Paramblynotus between
the Nearctic and East Asia, that is,
between P. virginianus and the rest of the
genus, probably resulted from the Terminal
Eocene Event (34–33 Ma), when the global
temperature dropped drastically (Wolfe,
1978, 1980, 1987; Potts and Behrensmeyer,
1992) and the climatic seasonality increased
(Wolfe 1978, 1980, Tiffney, 1985). This
disrupted the warm-temperate to subtropical
broadleaved evergreen forests that had
stretched from Asia to North America and
replaced them in the Bering area with a cooltemperate
deciduous forest (Wolfe, 1980;
Tiffney, 1985). Following the Terminal Eocene
Event, the climate continued to deteriorate
with short, warmer intervals in the
Oligocene and Miocene, and this trend of
climate deterioration gradually led to the
extreme cold of the Pleistocene (Wolfe, 1978;
Tiffney, 1985). Thus, suitable habitats for
hardwood-associated organisms like Paramblynotus
were generally lacking in the
Bering area after the Terminal Eocene Event
(Nordlander et al., 1996, and references
therein), making dispersal of such organisms
across the land bridge difficult.
According to the third alternative hypothesis
(fig. 18), the stem species of the Mayrellinae
was limited to the Nearctic. After
a vicariance event within the Nearctic, the
ancestral species of Paramblynotus expanded
its distribution by dispersal into the eastern
Palearctic, and a subsequent vicariance event
gave rise to P. virginianus and the clade
comprising the rest of Paramblynotus. In this
scenario, the formation of the Mid-continental
Seaway in North America in the mid-
Albian (ca. 100 Ma) (Hallam, 1981; Crabtree,
1987) might correlate with the splitting
between Paramblynotus and Kiefferiella. The
retreat of the seaway and reconnection of the
two parts of the continent shortly before the
end of the Cretaceous (70 Ma) (Hallam,
1981) allowed dispersal of Paramblynotus
from eastern North America to the eastern
Palearctic by way of Beringia. Alternatively,
as suggested in the previous scenario, the
event was caused by the formation of the
Rocky Mountains during latest Paleocene to
early Eocene, and the newly evolved Paramblynotus
then dispersed to eastern Palearctic
by way of Beringia. In either case, the
dispersal, as suggested earlier, most likely
took place before the Terminal Eocene
Event.
The genus Paramblynotus was probably
widely distributed in East Asia, and its
species may have differentiated in response
to the differentiation of the forest vegetations
of the region into temperate elements of the
north and subtropical to tropical elements in
the south. Currently, the terrestrial ecosystems
in continental East Asia stretch from
above the polar circle well into the tropics.
This large expanse of continuous inland has
existed since the latest Triassic (Metcalfe,
1988). Within this region, there has been no
major physical barrier impeding the migration
of plants (Latham and Ricklefs, 1993) or
associated organisms, such as Paramblynotus.
The cooling trend since the Oligocene led to
the selection of cool-adapted taxa from the
boreotropical flora and their addition to the
mixed mesophytic forest of the middle
latitudes (Wolfe, 1978; Tiffney, 1985). The
continued cooling of climates of later times,
which gradually led to the extreme cold of the