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

2007 LIU ET AL.: REVISION OF PARAMBLYNOTUS (HYMENOPTERA) 25
this floral segregation on Paramblynotus was
a division of the distribution of the genus in
East Asia, with the scaber group occurring in
the eastern Palearctic and its sister clade,
excluding the African species, in the Oriental
region.
In comparison with the poor representation
of Paramblynotus in eastern North
America with only one species, the genus is
represented by 15 species in the eastern part
of continental Asia. Similar asymmetric diversification
patterns also occur in other taxa
with eastern North America and eastern Asia
disjunction, including plants (Li, 1952; Latham
and Ricklefs, 1993; Qiu et al., 1995;
Wen and Zimmer, 1996; Wen et al., 1996) as
well as insects (Tangelder, 1988, Nordlander
et al., 1996), therefore requiring a general
explanation. It has been recognized for a long
time that the floras of eastern North America
and eastern Asia share many taxa (reviewed
by Graham, 1972; Boufford and Spongberg,
1983), primarily at the generic level (Li,
1952). It is also well known that the diversity
of plant species of eastern Asia is three times
as great as that of eastern North America
(Tiffney, 1985; Latham and Ricklefs, 1993).
This is at least partly due to the fact that the
genera shared between the two regions tend
to be more species-rich in eastern Asia (Li,
1952; Latham and Ricklefs, 1993). Tiffney
(1985) suggested that the greater plant species
diversity in eastern Asia occurred because
this region had suffered less extinction in the
Quaternary. If this applies to Paramblynotus,
we would expect to find some of the Asian
species near the base of the phylogenetic tree
of the genus. Instead, the genus is disjunct at
the very base of its phylogenetic tree, with all
the Asian species belonging to a monophyletic
clade. This distribution pattern strongly
indicates considerable diversification in eastern
Asia after the disjunction. Similar patterns
have also been found in several
phylogenetic studies on plants (Qiu et al.,
1995; Wen and Zimmer, 1996; Wen et al.,
1996). Therefore, the greater species diversity
in eastern Asia cannot be solely explained as
a refuge effect. Latham and Ricklefs (1993)
observed that the existing continuous corridor
of mesic forests connecting tropical and
temperate latitudes in eastern Asia might
have been continuously present since before
the Tertiary. Therefore, they suggested that
colonization of temperate biomes in Asia
from the tropics played an important role in
the development of biotic diversity in the
temperate forest communities there over long
periods. This is apparently supported by the
floral data from the two regions; genera with
tropical affinity have distinctly more species
in eastern Asia than in eastern North
America (Li, 1952; Latham and Ricklefs,
1993). The genus Paramblynotus provides an
additional example of this type. Similarly,
colonization of tropical biomes by temperate
elements has probably also occurred. Such
biotic exchanges between the tropical and the
temperate latitudes may have been augmented
by the rather frequent climatic oscillations
in the area since the Terminal Eocene Event,
particularly in the late Neogene and the
Quaternary (P.Wang, 1984; X. Wang, 1984).
Several monophyletic, predominantly tropical
Southeast Asian branches of Paramblynotus
have apparently secondarily recolonized
temperate eastern Asia. These include
(P. fretus, P. apeosus), (P. kosugii, P.
fraxinii), and certainly P. shimenensis, which
is the only known northern subtropical
continental species of a monophyletic group
that is otherwise exclusively found on Southeast
Asian islands (represented by F in
figs. 12–14 and in appendix 1).
All the Paramblynotus species from tropical
Southeast Asia constitute a monophyletic
group, together with some species from other
geographical regions (the punctulatus group;
figs. 12, 14, and appendix 1). The high diversity
of the genus in this part of the
Oriental realm might be due to the sea level
changes occurring there since the late Oligocene.
According to Hutchison (1989, and
references therein), the global sea levels
remained high from the Palaeocene through
Oligocene (65–30 Ma). By the late Oligocene
(29 Ma), sea levels fell spectacularly to about
250 m below the present level, and from then
onwards the sea levels progressively rose to
about 220 m above the present level in the
middle Miocene (13 Ma). The sea level then
fell again to 220 m below the present level in
late Upper Miocene (6.6 Ma), and rose once
again to 140 m above the present level at the
Miocene-Pliocene boundary (5.2 Ma). This
was followed by several cycles of rapidly