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

26 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 304
fluctuating sea levels. These sea level fluctuations
had relatively little effect on the land
area of Africa or South America, but they
drastically altered the land area configuration
in Southeast Asia (Heaney, 1991). During
times of low sea levels, Sumatra, Java, and
Borneo were part of a peninsula projecting
south from continental Asia (often referred
to as Sundaland) (Morley and Flenley, 1987;
Heaney, 1991), facilitating the dispersal of
plants and animals. At times when sea levels
became high, large land areas were inundated
by water and topological elevations became
isolated islands. The many cycles of sea level
fluctuations since the late Oligocene presumably
repeatedly caused plant and animal
species to expand their distributions to newly
connected areas and then become isolated in
subpopulations, giving rise to new taxa.
These cycles of land connection and island
isolation have probably caused the high level
of endemism and complicated phylogeny of
the Southeast Asian and East Asian faunas
of Paramblynotus, with sister relationships at
different levels (figs. 12–14). The apical
phylogenetic position, low phylogenetic resolution,
and relatively high species diversity
of the monophyletic clade comprising predominantly
species from the two areas indicate
rather recent and rapid diversification.
The few Paramblynotus species occurring
in southern North America and South
America are apparently the result of quite
recent dispersal. They form a monophyletic
clade nested within the diverse Southeast
Asian and eastern Palearctic branch of
Paramblynotus (figs. 12, 14). It is currently
difficult to understand how they reached the
New World. Probably a few colonizers
accidentally dispersed from Southeast Asia,
perhaps in a floating log, giving rise to the
stem species of the group, which subsequently
radiated.
The dispersal of the ancestral species of the
African clade from the eastern Palearctic, as
suggested by the biogeographic reconstructions
(figs. 17–19), probably occurred rather
early because of the basal position of this
clade. The route of dispersal could have been
either by way of Arabia or by way of the
Iberian Peninsula. However, the latter was
connected to Morocco in Africa only briefly
during the Messinian (6.0–5.5 Ma) (Rögl and
Steininger, 1984; Rage, 1988), and the
dispersal event probably occurred earlier.
Thus, the dispersal of Paramblynotus to
Africa most plausibly took place by the
Arabian Peninsula, more precisely during
the latest Oligocene to earliest Miocene (26–
23 Ma). Africa had been isolated from
Laurasia since the Mesozoic rifting, and it
only came into contact with Eurasia again
when the Afro-Arabian landmass, due to its
northward movement, collided with southern
Central Asia in the middle Miocene (18–
17 Ma) (Axelrod and Raven, 1978). However,
a land bridge between Arabia and Iran
had existed at least occasionally during the
latest Oligocene and earliest Miocene (26–
23 Ma), connecting Africa and Eurasia (Rögl
and Steininger, 1984; Potts and Behrensmeyer,
1992). During the latter period,
Arabia had scrubland communities with
wetter vegetation along waters (Potts and
Behrensmeyer, 1992), and northern Africa
was covered by Savanna woodland with
subtropical laurel forests along the northernmost
part (Axelrod and Raven, 1978; Potts
and Behrensmeyer, 1992). Subtropical savanna
woodland had also developed in southern
Eurasia during these periods (Axelrod and
Raven, 1978). In the Northern Hemisphere,
temperate deciduous forests replaced the
previous boreotropical flora from the latest
Oligocene to the mid-Miocene, and extended
from eastern Asia (Xu, 1984a, 1984b)
through western Siberia (Song et al., 1984;
Wolfe, 1985) to Central Asia (Song et al.,
1984; Zhilin, 1989). It appears very likely that
the ancestral species of the African Paramblynotus
dispersed in these extensive temperate
broadleaved deciduous forests to
reach Africa via the land bridge between
Arabia and Iran during the latest Oligocene
to earliest Miocene (26–23 Ma) (Potts and
Behrensmeyer, 1992). Later dispersal is less
likely because of the development of steppes
and semidesert in Central Asia during the late
Miocene (Song et al., 1984; X. Wang, 1984;
Xu, 1984a, 1984b).
Since the initial dispersal, the ancestral
species of the African group probably expanded
its distribution along with the montane
forest vegetation. The current records of
the African species are almost exclusively
from mountainous areas, mainly from local-