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

2007 LIU ET AL.: REVISION OF PARAMBLYNOTUS (HYMENOPTERA) 19
alternatives based on the majority consensus
tree of type III island trees. The reconstructions
based on type I and II island trees
correspond to these reconstructions with only
minor differences.
To distinguish the most likely scenario
among the competing alternatives, it is
necessary to take into account the paleoenvironmental
evidence as well as the current
distribution pattern.
The latest geological time when Africa was
united with the northern land mass of
Laurasia was in the Late Triassic (ca. 235–
210 Ma) (Axelrod and Raven, 1978; Wing
and Sues, 1992). However, the biotas of
Gondwana and Laurasia were not biogeographically
separated by impassable dispersal
barriers until the Middle to early Late
Jurassic (180–145 Ma). This is because the
rifting of Pangaea was a slow process that
continued through the Early Jurassic, and
dispersal of major continental areas and
separation by ocean basins probably did
not occur until then (Wing and Sues, 1992,
and references therein). On the other hand,
the Triassic biotas were remarkably provincial,
and they are commonly divided into
northern (Laurasian) and southern (Gondwananian)
realms (Wing and Sues, 1992, and
references therein). It seems likely that an
assumed widespread ancestor of Mayrellinae
and Paramblynotus, which had been distributed
so widely across Pangaea, had also
colonized and left some descendants in the
other southern continents besides Africa.
However, the only Southern Hemisphere
elements of the Mayrellinae outside Africa
are a few Paramblynotus species from Central
and South America, which are apparently
rather young and have dispersed there recently
(Ronquist, 1995a; figs. 12, 16–19).
Moreover, species of Kiefferiella and Paramblynotus
are only known to be associated
with angiosperm trees, which were generally
lacking in the earliest Cretaceous (Doyle and
Donoghue, 1986; Wing and Sue, 1992; Crane
et al., 1995). Thus, the Mayrellinae (Kiefferiella
and Paramblynotus) are unlikely to have
originated in a biogeographically united
Pangaea before the Middle to early Late
Jurassic. Therefore, a widespread ancestral
distribution of the Mayrellinae and/or Paramblynotus
is not plausible.
Ronquist (1995a) indicated an ancestral
distribution of Paramblynotus somewhat
narrower than the previous scenario of
a widespread ancestral distribution. According
to Ronquist, the split between Kiefferiella
and the stem species of Decellea + Paramblynotus
(i.e., the genus Paramblynotus
sensu lato) might correlate with the separation
of North America from western Africa
in the middle Jurassic (ca. 180 Ma). That
scenario is not supported by the DIVA
analysis of the present study because it
postulates the origination of Paramblynotus
either in Africa or in Gondwanaland including
Africa. With the changed placement
of Decellea, deeply nested within Paramblynotus,
Africa is not likely to be part of the
ancestral area of Paramblynotus. Instead, it
appears that the Mayrellinae originally were
in the Holarctic or the whole Northern
Hemisphere, and that some of the basal splits
in the subfamily were due to vicariance
between elements of the Nearctic and East
Palearctic or East Palearctic + Oriental.
These early vicariance events could have
resulted from biotic exchanges between the
Nearctic and East Palearctic either by way of
Europe or by way of the Bering land bridge.
The European route appears less likely
than the Bering route. Many of the lineages
close to the base of the phylogeny of the
Mayrellinae are restricted to or are at least
most diverse in the eastern Palearctic. In
contrast, no species of the subfamily has ever
been found in Europe. The thermophilic
elements of the boreotropical flora and the
succeeding mixed mesophytic forest, with
which the early Mayrellinae were probably
associated, extended to high latitudes of the
Northern Hemisphere in the late Cretaceous
and in the Tertiary when the global climate
was warmer and more equitable. It is
generally accepted that the adverse effects
of the advancing Pleistocene glaciers (Wolfe,
1978, 1985; Tiffney, 1985) on these elements
were more pronounced in Europe than in
other northern continents. However, remnants
of these thermophilic elements survived
in the so-called Tertiary refugia, particularly
in topographically complex areas such as the
Balkans and Caucasus (Tiffney, 1985). Nonetheless,
no Mayrellinae is known from these
areas.