Download The distribution of Apsilochorema Ulmer, 1907: biogeographic

Apsilochorema distribution
91
The distribution of Apsilochorema Ulmer, 1907: biogeographic evidence
for the Mesozoic accretion of a Gondwana microcontinent to Laurasia
Wolfram Mey
Museum für Naturkunde, Institut für Systematische Zoologie, Humboldt-Universität Berlin,
Invalidenstrasse 43, D - 10115 Berlin, Germany
Key words: historical biogeography, Asia, Australia, Gondwana, zoogeography, aquatic insects,
Trichoptera, Apsilochorema
Abstract
Apsilochorema is the only genus of the southern hemisphere family Hydrobiosidae that occurs on the Asian continent. The origin of the genus is obscure and enigmatic. A
phylogenetic analysis of the species reveals the existence of
2 different subgenera: Archichorema and Apsilochorema
sensu stricto. They show different distributional patterns on
the Asian continent, and in the SW Pacific region including
Australia. A hypothesis is proposed to explain the distribution based on the plate tectonic history of SE Asia. Ancestors
of Apsilochorema reached Asia by rafting on terranes of
Gondwana origin. This crossing of the Tethys ocean happened at least twice. The species migrated into Asia on the
Lhasa and West Burma terrane in the Cretaceous
(Archichorema) and on the Indian plate in the Tertiary
(Apsilochorema sensu stricto).
Introduction
The distribution of the caddisfly family
Hydrobiosidae has several times attracted the
attention of Trichoptera specialists. One reason
for this interest is the conspicuous distribution
pattern (Fig.1) of the family, which comprises 47
genera, with a disjunction between South America
and Australia. Only the genus Apsilochorema
Ulmer occurs on the Asian continent. Secondly,
the Hydrobiosidae are regarded as the sister
group of the Rhyacophilidae (Frania and
Wiggins, 1997), the most ancestral family of extant Trichoptera, which has a pronounced
northern hemisphere distribution in contrast to
the Hydrobiosidae (Fig.2). Within Hydrobiosidae Apsilochorema has a special position. It is
regarded as representing the oldest evolutionary
lineage of the family (Neboiss, 1962; Ross, 1951,
Biogeography and Geological Evolution of SE Asia, pp. 91-98
Edited by Robert Hall and Jeremy D. Holloway
© 1998 Backhuys Publishers, Leiden, The Netherlands
1956, 1967). The age of the family has been estimated as approximately 100 million years (Ross,
1951) meaning an early Cretaceous appearance.
This assumption is corroborated by the discovery of a fossil forewing in Upper Cretaceous
amber of North Siberia. It was assigned to
Hydrobiosidae and described as Palaeohydrobiosis simberambra (Botosaneanu and Wichard,
1983). However, the family must be even older.
The fossil record of the order indicates that the
first true caddisflies appeared in the Permian
(e.g., Ivanov, 1988), and in the Triassic the families Philopotamidae and Hydropsychidae were
already in existence (Sukatcheva, 1991). According to proposed phylogenies of the Trichoptera
(Frania and Wiggins, 1997; Ross, 1956, 1967;
Schmid, 1989; Weaver, 1984; Wiggins and
Wichard, 1989) these families are younger clades
than the Hydrobiosidae. Thus, the Hydrobiosidae should be at least Triassic in age. Therefore the family is old enough to have been in
existence during the breakup of Pangaea in the
Mesozoic. Accordingly, the complicated history
of Gondwana and its terranes in the SE Asian
and Australian region in the Mesozoic and Tertiary
(Audley-Charles, 1987; Metcalfe, 1996) should
have affected the distribution of Hydrobiosidae.
Biology of Apsilochorema
The species are inhabitants of small rivers and
brooks. In the north A. sutshanum Martynov
lives in mountain streams as well as lowland
streams. In SE and East Asia the genus is found
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Wolfram Mey
Fig.1. Distribution area of Hydrobiosidae. The main or core areas in South America and Australia are filled with black, and their
respective numbers of genera are indicated.
Fig.2. Distribution area of Rhyacophilidae, the sister family of Hydrobiosidae.
Apsilochorema distribution
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in mountains at heights from 1500m to 4000m
(Nepal). The larvae are free-living predators,
with 5 instars (Kotcharina, 1986). Pupation takes
place in a case, made of small stones and attached to larger stones in the current. The adults
are active in the daytime. There are no pronounced flight periods.
The problem
The south hemisphere disjunction of the family
Hydrobiosidae appears very pronounced, if the
ranges of Atopsyche Banks and Apsilochorema
Ulmer are omitted from the map of the distribution area of the family (Fig.1). The majority of
genera is confined to certain parts of South
America, Australia, New Guinea and the Southwest Pacific. In contrast, the areas of Atopsyche
and Apsilochorema are large and seem to be
simply northern extensions of the main range. If
this were the case, we might expect the more
primitive or ancestral forms to occur in the south
and more derived ones in the north. Surprisingly, the situation in Apsilochorema is the reverse.
The ancestral species live in the north. This exactly is the problem, because we have to find an
interpretation for this mysterious pattern.
Up to now, two hypotheses have been proposed to explain the occurrence of Apsilochorema in Asia. Both asserted the ancestry of the
Asian species. Ross (1951, 1956) assumed a SE
Asian origin for the ancestor of Hydrobiosidae.
According to this author the species spread into
the southern continents via Sundaland or across
an Alaska connection. After having reached Australia and South America, the ancestor started to
differentiate. Some populations remained in
Asia, became isolated and gave rise to the
Apsilochorema line, which subsequently extended its range towards Australia. Neboiss
(1962) agreed with Ross (1956) concerning the
dispersal of Apsilochorema from the north into
Australia. In contrast, Schmid (1989) proposed a
Gondwana origin and Gondwana differentiation
of the Hydrobiosidae. In coping with the problem of Apsilochorema he briefly discussed the
possibility that the northward-moving Indian
plate could have carried ancestral Apsilochorema species, which dispersed in Asia after the
collision with Laurasia. However, he rejected
this idea, because it implied a Jurassic or Cretaceous age of Apsilochorema. He was not prepared to accept such a great age. However, he
admitted the differentiation of the genus had
taken place in South Asia.
Fig.3. Cladogram of the phylogenetic relationships within
Apsilochorema Ulmer. The numbers refer to suggested
synapomorphies.
The arguments
These studies on Apsilochorema were started
with an examination of the morphology of the
species. The objective was to elucidate the phylogenetic relationships within the genus and to
construct a cladogram. The characters were polarised based on comparison to all other genera
of Hydrobiosidae as defined in Schmid (1989).
The phylogenetic reconstruction is based on cladistic principles. The second issue was the documentation of the range of the genus and the
production of a more detailed distribution map.
The phylogenetic relationships depicted in
the cladogram of Fig.3 show a clear separation
of the genus into 2 groups. For practical reasons
they were given subgeneric rank and were
named Archichorema and Apsilochorema sensu
stricto (Mey, 1998). The morphological basis for
this distinction is the presence or absence of a
chorema on the underside of the male forewing
(1 in Fig.3). The rather complex structure is illustrated in Figs. 4 and 5. It is regarded as a
synapomorphy of Apsilochorema sensu stricto.
Some additional 8 characters provide evidence
for the further branching of the subgenera into 7
species groups. The character descriptions are
listed in Mey (1998).
The mapping of the distribution of all
Apsilochorema species revealed a wide range,
extending from Tasmania in the south to the island of Sakhalin in the north, and from the Iranian Elburz Mountains in the west to the oceanic
islands of Fiji in the east (Fig.6). However, the
distribution is by no means homogeneous. It is a
mixture of smaller and larger areas with continuous distribution and a number of widely scattered localities of a single species. Regions with
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Archichorema annandalei
Apsilochorema indicum
Fig.4. Male forewings of A. annandalei Martynov
(Himalaya) and A. indicum Ulmer (Tianshan). The chorema
of A. indicum is situated below the discoidal cell (DC).
Wolfram Mey
enigma of the ancestral species in South Asia we
now have the additional problem of an explanation for the disjunction of the subgenus
Apsilochorema. The progress of plate tectonic
theory in the last decades has provided a firm
geophysical framework against which the evolution and biogeography of Apsilochorema can be
viewed (Hall and Blundell, 1996). Continental
SE Asia is an assemblage of small and large
terranes, which were rifted off the northern margin of Gondwanaland and were accreted to
Laurasia and/or to Protochina. Similarly, a
number of islands in the SW Pacific are continental terranes too, derived from Gondwana or
Australia (Audley-Charles, 1987; Burrett et al.,
1991; Metcalfe, 1996). There are several models
for how the SE Asian and SW Pacific region became assembled. They differ mainly from one
another on the timing of rift, drift and collision
histories of the terranes. However, all agree that
the amalgamating process forming SE Asia was
due to a series of arrivals of northward moving
microcontinents of Gondwana origin. The earliest arrived blocks are of Palaeozoic age. Further
accretion occurred during the Mesozoic and the
Tertiary.
Fig.5. Structure of the chorema of Apsilochorema indicum
Ulmer at the underside of male forewing.
the highest number of species are the southern
slope of the Himalayas (8 species; Schmid,
1970), New Guinea (8 species; Schmid, 1989)
and Borneo (5 species; Huisman, 1992).
After separating the distributional records according to the subgenera and plotting a map for
each subgenus, the following picture emerges
(Fig.7): Archichorema has a relatively compact
range with its ancestral species in the Himalaya
and Assam region. Surprisingly, the range of
Apsilochorema sensu stricto shows a disjunction
between India/Middle Asia and Sundaland/
Australia; there is a large gap in the distributions in SE Asia.
These are the new arguments. Besides the
Fig.6. Distribution area of Apsilochorema sensu lato, Ulmer
1907. Hatched areas indicate continuous distributions.
Numbers indicate the numbers of species in each area.
Apsilochorema distribution
Archichorema
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Apsilochorema
Fig.7. Distribution of the subgenera Archichorema and Apsilochorema sensu stricto.
The model
Before the separation of India from Australia/
Antarctica was accomplished in the late Jurassic
(Veevers, 1991) a microcontinent or several continental fragments detached from the northern
edge of eastern Gondwanaland and moved
northwards. The rifting started in the late Triassic
with the Lhasa block, followed by the West Burma and Woyla terranes (Metcalfe, 1996). They
might have carried populations of the ancestor
of Apsilochorema, which was possibly distributed in northeastern Gondwanaland in that time.
Drifting with one of these microcontinents the
species reached the Pan-Laurasian continent in
the Cretaceous. This would be the most simple
explanation for the occurrence of Apsilochorema in Asia. However, it does not provide an explanation for the disjunction of Apsilochorema
sensu stricto. It is questionable if the differentiation of the species had occurred before or during the journey with the Gondwana terrane, or if
it developed after the establishment of the species in SE Asia. Both possibilities appear to be
plausible, but they offer an explanatory potential
only for the splitting and spreading of Archichorema. The basal separation into the 2 subgen-
era must have happened in another way.
Returning to the rifting of terranes from the
margin of northern Gondwana, the process can
be regarded as removing only a part of the distributional area of the Apsilochorema ancestor
(Fig.8). The remaining part stayed on Gondwana. The subsequent isolation enabled the beginning of an independent evolution and divergence into Archichorema and Apsilochorema
sensu stricto. In the Gondwana species the development of the chorema on the male forewings probably started. It could have been either
an anagenetic or cladistic process. The species
with this evolutionary novelty was distributed
over the northern margin of Gondwana. In the
late Jurassic/early Cretaceous a western part of
the range was broken off with the Indian continent and started to move northwards. With the
accretion of the Indian continent to Asia the second immigration of Apsilochorema species into
Asia took place, this time by a species with a
wing chorema, i.e., a member of Apsilochorema
sensu stricto. It remained isolated on the Indian
subcontinent and the adjacent northwestern
area. The species in eastern Gondwana were
confined to the Australian continent and gave
rise to the development of 2 species groups.
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Wolfram Mey
Fig.8. Hypothetical range of an ancestral species of Apsilochorema in Eastern Gondwana. 140 Ma (Late Jurassic) map adapted
from Smith et al. (1981).
This scenario gives an explanation for the
stepwise formation of the distribution pattern of
Apsilochorema sensu lato. In the light of this hypothesis the different dispersal routes of Apsilochorema species become recognisable. They
are depicted in Fig.9. According to this notion
the species of Apsilochorema sensu stricto
known from northern Borneo originated from
Australian stock. Such a deep penetration of
Australian elements into the Oriental region is
rather unusual for the Trichoptera. However, the
species in North Sulawesi is A. gisbum Mosely,
which has a wide range in the Australian region
including Tasmania. The high dispersal capacity
of this species points possibly to an intrinsic
character of the species of the subgenus. It enabled the colonisation of various islands in the
SW Pacific (Fig.6), as well as Borneo on the Sunda shelf. But in contrast to this dispersal-based
interpretation it is possible to suggest an alternative explanation. The Gondwana terranes which
have been recognised in Sundaland offered the
same potential and possibility for transport of
Apsilochorema species in the past. Unfortunately, faunistic research in the region is at quite a
low level and does not permit the distinction
between a mobilistic or vicariant explanation in
the case of the Borneo species. The question is
left open for future research.
Conclusions
The proposed hypothesis allows some predictions. The most interesting one is the possible
occurrence of Apsilochorema in the southern
part of Africa and especially on Madagascar.
That island was very close to the Indian conti-
Apsilochorema distribution
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Archichorema
Apsilochorema
Fig.9. Presumed dispersal routes of Apsilochorema sensu lato in the SE Asian and SW Pacific/Australian region
nent and to western Gondwana at the time
when the two plates separated. If an Apsilochorema species really survived, than it should
belong to Apsilochorema sensu stricto and not to
Archichorema.
The predatory larvae of Apsilochorema feed
mainly on other aquatic insects (Kotcharina,
1986). Thus, the persistence of Apsilochorema
requires a diverse and rich community of aquatic insects offering enough prey species in adequate quantities. The co-evolution of the aquatic
biota should have resulted in a similar persistence of other species or groups, not only in Apsilochorema. In consequence, further congruent
patterns of distribution should exist. The most
promising insect groups, which could provide
further examples, should be found within the
ancient orders Ephemeroptera (Mayflies) and
Plecoptera (Stoneflies).
In conclusion, if the hypothesis proves to be
valid, we have an example of a very old genus
with two subgenera of at least Cretaceous age.
Further, the small morphological differences between nearly all Apsilochorema species points
to a remarkable property of this evolutionary
line: cohesion and stasis as successful mechanisms for survival through the Mesozoic and
Cenozoic until today.
Acknowledgements
Special gratitude is extended to H. Duffels and
R. Hall for their encouragement and help in preparing the manuscript. Thanks also to A.
Neboiss, H. Malicky and L. P. Hsu for sending
specimens of Apsilochorema. Most of the Asian
material studied comes from field work support-
98
ed by the Deutsche Forschungsgemeinschaft
(Me 1085/1, Me 1085/3, Me 1085/5).
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