Hydrobiologia 298: 281-286, 1995.
D. Belk, H. J. Dumont & G. Maier (eds), Studies on Large Branchiopod Biology and Aquaculture II.
©1995 Kluwer Academic Publishers.
281
Historical biogeography and morphological differentiation of
Streptocephalus torvicornis (Waga) since the Worm III-glaciation
Henri J. Dumont 1 , Johan Mertens 1 & Alejandro M. Maeda- Martinez 2
1 Laboratory of Animal Ecology, University of Ghent, K. L. Ledeganckstraat 35, B-9000 Ghent, Belgium
2 Current address: Centro de Investigaciones Biologicas del Noroeste, S. C, Division Biolog(a Marina, Apdo.
Postal 128, La Paz, Baja California Sur, Mexico
Key words: S. torvicornis, biogeography, pleistocene history, sUbspeciation
Abstract
We argue that the Wiirm III glaciation eradicated possible European populations of S. torvicornis, and that today,
a reconquest of Europe takes place on two fronts.
A western wave has reached the Pyrenees, an eastern one now occupies most of eastern and northern Europe.
The western route probably started in the Maghreb, the eastern one in the Levant and the Ponto-Caspian. Animals
in the west had to move north by crossing, at right angles, a series of east-west oriented river valleys and progressed
slowly; animals in the east could move up river valleys extending north and north-east, and moved quickly. Italy
was not occupied, because S. torvicornis is a warm stenotherm, and by the time the climate had warmed sufficiently
for it to reach the southern shore of the mediterranean (ca 6000 BP), the gap with Italy was probably too large for a
crossing. Cold-loving species (of the genera Branchipus, Chirocephalus) conversely, could freely flow across the
Central Mediterranean at low sea-levels (ca 12000 BP), and now occur in Italy (and the rest of Europe) as well as
in Northern Africa.
A prediction of our hypothesis is that the pioneer populations in Spain and Central Europe should have been
isolated longest. This is tested and confirmed by their comparative morphology, and two subspecies, S. t. torvicornis
and S. t. bucheti are reinstated.
A gap across the Nile Valley where only S. rubricaudatus seems to occur, deserves further study.
Introduction
It is often true that the known ranges of many smaller, less charismatic animal species more accurately
reflect the distribution of their (few) experts than that
of the animals themselves, and this handicap will be
with us for some time to come. However, there is
also an increasing number of instances where we are
now reaching the level of information required to contrast ranges with known historical phenomena, allowing us to formulate testable hypotheses on the causes
behind the observed phenomena. We here document
such a case for an anostracan, Streptocephalus torvicornis (Waga), derive a falsifiable hypothesis for it,
and test it by comparative morphology.
The range of s. torvicornis (Waga) s.l. (Fig. 1)
Originally described from the vicinity of Warsaw
(Waga, 1842), S. torvicornis was subsequently recorded from numerous localities in eastern Europe (Germany, Poland, Czechia, Slovakia, Bulgaria and Roumania), Russia, the Caucasus, the Caspian depression,
south Iran, the Levant, Arabia, northern Africa, and
the Iberian Peninsula. Relevant literature references
are listed (and marked with a asterisk) in the reference list to this article, and all are shown on the map
in Fig. 1 (full circles). Half-filled circled are original, unpublished records, situated mainly in Morocco,
Mauretania, Algeria (the north, Haggar, and Tassili-nAjjer), Niger republic (mainly Air Mountains), and the
Tibesti Mountains. New localities from Saudi-Arabia
and Yemen are also given.
Clearly, as in so many cases, the type locality of
this species is not representative of its range, a large
D. Belk, H. J. Dumont & G. Maier (eds), Studies on Large Branchiopod Biology and Aquaculture II.
©1995 Kluwer Academic Publishers.
281
Historical biogeography and morphological differentiation of
Streptocephalus torvicornis (Waga) since the Worm III-glaciation
Henri J. Dumont 1 , Johan Mertens 1 & Alejandro M. Maeda- Martinez 2
1 Laboratory of Animal Ecology, University of Ghent, K. L. Ledeganckstraat 35, B-9000 Ghent, Belgium
2 Current address: Centro de Investigaciones Biologicas del Noroeste, S. C, Division Biolog(a Marina, Apdo.
Postal 128, La Paz, Baja California Sur, Mexico
Key words: S. torvicornis, biogeography, pleistocene history, sUbspeciation
Abstract
We argue that the Wiirm III glaciation eradicated possible European populations of S. torvicornis, and that today,
a reconquest of Europe takes place on two fronts.
A western wave has reached the Pyrenees, an eastern one now occupies most of eastern and northern Europe.
The western route probably started in the Maghreb, the eastern one in the Levant and the Ponto-Caspian. Animals
in the west had to move north by crossing, at right angles, a series of east-west oriented river valleys and progressed
slowly; animals in the east could move up river valleys extending north and north-east, and moved quickly. Italy
was not occupied, because S. torvicornis is a warm stenotherm, and by the time the climate had warmed sufficiently
for it to reach the southern shore of the mediterranean (ca 6000 BP), the gap with Italy was probably too large for a
crossing. Cold-loving species (of the genera Branchipus, Chirocephalus) conversely, could freely flow across the
Central Mediterranean at low sea-levels (ca 12000 BP), and now occur in Italy (and the rest of Europe) as well as
in Northern Africa.
A prediction of our hypothesis is that the pioneer populations in Spain and Central Europe should have been
isolated longest. This is tested and confirmed by their comparative morphology, and two subspecies, S. t. torvicornis
and S. t. bucheti are reinstated.
A gap across the Nile Valley where only S. rubricaudatus seems to occur, deserves further study.
Introduction
It is often true that the known ranges of many smaller, less charismatic animal species more accurately
reflect the distribution of their (few) experts than that
of the animals themselves, and this handicap will be
with us for some time to come. However, there is
also an increasing number of instances where we are
now reaching the level of information required to contrast ranges with known historical phenomena, allowing us to formulate testable hypotheses on the causes
behind the observed phenomena. We here document
such a case for an anostracan, Streptocephalus torvicornis (Waga), derive a falsifiable hypothesis for it,
and test it by comparative morphology.
The range of s. torvicornis (Waga) s.l. (Fig. 1)
Originally described from the vicinity of Warsaw
(Waga, 1842), S. torvicornis was subsequently recorded from numerous localities in eastern Europe (Germany, Poland, Czechia, Slovakia, Bulgaria and Roumania), Russia, the Caucasus, the Caspian depression,
south Iran, the Levant, Arabia, northern Africa, and
the Iberian Peninsula. Relevant literature references
are listed (and marked with a asterisk) in the reference list to this article, and all are shown on the map
in Fig. 1 (full circles). Half-filled circled are original, unpublished records, situated mainly in Morocco,
Mauretania, Algeria (the north, Haggar, and Tassili-nAjjer), Niger republic (mainly Air Mountains), and the
Tibesti Mountains. New localities from Saudi-Arabia
and Yemen are also given.
Clearly, as in so many cases, the type locality of
this species is not representative of its range, a large