230
species samples from one locality (UJED 245)(MaedaMartInez et aI., 1995; this volume). Other instances in
which the females of one species can be differentiated from others are the females of S. lamellifer with
their characteristic lamellar cercopods, the females of
S. bidentatus and S. vitreus with their conical protuberances on the telson, and the females of the sudanicus
group, with their typical tetrahedral cysts.
It seems unlikely that two closely related streptocephalids would have a different type of peduncle.
This hypothesis is supported by the fact that closely
related species such as those of the sudanicus, vitreus,
dichotomus and gracilis groups (which share, among
other characters, a particular hand morphology) exhibit
the same type of peduncle. This provides what seems to
be a sound natural base to define different genetic lineages or species groups. Each of these species groups
probably have their own common ancestor, i.e. they
are probably monophyletic. On this basis, we propose
that nowadays' world distribution of the disjunct Streptocephalus is better explained by the vicariance model
(Croizat et al., 1974) than by a dispersalist hypothesis (Banarescu, 1990; Wiman, 1979a)(see MaedaMartinez et aI., 1995; this volume). For the diagnosis
of individual species, the more important characters
are the type of peduncle, the teeth, the distal part of
the finger, the distal part of the thumb, the spur, lateral
and inner lamellae, frontal appendage, linguiform genital outgrowths, cercopod morphology, type of ovaries,
and cyst morphology; conversely, in defining different
species groups and subgroups, it is important to consider that, unless the members of a group exhibit the
same type of peduncle and the same type of base of the
hand, similar morphological structures shared among
species may be homoplastic (e.g., the characters mentioned above). Without this caveat, a misinterpretation of interspecies relationships can occur. Daday's
(l91Oa) classification into subgenera based only on
the similarity of the frontal appendages is an example
of this.
In general, our sorting of the African species agree
with the species groups proposed by Hamer et ai.
(l994a,b). However, a number of discrepancies are
noticed: (1) while we group S. dendyi, S. purcelli, S.
bouvieri, S. rothschildi, and S. zeltneri in the dendyi
group, they split the same species in two groups (which
correspond in part, to the dendyi and bouvieri subgroups of the dendyi group); (2) Hamer et al. grouped
S. cafer, S. distinctus, S. indistinctus, and S. spinosus,
while we classify S. distinctus and S. spinosus in the
sealii group, and S. cafer and S. indistinctus in the
cafer group on the basis of a different morphology
of the peduncle, i.e. the species of the cafer group
show a hand rotation of c. 50° , and the proximal inner
side of the peduncle has conical protuberances, while
the species of the sealii group exhibit a hand rotation
of not more than 40°, and the proximal inner side
of the peduncle has no protuberances; (3) Hamer et
al. grouped S. neumanni, S. proboscideus, and S. trifidus on the basis of a similarity in the shape of the
finger, frontal appendage, and shape and number of
the teeth on finger; our results, however, reveal that
while S. trifidus has an intermediate peduncle with the
characteristics of the cafer group, S. neumanni and
S. proboscideus have a long peduncle with the characteristics of the proboscideus subgroup (torvicornis
group); (4) Hamer et al. formed a species group with
the single species S. cladophorus, while we colocated
it with S. dendrophorus, S. namibiensis, S. neumanni,
and S. proboscideus in the proboscideus subgroup.·
In no-choice mating tests, Wiman (1979a,b)
obtained viable adult hybrids not only between species
with the same peduncle type, but also between species
with different peduncle types, i.e. S. bouvieri of short
peduncle with S. mackini of long peduncle, between
S. mackini and S. sealii of intermediate peduncle as
well as with S. dorothae, linderi and texan us which
have long peduncles. On the basis of the hybridizability criterion proposed by Dubois (1988), Wiman's
results demonstrate that, in spite of their morphological differences, all these species belong to the same
genus.
Finally, according to the demarcation between
species groups and subgenera discussed by Dubois
(1988), it does not seem justitied, in spite of existing morphological differentiation, to name the nine
species groups as subgenera, since there is a lack of
evidence that sufficient ecological specialization has
occurred as well.
Acknowledgements
We thank these persons who made material available
for our study: Dr G. A. Boxshall, British Museum of
Natural History; M. C. M. Elias-Gutierrez, Escuela
Nacional de Estudios Profesionales, Iztacala, UNAM,
Mexico; Dr J. Brtek and Dr I. Geczyova, Horninitrianske Muzeum Prievidza, Slovakia; Dr L. Forro, Hungarian Natural History Museum; Dr L. Brendonck,
Koninklijk Belgisch Instituut voor Natuurwetenschappen; Dr J. W. Martin, Natural History Museum of
species samples from one locality (UJED 245)(MaedaMartInez et aI., 1995; this volume). Other instances in
which the females of one species can be differentiated from others are the females of S. lamellifer with
their characteristic lamellar cercopods, the females of
S. bidentatus and S. vitreus with their conical protuberances on the telson, and the females of the sudanicus
group, with their typical tetrahedral cysts.
It seems unlikely that two closely related streptocephalids would have a different type of peduncle.
This hypothesis is supported by the fact that closely
related species such as those of the sudanicus, vitreus,
dichotomus and gracilis groups (which share, among
other characters, a particular hand morphology) exhibit
the same type of peduncle. This provides what seems to
be a sound natural base to define different genetic lineages or species groups. Each of these species groups
probably have their own common ancestor, i.e. they
are probably monophyletic. On this basis, we propose
that nowadays' world distribution of the disjunct Streptocephalus is better explained by the vicariance model
(Croizat et al., 1974) than by a dispersalist hypothesis (Banarescu, 1990; Wiman, 1979a)(see MaedaMartinez et aI., 1995; this volume). For the diagnosis
of individual species, the more important characters
are the type of peduncle, the teeth, the distal part of
the finger, the distal part of the thumb, the spur, lateral
and inner lamellae, frontal appendage, linguiform genital outgrowths, cercopod morphology, type of ovaries,
and cyst morphology; conversely, in defining different
species groups and subgroups, it is important to consider that, unless the members of a group exhibit the
same type of peduncle and the same type of base of the
hand, similar morphological structures shared among
species may be homoplastic (e.g., the characters mentioned above). Without this caveat, a misinterpretation of interspecies relationships can occur. Daday's
(l91Oa) classification into subgenera based only on
the similarity of the frontal appendages is an example
of this.
In general, our sorting of the African species agree
with the species groups proposed by Hamer et ai.
(l994a,b). However, a number of discrepancies are
noticed: (1) while we group S. dendyi, S. purcelli, S.
bouvieri, S. rothschildi, and S. zeltneri in the dendyi
group, they split the same species in two groups (which
correspond in part, to the dendyi and bouvieri subgroups of the dendyi group); (2) Hamer et al. grouped
S. cafer, S. distinctus, S. indistinctus, and S. spinosus,
while we classify S. distinctus and S. spinosus in the
sealii group, and S. cafer and S. indistinctus in the
cafer group on the basis of a different morphology
of the peduncle, i.e. the species of the cafer group
show a hand rotation of c. 50° , and the proximal inner
side of the peduncle has conical protuberances, while
the species of the sealii group exhibit a hand rotation
of not more than 40°, and the proximal inner side
of the peduncle has no protuberances; (3) Hamer et
al. grouped S. neumanni, S. proboscideus, and S. trifidus on the basis of a similarity in the shape of the
finger, frontal appendage, and shape and number of
the teeth on finger; our results, however, reveal that
while S. trifidus has an intermediate peduncle with the
characteristics of the cafer group, S. neumanni and
S. proboscideus have a long peduncle with the characteristics of the proboscideus subgroup (torvicornis
group); (4) Hamer et al. formed a species group with
the single species S. cladophorus, while we colocated
it with S. dendrophorus, S. namibiensis, S. neumanni,
and S. proboscideus in the proboscideus subgroup.·
In no-choice mating tests, Wiman (1979a,b)
obtained viable adult hybrids not only between species
with the same peduncle type, but also between species
with different peduncle types, i.e. S. bouvieri of short
peduncle with S. mackini of long peduncle, between
S. mackini and S. sealii of intermediate peduncle as
well as with S. dorothae, linderi and texan us which
have long peduncles. On the basis of the hybridizability criterion proposed by Dubois (1988), Wiman's
results demonstrate that, in spite of their morphological differences, all these species belong to the same
genus.
Finally, according to the demarcation between
species groups and subgenera discussed by Dubois
(1988), it does not seem justitied, in spite of existing morphological differentiation, to name the nine
species groups as subgenera, since there is a lack of
evidence that sufficient ecological specialization has
occurred as well.
Acknowledgements
We thank these persons who made material available
for our study: Dr G. A. Boxshall, British Museum of
Natural History; M. C. M. Elias-Gutierrez, Escuela
Nacional de Estudios Profesionales, Iztacala, UNAM,
Mexico; Dr J. Brtek and Dr I. Geczyova, Horninitrianske Muzeum Prievidza, Slovakia; Dr L. Forro, Hungarian Natural History Museum; Dr L. Brendonck,
Koninklijk Belgisch Instituut voor Natuurwetenschappen; Dr J. W. Martin, Natural History Museum of