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Shamshev & Grootaert: A review of the genus Stilpon from the Oriental region
Fig. 85. Hypothesised phylogenetic patterns of the species of Stilpon. Number refer to characters discussed under “Phylogenetic relationships
within Stilpon”. Black dots = presumably non-homoplastic apomorphies; white dots = presumably homoplastic apomorphies. Strict consensus
tree (Length = 32, C.I. = 0.75, R.I. = 0.90) of the three most parsimonious cladograms produced by analysis of the data matrix in Table
1.
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THE RAFFLES BULLETIN OF ZOOLOGY 2004
on the male right cercus (character 19) and a feature of the
female terminalia, namely the fusion of sternite 10 with
anteroventral margin of tergite 8 (character 23). Additionally,
in the S. nubilus complex the surstylar comb of the male left
cercus (character 13) is absent. But the loss of the surstylar
comb of the male terminalia is likely to be a homoplastic
feature within the genus. We did not find any characters to
support the monophyly of the S. graminum complex of the
species sensu Cumming & Cooper (1992). In these species
the upper lobe of the left surstylus of the male terminalia is
completely divided. But, again, it is a homoplastic condition
within Stilpon.
The relationships of S. spinicercus and S. monospinatus,
which were described in the present paper, are not clear. In
S. spinicercus the male terminalia are more similar to those
in S. nubilus. However, the female terminalia resembles those
in S. graminum. S. spinicercus is the only known species of
this clade which has the abdominal gland-like structures in
the male. S. monospinatus is the most problematic species of
this lineage on the whole. It was included into the S. graminum
group primarily due to the presence of a single apical spine
on the left cercus of the male terminalia. If such, than S.
monospinatus might be most similar to the presumed basal
condition of the S. graminum lineage. Unfortunately, the
female is not found yet in this species. The presence of an
erect ventral bristle (character 8) on the male fore tibia may
suggest S. monospinatus is allied with S. spinicercus. The
abdominal gland-like structures are absent in this species.
The second lineage of the Stilpon clade with the shortened
female terminalia includes several phenetically very similar
and uniform species. The lineage is united on the bases of
the completely yellow thorax (character 3) and minute or
absent bristles in apical part of the left epandrial lamella of
the male terminalia (character 11). The additional characters
could be a complete division of the upper lobe of the left
surstylus, the lack of the surstylar comb and the gland-like
abdominal structures on the male abdomen. However, they
appear to be homoplastic within the genus. We ascribed all
species belonging to this lineage to as a separate species group
within Stilpon (S. seeluang species group). The group is likely
to constitute the sister relationships with the S. graminum
species group. Within this newly recognised group S. laawae,
S. crassinervis, S. nhamyaaw, and S. taksin are presumably
closely related, sharing the greatly reduced male cerci
(character 16) and 2 very long bristles on the male abdominal
segment 8 (character 10). The relationships within this
assemblage of the species are not resolved. The reduced inner
vertical (character 2) and postpronotal (character 5) bristles
may indicate the closer relationships between S. seeluang and
the preceded complex of species. The presence of 2 spines
on the male hind trochanter (character 7) may suggest some
affinity of S. seeluang and S. isaanensis. Both species,
especially S. isaanensis, appear to demonstrate the basal
condition of the male terminalia for this group in the whole.
One species included in S. seeluang group, namely S.
nhamyaaw, has 3 long spines on the left cercus of the male
terminalia. However, these spines are unlikely to be
homologous with those found in the species of the S.
graminum group. These spines are not apical in their position
(vs. apical in the S. graminum group). Additionally, the
topography of the strong long bristles on the left cercus in S.
crassinervis, apparently a sister species to S. nhamyaaw, may
indicate that just these bristles are homologous with the spines
in S. nhamyaaw.
The relationships of two remaining species of this clade, S.
paradoxus and S. yai are unclear. We have already discussed
the possible affinities of these species in details (see
“Phylogenetic relationships” under the respective
descriptions). To summarise, S. paradoxus possesses many
peculiar, autapomorphic features. It may represent a new,
hitherto unknown group of the Stilpon species. S. yai was
included in this clade provisionally since the female of this
species has not been found yet. Some features may suggest
these species to be closer related. However, this is speculation
only and future discoveries of the genus are needed to clarify
the relationships of these species.
The assemblage of the species ascribed to as the S. divergens
group is the most problematic unit within the genus. Cumming
& Cooper (1992) recognised this group based on the
plesiomorphic characters only: scutum entirely tomentose,
rows of acrostichal setulae complete, setose left cercus of
the male terminalia. Additionally, they noted that this group
may be paraphyletic or even represent the stem group within
the genus. Indeed, following this definition we should include
the S. seeluang species group just into the S. divergens group.
However, the S. seeluang group is quite distinctive lineage
within Stilpon and it constitutes the sister relationships with
S. graminum group. We consider that, preliminary, at least
one apomorphic feature (long ventral bristle on the left cercus
of the male terminalia, character 18) could support the
monophyly of the S. divergens species group. The
relationships within the S. divergens group and with other
groups of Stilpon are not resolved at present. Within the group
S. lekkwar and S. khorngkeun appear to be the sister species
based on the presence of the apical spines on the middle lobe
of the left surstylus (character 14). The precise recognition
of the Stilpon sister group relationships within the Drapetini
is likely to be especially important for the rigorous cladistic
analysis of this unit.
This also could be attributed to the S. varipes species group.
The monophyly of the group is well supported by the lack
of the scutal tomentum and incomplete acrostichal setulae.
However, the relationships of the S. varipes group with other
groups of Stilpon are not so evident. The main problem is
likely to deal with our insufficient knowledge of the genus
from the East Asia and western part of the North America.
Notes about the gland-like structures in Stilpon
In several Stilpon species studied from the Oriental region
we found, for the first time in the genus, gland-like structures
on the male abdomen. This character is a common and well
known feature of some Drapetini genera allied to Stilpon,
e.g. Elaphropeza, Drapetis, Crossopalpus, Dusmetina,
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Shamshev & Grootaert: A review of the genus Stilpon from the Oriental region
Isodrapetis, Nanodromia, and Austrodrapetis (Collin, 1961;
Smith, 1964; Smith and Davies, 1965; Cumming & Cooper,
1992; Plant, 1999, Grootaert & Shamshev, 2003). These
gland-like structures are considered to deal with epigamic
behaviour (Smith and Davies, 1965). Stark (1990) suggested
that the structures on the tergites were associated with a
stridulatory organ in Elaphropeza. An electronmicroscopic
study however showed the presence of glandular cells in
Elaphropeza so that we suppose that the glands produce
pheromones (Grootaert, unpublished observations).
The structures found in Stilpon are very similar, in their
external appearance, to those in Drapetis (A. Stark, personal
communication). However, the fine details should be checked
in the future. These structures were found in all species
belonging to the S. divergens group (unclear in S. divergens),
S. spinicercus (S. graminum group) and S. paradoxus and S.
yai (species with uncertain group position). The gland-like
structures are difficult to recognise without special preparation
in the dry specimens and, especially, in specimens with
shrunken abdomen. No any external features, that could
indicate the presence of the gland-like structures, have been
found. The gland-like structures usually look like simple,
elongate, narrow, darkened spaces with a pilose vestiture.
Rarely, they consist of three lobes (S. trilobatus and S.
malayensis) or, sometimes, they are partly concealed by the
corresponding tergites. In most species the gland-like
structures occupy intersegmental spaces between tergites 4-
3 and 3-2 (S. khorngkeun, S. lek, S. malayensis, S. nhamdam,
S. trilobatus), S. spinicercus – between tergites 3-2 and 2-1,
in S. lekkwar – between tergites 5-4, 4-3 and 3-2. In S.
paradoxus and S. yai they are indistinct and present between
tergites 5-4, 4-3 and tergites 6-5, 5-4, 4-3, 3-2, respectively.
The presence of the gland-like structures in Stilpon may
support the hypothesis that the genus is closer related to
Elaphropeza, Drapetis, Crossopalpus, Dusmetina, and
Austrodrapetis (Cumming & Cooper, 1992; Grootaert, 1994)
rather than to Chersodromia (Chvála, 1975). Within the genus
these structures were apparently lost in the S. varipes, S.
seeluang, and S. graminum (except S. spinicercus) species
groups.
To conclude, the genus Stilpon is very well represented in
the Oriental region. Seventeen species are now recognised
from this region, which is more than from other biotic regions.
The Oriental fauna of the genus demonstrates a great
morphological diversity, including both species with many
relatively plesiomorphic features and species possessing many
apomorphic characters. These arguments may support the
hypothesis that the early evolution of the genus occurred in
the Oriental region (Cumming & Cooper, 1992). Four
informal groups of species are now recognised within Stilpon.
The S. graminum group includes species from the Oriental,
Palaearctic, and Nearctic regions. The S. varipes and S.
divergens, and S. seeluang groups are only presented in the
Nearctic and Oriental regions, respectively. However, this
pattern of distribution reflects our insufficient knowledge of
the genus rather than the real relationships between the
regions. Undoubtedly, our paper is only first step toward a
detailed study of the genus Stilpon from the Oriental region.
ACKNOWLEDGEMENTS
This study was supported by a grant from the Belgian Federal
Services for Scientific, Technical and Cultural Affairs. We
thank the colleagues of Srinakharinwirot University in
Bangkok for their help in the field, especially Dr. Verapong
Kiatsoonthorn, Dr. La-aw Ampornpan and the technicians at
Na Haeo Field Research Station, Mr. Sai Dan and Mr. Ai
Patanajak. The second author thanks Prof. Dr. Peter Ng for
the grant to study at the National University of Singapore as
well as Mrs. Yang Chang Man, Dr. Darren Yeo Chong Yinn
and Dr. Daiqin Li for their help in the field. P.G. also thanks
Mr. J. Constant for his assistance in the field during May
2001 and 2003.
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Appendix. 1. Data matrix of character states for the phylogenetic analysis of species of Stilpon. 0, plesiomorphic state; 1, apomorphic state;
?, missing data. Characters are coded as binary, except character 17 (vestiture of the male left cercus) which was treated as an unordered
multistate character.
Characters
12345678911111111112222
01234567890123
Outgroup
00000000000000000000000
S. varipes
10010100100000000001000
S. chillcotti
10010100100000000001000
S. graminum
10000000100100102001110
S. nubilus
10000000100010102011111
S. subnubilus
10000000100010102011111
S. spinicercus
10000001000100102001100
S. monospinatus
10000001100100001001???
S. seeluang
11101010101110000001100
S. isaanensis
10100010101110000001100
S. laawae
11101000111110010001100
S. crassinervis
11101000111110010001???
S. nhamyaaw
11101000111110010001100
S. taksin
11101000111110010001100
S. lek
10000000000000000101000
S. lekkwar
10000000000001000101000
S. khorngkeun
10000000000001000101???
S. nhamdam
10000000000000000101000
S. trilobatus
10000000000000000101000
S. malayensis
10000000000000000101???
S. divergens
10000000?00000000101000
S. paradoxus
10000000000100000001100
S. yai
10000000000100000001???
346
Shamshev & Grootaert: A review of the genus Stilpon from the Oriental region
Appendix 2. List of characters for the analysis of the phylogenetic patterns within Stilpon.
1. Frons: triangular (0), linear (1).
2. Inner vertical bristles: long (0), hardly prominent (1).
3. Thorax colour: black (0), completely yellow (1).
4. Scutum vestiture: entirely tomentose (0), lacking tomentum (1).
5. Postpronotal bristle: long (0), hardly prominent (1).
6. Acrostichal setulae: complete (0), incomplete or absent (1).
7. Male hind trochanter: lacking spinules (0), with 2 spinules (1).
8. Erect ventral bristle on male fore tibia: absent (0), present (1).
9. Abdominal gland-like structures: present (0), absent (1).
10. Male segment 8: with moderately long bristles (0), with at least 2 very long bristles (1).
11. Bristle(s) in apical part of left epandrial lamella: long (0), hardly prominent or absent (1).
12. Upper lobe of left surstylus: undivided (0), partly or completely divided into 2 parts (1).
13. Surstylar comb: present (0), absent (1).
14. Apical spines on mid lobe of the left surstylus: absent (0), present (1).
15. Right surstylus: not prolonged apically (0), prolonged apically (1).
16. Male cerci: well prominent (0), reduced (1).
17. Apical spine(s) on the male left cercus: absent (0), 1 spine (1), 2-3 spines (2).
18. Long ventral bristle in basal part of the left cercus: absent (0), present (1).
19. Apical spines on the right cercus: absent (0), present (1).
20. Ejaculatory apodeme: paired (0), single (1).
21. Female terminalia: elongate (0), shortened (1).
22. Female cercus: elongate oval (0), broad oval (1).
23. Sternite 10 of female terminalia: not fused with ventroapical margin of tergite 8 (0), fused with ventroapical margin of tergite 8 (1).
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