CLADISTIC AND BIOGEOGRAPHIC ANALYSES OF HAWAIIAN PIPUNCULIDAE (DIPTERA) REVISITED

Cladistics (1996) 12:291–303

CLADISTIC AND BIOGEOGRAPHIC ANALYSES OF HAWAIIAN PIPUNCULIDAE (DIPTERA) REVISITED Marc De Meyer Department of Entomology, Koninklijk Belgisch Instituut voor Natuurwetenschappen, Brussels, Belgium* Received for publication 27 July 1995; accepted 21 March 1996 Abstract — Pipunculidae (Diptera) of the Hawaiian islands belong to the endemic hawaiiensis subgroup of the subgenus Cephalops (Semicephalops). In total 36 species are known from the Hawaiian islands. Cladistic analysis of 31 species, using 21 morphological characters from the male terminalia, resulted in 480 equally parsimonious trees. Three rounds of successive weighting resulted in 610 equally parsimonious trees. A biogeographic analysis was carried out, using the three-area statement technique and based on the strict consensus tree produced from the tree set obtained by successive weighting. The analysis puts the sequence of the island groups in congruence with the geological history of the islands. The results of the cladistic and biogeographic analyses were compared with earlier similar analyses.  1996 The Willi Hennig Society

Introduction Pipunculidae (Diptera) are a family of small, darkish and usually inconspicuous flies, recognised by the large compound eyes which occupy most of the hemispherical head and by the wing venation. Pipunculidae form the sister group to hoverflies (Syrphidae) and both families are grouped together in the superfamily Syrphoidea, forming the sister group of the Platypezoidea within the Aschiza (McAlpine, 1989). The family as a whole has a worldwide distribution and comprises about 1400 known species in 21 genera (Rafael and De Meyer, 1992; De Meyer, 1994). During the larval stage, they are parasitoids of Auchenorrhyncha (Homoptera). The first Pipunculidae of the Hawaiian islands were described by Grimshaw (1901) and Perkins (1905, 1910) mainly with relation to studies of natural enemies of the sugar cane leafhopper. More comprehensive studies of the Hawaiian fauna were carried out several decennia later by Hardy (1953, 1964). All species found on the Hawaiian Islands form a single ´ monophyletic group. Hardy (1964) first grouped them under Cephalops Fallen (considered a subgenus of Pipunculus Latreille) but later put them under Pipunculus s.s. (Hardy, 1989). De Meyer (1989) revised the Hawaiian fauna within the scope of a worldwide revision of the tribe Cephalopsini and placed all ´ Hawaiian species in the endemic hawaiiensis subgroup of the genus Cephalops Fallen, subgenus Semicephalops De Meyer (De Meyer, 1994). Geologically the Hawaiian chain forms a linear arrangement of islands with

*Present address: Department of Invertebrate Zoology, National Museums of Kenya, P.O.Box 40658, Nairobi, Kenya. 0748-3007/96/040291+13/$25.00/0

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successive age. This results from the sequential formation of the islands as the Pacific tectonic plate moves north-westward over a volcanic hot spot (Simon, 1987). Some of the islands are relatively young (the most recent, Hawaii, is estimated to be approximately 600,000 years old, Simon and Mueller-Dombois, 1987). Representatives of this dipteran family on the Hawaiian island chain appear to be the scions of one colonization by a single founder and successive radiation combined with island hopping as soon as new islands could be colonized, and further speciation (De Meyer, 1993). Because of the combined characteristics of strong isolation of the island group, linear arrangement of the islands in a chronological order, the large diversity of habitats present on the islands, and different forms of topographical and vegetational barriers being erected throughout history on the islands, this phenomenon is known for a variety of animal and plant groups on the islands (Otte, 1989; Simon, 1987; Simon et al., 1984). The most spectacular is Drosophilidae (Diptera), but the phenomenon exists also in other insect groups, passerine birds, plant groups like Bidens (beggar’s ticks) and Madiinae (tarweeds), and the snail genera Partulina and Achatinella (Simon, 1987). The pipunculid fauna was already the topic of an earlier analysis by the author (De Meyer, 1993). However, the cladistic analysis was then carried out with the PHYLIP software package (Felsenstein, 1986) version 2.9, which generated only a single most parsimonious tree. New analysis of the data with Hennig86 showed that a much larger tree set with the same tree length could be found, making it necessary to revise the proposed phylogeny and historical biogeographical deductions.

Materials and Methods TAXA AND CHARACTERS Hawaiian Pipunculidae belong to the hawaiiensis subgroup of the subgenus Cephalops (Semicephalops). The monophyly of the subgroup is supported by a single synapomorphy (the presence of an enlarged fan shaped ejaculatory apodema in the male genitalia). The phylogenetic relationships within the genus Cephalops and the tribe Cephalopsini are explained in detail by De Meyer (1994). In total, 36 Hawaiian species are known (Hardy, 1964; De Meyer, in press for full details). In the analysis only 31 species are included. The remaining species were excluded either because only the female sex is known or because the male genitalia could not be studied in detail. Pipunculidae show limited variation in general external morphology and most of the variation found in characters like setosity and pilosity of legs, colouration of abdomen, etc. is widespread over all the groups within the family and shows considerable variation. Male terminalia are one of the few structures that provide reliable characters for species recognition (Hardy, 1987; see also Ackland, 1993; Rafael, 1990 for applications) and phylogenetic reconstruction (Albrecht, 1990; Skevington, 1993). They show a strong intraspecific consistency but fairly large interspecific variation. Twenty-one morphological characters from the male terminalia were observed (Table 1) (for a detailed description of the male pipunculid postabdomen and genitalia, see Albrecht 1990). No synapomorphies for the group (large fan shaped ejaculatory apodema, see above) were included. Contrary

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to earlier analysis (De Meyer, 1993) autapomorphies were also excluded. All characters states are polarized through outgroup comparison with the semifumosus subgroup of the subgenus Semicephalops, and the characters are binary coded (Table 2). DISTRIBUTION Simon and Mueller-Dombois (1987) suggest grouping the Hawaiian island chain into four main groups, based on the geological age of the islands incorporated: Niihau and Kauai (approximately 5.1 Myr), Oahu (3.7–2.6 Myr), Molokai, Lanai, Maui and Kahoolawe (1.9–1.0 Myr) and the “Big Island” or Hawaii (600,000 yr). The distributional data as outlined in Hardy (1964) and summarized in De Meyer (in press) were adjusted to these groupings (Table 3). ANALYSES The data matrix of Table 2 was analysed with Hennig86, version 1.5 (Farris, 1988) applying mhennig* and bb* options for calculating trees. The ie option proved too time-consuming as no result was obtained after 3 consecutive days of running on a 486PC (25Mhz). The successive weighting method (xsteps w; Table 1. List of morphological characters for Hawaiian Pipunculidae with binary character states. 1. In dorsal view, surstylus evenly shaped in lower half (0); base of surstylus broad, gradually narrowing from median part onwards (1) 2. In dorsal view, surstylus apically evenly shaped or slightly broadened (0); distinctly broadened apically in comparison with median part (1) 3. In lateral view, surstylus straight or slightly curved (0); strongly bent (1) 4. In lateral view, surstylus not stout, slender shaped (0); stout and broad (1) 5. In lateral view, surstylus elongated (0); truncated (1) 6. In lateral view, surstylus without basal protuberance (0); with large basal protuberance directed ventrally (1) 7. In lateral view, surstylus without subapical protuberance (0); with small subapical protuberance directed ventrally (1) 8. In lateral view, surstylus not narrowed basally, as broad as or nearly as broad as apical part (0); base narrowed, apically much broader than basally (1) 9. In lateral view, surstylus without finger-like protuberance at apical margin (0); with finger-like protuberance at apical margin (1) 10. In dorsal view, surstylus without median protuberances (0); with median protuberance, directed inwards (1) 11. Epandrium normal in shape, not swollen (0); swollen (1) 12. Aedeagus simply pointed apically (0); not so, modified from basic ground plan (1) 13. Apical part aedeagus short, not reaching beyond half of length of surstylus (0); long, extending beyond half of surstylus (1) 14. In lateral view, tip aedeagus narrow, not flattened (0); tip broad, flattened (1) 15. In lateral view, aedeagus apically not strongly constricted (0); aedeagus very broad, apically strongly constricted and ending in thin pointed tip (1) 16. In lateral view, aedeagus without dorsal protuberance (0); with dorsal protuberance(1) 17. In lateral view, aedeagus without flanges (0); broadened, with subapical rounded flanges (1) 18. Ejaculatory ductuli short (0); long, longer than surstylus (1) 19. Membraneous area (=genital cleft) on abdominal syntergosternite 8 keyhole shaped (0); not keyhole shaped (1) 20. Membraneous area well developed (0); reduced in shape, only present as small area or as cleft (1) 21. Membraneous area placed terminally (0); directed to right side of sternum 8 (1)

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combined with tree generating command mh*; bb*) was applied on the set of most parsimonious trees produced with above calculation and this was repeated successively until the weights no longer changed. Consensus trees (strict consensus, semi-strict consensus and majority rule consensus trees) were obtained with consensus commands in the software package COMPONENT, version 2.0 (Page, 1993). In order to provide a support measure for the branches in the strict consensus tree, a bootstrap analysis was carried out. For this purpose, 100 new data matrices were produced by resampling the original data set in Table 2 randomly with the bootstrap method in the SEQBOOT programme of Felsenstein’s PHYLIP package version 3.5c (Felsenstein, 1993). Each of these 100 data sets was analysed with the hennig* option of Hennig86 and a majority rule consensus tree produced of the 100 resulting trees with the appropriate command in COMPONENT (mhennig* in combination of bb* produced too large a tree set for the COMPONENT programme to handle, and the ie- option proved to be too time-consuming. The hennig* option on the other hand produced a single tree for each data set very fast, albeit not necessarily the shortest possible). The strict consensus tree obtained after successive weighting was used for constructing an area cladogram by replacing the terminal taxon with the name of the Table 2. Character state matrix for Hawaiian Pipunculidae (0 and 1 refer to state as defined in Table 1; ?=unknown or both states present). Ancestor 1: cornutus 2: bicuspidis 3: obscuratus 4: juvencus 5: uluhe 6: perkinsiellae 7: juvator 8: euryhymenos 9: terryi 10: amplus 11: molokaiensis 12: filicolus 13: titanus 14: alienus 15: obstipus 16: rotundipennis 17: haleakalaae 18: timberlakei 19: chauliosternum 20: trichostylis 21: swezeyi 22: oahuensis 23: hawaiiensis 24: delomeris 25: apletomeris 26: megameris 27: sectus 28: proditus 29: laterisutilis 30: nigrotarsatus 31: canutifrons

00000000000000000?000 000000011001000000101 000000010001000001000 00000001100100010010? 000000000000000001000 000000000000000001101 000000000000000000100 000000000000100001000 000000000000100001?00 00000000010?000000100 000000000001010000000 000000000001010000000 000000000001010000000 000000000000100000001 000000000101000000001 000000000101000000101 000000000101000000001 000000000101000000101 100000000001000000001 110000000001000010001 110000000001000011001 110000000001000000011 110000000001000000111 101111000011001100101 101111100011001100111 101100100011001100111 101100100011001100111 101000000011001100111 101000000011001?00111 100000100011000?00111 100000100011000100111 110000000001000010101

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island group(s) where it occurs. This area-cladogram was used for obtaining a general area-cladogram under assumptions 0 and 1. The theoretical background of cladistic biogeography and different assumptions implied are discussed in detail by Nelson and Platnick (1981), Humphries and Parenti (1986), and Zandee and Roos (1987). A general area-cladogram was obtained by generating a data matrix through the three-area statement technique of software package TAS (Nelson and Ladiges, 1991) for assumptions 0 and 1. Three-area statement technique codes distributional data for area cladograms as a suite of three-area statements and produces a matrix for parsimony analysis as output. This technique was used previously for obtaining cladistic biogeographical information (Ladiges et al., 1992; Morrone, 1993). The matrix obtained with TAS was analysed with the ie* option of Hennig86. Results CLADISTIC ANALYSIS Analysis of the data matrix shown in Table 2 with mhennig* and bb* options, produced 480 equally parsimonious cladograms of length 37, CI 56 and RI 84. The

Table 3. Distributional data of Hawaiian Pipunculidae. Species cornutus bicuspidis obscuratus juvencus uluhe perkinsiellae juvator euryhymenos terryi amplus molokaiensis filicolus titanus alienus obstipus rotundipennis haleakalaae timberlakei chauliosternum trichostylis swezeyi oahuensis hawaiiensis delomeris apletomeris megameris sectus proditus laterisutilis nigrotarsatus canutifrons

Kauai

Oahu

Molokai

Hawaii

x x x x x x x x

x x

x

x

x x x x x

x

x x x x x

x

x x

x x x x x x x x x x x x

x x

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strict consensus tree from these 480 trees is shown in Fig. 1a. The consensus tree is only partly resolved with 15 branches in the initial node, 12 of them leading to terminal taxa. Furthermore, three species sets can be recognized: dichotomy cornutusobscuratus; trichotomy amplus-filicolus-molokaiensis; and the cluster timberlakei-delomeris (with 14 terminal taxa). The latter is also only partly resolved. After three rounds of successive weighting and tree calculating with option mh*; bb*, 610 trees were obtained with length 180, CI 86 and RI 96. As pointed out by one reviewer, the gaining of trees (from 480 to 610) is contradictory to the intention of successive weighting (i.e. reducing the number of trees) and seems to imply that the orginal search strategy of mh* and bb* missed one or more islands of trees that was or were discovered during the successive weighting. The original data set was therefore re-examined by reorganization of the taxa sequence. Kitching (1992) points out that the probability of locating different islands can be increased by repeated branch swapping from different initial trees. In Hennig86 this can be done by manual rearrangement of the order of taxa in Hennig86. Therefore 50 replicants (manual random rearrangements) of the original data set were analysed in a similar fashion as the original data matrix of Table 2 (mh*; bb* and successive weighting). In all cases however, the successive weighting increased the number of trees, and each profile had the identical length, CI and RI as the original set. Strict consensus trees produced for each of these profiles of trees before and after successive weighting were also identical to the strict consensus trees of the original profile from the data sequence of Table 2. The repeated examination of the data set with various addition sequences did not therefore result in the anticipated reduction of trees by successive weighting and no conflicting and/or additional information was produced. It was therefore decided to base further analysis on the strict consensus tree from the initial profile. The strict consensus tree produced from these 610 trees is shown in Fig. 2. The resolution with regard to the cluster timberlakei-delomeris is identical to the strict consensus tree of the initial profile of 480 equally parsimonious trees. However, with regard to the other branches the tree is much more resolved. The initial node consists of only five branches, three of which lead to terminal taxa. None of the new clusters in the strict consensus tree is, however, present in the majority of the initial profile. This is shown by comparing the strict consensus tree in Fig. 2 with the majority rule consensus tree obtained from the initial tree set (Fig. 1b) (a majority rule consensus tree of a profile contains only those clusters found in a majority of the trees in the profile, Margush and McMorris, 1981). Only the cluster juvator-euryhymenos (without titanus) was found in 75% of the initial 480 trees, and alienus-rotundipennis (without terryi, obstipus, and haleakalaae) in 68%. Also a comparison with the semi-strict consensus tree (Fig. 1c) of the initial set does not show any additional identical groups (a semi-strict consensus tree shows same clusters as strict consensus complemented with all uncontradicted clusters in the initial profile [Page, 1993]). The figures in Fig. 2 refer to those branches found in more than 50% of the trees from the new data sets produced by the bootstrap resampling. It is clear that only a limited number of the branches show some partial consistency in all these data sets and none of the branches is found in all sets. As outlined above (cf taxa and characters), male terminalia provide the sole reliable morphological structure for species recognition and phylogenetic reconstruction. This strongly

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(a) outgroup bicuspidis haleakalaae rotundipennis obstipus alienus titanus terryi euryhymenos juvator perkinsiellae uluhe juvencus cornutus obscuratus amplus filicolus molokaiensis timberlakei chauliosternum canutifrons trichostylis swezeyi oahuensis laterisutilis nigrotarsatus sectus proditus apletomeris megameris hawaiiensis delomeris

(b) outgroup juvencus juvator euryhymenos bicuspidis amplus filicolus molokaiensis uluhe haleakalaae obstipus titanus terryi perkinsiellae alienus rotundipennis cornutus obscuratus timberlakei chauliosternum canutifrons trichostylis swezeyi oahuensis laterisutilis nigrotarsatus sectus proditus apletomeris megameris hawaiiensis delomeris

Fig. 1. Consensus trees from initial profile of 480 equally parsimonious trees obtained through Hennig86 from matrix in Table 2: (a), strict consensus tree; (b), majority rule consensus tree; (c), semistrict consensus tree.

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(c) outgroup bicuspidis titanus terryi perkinsiellae uluhe juvencus obstipus haleakalaae alienus rotundipennis juvator euryhymenos cornutus obscuratus amplus filicolus molokaiensis timberlakei chauliosternum canutifrons trichostylis swezeyi oahuensis laterisutilis nigrotarsatus sectus proditus hawaiiensis delomeris apletomeris megameris

Fig. 1. Consensus trees from initial profile of 480 equally parsimonious trees obtained through Hennig86 from matrix in Table 2: (a), strict consensus tree; (b), majority rule consensus tree; (c), semistrict consensus tree.

limits thesource of morphological variation for analysis and a completely resolved phylogeny cannot be expected from a mere 21 characters among 31 taxa. BIOGEOGRAPHICAL ANALYSIS The strict consensus tree of Fig. 2, obtained after successive weighting, was used as the basis for the biogeographical analysis. Under assumption 1, 2623 statements were produced. Assumption 0 produced an additional 273 statements giving a total of 2896 (assumption 2 implementation is limited to hand resolution and not included here, see Ladiges et al., 1992). The total statements were grouped in a data matrix with 37 columns (Table 4) and analysed with option ie* of Hennig86. This resulted in one parsimonious tree with length 4578, CI 63 and RI 41. The tree is completely resolved and puts the Niihau/Kauai islands as the sister group of all other island groups, with Oahu as sister group of the Molokai group and Hawaii (Fig. 3).

Discussion The cladistic analysis produces a partly resolved tree (Fig. 2). Earlier analysis (De Meyer, 1993) with PHYLIP produced a single most parsimonious cladogram (fig. 1 in De Meyer, 1993) which was also only partly resolved. It is remarkable that none of the 480 trees in the initial profile is identical to the tree obtained with PHYLIP. Comparison (with the partition metric distance option of

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72 69

59

86 84 72 59

outgroup juvencus perkinsiellae uluhe juvator titanus euryhymenos bicuspidis cornutus obscuratus amplus filicolus molokaiensis terryi haleakalaae rotundipennis obstipus alienus timberlakei chauliosternum canutifrons trichostylis swezeyi oahuensis laterisutilis nigrotarsatus sectus proditus apletomeris megameris hawaiiensis delomeris

Fig. 2. Strict consensus tree from profile of 610 trees obtained after successive weighting and tree calculating method in Hennig86 of initial profile of 480 equally parsimonious trees; figures refer to bootstrap analysis (see text for further explanation)

Page’s COMPONENT programme) between the two sets shows that only one tree shows a minimal difference of placement of a single taxon (perkinsiellae and terryi placed in a dichotomy with uluhe as sistergroup or all three placed in a trichotomy). Overall the partition metric distances vary between 1 and 21. Earlier analysis with Page’s COMPONENT programme (1989, version 1.01) (see De Meyer, 1993) produced sets of area-cladograms under the different assumptions with the only area cladogram in common being the one that reflects the geological history of the islands. In this study TAS programme was chosen for a cladistic biogeographical analysis. Recently Morrone and Carpenter (1995) pointed out that none of the available methods is superior. They argued that congruence is the best way to choose a general area cladogram and that this

Table 4. Data matrix with 2896 statements obtained by analysis of area cladogram based on strict consensus tree of Fig. 2, under assumption 1 and 0 through TAS program and grouped in 37 columns (see text). Outgroup Kauai Oahu Molokai Hawaii

0000000000000000000000000000000000000 000000000011111?????111111?????111??? 1111111???0000000000111???111111??111 1111???111111??1111100000000000?11111 ????111111???1111111???11111111000000

Statements=2896, unique statements=37 (37 columns). Factor=1.00. Total round weight=2896.

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Oahu

Molokai

Hawaii Fig. 3. Area cladogram for Hawaiian islands and island groups, obtained through TAS.

congruence should be sought with an independently developed geological area cladogram. The latter is available for the Hawaiian islands through its origin (linear arrangement of the islands as a result of the sequential formation of the islands over a volcanic hot spot, see Materials and Methods). The present biogeographical analysis with TAS produces a similar result as the earlier analysis with COMPONENT and confirms the general congruity of the species succession with the geological history of the islands. Looking at the individual clusters and the known distribution of the species within each cluster, this congruity is obscured either because of the fact that the consensus tree (in Fig. 2) is only partly resolved and/or because of the presence of widespread species. In addition, the direction of the succession cannot be unambiguously established. It could be assumed that species were colonizing newer islands as soon as conditions were suitable to survive and that we would have merely a succession of founder events from geologically older to geologically younger islands. However, a founder event in the opposite direction (i.e. towards an older island) is also feasible. Carson (1987) has shown this to be the case in Hawaiian Drosophilidae lineages where, for example, between Oahu and the Molokai group 10 founder events took place from Oahu to the Molokai group while seven founder events took place in the opposite direction (the general tendency in Carson’s analysis however is in accordance with the geological history). Fig. 4 reflects the possible ancestor–descendant relationships for that part of the strict consensus tree that is largely resolved (i.e. clusters 1–3 and 18–31). Each horizontal line reflects the species present in a specific cluster; vertical solid lines indicate founder lineages towards apomorphic species groups; dotted lines present the lineage in general without implying a particular founder-descendant relation-

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Hawaii

2

1

3

18

19

20

19

31

21

22

29

28

30

30

27

26

25

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23

Fig. 4. Founder-descendant relationships for part of the strict consensus tree of Fig. 2 that is largely resolved (numbers refer to Table 2; see text for further explanation).

ship (i.e. the exact founder species is unknown). The rows reflect the four island groups as outlined above. Most of these branches, though not all, were found in the majority of the bootstrap analysis (cf percentages indicated in Fig. 2). It is clear from the lineages in Fig. 4 that more than one founder event took place. Cluster 1–3 places C. bicuspidis (No. “2”, found on Kauai) in an ancestral position to C. cornutus (“1”) and C. obscuratus (“3”), found on Oahu and Hawaii respectively. C. timberlakei (“18”) is placed in an immediate ancestral position to a cluster of three species found on three islands. The proposed tree does not allow an unambiguous indication of the precise succession. C. swezeyi (“21”) is placed in an immediate ancestral position to C. oahuensis (“22”), both occurring on the same island and therefore possibly the result of a speciation event within the island. C. oahuensis is then put in an ancestral position to C. laterisutilis (“29”) and C. nigrotarsatus (“30”), and reflects a founder event from Oahu to Molokai and/or Hawaii. The lineage of C. sectus (“27”) and C. proditus (“28”) could be an indication

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of a founder event in the opposite direction, i.e. the establishment of C. proditus on Oahu from an ancestor situated on a younger island. The remaining clusters depict founder events between Molokai and Hawaii. These proposed lineages could be further obscured either by extinction or inadequate sampling. For example, the interpretation of the reverse founder event of C. proditus may not hold if C. proditus once occurred on Molokai (and merely dispersed to Oahu) but is now extinct on this island, or when it turns out to occur on Molokai but just was not sampled. In general it can be noted that both dispersal and vicariance models (Humphries and Parenti, 1986; Humphries, 1992) can have a role in explaining the Hawaiian pipunculid fauna. However, because of the unique geological history of the Hawaiian islands, dispersal must have played at least an initial role in the lineages of Hawaiian Cephalops. Younger islands were originally devoid of taxa and had to be colonized from another source (i.e. an older island). Simultaneous occurrence of species within one cluster on the same island (e.g. C. laterisutilis and C. nigrotarsatus on Molokai) can be the result of a vicariance event by the appearance of barriers fragmenting the ancestral species range. A number of phenomena leading to vicariance events are described from the Hawaiian islands, like lava beds dividing forest patches and forming kipukas (habitat islands), formation of gulches, and further erosion producing narrow, parallel ridges and deep V-shaped valleys (Otte, 1989). In the above-mentioned cluster example, any of these phenomena could have produced a vicariance event with a subsequent dispersal event of C. nigrotarsatus to Hawaii. The alternative hypothesis of dispersal and founder event on Hawaii with subsequent dispersal to Molokai is, however, equally feasible and the present study does not allow the formulation of a decisive conclusion in this respect.

Acknowledgements The author would like to thank Prof D.E. Hardy and Dr N. Evenhuis for their assistance during a visit to Hawaii. Dr P. Grootaert kindly provided working facilities at the Institute for Natural Sciences (Brussels). Many thanks to Peter Cranston (CSIRO, Australia) and two anonymous reviewers whose comments greatly improved earlier drafts of this article. This study was partly financed with grants from the National Foundation for Scientific Research (NFWO, Brussels).

REFERENCES

´ ACKLAND, D. M. 1993. Notes on British Cephalops Fallen, 1810 with description of a new species and Microcephalops De Meyer, 1989, a genus new to Britain (Dipt., Pipunculidae). Ent. Month. Mag. 129: 95–105. ALBRECHT, A. 1990. Revision, phylogeny and classification of the genus Dorylomorpha (Diptera, Pipunculidae). Acta Zool. Fenn. 188: 1–240. CANSON, H. L. 1987. Tracing ancestry with chromosomal sequences. Trends Ecol. Evol. 2: 203–207. ¨ systematische en zoogeografische revisie van de DE MEYER, M. 1989. Een taxonomische, ´ genusgroep Cephalops Fallen (Diptera, Pipunculidae). Unpublished PhD thesis, University of Antwerp, 625 pp. DE MEYER, M. 1993. Phylogeny and evolutionary zoogeography of the Hawaiian Pipunculidae (Diptera). Z. Zool. Syst. Evolut.-Forsch. 31: 119–126.

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