A cladistic and biogeographic analysis is presented of Heterostylum Macquart (Diptera: Bombyliidae), a New World bee-fly genus with 14 species. A phylogenetic hypothesis was obtained based on a data matrix with 27 characters, using the cladogram analysis and search program, TNT, and the matrix editing and tree viewing program, WINCLADA. Character states were polarized by tree rooting with the following outgroup taxa: Toxophora aurea Macquart, Apiformyia australis Yeates, Triploechus novus Williston, T. bellus Philippi, and T. heteronevrus Macquart. The monophyly of Heterostylum was well supported, and after successive weighting was applied, 2 major clades were found: a Nearctic clade including H. robustum (Osten Sacken), H. helvolum Hall & Evenhuis, H. deani Painter, H. croceum Painter, and H. engelhardti Painter, and a Neotropical clade with H. haemorrhoicum (Loew), H. rufum (Olivier), H. evenhuisi Cunha & Lamas, H. maculipennis Cunha & Lamas, H. ferrugineum (Fabricius), H. hirsutum (Thunberg), and H. pallipes Bigot. For the biogeographic analysis we derived an area cladogram based on the phylogenetic hypothesis obtained to analyze the distributional pattern and spatial diversification of Heterostylum. The divergence between Nearctic and Neotropical clades is associated with a spatial disjunction along the Mexican Transition Zone, which supports evidence that an ancient Caribbean event was mainly responsible for the diversification of major lineages of Heterostylum. This biogeographic scenario, as well as alternative scenarios, was also analyzed and discussed along with the results obtained from an event-based biogeographical analysis (DIVA).
The genus Heterostylum Macquart, 1848 contains medium-sized species (10–15 mm) characterized primarily by a robust body covered with long pile and by an indented hind margin of the eye. It presently contains 14 New World species, 9 of them occurring in the Neotropical region [H. bicolor (Loew), 1861; H. duocolor (Painter & Painter), 1974; H. evenhuisi Cunha & Lamas, 2005; H. ferrugineum (Fabricius), 1805; H. haemorrhoicum (Loew), 1863; H. hirsutum (Thunberg), 1827; H. maculipennis Cunha & Lamas, 2005; H. pallipes Bigot, 1892 and H. rufum (Olivier), 1789] and 5 in the Nearctic region [H. croceum Painter, 1930; H. deani Painter, 1930; H. engelhardti Painter, 1930; H. helvolum Hall & Evenhuis, 1981 and H. robustum (Osten Sacken), 1877],
Hull (1973) proposed 10 tribes for the Bombyliinae, and placed Heterostylum (along with Triploechus Edwards, Efflatounia Bezzi, and Karakumia Paramonov) in his Heterostyliini, based on the indented hind margin of the eye. Hall (1976) suggested morphological similarities between Triploechus (which occurs in North America and in South America, only west of the Andes) and Heterostylum (which occurs in South America and is recorded only east of the Andes).
Bowden (1985) proposed a new classification for the Bombyliinae, synonymized Heterostylini with Dischistini, and presented characters to distinguish the 2 largest tribes, Bombyliini and Dischistini. However, Yeates (1994) considered the characters provided by Bowden (1985) to support Dischistini as plesiomorphies, thus making the tribe paraphyletic, and to be used only for taxonomic convenience. As a result of Yeates’s cladistic study, Heterostylum was transferred to the Bombyliini.
Cunha et al. (2007) revised Heterostylum and considered 14 species as valid. The authors redescribed the genus and species and also presented a key to all of them.
More recently Yeates (2008) erected Apiformyia, a new genus from Australia, to include a single species A. australis. The author placed the genus among the Bombyliinae and pointed out its remarkable anatomical affinities with Heterostylum.
In the present study, a cladistic analysis of Heterostylum was carried out including 12 New World species. The distributional pattern and diversification of Heterostylum. were analyzed through an area cladogram derived from the phylogenetic hypothesis. The historical context of divergent, non-overlapping clades in the area cladogram was discussed relied upon the geological history and the available molecular dating. Complementary analysis using an event-based method (DIVA) was performed to test and refine our proposed biogeographic hypothesis.
Material and Methods
The material studied is deposited in the collections of the Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil (MNRJ), Museu de Zoologia da Universidade de São Paulo, São Paulo, Brazil (MZUSP), Departamento de Zoologia, Universidade Federal do Paraná, Paraná, Brazil (DZUP), Museu Paraense Emílio Goeldi, Pará, Brazil (MPEG), National Museum of Natural History, Smithsonian Institution, Washington D.C., USA (USNM), and the Natural History Museum, London, UK (BMNH). Because no specimens of A. australis, T. novus, H. engelhardti, H. helvolum, and H. robustum were available for this study their data were obtained from literature sources (Hall & Evenhuis 1981; Yeates 2008).
For the cladistic analysis we included 12 New World species of Heterostylum. in the ingroup. The types of 2 species, H. bicolor and H. duocolor, are lost and no other specimen is known to be deposited in collections, and, because the original descriptions are insufficiently detailed to provide information for the great majority of characters, they were not included in the cladistic and biogeographic analyses. Only morphological characters of adults were used (Table 1) and all of them were treated as non-additive. The selected outgroup is composed by 3 species of Triploechus: one Nearctic (71 novus Williston, 1893) and 2 Andean species (T. bellus Philippi, 1865 and 71 heteronevrus Macquart, 1850), one species of the Australasian genus Apiformyia (A. australis Yeates, 2008), and one species of Toxophora (T. aurea Macquart, 1848), which was used to root the tree. Based on morphological similarities, Triploechus is herein considered a priori the hypothesized sister-group of Heterostylum, and A. australis is the single species of an Australasian genus that shares similarities with Heterostylum in the conformation of the posterior eye margin and wing venation (Yeates 2008). Because the indentation of the posterior eye margin is a variable character in A. australis, not observed in all specimens (N. L. Evenhuis, pers. comm.), we coded it in the data matrix (Table 2) as polymorphic for this species.
Characters and character states used in the cladistic analysis of Heterostylum.
We applied 2 different character weighting schemes: equal and successive. The successive weighting approach (Carpenter 1988, 1994) is an iterative scheme that applies different weights to characters according to their performance or fitness [interpreted as phylogenetic reliability by Carpenter (1994)] in the initial analysis with equal weights. Character performance can be quantified by several character indices [e.g. consistency index (CI), retention index (RI) or rescaled consistency index]. The tree searching commands (traditional search) used were: replications 1000, tbr, hold (max. trees) 10000, and the CI was used in the successive weighting with the macro “rewt.run”.
Data matrix of the cladistic analysis of Heterostylum macquart (? = missing data).
In an attempt to quantify support for the clades on the tree, we have calculated the Bremer support (Bremer 1994) with TNT. We followed 2 procedures, one ‘approximative’ and the other ‘exhaustive’. First, we calculated support values with TNT through the macro ‘dobrem.run’, although the macro file was modified in some commands at lines 72 (hold 20000) and 102 (hold 20 rep 100 tbr keep), with the strict consensus tree as the ‘reference tree’. This first procedure provided approximate and fractioned (median) support values for the clades. Then, knowing the approximate maximum support value, we calculated Bremer support in TNT under an ‘exhaustive’ approach, with the following commands: hold 100000, hold/100, hold*, replications 1000 suboptimal 6, Bremer absolute supports. Progressively, we increased both the maximum number of trees in the memory (hold 300000) and the number of trees saved in each replication (hold/300) and decreased the suboptimal trees retained (suboptimal 5). We continued this procedure until the analysis reached stable support values with hold 600000, hold/600, hold*, replications 1000, suboptimal 4. Branch support was also verified by using Bootstrap (replications 1000, mult*100).
Geographical data (longitude/latitude) gathered for the species of Heterostylum are presented in the Supplementary Material (Appendix S1). These data were gathered from bibliographic references (Evenhuis & Greathead 1999; Hall & Evenhuis 1981; Painter et al. 1978) and also from specimens hosted in collections. The complete list of material examined is also presented as Supplementary Material (Appendix S2). For some species no precise locality data were available (e.g., “Mexico, Sinaloa” or “Canada, Alberta”), and for these localities we used geographical coordinates that are central to the area (e.g., for “Mexico, Sinaloa” the coordinates plot one point in the center of the state of Sinaloa).
In the cladistic biogeographical analysis, we used the classification scheme proposed by Morrone (2002), wherein the New World is divided into 3 regions: Nearctic, Neotropical and Andean, and Morrone (2001, 2004), and in which the Neotropical region is divided into 4 subregions (Caribbean, Amazon, Chacoan and Parana) and then into provinces. The following transitional zones are included: Mexican Transition Zone (between the Nearctic and Neotropical regions), and South American Transition Zone (between the Neotropical and Andean regions).
In the event-based biogeographical analysis, we carried out a Dispersal-Vicariance Analysis as implemented in the DIVA software (Ronquist 1996, 1997). DIVA analyses optimize and infer the distribution of the ancestral nodes based on current distributions of terminal taxa. We used the same spatial areas as above, but we did not include the transitional areas (Mexican Transition Zone/MTZ and South American Transition Zone/ STZ). We tested different competing biogeographic scenarios by constraining the maximum number of areas (maxareas) allowed for the ancestral distribution. Therefore, we tested a more relaxed scenario with maxareas = 7 (which is the number of areas used) and then we defined a more restrict scenario with maxareas = 4.
Results and Discussion
From the data matrix (17 taxa × 27 characters) presented in Appendix 2, cladogram searches were carried out under the application of 2 different character weighting approaches: equal and successive weighting. The analysis using all characters, equally weighted, resulted in 6 most parsimonious cladograms with length = 68 steps, CI = 0.55, RI = 0.64. In the strict consensus tree (Fig. 1A), Heterostylum appears as monophyletic including 3 polytomic major clades, one formed by the Neotropical species: H. haemorrhoicum. (H. rufum (H. evenhuisi, H. maculipennis)), the second also with Neotropical members (H. ferrugineum (H. hirsutum, H. pallipes)) and a third one, including all the Nearctic species, with no internal resolution.
After successive weighting was applied, a better resolved topology was obtained and the analysis yielded a single most parsimonious cladogram (Fig. 1B) with length = 68 steps, CI = 0.55, RI = 0.64. This cladogram is identical to one of the 6 cladograms resulting under equal weighting analysis.
The results (both equal and successive weighting analyses) support the monophyly of Heterostylum based on 4 unambiguous synapomorphies: row of setae on the ocellar tubercle separating the anterior ocellus from the others (character 1); row of setae on the anterodorsal surface of femur III (character 10, state 1); veins M1 and R5 merging near or at the point where R4 arises (character 13, state 1); and sperm pump longer than spermathecae (character 25, state 1); and one ambiguous synapomorphy: head as wide as or wider than thorax (character 7, state 1).
Based on the cladogram from the successive weighting analysis (Fig. 1B), 2 major groups within the genus were found: one large clade (Clade B) including the Neotropical species (H. ferrugineum. (H. hirsutum, H. pallipes)) + (H. haemorrhoicum. (H. rufum. (H. evenhuisi, H. maculipennis))), the sister of a Nearctic clade (Clade A) with (H. helvolum, H. robustum) + H. deani + (H. croceum, H. engelhardti). With the acctran optimization, clade B appears supported by one synapomorphy, which is the presence of circular spots of different color on the tergites (character 19, state 1). However, this is misleading as, actually, only part of clade D presents this state. Therefore, the following corrected scenario for character 19 (pattern of coloration on abdominal tergites) in clade B is: presence of a central longitudinal stripe (state 2) ambiguously support the clade C (H. ferrugineum (H. hirsutum, H. pallipes)), while in clade D the loss of any mark (state 3) is observed in H. haemorrhoicum, and circular spots are present in the clade (H. rufum (H. evenhuisi, H. maculipennis)) This last clade is supported by one unambiguous synapomorphy, the presence of golden hairs on the mesonotum and dark brown hairs on the pleura (character 8, state 2).
Although no higher-level phylogeny that includes Heterostylum, Triploechus and Apiformyia together has been published to date, some authors have suggested and discussed their morphological affinities (Hall 1976; Hall & Evenhuis 1981; Yeates 2008). These affinities have been based mainly on the sinuous posterior eye margin, which is uncommon in Bombyliinae. Also, among the 3 genera, Apiformyia could possibly be recovered closer to the root in the phylogeny, because its female terminalia lacks the sand chamber and acanthophorite spines. In the present study, the outgroup was composed by A. australis and 3 species of Triploechus: 2 Andean (T. bellus and 71 heteronevrus) and one Nearctic (T. novus), besides Toxophora aurea, which was used to root the resulting trees. We did not include all 5 species of Triploechus in the analysis, but its monophyly was recovered using the 3 representative species. Furthermore, these preliminary data indicated a sister-group relationship between Triploechus and Heterostylum.
The origin of the Bombyliidae (in a broader sense, including Mythicomyiinae, as recently supported by Trautwein et al. 2010) was hypothesized to have taken place in the Middle Jurassic, based on congruence among biogeographical, molecular and fossil data (see Lamas & Nihei 2007), whereas the diversification of the Bombyliinae lineage has occurred since the Early Cretaceous (125 Mya), according to molecular dating (Wiegmann et al. 2003). Fossil records for Bombyliinae and Bombyliini, where Heterostylum, Triploechus, and Apiformyia have been allocated, are rare, and this scarcity has hampered to further discussions about the ancient diversification of these taxa and also of any other bombyliine group. For example, the oldest fossil records for Bombyliini are described from the Eocene epoch (Evenhuis 1997; Lamas & Nihei 2007). These fossil records are represented by Bombylius from Germany (Miocene), France (Oligocene), and the Baltic region (Eocene/Oligocene); and Dischistus from France (Oligocene). However, given its fragmentary nature, a literal reading of the fossil record should be regarded as misleading (Heads 2005), and although not yet found, it is still possible that pre-Cretaceous fossils of the Bombyliidae lineage will be discovered.
Based on the cladogram of Fig. 1B, the area cladogram derived for Heterostylum provides evidence for a spatial disjunction between the Nearctic and Neotropical clades (clades A and B) associated with the Mexican Transition Zone (MTZ, see Morrone 2004, 2006). The Nearctic clade ranges widely over the western and central USA and northern and central Mexico, with the MTZ as the southern boundary (Figs. 2 and 3). The Neotropical clade B extends throughout the Neotropical region (Figs. 2 and 3). It is interesting to note that the genus is absent towards northeastern USA and the south of Brazil and Paraguay, as well as in eastern North America and west of the Andes. On the other hand, some of the lacunae in the distributional pattern are probably due to deficient sampling efforts, as might be the case in Colombia, Guyana, Bolivia, Peru, and southern continental Central America.
Although the origin of Heterostylum. and the early diversification of Bombyliini lineages are not elucidated, a separate examination of the phylogenetic and distributional pattern of Heterostylum can add valuable data about the spatial history of the tribe. The distributional pattern of Heterostylum shows a generic distribution congruent with the phylogenetic pattern, as the basalmost dichotomy diverging to Nearctic and Neotropical clades (Fig. 1B) is congruent with the distributional disjunction between the Nearctic and Neotropical clades (Figs. 2 and 3). Although in close geographical proximity, the Nearctic and Neotropical clades do not overlap each other. The disjunction of Heterostylum. is spatially coincident with the boundaries of MTZ. The biogeographical scenario presented in Fig. 3 is suggested based upon the phylogenetic hypothesis proposed here (Fig. 1B). Yet, in our analysis the monophyly of clade B had no Bremer support, whereas clade A had bootstrap (51%) and Bremer supports (2). Furthermore, the ‘Nearctic’ definition is used here in the broad sense, as the Nearctic clade extends over areas within the Nearctic region and also southward through the MTZ (see Morrone 2004, 2006).
A number of biogeographers have been focusing their studies on the MTZ, correlating and explaining its biota with both Nearctic and Neotropical influences. Croizat (1958) suggested a node in southern Mexico as a major node regarding patterns on the intercontinental scales. Halffter (1964, 1987, and others) pioneered biogeographical studies on insects in the MTZ. In fact, Gonzalo Halffter was the most experienced authority on the MTZ history and biogeography. He regarded the complexity of MTZ as potentially responsible for the scarcity of biogeographical studies in that area (Halffter 1964). The Nearctic range of Heterostylum is congruent with the insect distributional patterns pointed out by Halffter (1987), wherein the species occurring north of the Transmexican Volcanic Belt have more affinities with the Nearctic fauna than with the Neotropical one.
What geological or biogeographical event could be associated with the basal divergence of Heterostylum (Figs 2 and 3)? The Transmexican Volcanic Belt has a recent origin, since its formation began during the Oligocene (Halffter 1987). Perhaps another ancient event in the Caribbean (and related to the formation of the Caribbean Plate) could be involved. Alternatively to the traditional northsouth Oligocene division across the Transmexican Volcanic Belt, Escalante et al. (2007) suggested the occurrence of an earlier Caribbean event during the Paleocene dividing the Mexican biota through an east-west division. These authors suggested a biogeographical relationship of eastern Mexico with the early supercontinent Gondwana, while its relationship with the adjacent areas (Central America and Caribbean) was not precisely discussed. The geological event argued as responsible for generating that pattern, the eastward movement of the Caribbean Plate, took place in the Paleocene (Escalante et al. 2007) and was related to the formation of the Proto-Greater Antilles during the Late Cretaceous. Nevertheless, we regard as equally valid the association of the east-west division of Mesoamerica with the early formation of the Proto-Greater Antilles. The Cretaceous Volcanic Arc formed during the Late Cretaceous and was deformed dynamically across the Paleogene while firmly accompanying the eastward movement of the Caribbean plate (Iturralde-Vinent & MacPhee 1999). The age of this geological event in dating the basal divergence of Heterostylum is congruent with the molecular dating of the subfamily Bombyliinae inferred by Wiegmann et al. (2003) as the Early Cretaceous (125 Mya).
In this context, the early formation of the Caribbean islands, derived from the Cretaceous-Paleogene Volcanic Arc, could explain the current distribution pattern of Heterostylum species throughout the Mesoamerican areas, with regard to both presence and absence of species. Heterostylum is highly diversified through the Caribbean islands, nearly absent on the Central American continental landmass, and reasonably diversified in the southern Nearctic (Mexico), but with no overlap between the Caribbean/Central American and the Nearctic species. The continuous eastward movement of the Cretaceous-Paleogene Volcanic Arc, since its formation in the Late Cretaceous and its dynamic conformation during the Paleogene until the current Caribbean was consolidated, paralleled the eastward movement of the Centroamerican Arc, a neighboring western plate bearing the early landmasses that formed the present continental region of Central America (Iturralde-Vinent & MacPhee 1999).
The basal diversification of the Neotropical clades C and D indicates a distributional fragmentation from the Caribbean areas (Figs. 4 and 5, see also Fig. 2). All species in clade C have a Caribbean distribution, and although most of the species have a widespread distribution in South American semiarid areas, this clade has not diversified outside the Caribbean (Fig. 2), i.e., there is no endemic species outside the Caribbean. With regard to clade D, the 2 species closest to the basal node (H. haemorrhoicum and H. rufum) occur in the Caribbean (Figs. 2 and 5). Similarly to some species in clade C, H. rufum, occurs in the Caribbean but is also widespread in South America, ranging through the Amazonia, Cerrado, Caatinga, to the Atlantic domains. However, unlike clade C, this other Neotropical clade is distinctive in having species occurring in the Atlantic Forest (Fig. 2). Both H. rufum and H. maculipennis occur in the Atlantic Forest, although only the latter actually occurs in humid environments of the Atlantic Forest (see discussion below). Again, unlike clade C, this clade has diversified into South America, with 3 endemic species in Brazil.
Alternative Biogeographic Scenarios
Besides the taxon-area cladograms (Fig. 2), we performed a DIVA analysis to test and refine the results obtained and discussed above. DIVA is an event-based analysis and can recognize biogeographical processes (vicariance, dispersal and dispersion) which possibly originated the current taxon distribution. The DIVA analysis performed using the phylogenetic hypothesis and distributional data of Heterostylum produced a similar interpretation but it also derived alternative scenarios (Figs. 6A–D), which will be discussed herein. In a relaxed analysis, not constraining the maximum number of areas of the ancestral distribution (maxareas = 7) (see methodology description above), DIVA resulted in a biogeographical scenario (Scenario 1, Fig. 6A) with ancient origin and diversification, wherein the ancestral distribution is inferred to be wide (= sum of all areas, ABCDEFG) with the occurrence of subsequent vicariant events. Sympatric distributions (overlapping) between terminal taxa and between clades were resolved by assuming at least 10 ad hoc events, however, the DIVA algorithm cannot correctly distinguish whether dispersion or dispersal occurred, i.e., simple range expansion or a true dispersal process. This correction can be made ‘manually’, post-algorithm. Moreover, DIVA may often produce some unrealistic optimizations for some nodes, as seen in Scenario 1 (Fig. 6A), when inferring the ancestral distribution BG (Caribbean + Atlantic Forest) for the node of terminals 9 to 12. This disjunct ancestral distribution is spurious. DIVA has some pitfalls and inherent problems, and many of them were raised and well discussed in Kondandaramaiah (2010). For this reason, one should be very careful when carrying out a DIVA analysis, especially in interpreting its results (the optimized scenarios).
Alternative (and more realistic) scenarios were optimized constraining maxareas on DIVA, as in Figs. 6B and 6C. Both scenarios applied maxareas = 4, and these 2 scenarios differ only in the ancestral distribution assumed for the basalmost node: ABC (Nearctic + Caribbean + Amazon) in Scenario 2, and AB (Nearctic + Caribbean) in Scenario 3. The former (Fig. 6B) proposes an ancient vicariant hypothesis for Heterostylum as in Scenario 1, although not completely widespread. In contrast, Scenario 3 proposes a northern origin for Heterostylum with a north-to-south dispersal - ist hypothesis. Both scenarios assume widespread distribution of the terminals by models involving events of dispersion (e.g., terminals 10 and 11 in Scenario 2) and dispersal (e.g., node of clade D in Scenario 2).
Interestingly, DIVA analyses did not infer any scenario with the basalmost distribution without including the Nearctic region. Meanwhile, another serious inherent problem is that DIVA is not able to infer any event in the basalmost node other than vicariance. This is to say that at this node, dispersion or dispersal events will never be inferred by DIVA analyses. (For that, there should be the addition of taxa intermittently joined to the root.) Hence, to regard such events inherently ignored by DIVA, we can manually include additional ad hoc events to the basalmost node, as in Scenario 4, where the ancestral distribution ABC would have been reached after a dispersal event (+A) with subsequent divergence into A and BC. Observe that this is the same as presented in Scenario 2, but contrasting in the explanation for the ancient distribution and the associated event (vicariance in Fig. 6B, dispersal in Fig. 6D). As a consequence, while Scenario 2 supports an ancient vicariant scenario with a widespread ancestral distribution, Scenario 4 supports a southern origin with a south-to-north dispersalist scenario. Did Heterostylum Species Diversify Mostly within Forested Areas?
The species distributions maps (Figs. 7 and 8) and the area cladogram (Fig. 2) provide interesting information about species distributions and endemicity. It is well known that bombyliids often inhabit drier environments, although this would not seem to be the case for Heterostylum species by a mere glance at the maps. Furthermore, it is quite curious that no endemic species occur in the semi-arid areas of South America east of the Andes, namely the Cerrado, Caatinga, and Chaco (although H. duocolor is known only from the type-locality in the Chaco). However, these superficial impressions are misleading.
Heterostylum rufum is widespread in the Caribbean and Amazonian subregions, and Cerrado, Caatinga and Atlantic Forest (Fig. 7). Heterostylum rufum certainly occurs in the Amazonian subregion, but in the Amazon Forest this appearance is artifactual for some localities (see Appendices 3 and 4). Some of the recorded localities within the Amazonian subregion are the following: 1) Serra Norte (Pará), in southeastern Pará, is known to have “campos rupestres” vegetation (a kind of Cerrado); 2) Alter do Chao (Pará, Rio Tapajás) has sandy beaches along the Tapajós River; 3) Imperatriz (Maranháo) has “mata dos cocais” vegetation, a transitional ecosystem between the Amazon Forest and the semi-arid Caatinga in northeastern Brazil; and 4) Porto Platon (Amapá) is covered by Cerrado vegetation. Similarly, H. rufum occurs in the Atlantic Forest (=Paraná subregion) but, in this case, in both humid and semi-arid environments: 1) the locality Sertãozinho (São Paulo) is covered mainly by Cerrado; 2) Conceição da Barra (Espirito Santo) is a coastal locality covered by “restinga”, a semi-arid vegetation bordering beaches; and 3) Marília (São Paulo) has semi-deciduous forest vegetation.
The occurrence of H. ferrugineum in the Amazonian subregion is based on a record from Boa Vista (Roraima), which is covered by Cerrado vegetation. The remaining records are in the Caribbean and in the semi-arid diagonal (Cerrado + Caatinga + Chaco). In the Caatinga, the species is widespread, reaching the northeastern Brazilian coast (Ceará) and also extending up to the transition between the Caatinga and Atlantic Forest (Santa Rita-Bahia). Its absence from the Amazon Forest is conspicuous, such as in the sister-clade H. hirsutum + H. pallipes.
The records known for H. hirsutum (Fig. 7) are located separately in 2 disjunct areas (as far as we know it): one north, on the coastal regions of Venezuela and Colombia, and another south, on northwestern Argentinean Andes and southwestern Brazilian Chacoan area. Besides these confirmed records, the type-locality is mentioned only as Brazil (Cunha et al. 2007). It is also recorded in Paraguay, but unfortunately, this occurrence was not confirmed during our search (by examination of collections and literature review). Based on the reliable records, the known and confirmed distribution of this species is restricted to the Caribbean subregion, Chacoan subregion, and the South American Transition Zone (STZ).
Only one species of Heterostylum, H. duocolor, occurs exclusively in the Chacoan subregion, with a single locality so far recorded in the Argentinean Patagonia (Córdoba). This species was not included in the cladistic analysis because of the unavailability of material for study (the type is lost, and it has not been recognized by subsequent authors).
On the other hand, H. maculipennis is actually endemic to humid environments of the Atlantic Forest (e.g., the localities of Nova Friburgo and Itatiaia in the state of Rio de Janeiro, and Nova Teutonia in Santa Catarina), although it also occurs in coastal areas with comparatively dry vegetation (e.g., the localities of Praia Grande, state of São Paulo, and Angra dos Reis, state of Rio de Janeiro).
The hypothesized phylogenetic pattern for Heterostylum separates the species into 2 clades, a Nearctic and a Neotropical, with 5 and 7 species, respectively. The phylogenetic pattern is congruent with the distributional pattern as the basalmost dichotomy between the Nearctic and Neotropical clades is congruent with the spatial disjunction between both clades. The disjunction of Heterostylum. is spatially coincident with the Mexican Transition Zone.
The biogeographical analysis presented and discussed above supports a Caribbean geological event (e.g., the formation and history of the Proto-Greater Antilles, and the eastward movement of the Caribbean Plate) as responsible for the ancient diversification of major lineages of Heterostylum. The absence of Heterostylum species from the Central American continental landmass, in contrast to the high diversity found in the Caribbean areas (5 species), reinforces the role of the Cretaceous-Paleogene Volcanic Arc for the diversification of the genus. It is quite contrasting how vicariance can be consistently postulated to explain the distributional pattern of the Neotropical species, whereas the Nearctic species overlap broadly in their distributions and are hence difficult to explain. On the other hand, the eventbased biogeographical analysis (DIVA) recognized events, which supported the same scenario discussed above, but also supported and indicated alternative scenarios for Heterostylum. However, unless we know the resolution of other Bombyliini closely related with Heterostylum, and reliable fossil record and dating of the lineages, the biogeographical history of the group will remain unclear.
The authors thank David Notton (BMNH), Neal Evenhuis (Bishop Museum, Hawaii, USA), curator of the USNM Bombyliidae collection, and Claudio José Barros de Carvalho (DZUP), for loaning us specimens of Heterostylum. Special thanks to Fernando Marques for help in calculating the Bremer support on TNT; to Peterson Lopes for providing the macro file for calculating characters indexes on TNT; to John Grehan and Augusto Ferrari for valuable comments on the manuscript; and to Isabel Sanmartín for discussion on DIVA methodology. Financial support from FAPESP (Fundação de Amparo à Pesquisa do Estado de São Paulo) (Proc. No. 2004/09431-5, 2009/17190-1, 2010/52314-0 to CJEL and 2007/50836-7 to SSN) and CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) (Proc. No. 563256/2010-9).
 Supplementary material for this article in Florida Entomologist 97(3) (2014) is online at http://purl.fcla.edu/fcla/entomologist/browse.