Phylogenetics and temporal diversification of the earliest true flies (Insecta: Diptera) based on multiple nuclear genes

Abstract Relationships among families of the lower Diptera (formerly suborder ‘Nematocera’) have been exceptionally difficult to resolve. Multiple hypotheses based on morphology have been proposed to identify the earliest lineages of flies and place the phylogenetic origin of the higher flies (Brachycera), but convincing support is limited. Here we resolve relationships among the major groups of lower Diptera using sequence data from four nuclear markers, including both ribosomal (28S rDNA) and protein‐coding (CAD, TPI and PGD) genes. Our results support both novel and traditional arrangements. Most unexpectedly, the small, highly‐specialized family Deuterophlebiidae appears to be sister to all remaining Diptera. Other results include the resolution of the traditional infra‐orders Culicomorpha (including a novel superfamily Simulioidea = Thaumaleidae + Simuliidae), Tipulomorpha (Tipulidae sensu lato + Trichoceridae) and Bibionomorpha sensu lato. We find support for a limited Psychodomorpha (Blephariceridae, Tanyderidae and Psychodidae) and Ptychopteromorpha (Ptychopteridae), whereas the placement of several enigmatic families (Nymphomyiidae, Axymyiidae and Perissommatidae) remains ambiguous. According to genetic data, the infra‐order Bibionomorpha is sister to the Brachycera. Much of the phylogenetic signal for major lineages was found in the 28S rDNA gene, whereas protein‐coding genes performed variably at different levels. In addition to elucidating relationships, we also estimate the age of major lower dipteran clades, based on molecular divergence time estimates using relaxed‐clock Bayesian methods and fossil calibration points.     

The complete mitochondrial genome of Nephrotoma scalaris parvinotata (Brunetti 1918) (Diptera: Tipulidae) and insights into the phylogeny of Tipulomorpha

Craneflies (Tipuloidea or Tipulidae sensu lato) are one of the most diverse groups of true flies (Insecta, Diptera). The Tipuloidea and perhaps the Trichoceridae formed the infraorder Tipulomorpha, which is traditionally considered the most basal group of Diptera. Relationships among Tipulomorpha and the phylogenetic position of this infraorder within the whole Diptera remain to be settled. A mitochondrial genome (mitogenome) phylogeny of Diptera was produced to test the relationships within Tipulomorpha and its phylogenetic position. A complete mitogenome of Nephrotoma scalaris parvinotata (Tipuloidea, Tipulidae) was firstly sequenced with a next-generation sequencing approach. Compared with the published mitogenomes of Tipuloidea, the new mitogenome had a larger genome size (17,862 nt), due to a longer non-coding control region. The gene order was identical to Drosophila yakuba. Phylogenetic reconstructions using different inference methods recovered Tipulomorpha as monophyletic. And the Tipulomorpha was retrieved in a relatively basal position in Diptera. Within Tipulomorpha, the Tipuloidea and the Trichoceridae were strongly supported as reciprocally monophyletic. Relationships within Tipuloidea were resolved as (Pedicidae + (Limoniidae + (Cylindrotomidae + Tipulidae))). Well supported relationships include: Pedicidae was the sister group of (Limoniidae + (Tipulidae + Cylindrotomidae)); Limoniidae was paraphyletic with respect to (Tipulidae + Cylindrotomidae); Cylindrotomidae was the sister group of Tipulidae. The newly sequenced N. scalaris parvinotata clustered with other two Nephrotoma species at a derived position in Tipuloidea.     

Neodiptera: New insights into the adult morphology and higher level phylogeny of Diptera (Insecta)

This paper outlines several aspects of the skeleto-muscular organization of the adult prothorax and cervix pertaining to the ground pattern of Diptera, which in turn leads to the characterization of Neodiptera, a higher level dipterous taxon which includes Brachycera and bibionomorph Nematocera ( sensu Hennig). The monophyly of Neodiptera is firmly supported by four skeleto-muscular modifications of the pronoto-cervical region. The bibionomorph Nematocera are shown to be paraphyletic in terms of Brachycera. On more preliminary evidence it is argued that the fundamental dichotomy of the extant Diptera lies between a 'polyneuran' clade which includes Trichoceridae, Tipuloidea, Tanyderidae, and Ptychopteridae and an 'oligoneuran' clade which includes all the remaining groups. Preliminary evidence for a sister group relationship between Blephariceroidea and Culicomorpha is also provided. The possible adaptational significance of the cervical specializations in Neodiptera is discussed.     

A phylogenetic interpretation of the Brachycera (Diptera) based on the larval mandible and associated mouthpart structures

Abstract. Based on outgroup comparison, the various components of the larval mandible of the Brachycera and their homologies are described. The final instar larval mandible of the Brachycera ground plan is comprised of a distal pointed hook and an inverted 'U'-shaped basal sclerite. The phylogenetic implications of the larval mandibular homologies and associated mouthpart structures for the current cladistic hypotheses of the Nematocera (Wood & Borkent, 1989) and orthorrhaphous Brachycera (Woodley, 1989) are evaluated.
A cladistic analysis of larval mouthpart characters largely supports the hypotheses of Wood & Borkent and Woodley. The presence of a pharyngeal filter is tentatively proposed as a synapomorphy of the Diptera exclusive of the Tipulomorpha and Bibionomorpha. Evidence is presented supporting a sister-group relationship between the Psychodomorpha ( sensu Wood & Borkent, 1989) and the Brachycera. The placement of the Pantophthalmidae in the Stratiomyomorpha is supported by the apomorphic development of the mandibular-maxillary complex and pharyngeal filter with posterior grinding mill. Additional larval mouthpart characters are proposed supporting the concept of the Eremoneura (Empidoidea + Cyclorrhapha). The ground plan of the Empidoidea appears to be characterized by the apomorphic development of a four-component mandible, in which the basal sclerite is subdivided into two connecting sclerites and a ventral sclerite. Morphological evidence is presented supporting the mandibular origin of the mouthhooks of the Cyclorrhapha.     

The male postabdomen and reproductive system of Bibio marci Linnaeus, 1758 (Hexapoda: Diptera: Bibionidae)

The male postabdomen and the internal parts of the male genital system of Bibio marci (Bibionomorpha) were examined and reconstructed 3‐dimensionally. Several features differ from the presumptive dipteran groundplan. The bases of the gonopods are fused with each other and with tergite IX. The penis is not tube‐shaped and only sclerotized on the ventral side. The vasa deferentia are S‐shaped, and two pairs of accessory glands are present. In contrast to these characteristics, the arrangement of the internal parts is probably close to the ancestral condition. With its specific shape, the penis is well suited for the transfer of a spermatophore. The dorsal sclerite of the copulatory organ probably represents the medially fused parameres. A cladistic analysis of 27 characters of the postabdomen yielded two most parsimonious trees, with the strict consensus as follows: Nannochoristidae (outgroup) + (Culicidae [Culicomorpha] + ((Nymphomyiidae + (Tipulidae + Trichoceridae)) + (Tabanidae [Brachycera] + (Bibionidae, Anisopodidae, Axymyiidae [Bibionomorpha])))). Potential synapomorphies of Bibionomorpha (including Axymyiidae) and Brachycera are the fusion of sternum IX with the gonocoxites, the fusion of the parameres forming the dorsal sclerite and the presence of an entire series of postabdominal muscles (M4, M20, M23, M26, M27, M31, M35 and M37). The results of the analysis are preliminary as it is based on a single‐character system with a limited taxon sampling. However, the main result – a clade Bibionomorpha + Brachycera – is fully compatible with current hypotheses on dipteran phylogeny.     

The morphology of the larval head of Tipulidae (Diptera, Insecta) - The dipteran groundplan and evolutionary trends

External and internal head structures of the larva of Tipula montium are described in detail. The results are compared to conditions found in other representatives of Tipuloidea and other dipteran and antliophoran lineages. Despite of the conceivably basal position of Tipulomorpha within Diptera, the larvae are mainly characterised by derived features. The partially retracted head, the specific hemicephalic condition and several other derived character states support the monophyly of Tipuloidea. A clade comprising Tipuloidea excluding Pediciidae is suggested by the strongly retracted head, by deep dorsolateral incisions of the head capsule, by a distinctly toothed anterior premental margin, by the loss of the second extrinsic maxillary muscle, and possibly by the loss of the pharyngeal filter. Eriopterinae and Hexatominae are characterised by a tendency towards an extreme reduction of the head capsule. Limoniinae, Cylindrotomidae, and Tipulidae form a clade supported by the presence of a premaxillary suture. This implies the non-monophyly of Limoniidae. A feature shared by Cylindrotomidae and Tipulidae is the presence of a movable lacinia mobilis. However, this is arguably a plesiomorphic feature, as it also occurs in Nannochoristidae. Features of the larval head of Trichoceridae, which were included in Tipulomorpha, do not show affinities with those of Tipuloidea. Trichocerid larvae share a specialised subdivided mandible with larvae of psychodomorph groups. Tipuloidea are a highly specialised group. The characters examined did not reveal plesiomorphic features supporting a basal position, and features suggesting closer affinities with Brachycera are vague. The evolution of dipteran larval head structures was apparently strongly affected by the loss of legs and the tendency to live in cryptic habitats. Diptera are the group of Endopterygota with the highest number of apomorphic features of the larval head. The appendages are generally simplified and the muscular apparatus is strongly reduced. Specialised features evolving within dipteran lineages include specifically arranged brushes of hairs on the labrum and epipharynx, movable messores, subdivided mandibles, different mandibular brushes, and a far-reaching reduction of labial parts.     

The mushroom bodies of the lower nematocera: A link between those of the higher diptera and other mecopteroids

Nematoceran Diptera are nonuniform in the structure of their mushroom bodies. Members of the more basal families (Ptychopteridae, Pediciidae, and Tipulidae) have bipartite mushroom bodies, characteristic of members of the other mecopteroid complex orders. In members of Bibionomorpha (Bibionidae and Anisopodidae), tripartite mushroom bodies have been found characteristic of Brachycera Orthorrhapha.     

The dipteran sperm tail: ultrastructural characteristics and phylogenetic considerations

The sperm tail from representatives of several families of Diptera has been examined by high resolution electron microscopy and a computer analysis that improved the visualization of recorded patterns. A considerable variability in sperm tail structure is found within Diptera, and is actually greater than that of any other insect order. The 'generalized insect sperm axoneme'. which is characterized as a 9+9+2 axoneme and by the accessory microtubules having 16 protofilaments, was found only in some dipterans; these are members of Mycetophilidae. From this fact we conclude that Mycetophilidae is likely to be the most primitive extant dipteran group. Another mycetophilid, Boletina , was seen to have accessory tubules with 15 protofilaments as have members of families Dixidae, Chironomidae, Culicidae, and Bibionidae. The last two families have spermatozoa of a type designated as 9+9+'1' there is a central rod rather than two microtubules. We regard this 9+9+'1'pattern with 15 protofilaments to represent a synapomorphic feature. Representatives of the neatoceran families Tipulidae and Trichoceridae have accessory tubules with 13 protofilaments as do examined members of several brachyceran families. Brachycera is hence likely to be derived from the vicinity of the tipulid family. The intertubular material is small in Mycetophilidae and most nematoceran groups, whereas in Tipulidae and Brachycera it is enlarged; here it bridges the space between the accessory tubules and contains various inclusions.     

常用核基因序列在双翅目昆虫系统学中的研究进展

双翅目昆虫分为长角亚目和短角亚目,前者主要类群包括蚊、蠓、蛉和蚋,后者主要类群为虻类和蝇类。国内外学者对双翅目昆虫形态分类和分子系统发育关系研究均较多。本文整理总结了几种主要核基因在双翅目昆虫进化和系统发育关系的研究资料,结果显示:双翅目的单系性得到了众多形态学、生物学和分子数据的支持,多数系统发育研究认为传统的长角亚目为并系,短角亚目是一个单系,其主要类群舞虻下目、环裂类、有缝组和有瓣蝇类均为单系,但非环裂类、无缝组为并系,无瓣类可能为并系;基本搞清了有重要医学意义和与环境关系密切的类群,特别是有瓣蝇类各科类群分类系统的进化关系;双翅目昆虫发生辐射进化的三个分支节点时间即:低等双翅目(蚊类)2.2亿年、低等短角亚目(虻类)1.8亿年、有缝组(蝇类)6500万年;大量双翅目昆虫自然生命史历经吸血性、植食性和寄生性,有2.6亿年以上的演化历程。从相关核基因研究中总结出:18SrRNA、28SrRNA和CAD基因能很好的解决高级阶元从目到属的系统发育问题;EF-1ɑ基因和White基因更适合从科到属水平的分类阶元;ITS基因一般应用在从属到种水平的低级分类阶元,并被广泛应用到双翅目昆虫分子系统学研究中。     

The adult head structures of Tipulomorpha (Diptera,Insecta) and their phylogenetic implications

Schneeberg, K. and Beutel, R.G. 2011. The adult head structures of Tipulomorpha (Diptera, Insecta) and their phylogenetic implications. —Acta Zoologica (Stockholm) 92 : 316–343. Head structures of adults of Tipula paludosa, Limonia sp. and Trichocera saltator were examined and described. The results are compared with conditions found in other dipterans and other antliophoran groups, notably Nannochoristidae. Several potential synapomorphies of a dipteran–nannomecopteran–siphonapteran clade are present in Tipuloidea and Trichocera, the labro‐epipharyngeal food channel, the loss of the galea and the postpharyngeal pumping apparatus. The sensorial field of the maxillary palpomere 3, a potential dipteran–nannomecopteran synapomorphy, is also present but modified. The presence of M. clypeolabralis, labellae and mandibular stylets are groundplan apomorphies of Diptera, with secondary loss of the mandibles in Tipuloidea, Trichoceridae and many other groups. Tipuloidea is supported by the origin of M. tentorioscapalis anterior on the head capsule, the reduction of M. frontobuccalis anterior and the loss of the ocelli. The reduced tentorium, the origin of two further antennal muscles on the head capsule, the maxillary sensorial field with sensilla in individual pits, the lacking dorsal prelabial concavity and the unpaired salivary channel entering the head are apomorphies of Tipulidae. Closer affinities of Tipulidae and Cylindrotomidae are suggested by pseudotracheae of the advanced type, which have evolved independently in this lineage. The results do neither support a basal placement of Tipuloidea nor close affinities with Brachycera.     

Comparison of Postembryonic Organization of the Genital Segments in Trichoceridae, Tipulidae, and Anisopodidae (Diptera, Nematocera)

The number of abdominal segments in Tipulomorpha and Bibionomorpha larvae and aduts is discussed. For Nematocera, the most primitive number of abdominal segments in both male and female larvae is nine. Reduction of the IX abdominal segment and its subsequent fusion with the VIII segment occurs in different phyletic lines in Nematocera and might have evolved several times. In Trichocera spp. nine abdominal segments are present. In the genital segments the main interrelationships in the position of the anus and some main innervation areas, especially the ventral lobes, and the derivatives of the genital primordia were followed during postembryonic reorganization by studying variously stained serial sections from all developmental stages from the first larval instar to the adult stage. Homologies between male and female derivatives of the IX segment genital primordium were established for Trichoceridae. The trichoceroid male claspers and female ovipositor were found to be of sternal origin and highly specialized structures. They appear to be unique features of the Tipulomorpha. Postembryonic development in Limonia nubeculosa Meigen, 1804 and Sylvicola cinctu (Fab-ricius, 1787) was studied in the same way. In Limonia males the trichoceroid functional system for grasping is present. In Anisopodidae ( Sylvicola ), another functional system for grasping has been evolved by the male, which only includes primordial derivatives. In the adults, fusion of the VIII and IX segments prevents development of outer clasping organs or special structures for egg guidance.     

The phylogenetic relationships among infraorders and superfamilies of Diptera based on morphological evidence

Members of the megadiverse insect order Diptera (flies) have successfully colonized all continents and nearly all habitats. There are more than 154 000 described fly species, representing 10–12% of animal species. Elucidating the phylogenetic relationships of such a large component of global biodiversity is challenging, but significant advances have been made in the last few decades. Since Hennig first discussed the monophyly of major groupings, Diptera has attracted much study, but most researchers have used non‐numerical qualitative methods to assess morphological data. More recently, quantitative phylogenetic methods have been used on both morphological and molecular data. All previous quantitative morphological studies addressed narrower phylogenetic problems, often below the suborder or infraorder level. Here we present the first numerical analysis of phylogenetic relationships of the entire order using a comprehensive morphological character matrix. We scored 371 external and internal morphological characters from larvae, pupae and adults for 42 species, representing all infraorders selected from 42 families. Almost all characters were obtained from previous studies but required revision for this ordinal‐level study, with homology assessed beyond their original formulation and across all infraorders. We found significant support for many major clades (including the Diptera, Culicomorpha, Bibionomorpha, Brachycera, Eremoneura, Cyclorrhapha, Schizophora, Calyptratae and Oestroidea) and we summarize the character evidence for these groups. We found low levels of support for relationships between the infraorders of lower Diptera, lower Brachycera and major lineages of lower Cyclorrhapha, and this is consistent with findings from molecular studies. These poorly supported areas of the tree may be due to periods of rapid radiation that left few synapomorphies in surviving lineages.     

Evolution and phylogeny of the Diptera: a molecular phylogenetic analysis using 28S rDNA sequences

Portions of the large ribosomal subunit RNA gene (28S rDNA) encompassing the D1 and the D7 region were obtained from 16 dipteran species and families to reconstruct early phylogenetic events in the order Diptera. For outgroup comparison, the corresponding sequences were used from representative taxa of the Siphonaptera, Mecoptera, and Lepidoptera. A subset of 488 unambiguously alignable sites was analyzed with respect to important sequence evolution parameters. We found (1) sequence variability is significantly higher in double-stranded sites than in single-stranded sites, (2) transitions are close to saturation in most pairwise sequence comparisons, (3) significant substitution rate heterogeneity exists across sites, and (4) significant substitution rate heterogeneity exists among lineages. Tree reconstruction was carried out with the neighbor joining, maximum parsimony, and maximum likelihood methods. Four major subgroups are consistently and robustly supported: the Brachycera, the Culicomorpha, the Tipulomorpha sensu stricto, and the hitherto controversial Bibionomorpha sensu lato, which includes the families Sciaridae, Mycetophilidae, Cecidomyiidae, Bibionidae, Scatopsidae, and Anisopodidae. The phylogenetic relationships within or among these subclades and the positions of the families Psychodidae and Trichoceridae were not robustly resolved. These results support the view that the mouthparts of extant dipteran larvae evolved from a derived ground state characterized by subdivided and obliquely moving mandibles. Furthermore, sequence divergence and the paleontological record consistently indicate that a period of rapid cladogenesis gave rise to the major dipteran subgroups.     

The male genital tract and aedeagal components of the Diptera with a discussion of their phylogenetic significance

The male genital tract of Diptera is surveyed, based on whole dissections, with emphasis on nematocerous infraorders and especially the Culicomorpha. The genital tracts of all available nematocerous families are described and illustrated, including, for the first time, those of the families Thaumaleidae, Dixidae, Hesperinidae, and Pachyneuridae, and, as an outgroup, the mecopteran family Nannochoristidae (Mecoptera). On the basis of outgroup comparison, the Diptera + Mecoptera + Siphonaptera share the synapomorphies of accessory gland continuous with the vas deferens and U-shaped vasa deferentia. Further synapomorphies of the male genital tract provide evidence of the monophyly of the Mecoptera + Siphonaptera, Boreidae + Siphonaptera, and the Blephariceridae + Psychodidae + Trichoceridae + Anisopodidae + Brachycera. The Bibionomorpha, Culicomorpha, and Ptychopteromorpha share the synapomorphy of paired, two- to three-chambered accessory gland complexes, with secondary losses in Corethrellidae + Culicidae. It is concluded that there is no convincing evidence for the monophyly of the Chironomoidea. A sperm pump with an ejaculatory apodeme and the absence of a spermatophore are considered to be part of the ground plan of Diptera, but, because of uncertainty as to the identity of the basal lineage within Diptera and the homology of the sperm pump outside of Diptera, the polarity of these features cannot be presently interpreted.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 711–742.     

Molecular phylogeny of the fungus gnat family Diadocidiidae and its position within the infraorder Bibionomorpha (Diptera)

The molecular phylogeny of the family Diadocidiidae (Diptera: Sciaroidea) is reconstructed based on the combined analysis of four mitochondrial (12S, 16S, COI, cytB) and two nuclear (28S, ITS2) gene markers. All the analyses strongly support Diadocidiidae as a monophyletic group. Genus Diadocidia Ruthe, 1831 includes monophyletic subgenera Diadocidia s. str. and Taidocidia Papp and ?ev?ík (Acta Zoologica Academiae Scientiarum Hungaricae, 51 , 2005b, 329). The monophyly of Adidocidia La?tovka & Matile, 1972 was not confirmed. The position of Diadocidiidae and relationships of the families within the infraorder Bibionomorpha are demonstrated in the analyses based on three gene markers (28S, 12S and 16S). The Bayesian and maximum likelihood analyses of 10 families of Bibionomorpha revealed Sciaridae as the closest relative of Diadocidiidae. Most of the currently recognised extant families of Bibionomorpha proved to be monophyletic. The family Keroplatidae revealed as paraphyletic, with the genera of Macrocerinae being more related to Cecidomyiidae, but the support is low.     

The taxonomic status of Architipula fragmentosa (Bode) and the family Eoasilidae (Diptera) from the Lower Jurassic

The fossil species Architipula fragmentosa (Bode) comb. nov. (Diptera: Nematocera: Limoniidae) from the German Upper Lias (Lower Jurassic) is redescribed. This species was originally described by Bode (1953) in a new monotypic genus as Eoasilidea fragmentosa and placed in the Brachycera, with Eoasilidea as the type-genus of a new family Eoasilidae. This family is here synonymized with the Limoniidae (Nematocera), and the genus Eoasilidea is synonymized with Architipula Handlirsch .     

P elements are found in the genomes of nematoceran insects of the genus Anopheles

We report the identification of genomic sequences in various anopheline mosquitoes (family Culicidae: suborder Nematocera: order Diptera) showing homology to the class II, short inverted-terminal-repeat (ITR) transposable element P from Drosophila melanogaster (family Drosophilidae; suborder Brachycera: order Diptera). Anopheles gambiae appears to have at least six distinct P elements. Other anopheline species, including four additional members of the An. gambiae species complex (An. arabiensis, An. merus, An. melas and An. quadriannulatus), Anopheles stephensi (all subgenus Cellia), An. quadrimaculatus (subgenus Anopheles) and Anopheles albimanus (subgenus Nyssorhynchus) also possess P elements similar to those found in An. gambiae. Ten distinct P element types were identified in the genus Anopheles. At least two of the An. gambiae elements appears to be intact and potentially functional. Phylogenetic analysis of the anopheline P elements reveals them to belong to a distinctly different clade from the brachyceran P elements.     

Taxonomic composition of dendrobiontic Diptera and the main trends of their adaptive radiation

Some dipterans breeding in the wood and bark of dying trees are analyzed. Nematocera are most closely associated with decaying wood; they play the predominant role in its decomposition. Among the higher Brachycera, the species dwelling in bark predominate. Directly in the wood substrate, specific characters of the wood favor the development of relic forms of Diptera. Nine ecological groups of xylo-and phlaeobionts were distinguished. Settlement on wood as a specific substrate is concluded to be one of the trends in the evolution of dipterans. Despite the breeding of the relic dipteran groups in wood, this fact cannot be the initial point for further radiation of dipterans.     

The amnioserosa is an apomorphic character of cyclorrhaphan flies

In developing insect eggs the cells of the blastoderm adopt either an embryonic or an extraembryonic fate. The extraembryonic tissue consists of epithelia, termed amnion and serosa, which wrap the germ band embryo. The serosa develops directly from part of the blastoderm and surrounds the embryo as well as the yolk. The amnion develops from the margins of the germ band and in most insect species generates a transient ventral cavity for the developing embryo. The amniotic cavity and the serosa have been reduced in the course of dipteran evolution. The insect order of Diptera includes the paraphyletic Nematocera, including gnats and mosquitoes, and the more derived monophyletic Brachycera, the true flies. Nematocera develop within an amniotic cavity and the surrounding serosa, whereas cyclorrhaphan Brachycera do not. This observation implies that the amnion and serosa have been reduced before the radiation of the monophyletic cyclorrhaphan flies. Here I show that an amniotic cavity is formed during embryogenesis of the horsefly Haematopota pluvialis (Tabanidae) and the dancefly Empis livida (Empididae). The results suggest that extraembryonic tissue was reduced in the stem lineage of cyclorrhaphan flies, with consequences for the molecular basis of pattern formation along the anterior-posterior axis of the embryo. Received: 21 October 1999 / Accepted: 17 January 2000     

Neurobiological constraints and fly systematics: how different types of neural characters can contribute to a higher level dipteran phylogeny

Much uncertainty still exists regarding higher level phylogenetic relationships in the insect order Diptera, and the need for independent analyses is apparent. In this paper, I present a parsimony analysis that is based on details of the nervous system of flies. Because neural characters have received little attention in modern phylogenetic analyses and the stability of neural traits has been debated, special emphasis is given to testing the robustness of the analysis itself and to evaluating how neurobiological constraints (such as levels of neural processing) influence the phylogenetic information content. The phylogenetic study is based on 14 species in three nematoceran and nine brachyceran families. All characters used in the analysis are based on anatomical details of the neural organization of the fly visual system. For the most part they relate to uniquely identifiable neurons, which are cells or cell types that can be confidently recognized as homologues among different species and thus compared. Parsimony analysis results in a phylogenetic hypothesis that favors specific previously suggested phylogenetic relationships and suggests alternatives regarding other placements. For example, several heterodactylan families (Bombyliidae, Asilidae, and Dolichopodidae) are supported in their placement as suggested by Sinclair et al. (1993), but Tipulidae and Syrphidae are placed differently. Tipulidae are placed at a derived rather than ancestral position within the Nematocera, and Syrphidae are placed within the Schizophora. The analysis suggests that neural characters generally maintain phylogenetic information well. However, by "forcing" neural characters onto conventional phylogenetic analyses it becomes apparent that not all neural centers maintain such information equally well. For example, neurons of the second-order visual neuropil, the medulla, contain stronger phylogenetic "signal" than do characters of the deeper visual center, the lobula plate. These differences may relate to different functional constraints in the two neuropils.