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.     

Evolution of the middle leg basal articulations in flies (Diptera)

The morphology of the coxa and trochanter was studied in 205 species from 68 fly families to compare these structures with respect to ability to fly in a streamlined posture, with the middle legs pointing forward and pressed to the thorax. Only Brachycera are able to attain this posture. The forward turn of the coxa at this position is hindered by the junction of the coxa with the pleuron. Recovery of mobility is gained in two ways. (1) By reduction of the contact zone between coxa and pleurite, as in Asiloidea, Bombyloidea, and Empidoidea. Within these flies, the streamlined posture was recorded in Bombyliidae and in a robber-fly, Laphria flava . Others fly with their middle legs straddled laterally or trailing backwards. (2) Longitudinal splitting of the coxa into three coxites provides intracoxal mobility in most Tabanoidea and Cyclorrhapha. The hind and medial coxites rotate about the front coxite and change the coxo-trochanteral axis, thus compensating for restricted protraction. Separation of the hind coxite appears in primitive Tabanoidea, and a separate middle coxite was found in several families among the Nematocera. The streamlined posture was recorded in horse-flies, stratiomyids, and in many Cyclorrhapha except Micropezidae and Hippoboscidae. There is morphological evidence for a possible secondary fusion of coxites at least in Dolichopodidae and Opetidae as well as for the origin of Cyclorrhapha from a miniature ancestor.     

Morphological and other observations on Chonocephalus (Phoridae) and phylogenetic implications for the Cyclorrhapha (Diptera)

Chonocephalus blackithorum sp. nov . is described from Sulawesi. Biological observations on it and five other species are reported. In describing the female it proved necessary to re-evaluate the morphology of the female abdomen both in Chonocephalus and in the Phoridae as a whole. This adds to the growing evidence that the ground-plan of the Phoridae, and hence the Cyclorrhapha, is plesiomorphic with respect to the Empidoidea. The supposed affinity between these two groups is called into question and it is suggested that the Cyclorrhapha could even be an independent lineage from the Nematocera. The case for continuing to regard the Brachycera as monophyletic is also called into question by casting doubt on the rotation of the larval mandibles as a synapomorphy.     

Phylogenetic relationships and the larval head of the lower Cyclorrhapha (Diptera)

We examined final‐stage larvae of all currently recognized lower cyclorrhaphan (= Aschiza) families, except Ironomyiidae and Sciadoceridae, and those of the higher cyclorrhaphan (= Schizophora) families Calliphoridae, Conopidae, Lonchaeidae, Muscidae, and Ulidiidae, and compared them with larvae of two out‐group families, Rhagionidae and Dolichopodidae, paying particular attention to structures of the head. A set of 86 morphological characters were analysed phylogenetically. The results show that the lower Cyclorrhapha is paraphyletic in relation to the higher Cyclorrhapha. The monophyly of the Cyclorrhapha is strongly supported. The lower Cyclorrhapha is resolved into two clades, based on the Lonchopteridae. Within the Syrphidae the traditional three‐subfamily system is supported, based on the Microdontinae. Within the lower Cyclorrhapha, the larval head is variable in form and arrangement of components. In Lonchopteridae, the mouth lies at the back of an open trough or furrow, comprising ventrally an elongate labium and laterally the maxilla. This arrangement of components appears to facilitate scooping food in water films. In Platypezoidea there is no furrow, and the dorsolateral lobes bearing the antennae are connected by a dorsal extension of the pseudocephalon. The main food‐gathering structure is the hooked apex of the labium, but in Phoridae the mandibles may also be important. In Eumuscomorpha the mandibles are at the apex of the head skeleton. The pseudocephalon is extended and infolded dorsally to form an oral pocket over the mouth. In the Pipunculidae, and the Microdontinae and Syrphinae of the Syrphidae, ventrally it forms a V‐shaped groove or guide along which the mandibles project. The labium is sclerotized apically, and forms a plate or tapered projection. This arrangement of components facilitates holding, piercing and extracting prey tissues. In Eristalinae the pseudocephalon is attached to the mandibles and is formed into a pair of cirri bearing mandibular lobes that lie either side of the mouth. Furthermore, the epipharynx is produced anteriorly in relation to the hypopharynx, and the labium is attached to the anterior part of the epipharynx to form a cavity or atrium. This arrangement is suited to fragmenting and imbibing solid food in Eristalinae with hooked mandibles, and when the mandibles are reduced and the mandibular lobes are inverted and sclerotized, these structures form a filter for separating fluid‐suspended particulate food. In higher Cyclorrhapha an atrium is present as in Eristalinae, but a connection between the pseudocephalon and the mandibles is absent. Instead, the pseudocephalon is bifurcate dorsally and forms a pair of cephalic lobes that ventrally ensheath each mandible. The surface of the sheath may be coated in cirri and other food‐gathering structures. The cephalic lobes, mandibular sheaths and the head skeleton are maneuverable and retractile to a higher degree than in lower Cyclorrhapha. This arrangement of components facilitates feeding on both solid food, in which the mouthooks may extend from the sheath to break the food up, and particulate and suspended food, in which the food‐gathering structures of the sheath scoop up the food. In many higher Cyclorrhapha, maneuverability is enhanced by a break between the labium and the basal sclerite, to which it is fused in all lower Cyclorrhapha. Intermediate characters and states for the structures of the higher cyclorrhaphan larval head are present in out‐groups, and lower Cyclorrhapha and homologies are discussed. Liquidity of the food is an important factor explaining the structure of the larval head in Cyclorrhapha. © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society, 2008, 153 , 287–323.     

A general theory of genital homologies for the Hexapoda (Pancrustacea) derived from skeletomuscular correspondences,with emphasis on the Endopterygota

No consensus exists for the homology and terminology of the male genitalia of the Hexapoda despite over a century of debate. Based on dissections and the literature, genital skeletomusculature was compared across the Hexapoda and contrasted with the Remipedia, the closest pancrustacean outgroup. The pattern of origin and insertion for extrinsic and intrinsic genitalic musculature was found to be consistent among the Ectognatha, Protura, and the Remipedia, allowing for the inference of homologies given recent phylogenomic studies. The penis of the Hexapoda is inferred to be derived from medially-fused primary gonopods (gonopore-bearing limbs), while the genitalia of the Ectognatha are inferred to include both the tenth-segmental penis and the ninth-segmental secondary gonopods, similar to the genitalia of female insects which comprise gonopods of the eighth and ninth segments. A new nomenclatural system for hexapodan genitalic musculature is presented and applied, and a general list of anatomical concepts is provided. Novel and refined homologies are proposed for all hexapodan orders, and a series of groundplans are postulated. Emphasis is placed on the Endopterygota, for which fine-grained transition series are hypothesized given observed skeletomuscular correspondences.     

Two remarkable new species of scuttle-fly (Diptera: Phoridae) that parasitize termites (Isoptera) in Sulawesi

ABSTRACT. Diplonevra mortimeri sp.nov. and D.watsoni. sp.nov. are described from specimens caught at Nasutitermitinae termite colonies in Sulawesi. The female of both species has a remarkable pre-oviposition behaviour in which she lures a worker termite into following her away from the colony. She then oviposits in the termite's abdomen. Pupation takes place within the remains of the host's abdomen. Both species only mature a single egg at a time. The female probably guards the comatose host termite during the period of larval development. The morphology of the male hypopygia of the new species allows reinterpretation of the peculiar anal tube in typical male Diplonevra. Furthermore the suggested homologies reinforce the view that the epandrium (tergite 9) has not been replaced by a periandrium (fused gonocoxites) in the Cyclorrhapha and consequently the latter cannot be derived from the Empidoidea.     

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.     

An interesting new species of Megaselia from Sulawesi, the ground plan of the Phoridae (Diptera) and phylogenetie implications for the Cyclorrhapha

Megaselia biarticulata sp.n. is described from Sulawesi. Its distinctly two-segmented palp reinforces the view that a two-segmented palp is part of the ground plan of the family. The tibial hair palisades are also postulated as part of the ground plan and serve to link the Phoridae to the Platypezidae. The median furrow on the frons is considered as part of the ground plan. Furthermore it is postulated that it is homologous with the frontal vitta in the Schizophora, and that its invaginated lower end gave rise to the ptilinum. The Empidoidea cannot be ancestral to the Cyclorrhapha and the case for regarding these two taxa as sister groups seems highly tenuous in the light of the inferred ground plan for the Phoridae.     

Evolution and phylogenetic utility of CAD (rudimentary) among Mesozoic-aged Eremoneuran Diptera (Insecta)

We sequenced nearly the entire carbomoylphosphate synthase (CPS) domain of CAD, or rudimentary, (ca. 4 kb) from 29 species of flies representing all major clades within Eremoneura, or higher flies, and several orthorrhaphous brachyceran outgroups. We compared these sequences with orthologs from Anopheles gambiae and Drosophila melanogaster to assess structure, compositional bias, and phylogenetic utility. CAD is large (6.6+ kb), complex (comprised of three major and myriad minor functional domains) and relatively free of introns, extreme nucleotide bias (except third codon positions), and large hypervariable regions. The CPS domain possesses moderate levels of nonsynonymous divergence among taxa of intermediate evolutionary age and conveys considerable phylogenetic signal. Phylogenetic analysis of CPS sequences under varying methods and assumptions resulted in well-resolved, strongly supported trees concordant with many traditional ideas about higher dipteran phylogeny and with prior inferences from 28S rDNA. The most robustly supported major eremoneuran clades were Cyclorrhapha, Platypezoidea, Eumuscomorpha, Empidoidea, Atelestidae, Empidoidea exclusive of Atelestidae, Hybotidae s.l., Microphoridae+Dolichopodidae, and Empididae s. str. Because CAD is ubiquitous, apparently single copy (at least within holometabolous insects), readily obtained from several insect orders using primers described herein, and exhibits considerable phylogenetic utility, it should have wide applicability in insect molecular systematics.     

The phylogenetic relationships of flies in the superfamily Empidoidea (Insecta: Diptera)

We conducted a molecular phylogenetic study of the Empidoidea, a diverse group of 10,000 species of true flies, with two major goals: to reconstruct a taxonomically complete and robustly supported phylogeny for the group and to use this information to assess several competing classifications for the clade. We amassed 3900+ nucleotides of coding data from the carbamoylphosphate synthase domain of the rudimentary locus (CAD) and 1200+ nucleotides from the large nuclear ribosomal subunit (28S) from 72 and 71 species, respectively, representing several orthorrhaphan and cyclorrhaphan families and all previously recognized empidoidean subfamilies. Independent and combined phylogenetic analyses of these data were conducted using parsimony, maximum likelihood, and Bayesian criteria. The combined matrix included 61 taxa for which both CAD and 28S sequences were obtained. Analyses of CAD first and second codon positions alone and when concatenated with 28S sequences yielded trees with similar and largely stable topologies. Analyses of 28S data alone supported many clades although resolution is limited by low sequence divergence. The following major empidoid clades were recovered with convincing support in a majority of analyses: Atelestidae, Empidoidea exclusive of Atelestidae, Hybotidae sensu lato, Dolichopodidae+Microphorinae (including Parathallassius), and Empididae sensu lato (including Brachystomatinae, Ceratomerinae, Clinocerinae, Empidinae, Hemerodromiinae, Oreogetoninae, and Trichopezinae). The branching arrangement among these four major clades was Atelestidae, Hybotidae, Dolichopodidae/Microphorinae, Empididae. Previously recognized subclades recovered with robust support included Hybotinae, Brachystomatinae, Tachydromiinae, Clinocerinae (in part), Hemerodromiinae, Empidinae, and Empidiini.     

Rejecting "the given" in systematics

How morphology and systematics come together through morphological analysis, homology hypotheses and phylogenetic analysis is a topic of continuing debate. Some contemporary approaches reject biological evaluation of morphological characters and fall back on an atheoretical and putatively objective (but, in fact, phenetic) approach that defers to the test of congruence for homology assessment. We note persistent trends toward an uncritical empiricism (where evidence is believed to be immediately “given” in putatively theory‐free observation) and instrumentalism (where hypotheses of primary homology become mere instruments with little or no empirical foundation for choosing among competing phylogenetic hypotheses). We suggest that this situation is partly a consequence of the fact that the test of congruence and the related concept of total evidence have been inappropriately tied to a Popperian philosophy in modern systematics. Total evidence is a classical principle of inductive inference and does not imply a deductive test of homology. The test of congruence by itself is based philosophically on a coherence theory of truth (coherentism in epistemology), which is unconcerned with empirical foundation. We therefore argue that coherence of character statements (congruence of characters) is a necessary, but not a sufficient, condition to support or refute hypotheses of homology or phylogenetic relationship. There should be at least some causal grounding for homology hypotheses beyond mere congruence. Such causal grounding may be achieved, for example, through empirical investigations of comparative anatomy, developmental biology, functional morphology and secondary structure. © The Willi Hennig Society 2006.     

ECOLOGICAL ORIGIN OF MORPHOLOGICAL DIVERSITY: A STUDY OF ALTERNATIVE TROPHIC PHENOTYPES IN LARVAL SALAMANDERS

The role of ecological factors in promoting morphological diversity within and among species is an area of debate among evolutionary biologists. Using morphological differences between sympatric species as evidence that competition promotes divergence (e.g., character displacement), has, in particular, drawn harsh criticism because morphological differences may have evolved during allopatry. In contrast to species, alternative phenotypes within a species have a common phylogenetic history, so differences between phenotypes are likely to result from ecological conditions experienced in sympatry. Using cannibal and typical larval phenotypes of the Arizona tiger salamander, Ambystoma tigrinum nebulosum, we tested two predictions of the hypothesis that resource competition promotes morphological divergence: (1) larval phenotypes should reduce competition by using different resources; and (2) the advantage to developing the alternative, cannibal phenotype should be highest when competition among typical larvae is most intense. We used field surveys and a field experiment to test these predictions. The two larval phenotypes used different resources, especially when competition was intense. The advantage to individual larvae of becoming cannibals was highest when competition for resources among typical larvae was high. These results support the hypothesis that resource competition can promote morphological divergence.     

Paraphyletic species no more – genomic data resolve a Pleistocene radiation and validate morphological species of the Melanoplus scudderi complex (Insecta: Orthoptera)

Rapid speciation events, with taxa generated over a short time period, are among the most investigated biological phenomena. However, molecular systematics often reveals contradictory results compared with morphological/phenotypical diagnoses of species under scenarios of recent and rapid diversification. In this study, we used molecular data from an average of over 29 000 loci per sample from RADseq to reconstruct the diversification history and delimit the species boundary in a short-winged grasshopper species complex (Melanoplus scudderi group), where Pleistocene diversification has been hypothesized to generate more than 20 putative species with distinct male genitalic shapes. We found that, based on a maximum likelihood molecular phylogeny, each morphological species indeed forms a monophyletic group, contrary to the result from a previous mitochondrial DNA sequence study. By dating the diversification events, the species complex is estimated to have diversified during the Late Pleistocene, supporting the recent radiation hypothesis. Furthermore, coalescent-based species delimitation analyses provide quantitative support for independent genetic lineages, which corresponds to the morphologically defined species. Our results also showed that male genitalic shape may not be predicted by evolutionary distance among species, not only indicating that this trait is labile, but also implying that selection may play a role in character divergence. Additionally, our findings suggest that the rapid speciation events in this flightless grasshopper complex might be primarily associated with the fragmentation of their grassland habitats during the Late Pleistocene. Collectively, our study highlights the importance of integrating multiple sources of information to delineate species, especially for a species complex that diversified rapidly, and whose divergence may be linked to ecological processes that create geographic isolation (i.e. fragmented habitats), as well as selection acting on characters with direct consequences for reproductive isolation (i.e. genitalic divergence).     

Farnesoid secretions of dipteran ring glands: what we do know and what we can know

Harnessing of the Drosophila genetic system toward ascertaining the molecular endocrinology of higher dipteran (cyclorrhaphan) larval development has been a goal for over 70 years, beginning with the data left to us by pioneer researchers from the classical endocrine era. The results of their experiments evidence numerous ring gland activities that are parsimoniously explained as arising from secretions of the larval corpora allatal cells. Utilization of those data toward an understanding of molecular endocrinology of cyclorrhaphan metamorphosis has not yet achieved its hoped for fruition, in part due to a perceived difficulty in identifying larval targets of the molecule "methyl epoxyfarnesoate" (=juvenile hormone III). However, as is reviewed here, it is important to maintain a conceptual distinction between "the target of JH III"Versus "the target(s) of products secreted by the larval corpora allatal cells of ring glands." Recent advances have been made on the identity, regulation and reception of ring gland farnesoid products. When these advances are evaluated together with the above data from the classical endocrine era, there is a new opportunity to frame experimental hypotheses so as to discern underlying mechanisms on cyclorrhaphan larval-pupal metamorphosis that have been heretofore intractable. This paper reconsiders a number of evidenced physiological targets of secretions of corpora allatal cells of the larval ring gland, and places them in the context of more recent biochemical and molecular advances in the field.     

Wing serial homologs and the origin and evolution of the insect wing

The origin and evolution of insect wings has been the subject of extensive debate. The issue has remained controversial largely because of the absence of definitive fossil evidence or direct developmental evidence of homology between wings and a putative wing origin. Recent identification of wing serial homologs (WSHs) has provided researchers with a potential strategy for identifying WSHs in other species. Future comparative developmental analyses between wings and WSHs may clarify the important steps underlying the evolution of insect wings.     

Species-specific genitalic copulatory courtship in sepsid flies (Diptera, Sepsidae, Microsepsis) and theories of genitalic evolution

Males of Microsepsis eberhardi and M. armillata use their genitalic surstyli to rhythmically squeeze the female's abdomen with stereotyped movements during copulation. Squeezing movements did not begin until intromission had occurred and, contrary to predictions of the conflict-of-interest hypothesis for genitalic evolution, did not overcome morphological or behavioral female resistance. Contrary to predictions of the lock-and-key hypothesis, female morphology was uniform in the two species and could not mechanically exclude the genitalia of either species of male. The complex pattern of squeezing movements differed between the two species as predicted by the sexual selection hypothesis for genitalic evolution. Also, evolutionarily derived muscles and pseudoarticulations in the male's genitalic surstyli facilitated one type of movement, whose patterns were especially distinct. The data support the hypothesis that the male surstyli evolved to function as courtship devices.     

Homologous Versus Antithetic Alternation of Generations and the Origin of Sporophytes

The late-nineteenth/early-twentieth century debate over homologous versus antithetic alternation of generations is reviewed. Supporters of both theories, at first, used Coleochaete as a model for the origin of land-plant life cycles. The early debate focused on the morphological interpretation of the sporophyte and on whether vascular cryptogams had bryophyte-like ancestors. The terms of the debate shifted after the discovery that the alternation of morphological generations was accompanied by an alternation of chromosome number. Supporters of homologous alternation now promoted a model in which land plants had been derived from an algal ancestor with an isomorphic alternation of haploid and diploid generations whereas supporters of antithetic alternation favored a model in which land plants were derived from a haploid algal ancestor with zygotic meiosis. Modern evidence that embryophytes are derived from charophycean green algae is more compatible with an updated version of the antithetic theory.     

Alternative techniques to study characters of the genitalia in Lepidoptera

The present note aims to describe two alternative methods for observing genitalia in Lepidoptera. The first one provides means to examine both male and female genitalia without spoiling the scales of the abdomen, preserving it attached to the thorax and aesthetically similar to an unexamined specimen. The second one provides ways of observing certain characters on the male genitalia in a non-destructive way, and does not depend on time-consuming removing and dissection of the abdomen. It is expected that the presented techniques will help on morphological studies and on identifying similar species which consistently differ in genitalic armatures.