Dorsocentral Bristles Research Articles

A new genus and species of subfamily Medeterinae (Diptera: Dolichopodidae) from Cameroon

Cameroonomiya matilei Grichanov, gen. et sp. n. is described from Cameroon. The presence of distinct anterior preaрiсаl seta on mid and hind femora places the new genus in the tribe Udzungwomyiini. It is considered close to the genus Udzungwomyia Grichanov, 2018, but differs from the latter in the wing distinctly longer than the body; the face almost parallel-sided, about 2 times as wide as height of the postpedicel; the postpedicel subtriangular, with dorsal arista-like stylus; six pairs of dorsocentral bristles; the male hind tibia and basitarsus simple, without modified setae or bristles; the sternum 2 with long and thin ventral process in both sexes; the hypopygium with epandrial foramen positioned left laterally; the hypandrium long and broad (ventral aspect), flat, with distal emargination; the surstylus with modified arms. Species of Udzungwomyia differ from Cameroonomiya gen. n. in the wing distinctly shorter than the body; the face in middle about as wide as height of postpedicel, half as wide as face at clypeus and under antenna; the postpedicel semiglobular, with preapical arista-like stylus; four pairs of strong dorsocentral bristles; the male hind tibia swollen at apex, with two long thick curved apicals; the hind basitarsus with basiventral process; the sternum 2 without ventral process; the hypopygium with epandrial foramen positioned basally; the hypandrium short, bifurcated from base; the surstylus with simple arms. A key to four genera of the tribe Udzungwomyiini is provided.

PM 7/53 (2) Liriomyza spp.

PM 7/53 (2) <i>Liriomyza</i> spp.

Albistyla, a new genus of Neotropical Limosininae (Diptera: Sphaeroceridae).

The genus Albistyla is described for a group of similar, highly distinctive Neotropical species that key out at couplet 55 of the key to Neotropical Sphaeroceridae in Marshall and Buck (2010). Albistyla is diagnosed by the combination of a single pair of strongly cruciate interfrontal bristles, two dorsocentral bristles, and the costa ending at the tip of R4+5. It is defined as a monophyletic group primarily on the basis of the unusually modified male sternite 5 and the distinctive white surstylus with broad apical scales. The genus is infrequently collected and only the type species is known from good series. Many of the specimens examined were taken in association with tree falls or similar habitats rich in green leaf litter.

Condition dependence of developmental stability in the sexually dimorphic flyTelostylinus angusticollis(Diptera: Neriidae)

Developmental stability is widely regarded as a condition-dependent trait, but its relation to genotype and environment, and extent of developmental integration, remain contentious. In Telostylinus angusticollis, the dorsocentral bristles exhibit striking variation in developmental stability, manifested as fluctuating asymmetry (FA) in bristle position ('positional FA') and failure to develop some bristles ('bristle loss'), in natural and laboratory populations. To determine whether this variation reflects condition, I tested for effects of genotype and environment (larval diet quality), and examined covariation with condition-dependent traits. Positional FA was not affected by genotype or environment. However, positional FA covaried negatively with secondary sexual trait expression in males, and with sexual dimorphism in body shape, but covaried positively with body size in females. Bristle loss reflected both genotype and larval diet. Flies reared on poor-quality diet exhibited a similar rate of bristle loss as wild flies. Both positional FA and bristle loss were greater in males. These results suggest that the relation between developmental stability and condition is complex and sex dependent.

A new genus and a new species of tachinids (Diptera, Tachinidae) from deserts of middle Asia

Ventoplagia gen. n. is described, with the type species Ventoplagia brevirostris sp. n. The frontal bristles extending only to the base of the pedicel, 2+3 dorsocentral bristles, 0+2 intraalar bristles, the absence of prealar bristle, the short and fine anepimeral (pteropleural) bristle, the scutellum without lateral bristles, and the welldeveloped posteroventral bristle of the hind tibia indicate that the new genus belongs to tribe Minthoini. Ventoplagia gen. n. is closely related to the genus Palmonia Kugler. The characters distinguishing these genera are given.

Drosophila LIM-Only Is a Positive Regulator of Transcription During Thoracic Bristle Development

The Drosophila LIM-only (LMO) protein DLMO functions as a negative regulator of transcription during development of the fly wing. Here we report a novel role of DLMO as a positive regulator of transcription during the development of thoracic sensory bristles. We isolated new dlmo mutants, which lack some thoracic dorsocentral (DC) bristles. This phenotype is typical of malfunction of a thoracic multiprotein transcription complex, composed of CHIP, PANNIER (PNR), ACHAETE (AC), and DAUGHTERLESS (DA). Genetic interactions reveal that dlmo synergizes with pnr and ac to promote the development of thoracic DC bristles. Moreover, loss-of-function of dlmo reduces the expression of a reporter target gene of this complex in vivo. Using the GAL4-UAS system we also show that dlmo is spatially expressed where this complex is known to be active. Glutathione-S-transferase (GST)-pulldown assays showed that DLMO can physically bind CHIP and PNR through either of the two LIM domains of DLMO, suggesting that DLMO might function as part of this transcription complex in vivo. We propose that DLMO exerts its positive effect on DC bristle development by serving as a bridging molecule between components of the thoracic transcription complex.

A review of Palaearctic Teuchophorus, with a new species from Bulgaria (Diptera: Dolichopodidae)

The Palaearctic species of Teuchophorus are reviewed and a key provided to males. T. chaetifemoratus is described as new from Bulgaria. The male of this species is easily recognized by the ventral and posteroventral rows of strong curved bristles on the hind femur and, in contrast to all other Palaearctic species, its hind tibia does not show any peculiar chaetotaxy. It shares the same habitat preference as most of its Western European congeners, whereas Mediterranean species occur in more open habitats. T. simplex Mik is recorded for the first time from Bulgaria. T. bisetus Loew is reinstated as a distinct species, whereas T. tenuemarginatus Strobl most probably does not belong to Teuchophorus and is regarded as nomen dubium. In contrast to the literature, European, African and some Oriental Teuchophorus species have 6 dorsocentral bristles instead of 5, and the entire generic range encompasses 4 to 6 dorsocentral bristles. Two morphological features are found in both sexes of all Teuchophorus species and are the only reliable characters to separate this genus from Sympycnus (sensu lato): the oblique position of crossvein dm-cu and the anterior bend at the base of the distal section of vein M 1 .

Two or Four Bristles: Functional Evolution of an Enhancer of scute in Drosophilidae

Changes in cis-regulatory sequences are proposed to underlie much of morphological evolution. Yet, little is known about how such modifications translate into phenotypic differences. To address this problem, we focus on the dorsocentral bristles of Drosophilidae. In Drosophila melanogaster, development of these bristles depends on a cis-regulatory element, the dorsocentral enhancer, to activate scute in a cluster of cells from which two bristles on the posterior scutum arise. A few species however, such as D. quadrilineata, bear anterior dorsocentral bristles as well as posterior ones, a derived feature. This correlates with an anterior expansion of the scute expression domain. Here, we show that the D. quadrilineata enhancer has evolved, and is now active in more anterior regions. When used to rescue scute expression in transgenic D. melanogaster, the D. quadrilineata enhancer is able to induce anterior bristles. Importantly, these properties are not displayed by homologous enhancers from control species bearing only two posterior bristles. We also provide evidence that upstream regulation of the enhancer, by the GATA transcription factor Pannier, has been evolutionarily conserved. This work illustrates how, in the context of a conserved trans-regulatory landscape, evolutionary tinkering of pre-existing enhancers can modify gene expression patterns and contribute to morphological diversification.

Systematic revision of Neotropical Achalcus and a related new genus (Diptera: Dolichopodidae, Achalcinae) with comments on their phylogeny, ecology and zoogeography

A revision of the species of the subfamily Achalcinae of the Neotropical region is presented. A new genus, Australachalcus gen. nov., is erected based on the presence of six dorsocentral bristles and synapomorphies in the hypopygium. Eight new Achalcus species (bilineatus, brevicornis, costaricensis, cyanocephalus, maculipennis, micromorphoides, niger, tibialis) and eight new Australachalcus species (acornis, browni, cummingi, incisicornis, pseudorobustus, robustus, setosus, variabilis) are described, and Achalcus albipalpus Parent, A. brevinervis Van Duzee, A. longicornis Van Duzee and Enlinia edwardsae (Van Duzee) are newly referred to Australachalcus and redescribed. A key to males of all species and females of eight species is provided. One Palaearctic species, Achalcus melanotrichus Mik, and nine New Zealand Achalcus species (chaetifemoratus, luteipes, medius, minor, minusculus, minutus, nigroscutatus, relictus, separatus) described by Parent are also transferred to Australachalcus. In Neotropical Achalcinae, three Achalcus and more than four different Australachalcus species groups can be distinguished, whereas all Holarctic Achalcus species belong to the single A. flavicollis species group. In the Neotropics, Australachalcus is nearly entirely confined to Chile, whereas Achalcus is recorded from Costa Rica, Venezuela, Ecuador, Colombia, Peru and Chile, with no or little overlap in distribution between the separate species groups. Beyond Chile, most achalcine species treated here were collected at higher altitudes. Most Chilean species are only active during the southern summer, whereas in Costa Rica achalcine representatives are encountered throughout the year. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 143, 27–73.

Scute expression in Calliphora vicina reveals an ancestral pattern of longitudinal stripes on the thorax of higher Diptera.

In Drosophila the stereotyped arrangement of sensory bristles on the notum is determined by the tightly regulated control of transcription of the achaete-scute (ac-sc) genes which are expressed in small proneural clusters of cells at the sites of each future bristle. Expression relies on a series of discrete cis-regulatory elements present in the ac-sc gene complex that are the target of the transcriptional activators pannier (pnr) and the genes of the iroquois complex. Stereotyped bristle patterns are common among species of acalyptrate Schizophora such as Drosophila, and are thought to have derived from an ancestral pattern of four longitudinal rows extending the length of the scutum, through secondary loss of bristles. To investigate evolutionary changes in bristle patterns and ac-sc regulation by pnr, we have isolated homologues of these genes from Calliphora vicina, a species of calyptrate Schizophora separated from Drosophila by at least 100 million years. Calliphora vicina displays a pattern of four rows of bristles on the scutum resembling the postulated ancestral one. We find that sc in Calliphora is expressed in two longitudinal stripes on the medial scutum that prefigure the development of the rows of acrostichal and dorsocentral bristles. This result suggests that a stripe-like expression pattern of sc may be an ancestral feature and may have preceded the evolution of proneural clusters. The implications for the evolution of the cis-regulatory elements responsible for sc expression in the proneural clusters of Drosophila, and function of Pnr are discussed.

Role of dpp signalling in prepattern formation of the dorsocentral mechanosensory organ in Drosophila melanogaster.

A proneural cluster of dorsocentral bristles forms adjacent to the dorsal side of wg-expressing cells in the notum region of the wing imaginal disc. It has been shown that wg activity is required for these structures to form. However, the restriction of this proneural cluster to the dorsal posterior side of the wg expression domain in the anterior compartment of the wing imaginal disc has suggested that Wg signalling itself is insufficient to establish the dorsocentral proneural cluster. Some factor(s) from the posterior side must participate in this action in cooperation with Wg signalling. We have examined the role of Dpp signalling in dorsocentral bristle formation by either ectopically activating or conditionally reducing Dpp signalling. Ubiquitous activation of Dpp signalling in the notum region of the wing imaginal disc induced additional dorsocentral proneural cluster all along the dorsal side of the wg expression domain, and altered wg expression. Conditional loss-of-function of Dpp signalling during disc development resulted in the inhibition of dorsocentral proneural cluster formation and expansion of the wg expression domain. These results suggest that Dpp signalling has two indispensable roles in dorsocentral bristle formation: induction of the dorsocentral proneural cluster in cooperation with Wg signalling and restriction of the wg expression domain in the notum region of the wing imaginal disc.

Systematic revision of Nearctic species of Achalcus Loew (Diptera: Dolichopodidae) with comments on their phylogeny, ecology and zoogeography

The species of the genus Achalcus Loew from the Nearctic Region are revised and a key to males and females is provided. Achalcus utahensis (Harmston &amp; Miller) and A. oregonensis (Harmston &amp; Miller) are redescribed, and A. californicus sp.n., A. dytei sp.n. and A. similis sp.n. are described. Together with eight of the nine known Palaearctic species of the genus, they represent a monophyletic species group, which is characterized by the presence of five pairs of dorsocentral bristles and the incorporation of the epandrial setae onto the shaft of the epandrial lobe. Like their Palaearctic congeners, most Nearctic species occur in damp habitats, such as coastal forests and riparian vegetation. Most specimens were collected in the Pacific coastal states from British Columbia to California, but one species occurs in Utah, and one of six species which were not described because males are lacking, was discovered in Ontario.

U-shaped encodes a zinc finger protein that regulates the proneural genes achaete and scute during the formation of bristles in Drosophila.

The pattern of the large sensory bristles on the notum of Drosophila arises as a consequence of the expression of the achaete and scute genes. The gene u-shaped encodes a novel zinc finger that acts as a transregulator of achaete and scute in the dorsal region of the notum. Viable hypomorphic u-shaped mutants display additional dorsocentral and scutellar bristles that result from overexpression of achaete and scute. In contrast, overexpression of u-shaped causes a loss of achaete-scute expression and consequently a loss of dorsal bristles. The effects on the dorsocentral bristles appear to be mediated through the enhancer sequences that regulate achaete and scute at this site. The effects of u-shaped mutants are similar to those of a class of dominant alleles of the gene pannier with which they display allele-specific interactions, suggesting that the products of both genes cooperate in the regulation of achaete and scute. A study of the sites at which the dorsocentral bristles arise in mosaic u-shaped nota, suggests that the levels of the u-shaped protein are crucial for the precise positioning of the precursors of these bristles.

Selection for canalization at extra dorsocentral and scutellar bristles in Drosophila melanogaster.

Direct artificial selection for a specific pattern, in the number and position of extra bristles, was carried out in a wild-type population of Drosophila melanogaster to canalize (estimated by probit width) the selected phenotypes. From the same population, independent lines were selected for extra dorsocentral bristles (lines D3 and D4) and for extra scutellar bristles (lines E2, E3, and E4). Differences at canalization between both dorsocentral and scutellar systems were detected. Results fit an independent control hypothesis for canalization, at two symmetrical extra bristles, in the main regions in which extra bristles appear.

Selection for canalization at two extra dorsocentral bristles in Drosophila melanogaster.

From 10 isofemale lines of D. melanogaster, the D2 line was established with the aim of obtaining an invariant phenotype at two extra dorsocentral bristles. Line D2 was also subdivided into two other lines, SA and ASD, based on their different bristle patterns. The SA line was selected for two symmetrical anterior extra bristles, and the ASD line was selected for two asymmetrical extra bristles, one anterior and one posterior. Only the SA line showed any canalizing response (estimated by the width of the probit transformation) at the two-extra-bristle class. Nevertheless, the results from the different lines were more consistent with the independent ones of both the anterior and posterior regions of the extra dorsocentral bristles. This analysis showed some independent genetic systems for each region, developmental canalization being at two extra symmetrical bristles per region in all the selected lines (D2, ASD, and SA). Therefore, this canalization did not depend directly on the extra-bristle positional pattern used in the selection. The wild-type canalizing system is suggested to explain the fast canalizing response in a phenotype that had not been previously canalized by natural selection.

Action of natural selection in lines of Drosophila selected for a new level of canalization

Four lines of Drosophila melanogaster previously selected for a stabilized phenotype of two extra dorsocentral bristles were examined for 20 generations of canalizing selection and relaxation of selection. A substantial frequency of flies with either two anterior or two posterior extra bristles was maintained in the relaxed lines. These patterns were the only ones tolerated by natural selection, i.e., the only symmetric ones. It was concluded that anterior and posterior dorsocentral bristles are two independent development structures, and the results are discussed in relation to two proposed genetic systems for bristle determination.

Chromosomal polymorphism and extra bristles of Drosophila melanogaster: joint variation under selection in isofemale lines

Selection for increased numbers of dorsocentral and scutellar bristles produced an increase of In(3R)C heterozygotes in isofemale lines of D. melanogaster. The influence of polygenic selection in the maintenance of the chromosomal polymorphism is discussed.

Selection and temperature effects on extra dorsocentral bristles in Drosophila melanogaster.

Starting from base populations which showed a tendency to form supernumerary dorsocentral bristles, selection for high numbers of dorsocentrals was carried out. In all, 9 lines were selected 6 to 14 generations. Selection proved to be effective in all but two lines. Selection for reduced numbers in one of the lines also proved effective.

CROSSING AND SEXUAL ISOLATION OF EGYPTIAN FORMS OFMUSCA DOMESTICA(DIPTERA, MUSCIDAE)

House flies are an important factor in the public health of Egypt. In order to assess fully thebest methods for control of flies in Egypt, the United States Naval Medical Research Unit .No. 3 and other institutions have undertaken studies on insecticides and bionomics of these insects (Peffly, 1952). As soon as these studies were begun, it became apparent that there was little agreement among taxonomists concerning the various forms of Musca domestica in Egypt. Morphological characters tended to be confusing, and biological differences werepoorly understood. It was therefore decided to attempt to clarify these matters on the basis of (1) field and laboratory biological studies, and (2) investigations of crossing and sexual isolation. In conjunction with the latter phase, a specialist in muscoid taxonomy made a brief field survey chiefly to advise on diagnostic morphological characters (Sabrosky, 1952). Although the typical form, Musca domestica L., must be frequently introduced into Egypt via ships and planes, it has seldom or never been recognized there. The chief forms in Egypt are vicina Macq. and cuthbertsoni Patton. They were considered valid and distinct species by Van Emden (1939), but Sabrosky (1952) tentatively regarded them as subspecies of domestica. These forms would not be regarded as subspecies by Mayr (1942) because they occur in the same geographic area. Sabrosky believed flies from Egypt identified as nebulo Fab; to be merely occasional variant individuals. Van Emden (1939) differentiated these forms from typical domestica and from each other chiefly by variations in length and strength of postsutural dorsocentral bristles (in both sexes) and by relation of frons width to width of the third antennal segment of males. Van Emden separated the forms in this complex as follows:

THE PROBLEM OF DIFFERENCES OF OFFSPRING IN RECIPROCAL CROSSES OF DROSOPHILA

1. To test for the existence of maternal effects in Drosophila melanogaster, approximately isogenic stocks of Dichaete, pyd, vg, M-3, M-4 were prepared. Reciprocal crosses were made between each stock and Dichaete, and between Dichaete and non-Dichaete siblings. The results, as indicated by posterior dorso-central (i.e., average number of dorsocentral bristles per hemithorax), of the Dichaete progeny show that no significant differences arose within six pairs of reciprocal crosses. The reciprocal crosses of four other pairs of experiments yielded significant differences in bristle indices. Two of these pairs were alike in type of crosses, but different in type of culture method. The sign of the differences in bristle indices was reversed in these two sets of experiments, the progeny with the higher indices coming from Dichaete mothers in one case, and from Dichaete fathers in the other.2. Tests of homogeneity show that within crosses, all bottles of which have had identical treatment, di...