Effects of the “sexcombless” chromosome (In(1)sx) on males and females ofDrosophila melanogaster

Summary The chromosome which carries the mutationsexcombless (In(1)sx) affects males and females ofD. melanogaster. In the male foreleg basitarsi the number of sexcomb teeth is dramatically reduced from 10 to 0.7 and the number of transverse rows of bristles is increased from 6 to 8. Females homozygous forIn(1)sx show a normal bristle pattern in the foreleg basitarsus. The genital disc derivatives of both male and femaleIn(1)sx flies are strongly affected. While the external genitalia show a duplicated or a reduced bristle pattern, the internal genitalia are mostly absent. However, the sexually dimorphic tergites and sternites of the abdomen remain unaffected. The male-specific effect on the basitarsus and the general effects on the genital disc derivatives are proposed to represent two different phenotypic effects ofIn(1)sx which may derive from mutations at different gene loci in the inverted chromosome.     

Phylogenetics of the Antopocerus-Modified Tarsus Clade of Hawaiian Drosophila: Diversification across the Hawaiian Islands

The Hawaiian Drosophilidae radiation is an ecologically and morphologically diverse clade of almost 700 described species. A phylogenetic approach is key to understanding the evolutionary forces that have given rise to this diverse lineage. Here we infer the phylogeny for the antopocerus, modified tarsus and ciliated tarsus (AMC) clade, a lineage comprising 16% (91 of 687 species) of the described Hawaiian Drosophilidae. To improve on previous analyses we constructed the largest dataset to date for the AMC, including a matrix of 15 genes for 68 species. Results strongly support most of the morphologically defined species groups as monophyletic. We explore the correlation of increased diversity in biogeography, sexual selection and ecology on the present day diversity seen in this lineage using a combination of dating methods, rearing records, and distributional data. Molecular dating analyses indicate that AMC lineage started diversifying about 4.4 million years ago, culminating in the present day AMC diversity. We do not find evidence that ecological speciation or sexual selection played a part in generating this diversity, but given the limited number of described larval substrates and secondary sexual characters analyzed we can not rule these factors out entirely. An increased rate of diversification in the AMC is found to overlap with the emergence of multiple islands in the current chain of high islands, specifically Oahu and Kauai.     

Pattern as a function of cell number and cell size on the second-leg basitarsus ofDrosophila

Summary The bristle pattern of the second-leg basitarsus inDrosophila melanogaster was studied as a function of the number and size of the cells on this segment in well-fed and starved wild-type flies, in triploid flies, and in two mutants (dachs andfour-jointed) that have abnormally short basitarsi. The second-leg basitarsi of well-fed, wild-type flies from 22 otherDrosophila species were studied in a similar manner. There are typically 8 longitudinal rows of evenly-spaced bristles on the second-leg basitarsus, and in each row the number of bristles was consistently found to vary in proportion to the estimated number of cells along the segment, and the interval between bristles was found to vary in proportion to the average cell diameter on the segment. These correlations are interpreted to mean that the spacing of the bristles within each row is controlled developmentally, whereas the number of bristles is not. The interval between bristles is evidently measured either as a fixed number of cells or as a distance which indirectly depends upon cell diameter.     

Vitellogenin protein diversity in the HawaiianDrosophila

Egg and female hemolymph proteins were resolved via SDS-polyacrylamide gel electrophoresis in a diverse array of 33 endemic Hawaiian drosophilids, encompassing 17 picture-winged species, 3 of theantopocerus species group, 9 fungus feeders, 1 species from each of the modified mouthparts,crassifemur and ciliated tarsus groups, and 1Scaptomyza species. Molecular weights of the two (10 species) or three vitellogenin bands (22 species) were highly variable, spanning a 7-kD range. The largest vitellogenin, V₁, was the most variable, showing a change of some 10% in its mean size of 47.6 kD. The smallest V₃ vitellogenin, mean size 44.1 kD, was evolutionarily the most conservative in size. The speciesDrosophila hawaiiensis was found to be polymorphic for two/three vitellogenin bands and, also, polymorphic with respect to the size of the V₁ protein. No inter- or intrapopulation variability in vitellogenin size was detected in 10 other species examined. The major features of vitellogenin protein evolution in the HawaiianDrosophila are change in molecular weight and regulatory differences that result in quantitative differences between species in patterns of vitellogenin protein production. This research was supported by NSF Grants DEB-7619872 and PCM-7913074. This paper is No. III in the series “Studies of Oogenesis in Natural Populations of Drosophilidae.”     

Structure of the tarsi in some Stenus species (Coleoptera,Staphylinidae): external morphology,ultrastructure, and tarsal secretion

SEM studies show that the differentiation among Stenus species with respect to the formation of the tarsi (wide bilobed vs. slender tarsomeres) takes place with a considerable augmentation of tarsal ventral setae in wide bilobed tarsomeres. The structural diversity of ventral tarsal setae among and within species is discussed with respect to 1) their different roles as mechanosensilla and tenent setae, respectively, and 2) the different selection pressures in terms of adhesive requirements along the longitudinal tarsus axis. The tarsi are provided with four groups of tarsal mechanosensilla, comprising hair and bristle sensilla, campaniform sensilla, and scolopidia. The tarsus wall is supported by an epidermis, which forms three different types of glands pouring their secretion via different exit paths onto the outer cuticle. The organization and ultrastructure of each of these glands is described. Only one (unicellular) gland is directly associated with the ventral tenent setae and is thus considered to form the main part of the adhesive secretion. The beetles appear to release the tarsal secretion through mediation of the tenent setae, which contains a lipid and a proteinaceous fraction. I propose that the secretion is discharged to the outside via a system of very fine pore canals in the wall of the setal shaft. Gas chromatography and infrared spectroscopy revealed that the lipid fraction of the secretion is a mixture of unsaturated fatty acid glycerides and aliphatic hydrocarbons whose spectra are similar to those of extractions of the superficial lipid coating of the body surface.     

Morphological diversity of setae on the second maxilliped of fiddler crabs (Decapoda: Ocypodidae) from the southwestern Atlantic coast

Fiddler crabs are deposit feeders, and use the setae on their mouth appendages to manipulate sediment particles to extract food. The number of spoon‐tipped setae on the second maxilliped is frequently related to the distribution of fiddler crabs on estuarine sediments, but no study has compared the morphological diversity of these setae among multiple fiddler crab species. Here, we describe and classify the setae of the second maxillipeds of the nine Uca spp. known from the Brazilian coast. The second maxilliped of each species was examined by scanning electron microscopy. Six types of setae (five papposerrate, and one pappose) were described on the meropodite of the second maxilliped. Among the papposerrate setae, one type had a spoon‐like tip, and the morphology of this type, especially the degree of curvature, differed between species. Members of Uca leptodactylus, U. uruguayensis, and U. maracoani had highly concave spoon‐tipped setae. In U. rapax and U. cumulanta, the setal tip was moderately curved, while in U. thayeri, U. burgersi, and U. mordax, this curvature was slight. At the other extreme, the meropodite of the second maxilliped of U. vocator lacked setae altogether. This is the first study that describes differences in the degree of curvature of spoon‐tipped setae in fiddler crabs. This trait may be strongly related to the distribution of these fiddler crabs on different estuarine substrates.     

A high-resolution morphogenetic map of the second-leg basitarsus inDrosophila melanogaster

Summary The lineages of cells on the second-leg basitarsus ofDrosophila melanogaster were analyzed by examining gynandromorphs andMinute mosaics. Bracts lie proximal to bristles on the adult basitarsus, yet bract precursor cells were found to originate lateral to bristle precursor cells. In 6 of the 8 longitudinal rows of bristles on this segment, the bract cells arise ventral to the bristle cells; in the others they arise dorsally. The lateral cell origins are interpreted as reflecting a pattern of lateral cell movements associated with evagination of the leg disc. An unusual discrepancy was observed in the relative frequencies of male vs. female bracts and bristles in gynandromorphs. The discrepancy suggests that there is a cell-autonomous sexual difference in either the time at which cells begin moving during evagination or the speed with which they move.On the basis of the results, it is reasoned that the bristle pattern of the basitarsus does not originate in its final form. Prior to evagination, the bristle cells of each row are apparently closer together than in the final pattern, and the rows are farther apart. Evidence is presented which suggests that the bristle cells of each row may originally be arranged in a jagged line which is later straightened by cell movements.The two locations where the anterior/posterior compartment boundary of the second leg passes through the basitarsus were found to vary relative to the bristle pattern. If this boundary is assumed to be a fixed line of positional values, then the extent of the observed variability — which is estimated to be ± 1 or 2 cell diameters — provides a measure of the precision of patterning around the circumference.     

Accuracy of bristle placement on a leg segment in Drosophila melanogaster

Bristle positions in two rows of bristles on the basitarsus of the second leg of the fruitfly Drosophila melanogaster were analyzed in order to determine the accuracy of bristle placement within these rows. Within each row the positions of the two terminal bristles were found to be approximately equally variable, and positional variability was found to increase toward the middle of each row. Rows having fewer bristles manifested more positional variability in their midsection. These results are interpreted in terms of a possible bristle spacing mechanism involving repulsive forces between mobile bristle cells.     

The development and evolution of bristle patterns in Diptera

The spatial distribution of sensory bristles on the notum of different species of Diptera is compared. Species displaying ancestral features have a simple organization of randomly distributed, but uniformly spaced, bristles, whereas species thought to be more derived bear patterns in which the bristles are aligned into longitudinal rows. The number of rows of large bristles on the scutum was probably restricted to four early on in the evolution of cyclorraphous Brachyceran flies. Most species have stereotyped patterns based on modifications of these four rows. The possible constraints placed upon the patterning mechanisms due to growth and moulting within the Diptera are discussed, as well as within hemimetabolous insects. The holometabolic life cycle and the setting aside of groups of imaginal cells whose function is not required during the growth period, may have provided the freedom necessary for the evolution of elaborate bristle patterns. We briefly review the current state of knowledge concerning the complex genetic pathways regulating achaete-scute gene expression and bristle pattern in Drosophila melanogaster, and consider mechanisms for the genetic regulation of the bristle patterns of other species of Diptera.     

OIL FLOWERS AND OIL BEES: FURTHER EVIDENCE FOR POLLINATOR ADAPTATION

We examined foreleg length and body size variation in two species of oil-collecting bees (Rediviva; Melittidae) in southern Africa. Oil-collecting bees harvest oil from host flowers by rubbing their forelegs against oil-secreting trichomes. Significant differences in foreleg length occur among populations of both species. Rediviva “pallidula” populations vary significantly in mean foreleg length (11.34 ± 0.42 mm to 12.67 ± 0.36 mm), but not in body length (10.59 ± 0.74 to 10.80 ± 0.64), and foreleg length and body size are not significantly correlated. Instead, foreleg variation appears to be a function of host plant spur length. Ninety-two percent of the variance in foreleg length of R. “pallidula” is explained by mean Diascia spur length. Rediviva rufocincta populations vary significantly in mean foreleg length (10.12 ± 0.70 mm to 12.34 ± 0.68 mm) and in body length (9.03 ± 0.26 mm to 10.56 ± 0.24 mm). Foreleg length scales allometrically with body size in this species as 90.5% of the variance in foreleg length can be explained as a function of body length. Body size appears to be constrained by the morphology of the oil-secreting host plant. Both bees collect floral oil with specially modified setae on the tarsi of their forelegs. The length of the disti- + mediotarsus (refered to here as “tarsus”) in relation to the entire foreleg is shorter in R. rufocincta and does not increase as rapidly with increasing foreleg length as for R. “pallidula.” These differences in variation can be attributed to differences in position of oil within the flowers of the respective host plants. Rediviva “pallidula” collects oil from Diascia species that have the oil deeply situated in narrow floral spurs of varying length, while R. rufocincta collects oil from the broadly saccate flowers of Bowkeria verticillata and B. citrina.     

Conservation of upstream regulators of scute on the notum of cyclorraphous Diptera

Bristles on the notum of many cyclorraphous flies are arranged into species-specific stereotyped patterns. Differences in the spatial expression of the proneural gene scute correlate with the positions of bristles in those species looked at so far. However, the examination of a number of genes encoding trans-regulatory factors, such as pannier, stripe, u-shaped, caupolican and wingless, indicates that they are expressed in conserved domains on the prospective notum. This suggests that the function of a trans-regulatory network of genes is relatively unchanged in derived Diptera, and that many differences are likely to be due to changes in cis-regulatory sequences of scute. In contrast, in Anopheles gambiae, a basal species with no stereotyped bristle pattern, the expression patterns of pannier and wingless are not conserved, and expression of AgASH, the Anopheles proneural gene, does not correlate in a similar manner with the bristle pattern. We discuss the possibility that independently acting cis-regulatory sequences at the scute locus may have arisen in the lineage giving rise to cyclorraphous flies.     

Ontogenetic variation in the sensory structures on the pedipalps of cosmetid harvestmen (Arachnida,Opiliones, Laniatores)

In arachnids, pedipalps are highly variable appendages that may be used in feeding, courtship, defense, and agonistic encounters. In cosmetid harvestmen, adults have pedipalps that feature flattened femora, spoon‐shaped tibiae, and robust tarsal claws. In contrast, the pedipalps of nymphs are elongate with cylindrical podomeres and are adorned with delicate pretarsi. In this study, we used scanning electron microscopy to examine the distribution of cuticular structures (e.g., sensilla chaetica, pores) on the elements of the pedipalps of adults and nymphs of three species of cosmetid harvestmen. Our results indicate that there is considerable ontogenetic variation in the morphology of the trochanter, femur, patella, tibia, and tarsus. The pretarsus of the nymph has a ventral patch of setae that is absent from the adult tarsal claw. We observed this structure on all three cosmetid species as well as on the pedipalps of an additional seven morphospecies of nymphs collected in Belize and Costa Rica. This structure may represent a previously unrecognized autapomorphy for Cosmetidae. Examinations of the pedipalps of antepenultimate nymphs of additional gonyleptoidean harvestmen representing the families Ampycidae, Cranaidae, Manaosbiidae, and Stygnidae revealed the occurrence of unusual, plumose tarsal setae, but no setal patches on the tarsal claw.     

INTERSPECIFIC HYBRIDS OF DROSOPHILA HETERONEURA AND D. SILVESTRIS I. COURTSHIP SUCCESS

Drosophila heteroneura and D. silvestris are well-defined, sympatric species of the planitibia subgroup of Hawaiian Drosophila. D. silvestris can be subdivided into two allopatric morphotypes that differ in the number of bristle rows on the front tibia (two rows versus three rows). We measured courtship success of intraspecific and interspecific hybrids as the proportion of females inseminated during a two-week period with a single sib male. Proportions were arcsin-transformed so that the values were asymptotically normal in distribution, and tests of homogeneity and of mean differences were performed. Of key importance is the discovery of genetic variation for the proportion of inseminated females within both D. heteroneura and D. silvestris. The interspecific crosses and the D. silvestris intraspecific crosses also provide evidence for a coadapted gene complex with some dominance or heterosis. This coadapted gene complex correlates with the morphotypes of these flies, rather than with the D. heteroneura/D. silvestris contrasts per se. This observation stresses the importance of recognizing both behavioral and morphological components of the mate-recognition system. The incompatible coadaptation that separates the two-row from the three-row forms also supports recent molecular studies which indicate that the three-row form split from the two-row form prior to the split between D. heteroneura and two-row D. silvestris. The observations of intraspecific variability and coadaptation support the predictions of a genetic-transilience model which explains the origin of a new mate-recognition system in terms of sexual selection in the context of a founder-flush event.     

Microstructure of the tarsal attachment devices in the earwig Timomenus komarovi

The biological attachment device on the tarsal appendage of the earwig, Timomenus komarovi (Insecta: Dermaptera: Forficulidae) was investigated using field emission scanning electron microscopy to reveal the fine structural characteristics of its biological attachment devices to move on smooth and rough surfaces. They attach to rough substrates using their pretarsal claws; however, attachment to smooth surfaces is achieved by means of two groups of hairy tarsal pads. This biological attachment device consists of fine hairy setae with various contact sizes. Three different groups of tenent setae were distinguished depending on the cuticular substructure of the endplates. Two groups of setae commonly had flattened surfaces, and they were covered with either spoon‐shaped or spatula‐shaped endplates, respectively. While the flattened tip setae were distributed at the central region, the pointed tip setae were characteristically found along the marginal region. There were no obvious gender‐specific differences between fibrillar adhesive pads in this insect mainly because the forceps‐like pincers are used during copulation to grasp the partner.     

Extra tarsal joints and abnormal cuticular polarities in various mutants ofDrosophila melanogaster

Summary The legs of flies from 16 different mutant strains ofDrosophila melanogaster were examined for abnormal cuticular polarities and extra joints. The strains were chosen for study because they manifest abnormal cuticular polarities in some parts of the body (10 strains) or because they have missing or defective tarsal joints (6 strains). All but three of the stocks were found to exhibit misorientations of either the bristles, hairs, or “bract-socket vectors” on the legs. The latter term denotes an imaginary vector pointing from a hairlike structure called a “bract” to the bristle socket with which it is associated. On the legs of wild-type flies nearly all such vectors point distally, as do the bristles and hairs. In the mutant flies, the most common vector misorientation is a 180° reversal. When the bract-socket vectors of adjacent bristle sites in the same bristle row point toward one another, the distance between the sites is frequently abnormally large, whereas when the vectors point in opposite directions, the interval is frequently abnormally small. This correlation is interpreted to mean that bristle cells actively repel one another via cytoplasmic extensions that are longer in the direction of the bract-socket vector than in the opposite direction. Repulsive forces of this kind may be responsible for “fine-tuning” the regularity of bristle spacing in wild-type flies. Extra tarsal joints were found in eight of the 16 strains. A ninth strain completely lacking tarsal joints appears in some cases to have an extra tibia-basitarsus joint in its tibia. Whereas the tarsi of wild-type flies contain four joints, the tarsi ofspiny legs mutant flies contain as many as eight joints. In this extreme extra-joint phenotype, four of the joints correspond to the normal wild-type joints, and there is an extra joint in every tarsal segment except the distal-most (fifth) segment. Nearly all such ectopic extra joints have inverted polarity. In other strains the extra tarsal joints are located mainly at the wild-type joint sites, and joints of this sort have wild-type polarity. The alternation of normal and inverted (extra) joints inspiny legs resembles the alternation of normal and inverted (extra) body segment boundaries in the embryonic-lethal mutantpatch, suggesting that tarsal and body segmentation may share a common patterning mechanism.     

An independently evolved Dipteran silk with features common to Lepidopteran silks

Male hilarine flies (Diptera: Empididae: Empidinae) present prospective mates with silk-wrapped gifts. The silk is produced by specialised cells located in the foreleg basitarsus of the fly. In this report, we describe 2.3 kbp of the silk gene from a hilarine fly (Hilara spp.) that was identified from highly expressed mRNA extracted from the prothoracic basitarsus of males. Using specific primers, we found that the silk gene is expressed in the basitarsi and not in any other part of the male fly. The silk gene from the basitarsi cDNA library matched an approximately 220 kDa protein from the silk-producing basitarsus. Although the predicted silk protein sequence was unlike any other protein sequence in available databases, the architecture and composition of the predicted protein had features in common with previously described silks. The convergent evolution of these features in the Hilarini silk and other silks emphasises their importance in the functional requirements of silk proteins.     

Patterned Arrays of Intramembranous Particles in the Bristle Cilia of Three Different Species of Euplotes1

Freeze-fractured cells of three marine species of Euplctes (E. crassus, E. raikovi, and E. rariseta) show bristle cilia with patterned arrays of intramembranous particles. Such arrays are essentially of three types, in different positions along the bristle shaft. One array is located near the bristle base and shows a plate-like shape. It appears in a close spatial correspondence with the lasiosome network, which is a structure consisting of interconnected electron-dense bodies lying in between the peripheral axonemal doublets and the bristle membrane. The second type of array, apparently typical of only E. raikovi, consists of eight to ten longitudinal rows of particles that occupy most of the intermediate portion of the bristle. The third type of array appears differently shaped in different species and occurs at the bristle apex.     

Updating the Trachelocercids (Ciliophora, Karyorelictea). I. A Detailed Description of the Infraciliature of Trachelolophos gigas N. G., N. Sp. and T. filum (Dragesco & Dragesco-Kernéis, 1986) N. Comb

ABSTRACT. Trachelolophos gigas n. g., n. sp. and T. filum (Dragesco & Dragesco-Kernéis, 1986) n. comb. (basionym: Tracheloraphis filum) were discovered in the mesopsammon of the French Atlantic coast at Roscoff. Their morphology and infraciliature were studied in live and protargol impregnated specimens. The new genus, Trachelolophos, belongs to the family Trachelocercidae and is unique in having a conspicuous ciliary tuft, which is very likely a highly modified brosse, in the oral cavity. The two species investigated have a very similar infraciliature, differing only in morphometric characteristics and in the nuclear configuration. The entire somatic and oral infraciliature consists of dikinetids which have both basal bodies ciliated or only the anterior or posterior ones, depending on the region of the cell. The right side is densely and uniformly ciliated. Its kineties extend onto the left side to the glabrous stripe, where an anterior and posterior secant system are formed, reducing the number of kineties in the narrowed neck and tail region. The left side bears a narrow glabrous stripe bordered by slightly irregularly arranged dikinetids having rather stiff cilia (bristles), possibly forming an uninterrupted, prolate ellipsoidal (bristle) kinety as indicated by their ciliation. The bristle kinety commences subapically at the right margin of the glabrous stripe, extends posteriorly, then anteriorly at the left, to end up at the right margin again. The dikinetids of the right posterior portion of the bristle kinety have the posterior basal bodies ciliated, whereas the anterior basal bodies are ciliated in its left and right anterior portion. The ends of the bristle kinety meet distinctly subapically at the right margin of the glabrous stripe, as indicated by the diametrically opposed ciliation of the dikinetids. The anterior region (head) of the cell bears a distinct circumoral kinety composed of very regularly arranged dikinetids, associated with nematodesmata forming an oral basket together with the nematodesmal bundles originating from the oralized somatic dikinetids at the anterior end of the somatic kineties. The systematics of trachelocercid ciliates are briefly reviewed and discussed.