Evolutionary pattern of the gtwin retrotransposon in the Drosophila melanogaster subgroup

The gtwin retrotransposon was recently discovered in the Drosophila melanogaster genome and it is evolutionarily closer to gypsy endogenous retrovirus. This study has identified gtwin homologous sequences in the genome of D. simulans, D. sechellia, D. erecta and D. yakuba by performing homology searches against the public genome database of Drosophila species. The phylogenetic analyses of the gtwin env gene sequences of these species have shown some incongruities with the host species phylogeny, suggesting some horizontal transfer events for this retroelement. Moreover, we reported the existence of DNA sequences putatively encoding full-length Env proteins in the genomes of Drosophila species other than D. melanogaster. The results suggest that the gtwin element may be an infectious retrovirus able to invade the genome of new species, supporting the gtwin evolutionary picture shown in this work.     

Utilization of a Photosystem by Drosophila melanogaster Larvae (Diptera: Drosophilidae)

Foraging-stage third-instar larvae from most wild-type (normal) Drosophila melanogaster stocks are generally repelled by light. To identify factors that affect the larval photoresponse, we elucidated the effects of age, temperature, and time on the photoresponse of larvae from a wild-type Canton-S stock. In addition, we analyzed the larvae from the LI2 isofemale line, which are unresponsive to light in a photoassay. To determine whether LI2 larvae behave abnormally on other behavioral paradigms, in comparison to Canton-S controls, we tested larvae in taste and olfactory assays and observed them to determine whether they dispersed in a food source. Like Canton-S larvae, LI2 larvae and other isofemale lines whose progenitors were collected from the same natural population are responsive to taste and olfactory stimuli. Moreover, LI2 larvae disperse in the food source, as do Canton-S larvae tested in the dark. Larvae expressing para^sbl mutations, which respond normally to light but not to chemical stimuli, do not disperse normally in the food source, suggesting that dispersal may be mediated by perception of chemical cues.     

Development time and pupation behavior in theDrosophila melanogaster subgroup (Diptera: Drosophilidae)

This study is an in-depth analysis of intersexual, intraspecific, and interspecific variability in larvopupal developmental time, pupation site preference, and larval and pupal survival of a number of isofemale lines of the speciesDrosophila mauritiana, D. melanogaster, D. sechellia, D. simulans, D. teissieri, andD. yakuba. There was no significant sex differences in pupation height, but females eclosed significantly earlier than males in all species. In addition, the suggestion of a strong negative correlation between larval developmental time and pupation height could not be confirmed in this study. The hypothesis that differences in pupation height provide a basis for niche partitioning between closely related species with overlapping distributions was tested by three planned orthogonal contrast analyses of variance. First, the two speciesD. teissieri andD. yakuba, with largely overlapping distribution, were significantly different in pupation height. Second, the two allopatric, nonoverlapping island speciesD. mauritiana andD. sechellia did not significantly differ in pupation height. However, the absence of a significant difference in the final contrast between the two cosmopolitan speciesD. melanogaster andD. simulans, which are often found together, makes us cautious to accept the hypothesis.     

Multiple events of horizontal transfer of the Minos transposable element between Drosophila species

In this study the Minos element was analyzed in 26 species of the repleta group and seven species of the saltans group of the genus Drosophila. The PCR and Southern blot analysis showed a wide occurrence of the Minos transposable element among species of the repleta and the saltans groups and also a low number of insertions in both genomes. Three different analyses, nucleotide divergence, historical associations, and comparisons between substitution rates (d(N) and d(S)) of Minos and Adh host gene sequences, suggest the occurrence of horizontal transfer between repleta and saltans species. These data reinforce and extend the Arca and Savakis [Genetica 108 (2000) 263] results and suggest five events of horizontal transfer to explain the present Minos distribution: between D. saltans and the ancestor of the mulleri and the mojavensis clusters; between D. hydei and the ancestor of the mulleri and the mojavensis clusters; between D. mojavensis and D. aldrichi; between D. buzzatii and D. serido; and between D. spenceri and D. emarginata. An alternative explanation would be that repeated events of horizontal transfer involving D. hydei, which is a cosmopolitan species that diverged from the others repleta species as long as 14Mya, could have spread Minos within the repleta group and to D. saltans. The data presented in this article support a model in which distribution of Minos transposon among Drosophila species is determined by horizontal transmission balanced by vertical inactivation and extinction.     

LTR Retrotransposon-Gene Associations in Drosophila melanogaster

Thirty-three percent (228/682) of all long terminal repeat (LTR) retrotransposon sequences (LRSs) present in the sequenced Drosophila melanogaster genome were found to be located in or within 1000 bp of a gene. Recently inserted LTR retrotransposons are significantly more likely to be located in or within genes than are older, fragmented LTR retrotransposon sequences, indicating that most LRS-gene associations are selected against over evolutionary time. LRSs associated with conserved genes (homologenes) are especially prone to negative selection. In contrast, fragmented LRSs that have persisted in the genome over long spans of evolutionary time are preferentially associated with genes involved in signal transduction and other newly evolved functions. Reviewing Editor: Dr. Juergen Brosius     

Chromosomal evolution in the Drosophila cardini group (Diptera: Drosophilidae): photomaps and inversion analysis

Detailed chromosome photomaps are the first step to develop further chromosomal analysis to study the evolution of the genetic architecture in any set of species, considering that chromosomal rearrangements, such as inversions, are common features of genome evolution. In this report, we analyzed inversion polymorphisms in 25 different populations belonging to six neotropical species in the cardini group: Drosophila cardini, D. cardinoides, D. neocardini, D. neomorpha, D. parthenogenetica and D. polymorpha. Furthermore, we present the first reference photomaps for the Neotropical D. cardini and D. parthenogenetica and improved photomaps for D. cardinoides, D. neocardini and D. polymorpha. We found 19 new inversions for these species. An exhaustive pairwise comparison of the polytene chromosomes was conducted for the six species in order to understand evolutionary patterns of their chromosomes.     

Multiple subfamilies of mariner transposable elements are present in stalk-eyed flies (Diptera: Diopsidae)

The Diopsid stalk-eyed flies are an increasingly well-studied group. Presented here is evidence of the first known transposable elements discovered in these flies. The vertumnana mariner subfamily was identified in the Diopsini tribe, but could not be amplified in species of the Sphyracephalini tribe. PCR screening with degenerate primers revealed that multiple mariner subfamilies are present within the Diopsidae. Most of the sequenced elements appear to be pseudogenes; however two subfamilies are shown to be evolving under purifying selection, raising the possibility that mariner is active in some Diopsid species. Evidence is presented of a possible horizontal transfer event involving an unknown Teleopsis species and the Tephritid fly Bactrocera neohumeralis. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Gene and species trees reveal mitochondrial and nuclear discordance in the Drosophila cardini group (Diptera: Drosophilidae)

Abstract. The Drosophila cardini group includes 15 species, which are subdivided into the D. cardini and D. dunni subgroups. Although many phylogenetic hypotheses have been proposed for this group during the last five decades (based on patterns of reproductive isolation, morphology of male genitalia, chromosomal inversions, isozyme variation, or molecular sequence data), these are mostly discordant with each other. We aimed to clarify some of the evolutionary patterns related to the origin of this incongruence, while also attempting to provide a better-supported phylogenetic hypothesis for the D. cardini subgroup. For this purpose, sequences from three mitochondrial and three nuclear loci were gathered for at least eight species, and both individual gene trees and joint species tree estimates were evaluated. Although there was concordance among gene trees within each of the nuclear and mitochondrial sets, considerable incongruence was revealed in the comparisons between these two data sets. The branching position of D. neocardini was the main source of incongruence, and species trees reconstructed using different approaches with and without this species were particularly incongruent. In addition to providing a better approximation of the evolutionary history of the D. cardini group, this study suggests that incomplete lineage sorting or introgression may be biasing previous species tree estimates. More generally, the results also suggest that the use of supermatrix methods can lead to an overestimation of support for the inferred relationships, and highlight the potential effects of different taxon sampling strategies in phylogenetic reconstruction.     

Molecular phylogeny of the subgenus Drosophila (Diptera, Drosophilidae) with an emphasis on Neotropical species and groups: a nuclear versus mitochondrial gene approach

The genus Drosophila has played an essential role in many biological studies during the last 100 years but much controversy and many incompletely addressed issues still remain to be elucidated regarding the phylogeny of this genus. Because information on the Neotropical species contained in the subgenus Drosophila is particularly incomplete, with this taxonomic group being underrepresented in many studies, we designed a study to answer some evolutionary questions related to these species. We subjected at least 41 Drosophilidae taxa to a phylogenetic analysis using a 516-base pair (bp) fragment of the alpha-methyldopa (Amd) nuclear gene and a 672 bp fragment of the mitochondrial cytochrome oxidase subunit II (COII) gene both individually and in combination. We found that the subgenus Drosophila is paraphyletic and subdivided into two main clusters: the first containing species traditionally placed in the virilis-repleta radiation and the second assembling species of the immigrans-Hirtodrosophila radiation. Inside the first of these clusters we could detect the monophyly of both the flavopilosa (the sister-clade of the annulimana group) and the mesophragmatica (closely related to the repleta group) species groups. Concerning the immigrans-Hirtodrosophila lineage, Zaprionus, Liodrosophila, Samoaia, and Hirtodrosophila were the early offshoots, followed by the immigrans, quinaria, testacea, and funebris species groups. The tripunctata radiation appears to be a derived clade, composed of a paraphyletic tripunctata group, intimately interposed with members of the cardini, guarani, and guaramunu species groups. Overall, the COII gene yielded a poor phylogenetic performance when compared to the Amd gene, the evolutionary hypothesis of which agreed with the total evidence tree. This phenomenon can be explained by the fast saturation of transitional substitutions in COII, due to strong biases in both base composition and substitution patterns, as also by its great among-site rate variation heterogeneity.     

Decline in photopositive tendencies with age inDrosophila melanogaster (Diptera: Drosophilidae)

Phototaxis was measured in young, middle-aged, and oldDrosophila melanogaster flies of both sexes. The apparatus allowed us to measure the tendency to go toward light, independently of the time needed to do so; under such conditions, phototaxis is dissociated from locomotor activity. The percentage of photopositive flies decreased slightly with age (93.96, 80.17, and 78.97%, respectively, in young, middle-aged, and old flies). Results are discussed in connection with previous data for which the tendency to go toward light and the time to do so were not dissociated.     

Variation of wing shape in the Drosophila virilis species group (Diptera: Drosophilidae)

Wing shape variation was analysed with geometric morphometric methods in 17 laboratory strains, representing 11 closely related species (including two subspecies) of the Drosophila virilis group: D. virilis, D. lummei, D. novamexicana, D. americana americana, D. americana texana, D. montana, D. lacicola, D. flavomontana, D. borealis, D. littoralis, D. ezoana and D. kanekoi. Overall shape estimated using Procrustes coordinates of 14 landmarks was highly variable among strains and very similar in females and males. The landmarks in the distal part of the wing showed higher variation across strains than those in the proximal part. Procrustes distances between species were not consistent with phylogenetic distances previously suggested for the virilis group. Moreover, Procrustes distances between strains within species and within two major phylads (virilis and montana) were comparable with those between species and between phylads, respectively. The most different from other members of the group was the endemic D. kanekoi species, currently viewed as separate subphylad within the montana phylad. Allometric effects were found to be partly responsible for shape differences between the strains. Three most significant shape transformations were considered using the relative warp analysis and the strains were ordinated in accordance with transformation values. The pattern of relative warp scores could be easily interpreted only for the third warp explaining about 13% of shape variation. It separated the largest species, D. montana, D. ezoana and D. kanekoi, from other ones and was mainly associated with shape changes in the proximal region of the wing. The results of the present work suggest that wing shape in the virilis species group is not related to the speciation process. The observed proximal‐distal contrasts and allometric effects are in agreement with data of other studies, in which wing shape variation was analysed within Drosophila species.     

Identification of acoustic stimuli that mediate sexual behavior inDrosophila busckii (Diptera: Drosophilidae)

We have shown that D. busckiimales and females, unlike other drosophilids that have been analyzed in this regard, court and copulate as well in relatively dim red light as they do in bright white light. We have also shown that males and females of this species flutter their wings during courtship and that wing fluttering in both sexes is associated with acoustic stimuli. Wingless males perform vigorous courtship but are incapable of mating, suggesting that females must perceive male song to be receptive to copulation. When they are tested with normal males, wingless females stimulate vigorous courtship, but their copulation frequencies are significantly lower than winged females. This observation suggests that perception of the female's song by either or both sexes facilitates mating.     

Male Sexual Signals and Female Choice in Drosophila grimshawi (Diptera: Drosophilidae)

Sexual selection and sexual signaling have been prominent topics in recent behavioral studies, but limited data have led to controversy regarding these topics. For example, the Hawaiian Drosophila are often cited as examples in which female choice has resulted in the evolution of elaborate male courtship signals, but relatively few data exist to test these claims adequately. We studied D. grimshawi, a lek-forming Hawaiian Drosophila, to determine whether there was evidence for female choice without male competition and to elucidate the possible cues females use to discriminate. Male mating success was found to be nonrandom and males that courted females intensely and deposited many pheromone-containing streaks on the substrate were the most successful. Hence, multiple cues seem to be involved in male mating success in this species. Some males performed only one display, however, and may represent an alternate male mating tactic. The protein content of the adult male diet significantly influenced the level of pheromone streak deposition, and thus, foraging environment may affect the outcome of sexual selection.     

The Evolutionary History of the Transposable Element Penelope in the Drosophila virilis Group of Species

We have used phylogenetic techniques to study the evolutionary history of the Penelope transposable element in the Drosophila virilis species group. Two divergent types of Penelope have been detected, one previously described, clade I, and a new one which we have termed clade III. The phylogeny of some copies of the Penelope clade I element was partially consistent with the species phylogeny of the D. montana subphylad, suggesting cospeciation and allowing the estimation of the evolutionary rate of Penelope. Divergence times of elements found in different species are younger than the age of the species, suggesting horizontal transfer events. Electronic Supplementary Material Electronic Supplementary material is available for this article at and accessible for authorised users. [Reviewing Editor: Dr. Dmitri Petrov]     

High transposition rates of Osvaldo, a new Drosophila buzzatii retrotransposon

Transposition of a new Drosophila retrotransposon was investigated. Total genomic Southern analysis and polytene in situ hybridizations in D. buzzatii strains and other related species using a 6 kb D. buzzatii clone (cDb314) showed a dispersed, repetitive DNA pattern, suggesting that this clone contains a transposable element (TE). We have sequenced the cDb314 clone and demonstrated that it contains all the conserved protein sequences and motifs typical of retrovirus-related sequences. Although cDb314 does not include the complete TE, the protein sequence alignment demonstrates that it includes a defective copy of a new long terminal repeat (LTR) retrotransposon, related to the gypsy family, which we have named Osvaldo. Using a D. buzzatii inbred line in which all insertion sites are known, we have measured Osvaldo transposition rates in hybrids between this D. buzzatii line and its sibling species D. koepferae. The results show that Osvaldo transposes in bursts at high rate, both in the D. buzzatii inbred line and in species hybrids.This paper is dedicated posthumously to Osvaldo A. Reig in recognition of his contributions to evolutionary biology and his early appreciation of the role of transposable elements in evolution     

Yeast communities as descriptors of habitat use by the Drosophila fasciola subgroup (repleta group) in Atlantic rain forests

Yeast communities associated with four species of the Drosophila fasciola subgroup (repleta group) in tropical rain forests were surveyed in an abandoned orchard, and rain forest sites of Rio de Janeiro and Ilha Grande, State of Rio de Janeiro, Brazil. Adult flies of Drosophila carolinae, Drosophila coroica, Drosophila fascioloides and Drosophila onca frequently carried Candida colliculosa, Geotrichum sp, Kloeckera apiculata and a Pichia membranaefaciens-like species. The most frequent yeasts in the crop of flies included Candida collicullosa, C. krusei, Pichia kluyveri and a P. membranaefaciens-like species. The physiological abilities and species composition of these yeast communities differed from those of other forest-inhabiting Drosophila. The narrow feeding niches of the fasciola subgroup suggested the use of only part of the substrates available to the flies as food in the forest environment, as noted previously for cactophilic Drosophila serido (mulleri subgroup of the repleta group) in a sand dune ecosystem. The cactophilic yeasts that were isolated have not been previously found in forests. The fasciola subgroup probably used epiphytic cactus substrates as breeding and feeding sites in the forest. The physiological profile of yeasts associated with the fasciola flies was broader than that of yeasts associated with the cactophilic Drosophila serido, suggesting that the fasciola subgroup represents an older lineage from which the South American repleta species evolved.     

Dynamics of mating success in experimental groups ofDrosophila melanogaster (Diptera: Drosophilidae)

Determinants of male courtship success in Drosophila melanogasterwere examined in groups of five males sequentially presented with five individual females. Thirty-three percent of males never mated, while approximately half of the males mated two or three times. Rapid courtship initiation was associated with male success in early matings only. Male size was important for courtship outcome, but the size distributions of mating and nonmating males and their progeny numbers indicate balancing rather than directional selection on size- dependent courtship success.