Interrelationships among three derivative forms of the immigrans-Hirtodrosophila radiation: evidence from heterochromatin and polytene chromosomes

The phylogenetic relationships among three derivative forms of the immigrans-Hirtodrosophila radiation viz. Chaetodrosophilella, Zaprionus and the immigrans species group are examined, by comparing the banding patterns of their polytene chromosomes and by analysing the nature of their heterochromatin. Based on the results of these studies it is concluded that D. quadrilineata has a very strong affinity with the members of the immigrans species group, while the genus Zaprionus represents a very distinct evolutionary lineage. This study further indicates that D. quadrilineata is a karyotypically primitive species having five pairs of rods and one pair of dots, while the karyotype of other members of the immigrans species group appears to have undergone modifications through fusions, fissions, inversions and the addition or deletion of heterochromatin to dots and other chromosomes.     

Phylogenetic relationships and macro-evolutionary patterns within the <Emphasis Type="Italic">Drosophila tripunctata</Emphasis> “radiation” (Diptera: Drosophilidae)

Despite previous efforts, the evolutionary history of the immigrans-tripunctata clade remains obscure in part due to its hypothesized origin through a rapid radiation. We performed a supermatrix analysis (3,243 base pairs) coupled with richness patterns, environmental phylogenetic signal and radiation tests in order to address phylogenetic relationships and macro-evolutionary hypotheses within this complex group of species. We propose a well-supported evolutionary scenario for the immigrans-tripunctata clade species, in which the tripunctata “radiation” was monophyletic and subdivided into three main lineages: the first including D. pallidipennis (pallidipennis group) imbedded among members of the tripunctata group; the second clustering the cardini and guarani groups; and the third grouping representatives from the tripunctata, calloptera and guaramunu groups. Therefore, we hypothesize that the tripunctata group encompasses a diphyletic taxon, with one clade including the pallidipennis group and the other showing a close affinity to the calloptera and guaramunu groups. Our results also suggest that niche evolution seems to have played a central role in the evolutionary history of the tripunctata species “radiation” allowing effective dispersion and diversification in the Neotropics, possibly in a southwards direction. Although the data as a whole support the notion that this occurred through rapid and successive speciation events, the radiation hypothesis remains to be further corroborated.     

Life history adaptations and stress tolerance of four domestic species of Drosophila

Life history traits and stress tolerance were studied in four domestic species of Drosophila–D. melanogaster, D. simulans, D. auraria and D. immigrans– to understand how they adapt to their environments. In all species, larval weight approximately doubled in 1 day. The relative egg weight (egg weight : pupal weight) was smaller and the larval period was longer in D. immigrans than in the other three species. The pupal period was the longest in D. auraria. However, the adaptive significance of these differences in larval and pupal periods was not clear. The pupal case was generally thicker in the larger species, probably to support the larger pupal body. The start of oviposition was earliest and reproductive effort was greatest in female D. simulans, followed by female D. melanogaster. In contrast, starvation tolerance and the increase in bodyweight after eclosion was greater in D. immigrans and D. auraria than in the other two species. Pupal desiccation tolerance was greatest in D. melanogaster and lowest in D. auraria, and the less tolerant species seemed to select more humid sites for pupation. Adult tolerance to desiccation was greatest in D. melanogaster and lowest in D. simulans. In contrast, adult cold tolerance was greater in D. auraria and adult heat tolerance was lower in D. immigrans than in the other species. These differences in life history traits and stress tolerance represent the Drosophila species differential adaptations, and are assumed to allow coexistence of the species.     

Karyotype differentiation among members of the immigrans species group of Drosophila

Karyotypes of ten species belonging to four of the five subgroups of the immigrans species group of Drosophila were examined. The group includes species with the most primitive form of karyotype as well as species with so-called recent karyotypic configurations. It is an assemblage of species with karyotypes representing five of the six successive stages involved in the evolution from 2n=12 to 2n=6. Implications of these findings are discussed.     

Variation in adult life history and stress resistance across five species of<Emphasis Type="Italic">Drosophila</Emphasis>

Dry weight at eclosion, adult lifespan, lifetime fecundity, lipid and carbohydrate content at eclosion, and starvation and desiccation resistance at eclosion were assayed on a long-term laboratory population ofDrosophila melanogaster, and one recently wild-caught population each of four other species ofDrosophila, two from themelanogaster and two from theimmigrans species group. The relationships among trait means across the five species did not conform to expectations based on correlations among these traits inferred from selection studies onD. melanogaster. In particular, the expected positive relationships between fecundity and size/lipid content, lipid content and starvation resistance, carbohydrate (glycogen) content and desiccation resistance, and the expected negative relationship between lifespan and fecundity were not observed. Most traits were strongly positively correlated between sexes across species, except for fractional lipid content and starvation resistance per microgram lipid. For most traits, there was evidence for significant sexual dimorphism but the degree of dimorphism did not vary across species except in the case of adult lifespan, starvation resistance per microgram lipid, and desiccation resistance per microgram carbohydrate. Overall,D. nasuta nasuta andD. sulfurigaster neonasuta (immigrans group) were heavier at eclosion than themelanogaster group species, and tended to have somewhat higher absolute lipid content and starvation resistance. Yet, these twoimmigrans group species were shorter-lived and had lower average daily fecundity than themelanogaster group species. The smallest species,D. malerkotliana (melanogaster group), had relatively high daily fecundity, intermediate lifespan and high fractional lipid content, especially in females.D. ananassae (melanogaster group) had the highest absolute and fractional carbohydrate content, but its desiccation resistance per microgram carbohydrate was the lowest among the five species. In terms of overall performance, the laboratory population ofD. melanogaster was clearly superior, under laboratory conditions, to the other four species if adult lifespan, lifetime fecundity, average daily fecundity, and absolute starvation and desiccation resistance are considered. This finding is contrary to several recent reports of substantially higher adult lifespan and stress resistance in recently wild-caught flies, relative to flies maintained for a long time in discretegeneration laboratory cultures. Possible explanations for these apparent anomalies are discussed in the context of the differing selection pressures likely to be experienced byDrosophila populations in laboratory versus wild environments. This paper is dedicated to the memory of our friend and former colleague Dr Hans Raj Negi, who tragically passed away at a very young age in a road accident in November 2003.     

Molecular phylogeny of Drosophila based on ribosomal RNA sequences

Nucleotide sequences of 72 species of Drosophilidae were determined for divergent D1 and D2 domains (representing 200 and 341 nucleotides respectively in D. melanogaster) of large ribosomal RNA, using the rRNA direct sequencing method. Molecular phylogenetic trees were reconstructed using both distance and parsimony methods and the robustness of the nodes was evaluated by the bootstrap procedure. The trees obtained by these methods revealed four main lineages or clades which do not correspond to the taxonomical hierarchy. In our results, the genus Chymomyza is associated with the subgenus Scaptodrosophila of the genus Drosophila and their cluster constitutes the most ancient clade. The two other clades are constituted of groups belonging to the subgenus Sophophora of the genus Drosophila: the so-called Neotropical clade including the willistoni and saltans groups and the obscura-melanogaster clade itself split into three lineages: (1) obscura group + ananassae subgroup, (2) montium subgroup, and (3) melanogaster + Oriental subgroups. The fourth clade, the Drosophila one, contains three lineages. D. polychaeta, D. iri, and D. fraburu are branched together and constitute the most ancient lineage; the second lineage includes the annulimana, bromeliae, dreyfusi, melanica, mesophragmatica, repleta, robusta, and virilis groups. The third lineage is composed of the immigrans and the cardini, funebris, guaramunu, guarani, histrio, pallidipennis, quinaria, and tripunctata groups. The genera Samoaia, Scaptomyza, and Zaprionus are branched within the Drosophila clade. Although these four clades appear regularly in almost all tree calculations, additional sequencing will be necessary to determine their precise relationships.Correspondence to: M. Pelandakis     

Inversion polymorphism in populations of Drosophila sulphurigaster albostrigata and Drosophila nasuta albomicans from Phuket,Thailand

Two species of the Drosophila nasuta subgroup of the Drosophila immigrans group, D. sulphurigaster albostrigata and D. nasuta albomicans were investigated in this study. Collections of both species were made from Phuket, Thailand. Both species have similar salivary chromosomes, with four autosomal arms and one sex chromosome arm, and both are highly polymorphic for paracentric inversions. D. s. albostrigata accounted for the majority of the isolines collected and exhibited the greater number of inversions. One inversion, C₁, was common to both species, indicating common ancestry.A non-random distribution of inversions was observed on the proximal end of chromosome II in both D. s. albostrigata and D. n. albomicans. An inter-collection comparison revealed that both rigid and flexible chromosomal polymorphism were operating in the two species, with a seasonal variation noted for one inversion in D. s. albostrigata. A non-random association of two inversions was observed in D. n. albomicans.Based on a comparison of the indices of crossing over, both D. s. albostrigata and D. n. albomicans were found to be more heterozygous than in previous studies, with D. n. albomicans appearing to have evolved further than D. s. albostrigata.Based on a thesis submitted for the degree of Ph. D. at the University of Queensland.     

Strategic differences in thermal adaptation between two Drosophila species,D. virilis and D. immigrans

Summary Preadult viability and developmental time at four different temperatures, heat and cold resistances of adult flies, effects of acclimatization on heat resistance, and preferred temperature of adult flies were compared between two species of Drosophila, D. virilis and D. immigrans. Four Japanese local populations were surveyed for each species. As compared with immigrans, virilis was higher in its ability to tolerate both heat and cold stresses and was viable over a broader temperature range. On the other hand, immigrans revealed a superior ability to acclimatize and a rigid preference for gradually changing thermal environment. Differences between geographical populations are remarkable for heat tolerance in virilis and cold tolerance in immigrans. In conclusion, thermal adaptation of virilis seems to be based on the high tolerance to extreme temperatures and that of immigrans mainly on the behavioural preference for viable temperatures.     

Evolutionary experimentation through hybridization under laboratory condition in <Emphasis Type="Italic">Drosophila</Emphasis>: Evidence for Recombinational Speciation

Background  

Drosophila nasuta nasuta (2n = 8) and Drosophila nasuta albomicans (2n = 6) are a pair of sibling allopatric chromosomal cross-fertile races of the nasuta subgroup of immigrans species group of Drosophila. Interracial hybridization between these two races has given rise to new karyotypic strains called Cytorace 1 and Cytorace 2 (first phase). Further hybridization between Thailand strain of D. n. albomicans and D. n. nasuta of Coorg strain has resulted in the evolution of two more Cytoraces, namely Cytorace 3 and Cytorace 4 (second phase). The third phase Cytoraces (Cytorace 5 to Cytorace 16) have evolved through interracial hybridization among first, second phase Cytoraces along with parental races. Each of these Cytoraces is composed of recombined genomes of the parental races. Here, we have made an attempt to systematically assess the impact of hybridization on karyotypes, morphometric and life history traits in all 16 Cytoraces.     

Electrophoretic variability in island populations of Drosophila simulans and Drosophila immigrans

Genetic structure and variability were investigated in several Hawaiian populations of D. simulans and D. immigrans. Genetic variability is lower in Hawaiian populations of D. simulans than in Texas populations, and allelic differences exist as well. For D. immigrans, Hawaiian and Korean populations are similar in variability, allelic content, and gene frequencies. Several hypothesis are advanced to account for the patterns in gene variation observed between island and continental populations of these two colonizing species.This research was supported by Grant GB-23230 to the Hawaii Subprogram of the International Biology Program, by Grant GB-27586 to Dr. H. L. Carson, and by the Research Board of the School of Life Sciences, University of Illinois, Urbana, Illinois.Technical Report No. 57 of the U.S. IBP, Hawaii Integrated Research Program.     

Molecular Characterization of Parabasalian Symbionts Coronympha clevelandii and Trichonympha subquasilla from the Hawaiian Lowland Tree Termite Incisitermes immigrans

An important and undervalued challenge in characterizing symbiotic protists is the accurate identification of their host species. Here, we use DNA barcoding to resolve one confusing case involving parabasalian symbionts in the hindgut of the Hawaiian lowland tree termite, Incisitermes immigrans, which is host to several parabasalians, including the type species for the genus Coronympha, C. clevelandii. We collected I. immigrans from its type locality (Hawaii), confirmed its identity by DNA barcoding, and characterized the phylogenetic position of two symbionts, C. clevelandii and Trichonympha subquasilla. These data show that previous molecular surveys of “I. immigrans” are, in fact, mainly derived from the Caribbean termite I. schwarzi, and perhaps also another related species. These results emphasize the need for host barcoding, clarify the relationship between morphologically distinct Coronympha species, and also suggest some interesting distribution patterns of nonendemic termite species and their symbionts.     

Species status of Incisitermes spp. (Isoptera: Kalotermitidae) in Japan

The species status of Japanese populations of Incisitermes immigrans from Iwo and Minami Daito Islands was examined using mitochondrial 16S molecular barcode sequences. The molecular sequences of these two populations were compared to those of other Incisitermes spp. deposited in the GenBank database using a maximum likelihood phylogenetic analysis. This analysis suggested that the Minami Daito population is indeed I. schwarzi, as suspected previously, while the sequence of the Iwo Island population was identical to that of authentic I. immigrans. In addition to I. minor, which is recorded from middle and southern Japan, the presence of three Incisitermes species in Japan was confirmed.     

The Adh in Drosophila: Chromosomal location and restriction analysis in species with different phylogenetic relationships

Restriction analysis of the genomic region containing the Adh gene and in situ hybridization assays were performed in six Drosophila species belonging to three different subgenera: D. ambigua, D. subobscura, D. madeirensis and D. guanche (sg. Sophophora); D. immigrans (sg. Drosophila); and D. lebanonensis (sg. Pholadoris). In agreement with previous observations, comparison of restriction maps of the Adh region shows that D. subobscura and D. madeirensis are very closely related. Partial homology is also observed with the rest of the obscura group species. Nevertheless, no resemblance at the restriction map level is detected when more distantly related species are compared. In D. ambigua, D. immigrans and D. lebanonensis in situ hybridization assays reveal a single chromosomal location for Adh, which in D. lebanonensis appears to be sex linked. In contrast, in D. subobscura, D. madeirensis and D. guanche multiple sites of hybridization with homologous and heterologous probes are observed. For example, in D. subobscura and D. madeirensis the functional Adh gene is located on the U chromosome and additional homologous retrosequences are found on the E chromosome.by H. Jäckle     

Breeding site specificity in the domestic species of Drosophila

Summary The emergences of domestic Drosophila species from fruits and vegetables in a market are analysed by partitioning the species diversity. Confidence limits are determined for the components of diversity.Despite some coexistence of different species within the same breeding site, ecological differences between them are revealed. Partitioning of the breeding sites is more important than partitioning of the season. D. melanogaster, D. simulans, and D. subobscura are specialised on fruits and D. busckii on vegetables. D. immigrans and D. hydei are less specialised. The coexistence is explained by reference to ecological theory.     

Evidence for no sexual isolation between Drosophila albomicans and D. nasuta

Sexual isolation, the reduced tendency to mate, is one of the reproductive barriers that prevent gene flow between different species. Various species‐specific signals during courtship contribute to sexual isolation between species. Drosophila albomicans and D. nasuta are closely related species of the nasuta subgroup within the Drosophila immigrans group and are distributed in allopatry. We analyzed mating behavior and courtship as well as cuticular hydrocarbon profiles within and between species. Here, we report that these two species randomly mated with each other. We did not observe any sexual isolation between species or between strains within species by multiple‐choice tests. Significant difference in the courtship index was detected between these two species, but males and females of both species showed no discrimination against heterospecific partners. Significant quantitative variations in cuticular hydrocarbons between these two species were also found, but the cuticular hydrocarbons appear to play a negligible role in both courtship and sexual isolation between these two species. In contrast to the evident postzygotic isolation, the lack of sexual isolation between these two species suggests that the evolution of premating isolation may lag behind that of the intergenomic incompatibility, which might be driven by intragenomic conflicts.     

Hybridization,transgressive segregation and evolution of new genetic systems in<Emphasis Type="Italic">Drosophila</Emphasis>

Introgressive hybridization facilitates incorporation of genes from one species into the gene pool of another. Studies on long-term effects of introgressive hybridization in animal systems are sparse.Drosophila nasuta (2n = 8) andD. albomicans (2n = 6)—a pair of allopatric, morphologically almost identical, cross-fertile members of thenasuta subgroup of theimmigrans species group-constitute an excellent system to analyse the impact of hybridization followed by transgressive segregation of parental characters in the hybrid progeny. Hybrid populations ofD. nasuta andD. albomicans maintained for over 500 generations in the laboratory constitute new recombinant hybrid genomes, here termed cytoraces. The impact of hybridization, followed by introgression and transgressive segregation, on chromosomal constitution and karyotypes, some fitness parameters, isozymes, components of mating behaviour and mating preference reveals a complex pattern of interracial divergence among parental species and cytoraces. This assemblage of characters in different combinations in a laboratory hybrid zone allows us to study the emergence of new genetic systems. Here, we summarize results from our ongoing studies comparing these hybrid cytoraces with the parental species, and discuss the implications of these findings for our understanding of the evolution of new genetic systems. This paper is dedicated to the memory of our teacher, Prof. N. B. Krishnamurthy.     

<Emphasis Type="Italic">Drosophila</Emphasis> pupation behavior in the wild

We investigated pupa distributions of D. simulans, D. buzzatii, D. melanogaster, D. immigrans and D. hydei on a number of natural breeding sites. Pupae of all five species showed aggregated distributions, which prompted us to examine these aggregations in a more detail for two species that commonly co-occur in breeding sites, D. simulans and D. buzzatii. We found that pupae of both species tend to be aggregated in conspecific clusters. Subsequent experiments revealed that both species are attracted to the odors of other larvae, though only D. buzzatii differentiated between conspecifics and heterospecifics (they preferred conspecific). Furthermore, third instar larvae of both species preferred more alkaline substrates. Altogether, our results demonstrate that Drosophila species form conspecific pupa aggregations in natural breeding sites, and that pupation site selection depends on interactions among conspecific and heterospecific larvae and on chemical characteristics of the breeding sites.     

Phylogeny,molecular ecology and taxonomy of southern Iberian lineages of <Emphasis Type="Italic">Triops mauritanicus</Emphasis> (Crustacea: Notostraca)

We investigated the phylogeography of the main lineages in the tadpole shrimp Triops mauritanicus Ghigi in the south-western Iberian Peninsula, using mitochondrial 12S and 16S rDNA sequences. Our results indicate that a fourth, hitherto unknown main phylogenetic lineage occurs in Iberia, so that in total, the species is divided into six distinct clades, comprising T. m. mauritanicus, T. m. simplex Ghigi, and four as yet unnamed lineages that appear to be endemic to Iberia. Percentages of sequence divergence among the main clades in T. mauritanicus reach the range reported for recognized species in other notostracan lineages. A thorough morphological investigation also revealed that the differentiation among these lineages is higher than previously thought, and that populations of three of the main clades within T. mauritanicus can be reliably separated from each other and from the remaining lineages based on the morphology of adult males. The remaining clades also show a significant level of morphological differentiation, but include a certain proportion of populations for which the additional application of molecular methods is needed for a reliable determination. The geographic distributions of 12S haplotypes are indicative of frequent dispersal events and gene flow among populations belonging to the same main lineage, but give no evidence of recent migration events among different main lineages, suggesting that there is no gene flow among the latter. Our data thus suggest that the six main lineages within T. mauritanicus represent distinct species. We therefore describe the Iberian lineages as T. baeticus Korn n. sp., T. emeritensis Korn & Pérez-Bote n. sp., T. gadensis Korn & García-de-Lomas n. sp., and T. vicentinus Korn, Machado, Cristo & Cancela da Fonseca n. sp., and reinstate T. simplex Ghigi to full species status. Our data confirm the general, previously recognized pattern of a lower dispersal probability in gonochoric Triops taxa. However, we found evidence that passive dispersal in Triops may be further complicated by a strong habitat dependence of dispersal probability, mediated by prevailing dispersal vectors.     

Number of primary spermatocytes in the Drosophila immigrans (Sturtevant) group (Diptera : Drosophilidae)

Nine species of the Drosophila immigrans (Sturtevant) group (Diptera Drosophilidae) were examined for the number of primary spermatocytes per cyst. Seven species (D. formosana, D. immigrans, D. kohkoa, D. nasuta, D. neohypocausta, D. quadrilineata and D. sulfurigaster albostrigata) showed nearly 16 primary spermatocytes per cyst, but 2 species (D. annulipes and D. curviceps) had mean numbers of 20.41 and 24.02 primary spermatocytes per cyst, respectively. The frequency distribution patterns of the numbers of primary spermatocytes suggest that the multiplication divisions do not occur synchronously in these species. The systematic positions of D. annulipes and D. curviceps are also discussed.     

Phylogeny of the Drosophila obscura group as inferred from one- and two-dimensional protein electrophoresis

The phylogenetic relationships of 15 species of the obscura group of Drosophila were analysed by use of one- and two-dimensional electrophoresis. Genetic distances based on two-dimensional data are five times smaller than those based on native proteins. From the data, it is proposed that the species radiation of the obscura group happened in two evolutionary bursts, the first one giving rise to at least four palearctic proto-lineages (bifasciata, obscura (including D. subsilvestris), subobscura, and microlabis) and one or two proto-nearctic lineages (affinis, pseudoobscura), and the second, more recent burst giving rise to the current speciation within lineages.