Search

The causes of high biological diversity in biodiversity hotspots have long been a major subject of study in conservation biology. To investigate this matter, we conducted a phylogeographic study of five Drosophila (Diptera: Drosophilidae) species from East and Southeast Asia: Drosophila albomicans Duda , D. formosana Duda, D. immigrans Sturtevant, D. melanogaster Meigen, and D. simulans Sturtevant. We collected 185 samples from 28 localities in eight countries. From each collected individual, we sequenced the autosomal extra sex comb gene ( esc ) and seven mitochondrial genes, including nicotinamide adenine dinucleotide hydrate-reductase dehydrogenase subunit 4 ( ND4 ), ND4L , tRNA-His , tRNA-Pro , tRNA-Thr , partial ND5 , and partial ND6 . Phylogenetic analyses using maximum- likelihood and Bayesian methods revealed interesting population structure and identified the existence of two distinct D. formosana lineages (Southeast Asian and Taiwanese populations). Genetic differentiation among groups of D. immigrans suggests the possibility of endemic speciation in Taiwan. In contrast, D. melanogaster remained one extensively large population throughout East and Southeast Asia, including nearby islets. A molecular clock was used to estimate divergence times, which were compared with past geographical events to infer evolutionary scenarios. Our findings suggest that interglacial periods may have caused population isolation, thus enhancing population differentiation more strongly for some of the Drosophila species. The population structure of each Drosophila species in East and Southeast Asia has been influenced by past geographic events.

The phylogeny of the Drosophila virilis species group was reevaluated by analyzing all previously published data sets. These included 1 developmental, 4 morphological, 6 chromosomal, 7 behavioral, and 10 molecular studies that have examined the group in a comparative way. It was concluded that there are four monophyletic clades within the D. virilis species group: (1) the virilis phylad, which includes D. virilis Sturtevant, D. lummei Hackman, D. novamexicana Patterson, D. americana Spencer, and D. texana Patterson; (2) the montana subphylad, which consists of D. montana Stone, Griffen & Patterson, D. lacicola Patterson, D. borealis Patterson, and D. flavomontana Patterson; (3) the littoralis subphylad consisting of D. littoralis Meigen and D. ezoana Takada & Okada; (4) and the monotypic kanekoi subphylad which includes D. kanekoi Watabe & Higuchi. The consensus phylogeny produced by this reanalysis does not support some of the systematic relationships that are currently accepted. The major division within the group, between the virilis phylad and the montana phylad (which consists of the montana, littoralis, and kanekoi subphylads), is found to be unsupported because in some reanalyses the littoralis and kanekoi subphylads cluster with the virilis phylad, and not the montana phylad. Consequently, the relationships among the phylads and subphylads are considered unresolved. The relationships of the virilis phylad are consistent with previous analyses, although the relationships among D. americana , D. texana , and D. novamexicana are considered unresolved based on the character evidence. Within the montana subphylad the only stable relationship appears to be the ancestral position of D. flavomontana relative to the other species in the subphylad.

The Drosophilidae Family of flies is cosmopolitan and is distributed in many types of ecosystems. The knowledge about the distribution of these species in Brazil has grown since the 1940s. However, the large extension of the Brazilian territory and the complexity of its ecosystems accounts for the fact of that this research field is still underexploited. The present study brings together survey data from 12 collection sites in Santa Catarina State, southern Brazil. The flies were collected over fermented banana baits, or over their natural trophic resources. This study expands the knowledge of the geographical distribution of Drosophila ananassae Doleschall, D. aff. elliptica, D. neosaltans Pavan & Magalh es, D. pulchella Sturtevant, D. bocainensis Pavan & Cunha and D. bocainoides Carson, all from the subgenus Sophophora.

Diagnostic studies on the relationship between Drosophila willistoni and Nosema kingi revealed that adult D. willistoni can acquire the microsporidian via the oral route from fecal contamination and transovarially. At least 50% of the flies exposed to fecal material from infected flies contained the parasite when examined two or three weeks later. 50–81% of the offspring which emerged from eggs laid by parasitized females were infected with N. kingi 14–21 days later. Infectivity experiments using other drosophilids indicated N. kingi infections can be transmitted to D. sturtevanti Duda, D. melanogaster Meigen, D. persimilis Dobzhansky and Epling, D. pseudoobscura Frolowa, D. virilis Sturtevant, D. simulans Sturtevant, and D. ananassae Doleshall without morphological changes occurring in the stages of the parasite and without changes of behavioural patterns in these experimental hosts.

The distribution of constitutive heterochromatin in mitotic chromosomes of four species (viz., Drosophila quadrilineata de Meijere, D. immigrans Sturtevant, D. pulaua Wheeler, and D. kohkoa Wheeler) was studied using C-banding and fluorescence staining techniques. The results of this study had revealed that the heterochromatic segments detected by C-banding in the species under study were found to coincide precisely with the areas giving bright fluorescence with the two fluorochromes, Hoechst 33258 and quinacrine. This suggested the presence of A–T rich base pairs in their heterochromatin. These studies further revealed that the modification of heterochromatin caused due to the additions or deletions in particular had also played a very significant role during the differentiation of these species.Key words: heterochromatin modification, immigrans species group, Drosophila.

The six sibling species of Drosophila willistoni group are among the most favorable, and at the same time challenging materials for studies on the genetics of speciation processes. The species are D. willistoni Sturtevant, D. paulistorum Dobzhansky & Pavan, D. pavlovskiana Kastritsis & Dobzhansky, D. equinoxialis Dobzhansky, D. tropicalis Burla & da Cunha, and D. insularis Dobzhansky. Burla et al. (1949) found slight morphological differences that were insufficient for identification of single individuals, but Spassky (1957) noted differences in the male genitalia which do permit such identification. Unambiguous discrimination is also possible through examination of the gene arrangements in the chromosomes of larval salivary glands (Burla et al., 1949; Dobzhansky et al., 1950), and of the variant enzymes detected by electrophoresis (Ayala et al., 1970). Owing to ethological isolation, crossmating of the species occurs rarely, although under laboratory conditions some cross-inseminations can be obtained (Burla et al., 1949). Intercrosses of D. insularis females with D. tropicalis and D. willistoni males, and occasionally with D. paulistorum

Drosophila affinis Sturtevant, D. quinaria Loew, D. putrida Sturt., D. robusta Sturt., D. tripunctata Loew, and D. immigrans Sturt. are the six native species most commonly encountered in north central Indiana, while D. melanogaster Meigen, D. hydei Sturt., and D. busckii Coquillett are introduced species which frequently attain large summer populations. Summer populations of the native species originate in deciduous woodlands, and during periods of population maxima in June the more prevalent species are widely dispersed through all of the major types of terrestrial habitats. Summer populations of the introduced species originate in proximity to human settlements and likewise disperse through a variety of habitats during periods of population increase, occurring with the native species in diverse situations in July but not achieving peak numbers until August. The species which infest tomatoes are widely, if thinly, dispersed at the time the crop ripens, and there is little expectation that preseason control efforts would be practicable. Despite disparate climatic conditions during the summers of 1958 and 1959, population developments in tomato fields were strikingly similar, thus indicating little correlation between normal weather extremes and population development. D. melanogaster is recognized as the principal species causing contamination of tomato products. Experimental evidence on comparative fecundity, developmental rates, and ovipositional behavior were obtained to explain the consistent prevalence of this species. Studies of diurnal activity and spatial distribution suggest that these facets of behavior are controlled principally by responses to atmospheric moisture. Adult flies were found to inhabit a space, only a few inches in height, directly above the soil surface. The micro environment provided by the foliage and fruit of the tomato plant does not require the insects to follow the pattern of peak activity at dawn and dusk often ascribed to Drosophila .

Host plant selection by insects has evolved through various interactions with their environments. In phytophagous insects, the chemistry and ecology of plants are important factors governing host selection. Plants have unique chemicals, some of which, such as toxicants, have evolved as defense mechanisms against insect attacks, and plants also show species specific distribution and phenology. Insects, then, have evolved metabolic systems to utilize such chemicals or to detoxify, and also bionomic strategies to adapt to the plant phenology. Specialization of phytophagous Lepidoptera is governed by interactions with host-plant chemistry, but also with host abundance and predictability (cf. Gilbert, 1979). In addition to plant chemistry and ecology, the existence of species having similar nutritional requirements influences their selection of hosts through interspecific competition. The validity of these conceptions needs to be examined in various phytophagous insects and also in insects feeding on materials other than plants. This paper deals with food preferences and nutritional requirements of the fungus-feeding Drosophila with reference to factors governing their selection of hosts. The original feeding habit of the family Drosophilidae was saprophagous: fermenting or decayed plant parts such as fruits, tree sap, leaves, stems, flowers, or mushrooms. Today many species belonging to various taxonomic units continue with this original feeding habit (Carson, 1971; Kimura et al., 1977). However, several species have come to feed and breed on living or fresh plant parts, e.g., the leaf miners of Scaptomyza (Frost, 1924) and the flower feeders of Drosophila (Brncic, 1966; Pipkin et al., 1966). Kimura (1976) observed that adults of some species of Hirtodrosophila were attracted to fresh mushrooms. In this study, the food preferences of these fungus feeders were examined in laboratory tests and field observations in relation to the phenology and abundance of mushrooms. The species studied included three members of the Hirtodrosophila radiation, D. trivittata Strobl, D. sexvittata Okada, and D. alboralis Momma and Takada, and five species of the immigrans radiation, D. immigrans Sturtevant, D. nigromaculata Kikkawa and Peng, D. brachynephros Okada, D. testacea van Roser, and D. confusa Staeger. All species except D. immigrans and D. nigromaculata depend on mushrooms. Drosophila immigrans feeds on fruit and D. nigromaculata feeds on leaves (Kimura et al., 1977).

The natural population of a site in Fusagasuga, Colombia, was sampled weekly from March 1964 to December 1965, and weights of the collected adult Drosophila were determined. D. melanogaster Meigen, D. immigrans Sturtevant, D. cardini Sturtevant, and D. capricorni Dobzhansky & Paven were the most abundant species. The total number collected of D. immigrans, D. bandcirantorum Dobzhansky& Pavan, the D, tripunctata Loew group, and 77. griscolineata Duda was higher after rainy months than after dry months. This correlation did not hold for D. mclanogaster or D. cardini . The average weight of female D. melanogaster and D. immigrans collected during rainy months was higher than that of females collected during dry months. However, the reverse was true for D. cardini . A greater variety of species of Drosophila was taken at Fusagasuga than in a previous study at a higher altitude in Colombia.

Sibling species are species morphologically so similar as to be practically indistinguishable from each other by inspection of their structural features. The Drosophila willistoni group consists of at least twelve species, six of which are siblings. Two of the sibling species, D. pavlovskiana Dobzhansky and Kastritis, and D. insularis Dobzhansky, are narrow endemics; the former in Guyana and the latter on some islands of the Lesser Antilles. The other four species, D. willistoni Sturtevant, D. equinoxialis Dobzhansky, D. paulistorum Dobzhansky and Pavan, and D. tropicalis Burla and de Canba, have wide and largely overlapping geographic distributions. The four species are sympatric through Central America and the northern half of continental South America; two or three of them are sympatric in the southern half of Mexico, the larger Caribbean islands, Peru, Bolivia, and the southern half of Brazil (Spassky et al., 1971). We have studied for several years genetic variation in the sibling species of the D. willistoni group, using techniques of gel electrophoresis and enzyme assay. D. equinoxialis consists of two subspecies, D. e. equinoxialis and D. e. caribbensis (Ayala, 1973). In this paper we report results of the study of reproductive isolation between these two subspecies, and we compare genetic variation within and between the subspecies. Ayala and Powell (1972) have