Drosophila Jambulina Research Articles

Drosophila hegdii (Diptera: Drosophilidae), a new species from Lumami, Nagaland (a sub-Himalayan hilly state, India): Its molecular phylogeny

Survey for Drosophila was carried out in Lumami (which is a hamlet in Zunheboto district of Nagaland and is head quarters of the Nagaland University) and Drosophila hegdii was one among the 16 species collected. Based on the morphological markers, internal characters a new species, Drosophila hegdii, was identified. Drosophila hegdii resembles Drosophila vulcana and Drosophila jambulina in certain morphological markers, but differed with them in multiple morphological markers. It also differs from other known species of montium sub group in characters such as the number of teeth in sex comb, and abdominal banding pattern. In order to confirm new species status with the aid of molecular markers and decipher molecular phylogeny we took advantage of “DNA Barcoding” by analysing sequences of mitochondrial cytochrome c oxidase subunit I (COI) (its 648 base pair fragment is the standard marker for “species identification” in the Barcode of Life Project). Neighbour joining trees were constructed using MEGA5 (Neighbor-Joining Tree (NJ) method with bootstrap test-1000 replicates) using the Kimura 2-parameter model, with gaps treated by pairwise deletion. Molecular phylogeny confirms the observations made with the help of morphological markers that Drosophila hegdii is a new species and closer to Drosophila vulcana and Drosophila jambulina.

Pupation site preference selection in Drosophila jambulina

Larvae of three latitudinally different populations of Drosophila jambulina belonging to the montium subgroup were tested for pupation site preference in relation to temperature. At 30 °C, larvae preferred to pupate on food whereas at 21 °C pupation occurred on the cotton. Genetic basis of larval pupation behavior was studied by conducting reciprocal crosses for 30 generations on food-selected and on cotton-selected pupae. Results from genetic analysis between food-selected and cotton-selected strains indicated a single gene responsible for the pupation site preference, with F1 progeny pupated on cotton and F2 (F1 × F1) larvae pupated on both food as well as on cotton. Although we found no change in morphological traits in food vs cotton selected populations, significantly different growth rate (body weight) between the two strains was observed. These results suggest that pupation site preferences can affect life-history traits in D. jambulina.

Effect of different light regimes on esterase isozyme profiles of three species of Drosophila

Circadian rhythm has been identified in every organism studied, from unicellular marine algae to man, and in virtually all physiological and biochemical functions. The endogenous circadian system functions to organize behaviour and physiology to adapt to and anticipate environment changes in light and temperature. The present study is an attempt to understand enzyme profiles (alpha and beta esterases) of Drosophila melanogaster (Oregon-K strain), Drosophila gangotrii and Drosophila jambulina under light/dark (LD), continuous light (LL) and continuous dark (DD) conditions over 30 generations. A polyacrylamide gel electrophoresis (7.5% – native gel) was used to study the esterase isozyme banding patterns in three species of Drosophila. It has been noticed that there were three alpha esterase loci in Drosophila species which were designated as α-est 1, α-est 2 and α-est 3. Similarly there were three beta esterase loci which were designated as β-est 1, β-est 2 and β-est 3. Flies maintained in different light regimes showed differences in their allelic patterns with respect to alpha and beta esterases. It was observed that there was expression of some bands at a given light regime and the absence of the same in another regime. This shows that the different light regimes affect the expression of esterase isozymes.

Varying the Length of Dim Nocturnal Illumination Differentially Affects the Pacemaker Controlling the Locomotor Activity Rhythm of Drosophila Jambulina

Photic entrainment of animals in the field is basically attributed to their exposure to the dimly lit nights flanked by the dawn and dusk twilight transitions. This implicates the functional significance of the dimly lit nights as that of the twilight transitions. Recently, the authors have demonstrated that the dimly lit night at 0.0006 lux altered the attributes of the circadian rhythm of locomotor activity of Drosophila jambulina. The present study examined whether the durations of such dimly lit nights affect the entrainment and free-running rhythmicity of D. jambulina. Flies were subjected for 10 days to two types of 24-h lighting regimes in which the photophase (L) was at 10 lux for all flies but the scotophase, which varied in duration from 9 to 15 h, was either at 0 lux (D phase) for control flies or 0.0006 lux (the artificial starlight or S phase) for experimental flies. Thereafter, they were transferred to constant darkness (DD) to compare the after-effects of the dimly lit nights on the period (τ) of free-running rhythm in DD with that of the completely dark nights. Control flies were entrained by all LD cycles, but the experimental flies were entrained only by five LS cycles in which the duration of the S phases ranged from 10 to 14 h. The two LS cycles with very short (9 h) and long (15 h) S phases rendered the flies completely arrhythmic. Control flies started activity shortly before lights-on and continued well after lights-off. The experimental flies, however, commenced activity several hours prior to lights-on but ended activity abruptly at lights-off as the result of a negative masking effect of nocturnal illumination. Length of the midday rest was considerably shorter in the control than in the experimental flies in each lighting regime. The active phase in the control flies was predictably shortened; nonetheless, it was invariable in the experimental flies as the nights lengthened. Transfer from lighting regimes to DD initiated robust free-running rhythmicity in all flies including the arrhythmic ones subjected to LS cycles with 9 and 15 h of scotophases. The τ was profoundly affected by the nocturnal irradiance of the prior entraining lighting regime, as it was always shorter in the experimental than in the control flies. Thus, these results indisputably demonstrate the changes in fundamental properties of the circadian pacemaker of D. jambulina were solely attributed to the extremely dim nocturnal irradiance. This strain of D. jambulina is entrained essentially by the dimly lit natural nights, since it is never exposed to the prevailing photic cues such as the twilight transitions or bright photoperiod, owing to the dense vegetation of its habitat. (Author correspondence: drdsjoshi08@gmail.com)

NOCTURNAL ILLUMINATION DIMMER THAN STARLIGHT ALTERED THE CIRCADIAN RHYTHM OF ADULT LOCOMOTOR ACTIVITY OF A FRUIT FLY

The effects of nocturnal irradiance tenfold dimmer than starlight intensity on the locomotor activity rhythm of Drosophila jambulina were investigated in two types of light-dark (12 h:12 h) cycles, in which light intensity of the photophase was 10 lux while that of the scotophase was either 0 lux for control flies or 0.0006 lux for experimental flies. Activity onset in the experimental flies was ∼5.4 h prior to lights-on, so it occurred around midnight. However, activity onset of the control flies coincided almost with the lights-on. Nevertheless, activity offset was the same in both groups, occurring at lights-off. Duration of the active phase (α) and activity passes/fly/cycle (APC) in the experimental flies was far greater than in controls. After-effects of the nocturnal illumination of the light-dark cycles when the flies were transferred to constant darkness were evident as the period of the free-running rhythm was shortened, α was lengthened, and APC was enhanced in the experimental compared to control flies. Thus, very low photic sensitivity of these flies appears to be a physiological adaptation to dim-light ambiance in its natural breeding site in the field. (Author correspondence: drdsjoshi08@gmail.com)

Seasonal changes in humidity level in the tropics impact body color polymorphism and desiccation resistance in Drosophila jambulina—Evidence for melanism-desiccation hypothesis

Drosophila jambulina exhibits color dimorphism controlled by a single locus but its ecological significance is not clear. Dark and light morphs differ significantly in body melanisation, desiccation resistance, rate of water loss, mating activity and fecundity. Interestingly, this species lacks clinal variation for body size, desiccation resistance and life history traits. For body melanisation, lack of geographical variation as well as plastic effects is not in agreement with a thermal melanism hypothesis. However, based on field data, there are seasonal changes in phenotypic frequencies of dark and light body color morphs which correlate significantly with variation in humidity levels. Under short-term (8 h) desiccation stress, we observed higher number of assortative matings, longer copulation period and increased fecundity for dark strains as compared with light strains. By contrast, both the morphs when exposed to high humid conditions exhibited higher assortative matings and fecundity for light strains as compared with dark strains. In tropical populations of D. jambulina, body color polymorphism seems to be maintained through humidity changes as opposed to thermal melanism. Thus, seasonal changes in the frequency of body color morphs in this tropical species supports melanism-desiccation hypothesis.

An Intron Loss of Dfak Gene in Species of the Drosophila melanogaster Subgroup and Phylogenetic Analysis

Drosophila focal adhesion kinase (Dfak) gene is a single-copy nuclear gene. Previous study revealed that Drosophila melanogaster and Drosophila simulans had lost an intron precisely within the tyrosine kinase (TyK) domain of this gene. However, this did not happen in several other Drosophila species, including Drosophila elegans, Drosophila ficusphila, Drosophila biarmipes, Drosophila jambulina, Drosophila prostipennis, Drosophila takahashii, and Drosophila pseudoobscura. In the current study, homologous sequences of Drosophila sechellia, Drosophila mauritiana, Drosophila yakuba, Drosophila teissieri, Drosophila santomea, and Drosophila erecta were amplified by polymerase chain reaction, and further sequencing analysis indicated that these species were missing a TyK domain intron, indicating they were closely related. The relationship of the D. melanogaster species group was reconstructed using TyK domain nucleotide sequences. The resulting phylogenetic tree revealed that these 8 species were the most related species in the melanogaster group. These results strongly support previously proposed classifications based on morphological and molecular data.

Mutations for activity level in Drosophila jambulina perturbed its pacemaker that controls circadian eclosion rhythm.

Mutations for activity level, designated hpa and hra, in Drosophila jambulina altered properties of the pacemaker controlling eclosion rhythm. Entrainment of eclosion rhythm was studied in light-dark (LD) cycles of 12:12 h at 28 degrees C. The wild type strain entrained to LD cycles but the hpa or hra strain did not. When these strains were released from constant light (LL) to constant darkness (DD), the wild type strain free-ran while other two strains were arrhythmic. Temperature cycles entrained the wild type and hpa strain in DD and LL, and when transferred to constant temperature following thermoperiodic entrainment, the wild type strain free-ran in DD, while the hpa strain free-ran in LL as if the input of LL was essential for its free-running state. Temperature cycles entrained the hra strain in DD but not in LL, and free-running rhythmicities were never established, suggesting that the hra mutation has altered the basic properties of its pacemaker.

Selection for activity level alters the properties of the circadian pacemaker in Drosophila jambulina.

Selection for activity level alters the properties of the circadian pacemaker in Drosophila jambulina.

Notes on the systematics of Drosophila jambulina.

Two different species which were originated from India and Indochina have been called Drosophila jambulina as the same species. They were compared genetically, cytologically and electrophoretically, as well as morphologically. From these results it was concluded that the Indian species was the realD. jambulinaand that the Indochinese species seemed to be a new species and was tentatively namedD. punjabiensis-likebecause it was closer to the sibling species, D. punjabiensis. D. jambulinashowed a color dimorphism in a terminal tergite of female. A light-type gene controlling the dimorphism was dominant over a dark-type gene. The heterozygote segregated into 3 light: 1 dark in the next generation.