Correlates of sexual dimorphism for dry weight and development time in five species of Drosophila

Genetic variation for sexual dimorphism in developmental traits in Drosophila melanogaster

Sexual dimorphism in traits of insects during the developmental stages could potentially be the direct or indirect result of sex-specific selection provided that genetic variation for sexual dimorphism is present. We investigated genetic variation in sexual dimorphism in a set of Drosophila melanogaster inbred lines for 2 traits: egg to adult development time and pupation site preference. We observed considerable genetic variation in sexual dimorphism among lines in both traits. The sexual dimorphic patterns remained relatively consistent across multiple trials, despite both traits being sensitive to environmental conditions. Additionally, we measured 2 sexually dimorphic adult morphological traits in 6 sampled lines and investigated correlations in the sexual dimorphism patterns with the 2 developmental traits. The abundance of genetic variation in sexual dimorphism for D. melanogaster developmental traits demonstrated in this study provides evidence for a high degree of evolvability of sex differences in preadult traits in natural populations.

Lipidomic profiling of Drosophila strains Canton-S and white1118 reveals intraspecific lipid variations in basal metabolic rate

Drosophila melanogaster is a well-established model system for studies on lipid metabolism and energy homeostasis. In this study, we identified and quantified the main components of the lipid profile of two widely utilized Drosophila strains, namely Canton-S and white1118, under identical experimental conditions. Differences observed between the strains can be attributed to inherent metabolic divergences, thus limiting the influence of confounding factors. Using the comprehensive lipid data acquired, we applied cluster analysis and PLS-DA techniques to ascertain whether the lipidome could effectively differentiate between the strains. Certain lipid features, such as triacylglycerols, polar lipids, and specific sterol components, could be distinguished between flies of both strains regardless of sex. Our results suggest that although Canton-S and white1118 have similar lipid profiles and distributions, a selected subset of lipids demonstrates clear discriminatory potential between strains, thereby bearing significant implications for planning biological studies using these strains as control references.

Resource use by individual Drosophila suzukii reveals a flexible preference for oviposition into healthy fruits

The invasive pest fruit fly Drosophila suzukii is thought to be a specialist on healthy, i.e. unwounded, non-fermenting fruits. Morphological (sharp ovipositor) and neurophysiological/behavioural adaptations have been suggested to contribute to distinct adult feeding (wounded/microbe-laden fruits) and reproductive (healthy fruits) sites. We tested whether (1) variation in the overall availability of fruits, (2) variation in fruit type (healthy, wounded, fermenting), and (3) the relative abundance of different fruit types are ecological determinants of D. suzukii egg-laying decisions. Even though individual flies reduced their reproductive output when resource availability (blueberries) was low, a significantly higher proportion of eggs was allocated to healthy fruits, relative to wounded and fermenting fruits. However, the preference for healthy over wounded fruits declined continuously with a decrease in the relative abundance of healthy fruits and the overall reproductive output did not change. Under laboratory conditions, D. suzukii larvae achieved a higher developmental success on wounded than on healthy blueberries, but suffered less from density-dependent competition in healthy fruits. These data suggest that D. suzukii, despite showing an egg-laying preference for healthy fruits, also uses wounded/fermenting fruits as egg-laying sites, and that it may thrive well in windfall fruits.

Adaptation to larval crowding in Drosophila ananassae and Drosophila nasuta nasuta: increased larval competitive ability without increased larval feeding rate

The standard view of adaptation to larval crowding in fruitflies, built on results from 25 years of multiple experimental evolution studies on Drosophila melanogaster, was that enhanced competitive ability evolves primarily through increased larval feeding and foraging rate, and increased larval tolerance to nitrogenous wastes, at the cost of efficiency of food conversion to biomass. These results were at odds from the predictions of classical K-selection theory, notably the expectation that selection at high density should result in the increase of efficiency of conversion of food to biomass, and were better interpreted through the lens of α-selection. We show here that populations of D. ananassae and D. n. nasuta subjected to extreme larval crowding evolve greater competitive ability and pre-adult survivorship at high density, primarily through a combination of reduced larval duration, faster attainment of minimum critical size for pupation, greater time efficiency of food conversion to biomass and increased pupation height, with a relatively small role of increased urea/ammonia tolerance, if at all. This is a very different suite of traits than that seen to evolve under similar selection in D. melanogaster, and seems to be closer to the expectations from the canonical theory of K-selection. We also discuss possible reasons for these differences in results across the three species. Overall, the results reinforce the view that our understanding of the evolution of competitive ability in fruitflies needs to be more nuanced than before, with an appreciation that there may be multiple evolutionary routes through which higher competitive ability can be attained.

Status of research on Drosophila ananassae at global level

Drosophila, a dipteran insect, has been found to be the best biological model for different kinds of studies. D melanogaster was first described by Meigen in 1830 , is most extensively studied species of the genus Drosophila and a number of investigations employing this species have been documented in areas such as genetics, behaviour, evolution, development, molecular biology, ecology, population biology, etc. Besides D. melanogaster, a number of other species of the genus Drosophila have also been used for different kinds of investigations. Among these, D. ananassae, a cosmopolitan and domestic species endowed with several unusual genetic features, is noteworthy. Described for the first time from Indonesia (Doleschall 1858), this species is commonly distributed in India. Extensive research work on D. ananassae has been done by numerous researchers pertaining to cytology, genetics, mutagenesis, gene mapping, crossing-over in both sexes, population and evolutionary genetics,behaviour genetics, ecological genetics, sexual isolation, fluctuating asymmetry, trade-offs etc. Genome of D. ananassae has also been sequenced. The status of research on D. ananassae at global level is briefly described in this review. Bibliography on this species from different countries worldwide reveals that maximum contribution is from India.

Estimation of Fitness of Normal and Stylopized Paddy Pest, White Leafhopper Cofana spectra (Distant) (Hemiptera: Cicadellidae), in West Bengal, India through Correlation of Life History Traits

The assessment of the morphological and reproductive features of white rice leafhopper Cofana spectra (Distant) was carried out using selected characters that bear importance in determining the fitness at the individual and population levels. Morphometric measurements of the individuals reared in the laboratory as normal and stylopized with the strepsipteran parasitoid, Halictophagus australensis Perkins, were recorded and analyzed. A t-test was performed to justify whether parasitization by H. australensis affected the traits. Correlations and regression analyses were carried out to deduce the difference in relative importance of the morphological features in the life history of C. spectra and their variation because of stylopization by H. australensis. A principal component analysis (PCA) was applied on the morphometric data to further substantiate the difference observed in the traits. In case of stylopized white leafhopper (WLH), fecundity was inhibited almost completely irrespective of seasons. The effect of stylopization on the life history traits of C. spectra has been noted that supports its possible use in biocontrol.

Correlation between body size and fecundity in fish louse Argulus bengalensis Ramakrishna, 1951 (Crustacea: Branchiura)

The life history traits like fecundity and body size are useful predictors of life history strategies of organisms. The information on these aspects provided necessary input for control measures for ectoparasites. In view of this, the variations in the life history traits of the fish louse Argulus bengalensis Ramakrishna (1951) were assessed using age as an explanatory factor. The analyses revealed that the body weight (BW) is related to age in males as: y (BW) = 0.03 × (Age)-2.58: and in females as: y (BW) = 0.89 + 0.13x (Age). The body length and age relationship in males is observed as: y (BL) = 2.94 + 0.01x (Age) and in females as: y (BL) = 2.89 + 0.06x (Age). The degree of sexual dimorphism (DD) for BL is positively correlated (r = -0.358; df = 43; P < 0.001) with age while DD for BW is negatively correlated (r = -0.525; df = 43; P < 0.001) with age. The eggs/clutch remained between 02 and 43 for the 21st and 38th day old females. The fecundity as a function of age could be represented as: y (Eggs) = 1.62x (Age)-27.92. The increase in BW with age in female A. bengalensis favoured greater resource allocation for egg production, while in males it likely favours dispersal ability. Since body size and fecundity varied with age, the relative abundance and extent of infestation in fish host would vary with age composition of the population and recruitment of juveniles. The impacts of host specific variations on these features need to be tested further.

Variation in adult life history and stress resistance across five species of Drosophila

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 of Drosophila melanogaster, and one recently wild-caught population each of four other species of Drosophila, two from the melanogaster and two from the immigrans 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 on D. 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 and D. sulfurigaster neonasuta (immigrans group) were heavier at eclosion than the melanogaster group species, and tended to have somewhat higher absolute lipid content and starvation resistance. Yet, these two immigrans group species were shorter-lived and had lower average daily fecundity than the melanogaster 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 of D. 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 discrete-generation laboratory cultures. Possible explanations for these apparent anomalies are discussed in the context of the differing selection pressures likely to be experienced by Drosophila populations in laboratory versus wild environments.