Phenotypic plasticity of body pigmentation in Drosophila: influence of a developmental thermoperiodic regime in two sibling species

Abstract Variation of body pigmentation according to growth temperature was analysed in two European populations (Bordeaux and Cordoba) of the two sibling species Drosophila melanogaster (Meigen) and D. simulans (Sturtevant). Results obtained at constant temperatures were compared with those observed under alternating thermal regimes of various amplitudes and with a daily periodicity of 12–12 h. Abdominal pigmentation in segments 5, 6 and 7, and of their sum, was investigated in both species in females only. Thoracic trident pigmentation was studied in males and females but in Drosophila melanogaster only.
Thoracic pigmentation exhibited curvilinear convex reaction norms under constant conditions, with a darker pigmentation in the population (Bordeaux) living in a colder climate. No specific effects of alternating regimes were seen. For abdomen pigmentation, slightly different reaction norms were observed under constant conditions between Bordeaux and Cordoba strains. There were also slight differences between the two species. Alternating temperatures produced a significant decrease in average pigmentation, roughly proportional to the thermal amplitude.
Alternating stressing conditions induced also an increase in the phenotypic variability of abdominal pigmentation, especially in segments 6 and 7. Finally, because an increase of growth temperature results in a monotonically decreasing reaction norm of both abdomen pigmentation in females and a size-related trait, the wing/thorax ratio, we found a linear relationship between the two variables, with a very high overall correlation at constant temperatures ( r  = 0.99). The correlation was slightly less under alternating conditions, due to a broader dispersal of the experimental values around the regression lines.     

Phenotypic plasticity of abdominal pigmentation in Drosophila kikkawai: multiple interactions between a major gene, sex, abdomen segment and growth temperature

Drosophila kikkawai is known to be polymorphic for a single autosomal locus controlling abdomen pigmentation in females. Two strains homozygous at this locus (Abdomen pigmentation, Abp) were established from a polymorphic Indian population: one was homozygous (DD) for the dark allele, the other (LL) for the light allele. A Mendelian analysis of crosses at 25°C confirmed the occurrence of a major locus, with dominance of the D allele. Phenotypic variation of pigmentation according to growth temperature was then analyzed in DD and LL male and female flies, and in reciprocal F1. A slight difference was found between reciprocal F1 females from a dark mother were darker but not at all temperatures. In females, the D allele exhibited an antero‐posterior gradient of increasing expression from segment 27, with dominance over L and an increased expression at low temperatures. In males, abdomen pigmentation was uniformly light in segments 25, the D allele being repressed by the sex genotype. In segment 6, the D allele was expressed but only at low temperatures, and was either recessive to L or codominant. Phenotypic plasticity that is, amount of change induced by different growth temperatures, was variable according to genotype and segment. It always corresponded to a darkening of the fly at lower temperatures, but was generally much less than in D. melanogaster. In D. kikkawai, climatic adaptation might occur more by changing the frequency of the D allele than by phenotypic plasticity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Phenotypic plasticity of body pigmentation in Drosophila melanogaster: genetic repeatability of quantitative parameters in two successive generations

In Drosophila melanogaster, body pigmentation is a quantitative trait that depends on developmental temperature. When investigated over the whole thermal range of the species, pigmentation exhibits nonlinear reaction norms that differ among segments. The isofemale line method was used to analyse the genetic variability in two natural populations that affected the shape of reaction norms. Each line was considered as an experimental repeat, and polynomial reaction norms fitted to calculate the characteristic values (eg the coordinates of a maximum). In total, 20 lines from two geographically distant populations (France and India) were investigated at seven developmental temperatures (12-31 degrees C) in two successive generations (G2 and G3). We analysed the genetic repeatability (ie the correlation between generations) of three kinds of parameters: intraclass correlation coefficients (isofemale heritability), family means at different temperatures and the characteristic values of the reaction norms. For intraclass correlation, a low genetic repeatability was found. For family mean values grown at various temperatures, an overall positive and highly significant repeatability was found (r=0.55+/-0.024). Finally, a positive significant G2-G3 correlation was also the rule for the characteristic values of the reaction norms. Significant differences could be found between values describing either the trait or its plasticity, but with no general trend. A slightly higher repeatability was observed in the Indian population. These results show that, with a family selection design, the shape of the reaction norms might be modified in various ways.     

Phenotypic plasticity of the aedeagus of Drosophila mediopunctata: Effect of the temperature

In this study, we analyzed the phenotypic plasticity of the male intromittent organ (aedeagus) of Drosophila mediopunctata genitalia in response to temperature. Size and shape of the aedeagus were examined with univariate statistics and geometric morphometrics. The following results emerged: firstly, flies raised at 16.5 °C had bigger aedeagi than those raised at 20 °C; secondly, significant differences in shape were also found between the two groups of flies, mainly in the apical area, located using the thin-plate spline interpolating function; thirdly, the coefficients of variation for the traits of the aedeagus were comparable to other traits in Drosophila and likewise to genital traits in other organisms. These findings were analyzed in an evolutionary context.     

Phenotypic variability of thoracic pigmentation in Indian populations of Drosophila melanogaster

Fourteen natural populations of Drosophila melanogaster collected along diverse latitudinal and altitudinal ranges, were analysed for thoracic trident pigmentation at two different breeding temperatures (17 and 25°C) for both sexes. Statistical analyses showed significant intra- as well as interpopulational genetic variations. Clinal patterns for thoracic trident pigmentation along latitude as well as altitude are significantly correlated with thermal amplitude ( T _cv). Crosses between dark (Shimla) and light (Kalka) variants of trident pigmentation produced intermediate phenotypes, and a clear maternal effect was observed in the reciprocal F ₁ crosses. Data suggest that the temperature differences have resulted in phenotypic plasticity of thoracic pigmentation across the Indian subcontinent.     

Phenotypic plasticity in temperature stress resistance is triggered by photoperiod in a fly

Temperature variation poses a substantial challenge for individual survival and reproductive success, warranting effective means to counter negative effects of temperature extremes. Phenotypic plasticity offers a particularly powerful mechanism to cope with short-time temperature fluctuations. While temperature-induced plasticity in thermal tolerance has been widely explored, effects of other environmental factors have received much less attention. Using a full-factorial design we here show that variation in temperature stress resistance can be triggered by photoperiod (and temperature) in the fly Protophormia terraenovae, with shorter day lengths inducing more cold- and longer day lengths more heat-tolerant phenotypes. Such plastic changes were not related to different developmental pathways (reproductive activity or reproductive diapause), and can be induced during development but also in the adult stage (at least for cold tolerance). We suggest that short-term, photoperiod-mediated changes in insect thermal tolerance represent a mechanism of adaptive seasonal plasticity. Photoperiod further affected development time and body size, the significance of which is currently unclear.     

Phenotypic plasticity of body size in Drosophila: effects of a daily periodicity of growth temperature in two sibling species

Abstract. Variation of wing and thorax length under thermoperiodic growth conditions was analysed in four strains of two sibling species, Drosophila melanogaster and D. simulans , from two European localities. Results were compared to those obtained with constant temperatures ranging from 12 to 31 °C.
Under constant temperatures the data basically confirmed previous results: concave reaction norms for wing and thorax length; a monotonically decreasing norm for wing : thorax ratio; and an increasing norm for sex dimorphism (female : male ratio). Phenotypic variability was maximum at extreme temperatures and minimum at middle ones. Slight differences were observed according to the geographical origin: the difference between strains from Bordeaux (France) and Cordoba (Spain) was maximum at low temperatures but disappeared at about 28 °C.
According to the temperatures chosen, alternating thermal regimens had either no effect or produced a significant size reduction, probably reflecting a periodic stress. The magnitude of this effect was proportional to the amplitude of the thermoperiod but not to the quality (cold or heat) of the stress. In a similar way, the wing : thorax ratio was either not modified or reduced significantly, indicating that wing length was relatively more affected than thorax length by alternating thermal regimens. Sex dimorphism also showed either no change or a significant increase, indicating that males were relatively more reactive than females to alternating conditions. Finally, regimens of broad amplitudes increased the phenotypic variability, again an indication of stressful effects. All these observations should be taken into account when analysing phenotypic variability in nature and trying to understand natural selection in wild-living populations.     

Phenotypic plasticity in morphological traits in two populations of Drosophila melanogaster

Isofemale lines of two populations of Drosophila melanogaster, originating from France and Tanzania, were examined over a range of temperatures. Morphological traits showed distinct patterns in phenotypic plasticity; flies of the two populations differed in shape. Genotype-by-Environment (G*E) interactions were frequently found in the Tanzania population, but were hardly present in the France population. If G*E interaction was present over temperature, estimates of additive genetic variance and additive genetic covariance were made to compare theoretical models with our data. The conclusion is that in France Drosophila melanogaster has been selected over a wider range of temperatures, resulting in parallel reaction norms of more optimal slope. In contrast, selection must have taken place over a narrower temperature range in Tanzanian flies, and will have exerted no direct influence on the slope of the reaction norm.     

Phenotypic plasticity across 50 MY of evolution: Drosophila wing size and temperature

We studied the response in wing size to rearing at different temperatures of nine strains of Drosophila representing six species. The species varied in their natural habitats from tropical to temperate and one cosmopolitan. The evolutionary divergence of the species spans 50 million years. While some quantitative differences were found, all species responded to temperature very similarly: females increased an average of ∼11% and males ∼14% when reared at 19 °C compared to 25 °C. The phenotypic plasticity in wing size in response to temperature appears to be a fixed trait in Drosophila across long evolutionary time and diverse ecological settings. This likely reflects the close relationship between wing area (and thus wing loading) and insect body mass that is a crucial factor for flight regardless of ecology and is, thus, maintained across long evolutionary time.     

Phenotypic plasticity of pigmentation and morphometric traits in Pnigalio soemius (Hymenoptera: Eulophidae)

Species of the genus Pnigalio Schrank are ectoparasitoids on several pest insects. Most species are polyphagous parasitoids of lepidopteran and dipteran leafminers. Despite their potential economic importance, information on intraspecific phenotypic variability is insufficient. Pnigalio soemius (Walker) was reared at five different temperatures (10, 15, 20, 25, 30 degrees C) on mature larvae of one of its natural hosts, Cosmopterix pulchrimella Chambers (Lepidoptera: Cosmopterigidae), to investigate the influence of temperature on size, colour and other morphological traits, and to measure the range of variation of several characters. Thermal developmental reaction norms, which represent the effect of temperature during growth and development on the value of some adult traits, were produced. The results confirmed the influence of temperature on numerous characters and that these characters had a larger range of variation than realized previously in the construction of taxonomic keys to species. In particular, the number and position of the costulae on the propodeum and colour of the gaster were affected by rearing temperature.     

Phenotypic plasticity of sternopleural bristle number in temperate and tropical populations of Drosophila melanogaster

We investigated the phenotypic plasticity of sternopleural bristle (SB) number as a function of growth temperature in isofemale lines from temperate (France) and tropical (Congo) populations of Drosophila melanogaster. We found concave reaction norms with a maximum in the middle of the thermal range, except in four African lines which exhibited a regularly decreasing response curve. Genetic variability (intraclass correlation) and evolvability (genetic CV, coefficient of variation) were independent properties and did not change with temperature. Residual, within-line variability was, however, strongly influenced by growth temperature, showing a U-shaped response curve and a minimum CV of 9% at 21.5 degrees C. As expected from a previously known latitudinal cline, maximum values (MV) were higher in temperate than in tropical flies. The temperature of maximum value (TMV) was observed at a higher temperature in the tropical population, in agreement with similar adaptive trends already observed for other quantitative traits. Significant negative correlations within each population were observed between a plasticity curvature parameter and MV or TMV. No difference in curvature was, however, observed between populations, in spite of their very different MVs.     

Phenotypic plasticity of a cooperative behaviour in bacteria

There is strong evidence that natural selection can favour phenotypic plasticity as a mechanism to maximize fitness in animals. Here, we aim to investigate phenotypic plasticity of a cooperative trait in bacteria – the production of an iron‐scavenging molecule (pyoverdin) by Pseudomonas aeruginosa. Pyoverdin production is metabolically costly to the individual cell, but provides a benefit to the local group and can potentially be exploited by nonpyoverdin‐producing cheats. Here, we subject bacteria to changes in the social environment in media with different iron availabilities and test whether cells can adjust pyoverdin production in response to these changes. We found that pyoverdin production per cell significantly decreased at higher cell densities and increased in the presence of cheats. This phenotypic plasticity significantly influenced the costs and benefits of cooperation. Specifically, the investment of resources into pyoverdin production was reduced in iron‐rich environments and at high cell densities, but increased under iron limitation, and when pyoverdin was exploited by cheats. Our study demonstrates that phenotypic plasticity in a cooperative trait as a response to changes in the environment occurs in even the simplest of organisms, a bacterium.