Drosophila suzukii wing spot size is robust to developmental temperature

Phenotypic plasticity is an important mechanism allowing adaptation to new environments and as such it has been suggested to facilitate biological invasions. Under this assumption, invasive populations are predicted to exhibit stronger plastic responses than native populations. Drosophila suzukii is an invasive species whose males harbor a spot on the wing tip. In this study, by manipulating developmental temperature, we compare the phenotypic plasticity of wing spot size of two invasive populations with that of a native population. We then compare the results with data obtained from wild‐caught flies from different natural populations. While both wing size and spot size are plastic to temperature, no difference in plasticity was detected between native and invasive populations, rejecting the hypothesis of a role of the wing‐spot plasticity in the invasion success. In contrast, we observed a remarkable stability in the spot‐to‐wing ratio across temperatures, as well as among geographic populations. This stability suggests either that the spot relative size is under stabilizing selection, or that its variation might be constrained by a tight developmental correlation between spot size and wing size. Our data show that this correlation was lost at high temperature, leading to an increased variation in the relative spot size, particularly marked in the two invasive populations. This suggests: (a) that D. suzukii's development is impaired by hot temperatures, in agreement with the cold‐adapted status of this species; (b) that the spot size can be decoupled from wing size, rejecting the hypothesis of an absolute constraint and suggesting that the wing color pattern might be under stabilizing (sexual) selection; and (c) that such sexual selection might be relaxed in the invasive populations. Finally, a subtle but consistent directional asymmetry in spot size was detected in favor of the right side in all populations and temperatures, possibly indicative of a lateralized sexual behavior.     

Body size patterns in Drosophila inhabiting a mesocosm: interactive effects of spatial variation in temperature and abundance

Body size is a major component of fitness. However, the relative contributions of different factors to optimal size, and the determinants of spatial and temporal variation in size, have not been fully established empirically. Here, we use a mesocosm of a Drosophilidae assemblage inhabiting decaying nectarines to investigate the influence of spatial variation in temperature on adult body size in Drosophila simulans Sturtevant. Two treatments were established; one in the sun where developing larvae were exposed to high temperatures and the other in the shade where temperature conditions were milder. The simple developmental effects of temperature differences (i.e. larger flies are likely to emerge from cooler environments), or the simple effects of stressful temperatures (i.e. high temperatures yield wing abnormalities and smaller flies), were overridden by interactive effects between temperature and larval density. Emergences were lower in the sun than shade, probably as a result of temperature-induced mortality. However, flies attained the same final sizes in the shade and sun. In addition, abnormally winged flies were clustered in the shaded treatments. In the shade treatments, where emergences were higher than in the sun, stressful conditions as a result of high larval density likely resulted in wing abnormalities and small size. Consequently, there was little spatial variation in size across the mesocosm, but substantial spatial variation in abundance. Under natural conditions both mortality and non-lethal effects of temperature and/or crowding are likely to play a role in the evolution of body size.     

Strong responses of Drosophila melanogaster microbiota to developmental temperature

Physiological responses to changes in environmental conditions such as temperature may partly arise from the resident microbial community that integrates a wide range of bio-physiological aspects of the host. In the present study, we assessed the effect of developmental temperature on the thermal tolerance and microbial community of Drosophila melanogaster. We also developed a bacterial transplantation protocol in order to examine the possibility of reshaping the host bacterial composition and assessed its influence on the thermotolerance phenotype. We found that the temperature during development affected thermal tolerance and the microbial composition of male D. melanogaster. Flies that developed at low temperature (13°C) were the most cold resistant and showed the highest abundance of Wolbachia, while flies that developed at high temperature (31°C) were the most heat tolerant and had the highest abundance of Acetobacter. In addition, feeding newly eclosed flies with bacterial suspensions from intestines of flies developed at low temperatures changed the heat tolerance of recipient flies. However, we were not able to link this directly to a change in the host bacterial composition.     

Chill-coma temperature in Drosophila: effects of developmental temperature, latitude, and phylogeny

We modify and apply a nonlethal technique for rapidly quantifying the cold tolerance of large numbers of Drosophila and other small insects. Flies are transferred to individual vials, cooled in groups in progressive 0.5 degrees C steps, and checked for loss of righting response (chill-coma temperature [T(cc)]). Flies recover quickly when transferred to ambient temperature, and thus this technique potentially can be used in selection experiments. We applied this technique in several experiments. First, we examined the sensitivity of T(cc) to developmental temperature. Drosophila melanogaster (Congo, France), Drosophila subobscura (Spain, Denmark), and Drosophila ananassae (India) were reared from egg to adult at 15 degrees, 18 degrees, 25 degrees, or 29 degrees C, transferred to 15 degrees C for several days, and then progressively chilled: T(cc) was positively related to developmental temperature, inversely related to latitude of the population, but independent of sex. The sensitivity of T(cc) to developmental temperature (acclimation flexibility) was marked: T(cc) shifted on average 1 degrees for each 4 degrees C shift in developmental temperature. Among 15 species of the obscura group of Drosophila, T(cc) varied from -0.1 degrees to 4.5 degrees C; T(cc) was inversely related to latitude in both nonphylogenetic and phylogenetically based ANCOVA (standardized independent contrasts) and was unrelated to body size.     

Prothoracicotropic hormone regulates developmental timing and body size in Drosophila

In insects, control of body size is intimately linked to nutritional quality as well as environmental and genetic cues that regulate the timing of developmental transitions. Prothoracicotropic hormone (PTTH) has been proposed to play an essential role in regulating the production and/or release of ecdysone, a steroid hormone that stimulates molting and metamorphosis. In this report, we examine the consequences on Drosophila development of ablating the PTTH-producing neurons. Surprisingly, PTTH production is not essential for molting or metamorphosis. Instead, loss of PTTH results in delayed larval development and eclosion of larger flies with more cells. Prolonged feeding, without changing the rate of growth, causes the overgrowth and is a consequence of low ecdysteroid titers. These results indicate that final body size in insects is determined by a balance between growth-rate regulators such as insulin and developmental timing cues such as PTTH that set the duration of the feeding interval.     

Temperature and developmental responses of body and cell size in Drosophila; effects of polyploidy and genome configuration

Increased adult body size in Drosophila raised at lower temperatures could be attributed both to an increase in the cell volume and cell number. It is not clear, however, whether increased cell size is related to (or even caused by) increased nuclear volume and genome size (or configuration). Experiments with Drosophila melanogaster stocks (Oregon-R and w1118) raised at 16, 22, 24, and 28 °C resulted in larger adult body and wing size with lower temperature, while eye size was less affected. The increase in wing size reflected an increase in cell size in both males and females of both stocks. The nucleus size, genome size, and DNA condensation of adult flies, embryos, and Schneider 2 cells (S2 cells, of larval origin) were estimated by flow cytometry. In both adult flies and S2 cells, both nucleus size and DNA condensation varied with temperature, while DNA content appears to be constant. From 12% to 18% of the somatic cells were tetraploid (4C) and 2–5% were octoploid (8C), and for the Oregon strain we observed an increase in the fraction of polyploid cells with decreasing temperature. The observed increase in body size (and wing size) at low temperatures could partly be linked with the cell size and DNA condensation, while corresponding changes in the haploid genome size were not observed.     

Genetic and developmental factors in the olfactory response of Drosophila melanogaster larvae to alcohols.

Olfactory responses of Drosophila melanogaster larvae to a homologous series of primary alcohols (methanol ... decanol) were tested. Alcohols at either extreme of the chain lengths studied (methanol, ethanol and decanol) evoked no significant responses. Heptanol and nonanol both produced dose-independent responses, larvae being attracted to heptanol and repulsed by nonanol. The remaining alcohols elicited dose-related attractive responses. Responses to hexanol and nonanol decline with increasing larval age. Genetic differences were found for the response to heptanol, with larvae from a Japanese strain, Katsunuma, being indifferent to this substance. Chromosome exchange revealed that a major factor involved in the response to heptanol is located on chromosome II; factors on chromosome III quantitatively modulate this response. Three mutant strains were isolated following EMS mutagenesis of chromosome III. These three strains, IndifferentA, IndifferentB and IndifferentC, show incomplete or total anosmia when stimulated with nonanol. Adult flies from these strains show similar effects. IndifferenB and C strains are dominant over the Canton-S control strain; the IndifferentA strain shows semi-dominance. Results are discussed in the light of the ecology of Drosophila larvae and the relation between olfactory stimulus and receptor conformation and number.     

Body size response to warming: time of the season matters in a tephritid fly

Whether shrinking body size is a universal response to climate change remains controversial. Moreover, the mechanisms underlying body size shifts are poorly understood. Here, assuming that life history traits evolve to maximize fitness according to life history plasticity theory, we hypothesized that under global warming temperate multivoltine insects should emerge earlier with a smaller body mass in the early growing season, but emerge later with a larger body mass in the late season. We tested this hypothesis by conducting two field artificial warming experiments in an alpine meadow: 1) with one pre‐dispersal seed predator species (tephritid flies, Tephritis femoralis) and its two host‐plant species flowering in early and late growing seasons, respectively, and 2) with the tephritid flies and one host species with a flowering season that occupies parts of both the early and late growing seasons. These experiments were complemented by a microcosm chamber warming experiment, in which increasing and decreasing temperature trends were set to simulate temperature variation pattern in early and late growing seasons, respectively, but photoperiod was held constant. Warming generally advanced the adult emergence and decreased the body size (adult body mass) in the early season but delayed the emergence and increased the size in the late season in both field experiments, indicating that the seasonally different effects of warming on the fly body size was constant regardless of host‐plant identity. The chamber warming resulted in consistent responses of emerging timing and body size to the simulated seasonal warming, demonstrating that the temperature increase per se and its interaction with direction of temperature change, but not other correlated effects, should be primarily responsible for the observed contrasting shifts of body size at different times of the season. Our results indicate that taking into account temperate seasonal patterns of temperature variation could be of general importance for predicting animal body size changes in the warmed future.     

Body size and the daily rhythm of body temperature in dogs

Practically every physiological variable exhibits daily rhythmicity. The daily rhythm of body temperature, like that of many other variables, is often weak in newborns and gains strength as the animals grow. Because of the natural association between physiological maturation and gain in body size, these two processes are naturally confounded. To differentiate between the effects of maturation and the effects of body growth, we took advantage of the large variation in body size that exists among different breeds of the domestic dog. We compared the body temperature rhythms of developing puppies of different dog breeds. Puppies of none of the breeds exhibited statistically significant daily rhythmicity for several days after birth. Regardless of breed or sex, rhythmicity matured over several weeks and attained a stable level by 6 weeks after birth. Body size did not seem to be an important element in the development of rhythmicity because the development was similar in three breeds that differed greatly in body size (Basset Hound, Boxer, and Neapolitan Mastiff). On the other hand, the difference in body size associated with the different breeds had a strong impact on the absolute level of body temperature regardless of age: we found a strong inverse correlation between temperature and body size among the puppies and dams of the three breeds and among 115 adult dogs from 19 different breeds ranging from 2-kg Yorkshire Terriers to 80-kg Great Danes.     

Allometric and nonallometric components of Drosophila wing shape respond differently to developmental temperature

Phenotypic plasticity of wing size and shape of Drosophila simulans was analyzed across the entire range of viable developmental temperatures with Procrustes geometric morphometric method. In agreement with previous studies, size clearly decreases when temperature increases. Wing shape variation was decomposed into its allometric (24%) and nonallometric (76%) components, and both were shown to involve landmarks located throughout the entire wing blade. The allometric component basically revealed a progressive, monotonous variation along the temperature. Surprisingly, nonallometric shape changes were highly similar at both extremes of the thermal range, suggesting that stress, rather than temperature per se, is the key developmental factor affecting wing shape.     

Growth rate adjustment of two Drosophila parasitoids in response to the developmental stage of hosts

1. Generalist koinobiont parasitoids often exhibit high flexibility in their development; their larvae shorten or prolong the developmental period depending on the host quality at parasitisation. However, flexibility of the growth rate of parasitoid larvae has rarely been investigated so far. 2. This study investigated how the koinobiont parasitoid wasps Asobara japonica and Leptopilina ryukyuensis regulate their larval growth when they parasitise host Drosophila larvae with varying larval periods. 3. In both parasitoid species, the preimaginal period was longer when they parasitised 1‐day‐old larvae of Drosophila rufa than when they parasitised older larvae of D. rufa or when they parasitised larvae of Drosophila simulans, a species with a shorter larval period than D. rufa. After host pupariation, A. japonica accelerated its growth, thereby showing a biphasic growth curve. On the other hand, L. ryukyuensis did not accelerate its growth after host pupariation. 4. Growth retardation of parasitoid larvae in 1‐day‐old D. rufa larvae would contribute to avoiding excess growth before host pupariation, because the excess growth of parasitoid larvae would have negative effects on host growth. The growth rate acceleration of A. japonica after host pupariation suggests that they enhance resource utilisation in a host that has reached maximum body mass. It remains uncertain as to why L. ryukuensis does not show clear accelerated growth after host pupariation. Nonetheless, these results suggest that parasitoid larvae have the ability to detect the developmental stage of hosts in a species‐specific manner.     

Ecology of body size in Drosophila buzzatii: untangling the effects of temperature and nutrition

Abstract.

• 1 A method of separating the effects of two important determinants of body size in natural populations, temperature of larval development and level of larval nutrition, by making measurements of thorax length and wing length of adult flies is investigated.
• 2 I show that at any given time variation in body size of Drosophila buzzatii from two sites in eastern Australia is determined primarily by variation in the quality of nutrition available to larvae.
• 3 Throughout the year adult flies are consistently at least 25% smaller in volume than predicted for optimal nutrition at their predicted temperature of larval development.
• 4 Nutritional stress is therefore a year-round problem for these flies.
• 5 Measurements of adult flies emerging from individual breeding substrates (rotting cactus cladodes) show that there is substantial variation among these substrates in the nutrition available to larvae.
• 6 This method will allow study of spatial and temporal variation in the temperature of larval substrates and in the nutritional resources available to flies in natural populations.

     

Body size and spatial scales in avian response to landscapes: a meta‐analysis

Response of species to their environment is dependent on the scales that individuals interact with landscapes. Several life‐history traits have been suggested to influence scales of response to landscapes, but little empirical work has addressed this issue, limiting our ability to predict the relevant scale(s) at which species respond to their environment. Body size is frequently hypothesized to be relevant for predicting the effects of landscape structure on species given correlations between body size and various measures of mobility or perceptual range, yet evidence of this relationship remains equivocal. We conducted a meta‐analysis of 22 studies to address the question of whether body size is related to the characteristic scale at which bird species respond to landscape structure. On the basis of correlation coefficients and linear mixed models, we show that body size is positively related to the characteristic scale of response to landscapes. The strength of this relationship is less than body size – dispersal allometries, suggesting that response to landscapes may be influenced, in part, by factors other than dispersal (e.g. territory size). However, the strength of the observed body size – scale relationship may have been affected by several factors, including limitations in the range of body sizes and landscape extents tested. Our findings suggest that life‐history traits mediate aspects of the scales at which species respond to the landscape and contribute to developing a more predictive framework for investigating scalar relationships in nature.     

Parental and developmental temperature effects on the thermal dependence of fitness in Drosophila melanogaster

Cross-generational effects refer to nongenetic influences of the parental phenotype or environment on offspring phenotypes. Such effects are commonly observed, but their adaptive significance is largely unresolved. We examined cross-generational effects of parental temperature on offspring fitness (estimated via a serial-transfer assay) at different temperatures in a laboratory population of Drosophila melanogaster. Parents were reared at 18 degrees C, 25 degrees C, or 29 degrees C (Tpar) and then their offspring were reared at 18 degrees C, 25 degrees C, or 29 degrees C (Toff) to evaluate several competing hypotheses (including an adaptive one) involving interaction effects of parental and offspring temperature on offspring fitness. The results clearly show that hotter parents are better; in other words, the higher the temperature of the parents, the higher the fitness of their offspring, independent of offspring thermal environment. These data contradict the adaptive cross-generational hypothesis, which proposes that offspring fitness is maximal when the offspring thermal regime matches the parental one. Flies with hot parents have high fitness seemingly because their own offspring develop relatively quickly, not because they have higher fecundity early in life.     

Temperature modulates epidermal cell size in Drosophila melanogaster

Most ectotherms show increased body size at maturity when reared under colder temperatures. In principle, temperature could produce this outcome by influencing growth, proliferation and/or death of epidermal cells. Here we investigated the effects of rearing temperature on the cell size and cell number in the wing blade, the basitarsus of the leg and the cornea of the eye of Drosophila melanogaster from two populations at opposite ends of a South American latitudinal cline. We found that, in both strains of D. melanogaster and in both sexes, a decrease in rearing temperature increases the size of the wings, legs and eyes through an effect on epidermal cell size, with no significant change in cell number. Our results indicate that temperature has a consistent effect on cell size in the Drosophila epidermis and this may also apply to other cell types. In contrast, the evolutionary effects of temperature on the different organs are not consistent. We discuss our findings in the context of growth control in Drosophila.     

Clinal variation in developmental time and viability,and the response to thermal treatments in two species of Drosophila

The present study first addressed the question of whether developmental time (DT) and viability (VT) vary clinally along latitudinal and altitudinal gradients in Drosophila buzzatii, an autochthonous specialist and the generalist invasive Drosophila melanogaster. Coincident and positive altitudinal clines across species and, direct and inverse latitudinal clines were observed for DT in D. melanogaster and D. buzzatii, respectively. Opposing latitudinal and altitudinal clines were detected for VT only in D. melanogaster. The patterns observed along altitudinal gradients prompted us to investigate whether flies living at lowland and highland environments may respond differentially to thermal treatments consisting of regimes of constant and alternating temperatures. Flies reared at higher mean temperature developed faster than at lower mean temperature in both species. By contrast, the response in VT differed greatly between species. Highland D. melanogaster were more viable than lowland regardless the treatment, whereas, in D. buzzatii, highland flies were more viable than lowland in alternating thermal regimes and the reverse was true in treatments of constant temperature. The results obtained suggest that thermal amplitude may be an important factor that should be considered in investigations of thermal adaptation. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95 , 233–245.