Fluctuating Temperature Regimes Research Articles

Temperature‐induced gene expression associated with different thermal reaction norms for growth rate

Although nearly all organisms are subject to fluctuating temperature regimes in their natural habitat, little is known about the genetics underlying the response to thermal conditions, and even less about the genetic differences that cause individual variation in thermal response. Here, we aim to elucidate possible pathways involved in temperature-induced phenotypic plasticity of growth rate. Our model organism is the collembolan Orchesella cincta that occurs in a wide variety of habitats and is known to be adapted to local thermal conditions. Because sequence information is lacking in O. cincta, we constructed cDNA libraries enriched for temperature-responsive genes using suppression subtractive hybridization. We compared gene expression of O. cincta with steep thermal reaction norms (high plasticity) to those with flat thermal reaction norms (low plasticity) for juvenile growth after exposure to a temperature switch composed of a cooling or a warming treatment. Using suppression subtractive hybridization, we found differential expression of ten nuclear genes, including several genes involved in energy metabolism, such as pantothenate kinase and carbonic anhydrase. In addition, seven mitochondrial genes were found in the cloned subtracted library, but further analysis showed this was caused by allelic variation in mitochondrial genes in our founder population, and that a specific haplotype was associated with high thermal responsiveness. Future work will focus on candidate genes from pathways such as the oxidative phosphorylation and biosynthesis of coenzyme A which are possibly involved in thermal responsiveness of juvenile growth rate.

Phenotypic Responses of Hatchlings to Constant Versus Fluctuating Incubation Temperatures in the Multi-banded Krait, Bungarus multicintus (Elapidae)

Most studies on egg incubation in reptiles have relied on constant temperature incubation in the laboratory rather than on simulations of thermal regimes in natural nests. The thermal effects on embryos in constant-temperature studies often do not realistically reflect what occurs in nature. Recent studies have increasingly recognized the importance of simulating natural nest temperatures rather than applying constant-temperature regimes. We incubated Bungarus multicintus eggs under three constant and one fluctuating-temperature regimes to evaluate the effects of constant versus fluctuating incubation temperatures on hatching success and hatchling phenotypes. Hatching success did not differ among the four treatments, and incubation temperature did not affect the sexual phenotype of hatchlings. Incubation length decreased as incubation temperature increased, but eggs incubated at fluctuating temperatures did not differ from eggs incubated at constant temperatures with approximately the same mean in incubation length. Of the hatchling phenotypes examined, residual yolk, fat bodies and locomotor performance were more likely affected by incubation temperature. The maximal locomotor speed was fastest in the fluctuating-temperature and 30 degrees C treatments and slowest in the 24 degrees C treatment, with the 27 degrees C treatment in between. The maximal locomotor length was longest in the fluctuating-temperature treatment and shortest in the 24 degrees C and 27 degrees C treatments, with the 30 degrees C treatment in between. Our results show that fluctuating incubation temperatures do not influence hatching success and hatchling size and morphology any differently than constant temperatures with approximately the same mean, but have a positive effect on locomotor performance of hatchlings.

Change in lipid composition in eastern oyster ( Crassostrea virginica Gmelin) exposed to constant or fluctuating temperature regimes

A temperature decrease usually induces an ordering effect in membrane phospholipids that can lead to membrane dysfunction. Ectotherms typically counteract this temperature effect by remodeling membrane lipids as stipulated in the homeoviscous adaptation theory (HVA). Previous studies mostly focused on the remodeling of membrane lipids during long-term acclimatization or acclimation at constant temperature regimes, whereas in nature, many organisms experience variations in temperature on a daily basis and must react to this changing thermal environment. The objective of this study was to examine the composition of membrane lipids in oysters subjected to long-term acclimation at constant temperatures (12 or 25 °C) or to environmentally realistic daily fluctuations in temperature between 12 and 25 °C for 7 d. The lipid composition of gill in oysters subjected to long-term acclimation at a constant temperature or to daily temperature fluctuations varied in a way consistent with HVA: oysters adjusted their phospholipid to sterol ratio in response to long-term acclimation to a constant temperature but not to daily temperature fluctuations. In contrast, the unsaturation index of polar lipids in oysters varied in response to both long-term acclimation to a constant temperature and to daily temperature fluctuations, mainly due to changes in 22:6n-3 and 20:5n-3. The 20:4n-6 levels in oyster gills increased as temperature rose, suggesting an increasing availability of this fatty acid for eicosanoid biosynthesis during stress responses.

Influence of temperature on the larval development of Upogebia africana and U. capensis (Decapoda: Thalassinidae: Upogebiidae) in the laboratory

The influence of constant temperature on the survival and development rate of Upoge- bia africana and U. capensis larvae was evaluated in the laboratory. U. africana larvae were reared at 7 constant temperatures between 12 and 29°C, and U. capensis larvae at 6 temperatures between 11 and 26°C. U. africana larvae were also exposed to fluctuating-temperature regimes, some of which simulated fluctuations in nearshore marine waters off the ovigerous female collection locality, to determine whether regression models describing the influence of constant temperature on the cumu- lative larval period can be extrapolated to predict the larval period under temperature conditions typ- ical of those in the natural environment. Larval development in both species comprised 3 zoeal stages prior to a metamorphic moult to the Decapodid. A stage intermediate between the Zoea 3 and Decapodid was occasionally detected at high temperatures (26 and 29°C) for U. africana, and at 26°C for U. capensis. U. africana larvae completed development to the Decapodid at all temperatures, with highest survival at 23°C. U. capensis larvae were unable to complete development to the Decapodid at 11°C, showing highest survival at 17°C. Stage-specific and cumulative duration of development in both species decreased sharply with increasing temperature until a threshold was reached, further increases in temperature having little additional effect on development rate. The temperature depen- dence of duration of development at temperatures below the threshold could be described by power functions for all zoeal stages as well as the cumulative larval period in both species. The thermal tolerance patterns for U. africana and U. capensis larvae agree well with geographical ranges of adults of both species along the southern African coastline, while differences in the optimal temper- ature for survival also agree with differences in their ranges. The effect of temperature fluctuations of the type simulated on U. africana larval development was expressed principally through variation in the rate of development, survival generally little affected, suggesting that U. africana larvae are physiologically well adapted to survive wide, rapid fluctuations in water temperature in the natural environment. Regression models describing the influence of constant temperature on the cumulative larval period appear to reliably predict the larval period under temperature conditions typical of those in the natural environment, with most reared larvae completing development at or shortly after the predicted period and with few exceptions within the predicted development period range.

Brief deviations from set point temperatures during normal airport handling operations negatively affect the quality of papaya ( Carica papaya) fruit

The consequences of poor temperature management during air transport were investigated by storing intact, abraded, or abraded + inoculated ( Colletotrichum gloeosporioides) papaya fruit (cv. Red Lady) for 76 h in three temperature regimes simulating different commercial air handling scenarios followed by storage for 7 days at 20 °C to simulate shelf life. The papayas in two fluctuating temperature regimes deviated from a semi-constant regime by being held for 1 h at 15 °C plus 1 h at 23.5 °C versus 2 h at 12 °C to simulate the period on the tarmac prior to loading onto an airplane, 7 h at 23.5 °C versus 7 h at 12 °C to simulate the flight period, and then for either 2 h at 1 °C or 2 h at 23.5 °C versus 2 h at 12 °C to simulate waiting on the tarmac after unloading the airplane. The fluctuating temperature regimes simulated actual conditions previously documented by us as encountered during ground and in-flight perishable handling operations. Overall, papayas handled in the fluctuating cold or warm temperature regimes lost more weight, developed objectionable color, were softer and more shriveled, had more decay, and had lower soluble solids, acidity and ascorbic acid contents than papayas handled in the semi-constant temperature regime. In addition, papaya handled in the fluctuating cold temperature regime that included exposure to 1 °C for 2 h developed chilling injury symptoms after being transferred to 20 °C for 7 days. Abraded and abraded + inoculated papaya fruit handled in semi-constant temperature developed less decay during shelf life than those stored in fluctuating temperatures. Loss of firmness and development of chilling injury symptoms were the primary quality factors that limited the shelf life of papaya fruit. Papaya from the first harvest and handled in a semi-constant temperature regime never became unacceptable for sale even after 7 days of shelf life. For papayas transported in fluctuating cold or warm temperature regimes, the greatest quality loss was noticeable during simulated air flight, during truck transportation from the airport to the warehouse and then to the supermarket, and during shelf life compared with warehouse storage at the grower, truck transportation to the airport, waiting on the tarmac, or backroom storage at the supermarket. The results indicate that fluctuating and/or high or low temperatures that are often encountered for as little as a few hours during handling operations, may result in a considerable amount of papaya rejected.

Short‐ and long‐term consequences of thermal variation in the larval environment of anurans

1. To survive adverse or unpredictable conditions in the ontogenetic environment, many organisms retain a level of phenotypic plasticity that allows them to meet the challenges of rapidly changing conditions. Larval anurans are widely known for their ability to modify behaviour, morphology and physiological processes during development, making them an ideal model system for studies of environmental effects on phenotypic traits. Although temperature is one of the most important factors influencing the growth, development and metamorphic condition of larval anurans, many studies have failed to include ecologically relevant thermal fluctuations among their treatments. 2. We compared the growth and age at metamorphosis of striped marsh frogs Limnodynastes peronii raised in a diurnally fluctuating thermal regime and a stable regime of the same mean temperature. We then assessed the long-term effects of the larval environment on the morphology and performance of post-metamorphic frogs. 3. Larval L. peronii from the fluctuating treatment were significantly longer throughout development and metamorphosed about 5 days earlier. Frogs from the fluctuating group metamorphosed at a smaller mass and in poorer condition compared with the stable group, and had proportionally shorter legs. 4. Frogs from the fluctuating group showed greater jumping performance at metamorphosis and less degradation in performance during a 10-week dormancy. Treatment differences in performance could not be explained by whole-animal morphological variation, suggesting improved contractile properties of the muscles in the fluctuating group.

Environmental fluctuations facilitate species co-existence and increase decomposition in communities of wood decay fungi

A fluctuating environment may facilitate co-existence of species, and high species richness may be important for maintaining ecosystem processes under changing environmental conditions. A positive relationship has been found between species richness and primary production in many experiments, and there is now an increasing interest whether similar relationships also apply to microorganisms and decomposition. Basidiomycete fungi are the primary decomposers of wood with the functional groups brown and white rot fungi, which differ with respect to decay strategy. In this study, 16 species of boreal wood decay fungi, 8 brown rot fungi and 8 white rot fungi, were assembled in artificial communities. The aims were to study species persistence, wood decomposition and metabolic efficiency in fungal communities of increasing levels of species richness under constant and fluctuating temperature regimes. Species persistence was generally low, but temperature fluctuations facilitated co-existence of species. Decomposition was highest at intermediate diversity levels under the fluctuating temperature regime. Metabolic efficiency, estimated as the amount of fungal mycelium formed per amount of degraded wood, decreased with increasing community complexity under the fluctuating temperature regime. Brown and white rot fungi differed in decomposition rates and metabolic efficiency, but no synergistic effects were found where the two functional groups were mixed. This study demonstrates how niche differentiation in a variable environment may act to maintain diversity and function. In our experiment, differences in functional responses to the varying temperature rather than resource partitioning between brown and white rot fungi had significant effects. Niche differentiation is likely to be particularly important in maintaining species diversity in communities of wood decaying fungi, which are known from previous studies to be characterised by intense competition, and where otherwise metabolically costly interactions lead to species exclusion and dominance by highly competitive species.

Effects of a fluctuating temperature regime experienced by Daphnia during diel vertical migration on Daphnia life history parameters

Many freshwater zooplankton species perform a diel vertical migration (DVM) and spend the day within the lower, colder hypolimnion of stratified lakes. Trade-offs that arise from this migration have already attracted much attention and the cold temperature in the hypolimnion is thought to be the main cost of this behaviour. In this study we additionally looked at the extra costs daphnids have from being exposed to a fluctuating temperature regime (cold during the day and warm during the night) which is less well studied until today. In our experiment Daphnia hyalina Leydig and Daphnia magna Straus either spent 24 h in constant warm water (19 °C), 24 h in constant cold water (12 °C), or spent 12 h in warm and 12 h in cold water in an alternating way (fluctuating temperature regime). We expected the values of the life history parameters of Daphnia in the fluctuating temperature regime to be exactly halfway between the values of the life history parameters in the warm and cold treatments because the daphnids spent exactly half of the time in warm water, and half of the time in cold water. Concordant with earlier studies our results showed that age at first reproduction and egg development time were reduced at higher temperatures. In the fluctuating temperature regime the values of both parameters were exactly halfway between the values at permanently warm and cold temperature regimes. In contrast, somatic growth was higher at higher temperatures but was lower in the fluctuating temperature regime than expected from the mean somatic growth rate. This suggests that a fluctuating temperature regime experienced by migrating daphnids in stratified lakes involves additional costs for the daphnids.

Modelling Development of Reptile Embryos under Fluctuating Temperature Regimes

An increase in temperature, within bounds, will accelerate development of reptile embryos, and morphogenesis can be normal over a range of temperatures despite those varying rates of development. Less well understood is the form of the relationship that best describes variation in developmental rate with temperature. In this article, we apply a linear degree.hour model, an empirical curvilinear model, a biophysical model, and a polynomial model to data on rates of embryonic development and temperature in the pig-nosed turtle Carettochelys insculpta from northern Australia. The curvilinear models, which have been applied with success to development of insects, describe the embryonic development of turtles well. When fluctuating temperatures extend beyond the constant temperatures that support successful incubation, the curvilinear models continue to perform well, whereas the linear model predictions fail. Sensitivity analysis indicates that under some circumstances, incubation duration may be increased by diel temperature fluctuations, independent of an influence of mean temperature. In other circumstances, incubation duration may be decreased, and in still other circumstances, diel temperature fluctuations will have no impact on incubation duration. This adds an additional dimension to our understanding of how thermal regimes can be selected or manipulated by reptiles to optimise incubation duration and the timing of offspring emergence.

Ecotypic differentiation and phenotypic plasticity in reproductive traits of Armadillidium vulgare (Isopoda: Oniscidea)

Armadillidium vulgare differed in growth and survivorship on two field sites. Growth rates were higher at a site with consistently higher quality food than at the other site where less high-quality food was produced and which was less predictably accessible. Survivorship was higher at the second site where temperature fluctuations were consistently smaller. Individuals from the two populations were kept for 6 months under the same food and temperature conditions and patterns of resource allocation to reproductive traits analysed. Members of the population from the site with good growth conditions had significantly higher reproductive allocation, by 13.5%, and larger broods, by 9.1%, than those from the site with poor growth conditions. Contrary to theoretical predictions, they also had significantly larger offspring, by 7.5% dry mass. Larger offspring survived better than small ones. This differential survivorship, by 20% for a 3.4% difference in live mass, was much more pronounced under conditions of moisture stress and under fluctuating temperature regimes. Larger offspring would therefore be at a selective advantage on the site with more severe temperature fluctuations. Phenotypic plasticity in reproductive traits in response to experimental changes in food quality, temperature and crowding were monitored. Reproductive allocation was increased by 20.8% under conditions of higher food quality, by 14.7% at higher temperatures, and by 12.5% under less crowded conditions. Brood size, but not offspring dry mass, increased when food quality increased. When crowding increased by 25.0%, the size of broods remained the same but the dry mass of individual offspring decreased by 11.2%. Members of the population from the site with more variable access to high-quality food showed more plasticity in reproductive traits in response to changes in food supply than members of the population from the site with the more predictable food supply. Members of the population from the site with more stable temperatures showed less plasticity to temperature changes than members of the population from the site with greater temperature fluctuations. It is concluded that the observed microevolutionary processes and phenotypic plasticity have adaptative value as responses to spatial and temporal heterogeneity in environmental conditions.

Developmental Time of <I>Melanoplus sanguinipes</I> (Orthoptera: Acrididae) at High Latitudes

Rates of development of Melanoplus sanguinipes F. from Alaska were determined at eight constant temperatures between 21 and 42°C. Diurnally alternating temperatures were used to estimate rates of development at temperatures too low for nymphs to complete development under constant temperatures. Two previously published equations were fit to these data and used to predict developmental rates as a function of temperature. The first equation, nonlinear and only approaching zero rate of development asymptotically, was fit to the data from constant and alternating temperature treatments. The second equation, which included an intercept, was fit to the data from constant temperature treatments only. Estimated developmental times based on these equations were tested against observed developmental times in two fluctuating temperature regimes in growth chambers, and two seasons of field sampling. Elevation of body temperature of grasshoppers above ambient temperatures in the field was modeled as a linear function of solar irradiance, based on field measurements. The effect of behavioral thermoregulation on nymphal developmental times in the field was estimated using standard air temperatures and solar-adjusted temperatures. Rates of development under most of the constant temperature treatments were higher than any previously published for M. sanguinipes. Estimated rates of development in the field using air temperatures only were about one-half those using solar-adjusted temperatures. Observed developmental times in the field were 45 and 42 d in 2000 and 2002, respectively. Because of local adaptation and behavioral thermoregulation, duration of nymphal stages in M. sanguinipes is relatively independent of latitude.

Spawning of captive Senegal sole ( Solea senegalensis) under a naturally fluctuating temperature regime

Senegal sole aquaculture is at present limited due to poor reproduction of captive breeders in many facilities. Temperature seems to play an important role in controlling reproduction of Solea senegalensis, and differences in temperature regimes followed by various hatcheries are likely to be responsible for lack of success in some of them. This work describes the reproduction of captive soles, held in facilities that used water at ambient temperature, from a marshy environment where this species naturally breeds. Acclimated sole breeders were kept for two consecutive years. The main spawning period occurred from February to May, with a secondary spawning in autumn. Total yearly fecundity ranged from 1.15×10 6 to 1.65×10 6 eggs kg −1 body weight. Of the total egg batches produced, only 5.4% corresponded to autumn spawns. The male population was found to produce sperm all year round, with a maximum proportion of 100% occurring in spring, and a minimum proportion of around 50% in summer. Females showed the more developed ovary stages from October to May, with partial regression in the summer months. During the main spawning period, eggs were produced between 46% and 69% of days. Spawning took place at temperatures from 13 to 23 °C, although higher fecundities ( P<0.05) occurred between 15 and 21 °C. Within the range between 17 and 20 °C, the mean number of spawned eggs was 29,600±21,600 eggs day −1 kg −1. Most of the eggs (65–73%) were produced after temperature increased up to 2.5 °C within 3 days prior to spawning. Mean egg fertilization was 63.1±17% (year 2002) and 44.9±18% (year 2003), and hatching rates varied from 69.7±24% (2002) to 56.5 ±25% (2003). Weak correlations were found between either fertilization or hatching and fecundity, whereas a positive regression ( P<0.05) indicated that higher hatching rates were achieved when fertilization increased. A weak, but significantly ( P<0.05) positive correlation was found between egg fertilization and the spawning temperature. Present results indicate temperature is an important control factor for reproduction of S. senegalensis, and suggest it can be used to properly manage controlled captive reproduction of this species.

Temperature and Pomaceous Flower Age Related to Colonization byErwinia amylovoraand Antagonists

ABSTRACT Fire blight of apple and pear is initiated by epiphytic populations of Erwinia amylovora on flower stigmas. Predicting this disease and managing it with microbial antagonists depends on an understanding of bacterial colonization on stigmas. Detached 'Manchurian' crab apple flowers were inoculated with E. amylovora and subjected to a range of constant temperatures or various fluctuating temperature regimes. Results may have application to disease risk assessment systems such as the Cougarblight model, which now are based on in vitro growth of the pathogen. In other experiments, detached crab apple flowers and attached 'Gala' apple flowers were maintained at different temperatures for various periods before inoculation with E. amylovora or antagonists (Pseudomonas fluorescens strain A506 and Pantoea agglomerans strains C9-1 and E325). Maximum stigma age supporting bacterial multiplication decreased as temperature increased, and was reduced by pollination. Stigmas were receptive to bacteria at ages older than previously reported, probably due to less interference from indigenous organisms. The study revealed antagonist limitations that possibly affect field performance (e.g., the inability of strain A506 to grow on relatively old stigmas conducive to the pathogen). Such deficiencies could be overcome by selecting other antagonists or using antagonist mixtures in the orchard.

Effects of temperature regime on the respiratory activity of developmental stages of Lumbricus rubellus (Lumbricidae)

Rates of carbon dioxide production of cocoons, juveniles and matures of Lumbricus rubellus were measured at five constant (2°C, 5°C, 10°C, 15°C, 20°C) and three diurnally fluctuating temperature regimes (0–10°C, 5–15°C, 10–20°C) covering the whole range of temperature conditions experienced by this species in forests in Central Germany. Respiration rates of developmental stages significantly increased with temperature both under constant and fluctuating regimes. Overall, at constant temperature regimes Q 10 values for cocoons, juvenile and mature earthworms were 1.6, 2.7 and 2.0, respectively. At fluctuating temperature regimes Q 10 values were generally higher with 2.4, 3.6 and 3.5 for cocoons, juvenile and mature earthworms, respectively. At the same mean temperature respiration rates at fluctuating regimes exceeded those at constant regimes in all developmental stages.

Effects of density and temperature regime on respiratory activity of the epigeic earthworm species Lumbricus rubellus and Dendrobaena octaedra (Lumbricidae)

Earthworm population densities vary strongly in space and time, and it has been hypothesised that the metabolic activity of the epigeic species Lumbricus rubellus and Dendrobaena octaedra is influenced by the presence of conspecifics. Carbon dioxide production of mature earthworms of these two species kept separately or in groups of two ( L. rubellus) and three individuals ( D. octaedra) were measured at constant and diurnally fluctuating temperature regimes. In L. rubellus respiration rates at constant and fluctuating regimes did not differ between specimens kept individually and in groups. In contrast, in D. octaedra both respiration rates and reproduction were significantly lower in earthworms kept in groups as compared to specimens kept individually.

Thermal Attributes of Rock Weathering: Zonal or Azonal? A Comparison of Rock Temperatures in Different Environments

Recent investigations into mechanical weathering in cold environments have highlighted products similarities to those of hot deserts. Although general temperature conditions between these two settings are obviously different on the basis of absolute air temperatures, the zonality with respect to thermal changes affecting the rock is less apparent. Data are presented here from four diverse environmental settings with particular emphasis on the fluctuating temperature regime as applicable to rock thermal stress fatigue and thermal shock. The data focus on diurnal oscillations and short-duration rapid changes on rock surfaces at sites in the Antarctic, sub-Antarctic, and at two southern African sites. Comparisons show that different climatic regimes may not be distinctive with respect to rock thermal changes. The azonality is strongly apparent when contrasting the two African sites, a hot desert and cooler alpine setting, in terms of diurnal fluctuations where very similar values are recorded. Overall temperature ranges measured at the Antarctic site approach the magnitude of those in southern Africa, and all sites show a high potential for thermal shock under rapid temperature changes. These findings highlight potential azonality with respect to thermally induced rock weathering and shift the emphasis in cross-climate comparisons to detailed considerations of the moisture regime.

Dormancy patterns, germination ecology, and seed-bank types of twenty temperate fen grassland species

Abstract The germination ecology, including primary and secondary dormancy, mortality of seeds, and seed-bank type, of 20 fen grassland species from Northern Germany was investigated using a combination of burial and germination experiments. To analyze primary dormancy and effects of after-ripening (dry storage for 28 days) on freshly matured seeds, germination was measured at two fluctuating temperature regimes (15/25°C and 5/15°C) in the light and in darkness. Temporal changes in dormancy were investigated by burying seeds at 8–10 cm depth in nylon bags, exhuming samples at bimonthly intervals over a period of two years, and analyzing germination at the above-mentioned temperature and light treatments. Additional seed samples were retrieved five years after burial to determine seed longevity and seed-bank type. Freshly matured seeds of all species except Bromus racemosus showed primary dormancy. Dry after-ripening significantly increased germination in Parnassia palustris and Triglochin palustre. Mortal...

A Comparison of the Development Rate of Protophormia Terraenovae (Robineau-Desvoidy) Raised under Constant and Fluctuating Temperature Regimes

ABSTRACTExperiments were conducted to compare development rates of the blow fly species Protophormia terraenovae (Robineau-Desvoidy) (Diptera Calliphoridae) at constant and fluctuating temperatures. Protophormia terraenovae were raised from egg to adult outdoors under naturally fluctuating temperatures. Minimum times to reach five stages of development were noted (1st, 2nd, and 3rd instar, pupae, and adult). A data logger recorded temperature every 30 minutes. Once the adult stage was reached, the overall mean temperature during the experiment was calculated (19.7°C ± 0.1 °C). Next, P. terraenovae were raised from egg to adult within an incubator in the laboratory at a constant temperature of 20°C ± 0.1°C. Accumulated degree hours (ADH) were calculated for both experiments, at all five stages of development. Protophormia terraenovae raised under a constant temperature regime reached 1st, 2nd, and 3rd instar stages significantly faster than those raised under a fluctuating temperature regime (P = 0.016, t = 3.99, df = 4; P = 0.007, t = 6.79, df = 3; P = 0.043, t = 2.92, df = 4, respectively). At the pupae and adult stages, there was no difference in the development rate between the two temperature regimes (P < 0.05).

Heat and cold-induced male sterility in Drosophila buzzatii: genetic variation among populations for the duration of sterility.

Here we studied three phenotypic traits in Drosophila buzzatii that are strongly effected by temperature, and are expected to be closely associated with fitness in nature. The traits measured were thermal threshold of male sterility, time for males to gain fertility when reared at a sterility-inducing temperature and transferred to 25 degrees C on eclosion and survival after development. The last two traits were measured under four temperature regimes, constant 12 degrees C, 25 degrees C, 31 degrees C, and fluctuating 25 degrees C (18 h) and 38 degrees C (6 h). We looked for genetic variation in these traits and relations among them in four lines of D. buzzatii originating from Argentina and Tenerife. The thermal threshold of heat-induced male sterility was found to lie within the range of 30.0-31.0 degrees C. When measuring the time for males to gain fertility, males reared at a nonstressful temperature (25 degrees C) were fertile 58-67 h after emergence with only minor differences among lines. When reared constant 31 degrees C, males were fertile 174-225 h after hatching. The Argentinean lines were significantly faster in recovering from sterility than were the lines from Tenerife. When reared in a fluctuating temperature regime, differences among lines increased, dividing the lines into three significantly different groups, with a sterility period of 135-215 h. When reared at 12 degrees C from the pupal stage, males were fertile after 106-130 h with significant difference in the variance but not in the mean duration of sterility. Significant differences in viability were found among development temperatures, but not among lines, and viability and the duration of sterility seem to be genetically independent.

Thermal adaptation in Drosophila serrata under conditions linked to its southern border: unexpected patterns from laboratory selection suggest limited evolutionary potential.

To investigate the ability of Drosophila serrata to adapt to thermal conditions over winter at the species southern border, replicate lines from three source locations were held as discrete generations over three years at either 19 degrees C (40 generations) or temperatures fluctuating between 7 degrees C and 18 degrees C (20 generations). Populations in the fluctuating environment were maintained either with an adult 0 degrees C cold shock or without a shock. These conditions were expected to result in temperature-specific directional selection for increased viability and productivity under both temperature regimes, and reduced development time under the fluctuating-temperature regime. Selection responses of all lines were tested under both temperature regimes after controlling for carry-over effects by rearing lines in these environments for two generations. When tested in the 19 degrees C environment, lines evolving at 19 degrees C showed a faster development time and a lower productivity relative to the other lines, while cold shock reduced development time and productivity of all lines. When tested in the fluctuating environment, productivity of the 7-18 degrees C lines selected with a cold shock was relatively lower than that of lines selected without a shock, but this pattern was not observed in the other populations. Viability and body size as measured by wing length were not altered by selection or cold shock, although there were consistent effects of source population on wing length. These results provide little evidence for temperature-specific adaptation in D. serrata-although the lines had diverged for some traits, these changes were not consistent with a priori predictions. In particular, there was no evidence for life-history changes reflecting adaptation to winter conditions at the southern border. The potential for D. serrata to adapt to winter conditions may therefore be limited.