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.     

Specific dynamic action in the shore crab,Carcinus maenas (L.), in relation to acclimation temperature and to the onset of the emersion response

The rate of oxygen uptake (MO(2)) of shore crabs following a period of fasting varied directly with acclimation temperature, with a Q(10) of 2.96 between 7 degrees and 15 degrees C and a Q(10) of 2.11 between 15 degrees and 22 degrees C. The factorial rise in MO(2) following a meal (specific dynamic action [SDA]) ranged between 1.9 and 3.1 and varied with temperature, being highest at 15 degrees C and significantly lower at both 7 degrees and 22 degrees C, despite similar ration sizes in all groups. At 7 degrees C, the SDA coefficient and magnitude were significantly lower than at 15 degrees C, possibly due in part to the inhibition of protein synthesis. Both the time to peak and the duration of the SDA response were inversely related to temperature. SDA coefficients were inversely related to the amount of food consumed. The critical oxygen tension of inspired water (P(I)O(2)), which evoked the emersion response in fasted animals, increased with temperature and further increased at each temperature when the animals were fed. Thus, the threshold P(I)O(2) evoking the emersion response is directly related to relative metabolic oxygen demand in Carcinus.     

Effects of temperature and larval diet on development rates and survival of the dengue vector Aedes aegypti in north Queensland, Australia

Immature development times, survival rates and adult size (wing-lengths) of the mosquito Aedes aegypti (L.) (Diptera: Culicidae) were studied in the laboratory at temperatures of 10-40 degrees C. The duration of development from egg eclosion (hatching of the first instar) to adult was inversely related to temperature, ranging from 7.2 +/- 0.2 days at 35 degrees C to 39.7 +/- 2.3 days at 15 degrees C. The minimum temperature threshold for development (t) was determined as 8.3 +/- 3.6 degrees C and the thermal constant (K) was 181.2 +/- 36.1 day-degrees above the threshold. Maximum survival rates of 88-93% were obtained between 20 and 30 degrees C. Wing-length was inversely related to temperature. The sex ratio (female:male) was 1:1 at all temperatures tested (15, 20, 25 and 35 degrees C) except 30 degrees C (4:3). Under field conditions at Townsville and Charters Towers, north Queensland, the duration of immature development varied according to the container position (i.e. shaded or exposed) and the availability of food resources, as well as inversely with temperature. These data indicate that containers with an abundance of organic matter (e.g. those used for striking plant cuttings) or those amongst foliage or under trees (e.g. discarded plastic tubs and tyres) tended to produce the largest adult Ae. aegypti, which had faster development and better immature survival. As such progeny have been linked to a greater risk of dengue transmission, it would seem important to focus on control of such containers.     

Effect of water temperature on the development, release and survival of the triactinomyxon stage of Myxobolus cerebralis in its oligochaete host.

The development of the triactinomyxon stage of Myxobolus cerebralis and release of mature spores from Tubifex tubifex were shown to be temperature dependent. In the present work, the effect of temperature over a range of 5-30 degrees C on the development and release of the triactinomyxon stages of M. cerebralis was studied. Infected T. tubifex stopped releasing triactinomyxon spores 4 days after transfer from 15 degrees C to 25 degrees C or 30 degrees C. Transmission electron microscopic examinations of the tubificids held at 25 degrees C and 30 degrees C for 3 days showed that all developmental stages degenerated and transformed to electron-dense clusters between the gut epithelial cells of T. tubifex. In contrast, tubificid worms held at 5 degrees C and 10 degrees C examined at the same time were heavily infected with many early developmental stages of triactinomyxon. At 15 degrees C, the optimal temperature for development, maturing and mature stages of the parasite were evident. Infected T. tubifex transferred from 15 degrees C to 20 degrees C stopped producing triactinomyxon spores after 15 days. However, 15 days at 20 degrees C was not sufficient to destroy all developmental stages of the parasite. When the tubificid worms were returned to 15 degrees C, the one-cell stages and the binucleate-cell stages resumed normal growth. It was also demonstrated that T. tubifex cured of infection by holding at 30 degrees C for 3 weeks and shifted to 15 degrees C could be re-infected with M. cerebralis spores. The waterborne triactinomyxon spores of M. cerebralis did not appear to be as short-lived as previously reported. More than 60% of experimentally produced waterborne triactinomyxon spores survived and maintained their infectivity for rainbow trout for 15 days at water temperatures up to 15 degrees C. In natural aquatic systems, the triactinomyxon spores may survive and keep their infectivity for periods even longer than 15 days.     

Plasticity of Drosophila melanogaster wing morphology: effects of sex, temperature and density

In this paper we use an adjusted ellipse to the contour of the wings of Drosophila as an experimental model to study phenotypic plasticity. The geometric properties of the ellipse describe the wing morphology. Size is the geometric mean of its two radii; shape is the ratio between them; and, the positions of the apexes of the longitudinal veins are determined by their angular distances to the major axis of the ellipse. Flies of an inbred laboratory strain of Drosophila melanogaster raised at two temperatures (16.5°C and 25°C) and two densities (10 and 100 larvae per vial) were used. One wing of at least 40 animals of each sex and environmental condition were analyzed (total = 380), a measurement of thorax length was also taken. Wing size variation could be approximately divided into two components: one related to shape variation and the other shape independent. The latter was influenced primarily by temperature, while the former was related to sex and density. A general pattern could be identified for the shape dependent variation: when wings become larger they become longer and the second, fourth and fifth longitudinal veins get closer to the tip of the wing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intraspecific variation in temperature dependence of gas exchange characteristics among Plantago asiatica ecotypes from different temperature regimes

There are large inter- and intraspecific differences in the temperature dependence of photosynthesis, but the physiological cause of the variation is poorly understood. Here, the temperature dependence of photosynthesis was examined in three ecotypes of Plantago asiatica transplanted from different latitudes, where the mean annual temperature varies between 7.5 and 16.8 degrees C. Plants were raised at 15 or 30 degrees C, and the CO(2) response of photosynthetic rates was determined at various temperatures. When plants were grown at 30 degrees C, no difference was found in the temperature dependence of photosynthesis among ecotypes. When plants were grown at 15 degrees C, ecotypes from a higher latitude maintained a relatively higher photosynthetic rate at low measurement temperatures. This difference was caused by a difference in the balance between the capacities of two processes, ribulose-1,5-bisphosphate regeneration (J(max)) and carboxylation (V(cmax)), which altered the limiting step of photosynthesis at low temperatures. The organization of photosynthetic proteins also varied among ecotypes. The ecotype from the highest latitude increased the J(max) : V(cmax) ratio with decreasing growth temperature, while that from the lowest latitude did not. It is concluded that nitrogen partitioning in the photosynthetic apparatus and its response to growth temperature were different among ecotypes, which caused an intraspecific variation in temperature dependence of photosynthesis.     

Variation in subsurface seawater temperature off Discovery Bay, Jamaica and the U.S. Virgin Islands

Long-term, high accuracy seawater temperature data sets are essential in studies assessing environmental changes that may alter coral reef communities. Located at the approximately the same latitude, the subsurface seawater temperature (S3T) off Discovery Bay, Jamaica (DBJ) and the U.S. Virgin Islands (USVI) had the same overall mean temperature. The USVI S3T during the winter months is approximately 0.5 degrees C warmer than DBJ, while May - July at DBJ is approximately 1 degrees C warmer than USVI S3T. With the passing of tropical storms in 1995 and 1997 in the USVI S3T dropped as much as 1.5 degrees C within a 20 hr period and did not revert to the previous temperature during that calendar year. Mean monthly S3T during 2000 and 2001 in the USVI was > 0.5 degrees C warmer than during similar periods in the early 1990s. Mean monthly S3T during 1999-2002 at DBJ was 0.27 degrees C cooler than during 1994-1995.     

Influence of photoperiod on low temperature acclimation for cold-hardiness in Drosophila auraria

ABSTRACT. Imagines of Drosophila auraria Peng, a reproductive diapause species, developed cold-hardiness at low temperatures to a greater extent when exposed to a diapause-inducing photoperiod (LD10:14 h) than when exposed to a diapause-preventing photoperiod (LD 16:8h). Imagines kept at 18°C, which was the temperature at which they were reared to eclosion, did not survive a test exposure to -5°C for 8 days regardless of age or photoperiod. When transferred to 10 or 5°C, either from eclosion or from 8 days after eclosion, the survival rate, on testing, rose with time since transfer and rose faster and higher with a photoperiod of LD 10:14h than with LD16:8h. Flies transferred to 15°C only showed improved ability to survive the test if they were kept in LD 10:14h. When cultured at 18°C to the age of 8 days after eclosion, diapause was terminated in about 30% of females even at LD 10:14h. In these post-diapause females the ability to develop cold-hardiness at lower temperatures was somewhat less than in the diapausing females, but apparently greater than in the non-diapause females. These results suggest that the physiological mechanism which promotes cold-hardiness under a diapause-inducing photoperiod is not directly linked to the process causing reproductive diapause.
In Sapporo, flies from a natural population became tolerant to cold in October when they entered diapause and daily mean temperature fell below 15°C and the light/dark cycle fell below LD 12:12h.     

Influence of temperature on developmental rate,wing length,and larval head capsule size of pestiferous midge Chironomus crassicaudatus (Diptera: Chironomidae)

Larvae of Chironomus crassicaudatus Malloch were reared individually at nine constant temperatures from 12.5 to 32.5 degrees C (2.5 degrees C increments) for 120 d. Duration of immature stages (egg, four instars, and pupa), head capsule width of fourth instars, and wing length were recorded. Some adults emerged at all temperatures, except at 12.5 degrees C where individuals developed to fourth instars during the experiment. Sharpe and DeMichele's four-parameter model with high-temperature inhibition described the temperature-dependent developmental rates. The slowest development was observed at 15 degrees C, with developmental rate peaking between 25 and 27.5 degrees C. Developmental rate increased rapidly with increasing temperature up to 20 degrees C, slowed between 20 and 27.5 degrees C, and decreased at temperatures >27.5 degrees C. No developmental inhibition at high temperatures was observed in eggs. The most apparent high-temperature inhibition of development was recorded in fourth instars, which comprised the largest proportion of developmental time. Males developed faster than females, but females had wider larval head capsules and longer wings than males. Adult size was negatively related with temperature in both sexes, but this relationship was steeper in males than in females. Larval size peaked at 20 degrees C, whereas the head capsule width was reduced at temperatures higher and lower than 20 degrees C.     

The effects of acute and developmental temperature on burst swimming speed and myofibrillar ATPase activity in tadpoles of the Pacific tree frog, Hyla regilla

The effects of acute and developmental temperature on maximum burst swimming speed, body size, and myofibrillar ATPase activity were assessed in tadpoles of the Pacific tree frog, Hyla regilla. Tadpoles from field-collected egg masses were reared in the laboratory at 15 degrees (cool) and 25 degrees C (warm). Body size, maximum burst swimming speed from 5 degrees to 35 degrees C, and tail myofibrillar ATPase activity at 15 degrees and 25 degrees C were measured at a single developmental stage. Burst speed of both groups of tadpoles was strongly affected by test temperature (P<0. 001). Performance maxima spanned test temperatures of 15 degrees -25 degrees C for the cool group and 15 degrees -30 degrees C for the warm group. Burst speed also depended on developmental temperature (P<0.001), even after accounting for variation in body size. At most test temperatures, the cool-reared tadpoles swam faster than the warm-reared tadpoles. Myofibrillar ATPase activity was affected by test temperature (P<0.001). Like swimming speed, enzyme activity was greater in the cool-reared tadpoles than in the warm-reared tadpoles, a difference that was significant when assayed at 15 degrees C (P<0. 01). These results suggest a mechanism for developmental temperature effects on locomotor performance observed in other taxa.     

Body size and cell size in Drosophila: the developmental response to temperature

In Drosophila, like most ectotherms, development at low temperature reduces growth rate but increases final adult size. Cultures were shifted from 25 degrees C to low (16.5 degrees C) or to high (29 degrees C) temperature at regular intervals through larval and pupal stages, and the flies of both sexes showed an increase or decrease, respectively, in the size of thorax, wing and abdominal tergite. Size changes in the wing blade resulted from changes in the size of the epidermal cells (with only a small increase in cell number in males reared at low temperature). The temperature-shifts became less effective as they were made at successively later developmental stages, demonstrating a cumulative effect of temperature on adult size. The thorax and wing develop from the same imaginal disc, with most cell division occurring in larval stages, but they differ in timing of temperature sensitivity, which extends only to pupariation or into the late pupal stage, respectively. Growth of the adult abdomen occurs largely after pupariation but its size is temperature-sensitive through both larval and pupal stages. We discuss growth control in Drosophila and the likely effects of temperature on food assimilation, growth efficiency and allocation of nutrients to the production of different tissues.     

Low temperature cure of a male killing agent in Drosophila melanogaster

Environmental factors can affect transmission or phenotype expression of selfish cytoplasmic endosymbionts such as embryonic male killers. Temperature is one factor that usually affects the transmission rate of selfish cytoplasmic endosymbionts. Heat cures have been described for several host-parasite systems, cold cures, however, are rare. We report a temperature cure of the Drosophila melanogaster male-killing agent, which occurs when flies are raised at 16.5 degrees C. Flies grown at 20, 24, and 28 degrees C maintained an extremely female biased sexual proportion.     

Expression of warm temperature acclimation-related protein 65-kDa (Wap65) mRNA, and physiological changes with increasing water temperature in black porgy, Acanthopagrus schlegeli

We isolated the warm temperature acclimation-related protein 65-kDa (Wap65) cDNA from the liver of black porgy and investigated the expression by increasing water temperature in black porgy, Acanthopagrus schlegeli. Black porgy Wap65 full-length cDNA consists of 1,338 nucleotides, including an open reading frame, predicted to encode a protein of 425 amino acids and showed high homology to pufferfish (79%), Medaka (73%), carp (70%), and goldfish (68%) Wap65. Increase in water temperature (20 degrees C --> 30 degrees C; 1 degrees C/day) induced the rise of Wap65 mRNA expression in liver of black porgy. Also, the levels of cortisol and glucose in plasma were significantly higher at 30 degrees C than at 20 degrees C. To determine the high water temperature stressor specificity of the induction of Wap65, black porgy were transferred from seawater (SW) to freshwater (FW) for 24 hr. Wap65 expression was not detected when the fish were transferred from SW to FW (in fish transferred from SW to FW), although the levels of cortisol and glucose in plasma were increased. These results suggest that increase in Wap65 gene is related to high water temperature stress and play important roles in high water temperature environment of black porgy.     

Ambient temperature modulates hypoxic-induced changes in rat body temperature and activity differentially

When rats, acclimated to an ambient temperature (T(a)) of 29 degrees C, are exposed to 10% O(2) for 63 h, the circadian rhythms of body temperature (T(b)) and level of activity (L(a)) are abolished, T(b) falls to a hypothermic nadir followed by a climb to a hyperthermic peak, L(a) remains depressed (Bishop B, Silva G, Krasney J, Salloum A, Roberts A, Nakano H, Shucard D, Rifkin D, and Farkas G. Am J Physiol Regulatory Integrative Comp Physiol 279: R1378-R1389, 2000), and overt brain pathology is detected (Krasney JA, Farkas G, Shucard DW, Salloum AC, Silva G, Roberts A, Rifkin D, Bishop B, and Rubio A. Soc Neurosci Abstr 25: 581, 1999). To determine the role of T(a) in these hypoxic-induced responses, T(b) and L(a) data were detected by telemetry every 15 min for 48 h on air, followed by 63 h on 10% O(2) from rats acclimated to 25 or 21 degrees C. Magnitudes and rates of decline in T(b) after onset of hypoxia were inversely proportional to T(a), whereas magnitudes and rates of T(b) climb after the hypothermic nadir were directly proportional to T(a). No hyperthermia, so prominent at 29 degrees C, occurred at 25 or 21 degrees C. The hypoxic depression of L(a) was least at 21 degrees C and persisted throughout the hypoxia. In contrast, T(a) was a strong determinant of the magnitudes and time courses of the initial fall and subsequent rise in T(b). We propose that the absence of hyperthermia at 21 and 25 degrees C as well as a persisting hypothermia may protect the brain from overt pathology.     

The effect of temperature and humidity on the bionomics of six African egg parasitoids (Hymenoptera: Trichogrammatidae)

The life table statistics of six native Kenyan species/strains of Trichogramma and Trichogrammatoidea were established using a factitious host Corcyra cephalonica, Stainton (Lepidoptera: Pyralidae), at eight different temperatures (10, 15, 20, 25, 28, 30, 32 and 35 degrees C) and two humidity levels (40-50 and 70-80%). The objective was to select insects with superior attributes for augmentative release against lepidopteran pests in horticultural crops. Both temperature and humidity affected developmental time and life table parameters of the parasitoids but temperature played a more critical role. Developmental time was inversely related to temperature. The intrinsic and finite rates of increase increased with temperature up to 30 degrees C. Both net reproduction rate and intrinsic rate of increase were higher at the lower humidity. Temperature inversely affected generation time of parasitoid strains regardless of the relative humidity. Two strains of Trichogramma sp. nr. mwanzai collected from both low and medium altitudes and Trichogrammatoidea sp. nr. lutea from the mid-altitudes, were better adapted to both low and high temperatures than the other strains, as indicated by the high intrinsic and net reproductive rates, at both humidity levels. These three strains appear to be promising candidates for augmentation biocontrol against the African bollworm Helicoverpa armigera in Kenya.     

Effects of temperature and temperature-steps on circadian locomotor rhythmicity in the blow fly Calliphora vicina

The free-running period (in darkness) of the locomotor activity rhythm in adult blow flies (Calliphora vicina) was temperature-compensated between 15 and 25 degrees C, showing Q(10) values between 0.98 and 1.04. Single steps-up (20 to 25 degrees C) or steps-down (20 to 15 degrees C) in temperature caused stable phase shifts of the activity rhythm, giving rise to temperature-step phase response curves (PRCs) with both advances and delays. Phase advances, however, were dominant for steps-up, and phase delays for steps-down; the two PRCs were almost "mirror images" of each other. Following protocols introduced by Zimmerman et al. [(1968) Temperature compensation of the circadian oscillation in Drosophila pseudoobscura and its entrainment by temperature cycles, Journal of Insect Physiology, 14, 669-684] for the rhythm of pupal eclosion in Drosophila pseudoobscura, the steps-up and steps-down PRCs for C. vicina were used to compute a theoretical PRC for a 6 h low temperature pulse, and from this a theoretical steady-state phase relationship of the locomotor activity rhythm to a train of such pulses making up a temperature cycle (18 h at 20 degrees and 6 h at 15 degrees C).     

Effects of temperature on the immature development of the stone leek leafminer Liriomyza chinensis (Diptera: Agromyzidae)

The effect of nine constant temperatures (15, 17.5, 20, 22.5, 25, 27.5 30, 32.5, and 35 degrees C) on the development of the stone leek leafminer, Liriomyza chinensis (Kato), on Japanese bunching onion, Allium fistulosum L., was studied in the laboratory. Developmental times for immature stages were inversely proportional to temperature between 15 and 30 degrees C but increased at 32.5 degrees C. Total developmental times from egg to adult emergence decreased from 69.6 to 17.1 d for temperatures from 15 to 30 degrees C, with pupae requiring more time for development than the combined egg and larva stages. Both linear and nonlinear (Logan equation VI) models provided a reliable fit of development rates versus temperature for all immature stages. The lower developmental thresholds that were estimated from linear regression equations for the egg, first, second, and third instars, total larva, egg-larval, pupa, and total combined immature stages were 12.1, 10.6, 13.6, 8, 9.6, 11.3, 11.2, and 11.4 degrees C, respectively. The degree-day accumulation was calculated as 312.5 DD for development from egg to adult emergence. By fitting the nonlinear models to the data, the upper and optimal temperatures for egg, larva, pupa, and total immature stages were calculated as 37.8 and 31.7, 34.9 and 30.1, 35.8 and 30.6, and 35.0 and 30.9 degrees C, respectively. These data are useful for predicting population dynamics of L. chinensis under field conditions and determining the maximum proportion of susceptible individuals for facilitating improved timing of application of control measures.     

Development, survival and reproduction of black citrus aphid, Toxoptera aurantii (Hemiptera: Aphididae), as a function of temperature

The development, survival, and reproduction of the black citrus aphid Toxoptera aurantii (Boyer de Fonscolombe) were evaluated at ten constant temperatures (4, 7, 10, 15, 20, 25, 28, 30, 32 and 35 degrees C). Development was limited at 4 and 35 degrees C. Between 7 and 32 degrees C, developmental periods of immature stages varied from 44.2 days at 7 degrees C to 5.3 days at 28 degrees C. Overall immature development required 129.9 degree-days above 3.8 degrees C. The upper temperature thresholds of 32.3, 28.6, 29.3, 27.2, and 28.6 degrees C were determined from a non-linear biophysical model for the development of instars 1-4 and overall immature stages, respectively. Immature survivorship varied from 82.1 to 97.7% within the temperature range of 10-30 degrees C. However, immature survivorship was reduced to 26.3% at 7 degrees C and 33.1% at 32 degrees C. Mean adult longevity was the longest (44.2 days) at 15 degrees C and the shortest (6.2 days) at 32 degrees C. The predicted upper temperature limit for adult survivorship was at 32.3 degrees C. Total nymph production increased from 16.3 nymphs per female at 10 degrees C to 58.7 nymphs per female at 20 degrees C, declining to 6.1 nymphs per female at 32 degrees C. The estimation of lower and upper temperature limits for reproduction was at 8.2 and 32.5 degrees C, respectively. The population reared at 28 degrees C had the highest intrinsic rate of increase (0.394), the shortest population doubling time (1.8 days), and shortest mean generation time (9.5 days) compared with the populations reared at six other temperatures. The population reared at 20 degrees C had the highest net reproductive rate (54.6). The theoretical lower and upper temperature limits for population development, survival and reproduction were estimated at 9.4 and 30.4 degrees C, respectively. The biology of T. aurantii was also compared with three other citrus aphid species.     

WITHIN- AND BETWEEN-GENERATION EFFECTS OF TEMPERATURE ON THE MORPHOLOGY AND PHYSIOLOGY OF DROSOPHILA MELANOGASTER

We investigated the effects of developmental and parental temperatures on several physiological and morphological traits of adult Drosophila melanogaster. Flies for the parental generation were raised at either low or moderate temperature (18°C or 25°C) and then mated in the four possible sex-by-parental temperature crosses. Their offspring were raised at either 18°C or 25°C and then scored as adults for morphological (dry body mass, wing size, and abdominal melanization [females only]), physiological (knock-down temperature, and thermal dependence of walking speed), and life history (egg size) traits. The experiment was replicated, and the factorial design allows us to determine whether and how paternal, maternal, and developmental temperatures (as well as offspring sex) influence the various traits. Sex and developmental temperature had major effects on all traits. Females had larger bodies and wings, higher knock-down temperatures, and slower speeds (but similar shaped performance curves) than males. Development at 25°C (versus at 18°C) increased knock-down temperature, increased maximal speed and thermal performance breadth, decreased the optimal temperature for walking, decreased body mass and wing size, reduced abdominal melanization, and reduced egg size. Parental temperatures influenced a few traits, but the effects were generally small relative to those of sex or developmental temperature. Flies whose mother had been raised at 25°C (versus at 18°C) had slightly higher knock-down temperature and smaller body mass. Flies whose father had been raised at 25°C had relatively longer wings. The effects of paternal, maternal, and developmental temperatures sometimes differed in direction. The existence of significant within- and between-generation effects suggests that comparative studies need to standardize thermal environments for at least two generations, that attempts to estimate “field” heritabilities may be unreliable for some traits, and that predictions of short-term evolutionary responses to selection will be difficult.     

Effect of low stressful temperature on genetic variation of five quantitative traits in Drosophila melanogaster

A half-sib analysis was used to investigate genetic variation for three morphological traits (thorax length, wing length and sternopleural bristle number) and two life-history traits (developmental time and larva-to-adult viability) in Drosophila melanogaster reared at a standard (25 degrees C) and a low stressful (13 degrees C) temperature. Both phenotypic and environmental variation showed a significant increase under stressful conditions in all traits. For estimates of genetic variation, no statistically significant differences were found between the two environments. Narrow heritabilities tended to be higher at 13 degrees C for sternopleural bristle number and viability and at 25 degrees C for wing length and developmental time, whereas thorax length did not show any trend. However, the pattern of genetic variances and evolvability indices (coefficient of genetic variation and evolvability), considered in the context of literature evidence, indicated the possibility of an increase in additive genetic variation for the morphological traits and viability and in nonadditive genetic variation for developmental time. The data suggest that the effect of stressful temperature may be trait-specific and this warns against generalizations about the behaviour of genetic variation under extreme conditions.