Hormonal control of pupal coloration in the painted lady butterfly Vanessa cardui

Pupae of the painted lady butterfly Vanessa cardui exhibit pupal color polyphenism consisting of white, dark and intermediate types. We investigated environmental factors affecting pupal coloration and the physiological mechanisms underlying the control of pupal color polyphenism in this species. Over 80% of larvae reared at 16 °C developed into pupae of dark types, whereas over 82% of larvae at 32 °C developed into pupae of white types irrespective of long/short-day photoperiod conditions. When mature larvae reared at 32 °C were ligatured between thoracic and abdominal parts at three different pharate pupal stages, all of the head-thoracic parts developed into white pupae regardless of pupal stage, but all abdominal parts ligatured at the early pharate pupal stage only developed into dark pupae. These results indicate that temperature during larval stages is an important element affecting pupal coloration as an environmental cue in V. cardui, and that a factor(s) inducing white pupae is released from head-thoracic parts under conditions of high temperature. Additionally, when ligatured abdomens destined to develop into dark pupae were treated with crude extracts prepared from the central nervous system, all of the ligatured abdomens developed into white pupae at a level dependent on dose and pupal stage. These results suggest that the factor inducing white pupae is a key molecule controlling pupal color polyphenism in V. cardui.     

幼虫密度对草地螟食物利用率及消化酶活性的影响

为了阐明草地螟Loxostege sticticalis大发生种群幼虫取食行为特征, 在室内条件下（温度22±1℃, 相对湿度70%）对不同幼虫密度［1, 10, 30头/瓶（650 mL）］饲养草地螟幼虫的食物利用率及消化酶活性进行了研究。结果表明： 幼虫中等（或高）密度对草地螟幼虫相对中肠重量、 相对取食量、 粪便干重、 食物利用率和近似消化率及总蛋白酶和亮氨酸氨肽酶活性影响显著。幼虫相对中肠重量以10头/瓶的幼虫密度最大, 1头/瓶的幼虫密度最小。随着幼虫密度的增加, 幼虫相对取食量和粪便干重增加, 而虫体干重减轻, 幼虫食物利用率降低。幼虫密度30头/瓶的幼虫相对取食量和粪便干重显著高于1和10头/瓶的, 而30头/瓶的幼虫食物利用率显著低于1头/瓶的。幼虫近似消化率随幼虫密度的逐渐增加而显著降低。幼虫密度10头/瓶的幼虫总蛋白酶和亮氨酸氨肽酶的活性显著高于1和30头/瓶的, 而淀粉酶的活性受幼虫密度影响不显著。随幼虫密度的增加, 幼虫相对中肠重量与总蛋白酶和亮氨酸氨肽酶活性变化趋势较为一致, 消化酶活性的变化可能与相对中肠重量大小有关。因此, 幼虫密度是影响草地螟幼虫取食行为的重要因子, 这些结果为阐明草地螟大发生种群与一般种群的为害特征提供了重要理论依据。     

How caterpillars avoid overheating: behavioral and phenotypic plasticity of pipevine swallowtail larvae

We tested the hypothesis that larvae of the pipevine swallowtail butterfly, Battus philenor, employ behavioral and phenotypic plasticity as thermoregulatory strategies. These larvae are phenotypically varied across their range with predominantly black larvae (southeastern USA and California) and red larvae (western Texas, Arizona) occurring in different regions. Two years of field observations in south Texas indicate that the proportion of red larvae increases with increasing daily temperatures as the growing season progresses. Larvae were also observed to shift their microhabitats by climbing on non-host vegetation and avoided excessive heat in their feeding microhabitat. Larvae of ten half-sib families from populations in south Texas and California, reared under different temperature regimes in common garden experiments, exhibited plasticity in larval phenotype, with larvae from both populations producing the red phenotype at temperatures greater than 30°C and maintaining the black phenotype at cooler temperatures. However, larvae from Texas were more tolerant of higher temperatures, showing no decrease in growth rate in the highest temperature (maximum seasonal temperature) treatment, compared to the California population. In a field experiment, black larvae were found to have higher body temperatures when exposed to sunlight compared to red larvae. These results suggest that microhabitat shifts and the color polyphenism observed in pipevine swallowtail larvae may be the adaptive strategies that enable larvae to avoid critical thermal maximum temperatures.     

Seasonal polyphenism in larval type: rearing environment influences the development mode expressed by adults in the sea slug Alderia willowi

Dimorphisms occur when alternative developmental pathways produce discrete phenotypes within a species, and may promote evolutionary novelty in morphology, life history, and behavior. Among marine invertebrates, intra-specific dimorphism in larval type (poecilogony) is notably rare, but should provide insight into the selective forces acting on larval strategies. Most established cases of poecilogony appear to be allelic polymorphisms, with local expression regulated by population-genetic processes. Here, we present evidence that dimorphic larval development in the sea slug Alderia willowi is a seasonal polyphenism; the type of larvae produced by an adult slug depends on the rearing environment in which that slug matured. In field surveys of 1996-1999 and 2007-2009, the population in Mission Bay, San Diego (California, USA) produced only short-lived lecithotrophic larvae in summer and early fall, but a varying proportion of slugs expressed planktotrophy in winter and spring. In laboratory experiments, slugs reared under summer conditions (high temperature, high salinity) produced the highest proportion of lecithotrophic offspring, whereas winter conditions (low temperature, low salinity) induced the lowest proportion of lecithotrophy. The shift to a nondispersive morph under summer conditions may be an adaptive response to historical closure of coastal wetlands during the dry season in southern California, which would inhibit dispersal by larvae of back-bay taxa. In most animal polyphenisms, a single larval type is produced and the rearing environment determines which adult phenotype develops. In contrast, alternative larval morphs are produced by A. willowi in response to seasonal cues experienced by the adult stage, varying the phenotype and dispersal potential of offspring. As the only known case of polyphenism in mode of larval development, A. willowi should become a model organism for mechanistic studies of dimorphism and the evolution of alternative life histories.     

Entrainment of the circadian rhythm in larval release of the crab Dyspanopeus sayi by temperature cycles

Marine and estuarine crabs brood attached eggs, which hatch synchronously releasing larvae at precise times relative to environmental cycles. The subtidal crab Dyspanopeus sayi has a circadian rhythm, in which larvae are released within the 4-h interval after the time of ambient sunset. Previous studies demonstrated that the rhythm can be entrained by the light:dark cycle. Since subtidal crabs are also exposed to temperature fluctuations, an unstudied question was whether the circadian rhythm could be entrained by the diel temperature cycle. To answer this question, ovigerous D. sayi were entrained in darkness to 2.5, 5, and 10 °C temperature cycles that were reverse in phase from the ambient temperature cycle. After entrainment, larval release times were monitored in constant conditions of temperature and darkness with a time-lapse video system. The effectiveness of a temperature cycle to shift the timing of larval release increased as the magnitude of the temperature cycle increased and as crabs were exposed to increasing numbers of entrainment cycles. However, entrainment to a 10 °C cycle only lasted 2 days in constant conditions. When crabs were entrained to a light:dark vs. a 10 °C temperature cycle, the light:dark cycle was dominant for entrainment. Nevertheless, ovigerous crabs do sense temperature cycles and in areas where daylight is too low for entrainment, temperature cycles can be used to regulate the time of larval release.     

Density‐dependent polyphenism and baculovirus resistance in teak defoliator,Hyblaea puera (Cramer)

1. Field populations of the teak defoliator larvae, Hyblaea puera Cramer exhibit colour polyphenism under different population densities: greyish‐green with black‐ and orange‐coloured dorsal bands in low‐density endemic populations and uniformly black or intermediate colour during high‐density population. 2. The density dependence of colour polyphenism was confirmed by field monitoring of H. puera populations during 2008–2010. 3. The above findings were later substantiated by rearing H. puera larvae under different densities (i.e. solitary and crowded in the laboratory). Ninety one per cent of the solitary reared laboratory population developed bright coloration whereas, 92% of the group reared larvae turned to black. Eight per cent of larvae from both the rearing densities were of intermediate colour. 4. Density‐dependent resistance build‐up against H. puera nucleopolyhedrovirus by H. puera were tested using the fifth instar larvae. The results showed three‐fold increase of median lethal dose (LD₅₀) value for the group reared larvae (5332 polyhedral occlusion bodies/larvae) compared to the solitary reared ones (1727 polyhedral occlusion bodies/larva) and also significant difference for the mean time to death (3.6 and 3.3 days, respectively). 5. The study revealed the strong influence of larval density on H. puera larval melanism and resistance build‐up against H. puera nucleopolyhedrovirus.     

Fish drift in a Danube sidearm‐system: II. Seasonal and diurnal patterns

Seasonal and diurnal patterns of larval and juvenile fish drift were investigated in the Marchfeldkanal, a man‐made side branch of the Danube River near Vienna, Austria. A clear seasonal pattern with peak densities in mid‐June was found. Species composition varied over time, showed a site specific pattern and was dominated by tubenose goby Proterorhinus marmoratus . Water temperature was the main factor responsible for the increase of drift densities until the median drift date and repeated occurrence of early larval stages in drift indicated repeated spawning for many species. Significant differences in drift densities between different time periods of the day (day, dusk, night and dawn) were found for common bream Abramis brama , barbel Barbus barbus , chub Leuciscus cephalus , tubenose goby and roach Rutilus rutilus . The highest drift rates occurred at night (2200–0400 hours), with 86% of all larvae drifting during the hours of darkness. Fish larvae of different lengths drifting at different phases of the day were found for common bream, bleak Alburnus alburnus and chub, with largest larvae drifting during dusk (chub) and day (bleak and common bream). For bleak, all gudgeon species Gobio spp., tubenose goby, roach and for all cyprinid species combined, one 2 h night sample was found to be sufficient to predict the total 24 h drift.     

Matching field and laboratory environments: effects of neglecting daily temperature variation on insect reaction norms

The tropical butterfly, Bicyclus anynana, exhibits seasonal polyphenism. The wet season form has large eyespots and a pale band while these characters are much less conspicuous or absent in the dry season form. This plasticity is induced in the laboratory by use of a standard series of constant temperatures in the larval stage yielding a continuous norm of reaction. Butterflies in this study were reared from hatchling larvae in seven regimes which differed with respect to thermoperiod or photoperiod. The effect of rearing treatment on the phenotypic plasticity of the adult wing pattern, on life history traits and on larval feeding rhythms was investigated. Photoperiod had little effect except that constant light produced a higher mortality and tended to produce a longer development time. Thermoperiod had a major effect on the life history traits in comparison to a constant temperature regime with the same daily mean: development time was shorter with higher growth rates. The faster development was associated with a substantial shift in the wing pattern towards the wet season form. Larvae feed mostly at night both under constant and thermoperiod (cool nights) conditions. The results are discussed with respect to the necessity of matching field and laboratory environments in studies of norms of reaction or of life history traits where the adaptive significance of the variation is important. Fluctuating conditions in nature, especially with respect to thermoperiod, must be taken into account.     

Folivorous larvae on flowers: do autumnal moths benefit from catkins of the mountain birch?

Immature leaves of birches and other deciduous trees and shrubs are the principal food resource for the larvae of the autumnal moth, Epirrita autumnata (Borkhausen) (Lepidoptera: Geometridae). However, the larvae of this geometrid, which displays pronounced population cycles and causes massive forest defoliations in northernmost Europe, are also frequently found on the catkins of mountain birch, Betula pubescens ssp. czerepanovii (Orlova) Hämet-Ahti (Betulaceae). To examine whether autumnal moth larvae visit birch catkins for their high nutritional value, we conducted two growth experiments in which the larval diet was supplemented with male catkins, and a single test where female catkins were used. We found that the presence of male catkins in the larval diet had a positive effect on the larvae, in relation to their pupal mass (reflecting life span fecundity), survival probability, as well as the duration of the larval period. The presence of female catkins in the diet did not affect larval performance. Our findings suggest that young autumnal moth larvae actively move to male catkins, which provide a nutritional benefit and thus lead to a better performance compared with those feeding elsewhere. Another possible benefit for young larvae choosing the catkins instead of leaves may involve predator or parasitoid avoidance.     

Genetic and environmental sources of egg size variation in the butterfly Bicyclus anynana

By dividing families of the tropical butterfly, Bicyclus anynana, among different larval (including early pupal) and adult (including late pupal) temperatures, we investigate the genetic and environmental effects on egg size. Both sources of variation affected egg size to similar extents. As previously found in other arthropods, egg size tended to increase at lower temperatures. Our data suggest that the plastic response in egg size can be induced during the pupal stage. Females reared as larvae at the same high temperature tended to lay larger eggs when transferred to a lower temperature, either as prepupae or pupae, compared to those remaining at the high temperature. Additionally, females reared as larvae at different temperatures, but maintained at the same temperature from the early pupal stage onwards, laid larger eggs after larval growth at a low temperature. Heritability estimates for egg size were about 0.4 (parent-offspring regression) and 0.2 (variance component estimates using the full-sib families). Although there seemed to be some variation in the plastic response to temperature among families, genotype-environment interactions were nonsignificant.     

Seasonal distribution and duration of the planktonic stage of Dover sole, Solea solea, larvae in the Bay of Biscay: an hypothesis

The possibility of deriving a prediction about the effect of seasonal variations in the duration of the planktonic larval phase on the dispersal of larval Dover sole was investigated. During six cruises, from February to May 1992, the distribution of sole larvae was studied along a 100-km transect, from the offshore spawning grounds to the coastal nurseries of the Bay of Biscay (France). Samples ( n = 189) were collected with a suprabenthic sampler, and vertical profiles of water temperature and salinity were recorded simultaneously. Counts of otolith increments of larval stage 4b (onset of metamorphosis) were used to estimate the duration of the planktonic life. Duration of the larval phase decreases by about 15 days (37%) with water temperature increase (between 8° in February and 11.2° C in May). Sole larvae occur from the coastal area to 100 km offshore. Within the same cruise, no difference in the duration of the planktonic life was observed between the larvae caught in the onshore and the offshore area. In spite of seasonal differences in abundance, the extent and the shape of the larval distributions during the period of study suggest that the seasonal variations in the duration of the planktonic life did not affect the larval distribution.     

Effects of constant and varying temperatures on the development of blue swimmer crab (Portunus pelagicus) larvae: Laboratory observations and field predictions for temperate coastal waters

Temperature is widely held to be a critical factor for the development of marine invertebrate larvae. We investigated three specific aspects of this relationship for the blue swimmer crab, Portunus pelagicus, in a temperate gulf: (1) the effects of different but temporally constant temperatures on the survival and developmental period of larvae reared in the laboratory, (2) the effects of varying temperatures on the survival and developmental period of larvae reared in the laboratory, and (3) prediction of larval developmental periods under seasonal temperature changes found in the field. Temperature had a marked effect on larval survival. At constant temperatures of 22.5 and 25 °C larval survival was far greater than at lower temperatures down to 17 °C, and developmental period of the larval period was inversely related to (constant) temperature. However, larvae in temperate coastal waters will usually be exposed to seasonally varying, rather than constant, temperatures. To account for this, a larval developmental period model was created and then verified in the laboratory by rearing larvae under varying temperatures. Results of this work demonstrated that developmental periods were markedly different under constant versus varying temperature regimes. Using different temperature simulations for a temperate gulf (Gulf St Vincent, South Australia), the developmental period model predicted that in years of ‘average’ seasonal temperature changes, total larval developmental period could range from 26 to 45 days depending on the day of hatching. In such cases, peak postlarval settlement was predicted to occur between mid January and mid March. Results from this study also predict that larval survival (and thus postlarval settlement) will be maximised in years with abnormally warm summers. Whilst the developmental period model was used to make predictions of developmental period for P. pelagicus in a temperate gulf, it could readily be adapted to predict developmental periods in other coastal environments.     

Photoperiodic control of reproduction in the milkweed leaf beetle, Labidomera clivicollis

ABSTRACT. Photoperiod significantly affected reproduction in a central Texas population of the milkweed leaf beetle Labidomera clivicollis (Kirby) (Chrysomelidae). Laboratory reared beetles responded to a critical photoperiod of LD 12.5: 11.5; longer photoperiods induced reproduction, while shorter photoperiods induced diapause. Both larval and adult stages exhibited sensitivity to photoperiod. Beetles exposed to long days as adults reproduced regardless of photoperiod experienced as larvae. However, exposure to long days, as larvae but short days as adults also induced reproduction in an intermediate portion of the population. No larval instar appeared to be more sensitive than the others, and the proportion of the population responding did not increase with cumulative larval exposure to long days. Larval sensitivity to photoperiod may be ecologically significant to central Texas populations because it permits a substantial portion of the autumn generation to initiate a third generation in favourable years.     

Diapause and polyphenism of life-history of Lagria hirta

This paper is focused on diapause and polyphenism of development of Lagria hirta L. and tries to unravel its mechanism of life-history adaptation. Lagria hirta, distributed widely in Europe, has a strictly univoltine life cycle. The results showed that larval diapause and moulting polymorphism were the deciding factors that made L. hirta maintain its univoltinism and keep a flexible relation between seasonal changes and life-history phases. In the laboratory, larvae of this species were not able to pupate if kept at constant temperatures of 5 °, 10 °, 15 °, 20 °, 25 ° or 30 °C combined with a photoperiod of either LD (L16:D8) or SD (L8:L16). Pupation only occurred if larvae were reared at 15 °–25 °C when intervened by a three-month chilling at 5 °C in stages L₃, L₄, L₅ or L₆. A chilling treatment was shown to be obligatory for the termination of its larval diapause and had an accelerating and synchronizing effect on larval development. Larval diapause of L. hirta was characterized by no pupation and more moulting in advanced instars, longer duration of each single stage, and moulting desynchronization. Larval development was found to be variable with respect to the total number of instars: most larvae underwent a total of seven or eight moults; some larvae might even moult once or twice more, but they seldom pupated. It seemed that the choice for the 7-instar or the 8-instar development did not directly relate to any of the external conditions, such as temperature, photoperiod, and stages with chilling treatment. This polyphenism was observed in the same group under identical conditions and even in a single egg clutch. In L. hirta, overwintering in different stages of L₃–L₆, and choosing the 7- or 8-instar pathway of development are two features that increase the plasticity and flexibility in coordinating its life cycle with seasonal change, that varies unpredictably from year to year.     

A field study of potential ecological costs of resistance by ‘stem ducking’ in tall goldenrod,Solidago altissima

Culex quinquefasciatus Say (Diptera: Culicidae) is an abundant urban mosquito that is the vector of filariasis. Breeding in septic tanks, where there are very high levels of bacterial food, it is likely to have a different reaction to crowding compared with other mosquitoes. To test for the presence and type of crowding effects, four larval densities of C. quinquefasciatus varying from 0.4 to 3.2 larvae ml^?1 of water were reared in tubes. Mortality was found to greatly increase at densities above 0.8 larvae, whereas larval duration increased even above 0.4 larvae ml^?1. Changing the water in the tubes daily gave a small (but significant) response in reducing mortality and larval duration. However, when larvae kept at a low density shared the same water with larvae at high density, there was no chemical influence on their growth rate and mortality. The effect of crowding was primarily due to physical disturbances between larvae. When larvae were kept at a high density in the same volume of water, but in shallow trays with a large surface area and therefore much less contact between them, mortality was the same as for the lowest density. There was still, however, a significant increase in larval duration from 8.6 days at 0.4 larvae ml^?1 to 12.1 days at 3.2 larvae ml^?1. It is therefore concluded that the larvae respond to physical rather than chemical factors by prolonging larval development and having some increase in mortality.     

Sex-specific effects of developmental environment on reproductive trait expression in Drosophila melanogaster

Variation in the expression of reproductive traits provides the raw material upon which sexual selection can act. It is therefore important to understand how key factors such as environmental variation influence the expression of reproductive traits, as these will have a fundamental effect on the evolution of mating systems. It is also important to consider the effects of environmental variation upon reproductive traits in both sexes and to make comparisons with the environment to which the organism is adapted. In this study, we addressed these issues in a systematic study of the effect of a key environmental factor, variation in larval density, on reproductive trait expression in male and female Drosophila melanogaster. To do this, we compared reproductive trait expression when flies were reared under controlled conditions at eight different larval densities that covered a 20-fold range. Then, to place these results in a relevant context, we compared the results to those from flies sourced directly from stock cages. Many reproductive traits were surprisingly insensitive to variation in larval density. A notable exception was nonlinear variation in female fecundity. In contrast, we found much bigger differences in comparisons with flies from stock cages-including differences in body size, latency to mate, copulation duration, fecundity, and male share of paternity in a competitive environment. For a number of traits, even densities of 1000 larvae per vial (125 larvae per mL of food) did not phenocopy stock cage individuals. This study reveals novel patterns of sex-specific sensitivity to environmental variation that will influence the strength of sexual selection. It also illustrates the importance of comparisons with the environment to which individuals are adapted.     

Larval temperature experience determines sensitivity to cold-shock-induced wing color pattern changes in the blue pansy butterfly Junonia orithya

The butterfly wing color patterns are unique to a species but are modified in response to cold-shock and tungstate treatments at the pupal stage, producing characteristic temperature–shock (TS) phenotypes that are distinct from the color patterns of seasonal polyphenism. In this study, we examined the efficiency of cold-shock and tungstate treatments for color pattern modifications at the pupal stage in relation to larval rearing conditions for the fall or summer morph using the blue pansy butterfly Junonia orithya. We found that larvae reared under the low-temperature condition that induces the fall morph exhibited hardiness against the color pattern changes imposed by cold-shock or tungstate treatment at the pupal stage. When larvae were fed an artificial diet containing tungstate under the high-temperature condition that induces the summer morph, they were still vulnerable to color pattern changes imposed by cold-shock or tungstate treatment at the pupal stage. Furthermore, larvae reared under the high-temperature condition were subjected to cold-shock or tungstate treatments at the pupal stage. In addition to the expected TS-type changes, these individuals exhibited a reduced number of eyespots in adults, which is a feature of the fall morph. These results suggest that the temperature condition experienced by the larvae, but not their consumption of tungstate, determines the sensitivity of the wing imaginal discs to cold-shock and tungstate treatments at the pupal stage.     

Temporal Gene Expression Variation Associated with Eyespot Size Plasticity in Bicyclus anynana

Seasonal polyphenism demonstrates an organism''s ability to respond to predictable environmental variation with alternative phenotypes, each presumably better suited to its respective environment. However, the molecular mechanisms linking environmental variation to alternative phenotypes via shifts in development remain relatively unknown. Here we investigate temporal gene expression variation in the seasonally polyphenic butterfly Bicyclus anynana. This species shows drastic changes in eyespot size depending on the temperature experienced during larval development. The wet season form (larvae reared over 24°C) has large ventral wing eyespots while the dry season form (larvae reared under 19°C) has much smaller eyespots. We compared the expression of three proteins, Notch, Engrailed, and Distal-less, in the future eyespot centers of the two forms to determine if eyespot size variation is associated with heterochronic shifts in the onset of their expression. For two of these proteins, Notch and Engrailed, expression in eyespot centers occurred earlier in dry season than in wet season larvae, while Distal-less showed no temporal difference between the two forms. These results suggest that differences between dry and wet season adult wings could be due to a delay in the onset of expression of these eyespot-associated genes. Early in eyespot development, Notch and Engrailed may be functioning as repressors rather than activators of the eyespot gene network. Alternatively, temporal variation in the onset of early expressed genes between forms may have no functional consequences to eyespot size regulation and may indicate the presence of an ''hourglass'' model of development in butterfly eyespots.     

Immunological larval polyphenism in the map butterfly Araschnia levana reveals the photoperiodic modulation of immunity

The bivoltine European map butterfly (Araschnia levana) displays seasonal polyphenism characterized by the formation of two remarkably distinct dorsal wing phenotypes: The spring generation (A. levana levana) is predominantly orange with black spots and develops from diapause pupae, whereas the summer generation (A. levana prorsa) has black, white, and orange bands and develops from subitaneous pupae. The choice between spring or summer imagoes is regulated by the photoperiod during larval and prepupal development, but polyphenism in the larvae has not been investigated before. Recently, it has been found that the prepupae of A. levana display differences in immunity‐related gene expression, so we tested whether larvae destined to become spring (short‐day) or summer (long‐day) morphs also display differences in innate immunity. We measured larval survival following the injection of a bacterial entomopathogen (Pseudomonas entomophila), the antimicrobial activity in their hemolymph and the induced expression of selected genes encoding antimicrobial peptides (AMPs). Larvae of the short‐day generation died significantly later, exhibited higher antibacterial activity in the hemolymph, and displayed higher induced expression levels of AMPs than those of the long‐day generation. Our study expands the seasonal polyphenism of A. levana beyond the morphologically distinct spring and summer imagoes to include immunological larval polyphenism that reveals the photoperiodic modulation of immunity. This may reflect life‐history traits that manifest as trade‐offs between immunity and fecundity.