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.     

Ecdysteroids control eyespot size and wing color pattern in the polyphenic butterfly Bicyclus anynana (Lepidoptera: Satyridae)

The strongly polyphenic African butterfly, Bicyclus anynana, shows conspicuous ventral eyespots and a transverse band in the wet-season form and small eyespots and no band in the dryseason form. These forms are produced when larvae are reared at high and low temperatures, respectively. Truncation selection was applied to a stock population (UNSELECTED-LINE) to produce lines which, at a constant intermediate temperature of 20 °C, always produced the dry season form (LOW-LINE) and the wet-season form (HIGH-LINE) in addition to a line of fast development (FAST-LINE). A relationship between wing pattern and development time was apparent: the FAST-LINE displayed larger eyespots and HIGH-LINE pupae developed faster (mean = 12.5 days) than LOW-LINE pupae (14.1 days). Differences were found among the lines in ecdysteroid titers after pupation. Hemolymph ecdysteroids in HIGH-LINE pupae increased earlier and reached twice the level of those in LOW-LINE pupae during the first 3 days after pupation. FAST-LINE pupae developed faster (11.7 days) than UNSELECTED-LINE pupae (12.8 days) and ecdysteroids in the FAST-LINE increased more quickly and reached higher levels. In the four LINES, ecdysteroid titers in 3 day old pupae were in the order UNSELECT ≈ LOW ⪡ FAST ⪡ HIGH. Thereafter the titers overlapped.An injection of 20-hydroxyecdysone (20E) inhibited pupal development at a dose between 2.5 and 5 μg when it was injected into pupae within 24 h after pupation. At lower doses (0.25–0.5 μg 20E) 22–100% of the pupae in different experimental groups in the LOW- as well as in the HIGH-LINE developed successfully. The pupal stage was significantly shortened, especially in the LOW-LINE. Additionally, 0.25 and 0.5 μg 20E injected into 0–12 h LOW-LINE pupae shifted the wing color pattern towards the wet season form: eyespots increased in size and the transverse wing band appeared in the more conspicuous pattern characteristic of the wet season form. The results demonstrate that ecdysteroids appearing early in the young pupa produce the wet season form of the wings. The same hormonal system mediates both developmental time and wing pattern determination.     

The critical period for wing pattern induction in the polyphenic tropical butterfly Bicyclus anynana (Satyrinae)

Adults of the butterfly Bicyclus anynana express striking phenotypic plasticity. A wet season form has conspicuous marginal eyespots and a medial pale band which are much reduced in the dry season form. These alternative forms are produced after rearing at high or low temperatures, respectively. We used 'window' experiments involving switching of larvae and pupae between high and low temperatures at different stages during development to examine the timing of sensitivity to environmental temperature. The final, fifth larval instar is shown to be especially sensitive. The fourth larval instar and the very early pupal period are also sensitive. It is argued that an increasing sensitivity during growth is ecologically adaptive since the late larval environment will be the most accurate predictor for the adult environment in which the wing phenotype is subject to selection. The period of sensitivity is not as short as a few days. This may minimize the chance of any 'mistakes' in matching the adult phenotype to the season because of short-term environmental fluctuations during the larval period. The observed sensitivity occurs as late as possible during growth since the wing pattern is developmentally determined at the end of the early part of the pupal stage.     

Hormonal control of seasonal morphs by the timing of ecdysteroid release in Araschnia levana L. (Nymphalidae: Lepidoptera)

Araschnia levana L. occurs in two seasonal morphs. Larvae reared under short-day conditions become diapause pupae and emerge as red spring-morph butterflies. Long-day larvae become non-diapause pupae, which emerge as black and white summer morphs. Pupae reared under these different conditions were joined in parabiosis. Both underwent adult development without diapause and the long-day animals developed into the summer morph as normal. The morph of short-day animals depended on the time of parabiosis. When they were joined to fresh long-day pupae 1 day after their own pupation, summer morphs resulted. When parabiosis began 4 days after pupation or later, spring morphs resulted. Extirpation of the brain-corpora cardiaca-allata complex from long-day pupae affected neither non-diapause development nor the summer morph. Adult development could be prevented by removal of head and prothorax. When adult development was initiated in the remaining bodies by 20-hydroxyecdysone 14 days after pupation, the spring morph resulted.—Injection of 20-dydroxyecdysone into 3-day-old short-day pupae initiated adult development and led to the summer morph. Injections into 10-day-old short-day pupae led to the spring morph. The same was true in diapause pupae deprived of their brain-corpora cardiaca-allata complex. These results indicate that seasonal diphenism in A. levana is controlled only by the timing of ecdysteroid release, which initiates adult development. There is no direct influence of the brain on wing coloration.     

Abnormalities of wing pattern in the Eastern Tiger Swallowtail butterfly, Papilio glaucus

Abstract In much of its range Papilio glaucus L. has two forms of female, black and yellow, and the gene controlling the colour pattern is on the Y chromosome. Thus black mothers produce only black daughters and yellow mothers produce yellow daughters. Reasons are given to explain the occasional exceptions to this rule. The black female form mimics Battus philenor (L.), and an autosomal mutant is described in P.glaucus which is paralleled by a similar aberration in the model - a possible example of a model 'escaping' from a mimic and the mimic 'catching up' at one step.
Sex mosaics are readily seen in the black form of glaucus females and a numberare described from the Strecker collection. The probable cytogenetic constitution of these aberrations is discussed.
Hybrids are described between glaucus and its near relatives, P.rutulus Lucas, P.eurymedon Lucas and P.multicaudatus Kirby. These crosses produce mainly males but, by the use of ecdysterone, females have been obtained in the cross between the black female form of glaucus and the male of rutulus .     

A model for colour pattern formation in the butterfly wing of Papilio dardanus

The butterfly Papilio dardanus is well known for the spectacular phenotypic polymorphism in the female of the species. We show that numerical simulations of a reaction diffusion model on a geometrically accurate wing domain produce spatial patterns that are consistent with many of those observed on the butterfly. Our results suggest that the wing coloration is due to a simple underlying stripe-like pattern of some pigment-inducing morphogen. We focus on the effect of key factors such as parameter values for mode selection, threshold values which determine colour, wing shape and boundary conditions. The generality of our approach should allow us to investigate other butterfly species. The relationship between these key factors and gene activities is discussed in the context of recent biological advances.     

Color pattern formation on the wing of a butterfly Pieris rapae. 2. Color determination and scale development

It has been shown that microcautery on the prospective apical black region of the early pupal forewing of a butterfly, Pieris rapae , causes alteration of the scale color on the adult wing and a delay in histogenesis of the pupal wing. From these results, it has been assumed that the developmental delay of scale cells in the pupal wing alters their developmental fate and the hypothesis that different color fates of scales are determined by differences in the developmental timetables between scale cells is proposed. In this study, we attempted to find the developmental timetables of individual scales expressing specific color to test this hypothesis. It was found that the holes on the upper surface of a scale become larger as they develop and the hole sizes of scales in the white region are always larger than in the black region on the same wings either during pupal period or after eclosion. This suggests that the scale hole size is a good index that reflects developmental rate of the scale and a difference in the hole size between adult scales is attributed to a difference in the developmental timetables when their ancestral scale precursor cells were in the pupal period. A comparison of the hole sizes between adult scales in different color regions suggested that normal white scales were in a more advanced state than were the black ones but white scales induced by microcautery were in a less advanced state than black ones on the same wing. This supports our hypothesis.     

Wnt signaling underlies evolution and development of the butterfly wing pattern symmetry systems

Most butterfly wing patterns are proposed to be derived from a set of conserved pattern elements known as symmetry systems. Symmetry systems are so-named because they are often associated with parallel color stripes mirrored around linear organizing centers that run between the anterior and posterior wing margins. Even though the symmetry systems are the most prominent and diverse wing pattern elements, their study has been confounded by a lack of knowledge regarding the molecular basis of their development, as well as the difficulty of drawing pattern homologies across species with highly derived wing patterns. Here we present the first molecular characterization of symmetry system development by showing that WntA expression is consistently associated with the major basal, discal, central, and external symmetry system patterns of nymphalid butterflies. Pharmacological manipulations of signaling gradients using heparin and dextran sulfate showed that pattern organizing centers correspond precisely with WntA, wingless, Wnt6, and Wnt10 expression patterns, thus suggesting a role for Wnt signaling in color pattern induction. Importantly, this model is supported by recent genetic and population genomic work identifying WntA as the causative locus underlying wing pattern variation within several butterfly species. By comparing the expression of WntA between nymphalid butterflies representing a range of prototypical symmetry systems, slightly deviated symmetry systems, and highly derived wing patterns, we were able to infer symmetry system homologies in several challenging cases. Our work illustrates how highly divergent morphologies can be derived from modifications to a common ground plan across both micro- and macro-evolutionary time scales.     

Reaction norms and the genetic basis of phenotypic plasticity in the wing pattern of the butterfly Bicyclus anynana

The genetic basis of the dry-wet season polyphenism of wing pattern in response to temperature shown by Bicyclus anynana was studied, using a split-family design over four temperatures. Reaction norms crossed, but were only linear in the three highest temperatures, and only when larval development time was used as the environmental axis. Significant full-sib additive variances (V_A) and heritabilities (h²) for plasticity were found using slopes of reaction norms in a bootstrap procedure. Heritabilities were lower in intermediate temperatures, mainly due to differences in the residual variances (V_R). There was no clear trend in V_A across temperatures, contrary to the expectation that V_A would have been depleted by natural selection at the extreme temperatures and not depleted at the intermediate temperatures which occur less frequently in the field. Unpredictability in the onset of the following season at intermediate temperatures might lead to selection for diverse flresponses resulting in relatively high V_Rs. Theoretical models linking reaction norms to genetic parameters in separate environments were difficult to apply in this study, particularly because they are based on the assumption that V_Rs are constant. However the reaction norm approach combined with quantitative genetics provided a valuable insight into the evolution of the observed polyphenism.     

Seasonal phenotypic plasticity of wing melanisation in the cabbage white butterfly, Pieris rapae L. (Lepidoptera: Pieridae)

Abstract.  1. Effective thermoregulation is crucial for the fitness of small flying insects. Phenotypic plasticity of the ventral hindwing of pierid butterflies is widely recognised as adaptive for effective thermoregulation. Butterflies eclosing in cooler environments have more heavily melanised wings that absorb solar radiation, thus allowing flight under these cool conditions.
2. Many pierids also exhibit phenotypic plasticity of dorsal forewing melanisation but in this case, cooler environments reduce melanisation. It has been hypothesised that this plasticity is also adaptive because it increases solar reflection from the wing surfaces onto the body in certain basking postures.
3. The degree of seasonal variation in ventral hindwing and dorsal forewing melanisation of wild-caught Pieris rapae was quantified to determine if it shows patterns of plasticity similar to that documented for other Pieris species.
4. Male wing melanisation on both wing surfaces shows the characteristic seasonal, adaptive plasticity. However, only some dorsal forewing pattern elements of females conformed to the predictions of the hypothesis of adaptive dorsal forewing melanisation. Sexual dimorphism of wing pattern plasticity may result from, and/or affect, sexual dimorphism of behaviour and physiology of these butterflies.     

Geographical distribution of morphological abnormalities and wing color pattern modifications of the pale grass blue butterfly in northeastern Japan

The pale grass blue butterfly Zizeeria maha has been used as an environmental indicator to evaluate the biological impacts of the Fukushima nuclear accident. A high morphological abnormality rate (AR) of this butterfly was detected in 2011 from radioactively contaminated areas at 37–38°N. However, the geographical AR distribution has not been documented for the entirety of northeastern Japan. Additionally, the geographical distribution of the wing color pattern modification rate (MR) of temperature‐shock type remains undocumented. Here, we collected adult butterflies from many localities in northeastern Japan in 2014 and examined the local AR and MR. Both AR and MR were generally low throughout the 44 local populations surveyed. Latitudinal AR and MR distributions indicated a gap zone at approximately 39°N. The mean AR and the mean MR of the populations south of the gap zone were low (AR = 3.0%, MR = 1.1%), whereas those of the northern populations were relatively high (AR = 10.6%, MR =10.3%). Logistic regression analyses revealed that abnormalities and modifications were associated with temperature‐related variables. We conclude that abnormalities and modifications are generally rare, but that their rates are higher in the northern populations than in the southern ones. These results, along with evidence from other studies, strongly suggest that the high AR detected in 2011 from contaminated areas was induced by anthropogenic radioactive mutagens. This study presents a basic dataset of the current wildlife state of Z. maha in northeastern Japan, which facilitates a future use of this butterfly species as an environmental indicator.     

Quantitative genetic analysis of responses to larval food limitation in a polyphenic butterfly indicates environment‐ and trait‐specific effects

Different components of heritability, including genetic variance (V_G), are influenced by environmental conditions. Here, we assessed phenotypic responses of life‐history traits to two different developmental conditions, temperature and food limitation. The former represents an environment that defines seasonal polyphenism in our study organism, the tropical butterfly Bicyclus anynana, whereas the latter represents a more unpredictable environment. We quantified heritabilities using restricted maximum likelihood (REML) procedures within an “Information Theoretical” framework in a full‐sib design. Whereas development time, pupal mass, and resting metabolic rate showed no genotype‐by‐environment interaction for genetic variation, for thorax ratio and fat percentage the heritability increased under the cool temperature, dry season environment. Additionally, for fat percentage heritability estimates increased under food limitation. Hence, the traits most intimately related to polyphenism in B. anynana show the most environmental‐specific heritabilities as well as some indication of cross‐environmental genetic correlations. This may reflect a footprint of natural selection and our future research is aimed to uncover the genes and processes involved in this through studying season and condition‐dependent gene expression.     

The pigments of Papilio graphium weiskei: Sarpedobilin and ommin responsible for a unique pattern in a butterfly wing membrane

• 1.1. The pigments of the butterfly Papilio graphium weiskei have been separately extracted from the different coloured zones of the wing membrane and analyzed.
• 2.2. Sarpedobilin 3, a neopterobilin, is present in all parts of the wing, at higher concentrations in the green and blue areas, in traces in the pink zones, the total amount being spectrophotometrically determined at 50 μg per individual.
• 3.3. The pigment from the pink and mauve areas cannot be extracted in the usual conditions, but only after in-situ destruction of the membrane under strong acidic conditions. The substance thus obtained shows redox properties. It is identified with ommin on the basis of the already reported similar red pigment obtained in such conditions “Farbstoffe IV” from other insect species.
• 4.4. In conclusion, the unique wing pattern of P. weiskei where green, blue, mauve and pink zones occur, is due to the superposition of two pigments, sarpedobilin (a derivative of pterobilin) and ommin, present within the membrane.

     

Formation of hydroxanthommatin-derived radical in the oxidation of 3-hydroxykynurenine.

Using ESR, a radical (g = 2.004) was detected in the reaction mixture of 3-hydroxykynurenine (3-HKY), H2O2, and horseradish peroxidase. The radical was stable and was detected even after 5 h. On HPLC analysis of the reaction mixture, two radical peaks (Peak-1 and Peak-2) were detected using ESR. The ESR spectra of Peak-1 and Peak-2 radicals were the same and identical with that of the original radical in the reaction mixture. The retention times of Peak-1 and Peak-2 corresponded to those of authentic xanthommatin (XA) and hydroxanthommatin (Hydro-XA), respectively, XA being formed in the oxidation of 3-HKY by potassium ferricyanide and Hydro-XA being formed in the reduction of XA by sodium metabisulfite. The absorbance spectra of Peak-1 and Peak-2 were nearly identical with those of authentic XA and Hydro-XA. The absorbance spectrum of Peak-2 changed from that of Hydro-XA to that of XA, indicating that Hydro-XA auto-oxidized to XA in the air. The ESR signal intensity of the Peak-2 radical developed in accordance with the progress of this auto-oxidation of Hydro-XA to XA. It was supposed that the Peak-2 radical was generated in the auto-oxidation of Hydro-XA after its elution from the HPLC column. Thus, the radical seemed to be the one-electron oxidized form of Hydro-XA. The Peak-1 radical appeared to be the true retention of the radical on the column and to be eluted with a much larger amount of XA. The separation of the radical from XA was impossible on the column. Hemoglobin (Hb) or hematin also induced the same radical in the reaction mixture of 3-KHY, H2O2, and Hb or hematin.     

Color pattern formation on the wing of the butterfly Pieris rapae. 1. Cautery induced alteration of scale color and delay of arrangement formation

Experimental approaches to color pattern formation of lepidopteran insects have been made exclusively by analyzing pattern alterations in adult wings induced by operations. We microcauterized the presumptive black region of the dorsal forewing of the butterfly Pieris rapae and analyzed not only the resultant color pattern in the adult wing but also the cell behavior in the pupal wing epidermis around the injury. Cautery induced color alterations were as follows: (i) cautery up to 49.5 h after pupation resulted in white regions appearing within the black region while later cauteries induced larger white regions; (ii) cautery between 50 and 59.5 h resulted in the white regions induced by the cauteries being dramatically decreased; (iii) cautery after 60 h resulted in white regions that had almost disappeared. The examination of the cell behavior in the pupal wing epidermis after cauteries showed that the row formation of scale precursor cells was delayed. This delayed area varied with the time of cautery, in the same manner as that in the induced white area in the adult wing ((i) – (iii) above). The relationship between scale color alteration and the developmental delay of the scale row formation is discussed.     

Evolution of the wave: aerodynamic and aposematic functions of butterfly wing motion

Many unpalatable butterfly species use coloration to signal their distastefulness to birds, but motion cues may also be crucial to ward off predatory attacks. In previous research, captive passion-vine butterflies Heliconius mimetic in colour pattern were also mimetic in motion. Here, I investigate whether wing motion changes with the flight demands of different behaviours. If birds select for wing motion as a warning signal, aposematic butterflies should maintain wing motion independently of behavioural context. Members of one mimicry group (Heliconius cydno and Heliconius sapho) beat their wings more slowly and their wing strokes were more asymmetric than their sister-species (Heliconius melpomene and Heliconius erato, respectively), which were members of another mimicry group having a quick and steady wing motion. Within mimicry groups, wing beat frequency declined as its role in generating lift also declined in different behavioural contexts. In contrast, asymmetry of the stroke was not associated with wing beat frequency or behavioural context-strong indication that birds process and store the Fourier motion energy of butterfly wings. Although direct evidence that birds respond to subtle differences in butterfly wing motion is lacking, birds appear to generalize a motion pattern as much as they encounter members of a mimicry group in different behavioural contexts.     

Perturbation of the wing color pattern of a swallowtail butterfly,Papilio xuthus,induced by acid carboxypeptidase

Hypodermal injection of Toughmac-E, a digestive mixture composed of nine digestive components, or Molsin induced perturbation of the wing color pattern in 0- to 2-day-old pupae of Papilio xuthus, but had no effect on prepupae or 3- to 4-day-old pupae. The effective component in Toughmac-E was identified as Molsin, an acid carboxypeptidase of Aspergillus saitoi which specifically liberates tyrosine and phenylalanine from the C-terminal residues of proteins. The pattern perturbation occurred in either side of the fore- and hindwings of both sexes. When this enzyme was administered, stronger melanization than in the normal wings was found in the whole wings of most butterflies, but in other butterflies, the yellow region was enlarged. These findings suggest that the pattern perturbation was caused by changes in the levels of melanin and papiliochromes in scales. Melanin is a black pigment and papiliochromes are yellow pigments; their common precursor is dopamine. The normal pattern is formed by a predetermined balance of melanin and papiliochromes, whereas the deposit of an excess amount of tyrosine and/or phenylalanine disturbs this balance and results in perturbation of the color pattern. Administration of L-dopa or dopamine had no effect on the wing pattern. When the activity of an endogenous acid carboxypeptidase similar to Molsin appears in the early pupa, the summed activities of the endogenous and exogenous acid carboxypeptidases must induce a pattern perturbation. The relations between the endogenous acid carboxypeptidase and its probable substrate, the reserve protein, and the physiological roles of these relations in the regulation, utilization and excretion of amino acids are discussed.