Detection of juvenile hormone I, II and III in adult monarch butterflies (Danaus plexippus)

Monarch Butterfly Migration as an Integrative Model of Complex Trait Evolution

AbstractUnderstanding the genetic architecture of complex trait adaptation in natural populations requires the continued development of tractable models that explicitly confront organismal and environmental complexity. A decade of high-throughput sequencing-based investigations into the genomic basis of migration points to an integrative framework that incorporates quantitative genetics, evolutionary developmental biology, phenotypic plasticity, and epigenetics to explain migration evolution. In this perspective, I argue that the transcontinental migration of the monarch butterfly (Danaus plexippus) can serve as a compelling system to study the mechanism of evolutionary lability of a complex trait. Monarchs show significant phenotypic and genotypic diversity across their global range, with phenotypic switching that allows for explicit study of evolutionary lability. A developmental approach for elucidating how migratory traits are generated and functionally integrated will be important for understanding the evolution of monarch migration traits. I propose a plasticity threshold model to describe migration lability, and I describe novel functional techniques that will help resolve open questions and model assumptions. I conclude by considering the relationships between adaptive genetic architecture, anthropogenic climate change, and conservation management practice and the timeliness of the monarch migration model to illuminate these connections given the rapid decline of the North American migration.

Monarch butterflies use an environmentally sensitive, internal timer to control overwintering dynamics

The monarch butterfly (Danaus plexippus) complements its iconic migration with diapause, a hormonally controlled developmental programme that contributes to winter survival at overwintering sites. Although timing is a critical adaptive feature of diapause, how environmental cues are integrated with genetically-determined physiological mechanisms to time diapause development, particularly termination, is not well understood. In a design that subjected western North American monarchs to different environmental chamber conditions over time, we modularized constituent components of an environmentally-controlled, internal diapause termination timer. Using comparative transcriptomics, we identified molecular controllers of these specific diapause termination components. Calcium signalling mediated environmental sensitivity of the diapause timer, and we speculate that it is a key integrator of environmental condition (cold temperature) with downstream hormonal control of diapause. Juvenile hormone (JH) signalling changed spontaneously in diapause-inducing conditions, capacitating response to future environmental condition. Although JH is a major target of the internal timer, it is not itself the timer. Epigenetic mechanisms are implicated to be the proximate timing mechanism. Ecdysteroid, JH, and insulin/insulin-like peptide signalling are major targets of the diapause programme used to control response to permissive environmental conditions. Understanding the environmental and physiological mechanisms of diapause termination sheds light on fundamental properties of biological timing, and also helps inform expectations for how monarch populations may respond to future climate change.

In vivo real-time monitoring of aphrodisiac pheromone release of small white cabbage butterflies (Pieris rapae)

The study of insect behavior is of practical importance for developing possible control methods in Integrated Pest Management. Currently, one model of butterfly mating behavior suggests that the initial location of potential mates occurs visually followed by the release of one or more short-range male aphrodisiac pheromones. This model is supported by data obtained from field observations and inferences based on the behavioral effects of chemicals extracted or isolated using indirect and offline techniques. In this study, we performed in vivo real-time monitoring of the male aphrodisiac pheromones released by the small white cabbage male butterfly (Pieris rapae Linnaeus) using confined direct analysis in real time (cDART) mass spectrometry. cDART is a new method easily adapted to the study in real time of chemicals released into the environment by virtually any insect. The major compound released by the male Pieris rapae was identified as ferrulactone. The experimental results reported here indicate that the release of ferrulactone occurs less than 1s after the male visualizes its partner, and reaches a maximum after about one half minute. This study is the first reported in vivo detection and monitoring of butterfly male aphrodisiac pheromones in real time.

Identification of methyl farnesoate from in vitro culture of the retrocerebral complex of adult females of the moth, Heliothis virescens (Lepidoptera: Noctuidae) and its conversion to juvenile hormone III

Gas chromatographic-mass spectral analysis of extracts obtained from in vitro culture of isolated retrocerebral complexes obtained from adult females of the moth Heliothis virescens resulted in identification of methyl farnesoate as well as juvenile hormone III (JH III) but not JH III acid. Inhibition of JH biosynthesis by incubation of tissue in synthetic Manduca sexta allatostatin (Manse-AST, pGlu-Val-Arg-Phe-Arg-Gln-Cys-Tyr-Phe-Asn-Pro-Ile-Ser-Cys-Phe-COOH) reduced production of these chemicals to negligible levels. However, incubation of tissue in the presence of Manse-AST plus farnesol resulted in production of significant amounts of both methyl farnesoate and JH III. Tissue incubated in the presence of Manse-AST plus methyl farnesoate produced only JH III. The results indicated that methyl farnesoate is naturally produced by the corpora allata of adult females of Heliothis virescens. However, tissue incubated in the presence of Manse-AST plus JH III acid also produced JH III in amounts equivalent to that produced by tissue incubated with methyl farnesoate. Thus, both methyl farnesoate and JH III acid could serve as a precursor for biosynthesis of JH III.

Juvenile hormone catabolism and oviposition in the codling moth, Cydia pomonella, as functions of age, mating status, and hormone treatment

In vitro catabolism of juvenile hormone (JH) in haemolymph of adult female Cydia pomonella was ascribed mainly to juvenile hormone esterase (JHE) activity. No significant differences were noted between virgin and mated females 0-96 h post-emergence. Changes in JHE activity did not appear dependent upon fluctuations in JH titre; conversely, changes in JHE activity could not explain the changes in JH titres. Maximal JHE activity was recorded at 24 h (331.47 +/- 47.25 pmol/h/microl; 355.93 +/- 36.68 pmol/h/microl, virgin; mated insects, respectively) and preceded the peak in JH titres at 48 h. Topical application of JH II (10 ng-10 microg) or fenoxycarb (50 ng) enhanced JHE activity up to 640 and 56%, respectively. Treatment upon emergence with 10 microg JH II induced enzymic activity for less than 24 h, and when 10 microg JH II or 50 ng fenoxycarb were applied, circulating JH titres returned to control levels within 24 h. Oviposition was highly sensitive to exogenous JH and declined significantly with dosages >100 pg. To allow a degree of oocyte maturation before JH treatment, the hormone was administered at 6, 12, 24, or 48 h post-emergence and/or females were mated. Neither measure "protected" the system; oviposition declined immediately after JH application.

Influence of juvenile hormone and mating on oogenesis and oviposition in the codling moth, cydia pomonella

Oogenesis in the codling moth, Cydia pomonella, and the role of juvenile hormones (JHs) were addressed. Rudimentary ovarian structures were recognisable in day 3-4 pupae, when haemolymph JH was still undetectable by coupled gas chromatography-mass spectrometry in the selected ion mode (GC-MS/SIM). The presence of developing oocytes was observed by light microscopy on day 8, coincident with very low JH titres (0.74 +/- 0.05 ng/ml JH II). Chorionation was only evident upon emergence, following an increase in JH in the pharate adult (0h old: 4.71 +/- 0.34 ng/ml JH II). Analysis of haemolymph from virgin and mated females indicated that JH II was predominant, with approximately equal and lower quantities of JHs I and III (3.3- to 5.0-fold less). When pupae or newly emerged adults were treated with JH homologues, no alteration in ovarian protein content was apparent, but the JH mimetic, fenoxycarb, depressed the number of oocytes filling >/= 50% follicular volume. Chorion deposition was stimulated by JHs I, II, or III (10 &mgr;g), but not by fenoxycarb (0.05 &mgr;g, 10 &mgr;g). Mating provided correct stimuli for enhanced choriogenesis and egg laying, and, since haemolymph JH titres were concomitantly elevated (approximately 2-fold), it was postulated that the rise in JH elicited both these events. Application of JHs to virgin females, however, could not mimic mating; only increases in choriogenesis were induced: JH-treatment of virgins (or mated insects) significantly decreased oviposition rates over 24 and 48 h and markedly reduced the life-time total number of eggs. Arch. Copyright 1999 Wiley-Liss, Inc.

Temporal profiles of juvenile hormone titers and egg production in virgin and mated females of Heliothis virescens (Noctuidae)

Juvenile hormones (JH) I, II, and III were monitored in hemolymph of virgin and mated females of various ages in Heliothis virescens. JH I was the predominant homologue followed by JH II, but JH II was present at a higher level in young virgin females. JH III was detectable only at a low level. In virgin females, hemolymph JH titers were low at emergence (2.2ng/ml-total amount of JH I and JH II), but increased thereafter and reached a maximum at 24h of age (53.5ng/ml). At 30h and 36h of age, JH titers dropped to a low level, but increased again in older virgin females. After mating, JH titers increased significantly. JH titers at 0h after uncoupling (137.4ng/ml) were nearly 3 times as high as those in 24-h-old virgin females. Within 6h after uncoupling, JH titers decreased slightly, but titers increased with age of mated females and reached a level of 320.2ng/ml hemolymph at 72h after uncoupling. The titer of JH I and JH II was correlated highly with total number of eggs produced (r(2)=0.70, P<0.001). Mating stimulated JH production, resulting in an increase in egg production.