Temporal and spatial variation of mortality in field populations of Danaus plexippus L. and D. chrysippus L. Larvae (Lepidoptera: Nymphalidae)

Summary Mortality estimates for the immature stages of two butterfly species, Danaus plexippus and D. chrysippus, were obtained by observing the survival of egg cohorts on different sized patches of food plants (Asclepias spp.), over a one-year period. Losses were variable (0–100%) but usually high (90% and over) throughout the year for both species. Most of the losses in both species occurred in the early stages. The mortality by the third instar accounts for 86–100% of the total losses by instar V. Accordingly both species fall into Price's (1975) type A survivorship category. The size of patches of host plants affected losses. The trend was for increasing losses with increasing patch size. A full life-budget is presented for D. plexippus and implications of the observed mortality levels for competition between the two butterfly species is discussed.     

Fire creates host plant patches for monarch butterflies

Monarch butterflies (Danaus plexippus) depend on the presence of host plants (Asclepias spp.) within their breeding range for reproduction. In the southern Great Plains, Asclepias viridis is a perennial that flowers in May and June, and starts to senesce by August. It is locally abundant and readily used by monarchs as a host plant. We evaluated the effects of summer prescribed fire on A. viridis and the use of A. viridis by monarch butterflies. Summer prescribed fire generated a newly emergent population of A. viridis that was absent in other areas. Pre-migrant monarch butterflies laid eggs on A. viridis in summer burned plots in late August and September, allowing adequate time for a new generation of adult monarchs to emerge and migrate south to their overwintering grounds. Thus, summer prescribed fire may provide host plant patches and/or corridors for pre-migrant monarchs during a time when host plant availability may be limited in other areas.     

Evidence for Partial Migration in the Southern Monarch Butterfly,Danaus erippus,in Bolivia and Argentina

Migration is a common life‐history strategy that includes traits such as directed flight, increased wing size, seasonal lipid deposition and reproductive arrest. The degree of investment in these traits ultimately determines the life‐history strategy of individuals. Partial migration is a common mixed life‐history strategy where species or populations consist of both migrant and resident individuals. While this phenomenon is widespread across taxa, the ecological factors that select for and maintain partial migration are poorly understood, especially among insects. Here, we investigate regional life‐history traits associated with migration in the southern monarch, Danaus erippus, and describe a mixed life‐history strategy in this butterfly. Individuals from the Bolivian lowlands were observed throughout the year exhibiting mate‐ and milkweed‐directed behaviors. These butterflies had smaller wings, lower wing loads and maintained constant lipid and egg loads across summer and autumn months. Danaus erippus in the highlands of the Bolivian Andes were observed only in the summer and autumn months, during which they also showed mate‐ and milkweed‐directed behaviors. These individuals possessed similar‐sized wings and maintained similar lipid and egg loads as the lowland butterflies. In contrast, individuals from northwest Argentina showed persistent, directed, southwesterly flight during the autumn (March–May), larger wing size, higher wing loads, and increased autumn lipid deposition along with decreased egg production. These data indicate that D. erippus utilizes a mixed life‐history strategy with a combination of residents and migrants in the Bolivian lowlands, elevational migrants in the Bolivian Andes, and latitudinal migrants in northwestern Argentina.     

Crowding does not affect monarch butterflies’ resistance to a protozoan parasite

Host density is an important factor when it comes to parasite transmission and host resistance. Increased host density can increase contact rate between individuals and thus parasite transmission. Host density can also cause physiological changes in the host, which can affect host resistance. Yet, the direction in which host density affects host resistance remains unresolved. It is also unclear whether food limitation plays a role in this effect. We investigated the effect of larval density in monarch butterflies, Danaus plexippus, on the resistance to their natural protozoan parasite Ophryocystis elektroscirrha under both unlimited and limited food conditions. We exposed monarchs to various density treatments as larvae to mimic high densities observed in sedentary populations. Data on infection and parasite spore load were collected as well as development time, survival, wing size, and melanization. Disease susceptibility under either food condition or across density treatments was similar. However, we found high larval density impacted development time, adult survival, and wing morphology when food was limited. This study aids our understanding of the dynamics of environmental parasite transmission in monarch populations, which can help explain the increased prevalence of parasites in sedentary monarch populations compared to migratory populations.     

Patterns of parasitism in monarch butterflies during the breeding season in eastern North America

1. Migratory behaviour can result in reduced prevalence of pathogens in host populations. Two hypotheses have been proposed to explain this relationship: (i) ‘migratory escape’, where migrants benefit from escaping pathogen accumulation in contaminated environments; and (ii) ‘migratory culling’, where the selective removal of infected individuals occurs during migration. 2. In the host–parasite system between the monarch butterfly (Danaus plexippus Linn.) and its obligate protozoan parasite Ophryocystis elektroscirrha (OE), there is evidence to support both hypotheses, particularly during the monarchs' autumn migration. However, these processes can operate simultaneously and could vary throughout the monarchs' annual migratory cycle. Assessing the relative strength for each hypothesis has not previously been done. 3. To evaluate both hypotheses, parasite infection prevalence was examined in monarchs sampled in eastern North America during April–September, and stable isotopes (δ²H, δ¹³C) were used to estimate natal origin and infer migration distance. There was stronger support for the migratory escape hypothesis, wherein infection prevalence increased over the breeding season and was higher at southern latitudes, where the breeding season tends to be longer compared with northern latitudes. Little support was found for the migratory culling hypothesis, as infection prevalence was similar whether monarchs travelled shorter or longer distances. 4. These results suggest that migration allows individuals to escape parasites not only during the autumn, as shown in previous work, but during the monarchs' spring and summer movements when they recolonise the breeding range. These results imply a potential fitness advantage to monarchs that migrate further north to exploit parasite‐free habitats.     

A classification of Danaus butterflies (Lepidoptera: Nymphalidae) based upon data from morphology and DNA

Classification of the cosmopolitan butterfly genus Danaus (Nymphalidae: Danainae) is revised at subgeneric, specific and subspecific levels, combining for the first time mitochondrial and nuclear DNA sequence information with morphological data. Tree topologies based on the nuclear genome (allozymes, pheromone components, the morphology of all life history stages and nuclear DNA sequences), on the one hand, and mitochondrial DNA, on the other, are incongruent and challenge the current taxonomy of the genus. Although earlier classifications, based on adult morphology alone, are, in general, well supported by an analysis of total evidence, the mitochondrial phylogeny shows that the species D. chrysippus and its subgenus Anosia are deeply paraphyletic. Subspecies dorippus of D. chrysippus is the basal clade of the genus and is reinstated as the species D. dorippus. The former species D. plexaure is demoted to a subspecies of D. eresimus. The specific status of D. erippus, as distinct from D. plexippus, is tentatively supported. On the strength of the new data, division of the monophyletic genus Danaus s.l. into three subgenera Danaus s.s., Salatura and Anosia is unsustainable and is abandoned. Of the 15 terminal clades (taxa) of Danaus s.l. included in the study, 11 are species that broadly conform to the biological species concept. (The West Indian species D. cleophile, missing from our analysis, is the twelfth species). The remaining terminal clades are subspecies of D. chrysippus comb. nov. and D. dorippus stat. rev. Two sympatric Neotropical species, D. eresimus and D. gilippus, are morphologically distinct and sexually isolated but have nearly identical mitochondrial genomes. In contrast, two partially sympatric Palaeotropical species, D. chrysippus and D. dorippus, are cryptic species that share structural morphology and hybridize but have highly differentiated mitochondrial genomes. D. dorippus is polymorphic for two anciently diverged haplotypes and its history has possibly involved recombinational speciation and/or hybridism. © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005, 144 , 191?212.     

Spatial patterns of correlated scale size and scale color in relation to color pattern elements in butterfly wings

Complex butterfly wing color patterns are coordinated throughout a wing by unknown mechanisms that provide undifferentiated immature scale cells with positional information for scale color. Because there is a reasonable level of correspondence between the color pattern element and scale size at least in Junonia orithya and Junonia oenone, a single morphogenic signal may contain positional information for both color and size. However, this color–size relationship has not been demonstrated in other species of the family Nymphalidae. Here, we investigated the distribution patterns of scale size in relation to color pattern elements on the hindwings of the peacock pansy butterfly Junonia almana, together with other nymphalid butterflies, Vanessa indica and Danaus chrysippus. In these species, we observed a general decrease in scale size from the basal to the distal areas, although the size gradient was small in D. chrysippus. Scales of dark color in color pattern elements, including eyespot black rings, parafocal elements, and submarginal bands, were larger than those of their surroundings. Within an eyespot, the largest scales were found at the focal white area, although there were exceptional cases. Similarly, ectopic eyespots that were induced by physical damage on the J. almana background area had larger scales than in the surrounding area. These results are consistent with the previous finding that scale color and size coordinate to form color pattern elements. We propose a ploidy hypothesis to explain the color–size relationship in which the putative morphogenic signal induces the polyploidization (genome amplification) of immature scale cells and that the degrees of ploidy (gene dosage) determine scale color and scale size simultaneously in butterfly wings.     

Does Skipping a Meal Matter to a Butterfly's Appearance? Effects of Larval Food Stress on Wing Morphology and Color in Monarch Butterflies

In animals with complex life cycles, all resources needed to form adult tissues are procured at the larval stage. For butterflies, the proper development of wings involves synthesizing tissue during metamorphosis based on the raw materials obtained by larvae. Similarly, manufacture of pigment for wing scales also requires resources acquired by larvae. We conducted an experiment to test the effects of food deprivation in the larval stage on multiple measures of adult wing morphology and coloration of monarch butterflies (Danaus plexippus), a species in which long-distance migration makes flight efficiency critical. In a captive setting, we restricted food (milkweed) from late-stage larvae for either 24 hrs or 48 hrs, then after metamorphosis we used image analysis methods to measure forewing surface area and elongation (length/width), which are both important for migration. We also measured the brightness of orange pigment and the intensity of black on the wing. There were correlations between several wing features, including an unexpected association between wing elongation and melanism, which will require further study to fully understand. The clearest effect of food restriction was a reduction in adult wing size in the high stress group (by approximately 2%). Patterns observed for other wing traits were ambiguous: monarchs in the low stress group (but not the high) had less elongated and paler orange pigmentation. There was no effect on wing melanism. Although some patterns obtained in this study were unclear, our results concerning wing size have direct bearing on the monarch migration. We show that if milkweed is limited for monarch larvae, their wings become stunted, which could ultimately result in lower migration success.     

Do Healthy Monarchs Migrate Farther? Tracking Natal Origins of Parasitized vs. Uninfected Monarch Butterflies Overwintering in Mexico

Long-distance migration can lower parasite prevalence if strenuous journeys remove infected animals from wild populations. We examined wild monarch butterflies (Danaus plexippus) to investigate the potential costs of the protozoan Ophryocystis elektroscirrha on migratory success. We collected monarchs from two wintering sites in central Mexico to compare infection status with hydrogen isotope (δ ²H) measurements as an indicator of latitude of origin at the start of fall migration. On average, uninfected monarchs had lower δ ²H values than parasitized butterflies, indicating that uninfected butterflies originated from more northerly latitudes and travelled farther distances to reach Mexico. Within the infected class, monarchs with higher quantitative spore loads originated from more southerly latitudes, indicating that heavily infected monarchs originating from farther north are less likely to reach Mexico. We ruled out the alternative explanation that lower latitudes give rise to more infected monarchs prior to the onset of migration using citizen science data to examine regional differences in parasite prevalence during the summer breeding season. We also found a positive association between monarch wing area and estimated distance flown. Collectively, these results emphasize that seasonal migrations can help lower infection levels in wild animal populations. Our findings, combined with recent declines in the numbers of migratory monarchs wintering in Mexico and observations of sedentary (winter breeding) monarch populations in the southern U.S., suggest that shifts from migratory to sedentary behavior will likely lead to greater infection prevalence for North American monarchs.     

Hologenomic speciation: synergy between a male‐killing bacterium and sex‐linkage creates a ‘magic trait’ in a butterfly hybrid zone

Danaus chrysippus (L.) in Africa comprises four substantially isolated semispecies that are migratory and hybridize on a seasonal basis throughout the eastern and central part of the continent. In the hybrid zone (but not elsewhere), the butterfly is commonly host to a male killing endosymbiotic bacterium, Spiroplasma sp., which principally infects one semispecies, Danaus chrysippus chrysippus in Kenya. A W‐autosome mutation, inherited strictly matrilinearly, links B and C colour gene loci, which have thus gained sex‐linkage in chrysippus. We have monitored variation in sex ratio and genotype at the A and C colour gene loci for two extended periods of 18 months (2004–5) and 12 months (2009–10) in adults reared from wild eggs laid on trap plants in Kasarani, near Nairobi, Kenya. Additionally, in 2009–10, all surviving adult butterflies were screened for Spiroplasma infection. The hybridizing Kasarani population is highly atypical in three respects, and has apparently been so for some 30 years: first, the sex ratio is permanently female‐biased (as expected), although subject to seasonal fluctuation, being lowest (male/female) when D. c. chrysippus (cc) peaks and highest when Danaus chrysippus dorippus (CC) predominates; second, the population is invariably dominated by Cc heterozygotes of both sexes but especially females; and third, cc males are always scarce because they are systematically eliminated by male killing, whereas the CC genotype is male‐biased. It is this imbalance of sex versus genotype that determines the massive departure from Hardy–Weinberg equilibrium in the population, in part because cc females have little choice but to pair with C‐ males. We suggest that: first, Cc hybrids of both sexes fail to disperse in the company of either parental semispecies; second, Spiroplasma positive females carrying the W‐autosome mutation have a selective advantage over females that lack the translocation; third, the endoparasite and the translocation create a ‘magic trait’ linkage group that underlies hologenomic reproductive isolation between two emerging species, D. c. chrysippus and D. c. dorippus; and, fourth, that the predominance of males in dorippus suggests that individuals must be protected by a male‐killing suppressor gene. By contrast to the C locus, Aa heterozygotes are in substantial and permanent deficit, suggesting either assortative mating between AA (chrysippus and dorippus) and aa (Danaus chrysippus alcippus), or heterozygote unfitness, or both. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 92–109.     

The endocrine basis of reproductive inactivity in Monarch butterflies overwintering in central California

Monarch butterflies (Danaus plexippus) collected during winter in central California are reproductively inactive. Oögenesis is stimulated in such animals by environments simulating summer conditions. Allatectomized or neck-ligatured winter animals do not normally undergo oögenesis when placed in summer conditions, but apparently normal oögenesis occurs if they are injected with juvenile hormone isomers. Injections of such isomers into winter animals held in environments simulating winter also promote oögenesis, even though winter conditions typically inhibit ovarian development. Reproductive dormany in winter Monarchs of central California therefore appears to be due (at least partially) to environmentally induced inactivity of the corpora allata.     

A record of the Plain Tiger,Danaus chrysippus,in Western Anatolia

Abstract

The Plain Tiger Danaus chrysippus was recorded in Western Anatolia in 1993 for the first time. There are only a few records from Turkey.     

Directional and stabilizing selection on wing size and shape in migrant and resident monarch butterflies, Danaus plexippus (L.), in Cuba

The majority of migrant monarchs (Danaus plexippus) from the eastern USA and south‐eastern Canada migrate to Mexico; however, some of them migrate to Cuba. Cuban migrants hatch in south‐east Canada and eastern USA, and then engage in a southern trip of 4000 km to this Caribbean island. In Cuba, these migrants encounter resident monarchs, which do not migrate, and instead move between plant patches looking for nectar, mating partners and host plants. These differences in flight behaviour between migrant and resident Cuban monarchs may have resulted in different selective pressures in the wing size and shape. Two modes of selection were tested, directional and stabilizing. In addition, wing condition was compared between these two groups. Monarchs were collected for 4 years in Cuba and classified as resident or migrant using two independent techniques: Thin‐layer chromatography and stable hydrogen and stable carbon isotope measurements. Wing size was measured and wing condition was rated in the butterflies. Fourier analysis and wing angular measurements were used to assess wing shape differences. Migrants have significantly longer wings than residents, thus supporting the action of directional selection on wing size. In addition, directional selection acts on wing shape; that is, migrant females differ significantly from resident females in their wing angles. However, the results do not support the action of stabilizing selection: there was no significant variance between migrant and resident monarchs in their wing size or shape. Also, migrant females and males differed in wing condition as a result of differences in flight behaviour. In conclusion, eastern North American monarchs offer a good opportunity to study the selective pressures of migration on wing morphology and how different migratory routes and behaviours are linked to wing morphology and condition. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 92 , 605–616.     

Defining behavioral and molecular differences between summer and migratory monarch butterflies

Background  

In the fall, Eastern North American monarch butterflies (Danaus plexippus) undergo a magnificent long-range migration. In contrast to spring and summer butterflies, fall migrants are juvenile hormone deficient, which leads to reproductive arrest and increased longevity. Migrants also use a time-compensated sun compass to help them navigate in the south/southwesterly direction en route for Mexico. Central issues in this area are defining the relationship between juvenile hormone status and oriented flight, critical features that differentiate summer monarchs from fall migrants, and identifying molecular correlates of behavioral state.     

Insensitivity of lepidopteran tissues to ouabain: Physiological mechanisms for protection from cardiac glycosides

Neuronal tissues from Manduca sexta, the tobacco hornworm, Hyalophora cecropia, the silkmoth and Danaus plexippus, the Monarch Butterfly, contain Na⁺K⁺-ATPase which is sensitive to cardiac glycoside (ouabain). The K_m for K⁺ stimulation of Na⁺K⁺-ATPase in M. sexta and D. plexippus is 2.2 mM and for Na⁺ stimulation in D. plexippus, 6.0 mM. In vitro ouabain concentrations of 1.0 × 10^?5 M and 5.0 × 10^?5 M in the presence of 7.5 mM K⁺ inhibited Na⁺K⁺-ATPase activity in H. cecropia and M. sexta by 50% respectively. Na⁺K⁺-ATPase from D. plexippus was approximately 300 times less sensitive. High concentrations (10^?3 M in haemolymph) of ouabain had no effect on M. sexta in vivo. This is largely explained by haemolymph K⁺ (>; 30 mM) antagonizing the binding of ouabain to Na⁺K⁺-ATPase. As demonstrated in vitro, 30 mM K⁺ totally protects Na⁺K⁺-ATPase from inhibition by 7.5 × 10^?3 M ouabain in D. plexippus and protects the enzyme by 65% in M. sexta. At least part of the physiological burden incurred in utilization of cardiac glycoside ingestion and storage for protection from predation, however, is probably related to the toxic effects of cardiac glycosides on neuronal Na⁺K⁺-ATPase.     

Insensitivity of lepidopteran tissues to ouabain: Absence of ouabain binding and Na+K+ ATPases in larval and adult midgut

Insensitivity of midgut epithelium to ouabain was studied in three phytophyagous Lepidoptera: the tobacco hornworm. Manduca sexta, the Cecropia silkmoth. Hyalophora cecropia, and the Monarch butterfly, Danaus plexippus. The midgut failed to selectively bind ouabain in the presence of 8 mM K^?. The presence of K⁺ stimulated ouabain sensitive Na⁺K⁺-ATPases in midgut could not be confirmed. Neuronal tissues collected from the same species at the same stages in development bound ouabain readily, and possessed K⁺ stimulated ouabain sensitive Na⁺K⁺-ATPases. It is proposed that alkali metal transport across the midgut epithelium of these phytophagous Lepidoptera occurs via energy-linked processes not requiring Na⁺K⁺-ATPases.     

Leaf litter patches in stream create overwintering habitats for Ezo brown frog (<Emphasis Type="Italic">Rana pirica</Emphasis>)

Only fragments are known about the functions of leaf litter patches in streams for terrestrial organisms. We investigated the movement patterns of Ezo brown frogs (Rana pirica) on two occasions, in autumn 2014 and summer 2015, and the occurrence of frogs in rivers and along riverbanks on three occasions from summer to autumn 2014 along a 1.5-km stream segment that flows through the Bekanbeushi wetland, northern Japan. Ezo brown frog movement was biased toward the river channel in late autumn and this movement pattern coincided with relatively abundant Ezo brown frogs on the riverbed from autumn to winter 2014. The distribution shift was also supported by decreasing abundance of Ezo brown frogs on riverbanks from autumn to winter (no sighting in winter) during daytime observations. The abundance of overwintering Ezo brown frogs in the channel was associated most positively with leaf litter dry mass and depth, with flow velocity being relatively less important at the quadrat scale (0.063 m²). Our results demonstrated that Ezo brown frogs overwinter in the stream and suggest that leaf litter patches positively affect the quality of the overwintering habitat.     

Diuresis and its hormonal control in butterflies

The sudden weight loss after eclosion in the butterflies Acraea horta, Danaus chrysippus and Papilio demodocus is largely due to diuresis. The potassium concentration of the haemolymph is approximately halved as a result, and extensive diuresis leads to increases in sodium concentration and total osmolarity. The isolated Malpighian tubules of all three species are stimulated to fast rates of fluid secretion by cyclic AMP and by homogenates of the brains and corpora cardiaca. The tubules of Papilio lose their sensitivity to stimulation after the first day of adult life, and ingestion of a large volume of artificial nectar by this butterfly does not cause diuresis.     

Spatial metabolomics reveal divergent cardenolide processing in the monarch (Danaus plexippus) and the common crow butterfly (Euploea core)

Although being famous for sequestering milkweed cardenolides, the mechanism of sequestration and where cardenolides are localized in caterpillars of the monarch butterfly (Danaus plexippus, Lepidoptera: Danaini) is still unknown. While monarchs tolerate cardenolides by a resistant Na⁺/K⁺-ATPase, it is unclear how closely related species such as the nonsequestering common crow butterfly (Euploea core, Lepidoptera: Danaini) cope with these toxins. Using novel atmospheric-pressure scanning microprobe matrix-assisted laser/desorption ionization mass spectrometry imaging, we compared the distribution of cardenolides in caterpillars of D. plexippus and E. core. Specifically, we tested at which physiological scale quantitative differences between both species are mediated and how cardenolides distribute across body tissues. Whereas D. plexippus sequestered most cardenolides from milkweed (Asclepias curassavica), no cardenolides were found in the tissues of E. core. Remarkably, quantitative differences already manifest in the gut lumen: while monarchs retain and accumulate cardenolides above plant concentrations, the toxins are degraded in the gut lumen of crows. We visualized cardenolide transport over the monarch midgut epithelium and identified integument cells as the final site of storage where defences might be perceived by predators. Our study provides molecular insight into cardenolide sequestration and highlights the great potential of mass spectrometry imaging for understanding the kinetics of multiple compounds including endogenous metabolites, plant toxins, or insecticides in insects.     

Male monarch butterfly spermatophore mass and mating strategies

Male monarch butterflies, Danaus plexippus, produce a spermatophore which can represent approximately 10% of their body mass. Spermatophore mass increased with age in virgin males, and with the time since last mating in non-virgin males. Male monarchs did not delay re-mating until they were able to produce a large spermatophore. Recently mated males were as likely as virgins to copulate with both virgin and non-virgin females. Monarchs provide an example of Bateman's principle, mating whenever possible, despite the non-trivial cost involved.