Monarch Butterflies Danaus Plexippus Research Articles

Endemic Galapagos Tree Daisy Scalesia pedunculata Threatened by Competition with Nonnative Blackberry Rubus niveus

Photo 1. (A) The distribution and population size of the Galapagos Tree Daisy Scalesia pedunculata (1) suffers from competition with nonnative trees such as Cedrela odorata (2), Cinchona pubescens (3) and (B) nonnative undergrowth bushes, most seriously from Rubus niveus (4). (C) A removal experiment and subsequent 8 years of monitoring showed that S. pedunculata can successfully recruit in areas with low undergrowth such as non-native Tradescantia fluminensis (5), but it fails completely to recruit in the presence of R. niveus. Photo credit: B. Riegl (A), H. Jäger (B), M. San José (C). Photo 2. (A) Scalesia pedunculata trees are true trees and follow an asymptotic growth function. Under competition with Rubus niveus, S. pedunculata produces thinner, shorter trees with a reduced life-span. (B) Scalesia pedunculata is a relatively short-lived species and shows strong, pulsed, recruitment dynamics in undisturbed habitat. The shown high density of recruits was only observed in the immediate aftermath of R. niveus removal, but later decreased. However, in the continued presence of R. niveus, no recruitment at all was observed over the 8-year study period. Photo credit: H. Jäger. Photo 3. The endemic Scalesia pedunculata forest is a unique ecosystem that provides an important habitat for many invertebrates and vertebrates, such as this (A) Monarch Butterfly Danaus plexippus megalippe and the (B) endangered Little Vermillion Flycatcher Pyrocephalus nanus. Past control of invasive Rubus niveus has had temporary negative effects on arthropod biomass and bird breeding success of Darwin's finches, but is outweighted by long-term habitat restoration benefits. Photo credit: M. San José. These photographs illustrate the article “Invasive blackberry outcompetes the endemic Galapagos tree daisy Scalesia pedunculata” by Bernhard Riegl, Anna Walentowitz, Christian Sevilla, Rafael Chango, and Heinke Jäger, published in Ecological Applications. https://doi.org/10.1002/eap.2846

History of colonisation and updated distribution of the Monarch butterfly Danaus plexippus (Linnaeus, 1758) and its hostplants in mainland Portugal, Azores and Madeira

The first observations of the Monarch butterfly (Danaus plexippus) in Iberia date from 1886, although breeding records emerged almost a century later: 1960 in Spain, 1980s–1990s in Madeira and Azores, and 2003 in mainland Portugal. We reviewed the history of the colonisation of mainland and insular Portugal by the Monarch butterfly and its hostplants (Gomphocarpus fruticosus, G. physocarpus and Asclepias curassavica). We also compiled available historical and recent occurrence records as a basis for countrywide surveys of the butterfly and hostplants, to update their current distributions in Portugal. Locations for only a few of the older records represented newly rediscovered populations in the field, although recent occurrences were often confirmed. Hostplants were scarce and monarchs absent in northern and central mainland Portugal, but both were quite common in the southwest. In Madeira, hostplants were found in two locations, while monarchs were common and widespread. In the Azores, small hostplant patches were observed on four of seven surveyed islands, whereas monarchs were rare and restricted to two islands. Abandoned/semi-abandoned orange orchards represent the butterfly’s stronghold in Portugal, with the species being increasingly scarce along rivers and road verges where hostplants are declining. Hostplant persistence is unstable, with many patches removed, while others have expanded or colonised new areas. Overall, hostplants appear to be declining, with implications for the persistence of monarch butterflies in the country.

Parasite dynamics in North American monarchs predicted by host density and seasonal migratory culling.

Insect-pathogen dynamics can show seasonal and inter-annual variations that covary with fluctuations in insect abundance and climate. Long-term analyses are especially needed to track parasite dynamics in migratory insects, in part because their vast habitat ranges and high mobility might dampen local effects of density and climate on infection prevalence. Monarch butterflies Danaus plexippus are commonly infected with the protozoan Ophryocystis elektroscirrha (OE). Because this parasite lowers monarch survival and flight performance, and because migratory monarchs have experienced declines in recent decades, it is important to understand the patterns and drivers of infection. Here we compiled data on OE infection spanning 50years, from wild monarchs sampled in the United States, Canada and Mexico during summer breeding, fall migrating and overwintering periods. We examined eastern versus western North American monarchs separately, to ask how abundance estimates, resource availability, climate and breeding season length impact infection trends. We further assessed the intensity of migratory culling, which occurs when infected individuals are removed from the population during migration. Average infection prevalence was four times higher in western compared to eastern subpopulations. In eastern North America, the proportion of infected monarchs increased threefold since the mid-2000s. In the western region, the proportion of infected monarchs declined sharply from 2000 to 2015, and increased thereafter. For both eastern and western subpopulations, years with greater summer adult abundance predicted greater infection prevalence, indicating that transmission increases with host breeding density. Environmental variables (temperature and NDVI) were not associated with changes in the proportion of infected adults. We found evidence for migratory culling of infected butterflies, based on declines in parasitism during fall migration. We estimated that tens of millions fewer monarchs reach overwintering sites in Mexico as a result of OE, highlighting the need to consider the parasite as a potential threat to the monarch population. Increases in infection among eastern North American monarchs post-2002 suggest that changes to the host's ecology or environment have intensified parasite transmission. Further work is needed to examine the degree to which human practices, such as mass caterpillar rearing and the widespread planting of exotic milkweed, have contributed to this trend.

Experimental field evidence shows milkweed contaminated with a common neonicotinoid decreases larval survival of monarch butterflies.

Neonicotinoid insecticides are the most widely used class of insecticides in the world and can have both lethal and sub-lethal effects on non-target organisms in agricultural areas. Monarch butterflies Danaus plexippus have experienced dramatic declines in recent decades and, given that a large proportion of milkweed on the landscape grows in agricultural areas, there is concern about the negative effects of neonicotinoids on this non-target insect. In the field, we exposed common milkweed Asclepias syriaca, an obligate host plant of monarch butterflies, to agriculturally realistic levels of clothianidin, a widely used neonicotinoid insecticide. We tested whether this treatment influenced the number of eggs laid and larval survival over 2years. Milkweeds were transplanted into 60 experimental plots alongside a corn crop planted with a clothianidin seed coat and 60 control plots alongside an untreated corn crop. The number of eggs, larvae at each stage (first to fifth instar), and the presence of other arthropods were recorded weekly from June to the end of August and survival from egg to fifth instar was estimated using a Bayesian state-space statistical model. We counted more eggs in treated plots compared to control plots, suggesting a preference for treated milkweed. The number of plots with arthropods did not differ between treatments, but within treated plots, there was a greater decrease in the number of arthropods throughout the season. There was no evidence that monarchs selected plots with fewer arthropods for oviposition. Larval survival was lower in clothianidin-treated plots compared to control plots. Our results suggest milkweed near clothianidin-treated crops can reduce larval survival of monarch butterflies. While we provide some evidence that clothianidin could also act as an ecological trap for this species, further work is needed to identify additional components of fitness, including individual egg-laying rates and survival beyond the pupal stage. Our findings add to a growing body of evidence that neonicotinoids can negatively affect non-target organisms. ​.

Elevated atmospheric concentrations of CO2 increase endogenous immune function in a specialist herbivore.

Animals rely on a balance of endogenous and exogenous sources of immunity to mitigate parasite attack. Understanding how environmental context affects that balance is increasingly urgent under rapid environmental change. In herbivores, immunity is determined, in part, by phytochemistry which is plastic in response to environmental conditions. Monarch butterflies Danaus plexippus, consistently experience infection by a virulent parasite Ophryocystis elektroscirrha, and some medicinal milkweed (Asclepias) species, with high concentrations of toxic steroids (cardenolides), provide a potent source of exogenous immunity. We investigated plant-mediated influences of elevated CO2 (eCO2 ) on endogenous immune responses of monarch larvae to infection by O. elektroscirrha. Recently, transcriptomics have revealed that infection by O. elektroscirrha does not alter monarch immune gene regulation in larvae, corroborating that monarchs rely more on exogenous than endogenous immunity. However, monarchs feeding on medicinal milkweed grown under eCO2 lose tolerance to the parasite, associated with changes in phytochemistry. Whether changes in milkweed phytochemistry induced by eCO2 alter the balance between exogenous and endogenous sources of immunity remains unknown. We fed monarchs two species of milkweed; A. curassavica (medicinal) and A. incarnata (non-medicinal) grown under ambient CO2 (aCO2 ) or eCO2 . We then measured endogenous immune responses (phenoloxidase activity, haemocyte concentration and melanization strength), along with foliar chemistry, to assess mechanisms of monarch immunity under future atmospheric conditions. The melanization response of late-instar larvae was reduced on medicinal milkweed in comparison to non-medicinal milkweed. Moreover, the endogenous immune responses of early-instar larvae to infection by O. elektroscirrha were generally lower in larvae reared on foliage from aCO2 plants and higher in larvae reared on foliage from eCO2 plants. When grown under eCO2 , milkweed plants exhibited lower cardenolide concentrations, lower phytochemical diversity and lower nutritional quality (higher C:N ratios). Together, these results suggest that the loss of exogenous immunity from foliage under eCO2 results in increased endogenous immune function. Animal populations face multiple threats induced by anthropogenic environmental change. Our results suggest that shifts in the balance between exogenous and endogenous sources of immunity to parasite attack may represent an underappreciated consequence of environmental change.

Local and cross‐seasonal associations of climate and land use with abundance of monarch butterflies Danaus plexippus

Quantifying how climate and land use factors drive population dynamics at regional scales is complex because it depends on the extent of spatial and temporal synchrony among local populations, and the integration of population processes throughout a species’ annual cycle. We modeled weekly, site‐specific summer abundance (1994–2013) of monarch butterflies Danaus plexippus at sites across Illinois, USA to assess relative associations of monarch abundance with climate and land use variables during the winter, spring, and summer stages of their annual cycle. We developed negative binomial regression models to estimate monarch abundance during recruitment in Illinois as a function of local climate, site‐specific crop cover, and county‐level herbicide (glyphosate) application. We also incorporated cross‐seasonal covariates, including annual abundance of wintering monarchs in Mexico and climate conditions during spring migration and breeding in Texas, USA. We provide the first empirical evidence of a negative association between county‐level glyphosate application and local abundance of adult monarchs, particularly in areas of concentrated agriculture. However, this association was only evident during the initial years of the adoption of herbicide‐resistant crops (1994–2003). We also found that wetter and, to a lesser degree, cooler springs in Texas were associated with higher summer abundances in Illinois, as were relatively cool local summer temperatures in Illinois. Site‐specific abundance of monarchs averaged approximately one fewer per site from 2004–2013 than during the previous decade, suggesting a recent decline in local abundance of monarch butterflies on their summer breeding grounds in Illinois. Our results demonstrate that seasonal climate and land use are associated with trends in adult monarch abundance, and our approach highlights the value of considering fine‐resolution temporal fluctuations in population‐level responses to environmental conditions when inferring the dynamics of migratory species.

Intra‐population variation in the natal origins and wing morphology of overwintering western monarch butterflies Danaus plexippus

Understanding the natal origins of migratory animals is critical for understanding their population dynamics and conservation. However, quantitative estimates of population recruitment from different natal habitats can be difficult to assess for many species, especially those with large geographic ranges. These limitations hinder the evaluation of alternative hypotheses about the key movements and ecological interactions of migratory species. Here, we quantitatively investigated intra‐population variation in the natal origins of western North American monarch butterflies Danaus plexippus using spatial analyses of stable isotope ratios and correlations with wing morphology. A map of hydrogen isotope values in western monarch butterfly wings (δ2Hm) was estimated using a transfer function that relates the δ2Hm values of monarch butterfly wing keratin to a long‐term dataset of precipitation isotope (δ2Hp) values across the western United States. Isotopic analyses of 114 monarch butterfly wings collected at four California overwintering locations indicated substantial individual variation in natal origins, with most recruitment coming from broad regions along the Pacific coast, the southwestern US and the northern intermountain region. These observed patterns may partially resolve and reconcile several past hypotheses about the natal origins of western monarch butterflies, while also raising new questions. More negative δ2Hm values (associated with longer migratory distance) were significantly correlated with larger forewing sizes, consistent with expectations based on the aerodynamic and energetic costs of long‐distance migration, while analyses of wing shape suggest potential differences in the movement behaviors and constraints observed in the western range, compared with previous observations in eastern North America. Taken together, the results of this study indicate substantial individual variation in the natal origins of overwintering western monarch butterflies, suggesting both local and long‐distance movement to overwintering sites.

Disease ecology across soil boundaries: effects of below-ground fungi on above-ground host-parasite interactions.

Host-parasite interactions are subject to strong trait-mediated indirect effects from other species. However, it remains unexplored whether such indirect effects may occur across soil boundaries and connect spatially isolated organisms. Here, we demonstrate that, by changing plant (milkweed Asclepias sp.) traits, arbuscular mycorrhizal fungi (AMF) significantly affect interactions between a herbivore (the monarch butterfly Danaus plexippus) and its protozoan parasite (Ophryocystis elektroscirrha), which represents an interaction across four biological kingdoms. In our experiment, AMF affected parasite virulence, host resistance and host tolerance to the parasite. These effects were dependent on both the density of AMF and the identity of milkweed species: AMF indirectly increased disease in monarchs reared on some species, while alleviating disease in monarchs reared on other species. The species-specificity was driven largely by the effects of AMF on both plant primary (phosphorus) and secondary (cardenolides; toxins in milkweeds) traits. Our study demonstrates that trait-mediated indirect effects in disease ecology are extensive, such that below-ground interactions between AMF and plant roots can alter host-parasite interactions above ground. In general, soil biota may play an underappreciated role in the ecology of many terrestrial host-parasite systems.

Lipid reserves and immune defense in healthy and diseased migrating monarchs Danaus plexippus

Abstract Recent studies suggest that the energetic demands of long-distance migration might lower the pool of resources available for costly immune defenses. Moreover, migration could amplify the costs of parasitism if animals suffering from parasite-induced damage or depleted energy reserves are less able to migrate long distances. We investigated relationships between long-distance migration, infection, and immunity in wild fall-migrating monarch butterflies Danaus plexippus. Monarchs migrate annually from eastern North America to central Mexico, accumulating lipids essential for migration and winter survival as they travel southward. Monarchs are commonly infected by the debilitating protozoan parasite Ophryocystis elektroscirrha (OE). We collected data on lipid reserves, parasite loads, and two immune measures (hemocyte concentration and phenoloxidase activity) from wild monarchs migrating through north GA (USA) to ask whether (1) parasite infection negatively affects lipid reserves, and (2) greater investment in lipid reserves is associated with lower immune measures. Results showed that monarchs sampled later in the fall migration had lower but not significantly different immune measures and significantly higher lipid reserves than those sampled earlier. Lipid measures correlated negatively but only nearly significantly with one measure of immune defense (phenoloxidase activity) in both healthy and infected monarchs, but did not depend on monarch infection status or parasite load. These results provide weak support for a trade-off between energy reserves and immune defense in migrants, and suggest that previously-demonstrated costs of OE infection for monarch migration are not caused by depleted lipid reserves.

Combining Stochastic Models with Experiments to Understand the Dynamics of Monarch Butterfly Colonization

Stochastic models are of increasing importance in ecology but are usually only applied to observational data. Here we use a stochastic population model to combine experimental and observational data to understand the colonization of old fields by monarch butterflies Danaus plexippus. We experimentally tested for density dependence in oviposition rates when predators were excluded, and we measured predation rates under natural conditions. Significance tests on the resulting data showed that both oviposition and predation were density dependent but could not show how oviposition and mortality combine to determine egg densities in nature. We therefore used our data to calculate the Akaike Information Criterion to choose between a nested suite of stochastic models that differed in their oviposition and mortality terms. When we simply fit the models to the observational data, the best model assumed density independence in both oviposition and predation. When we instead first estimated the oviposition rate at low density from experimental data, however, the best model included density dependence in oviposition, and a model that included density dependence in both oviposition and predation performed nearly as well. This result is consistent with our experiments and suggests that experiments can enhance the usefulness of stochastic models in ecology.

Combining Stochastic Models with Experiments to Understand the Dynamics of Monarch Butterfly Colonization

Stochastic models are of increasing importance in ecology but are usually only applied to observational data. Here we use a stochastic population model to combine experimental and observational data to understand the colonization of old fields by monarch butterflies Danaus plexippus. We experimentally tested for density dependence in oviposition rates when predators were excluded, and we measured predation rates under natural conditions. Significance tests on the resulting data showed that both oviposition and predation were density dependent but could not show how oviposition and mortality combine to determine egg densities in nature. We therefore used our data to calculate the Akaike Information Criterion to choose between a nested suite of stochastic models that differed in their oviposition and mortality terms. When we simply fit the models to the observational data, the best model assumed density independence in both oviposition and predation. When we instead first estimated the oviposition rate at low density from experimental data, however, the best model included density dependence in oviposition, and a model that included density dependence in both oviposition and predation performed nearly as well. This result is consistent with our experiments and suggests that experiments can enhance the usefulness of stochastic models in ecology.

Effects of photoperiod, temperature, and host plant age on induction of reproductive diapause and development time in Danaus plexippus

Abstract 1. Diapause induction in monarch butterflies Danaus plexippus was studied using adults captured from the wild in Minnesota and Wisconsin, and individuals reared under outdoor and controlled conditions.2. Oocyte presence in females and ejaculatory duct mass in males were used to indicate reproductive status.3. Some wild individuals were in diapause in mid‐August, and all males and females were in diapause by late August and early September respectively.4. Individuals reared under decreasing day lengths and fluctuating temperatures were more likely to be in diapause than were individuals reared under long or short day lengths or constant temperatures.5. Individuals fed potted old Asclepias curassavica plants were more likely to be in diapause than were those fed potted young host plants; when cuttings of Asclepias syriaca plants from the field or greenhouse pots were used, there was no effect of host plant age.6. Extremely high temperatures increased the number of day‐degrees required for development from egg to adult, while decreasing day lengths and older host plants tended to decrease the number of day‐degrees required for development.7. There appears to be a continuum of reproductive development in monarchs, with gradual declines in mean ejaculatory duct mass and oocyte production during the late summer.8. None of the experimental treatments led to 100% diapause, and diapause was more likely to occur in monarchs subjected to more than one diapause‐inducing cue.

Associations between host migration and the prevalence of a protozoan parasite in natural populations of adult monarch butterflies

Summary1. Monarch butterfliesDanaus plexippus(L.) (Lepidoptera: Nymphalidae) are susceptible to infection by the obligate protozoan parasiteOphryocystis elektroscirrha(McLaughlin and Myers) (Apicomplexa: Neogregarinida). Because monarchs form resident and migratory populations in different parts of the world, this host–parasite system provides the opportunity to examine how variation in parasite prevalence relates to host movement patterns.2. Parasite prevalence was evaluated using 14 790 adult monarchs captured between 1968 and 1997. Comparison of three populations in North America indicated that parasite prevalence is associated negatively with host dispersal distances. A continuously breeding, nonmigratory population in southern Florida showed high prevalence (over 70% heavily infected). The western population migrates moderate distances to overwintering sites on the Pacific Coast and has intermediate prevalence (30% heavily infected). The eastern migratory population, which travels the longest distance to Mexican overwintering sites, has exhibited less than 8% infection throughout the past 30 years.3. Variation in parasite loads within North American migratory populations was investigated to determine whether the prevalence of heavy infection and average parasite loads declined during migration or overwintering. Average parasite loads of summer‐breeding adults in western North America decreased with increasing distance from overwintering sites. This suggests that heavily infected monarchs are less likely to remigrate long distances in spring. No differences in the frequency of heavily infected adults were found among eastern or western North American monarchs throughout the overwintering period, however, suggesting that this parasite does not affect overwintering mortality.4. Changes in the prevalence of monarchs with low parasite loads demonstrate that spore transfer occurs during migration and overwintering, possibly when adult butterflies contact each other as a result of their clustering behaviour.5. This study of geographical and temporal variation inO. elektroscirrhaamong populations ofD. plexippusdemonstrates the potential role of seasonal migration in mediating interactions between hosts and parasites, and suggests several mechanisms through which migratory behaviour may influence parasite prevalence.

Influence pf forest canopy closure on rates of bird predation on overwintering Monarch butterflies Danaus plexippus L.

The Monarch Butterfly Special Biosphere Reserve (MBSBR) was created in 1986 to protect the overwintering sites of the monarch butterfly Danaus plexippus. However, current political and economic pressures are leading government officials to consider the authorization of logging permits in the core areas of the reserve. In order to investigate how increased logging may impact monarch survival in the MBSBR, we studied how monarch butterfly mortality caused by bird predation is currently affected by logging extractions that occurred in the early 1980s. We monitored daily bird predation in closed and opened areas and found that monarch butterflies overwintering in areas with low tree density, low basal area, and low canopy coverage suffered higher mortality rates than monarchs in quadrats with closed forest. Since bird predation is only one of several negative effects that logging may have on the survival of monarchs overwintering in México, we recommend that logging permits should not be authorized by the government in the core areas of the MBSBR.

Oviposition stimulants for the monarch butterfly: Flavonol glycosides from Asclepias curassavica

The monarch butterfly Danaus plexippus oviposits on milkweed plants, primarily within the Asclepiadaceae. Oviposition stimulants responsible for host plant recognition were isolated from Asclepias curassavica. Six flavonoid glycosides-quercetin 3-O-(2″,6″-α- l-dirhamnopyranosyl )-β- d-galactopyranoside , quercetin 3-O-β- d-glucopyranosyl -(1 → 6)-β- d-galactopyranoside , quercetin 3-O-(2″-O-α- l-rhamnopyranosyl )-β- d-galactopyranoside , quercetin 3-O-α- l-rhamnopyranosyl -(1 → 6-β- d-glucopyranoside , quercetin 3-O-β- d-galactopyranoside , quercetin 3-O-β- d-glucopyranoside , and an unidentified flavonoid mixture were isolated and characterized from this plant. An additional glycoside, possibly quercetin 3-O-(2″,6″-α- l-dirhamnopyranosyl )-β- d-glucopyranoside , which could not be separated from the first triglycoside, was also found in some batches of plant extract. The two dirhamnosyl glycosides, the glucosylgalactose and the rutinoside were found to be active as oviposition stimulants at 0.5 g leaf equivalents.

The relationship between the Pgi locus and the ability to fly at low temperatures in the monarch butterfly Danaus plexippus.

Differences in genetic structure of samples of monarch butterflies caught at different times of day have been reported previously. This paper compares differences in allele and heterozygote frequencies at the Pgi locus between animals flying early and those flying late in outdoor flight cages and between animals able and animals unable to fly at a constant low temperature. There were consistent effects across a number of tests and in comparisons with field data, especially in males. Animals with the M allele were more likely to be able to fly at low temperatures, to become active early in outdoor flight cages, and to be caught early in the field. Also, differences were observed between males and females in the effect of allele on flight activity.

The relationship between thePgi locus and the ability to fly at low temperatures in the monarch butterflyDanaus plexippus

The relationship between thePgi locus and the ability to fly at low temperatures in the monarch butterflyDanaus plexippus

Prolonged Mating in the Monarch Butterfly Danaus plexippus and Nightfall as a Cue for Sperm Transfer

Theory predicts that paternity assurance adaptations should be associated especially with species in which there is strong male competition for females, e.g. as in insects like the monarchs butterfly, Danaus plexippus, where males can enforce copulations on females which, in turn, exhibit strong polyandry. Observations on mating monarchs showed that copula termination almost exclusively occurred after darkness had fallen, and by interrupting mating pairs and dissecting females, we showed that sperm transfer did not start until after dark, irrespective of the time spent in copula in light. This, together with the observation that copula duration increased from 9 to 27 h when pairs mated in constant light, suggested that nightfall per se is the stimulus that initiates sperm transfer and determines the timing of copula termination. These prolonged matings in liaison with the duration of the night, allow time for sperm delivered by a male to be used for fertilizing eggs by the female on the day after copulation.

Energy, Matter and Nitrogen Utilization by the Larvae of the Monarch Butterfly Danaus plexippus

were evaluated for the larvae of Danaus plexippus (L.) fed Asclepias syriaca at 27?C, 80-900% RH, 14 h light. Gross efficiencies of growth (100 G/I), 16 % (dry weight), 21 % (caloric equivalents) and 480% (nitrogen) are similar to the efficiencies of other lepidoptera while net efficiencies of growth (100 G/(I-F)), 35 %O (dry weight) and 4400 (caloric equivalents), are lower. The average to low efficiencies of D. plexippus do not support the hypothesis that oligophagous lepidoptera are more efficient at utilizing their resources than polyphagous lepidoptera.