Monarch butterfly population decline in North America: identifying the threatening processes

Changes in landscape and climate in Mexico and Texas reveal small effects on migratory habitat of monarch butterflies (Danaus plexippus)

The decline of the iconic monarch butterfly (Danaus plexippus) in North America has motivated research on the impacts of land use and land cover (LULC) change and climate variability on monarch habitat and population dynamics. We investigated spring and fall trends in LULC, milkweed and nectar resources over a 20-year period, and ~ 30 years of climate variables in Mexico and Texas, U.S. This region supports spring breeding, and spring and fall migration during the annual life cycle of the monarch. We estimated a - 2.9% decline in milkweed in Texas, but little to no change in Mexico. Fall and spring nectar resources declined < 1% in both study extents. Vegetation greenness increased in the fall and spring in Mexico while the other climate variables did not change in both Mexico and Texas. Monarch habitat in Mexico and Texas appears relatively more intact than in the midwestern, agricultural landscapes of the U.S. Given the relatively modest observed changes in nectar and milkweed, the relatively stable climate conditions, and increased vegetation greenness in Mexico, it seems unlikely that habitat loss (quantity or quality) in Mexico and Texas has caused large declines in population size or survival during migration.

Animal migration in the Anthropocene: threats and mitigation options

Animal migration has fascinated scientists and the public alike for centuries, yet migratory animals are facing diverse threats that could lead to their demise. The Anthropocene is characterised by the reality that humans are the dominant force on Earth, having manifold negative effects on biodiversity and ecosystem function. Considerable research focus has been given to assessing anthropogenic impacts on the numerical abundance of species/populations, whereas relatively less attention has been devoted to animal migration. However, there are clear linkages, for example, where human-driven impacts on migration behaviour can lead to population/species declines or even extinction. Here, we explore anthropogenic threats to migratory animals (in all domains - aquatic, terrestrial, and aerial) using International Union for the Conservation of Nature (IUCN) Threat Taxonomy classifications. We reveal the diverse threats (e.g. human development, disease, invasive species, climate change, exploitation, pollution) that impact migratory wildlife in varied ways spanning taxa, life stages and type of impact (e.g. from direct mortality to changes in behaviour, health, and physiology). Notably, these threats often interact in complex and unpredictable ways to the detriment of wildlife, further complicating management. Fortunately, we are beginning to identify strategies for conserving and managing migratory animals in the Anthropocene. We provide a set of strategies that, if embraced, have the potential to ensure that migratory animals, and the important ecological functions sustained by migration, persist.

Monarch Butterflies in Western North America: A Holistic Review of Population Trends, Ecology, Stressors, Resilience and Adaptation

Monarch butterfly populations in western North America suffered a substantial decline, from millions of butterflies overwintering in California in the 1980s to less than 400,000 at the beginning of the 21st century. The introduction of neonicotinoid insecticides in the mid-1990s and their subsequent widespread use appears to be the most likely major factor behind this sudden decline. Habitat loss and unfavorable climates (high temperatures, aridity, and winter storms) have also played important and ongoing roles. These factors kept overwintering populations stable but below 300,000 during 2001-2017. Late winter storm mortality and consequent poor spring reproduction drove winter populations to less than 30,000 butterflies during 2018-2019. Record high temperatures in California during the fall of 2020 appeared to prematurely terminate monarch migration, resulting in the lowest overwintering population (1899) ever recorded. Many migrants formed winter-breeding populations in urban areas. Normal seasonal temperatures in the autumns of 2021 and 2022 enabled overwintering populations to return to around the 300,000 level, characteristic of the previous two decades. Natural enemies (predators, parasitoids, parasites, and pathogens) may be important regional or local drivers at times but they are a consistent and fundamental part of monarch ecology. Human interference (capture, rearing) likely has the least impact on monarch populations. The rearing of monarch caterpillars, particularly by children, is an important human link to nature that has positive ramifications for insect conservation beyond monarch butterflies and should be encouraged.

Forecasting insect dynamics in a changing world

Predicting how insects will respond to stressors through time is difficult because of the diversity of insects, environments, and approaches used to monitor and model. Forecasting models take correlative/statistical, mechanistic models, and integrated forms; in some cases, temporal processes can be inferred from spatial models. Because of heterogeneity associated with broad community measurements, models are often unable to identify mechanistic explanations. Many present efforts to forecast insect dynamics are restricted to single-species models, which can offer precise predictions but limited generalizability. Trait-based approaches may offer a good compromise that limits the masking of the ranges of responses while still offering insight. Regardless of the modeling approach, the data used to parameterize a forecasting model should be carefully evaluated for temporal autocorrelation, minimum data needs, and sampling biases in the data. Forecasting models can be tested using near-term predictions and revised to improve future forecasts.

Using community science to map western monarch butterflies (Danaus plexippus) in spring

Migratory animals follow seasonal cycles comprising linked phases often with different habitat requirements and demographic processes. Conservation of migratory species therefore must consider the full seasonal cycle to identify points limiting population viability. For western monarch butterflies, which have experienced significant declines, early spring is considered a critical period in the annual population cycle. However, records of western monarchs in early spring, when overall abundance is lowest, have historically been extremely limited. We used a community science initiative, the Western Monarch Mystery Challenge, to collect data on monarch distribution throughout the western United States between February 14th and April 22nd over 3 years. Using data from the Western Monarch Mystery Challenge and iNaturalist, we identified potential breeding habitat for western monarchs in early spring that spanned a large geographic area and several ecoregions. We observed monarchs in early spring that likely eclosed in the current year, suggesting that population expansion from overwintering sites reflects both movement and population growth. The number of records of western monarchs from early spring was higher during the Mystery Challenge (33.0/year) than earlier years (5.1/year). This study demonstrates the potential for and limitations of community science to increase our understanding of species at points in the life cycle when they are rare.

Population dynamics and drivers of the eastern monarch (Danaus plexippus) across its full annual cycle: a cross-scale synthesis of a model migratory species

The monarch butterfly is arguably the best-known butterfly species throughout its global range. Declines in the size of the overwintering colonies in Mexico have sparked controversy regarding the conservation of the species and this controversy has been heightened since the United States Fish and Wildlife Service and International Union for the Conservation of Nature concluded that the eastern monarch populations were threatened (or in the case of United States Fish and Wildlife Service, warranted listing). Drivers of decline vary through space and time. Here, we present a synthesis of longitudinal monarch abundance studies that aim to disentangle the putative drivers of decline from one another. We find remarkable consistency that suggests monarch populations are indeed declining and that potential drivers of such decline shift over time. We strongly encourage future work on the species paired with mechanistic, experimental designs to address some long-standing knowledge gaps.

The monarch butterfly in Mexico: a conservation model

Each fall, millions of monarch butterflies (Danaus plexippus L.) travel from Canada and the United States to overwinter in Mexico and California. In 2022, the IUCN listed migratory monarchs as endangered because of their population decline. The main accepted drivers are widespread use of herbicides, effects of climate, and land use change that causes habitat loss. We analyzed the main actions taken to officially protect the overwintering sites and the migration phenomenon with the establishment of the Monarch Butterfly Biosphere Reserve in 2000. The conservation of the monarch overwintering sites in Mexico is an example of continuous work from their discovery to the present. We highlight the importance of monitoring the areas covered by overwintering monarchs in Mexico. These colonies represent the largest concentrations of monarch populations in the world. In the last 10 years, the average area covered by monarchs was 2.72 ( ± 0.47 SE) hectares.

Dynamics of stored lipids in fall migratory monarch butterflies (Danaus plexippus): Nectaring in northern Mexico allows recovery from droughts at higher latitudes

The eastern population of the North American monarch butterfly (Danaus plexippus) overwinters from November through March in the high-altitude (3000 m+) forests of central Mexico during which time they rely largely on stored lipids. These are acquired during larval development and the conversion of sugars from floral nectar by adults. We sampled fall migrant monarchs from southern Canada through the migratory route to two overwintering sites in 2019 (n = 10 locations), 2020 (n = 8 locations) and 2021 (n = 7 locations). Moderate to extreme droughts along the migratory route were expected to result in low lipid levels in overwintering monarchs but our analysis of lipid levels of monarchs collected at overwintering sites indicated that in all years most had high levels of lipids prior to winter. Clearly, a significant proportion of lipids were consistently acquired in Mexico during the last portion of the migration. Drought conditions in Oklahoma, Texas and northern Mexico in 2019 resulted in the lowest levels of lipid mass and wing loading observed in that year but with higher levels at locations southward in Mexico to the overwintering sites. Compared with 2019, lipid levels increased during the 2020 and 2021 fall migrations but were again higher during the Mexican portion of the migration than for Oklahoma and Texas samples, emphasizing a recovery of lipids as monarchs advanced toward the overwintering locations. In all 3 years, body water was highest during the Canada-USA phase of migration but then declined during the nectar foraging phase in Mexico before recovering again at the overwintering sites. The increase in mass and lipids from those in Texas to the overwintering sites in Mexico indicates that nectar availability in Mexico can compensate for poor conditions experienced further north. Our work emphasizes the need to maintain the floral and therefore nectar resources that fuel both the migration and storage of lipids throughout the entire migratory route.

The cost of movement: assessing energy expenditure in a long-distant ectothermic migrant under climate change

Migration is an energetically taxing phenomenon as animals move across vast, heterogeneous landscapes where the cost of transport is impacted by permissible ambient conditions. In this study, we assessed the energetic demands of long-distance migration in a multigenerational ectothermic migrant, the monarch butterfly (Danaus plexippus). We tested the hypotheses that temperature-dependent physiological processes reduce energy reserves faster during migration than previously estimated, and that increasing climatic temperatures resulting from the climate crisis will intensify baseline daily energy expenditure. First, we reared monarchs under laboratory conditions to assess energy and mass conversion from fifth instar to adult stages, as a baseline for migratory adult mass and ontogenetic shifts in metabolic rate from larvae to adult. Then, using historical tag-recapture data, we estimated the movement propensity and migratory pace of autumn migrants using computer simulations and subsequently calculated energy expenditure. Finally, we estimated the energy use of monarchs based on these tag-recapture data and used this information to estimate daily energy expenditure over a 57 year period. We found support for our two hypotheses, noting that incorporating standard metabolic rate into estimates of migratory energy expenditure shows higher energy demand and that daily energy expenditure has been gradually increasing over time since 1961. Our study shows the deleterious energetic consequences under current climate change trajectories and highlights the importance of incorporating energetic estimates for understanding migration by small, ectothermic migrants.

Migration genetics take flight: genetic and genomic insights into monarch butterfly migration

Monarch butterflies have emerged as a model system in migration genetics. Despite inherent challenges associated with studying the integrative phenotypes that characterize migration, recent research has highlighted genes and transcriptional networks underlying aspects of the monarch's migratory syndrome. Circadian clock genes and the vitamin A synthesis pathway regulate reproductive diapause initiation, while diapause termination appears to involve calcium and insulin signaling. Comparative approaches have highlighted genes that distinguish migratory and nonmigratory monarch populations, as well as genes associated with natural variation in propensity to initiate diapause. Population genetic techniques demonstrate that seasonal migration can collapse patterns of spatial structure at continental scales, whereas loss of migration can drive differentiation between even nearby populations. Finally, population genetics can be applied to reconstruct the monarch's evolutionary history and search for contemporary demographic changes, which can provide relevant context for understanding recently observed declines in overwintering North American monarch numbers.

Complexity, humility, and action: a current perspective on monarchs in Western North America

Recent studies have continued to shed light on the ecology of monarch butterflies (Danaus plexippus) in western North America. These studies have documented a declining overwintering population over several decades, punctuated by unexpected variability in recent years. Understanding this variability will require grappling with the spatial and temporal heterogeneity of resources and risks presented to western monarchs throughout their annual life cycle. Recent changes in the western monarch population further illustrate how interacting global change drivers can create complex causes and consequences in this system. The complexity of this system should inspire humility. However, even recognizing the limits of our current understanding, there is enough scientific common ground to take some conservation actions now.

Temporal matches between monarch butterfly and milkweed population changes over the past 25,000 years

In intimate ecological interactions, the interdependency of species may result in correlated demographic histories. For species of conservation concern, understanding the long-term dynamics of such interactions may shed light on the drivers of population decline. Here, we address the demographic history of the monarch butterfly, Danaus plexippus, and its dominant host plant, the common milkweed Asclepias syriaca (A. syriaca), using broad-scale sampling and genomic inference. Because genetic resources for milkweed have lagged behind those for monarchs, we first release a chromosome-level genome assembly and annotation for common milkweed. Next, we show that despite its enormous geographic range across eastern North America, A. syriaca is best characterized as a single, roughly panmictic population. Using approximate Bayesian computation with random forests (ABC-RF), a machine learning method for reconstructing demographic histories, we show that both monarchs and milkweed experienced population expansion during the most recent recession of North American glaciers 10,000-20,000 years ago. Our data also identify concurrent population expansions in both species during the large-scale clearing of eastern forests (∼200 years ago). Finally, we find no evidence that either species experienced a reduction in effective population size over the past 75 years. Thus, the well-documented decline of monarch abundance over the past 40 years is not visible in our genomic dataset, reflecting a possible mismatch of the overwintering census population to effective population size in this species.

Aphid infestations reduce monarch butterfly colonization, herbivory, and growth on ornamental milkweed

Anthropogenic disturbance is driving global biodiversity loss, including the monarch butterfly (Danaus plexippus), a dietary specialist of milkweed. In response, ornamental milkweed plantings are increasingly common in urbanized landscapes, and recent evidence indicates they have conservation value for monarch butterflies. Unfortunately, sap-feeding insect herbivores, including the oleander aphid (Aphis nerii), frequently reach high densities on plants in nursery settings and urbanized landscapes. Aphid-infested milkweed may inhibit monarch conservation efforts by reducing host plant quality and inducing plant defenses. To test this, we evaluated the effects of oleander aphid infestation on monarch oviposition, larval performance, and plant traits using tropical milkweed (Asclepias curassavica), the most common commercially available milkweed species in the southern U.S. We quantified monarch oviposition preference, larval herbivory, larval weight, and plant characteristics on aphid-free and aphid-infested milkweed. Monarch butterflies deposited three times more eggs on aphid-free versus aphid-infested milkweed. Similarly, larvae fed aphid-free milkweed consumed and weighed twice as much as larvae fed aphid-infested milkweed. Aphid-free milkweed had higher total dry leaf biomass and nitrogen content than aphid-infested milkweed. Our results indicate that oleander aphid infestations can have indirect negative impacts on urban monarch conservation efforts and highlight the need for effective Lepidoptera-friendly integrated pest management tactics for ornamental plants.

Additive and interactive effects of anthropogenic stressors on an insect herbivore

The pressures of global change acting on wild plants and animals include exposure to environmental toxins, the introduction of non-native species, and climate change. Relatively few studies have been reported in which these three main classes of stressors have been examined simultaneously, allowing for the possibility of synergistic effects in an experimental context. In this study, we exposed caterpillars of the Melissa blue butterfly (Lycaeides melissa) to three concentrations of chlorantraniliprole, under three experimental climates, on a diet of a native or a non-native host plant throughout larval development in a fully factorial experiment. We find that high pesticide exposure and a non-native diet exhibit strong negative effects on caterpillars, resulting in 62% and 42% reduction in survival, respectively, while interactive effects tend to be weaker, ranging from 15% to 22% reduction in survival. Interactive effects have been shown to be strong in other contexts, but do not appear to be universal; however, our study shows that the cumulative effects of stressors acting in isolation (additively) are sufficiently strong to severely reduce survival and by extension population persistence in the wild.

The effects of glyphosate exposure on gene transcription and immune function of the silkworm, Bombyx mori

Glyphosate is a widely used herbicide and crop desiccant. However, whether its extensive use has any effect on the species diversity of nontarget organisms is still unclear. In this study, we used the silkworm, Bombyx mori, as the research subject, and performed RNA sequencing to analyze the transcriptional profile of silkworm midgut after exposure to glyphosate at 2975.20 mg/L (a concentration commonly used at mulberry fields). A total of 125 significantly differentially expressed genes (DEGs) were detected in the midgut of glyphosate-exposed silkworm (q < 0.05), of which 53 were upregulated and 72 were downregulated. Gene ontology enrichment analysis showed that the DEGs were mainly enriched in biological process, cellular component, and molecular function. Kyoto encyclopedia of genes and genomes analysis showed that the differential genes were mainly related to oxidative stress, nutrient metabolism, and immune defense pathways, including oxidative stress-related Cat and Jafrac1, nutrient metabolism-related Fatp and Scpx, and immune-related CYP6AN2, UGT40B4, CTL11, serpin-2, and so forth. Experimental verification showed that glyphosate exposure led to a 4.35-fold increase in the mortality of silkworm after Beauveria bassiana infection, which might be caused by the decreased PO (phenoloxidase) activity and impaired immunity. These results provide evidence for the potential effects of residue glyphosate on the physiological functions of silkworm, and also provide a reference for the biosafety evaluation of glyphosate.

Timing of a plant-herbivore interaction alters plant growth and reproduction

Phenological shifts have the potential to change species interactions, but relatively few studies have used experimental manipulations to examine the effects of variation in timing of an interspecific interaction across a series of life stages of a species. Although previous experimental studies have examined the consequences of phenological timing in plant-herbivore interactions for both plants and their herbivores, less is known about their effects on subsequent plant reproduction. Here, we conducted an experiment to determine how shifts in the phenological timing of monarch (Danaus plexippus) larval herbivory affected milkweed (Asclepias fascicularis) host plant performance, including effects on growth and subsequent effects on flower and seed pod phenology and production. We found that variation in the timing of herbivory affected both plant growth and reproduction, with measurable effects several weeks to several months after herbivory ended. The timing of herbivory had qualitatively different effects on vegetative and reproductive biomass: early-season herbivory had the strongest effects on plant size, whereas late-season herbivory had the strongest effects on the production of viable seeds. These results show that phenological shifts in herbivory can have persistent and qualitatively different effects on different life stages across the season.

Pollinator biological traits and ecological interactions mediate the impacts of mosquito-targeting malathion application

Mosquito adulticides are perceived by the public as detrimental to nontarget arthropods, contributing to declines of native and beneficial insects. However, the actual impact of adulticides on nontarget arthropods in nature needs to incorporate biological and ecological elements. Here, we investigated the effect of biological/behavioral traits (butterfly roosting at different heights, roosting in sites underneath foliage, bumblebee hive usage) and interactions (parasitism, predation) of pollinators (butterflies and bumblebees) that could mediate the impacts of malathion application in manipulative semi-field experiments in Florida, USA. Roosting height from the spray route had a significant negative relationship with mortality of butterflies treated with ULV malathion, with high survival at the highest roosting height (7 m), but butterflies roosting among vegetation did not have higher survival. Bumblebees with hive access had significantly higher survival than bumblebees without hive access. Host plants treated with ULV malathion significantly reduced parasitism of monarch eggs by Trichogramma platneri, but increased predation of monarch caterpillars by Polistes paper wasps. These data provide insight into the realistic impacts of adulticide applications on pollinators in nature which will enable mosquito control districts to better limit nontarget effects of adulticide treatments and may help to address concerns related to potential nontarget effects.

Impact of multiple small and persistent threats on extinction risk

Many species may face multiple distinct and persistent drivers of extinction risk, yet theoretical and empirical studies tend to focus on the single largest driver. This means that existing approaches potentially underestimate and mischaracterize future risks to biodiversity. We synthesized existing knowledge on how multiple drivers of extinction can interact to influence a species' overall extinction probability in a probabilistic model of extinction risk that incorporated the impacts of multiple drivers of extinction risk, their interactions, and their accumulative effects through time. We then used this model framework to explore how different threats, interactions between them, and time trends may affect a species' overall extinction probability. Multiple small threats together had potential to pose a large cumulative extinction risk; for example, 10 individual threats posed a 1% extinction risk each and cumulatively posed a 9.7% total extinction risk. Interactions among drivers resulted in escalated risk in some cases, and persistent threats with a small (1%) extinction risk each decade ultimately posed large extinction risk over 100 (9.6% total extinction risk) to 200 years (18.2% total extinction risk). By estimating long-term extinction risk posed by several different factors and their interactions, this approach provides a framework to identify drivers of extinction risk that could be proactively targeted to help prevent species currently of least concern from becoming threatened with extinction.

Collaborative Conservation by Botanical Gardens: Unique Opportunities for Local to Global Impacts

Conservation organizations with common missions can find strength and synergy in collaboration. Collaboration can also be challenging, especially finding the right partnerships or organizations to lead. Within the “ecosystem” of conservation organizations, botanical gardens have a unique array of resources and expertise which make them ideal candidates for leadership or partnership in collaborative conservation efforts. We will explore this idea by examining four conservation initiatives at Desert Botanical Garden (Phoenix, AZ, USA) that approach collaborative conservation on regional, state, and international scales. On a regional scale, Metro Phoenix EcoFlora and the Central Arizona Conservation Alliance lead landscape-level conservation by providing a structure for more than 60 official conservation partners, by generating data, and through public engagement needed in a rapidly developing region. On the state scale, Great Milkweed Grow Out is an initiative for pollinator conservation that provides expertise, materials, and opportunities for a wide range of partners across Arizona. Desert Botanical Garden’s endangered plant species conservation efforts provide expertise and resources through horticulture and seed preservation for threatened and endangered plants across the US and internationally. We will share the structure of each program where applicable, how they came to fruition, and their successes. Through each case study, we will highlight the ways positioning within a botanical garden has benefitted the program and success in collaboration. We will also highlight unique challenges. Botanical gardens provide unique opportunities, and they should not be overlooked when seeking a conservation partner or leader.

Opposing global change drivers counterbalance trends in breeding North American monarch butterflies

Many insects are in clear decline, with monarch butterflies (Danaus plexippus) drawing particular attention as a flagship species. It is well documented that, among migratory populations, numbers of overwintering monarchs have been falling across several decades, but trends among breeding monarchs are less clear. Here, we compile >135,000 monarch observations between 1993 and 2018 from the North American Butterfly Association's annual butterfly count to examine spatiotemporal patterns and potential drivers of adult monarch relative abundance trends across the entire breeding range in eastern and western North America. While the data revealed declines at some sites, particularly the US Northeast and parts of the Midwest, numbers in other areas, notably the US Southeast and Northwest, were unchanged or increasing, yielding a slightly positive overall trend across the species range. Negative impacts of agricultural glyphosate use appeared to be counterbalanced by positive effects of annual temperature, particularly in the US Midwest. Overall, our results suggest that population growth in summer is compensating for losses during the winter and that changing environmental variables have offsetting effects on mortality and/or reproduction. We suggest that density-dependent reproductive compensation when lower numbers arrive each spring is currently able to maintain relatively stable breeding monarch numbers. However, we caution against complacency since accelerating climate change may bring growing threats. In addition, increases of summer monarchs in some regions, especially in California and in the south, may reflect replacement of migratory with resident populations. Nonetheless, it is perhaps reassuring that ubiquitous downward trends in summer monarch abundance are not evident.

Flying on empty: Reduced mitochondrial function and flight capacity in food-deprived monarch butterflies

Mitochondrial function is fundamental to organismal performance, health, and fitness - especially during energetically challenging events, such as migration. With this investigation, we evaluated mitochondrial sensitivity to ecologically relevant stressors. We focused on an iconic migrant, the North American monarch butterfly (Danaus plexippus), and examined the effects of two stressors: seven days of food deprivation, and infection by the protozoan parasite Ophryocystis elektroscirrha (known to reduce survival and flight performance). We measured whole-animal resting (RMR) and peak flight metabolic rate, and mitochondrial respiration of isolated mitochondria from the flight muscles. Food deprivation reduced mass-independent RMR and peak flight metabolic rate, whereas infection did not. Fed monarchs used mainly lipids in flight (respiratory quotient 0.73), but the respiratory quotient dropped in food-deprived individuals, possibly indicating switching to alternative energy sources, such as ketone bodies. Food deprivation decreased mitochondrial maximum oxygen consumption but not basal respiration, resulting in lower respiratory control ratio (RCR). Furthermore, food deprivation decreased mitochondrial complex III activity, but increased complex IV activity. Infection did not result in any changes in these mitochondrial variables. Mitochondrial maximum respiration rate correlated positively with mass-independent RMR and flight metabolic rate, suggesting a link between mitochondria and whole-animal performance. In conclusion, low food availability negatively affects mitochondrial function and flight performance, with potential implications on migration, fitness, and population dynamics. Although previous studies have reported poor flight performance in infected monarchs, we found no differences in physiological performance, suggesting that reduced flight capacity may be due to structural differences or low energy stores.

Bumble bees exhibit body size clines across an urban gradient despite low genetic differentiation

Environmental heterogeneity resulting from human-modified landscapes can increase intraspecific trait variation. However, less known is whether such phenotypic variation is driven by plastic or adaptive responses to local environments. Here, we study five bumble bee (Apidae: Bombus) species across an urban gradient in the greater Saint Louis, Missouri region in the North American Midwest and ask: (1) Can urban environments induce intraspecific spatial structuring of body size, an ecologically consequential functional trait? And, if so, (2) is this body size structure the result of plasticity or adaptation? We additionally estimate genetic diversity, inbreeding, and colony density of these species—three factors that affect extinction risk. Using ≥ 10 polymorphic microsatellite loci per species and measurements of body size, we find that two of these species (Bombus impatiens, Bombus pensylvanicus) exhibit body size clines across the urban gradient, despite a lack of population genetic structure. We also reaffirm reports of low genetic diversity in B. pensylvanicus and find evidence that Bombus griseocollis, a species thought to be thriving in North America, is inbred in the greater Saint Louis region. Collectively, our results have implications for conservation in urban environments and suggest that plasticity can cause phenotypic clines across human-modified landscapes.

Does the Presence of the Biological Control Agent, Hypena opulenta (Lepidoptera: Erebidae) on Swallow-Worts Deter Monarch Oviposition?

Invasive black and pale swallow-worts (Vincetoxicum nigrum (L.) Moench, and Vincetoxicum rossicum Kelopow), which are related to milkweeds, can act as ecological traps for monarch butterflies (Danaus plexippus L. (Lepidoptera: Nymphalidae)) as they lay eggs on them that fail to develop. A recently approved biological control agent against swallow-worts, Hypena opulenta Christoph, occupies the same feeding guild on swallow-worts as monarch larvae and could be perceived as a competitor to monarchs. We tested how the presence of this defoliating moth on swallow-worts may influence monarch host selection. In a two-year field experiment, we placed pale swallow-wort plants that were either infested with H. opulenta or noninfested as well as common milkweed (Asclepias syriaca L.), into monarch habitats to assess oviposition rates. In the laboratory, monarchs were either given a choice or not between milkweeds and black swallow-worts with or without H. opulenta. While monarchs strongly preferred common milkweed in the field, up to 25% of the eggs we observed were laid on pale swallow-wort, without preference for swallow-wort with (10.7%) or without (14.3%) H. opulenta. In laboratory choice and no-choice tests, monarchs did not lay any eggs on black swallow-wort, likely because of the long-term laboratory rearing on common milkweeds. Our results confirm that pale swallow-wort may act as an oviposition sink to monarchs in Michigan as well. Since the biological control program is still in its infancy, the nature of interactions between monarchs and H. opulenta may change as the biocontrol agent becomes more widespread.

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

Insect-pathogen dynamics can show seasonal and inter-annual variation that covaries 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 patterns and drivers of infection. 3. Here we compiled data on OE infection spanning 50 years, from wild monarchs sampled in the USA, 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. 4. Average infection prevalence was four times higher in western compared to eastern subpopulations. In eastern North America, the proportion of infected monarchs increased three-fold since the mid-2000s. In the western region, the proportion of infected monarchs declined sharply from 2000-2015, 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 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. 5. 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.

Long-term monitoring indicates shifting fall migration timing in monarch butterflies (Danaus plexippus)

Eastern North American monarch butterflies (Danaus plexippus) embark on a yearly migration between summer breeding grounds in the northern United States and southern Canada and overwintering sites in central Mexico, traveling up to 4300 km. This annual multi-generational migration cycle, like many seasonal natural phenomena, may be impacted by recent changes in climate and habitat. We investigated long-term trends in monarch abundance and fall migration timing over a 29-year period in Cape May, New Jersey, using data collected from daily population surveys designed to track patterns of occurrence during the fall migration period through Cape May (1 Sept-31 Oct). Between 1992 and 2020, the migration midpoint, average peak migration day and first peak migration day shifted between 16 and 19 days later in the season, an average of approximately six days per decade. This observed shift in migration timing is correlated with increasing temperatures in September and October in northeastern monarch breeding grounds over the study period. Our data do not demonstrate a significant directional trend in monarch abundance over the study period, yet population data collected at overwintering sites in Mexico indicate a substantial decline over the same period. Further postponement of fall migration may lead to lower migration success and exacerbate the overall decline of this iconic species.

The Role of Experiments in Monarch Butterfly Conservation: A Review of Recent Studies and Approaches

Monarch butterflies (Danaus plexippus) (Lepidoptera Danaidae Danaus plexippus (Linnaeus)) are an iconic species of conservation concern due to declines in the overwintering colonies over the past twenty years. Because of this downward trend in overwintering numbers in both California and Mexico, monarchs are currently considered 'warranted-but-precluded' for listing under the Endangered Species Act. Monarchs have a fascinating life history and have become a model system in chemical ecology, migration biology, and host-parasite interactions, but many aspects of monarch biology important for informing conservation practices remain unresolved. In this review, we focus on recent advances using experimental and genetic approaches that inform monarch conservation. In particular, we emphasize three areas of broad importance, which could have an immediate impact on monarch conservation efforts: 1) breeding habitat and host plant use, 2) natural enemies and exotic caterpillar food plants, and 3) the utility of genetic and genomic approaches for understanding monarch biology and informing ongoing conservation efforts. We also suggest future studies in these areas that could improve our understanding of monarch behavior and conservation.

Host Plant Species Mediates Impact of Neonicotinoid Exposure to Monarch Butterflies

Simple Summary

Neonicotinoids are the most widely used insecticides in North America and many studies document the negative effects of neonicotinoids on bees. Monarch butterflies are famous for their long-distance migrations, and for their ability to sequester toxins from their milkweed host plants. The neonicotinoids imidacloprid and clothianidin were suggested to correlate with declines in North American monarchs. We examined how monarch development, survival, and flight were affected by exposure to neonicotinoids, and how these effects depend on milkweed host plant species that differ in their cardenolide toxins. Monarch survival and flight were unaffected by low and intermediate neonicotinoid doses. At the highest dose, neonicotinoids negatively affected monarch pupation and survival, for caterpillars that fed on the least toxic milkweed. Monarchs fed milkweed of intermediate toxicity experienced moderate negative effects of high insecticide doses. Monarchs fed the most toxic milkweed species had no negative consequences associated with neonicotinoid treatment. Our work shows that monarchs tolerate low neonicotinoid doses, but experience detrimental effects at higher doses, depending on milkweed species. To our knowledge, this is the first study to show that host plant species potentially reduce the residue of neonicotinoid insecticides on the leaf surface, and this phenomenon warrants further investigation.

Abstract

Neonicotinoids are the most widely used insecticides in North America. Numerous studies document the negative effects of neonicotinoids on bees, and it remains crucial to demonstrate if neonicotinoids affect other non-target insects, such as butterflies. Here we examine how two neonicotinoids (imidacloprid and clothianidin) affect the development, survival, and flight of monarch butterflies, and how these chemicals interact with the monarch’s milkweed host plant. We first fed caterpillars field-relevant low doses (0.075 and 0.225 ng/g) of neonicotinoids applied to milkweed leaves (Asclepias incarnata), and found no significant reductions in larval development rate, pre-adult survival, or adult flight performance. We next fed larvae higher neonicotinoid doses (4–70 ng/g) and reared them on milkweed species known to produce low, moderate, or high levels of secondary toxins (cardenolides). Monarchs exposed to the highest dose of clothianidin (51–70 ng/g) experienced pupal deformity, low survival to eclosion, smaller body size, and weaker adult grip strength. This effect was most evident for monarchs reared on the lowest cardenolide milkweed (A. incarnata), whereas monarchs reared on the high-cardenolide A. curassavica showed no significant reductions in any variable measured. Our results indicate that monarchs are tolerant to low doses of neonicotinoid, and that negative impacts of neonicotinoids depend on host plant type. Plant toxins may confer protective effects or leaf physical properties may affect chemical retention. Although neonicotinoid residues are ubiquitous on milkweeds in agricultural and ornamental settings, commonly encountered doses below 50 ng/g are unlikely to cause substantial declines in monarch survival or migratory performance.

Changes in climate drive recent monarch butterfly dynamics

Declines in the abundance and diversity of insects pose a substantial threat to terrestrial ecosystems worldwide. Yet, identifying the causes of these declines has proved difficult, even for well-studied species like monarch butterflies, whose eastern North American population has decreased markedly over the last three decades. Three hypotheses have been proposed to explain the changes observed in the eastern monarch population: loss of milkweed host plants from increased herbicide use, mortality during autumn migration and/or early-winter resettlement and changes in breeding-season climate. Here, we use a hierarchical modelling approach, combining data from >18,000 systematic surveys to evaluate support for each of these hypotheses over a 25-yr period. Between 2004 and 2018, breeding-season weather was nearly seven times more important than other factors in explaining variation in summer population size, which was positively associated with the size of the subsequent overwintering population. Although data limitations prevent definitive evaluation of the factors governing population size between 1994 and 2003 (the period of the steepest monarch decline coinciding with a widespread increase in herbicide use), breeding-season weather was similarly identified as an important driver of monarch population size. If observed changes in spring and summer climate continue, portions of the current breeding range may become inhospitable for monarchs. Our results highlight the increasingly important contribution of a changing climate to insect declines.

Modeling an aspirational connected network of protected areas across North America

Connecting protected areas remains an important global conservation strategy in the face of ongoing and future threats to biodiversity. Amid our growing understanding of how species' distributions will respond to climate change, conservation scientists need to plan for connectivity conservation across entire continents. We modeled multiscale connectivity priorities based on the least human-modified lands between large protected areas of North America using least-cost and circuit theory approaches. We first identified priority corridors between large protected areas, then characterized the network's structure to unveil priority linkages most important for maintaining network- and regional-level connectivity. Agreement between least-cost corridors and current flow varied throughout North America, reflecting permeable landscape conditions and "pinch points" where potential ecological flows may concentrate between protected areas. Priority network-level linkages derived from each approach were similar throughout the continental network (e.g., Rocky Mountains and Canadian boreal), but critical linkages that bridged regional protected-area networks varied. We emphasize the importance of planning for connectivity at continental scales and demonstrate the utility of multiple methods when mapping connectivity priorities across large spatial extents with wide gradients in landscape conditions.

Capabilities and limitations of using DNA metabarcoding to study plant-pollinator interactions

Many pollinator populations are experiencing declines, emphasizing the need for a better understanding of the complex relationship between bees and flowering plants. Using DNA metabarcoding to describe plant-pollinator interactions eliminates many challenges associated with traditional methods and has the potential to reveal a more comprehensive understanding of foraging behavior and pollinator life history. Here we use DNA metabarcoding of ITS2 and rbcL gene regions to identify plant species present in pollen loads of 404 bees from three habitats in eastern Oregon. Our specific objectives were to 1) determine whether plant species identified using DNA metabarcoding are consistent with plant species identified using observations, 2) compare characterizations of diet breadth derived from foraging observations to those based on plant species assignments obtained using DNA metabarcoding, and 3) compare plant species assignments produced by DNA metabarcoding using a "regional" reference database to those produced using a "local" database. At the three locations, 31-86% of foraging observations were consistent with DNA metabarcoding data, 8-50% of diet breadth characterizations based on observations differed from those based on DNA metabarcoding data, and 22-25% of plant species detected using the regional database were not known to occur in the study area in question. Plant-pollinator networks produced from DNA metabarcoding data had higher sampling completeness and significantly lower specialization than networks based on observations. Here, we examine some strengths and limitations of using DNA metabarcoding to identify plant species present in bee pollen loads, make ecological inferences about foraging behavior, and provide guidance for future research.

Can the growing of transgenic maize threaten protected Lepidoptera in Europe?

We evaluated whether protected European butterflies can potentially be at risk if transgenic maize is extensively grown in Central Europe. We explored potential consequences of both insect resistant (IR) and herbicide resistant (HR) transgenic maize. IR maize can produce pollen that is toxic to lepidopteran larvae, and this puts butterfly species at possible risk if the presence of young larvae coincides with maize flowering, during which large quantities of maize pollen can be deposited on vegetation. By considering the timing of maize flowering in Europe and the phenology of the protected Lepidoptera species, we found that 31 species had at least one generation where 50% of the larval stage overlapped with maize flowering, and 69 species for which first instar larvae were present during maize pollen shedding. HR maize allows high concentration herbicide treatments on fields without seasonal limitation, which can drastically reduce weed densities. In cases where such weed species are host plants for protected butterflies, reduced host plant/food availability can result, causing population decreases. By using published information, we first identified the important weed species in major maize-growing European countries. Subsequently, we checked whether the host plants of protected Lepidoptera included species that are common maize weeds. We identified 140 protected species having food plants that are common weeds in one or more of the major European maize-growing countries. If HR maize is grown in Europe, there is a potential hazard that their food plants will seriously decline, causing a subsequent decline of these protected species.

Mapping the premigration distribution of eastern Monarch butterflies using community science data

Knowing the distribution of migratory species at different stages of their life cycle is necessary for their effective conservation. For the Monarch butterfly (Danaus plexippus), although its overwintering distribution is well known, the available information on premigration distribution is limited to the studies estimating the natal origins of overwintering Monarchs in Mexico (i.e., postmigration data). However, the premigration distribution and the natal origins of overwintering Monarchs can be equivalent only if we assume that migrating Monarchs have the same mortality rate irrespective of their origins. To estimate Monarchs' premigration distribution, we used data reported by community scientists before Monarchs start their fall migration, that is, before migration mortality, and controlled for sampling bias. Our premigration distribution map indicated that Minnesota, Texas, and Ontario are the states/provinces with the highest abundance of Monarch in North America. Although this higher estimated abundance can be related to the large sizes of these states/provinces, this information is still important because it identifies the management jurisdictions with the largest responsibility for the conservation of the premigration population of Monarchs. Our premigration distribution map will be useful in future studies estimating the rates, distribution, and causes of mortality in migrating Monarchs.

High Survivorship of First-Generation Monarch Butterfly Eggs to Third Instar Associated with a Diverse Arthropod Community

Simple Summary

The eastern migratory population of the monarch butterfly has been the focus of extensive conservation efforts in recent years. However, there are gaps in our knowledge about the survival of first, or spring generation, monarchs in their core areas of Texas, Oklahoma, and Louisiana. This is important because the spring generation represents the first stage of annual recovery from overwinter mortality. It is, therefore, an important stage for monarch conservation efforts. This study showed that, in the context of a complex arthropod community in north Texas, first generation monarch survival was high. The study found that survival was not directly related to predators on the host plant, but was higher on host plants that harbored a greater number and variety of other, non-predatory arthropods. This is possibly because the presence of alternate, preferable prey enabled monarch eggs and larvae to be overlooked by predators. The implication is that, at least in the southern U.S., monarch conservation should consider strategies that promote diverse functional arthropod communities.

Abstract

Based on surveys of winter roost sites, the eastern migratory population of the monarch butterfly (Danaus plexippus) in North America appears to have declined in the last 20 years and this has prompted the implementation of numerous conservation strategies. However, there is little information on the survivorship of first-generation monarchs in the core area of occupancy in Texas, Oklahoma, and Louisiana where overwinter population recovery begins. The purpose of this study was to determine the survivorship of first-generation eggs to third instars at a site in north Texas and to evaluate host plant arthropods for their effect on survivorship. Survivorship to third instar averaged 13.4% and varied from 11.7% to 15.6% over three years. The host plants harbored 77 arthropod taxa, including 27 predatory taxa. Despite their abundance, neither predator abundance nor predator richness predicted monarch survival. However, host plants upon which monarchs survived often harbored higher numbers of non-predatory arthropod taxa and more individuals of non-predatory taxa. These results suggest that ecological processes may have buffered the effects of predators and improved monarch survival in our study. The creation of diverse functional arthropod communities should be considered for effective monarch conservation, particularly in southern latitudes.

Seasonal spatial dynamics of butterfly migration

Understanding the seasonal movements of migratory species underpins ecological studies. Several hundred butterfly species show migratory behaviour, yet the spatial pattern of these migrations is poorly understood. We developed climatic niche models for 405 migratory butterfly species globally to estimate patterns of seasonal movement and the distribution of seasonal habitat suitability. We found strong seasonal variation in habitat suitability for most migratory butterflies with >75% of pixels within their distributions showing seasonal switching in predicted occupancy for 85% of species. The greatest rate of seasonal switching occurred in the tropics. Several species showed extreme range fluctuations between seasons, exceeding 10-fold for 53 species (13%) and more than 100-fold for nine species (2%), suggesting that such species may be at elevated extinction risk. Our results can be used to search for the ecological processes that underpin migration in insects, as well as to design conservation interventions for declining migratory insects.

Recent climate change is creating hotspots of butterfly increase and decline across North America

Some insect populations are experiencing dramatic declines, endangering the crucial ecosystem services they provide. Yet, other populations appear robust, highlighting the need to better define patterns and underlying drivers of recent change in insect numbers. We examined abundance and biodiversity trends for North American butterflies using a unique citizen-science dataset that has recorded observations of over 8 million butterflies across 456 species, 503 sites, nine ecoregions, and 26 years. Butterflies are a biodiverse group of pollinators, herbivores, and prey, making them useful bellwethers of environmental change. We found great heterogeneity in butterfly species' abundance trends, aggregating near zero, but with a tendency toward decline. There was strong spatial clustering, however, into regions of increase, decrease, or relative stasis. Recent precipitation and temperature appeared to largely drive these patterns, with butterflies generally declining at increasingly dry and hot sites but increasing at relatively wet or cool sites. In contrast, landscape and butterfly trait predictors had little influence, though abundance trends were slightly more positive around urban areas. Consistent with varying responses by different species, no overall directional change in butterfly species richness or evenness was detected. Overall, a mosaic of butterfly decay and rebound hotspots appeared to largely reflect geographic variability in climate drivers. Ongoing controversy about insect declines might dissipate with a shift in focus to the causes of heterogeneous responses among taxa and sites, with climate change emerging as a key suspect when pollinator communities are broadly impacted.

Glyphosate inhibits melanization and increases susceptibility to infection in insects

Melanin, a black-brown pigment found throughout all kingdoms of life, has diverse biological functions including UV protection, thermoregulation, oxidant scavenging, arthropod immunity, and microbial virulence. Given melanin's broad roles in the biosphere, particularly in insect immune defenses, it is important to understand how exposure to ubiquitous environmental contaminants affects melanization. Glyphosate-the most widely used herbicide globally-inhibits melanin production, which could have wide-ranging implications in the health of many organisms, including insects. Here, we demonstrate that glyphosate has deleterious effects on insect health in 2 evolutionary distant species, Galleria mellonella (Lepidoptera: Pyralidae) and Anopheles gambiae (Diptera: Culicidae), suggesting a broad effect in insects. Glyphosate reduced survival of G. mellonella caterpillars following infection with the fungus Cryptococcus neoformans and decreased the size of melanized nodules formed in hemolymph, which normally help eliminate infection. Glyphosate also increased the burden of the malaria-causing parasite Plasmodium falciparum in A. gambiae mosquitoes, altered uninfected mosquito survival, and perturbed the microbial composition of adult mosquito midguts. Our results show that glyphosate's mechanism of melanin inhibition involves antioxidant synergy and disruption of the reaction oxidation-reduction balance. Overall, these findings suggest that glyphosate's environmental accumulation could render insects more susceptible to microbial pathogens due to melanin inhibition, immune impairment, and perturbations in microbiota composition, potentially contributing to declines in insect populations.

Spatial phylogenetics of butterflies in relation to environmental drivers and angiosperm diversity across North America

Broad-scale, quantitative assessments of insect biodiversity and the factors shaping it remain particularly poorly explored. Here we undertook a spatial phylogenetic analysis of North American butterflies to test whether climate stability and temperature gradients have shaped their diversity and endemism. We also performed the first quantitative comparisons of spatial phylogenetic patterns between butterflies and flowering plants. We expected concordance between the two groups based on shared historical environmental drivers and presumed strong butterfly-host plant specializations. We instead found that biodiversity patterns in butterflies are strikingly different from flowering plants, especially warm deserts. In particular, butterflies show different patterns of phylogenetic clustering compared with flowering plants, suggesting differences in habitat conservation between the two groups. These results suggest that shared biogeographic histories and trophic associations do not necessarily assure similar diversity outcomes. The work has applied value in conservation planning, documenting warm deserts as a North American butterfly biodiversity hotspot.

Migration in butterflies: a global overview

Insect populations including butterflies are declining worldwide, and they are becoming an urgent conservation priority in many regions. Understanding which butterfly species migrate is critical to planning for their conservation, because management actions for migrants need to be coordinated across time and space. Yet, while migration appears to be widespread among butterflies, its prevalence, as well as its taxonomic and geographic distribution are poorly understood. The study of insect migration is hampered by their small size and the difficulty of tracking individuals over long distances. Here we review the literature on migration in butterflies, one of the best-known insect groups. We find that nearly 600 butterfly species show evidence of migratory movements. Indeed, the rate of 'discovery' of migratory movements in butterflies suggests that many more species might in fact be migratory. Butterfly migration occurs across all families, in tropical as well as temperate taxa; Nymphalidae has more migratory species than any other family (275 species), and Pieridae has the highest proportion of migrants (13%; 133 species). Some 13 lines of evidence have been used to ascribe migration status in the literature, but only a single line of evidence is available for 92% of the migratory species identified, with four or more lines of evidence available for only 10 species - all from the Pieridae and Nymphalidae. Migratory butterflies occur worldwide, although the geographic distribution of migration in butterflies is poorly resolved, with most data so far coming from Europe, USA, and Australia. Migration is much more widespread in butterflies than previously realised - extending far beyond the well-known examples of the monarch Danaus plexippus and the painted lady Vanessa cardui - and actions to conserve butterflies and insects in general must account for the spatial dependencies introduced by migratory movements.

Effects of early-life exposure to sublethal levels of a common neonicotinoid insecticide on the orientation and migration of monarch butterflies (Danaus plexippus)

Migratory insects use a variety of innate mechanisms to determine their orientation and maintain correct bearing. For long-distance migrants, such as the monarch butterfly (Danaus plexippus), these journeys could be affected by exposure to environmental contaminants. Neonicotinoids are synthetic insecticides that work by affecting the nervous system of insects, resulting in impairment of their mobility, cognitive performance, and other physiological and behavioural functions. To examine how neonicotinoids might affect the ability of monarch butterflies to maintain a proper directional orientation on their ∼4000 km migration, we grew swamp milkweed (Asclepias incarnata) in soil that was either untreated (0 ng g-1: control) or mixed with low (15 ng g-1 of soil) or high (25 ng g-1 of soil) levels of the neonicotinoid clothianidin. Monarch caterpillars were raised on control or clothianidin-treated milkweed and, after pupation, either tested for orientation in a static flight simulator or radio-tracked in the wild during the autumn migration period. Despite clothianidin being detectable in milkweed tissue consumed by caterpillars, there was no evidence that clothianidin influenced the orientation, vector strength (i.e. concentration of direction data around the mean) or rate of travel of adult butterflies, nor was there evidence that morphological traits (i.e. mass and forewing length), testing time, wind speed or temperature impacted directionality. Although sample sizes for both flight simulator and radio-tracking tests were limited, our preliminary results suggest that clothianidin exposure during early caterpillar development does not affect the directed flight of adult migratory monarch butterflies or influence their orientation at the beginning of migration.

Evolutionary developmental biology and sustainability: A biology of resilience

Evolutionary developmental biology, and especially ecological developmental biology, is essential for discussions of sustainability and the responses to global climate change. First, this paper explores examples of animals that have successfully altered their development to accommodate human-made changes to their environments. We next document the ability of global warming to disrupt the development of those organisms with temperature-dependent sex-determination or with phenologies coordinating that organism's development with those of other species. The thermotolerance of Homo sapiens is also related to key developmental factors concerning brain development and maintenance, and the development of corals, the keystone organisms of tropical reefs, is discussed in relation to global warming as well as to other anthropogenic changes. While teratogenic and endocrine-disrupting compounds are not discussed in this essay, the ability of glyphosate herbicides to block insect development is highlighted. Last, the paper discusses the need to creatively integrate developmental biology with ecological, political, religious, and economic perspectives, as the flourishing of contemporary species may require altering the ways that Western science has considered the categories of nature, culture, and self.

Captive-reared migratory monarch butterflies show natural orientation when released in the wild

Eastern North American migratory monarch butterflies (Danaus plexippus) have faced sharp declines over the past two decades. Captive rearing of monarch butterflies is a popular and widely used approach for both public education and conservation. However, recent evidence suggests that captive-reared monarchs may lose their capacity to orient southward during fall migration to their Mexican overwintering sites, raising questions about the value and ethics of this activity undertaken by tens of thousands of North American citizens, educators, volunteers and conservationists each year. We raised offspring of wild-caught monarchs on swamp milkweed (Asclepias incarnata) indoors at 29°C during the day and 23°C at night (~77% RH, 18L:6D), and after eclosion, individuals were either tested in a flight simulator or radio tracked in the wild using an array of automated telemetry towers. While 26% (10/39) of monarchs tested in the flight simulator showed a weakly concentrated southward orientation, 97% (28/29) of the radio-tracked individuals that could be reliably detected by automated towers flew in a south to southeast direction from the release site and were detected at distances of up to 200 km away. Our results suggest that, although captive rearing of monarch butterflies may cause temporary disorientation, proper orientation is likely established after exposure to natural skylight cues.