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Shirey V, Ries L. Population dynamics and drivers of the eastern monarch (Danaus plexippus) across its full annual cycle: a cross-scale synthesis of a model migratory species. CURRENT OPINION IN INSECT SCIENCE 2023; 60:101132. [PMID: 37871775 DOI: 10.1016/j.cois.2023.101132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Revised: 10/11/2023] [Accepted: 10/12/2023] [Indexed: 10/25/2023]
Abstract
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.
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Affiliation(s)
- Vaughn Shirey
- Department of Biology, Georgetown University, 37th and O Streets NW, Washington, DC 20057, USA; Marine and Environmental Biology Section - Department of Biological Sciences, University of Southern California, Allan Hancock Foundation Building, Los Angeles, CA 90089, USA.
| | - Leslie Ries
- Department of Biology, Georgetown University, 37th and O Streets NW, Washington, DC 20057, USA
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2
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Boyle JH, Strickler S, Twyford AD, Ricono A, Powell A, Zhang J, Xu H, Smith R, Dalgleish HJ, Jander G, Agrawal AA, Puzey JR. Temporal matches between monarch butterfly and milkweed population changes over the past 25,000 years. Curr Biol 2023; 33:3702-3710.e5. [PMID: 37607548 DOI: 10.1016/j.cub.2023.07.057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Revised: 04/13/2023] [Accepted: 07/26/2023] [Indexed: 08/24/2023]
Abstract
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.
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Affiliation(s)
- John H Boyle
- Biology Department, College of William & Mary, 540 Landrum Dr., Williamsburg, VA 23185, USA; Biology Department, University of Mary, 7500 University Dr., Bismarck, ND 58504, USA
| | - Susan Strickler
- Boyce Thompson Institute, 533 Tower Rd., Ithaca, NY 14853, USA; Chicago Botanic Garden, Plant Science and Conservation, 1000 Lake Cook Rd., Glencoe, IL 60022, USA; Northwestern University, Plant Biology and Conservation Program, 2145 Sheridan Rd., Evanston, IL 60208, USA
| | - Alex D Twyford
- Institute of Ecology and Evolution, University of Edinburgh, Charlotte Auerbach Rd., Edinburgh EH9 3FL, UK; Royal Botanic Garden Edinburgh, Edinburgh EH3 5NZ, UK
| | - Angela Ricono
- Biology Department, College of William & Mary, 540 Landrum Dr., Williamsburg, VA 23185, USA
| | - Adrian Powell
- Boyce Thompson Institute, 533 Tower Rd., Ithaca, NY 14853, USA
| | - Jing Zhang
- Boyce Thompson Institute, 533 Tower Rd., Ithaca, NY 14853, USA
| | - Hongxing Xu
- Boyce Thompson Institute, 533 Tower Rd., Ithaca, NY 14853, USA; College of Life Sciences, Shaanxi Normal University, South Chang'an Rd., Xi'an 710062, China
| | - Ronald Smith
- Data Science Program, College of William & Mary, 540 Landrum Dr., Williamsburg, VA 23185, USA
| | - Harmony J Dalgleish
- Biology Department, College of William & Mary, 540 Landrum Dr., Williamsburg, VA 23185, USA
| | - Georg Jander
- Boyce Thompson Institute, 533 Tower Rd., Ithaca, NY 14853, USA
| | - Anurag A Agrawal
- Department of Ecology and Evolutionary Biology, Cornell University, Corson Hall, Ithaca, NY 14853, USA
| | - Joshua R Puzey
- Biology Department, College of William & Mary, 540 Landrum Dr., Williamsburg, VA 23185, USA.
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3
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Pocius VM, Majewska AA, Freedman MG. The Role of Experiments in Monarch Butterfly Conservation: A Review of Recent Studies and Approaches. ANNALS OF THE ENTOMOLOGICAL SOCIETY OF AMERICA 2022; 115:10-24. [PMID: 35069967 PMCID: PMC8764570 DOI: 10.1093/aesa/saab036] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Indexed: 06/14/2023]
Abstract
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.
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Affiliation(s)
- Victoria M Pocius
- Department of Biological Sciences, University of Alabama, Tuscaloosa, AL, USA
| | | | - Micah G Freedman
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
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Zylstra ER, Ries L, Neupane N, Saunders SP, Ramírez MI, Rendón-Salinas E, Oberhauser KS, Farr MT, Zipkin EF. Changes in climate drive recent monarch butterfly dynamics. Nat Ecol Evol 2021; 5:1441-1452. [PMID: 34282317 DOI: 10.1038/s41559-021-01504-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Accepted: 06/07/2021] [Indexed: 02/06/2023]
Abstract
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.
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Affiliation(s)
- Erin R Zylstra
- Department of Integrative Biology, Ecology, Evolution, and Behavior Program, Michigan State University, East Lansing, MI, USA.
| | - Leslie Ries
- Department of Biology, Georgetown University, Washington, DC, USA
| | - Naresh Neupane
- Department of Biology, Georgetown University, Washington, DC, USA
| | - Sarah P Saunders
- Department of Integrative Biology, Ecology, Evolution, and Behavior Program, Michigan State University, East Lansing, MI, USA.,National Audubon Society, New York, NY, USA
| | - M Isabel Ramírez
- Centro de Investigaciones en Geografía Ambiental, Universidad Nacional Autónoma de México, Morelia, Mexico
| | | | - Karen S Oberhauser
- University of Wisconsin Arboretum, University of Wisconsin-Madison, Madison, WI, USA
| | - Matthew T Farr
- Department of Integrative Biology, Ecology, Evolution, and Behavior Program, Michigan State University, East Lansing, MI, USA
| | - Elise F Zipkin
- Department of Integrative Biology, Ecology, Evolution, and Behavior Program, Michigan State University, East Lansing, MI, USA
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He E, Agrawal AA. Clonal versus non-clonal milkweeds ( Asclepias spp.) respond differently to stem damage, affecting oviposition by monarch butterflies. PeerJ 2020; 8:e10296. [PMID: 33194443 PMCID: PMC7646301 DOI: 10.7717/peerj.10296] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Accepted: 10/13/2020] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND Oviposition decisions are critical to the fitness of herbivorous insects and are often impacted by the availability and condition of host plants. Monarch butterflies (Danaus plexippus) rely on milkweeds (Asclepias spp.) for egg-laying and as food for larvae. Previous work has shown that monarchs prefer to oviposit on recently regrown plant tissues (after removal of above-ground biomass) while larvae grow poorly on plants previously damaged by insects. We hypothesized that these effects may depend on the life-history strategy of plants, as clonal and non-clonal milkweed species differ in resource allocation and defense strategies. METHODOLOGY/PRINCIPAL FINDINGS We first confirmed butterfly preference for regrown tissue in a field survey of paired mowed and unmowed plots of the common milkweed A. syriaca. We then experimentally studied the effects of plant damage (comparing undamaged controls to plants clipped and regrown, or damaged by insects) on oviposition choice, larval performance, and leaf quality of two closely related clonal and non-clonal species pairs: (1) A. syriaca and A. tuberosa, and (2) A. verticillata and A. incarnata. Clonal and non-clonal species displayed different responses to plant damage, impacting the proportions of eggs laid on plants. Clonal species had similar mean proportions of eggs on regrown and control plants (≈35-40% each), but fewer on insect-damaged plants (≈20%). Meanwhile non-clonal species had similar oviposition on insect-damaged and control plants (20-30% each) but more eggs on regrown plants (40-60%). Trait analyses showed reduced defenses in regrown plants and we found some evidence, although variable, for negative effects of insect damage on subsequent larval performance. CONCLUSIONS/SIGNIFICANCE Overall, non-clonal species are more susceptible and preferred by monarch butterflies following clipping, while clonal species show tolerance to clipping and induced defense to insect herbivory. These results have implications for monarch conservation strategies that involve milkweed habitat management by mowing. More generally, plant life-history may mediate growth and defense strategies, explaining species-level variation in responses to different types of damage.
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Affiliation(s)
- Elise He
- Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
| | - Anurag A. Agrawal
- Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
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Lark TJ, Spawn SA, Bougie M, Gibbs HK. Cropland expansion in the United States produces marginal yields at high costs to wildlife. Nat Commun 2020; 11:4295. [PMID: 32908130 PMCID: PMC7481238 DOI: 10.1038/s41467-020-18045-z] [Citation(s) in RCA: 54] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2019] [Accepted: 07/15/2020] [Indexed: 11/09/2022] Open
Abstract
Recent expansion of croplands in the United States has caused widespread conversion of grasslands and other ecosystems with largely unknown consequences for agricultural production and the environment. Here we assess annual land use change 2008-16 and its impacts on crop yields and wildlife habitat. We find that croplands have expanded at a rate of over one million acres per year, and that 69.5% of new cropland areas produced yields below the national average, with a mean yield deficit of 6.5%. Observed conversion infringed upon high-quality habitat that, relative to unconverted land, had provided over three times higher milkweed stem densities in the Monarch butterfly Midwest summer breeding range and 37% more nesting opportunities per acre for waterfowl in the Prairie Pothole Region of the Northern Great Plains. Our findings demonstrate a pervasive pattern of encroachment into areas that are increasingly marginal for production, but highly significant for wildlife, and suggest that such tradeoffs may be further amplified by future cropland expansion.
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Affiliation(s)
- Tyler J Lark
- Center for Sustainability and the Global Environment (SAGE), Nelson Institute for Environmental Studies, University of Wisconsin-Madison, 1710 University Ave, Madison, WI, 53726, USA. .,DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA.
| | - Seth A Spawn
- Center for Sustainability and the Global Environment (SAGE), Nelson Institute for Environmental Studies, University of Wisconsin-Madison, 1710 University Ave, Madison, WI, 53726, USA.,DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA.,Department of Geography, University of Wisconsin-Madison, Madison, WI, USA
| | - Matthew Bougie
- Center for Sustainability and the Global Environment (SAGE), Nelson Institute for Environmental Studies, University of Wisconsin-Madison, 1710 University Ave, Madison, WI, 53726, USA.,DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA
| | - Holly K Gibbs
- Center for Sustainability and the Global Environment (SAGE), Nelson Institute for Environmental Studies, University of Wisconsin-Madison, 1710 University Ave, Madison, WI, 53726, USA.,DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA.,Department of Geography, University of Wisconsin-Madison, Madison, WI, USA
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Associational effects of plant ontogeny on damage by a specialist insect herbivore. Oecologia 2020; 193:593-602. [PMID: 32621031 DOI: 10.1007/s00442-020-04702-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 06/30/2020] [Indexed: 10/23/2022]
Abstract
Intraspecific variation in plant traits is a major cause of variation in herbivore feeding and performance. Plant defensive traits change as a plant grows, such that ontogeny may account for a substantial portion of intraspecific trait variation. We tested how the ontogenic stage of an individual plant, of an individual in the context of its neighboring plants, and of a patch of plants with mixed or uniform stages affect plant-herbivore interactions. To do this, we conducted an experimental study of the interactions between Lepidium draba, a perennial brassicaceous weed, and Plutella xylostella, a common herbivore of L. draba. We found that L. draba foliar glucosinolates, secondary metabolites often implicated in defense, decreased in concentration with plant age. In single-stage patches, herbivores performed similarly on L. draba plants of different ages. Furthermore, we found no difference in the cumulative performance of herbivores reared on mixed- or even-staged patches of L. draba. However, in mixed-stage patches, the damage experienced by a focal plant depended on the stage of neighboring plants, suggesting a preference hierarchy of the herbivore among plant stages. In our study, the amount of herbivory depended on the ontogenic neighborhood in which the plant grew. However, from the herbivore's perspective, variation in plant ontogenic stage was unimportant to its success in terms of feeding rate and final weight.
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Grant TJ, Flockhart DTT, Blader TR, Hellmich RL, Pitman GM, Tyner S, Norris DR, Bradbury SP. Estimating arthropod survival probability from field counts: a case study with monarch butterflies. Ecosphere 2020. [DOI: 10.1002/ecs2.3082] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Affiliation(s)
- Tyler J. Grant
- Department of Natural Resource Ecology and Management Iowa State University Ames Iowa USA
| | - D. T. Tyler Flockhart
- University of Maryland Center for Environmental Science – Appalachian Laboratory Frostburg Maryland USA
| | | | | | | | - Sam Tyner
- Department of Statistics Iowa State University Ames Iowa USA
| | - D. Ryan Norris
- The Nature Conservancy of Canada Toronto Ontario Canada
- Department of Integrative Biology University of Guelph Guelph Ontario Canada
| | - Steven P. Bradbury
- Department of Natural Resource Ecology and Management Iowa State University Ames Iowa USA
- Department of Entomology Iowa State University Ames Iowa USA
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