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.

Assembly and operation of an imaging system for long-term monitoring of bioluminescent and fluorescent reporters in plants.

BACKGROUND: Non-invasive reporter systems are powerful tools to query physiological and transcriptional responses in organisms. For example, fluorescent and bioluminescent reporters have revolutionized cellular and organismal assays and have been used to study plant responses to abiotic and biotic stressors. Integrated, cooled charge-coupled device (CCD) camera systems have been developed to image bioluminescent and fluorescent signals in a variety of organisms; however, these integrated long-term imaging systems are expensive. RESULTS: We have developed self-assembled systems for both growing and monitoring plant fluorescence and bioluminescence for long-term experiments under controlled environmental conditions. This system combines environmental growth chambers with high-sensitivity CCD cameras, multi-wavelength LEDs, open-source software, and several options for coordinating lights with imaging. This easy-to-assemble system can be used for short and long-term imaging of bioluminescent reporters, acute light-response, circadian rhythms, delayed fluorescence, and fluorescent-protein-based assays in vivo. CONCLUSIONS: We have developed two self-assembled imaging systems that will be useful to researchers interested in continuously monitoring in vivo reporter systems in various plant species.

Long- and short-term responses of Asclepias species differ in respect to fire, grazing, and nutrient addition.

PREMISE OF THE STUDY: The tallgrass prairie ecosystem has experienced a dramatic reduction over the past 150 yr. This reduction has impacted the abundance of native grassland species, including milkweeds (Asclepias). METHODS: We used two long-term (27 yr) data sets to examine how fire, grazing, and nutrient addition shape milkweed abundance in tallgrass prairie. We compared these results to those of a greenhouse experiment that varied nutrient levels in the absence of competition, herbivory, and mutualistic relationships. KEY RESULTS: Asclepias species exhibited broad patterns in response to burning regimes that did not include grazing, but experienced more species-specific patterns in other combinations. Asclepias syriaca was the only species to increase in abundance in plots that included burning and nutrient addition. In the greenhouse we found that nitrogen significantly increased biomass, while no effect of phosphorus was detected. CONCLUSIONS: These results indicate that A. syriaca will do best in settings with high nutrient loads, low competition, and no grazers. These characteristics define a small portion of the tallgrass prairie but exemplify modern agricultural settings, which have replaced prairies. However, other milkweeds examined did not share this pattern, which indicates that milkweed species will respond differently when exposed to agricultural settings, with some less able to cope with land conversion to pasture or row-crop agriculture.

Development and characterization of microsatellite loci for the endangered scrub lupine, Lupinus aridorum (Fabaceae).

PREMISE OF THE STUDY: Microsatellite primers were developed in scrub lupine (Lupinus aridorum, Fabaceae), an endemic species to Florida that is listed as endangered in the United States, to assess connectivity among populations, identify hybrids, and examine genetic diversity. METHODS AND RESULTS: We isolated and characterized 12 microsatellite loci polymorphic in scrub lupine or in closely related species (i.e., sky-blue lupine [L. diffusus] and Gulf Coast lupine [L. westianus]). Loci showed low to moderate polymorphism, ranging from two to 14 alleles per locus and 0.01 to 0.86 observed heterozygosity. CONCLUSIONS: These loci are the first developed for Florida species of lupine and will be used to determine differentiation among species and to aid in conservation of the endangered scrub lupine.