Biology subjects

Dalgleish, H. J.

Publications and source records attributed to Dalgleish, H. J..

5 recordsLinked to original sources

bioRxiv2026

Plant microbiomes have a greater effect than plant size on flowering and growth in Asclepias syriaca

Plants strike a balance between growth and defense. The calculus of how to defend against herbivores, and maximize growth and reproduction, can differ between annuals and perennials. Annuals have a live fast, reproduce young strategy; while perennials may maximize fecundity over years. Milkweed, a herbaceous perennial, is a mix of these two strategies. On one hand, a single individual ramet is functionally a herbaceous annual and vulnerable to herbivory. On the other hand, below ground connections allow ramets to share resources and persist for multiple years, perhaps lowering the cost of localized herbivory. Here, we study the impact of herbivory on the leaf and soil microbiome on milkweed growth and flowering in naturally occurring populations. After controlling for plant size and plant genotype, we asked how the microbiome composition was related to flowering time and growth. We find that the leaf microbiome is a strong predictor of plant growth rate, but not flowering. Conversely, we find that the soil microbiome and plant size predict flowering probability. We found no evidence that herbivory altered the leaf or soil microbiome composition. Together these results provide evidence that plant microbiomes also influence growth and fecundity in natural populations of milkweed. These results also provide evidence that the leaf microbiome in milkweed is stable in the face of herbivory. This study expands our knowledge of the contribution of microbiomes to plant demography in a clonal perennial plant.

ecology↗

bioRxiv2025

The reproductive microbiome inhibits pollen germination in milkweed

We know very little about the reproductive microbiomes of plants. Microbes may play important roles in shaping pollination, fertilization, and seed production - processes which are important evolutionarily, ecologically, and agriculturally. Through a series of field and laboratory experiments, we show that the stigmatic microbiome in milkweeds influences the success of pollination. Isolation of individual bacterial and fungal taxa from stigmatic secretions allowed us to experimentally test their effects on pollen germination. These experiments demonstrate that individual taxa impact pollen differently, with many microbial taxa being neutral, but some being deleterious. Through isolation of microbes from the legs of pollinator insects we found that pollinators are a likely source for pollen-harmful bacterial taxa. Next, by utilizing a natural hybrid zone, we demonstrate species-specific responses to the stigmatic microbiome that be driving asymmetric patterns of gene-flow between species - with Asclepias exaltata being a better pollen host than A. syriaca. This study demonstrates that the reproductive microbiome is an underappreciated player in sexual reproduction of plants. Significance StatementThe results presented here demonstrate an important but previously unappreciated role of stigmatic microbes in plant sexual reproduction. This study demonstrates that the microbial taxa living in stigmatic secretions in milkweed impact pollen germination. We found that filtering out the microbes from stigmatic secretions of milkweed flowers dramatically increases pollen germination. Through isolating microbial taxa from both stigmatic secretions, and pollinator legs, we found that individual microbial taxa impact pollen differently, with many taxa being neutral, but some being deleterious. Finally, by utilizing a naturally occurring milkweed hybrid zone we demonstrated that microbial taxa in stigmatic secretions may be acting as asymmetric prezygotic barrier.

plant biology↗

bioRxiv2025

A high degree of clonal reproduction and aggregated structure of milkweed clones does not affect ramet sexual reproduction

1. Clonal plants have unique population structures where genetic individuals can occupy many locations at once, but the effect of ramet spatial arrangement on demography is poorly understood. 2. We analyzed the spatial, genetic, and demographic characteristics of 798 ramets from four populations of Asclepias syriaca, a highly clonal plant, in northern Virginia. 3. Asclepias syriaca clones varied in size and spatial aggregation: ramets of the same genotype were more likely to be spatially clustered but when clones were small, we observed more spatial dispersion, potentially to avoid competition with self. Despite low genetic variation over all (Genotypes/Number of Individuals = 0.1), ramet sexual reproduction was not related to local genetic variation. Synthesis High rates of clonality in A. syriaca spatially structures demographic and competitive dynamics without impeding sexual reproduction, highlighting how reproductive allocation shapes the population ecology of plants.

ecology↗

bioRxiv2022

Temporal matches and mismatches between monarch butterfly and milkweed population changes over the past 12,000 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, 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 via Random Forests (ABC-RF), a machine learning method for reconstructing demographic histories, we show that both monarchs and milkweed experienced concurrent range expansion during the most recent recession of North American glaciers [~]12,000 years ago. Our data identify an expansion of milkweed during the large-scale clearing of eastern forests ([~]200 years ago) but was inconclusive as to expansion or contraction of the monarch butterfly population during this time. Finally, our results indicate that neither species experienced a population contraction 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.

evolutionary biology↗

bioRxiv2018

Monarch butterfly and milkweed declines substantially predate the use of genetically modified crops

Monarch butterfly (Danaus plexippus) decline over the past 25 years has received considerable public and scientific attention, in large part because its decline, and that of its milkweed (Asclepias spp.) host plant, have been linked to genetically modified (GM) crops and the associated herbicide use. Therefore, the monarch has emerged as a poster child for the anti-GM movement. Here we use museum and herbaria specimens to extend our knowledge of the dynamics of both monarchs and milkweeds in the United States to more than a century, from 1900-2016. We show that monarch population trends closely follow those of their milkweed hosts; that both monarchs and milkweeds increased during the early 20th century, and that recent declines are actually part of a much longer term decline in both monarchs and milkweed beginning around 1950. Herbicide resistant crops, therefore, are clearly not the only culprit, and likely not even the primary culprit, as these declines began decades before GM crops were introduced.

ecology↗